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CaraterizaçãoeProcessosFísico-QuímicosdeRecuperaçãode
TerrasRarasemResíduos
JoanaRitaMeirelesFonseca
DissertaçãoparaaobtençãodograudeMestreem
EngenhariadeMateriais
Orientadores
ProfessoraDoutoraFernandaMariaRamosdaCruzMargarido
DoutorCarlosAlbertoGonçalvesNogueira
Júri
Presidente:ProfessorDoutorJoséPauloSequeiraFarinha
Orientador:DoutorCarlosAlbertoGonçalvesNogueira
Vogal:ProfessorDoutorManuelFranciscoCostaPereira
Outubrode2017
Declaration
Ideclarethatthisdocumentisanoriginalworkofmyownauthorshipandthatitfulfilsalltherequirements
oftheCodeofConductandGoodPracticesoftheUniversidadedeLisboa.
Declaração
Declaroqueopresentedocumentoéumtrabalhooriginaldaminhaautoriaequecumpretodososrequisitos
doCódigodeCondutaeBoasPráticasdaUniversidadedeLisboa.
“Ourimaginationistheonlylimittowhatwecanhopetohaveinthefuture.”
CharlesF.Kettering
ÀminhaMaria.
AomeuManuel.
i
AgradecimentosQueria começar por agradecer aosmeus orientadores, que sempre com umamaravilhosa disposição e
simpatia me transmitiram os conhecimentos necessários e permitiram crescer e desenvolver para além da
dissertaçãoedoTécnico.
Queriaagradeceraosmeuspais.Aocarinhodaminhamãe:osbeijoseabraçosdeconsoloou,somente
amizade,asrefeiçõeslevadasaoquarto,asvisitasàs5hdamanhãasuplicarparaeumeirdeitar,.Agradecero
facto de me ir buscar ao IST repetidamente, só porque já não haviam comboios para voltar para casa. À
intelectualidadeeperfecionismodomeupai.Semelenãoeratãopersistentenemtrabalhadora.Obrigadaaos
dois pelas oportunidades que sempre trabalharam para me proporcionar; pelo apoio incondicional e pelas
palavrasdesabedoria.
Aomeuirmão,queaindanoutropaís,sempremeapoiou,aindaquemecontinueatratarcomoumbebé.
Obrigadapelosconselhosde“comolidarcomoTécnico”,semelesnãotinhaalentoparaterminarocursoem5
anos.
Aos meus amigos de Materiais, que me acompanharam nesta viagem. Obrigada em especial à Rita
Faustino,ao André Estêvão, à Inês Cunha, aoMiguelMiguel, aoMiguel Costa, ao JoãoMiguel, ao Kiko, ao
HuguinhoeàPiquena,àMadalena,àsBias,àCatarina,aosmeusmeninosBernardo,Sempiterno,AndréeAdolfo
eaoMatepelasnoitesdeestudo,destresse,derisada,decopofonia.Pelaamizade.
Omesmoagradeçoaosmeusamigos,vulgo,daMargemSul.Quejápartilhamcomigomuitosmaisanose
muitasmaisaventuras.EmespecialaoLuísSantos,FredericoVelez,InêsAlexandre,InêsSerafim,ValériyaZaruba,
VicthorBörrénDias,JoanaFrancisco,DanielaMartinsCoelhoe,aindaquelonge,Di.
Finalmente,emais importante,aosmeusavósmaternos.Aindaqueumdelesnãoesteja jácomigo,não
possodeixardeestaragradecidaporter[tido]pessoastãofantásticaseamáveisnaminhavida.Pelosverõesna
“terrinha”, pelos lanches e refeições enormes feitas propositadamente ao meu gosto, pelo colinho, pelos
beijinhos,peloamorincondicionalquemederamequeserá,sempre,massempre,mútuo.
ii
iii
ResumoAs lâmpadas fluorescentes contêmessencialmente seiselementosde terras-raras (ETRs): cério, európio,
gadolínio,lantânio,térbioeítrio.
NapresentedissertaçãoforamtestadasváriasmetodologiasderecuperaçãodosETRsdalamaproveniente
daoperaçãodepré-processamentodelâmpadasfluorescentes:1)doisprocessosdelixiviaçãosimples;2)dois
processos de lixiviação em vários passos com ácido clorídrico e/ou nítrico (testando diversas temperaturas,
concentraçãodeácido)e.3)doisprocessosdedigestãocomácidosulfúrico.
AssoluçõesdelixiviaçãonãoforamsubmetidasanenhumprocessoderecuperaçãodasETRs.
Os resíduos dos diferentes ensaios, após secagem foram submetidos a processos de caracterização por
pulverodifractometria de raios-X (DRXP),microscopia eletrónica de varrimento (MEV), granulometria laser e
espectrometriadeemissãoatómicaporplasmaacopladoindutivamente(ICP-AES).
Os seis ETRs foram identificados, e correspondem a aproximadamente 18% (peso seco) da amostra. O
processodedigestãosulfúricasimples(1,1mLg-1,3h,150°C)permitiuobterumrendimentodelixiviaçãosuperior
a99%paraolantânio,cérioetérbio,edeaproximadamente68%e73%paraoeurópioeoítrio,respetivamente.
Utilizandoumprocessoreativoadoispassos,oprimeirocomumalixiviaçãoácida(4MHCl,6h,90°C),seguido
por uma digestão sulfúrica (1,1mLg-1,3h, 150°C), obtiveram-se rendimentos de recuperação de ítrio mais
elevados(cercade86%),masvaloresmaisbaixosparaoeurópio(28%).
Os melhores resultados alcançados neste trabalho foram obtidos nas experiências com um passo de
digestão,sugerindoqueareatividadedosmetaiscomoácidosulfúricofoimaiordoquecomoácidoclorídrico
ounítrico.
Palavras-chave: Reciclagem, Lâmpadas fluorescentes, Fósforos luminescentes, elementos de terras-
raras,lixiviação.
iv
v
AbstractThere are six main rare-earth elements (REEs) in fluorescent lighting: cerium, europium, gadolinium,
lanthanum,terbiumandyttrium.
ThepresentpublicationreviewsseveralleachingtechniquestoreclaimREEsfromfluorescentlampwaste.
Theinvestigationwasconductedinbench/laboratoryscaletoassesswhichleachingbasedprocesshasthemost
potential.Severalmulti-stepleachingprocesseswereinvestigatedsuchasleachingwithhydrochloricacidand/or
nitric or water (also named washing) as well as different parameters (temperature,leaching agent
concentration). A digestion with sulphuric acid was also studied. Separation of the leached REEs was not
performed.
The characterization of the waste was made using X-ray powder diffraction (XRD), scanning electron
microscopy (SEM), laser diffraction granulometry and Inductively Coupled Plasma – Atomic Emission
Spectrometer(ICP-AES).AllsixREEswereidentified,correspondingtoapprox.18%(drywt.)ofthesample.
Thepresentworkgaverisetothe leachingofallsix identifiedrareearthelements.Asulphuricdigestion
process(1,1mLg-1,3h,150°C)ledtoaleachingyieldofover99%forlanthanum,ceriumandterbiumandapprox.
68%and73%foreuropiumandyttrium,respectively.Atwo-stepreaction,startingwithanacidleaching(4M
HCl, 6h, 90°C), followed by a sulphuric acid digestion step (1,1mLg-1, 3h, 150°C), promoted higher yttrium
leachingyields(approx.86%),butlowervaluesforeuropium(approx.28%).Experimentswithadigestionstep
resulted in the best results attained in this work, consequently, it suggests that the metals reactivity with
sulphuricacidwashigherthanwithhydrochloricornitricacid.
Key-words:Recycling,FluorescentLamps,Phosphors,Rare-earthelements,Leaching.
vi
vii
SummaryAGRADECIMENTOS...................................................................................................................................I
RESUMO.................................................................................................................................................III
ABSTRACT................................................................................................................................................V
SUMMARY.............................................................................................................................................VII
LISTOFFIGURES......................................................................................................................................IX
LISTOFTABLES.......................................................................................................................................XI
LISTOFACRONYMS...............................................................................................................................XIII
CHAPTER1. INTRODUCTION................................................................................................................1
1.1. GeneralRemarks.............................................................................................................................1
1.2. ProblemOverview...........................................................................................................................3
1.2.1. Rare-earthsascriticalelements..............................................................................................3
1.2.2. Geopoliticalproblem...............................................................................................................5
1.3. Scopeofthework............................................................................................................................7
CHAPTER2. RARE-EARTHELEMENTS...................................................................................................9
2.1. Rare-earthElements........................................................................................................................9
2.2. Depositsandmineralogy...............................................................................................................10
2.2.1. Maindeposits........................................................................................................................10
2.2.2. MineralogyofREEs................................................................................................................13
2.3. Balanceproblem............................................................................................................................14
2.4. Extractionandprocessing.............................................................................................................16
2.4.1. EnvironmentalImplications...................................................................................................18
2.4.2. HealthImpacts.......................................................................................................................19
2.5. REEsspecificationsanduses.........................................................................................................20
CHAPTER3. RECYCLING.....................................................................................................................23
3.1. RecyclingofEOLproductscontainingREEs....................................Erro!Marcadornão definido.
3.2. RecyclingofREEsinlampphosphors............................................................................................25
CHAPTER4. EXPERIMENTAL..............................................................................................................29
CHAPTER5. RESULTS.........................................................................................................................36
5.1. SamplingandPhysicalProcessing.................................................................................................36
viii
5.2. Characterization............................................................................................................................39
5.2.1. GrainsizemeasurementbyLaserDiffraction........................................................................39
5.2.2. X-RayPowderDiffraction......................................................................................................40
5.2.3. ScanningElectronMicroscopy...............................................................................................43
5.2.4. ElementalanalysisbyICP-AESofinitialsamples...................................................................46
5.3. Leachingofphosphormaterials....................................................................................................47
5.3.1. LeachingwithHClsolutions...................................................................................................47
5.3.2. Evaluationofseveralacidleachatesandmultistepleaching................................................48
CHAPTER6. CONCLUSIONANDFUTUREWORK..................................................................................53
BIBLIOGRAPHY.......................................................................................................................................55
ix
ListofFiguresFigure1.1–DivergenceofChinaExportquotaandROWdemand(adaptedfrom[6])..........................................3Figure1.2–Mediumtermcriticality(10years))ofsomeelementsaccordingtotheirsupplyriskandimportance
tocleanenergy(adaptedfrom[2,10])..........................................................................................................4Figure1.3–GlobalRare-earthOxide(REO)productiontrends[adaptedfrom[14]).............................................7Figure2.1–The17elements thatcomprise theREEsgroup.Theelementswithagreen frameare theLREE,
whereastheoneswiththeblueframe,theHREE.........................................................................................9Figure2.2–MainworldREEsdeposits(adaptedfrom[22])................................................................................11Figure2.3–Portugal’sregionswith[possible]REEoccurance.............................................................................12Figure2.4–Large/mediumoccurrenceofREEinValedeCavalosidentifiedbythebrowncircle(adaptedfrom
[24]...............................................................................................................................................................12Figure2.5–Resultingoutcomeofminingonetonofeuropiumoxide[5,15].....................................................15Figure2.6–General extractionandprocessingofREEsores. Theoperationsdesignatedby SXmean solvent
extraction:amulti-stepprocess[28]...........................................................................................................17Figure2.7–Productsofrefining1toneofREOs[22]...........................................................................................18
Figure2.8–Publishedarticlesreportingoneithertoxic(■)orstimulatory(o)effectsofindividualREE[31]..19Figure2.9–REEsingreentechnology(adaptedfrom[28])..................................................................................20Figure 3.1 – Alternative supplying: direct recycling of pre-consumer scrap or residues; urbanmining of EOL
consumergoodsandotherproducts;landfillminingoflandfilledpre-consumerandpost-consumerwaste
streams(adaptedfrom[2]).........................................................................................................................24Figure3.2–LifecycleofREEsinmajortechnologicalapplications(adaptedfrom[2])........................................24Figure3.3– Fluorescentlampdiagramwiththemainconstituents....................................................................26Figure4.1– Simplifiedsamplingdiagram.............................................................................................................33Figure5.1–IL3.15sample.....................................................................................................................................36Figure5.2–XRPDpatterns(Intensityvs2θ)forthedrysamplesanalysed.Fromtoptobottomorder:P.SP,P1,
P12,P19andPG...........................................................................................................................................41Figure5.3–XRPDpattern(Intensityvs2θ),with40 < 2θ < 60.Thephase(s)ofthecompoundscorrespondent
tothepeakis(are)identifiedbythesymbols:p-YOX;¿-Monazite;�-Hydroxylapatiteand¢-Alumina.
.....................................................................................................................................................................42Figure5.4–XRPDpattern(Intensityvs2θ),with60 < 2θ < 80.Thephase(s)ofthecompoundscorrespondent
tothepeakis(are)identifiedbythesymbols:p-YOX;¿-Monazite;�-Hydroxyapatiteand¢-Alumina.
.....................................................................................................................................................................42Figure5.5–SEMmicrographofP.12sample(200x).............................................................................................43Figure5.6–SEMmicrographofPGsample(200x)...............................................................................................43Figure5.7–SEMmicrographofP.SPsample(1500x),withtheeightstudiedparticles......................................44Figure5.8–SEMmicrographofPGsample(1500x).Particlesare:p–Calciumhalophosphate;u–YOX;À–
BAM;l–CAT;n–strontiumhalophosphate;–particlerichinFe.........................................................46
x
xi
ListofTablesTable1.1–Supplyanddemandfor2016,expressedinrare-earthoxides(REOs)[6]............................................2Table1.2–SummaryoftheBottleneckAnalysis:redimpliesahighrisk,yellowamediumriskandgreenalow
risk[8]............................................................................................................................................................4Table1.3–Considerablereserves,basicsupplyanddemandstatistics[11]..........................................................5Table2.1–Applicationanddemandgrowth(2011to2016).UnitsareintonsofREOs[6].................................16Table2.2–Rare-earthsusagebyapplicationinpercentage[31].Percentagesareroundedtothenearestdecimal.
Valuesmaynotaddtototalsshownowningtoindependentrounding.–noconsumption......................21Table2.3–DistributionofREOsconsumptionbymarketsectorin2008[31].ValuesareinmetrictonsofREOs.
.....................................................................................................................................................................21Table2.4–Useofrare-earthelementsinavarietyofdefence-relatedapplications[18]....................................22Table3.1–RecyclingpotentialsforREEsfromphosphors[2]..............................................................................25Table3.2–PublicationsregardingtheleachingofREEsfromlampphosphors...................................................28Table3.3–PublicationsdealingwithseparationsofREEsfromlampphosphorsbysolventextraction.............28Table4.1–TypesofSamples.The“X”codeimpliesthereareseveralsampleswithinagroup.Furthermore,the
valuetakenbytheXsisrelatedtotheLsamplesifX=number,ortothepulpfsX=SP..............................32Table4.2–Determinedleachingconditionsforexperiments1and2.................................................................34Table4.3–Determinedleachingconditionsforexperimentsthreetosix...........................................................35Table5.1–MoisturecontentofsamplesSP,L1,L12andL19...............................................................................37Table5.2–Masslosssintheproductionofthedrysamples.Massisexpressedisgrams(g).............................37Table5.3–Weightofthe32P.Xsamples,togetherwiththemasslossoftheprocess.Massisexpressedisgrams
(g).................................................................................................................................................................38Table5.4–MasslosssintheproductionoftheLGsamples.Massisexpressedisgrams(g)..............................38Table5.5–WeightoftheLGsamples,togetherwiththemasslossoftheprocess............................................38Table 5.6 – Particle SizeDistribution -D10,D50&D90 - SieveAnalysis. AM– arithmeticmean; SD – standard
deviation......................................................................................................................................................40Table5.7–NameofthecompoundsidentifiedbytheXRPDtechnique..............................................................41Table5.8–Atomicpercentageof theelementsconstitutingeachparticle (P.SPsample,particlenumbersare
thosefromFigure5.7)andmaininferredchemicalcompounds................................................................44Table5.9–Elementalcompositionof severalmetals inwaste fractions (wt.%).AM–arithmeticmean;SD–
standarddeviation.......................................................................................................................................46Table5.10–LeachingyieldsofREEsafterleachinginHClaccordingtoconditionsinTable4.2.Resultsin%.....47Table5.11–MassbalanceandvolumeofsolutionusedinexperimentsE1andE2.Samplesbythesameorderas.
Table5.10....................................................................................................................................................48Table5.12–MassbalanceandvolumeofsolutionusedineachexperimentE3-E6............................................49Table 5.13 –Overviewof the leaching behaviour of REEs (values of extractionpercentage for each step, not
accumulated)...............................................................................................................................................49Table5.14–Overallleachingyieldsattainedaftereachtreatmentprocess(6hofresidencetime)....................50
xii
Table5.15–ComparisonofREEsrecoverybetweenliteraturedataandpresentwork.......................................51
TableI.1–Selectedrare-earthmineralsbearingeitherLREEand/orHREE.........................................................59TableII.1–Summaryoftoxicologicalinformationwithrare-earths[30]............................................................63
xiii
ListofAcronymsBAM–BariumMagnesiumAluminate:Europiumdoped
CAT–CeriumMagnesiumAluminate:Terbium-doped
CBT–GadoliniumMagnesiumPentaborate:Cerium,erbiumdoped
CFL–CompactFluorescentLight
EOL–EndofLife
HREEs–HeavyRare-EarthElements
ICP-AES–InductivelyCoupledPlasma–AtomicEmissionSpectrometer
LAP–LanthanumPhosphate:Cerium,Terbiumdoped
LED–LightEmittingDiode
LREEs–LightRare-EarthElements
REEs–Rare-EarthElements
REMs–Rare-EarthMetals
REOs–Rare-EarthOxides
ROW–RestoftheWorld
SEM–ScanningElectronMicroscope
SX–SolventExtraction
XRD–X-RayDiffraction
YBCO–Yttrium-Barium-Copper-Oxide
YOX–YttriumOxide,EuropiumDoped
xiv
1
Chapter1. Introduction1.1. GeneralRemarks
Rare-earth elements (REEs) are specialty metals that comprise 15 lanthanides (from lanthanum up to
lutetium)togetherwithyttriumandscandium[1–3]sincetheseelementsarechemicallysimilar[4].
Since2010,REEshavebecomecriticalelementsfordevelopedanddevelopingcountries.Eventhoughmost
datafocusesonthelastdecadeandahalf,thefirstdiscoverywasmadein1788.
Thegivennameisrelatedtothefactthatupto1800noore,containingtheseelements,wasfoundexcept
oneinSweden.
Theseelementsareofparamount importance intermsof technology,especially in the latest technology
boom.REEsarecomprisedeverywhere inactual technology,namely inelectroniccomponents incomputers,
mobilesandTVscreens;ingreentechnologies,suchasmagnetsforwindgenerators,inductionelectricengines,
and war/defence industry. Although technology is presented as a life saver, problems arise with further
innovation.
Thefirstsuccessfulapplicationremotesto1880bythehandofCarlAuervonWelsbach.Itconsistedonagas
mantlewith1%ofCerium.Theproductionwasimmense,sinceby1930morethanfivebillionmantlesweresold
[4].
Afterwards,alightREEsalloynamed“mischmetal”madeuseoflargequantitiesofREEs’wastesfromthe
productionofWelsbach’smantelsandiron,ina7:3ratio.
Welsbach’stechnologicalandcommercialsuccesssparkedgreater interest inthebroaderapplicationsof
rare-earths,whichexpandedtherare-earthindustrydramaticallyanddrovethequestforrawmaterialsbeyond
Europe,totheAmericas,colonialIndia,andChina[4].
DuringWorldWarI,thepyrophoricpropertiesofrare-earthswereusedinfusesandexplosives.
InJuly1927,thegeologistDingDaohengdiscoveredtheresourcesatBayanObowhichisnowknownas‘the
rare-earthcapitaloftheworld.Thepresenceofrare-earthsatBayanObowasnotdemonstrateduntil10years
laterbythechemistHeZuolin[4].ThisdiscoveryshapedthenascentcommunistChineseindustrialgeography
asthenewlyestablishedPeople'sRepublicofChinarequiredthedevelopmentofnuclearweapons[4].
Inthefirsthalfofthedecade,researchersacrossEurasiaweredevelopingrare-earthsuperalloystousein
thesteelproductionprocesstotransformtheskeletalsystemofmodernityfromheavy,rust-proneandbrittle
to stronger, lighter, and more durable and to make the weapons of war more precise, long-range, and
devastating.Rare-earthswerethekeytodevelopingmaterials that remainstable in temperaturesashighas
1500degreesCelsius,thesortsoftemperaturesneededforrocketsandlong-rangemissiles[4].
The earliest application of pure REEs in the mid-1960s/early 1970s arises from the improvements in
separationtechniquesthusreducedthecostofeuropium[4,5].Europiumwasused inredphosphorsforTV
screens.TheimprovementintelevisionresultedinaburstofREEsapplications.Aroundthisera,europiumwas
themostcriticalREEduetoitslowabundanceandhighdemand[5].
2
These elements’ exceptional magnetic and conductive properties enabled in the 1970s and 80s the
production of samarium-cobalt magnets, thus turning samarium into the most critical REE. Nowadays, this
productrepresentslessthan2%ofpermanentmagnets’types.
Currentlythemarketisdictatedbytherequirementofneodymiumanddysprosium(Table1.1).Thefirstis
usedforNdFeBmagnets;onlyin2011,25000tonswereneededformagnetsproduction.Byminingthisnaturally
lowinabundanceconstituent,excessesofcerium,praseodymiumandsamariumwereproduced.
SinceheavyREEs(HREEs1)areproducedinmuchsmallerquantitiesthanlightREEs(LREEs2),thebalancing
problemisalotmoresignificantintheLREEmarket.Nowadays,theHREEsmarketis,asmentioned,drivenby
dysprosiumbecauseofitscapabilitytoincreasehigh-temperatureperformanceanddemagnetizationresistance
ofNdFeBmagnets.So,for25000tonsofNdusedtoproducethemagnets,1600tonsofDywhereneededto
fulfilthesameproduction.
ForsomeREEs(Eu,Y,ErandLa)theexistentsupplyequalsthedemand.Gd,Ho,Tm,YbandLuareproduced
inexcessand,therefore,stockpiled.AshortageinTbisverified.
Nowadays’demandsforNdandDyarenotthesameasbeforeastheseelementshavenotalwaysbeenthe
mostcritical.Thatcanbeidentifiedbythehistoricalevolution.
Table1.1–Supplyanddemandfor2016,expressedinrare-earthoxides(REOs)[6].
ElementDemand Supply Surplus(+)
tonnes % tonnes % Deficit(-)
La 36750 23.0 52000 26.7 15250
Ce 65000 40.6 81000 41.5 16000
Pr 7500 4.7 9500 4.9 2000
Nd 30000 18.8 31500 16.2 1500
Sm 1000 0.6 3750 1.9 2750
Eu 780 0.5 500 0.3 -280
Gd 2225 1.4 2750 1.4 525
Tb 450 0.3 350 0.2 -100
Dy 1650 1.0 1450 0.7 -200
Er 1000 0.6 800 0.4 -200
Y 13350 8.3 10000 5.1 -3350
Ho-Tm-Yb-Lu 250 0.2 1400 0.7 1150
Total 159955 100 195000 100 35045
1HeavyREEs:TerbiumuptoLutetium,aswellasYttriumandScandium;2LightREEs:LanthanumuptoGadolinium.
3
TheREEisafastmutablemarket.Newapplicationsand/orvanishingofcurrentwell-establishedapplications
canbringthemarketfurtheroutofbalance.Forthepasttwodecades,globaldemandforREEshasexperienced
arisingtendency.ThisisprojectedtocontinuetogrowasaresultofthedevelopingREEsupplychain.
WithChina’sdominanceofthesupplyofREEs,therestoftheworld(ROW)iscurrentlydependentonChinese
exportstomeetitsowngrowingneeds;however,recentbehaviourshavedemonstratedadesiretoretainmore
ofthematerialsforinternalconsumption.Chineseexportquotashavedeclinesince2012(Figure1.1).
Figure1.1–DivergenceofChinaExportquotaandROWdemand(adaptedfrom[6]).
1.2. ProblemOverview
1.2.1. Rare-earthsascriticalelements
Inrecentyears,therehavebeenexpressedconcerns,andmanyassessments,regardingthecriticalnature
ofthesupplyofcertainmineralrawmaterialstonationaleconomies.Majorriskfactorshavebeenidentified
includingtheconcentrationofproductionatthenationallevel,thepoliticalstabilityofproducingcountries,and
sudden demand peaks. The essential role high tech materials are playing in the developed countries for
innovativeapplicationsisnowwellrecognized.
In2008severalcommissionsoftheEU,USAandJapanamongstnumerousothers[3,7]releasedreportson
the roleof strategicminerals in their economy.An increasingnumberofelementswereassessedas “highly
critical” (Table 1.2) such as indium, cobalt, niobium, tantalum, rare-earth elements (REEs),lithiumand the
platinumgroupmetals[2,8].
4
Table1.2–SummaryoftheBottleneckAnalysis:redimpliesahighrisk,yellowamediumriskandgreenalowrisk[8].
Metal
MarketFactors PoliticalFactorsOverall
riskLikelihoodofrapid
demandgrowth
Limitationstoexpanding
productioncapacity
Concentrationof
supply
Political
risk
Dysprosium High High High High
High
Neodymium High Medium High High
Tellurium High High Low Medium
Gallium High Medium Medium Medium
Indium Medium High Medium Medium
Niobium High Low High Medium
MediumVanadium High Low Medium High
Tin Low Medium Medium High
Selenium Medium Medium Medium Low
Silver Low Medium Low High
Low
Molybdenum Medium Low Medium Medium
Hafnium Low Medium Medium Low
Nickel Medium Low Low Medium
Cadmium Low Low Low Medium
AccordingtoErdman[7],afteranalysingtenreportstudies(EUandUSAincluded),alldenotatedREEsas
critical.Thefivemostcriticalareneodymium(Nd),europium(Eu),terbium(Tb),dysprosium(Dy)andyttrium
(Y),ascanbeseeninFigure1.2,andareexpectedtobeshortinsupplyoverthenext10years[2,9,10].
Figure1.2–Mediumtermcriticality(10years))ofsomeelementsaccordingtotheirsupplyriskandimportancetoclean
energy(adaptedfrom[2,10]).
5
1.2.2. Geopoliticalproblem
Geological availability of REEs iswidespread.However, only a small proportion of these deposits are of
sufficient size that they can be explored economically [1]. In fact, there is a rare-earth elements’ Chinese
monopoly,nowthatChinaspecializesintheextractionofREOs3anddown-streamactivities,controlling97%of
the production and 89.7% of EU imports (Table 1.3). Worldwide reserves of rare-earth metals (excluding
scandium)areestimatedtobearound99milliontonnes(dataof2009)[11].
Giventhedemandfortheseelementsitisofimportancetoexaminewhethertheresourcesmeetmodern
societyneeds.Thereare largereservationsaboutestimatesofREEsavailability. It ispredictedthat,by2020,
therewillbeshortagesofNb,Dy,Eu,TbandY,asitisanticipatedthatoverthenext25yearsthedemandfor
neodymiumanddysprosiumwillriseby700%and2600%respectively[12].
Untilthe1980s,USwastheleaderinREEproductionandexploration.Withtimethatchanged,andcurrently
Chinaismanagingalmostallrare-earths’productionanddownstreamactivitiesdespiteonlypossessinglessthan
40%oftheworldreserves[2,3].Theproblemthatariseshereisageopolitical-economicavailability:highlevel
ofproductionconcentratedinfewcountries.Moreover,duetolargeandincreasingdomesticdemands,China
tighteneditsREEexportquotafrom50145tonsin2009toonly31130tons in2012,andareconstrainingit
increasingly.
Inanefforttomitigatethedamages,miningcompaniesarenotonlyreopeningoldmines,butalsoactively
seekingnewexploitableREEdeposits.Manycountrieswithoutoperationalprimarydepositsontheirterritory
willjusthavetorelyonrecyclingofREEsfromsecondarydeposits(pre-consumerscrap,industrialresiduesand
REE-containingEnd-of-Lifeproducts).
Table1.3–Considerablereserves,basicsupplyanddemandstatistics[11].
Reserves
(in103tons;2009)Production
(in103tons;2009)EUimports
(in103tons;2007)
USA 13000 13.2% - - -
Australia 5400 5.5% - - -
Brazil 48 <0.1% 0.65 0.5% -
China 36000 36.5% 120 97.0% 15.8 89.7%
India 3100 3.1% 2.7 2.2% 0.07 0.4%
Malaysia 30 <0.1% 0.38 0.3% - -
Kazakhstan - - - 0.1 0.6%
Russia - - - 1.6 9.2%
Vietnam - - - 0.01 0.1%
Others 41000 41.6% - - - -
Total 98578 123.7 17.6
3TheglobalproductionofREEistypicallyexpressedintonnesofrare-earthoxides(REOs).
6
By1970ChinaoverpassedtheUSdominationintheREEmarket(Figure1.3),floggingthemarket,inpartdue
tolowerlabourcostsandenvironmentalstandards.Thisresultedinapricedecrease,inhibitionofnewmining
projectsotherthaninChina.Beijingcontrolledtheentireproductionflowbyofferingindustriesandcompanies
reducedprices.Therewerescarcelyanyenvironmentalcontrol[13].
AccordingtotheCentreforEuropeanPolicyStudies(CEPS)PolicyBrief[13],by2010,Chinahadreduced
exportsby72%andincreasedexporttaxeson23rare-earthscategories(rare-earthoxides,unmixedandmixed
rare-earthchlorinates,oresofrare-earthmetals,rare-earthmaterialsintermixedorinter-alloyed,etc.)ranging
from25%onselectedrare-earths,primarilyheavyones,toupto15%onlightrare-earths.Forinstanceeuropium
rosewentfrom205.2€/kg(pricefrom2006)tonearly503.9€/kgwhileceriumfrom1.38€/kgto21.16€/kg[13].
Chinareducedexportratesfor3mainreasons.Firstandforemost,itaimstoincreaseself-manufactureofhigh-
techproducts.
ThisresultsinaneedandwantingfromWesternindustriestomovetheirfacilitiesandpatentsintoChinain
order to have more accessible rare-earths. China has a bonus of having access to new technologies and
innovationsgiventheshadowypropertyrightsenvironment/mentality.Therearealsouncertaintiesrelatedto
demand,supply,pricesandtheconceptofChinaitself,thatresultsinthemajorityofintervenientmarketsbeing
reluctant,uptonow,tore-locateproductiontoChina.[13].
Second,“Beijingaimstoincreaseitscontrolandconsolidateitsdomesticrare-earthsindustry”[13]by:
• Mergingminingcompanies(from120to10);
• Mergingprocessingfirms(from73to20);
• Establishingastockpilingsystem;
• Unifyingsupervisionofextraction;
• Settingupmonitoringsystemsforproduction,transportationandsales;
• Eliminatingproducerswithlessthan8000tonsofannualproduction[capacity].
Furthermore,BaotouSteelRare-earth,(supplies46%oftheglobalMarket)togetherwithJiangxiCopperare
interested in creating a unified pricing system for LREE. For analysts, these intended measures increased
significantly the prices. These measures also allow a strict control of production (by decreasing, for
instance,illegalminingandexports)andineconomicmonopoly[13].
Finally,Chinawantsthe“extremelyhighenvironmentalburden”.Likementionedbefore,theminingofREEs
anditsrefiningis,sometimes,associatedwithradioactiveslurriesandwiththetoxicacidused[13].
Regulationsarebeingdiscussedtoimproveproductiontechniques,whichwillimplytheclosingofnumerous
companies,affectingsuppliesandcontributing,furthermore,totherestrictiveconditions,i.e.reducedoutput
[13].
SinceexportsarecontrolledandcrampedbyChinesefees,environmentalregulationisauxiliaryinsteadof
havingaprimaryeffect.
7
Figure1.3–GlobalRare-earthOxide(REO)productiontrends[adaptedfrom[14]).
1.3. Scopeofthework
Duetotheincreasingsupplyrisk,thereisaninterestinrecyclingREEsfromend-of-lifeproducts.
It has been reported that recycling REEs would mitigate the main problem that arises from primary
exploitation, therefore having a stabilizing effect on prices, supply andquality of these elements andbased
materials[2,5,15].
Recyclingthemainwastestreamsimplies:
1. Recoveringhigherpercentageofelements,whencomparedtothepercentageobtainedwithprimary
ores;
2. Thereductionofthetotalamountoforesthatneedtobeexploitedinordertomeettheglobaldemand;
3. Thedecreaseofthebalancingproblemduetolessoverproduction;
4. ThepossibilityofmanycountriestohaveREEswithoutrelyingonnationaloperationalprimarydeposits
[iftheyexist]and/orabroadstocks.Despitethe[mandatory]needforrecyclingandthevastresearch
effort,upto2011lessthan1%wasrecycled[1].
Notwithstanding the environmental significance, it is industrially relevant to recycle the most valuable
applications:permanentmagnets,lampphosphors,Ni-MHbatteriesandcatalysts.Inthissense,theobjectiveof
thisworkistocontributetothedevelopmentofrecyclingprocessesofrare-earthscontainedinwastestreams,
namelyfocusingtheexperimentalworkinonespecificwaste,thefluorescentlamps.
ThisresearchworkhadbeencarriedoutinsideInstitutoSuperiorTécnico’sfacilities(IST,Lisboa,Portugal)
namelyMicroLab - ElectronMicroscopy Laboratory; Laboratory ofMineralogy and Petrology (LAMPIST) and
8
Laboratory ofWaste Processing andManagement, in collaboration with Laboratório Nacional de Energia e
Geologia(LNEG,Lisboa,Portugal).
SummarizingChapter1 ismeant to set the scenariowithinwhich thiswork stands, topresent themain
impedimentsregardingrare-earthandtofamiliarisethereaderwiththeresearchcarriedoutanditsgoals.
InChapter2,afteranintroductoryfirstsubchapterthatbrieflyexplainswhatREEare,ispresentedastateof
theartoftheprimaryexploitationofthesemetals.
Chapter3relatesthestateoftheartoftheprocessingofREEend-of-life(EOL)products.OverviewofREE
commercialapplicationsandsomeconsiderationsaboutrecyclingratesarepresented.
Chapter4iscommittedtothepresentationoftheworkplanrelatedtotheseveralleachingtechniquesto
reclaimREEsinrealfluorescentlampwaste,containingparticularly:cerium,europium,gadolinium,lanthanum,
terbiumandyttrium.
Chapters5referstothepresentationoftheresultstogetherwithasignificantdiscussionregardingthefinal
REErecovery.
Chapter6containsthestudy’sconclusionsandsomeinsightsforapossiblefuturecontinuationofthiswork.
9
Chapter2. Rare-earthElements2.1. Rare-earthElements
The rare-earthelements (REEs) area groupof seventeenelements: fifteen lanthanides (lanthanum (La),
cerium(Ce),praseodymium(Pr),neodymium(Nd),promethium(Pm),samarium(Sm),europium(Eu),gadolinium
(Gd),terbium(Tb),dysprosium(Dy),holmium(Ho),erbium(Er),thulium(Tm),ytterbium(Yb)andlutetium(Lu))
andtwotransitionmetals(yttrium(Y)andscandium(Sc)),sincetheseelementshavesimilarproperties[1–3].
REEsareinfactmetals.Metalsaredividedintofourcategories:ferrous,non-ferrous,preciousandspecialty.
REESareincludedinthespecialtymetals.[16]
AccordingtoREEHandbook,elementsfromlanthanum(atomicnumber57)togadolinium(atomicnumber
64), the ones with the lowest atomic weight, comprise the light rare-earth elements (LREEs) [17]. Terbium
(atomicnumber65)uptolutetium(atomicnumber71),aswellasyttrium(atomicnumber39)andscandium
(atomicnumber21)aretheheavyrare-earthelements(HREEs).Thisdivision,changesaccordingtosources.For
instance,in[1]and[18],LREEsgouptosamarium,whereasin[19]isuptoeuropium.
In this thesis, it is considered the division defended by the REE Handbook (Figure 2.1). The difference
between LREEs and HREEs, also named, cerium and yttrium group, respectively, is the electronic
configuration;thisdifferenceiscriticaltothepropertiesthateachREEdisplaysandhowitinteractswithother
elementsand/orcompounds.
Figure2.1–The17elementsthatcomprisetheREEsgroup.TheelementswithagreenframearetheLREE,whereasthe
oneswiththeblueframe,theHREE.
Despitetheirgroupnametheseelementsaremorefrequentthanmanyotherknownelements.REEsare
relativelyabundantintheearth’scrust,butminableconcentrationsarelesscommonthanformanyotherores.
Their natural occurrence is strongly dependent on geological features, and they are only found in sufficient
quantityandconcentrationinafewlocations,andinasuitableformandsetting,tomaketheirextractionand
exploitationeconomicallyviable.
10
LREEscoverupto99%oftheREEsresourses[1].Table2.1showstheaverageamountofsomeREEs,aswell
asotherelementsasaproportionoftheEarth’scontinentalcrust.TherarestREEisthulium(Tm)ifwedisregard
promethium(Pm)whichis,sinceitisaradioactiveelementwithashorthalf-life.Therecanbenoticedthatthese
elementshaveamuchhighervalueand,whencomparedtootherimportantelements,REEsabundancesarenot
soapart.
Table2.1– Abundanceofsomeelements[1].
Element Quantity(ppm)
Ce 43
La 20
Nd 20
Y 19
Tm 0,28
Cu 27
Li 17
Sn 1.7
Ge 1.3
U 1.3
2.2. Depositsandmineralogy
2.2.1. Maindeposits
Overtwohundredrare-earthmineralshavebeendescribed[1,19].However, inmanycasesthere isnot
enoughconcentrationofthesemineralstoeconomicallyjustifyminingandinothersthereisnoknownmethod
toextracttheREEfromtheoreeconomically.MineralstendtoberichineitherLREEsorHREEs,proportionsof
thedifferentREEswithinmineralsvarybetweendeposits. Ingeneral,REEsbearingmineralsare found in the
followingprimaryandsecondarygeologicalsettings[1,20,21]:
• Primary:
o Carbonatites(almostexclusivelyLREEs);
o Pegmatites(oralkalineigneousintrusivecomplexes);
o Hydrothermalveins(enrichedinHREEs);
• Secondary:
o Weathereddeposits/Laterites;
o Placers(mostlysandsofmarineorigin).
The main reserves are located in China (including Bayan Obo), Russia, Kyrgyzstan, Kazakhstan), USA
(including Mountain Pass) and Australia (including Mount Weld) (Figure 2.2). There are also resources in
India,Vietnam, Malaysia, Thailand, Indonesia, South Africa, Namibia, Mauritania, Burundi, Malawi,
Greenland,Canada,BrazilandPortugal[1].ThelargestknowndepositisinBayanObo,InnerMongolia,where
threedifferenttypesoforearedistinguished:Iron-REEsore,REEsoreindolomiteandREEsoreinsilicaterock
[1, 21]. Considerable REEs resources are related to pegmatites and carbonatites, such asMountain Pass, in
11
California,USA,andMountWeld,inWesternAustralia.Infact,beforeBayanObocameonstream,thelargest
singlesourceofREEswasMountainPass(whereminingceasedin2002).MountainPassisexpectedtomakea
significantcontributiontoglobalsupply,asarethedepositinweatheredcarbonatiteatMountWeld;thealkali
trachyte intrusionatDubbo,NewSouthWales,Australia(whereREEwillbeco-producedwithzirconiumand
othermetals);andafurthersmallermonazitedepositatSteenkampskraal,WesternCape,SouthAfrica[1].
Figure2.2–MainworldREEsdeposits(adaptedfrom[22]).
2.2.1.1. DepositsinPortugal
StudiesdemonstratedthatPortugal’sgeostructuralcharacteristicscontributetoagreatpotential for the
occurrence of rare-earths. Until recently, REEs were never mined in Portugal, apart from Alter Pedroso
zone,wherehyperalkalinerockshavebeeninvestigated[23].
Ageological survey, throughgeologicalmapping,alluvialandstreamsedimentsamplingandradiometric
surveys,exploredBeiraBaixaandAltoAlentejoregions.MiningaimsatthedetectionofREEsbearingminerals
suchasmonazite-nodularmonaziteinparticular-insedimentaryrockareas(moreorlessmetamorphosed)and
xenotime,apatiteandallanite[23].
DataaboutAltoAlentejosuggeststhat[nodular]monaziterichinLREEshasoriginatedprimarilyfromthe
disintegration of Ordovician quartzites on the southwest flank of the Portalegre Syncline. Normalmonazite
appearstobemainlyassociatedwithgranite(Fronteiragranite)[23].ReferredzonescanbeseeninFigure2.3.
12
Figure2.3–Portugal’sregionswith[possible]REEoccurance.
DatasuggeststhattheradioactivequartzitesinterstratifiedintheschistsareconstituentrichinREEs,and
nottheschistsitself.Thisverdict,goesagainstexistingdataonthelevelsofschistswithnodularmonazite(rich
inrare-earths,particularlyeuropium),inotherplacesinEuropeandAmerica[23].
Another study, taken by LNEG in 2010 [24], defined a feature of intra-xistent ordovician radioactive
quartzites(containingnodularmonazite),withanaveragethicknessof1mandanextensionof5.5kminValede
Cavalosregion(Figure2.4).
Figure2.4–Large/mediumoccurrenceofREEinValedeCavalosidentifiedbythebrowncircle(adaptedfrom[24].
13
Furtherstudyingwasmaderegardingthemainphasesthatcarrytherareearth(REEs)andtherearealso
evidencesofrareearthelementsinthePliocenesedimentsbetweenriversVougaandMondego[25].
2.2.2. MineralogyofREEs
Mineral groups include silicates (e.g.eudialyte, allanite); carbonates (e.g.bastnäsite, synchisite,
parasite,fluocerite, ancylite), oxides (e.g.euxenite, aeschnite, fergusenite, loparite) and phosphates (e.g.
xenotime,florencite,monazite)(AnnexI–TableI.1)[19,20].
NowadaystherearefourREEsbearingmineralspeciesbeingexploitedcommercially:
• Bastnäsite,aLREEfluorocarbonate(ChinaandUSA);
• Monazite,aLREE/HREEphosphate(Australia);
• Xenotime,aHREEyttriumphosphate(Malyasia);
• LateriticorecontainingHREErichionadsorptionclaysinChina.
SinceseveralREEshavesimilarproperties(physicalandchemical)theytendtooccurtogetherthereforethey
arerecoveredfromthesamemineralhost(AnnexI–TableI.1).Succeedingthatfact,thechemicalprocessesto
separateandconcentratetheseelementsinvolveadditionalcost.
Bastnäsite[20]
Thisfluorocarbonatemineral,(Ce,La,Nd,Pr)CO3F,isthemostimportantsourceforREEs.Ittendstocontain
copiousLREEs(specificallycerium,lanthanum,yttrium,andneodymium)andverylowproportionsofHREEs.
The realmineral environment inwhich bastnäsite is recovered is farmore complex than the simplified
chemicalformulaofthesinglemineralinfact,severalREEfluorocarbonatemineralsareknown.Variouscommon
substitutions in thechemistryofbastnäsite, i.e. ranges in themetalportionof thesolid solution,generatea
seriesofrelatedmineralsthatmaybefoundtogetherinbastnäsiticores.Threevariationsinnomenclatureare
usedtodescribeafewcommonranges:bastnäsite-(Ce),bastnäsite-(Y),andbastnäsite-(La).
It isalsopossible,bythesubstitutionofthefluorineorcarbonateanions,toobtainrelatedmineralslike:
parisite,andvarioushydroxylbastnäsites,interalia.
Bastnäsite ores have been found in a variety of igneous environments: carbonatites,
granites,pegmatites,hydrothermalandbauxitedeposits.
Monazite[20]
Monazite is the second most common mineral used as a rare-earth ore. It has also variations in the
nomenclatures according to the primary elemental composition of the ores: monazite-Ce, monazite-
La,monazite-Nd,andmonazite-Pr.Theoverallchemicalformulais(Ce,La)PO4.
ItcontainspredominantlyLREEsandcomprises,always,amixofvariousrare-earths.However,itishabitually
associatedwithslightlyhigherratiosofHREEsthantheonesfoundinbastnäsite.
Radioactive spin-offs are a dare in somemonazitemining locations, due to the capability of thorium, a
radioactiveelement,tosubstitutefortherare-earths inthemonazitestructure.Theseby-products, including
uranium,maybecomemineableco-productsinextremecases.
14
Xenotime[20]
Isthethirdmostimportantrare-earthelementoreandit,typically,containsthehighestratiosofHREEsout
ofthethreemainmineralores.
ThegeneralizedchemicalformulaisYPO4.TheyttriumiseasilysubstitutedbyseveralHREEsasdysprosium,
ytterbium,erbium,andgadolinium.Nevertheless,itcanbereplacedbyfewerquantitiesofterbium,holmium,
thulium,andlutetium,aswellasuraniumandthorium.Notethaturaniumandthoriumarenot insignificant
quantities, like inxenotimeores,howeverarepresenteitherasmineableby-productor impurity,depending
entirelyupontheminecontext,quantityandlocation.
Xenotimeandmonazitecanberelatedsincetheyaresimilarphosphates.Thefirstiscomposedmainlyby
yttrium,who is then freely substitutedby variousHREEs, asmentioned.Whereasmonazite is developedby
cerium,whichissubstitutedbythevariousLREEs.
These two ores can be found together, representing a continuous mineral formation established upon
modifications in temperature and pressure. At lower temperatures and pressures occurs the formation of
monazite,while athigher temperatures andpressures, xenotime is formed. The variationof the conditions
resultsinchangesinthecrystalstructureofthephosphateasoneortheotherREEsgroup(LREEsandHREEs)
getsexcludedfromthelattice.Thephosphateportionofxenotimeandmonaziteconstitutessignificantmineable
co-productsintheseores.
2.3. Balanceproblem
AnotherproblemarisesfromtheprimaryexplorationofREEs,thesocalled“balanceproblem”.Notonly
theseelementsoccurtogether,but,andmoreimportant,theyoccurindifferentratiosintheirselectedminerals
andores,asitwasobservedin2.2.2.
BastnäsiteandmonazitearerichinLREEs,whilstxenotimeandionadsorptionclaysarerichinHREEs.
Asmentioned before, the balance is tipped towards LREEs since they comprise 99% of resources, then
depositswithahighproportionofHREEareveryrare.Thisfactisrelatedtothegeneraltrendthattheseelements
verify.WithincreasingatomicnumberZ,therarertheybecome,i.e.abundancedecreasesalongthelanthanide
series.Soitcanbestated[andre-confirmed]thatHREEsaremuchlessplentifulthanLREEs.
AssaidbytheSwissAcademyofEngineering[26],globaldemandinREEsannuallyis132500tonnes(data
of 2008). Even though rare-earths are found in the crust, few are the depositsworth exploring.Worldwide
reservesareestimatedataround99milliontonnes(dataof2009),andthemajorityofdepositsarelocatedin
China(38%),CommonwealthofIndependentStates(19%)andUS(13%).
Apartfromtheseelementsnaturaltippedoccurrence(geographicallyandquantitiesintheores),thereis
also the fact that the majority of HREEs play a crucial role in emerging green energy and high tech
applications,and,therefore,aremorevaluablethanLREEs(Table2.2).Thisresults inaveryhighdemandfor
specificREEs, that areaminor constituent,while thedemandof themajor constituent ismuch lower. Even
thoughthedemandandsupplymustbeequal[atanygiventime],duetothedifferentabundancetherewillbe
lacking or overloading of certain elements. This will increase even more the overall price of REEs due to
stockpiling.
15
Forexample, theminingofeuropium (that ismuch less) frombastnäsite4willproduce largeamountsof
lanthanum,cerium,praseodymium(muchmorecommonsincetheyareinhigherrateintheminerals),thathave
tobesoldthen(Figure2.5)[15].
Figure2.5–Resultingoutcomeofminingonetonofeuropiumoxide[5,15].
Thedeficientbalancebetweenthedemandbythe[economic]marketsandthenaturaloccurrenceofthese
elementscreatesthe,socalled,“balanceproblem”or“balancingproblem”.
Thisproblemimplicatesthattheindustrymustfirstly,findnewapplicationsfortheREEsinexcessandsearch
forsubstitutionalelements for thoseminorREEs.Tobalance theLREEsmarket,high-volumeapplications for
samarium,praseodymiumandceriumareessential.AsecondoptionistodiversifythetypesofexploredREEs
ores,consideringlesscommononeslikeloparite(Ce,Na,Ca)(Ti,Nb)2O6[5,15].
Athirdapproachisrecycling.SpeciallycomparedtotheprimaryminingofREEs,notonlysolvesthebalance
problembutalsoreducesthetotalamountofREEsoresthatneedtobeextractedandallowstheattainmentof
REEswithhigherandsimplerconcentration[5].Forinstance,byrecyclingphosphorslampswewouldbeableto
recoverY,Ce,La,Eu,Tb(Table2.3).
DependenceonChina,whichhasreinedinitsexportsofrare-earths,asitwillbediscussedahead,canonly
be reduced if deposits outside China are mined, or if recycling is intensified. Therefore, to fulfil this
purpose,processes, inorder toextractREEs fromoresand recycleREEs’endof life (EOL)products,mustbe
developed.
Currentmarketreliesonthemaincomponents indemand:magnetsandmetalalloys,bothofwhichare
responsible forconsumingapproximately21000 tonnesofREOequivalents in2011.Magnetsconstitute the
largestportionofdemandin2016(Table2.2),reaching36000tonnes[6].
4Bastnäsiteisricherineuropiumthanmonazite:0.1%versus<0.05%.
16
Table2.2–Applicationanddemandgrowth(2011to2016).UnitsareintonsofREOs[6].
2011 2016
Application China ROW TOTAL % China ROW TOTAL %
Catalyst 11000 9000 20000 19 1500 9500 25000 16
Glass 5500 2500 8000 8 7000 3000 10000 6
Polishing 10500 3500 14000 13 13000 5000 18000 11
Metalalloys 15000 6000 21000 20 23000 7000 30000 19
Magnets 16500 4500 21000 20 28000 8000 36000 23
Phosphors 5000 3000 8000 8 8000 3500 12000 8
Ceramics 3000 4000 7000 7 4000 6000 10000 6
Other 3500 2500 6000 6 5000 14000 19000 12
Σ 70000 35000 105000 100 104000 56000 160000 100
TheindustrycontinuestoincreaseanddiversifythesupplychainandnewsourcesofdemandforREEswill
arise.Inbrief,theavailabilityoftheseelementsisdeterminedbytheproductionvolumesofREEsores,natural
abundanceandtherequestsituation.
Theexpectedsourcesthatwillhaveanimpactonthemarketdynamicinclude[6]:
• Magnetorestrictors[foractuators,acoustics,micropositioner,sonar,valves,micropumps,andsatellite
telescopes];
• Magnetic Refrigeration: Applications in home/auto air conditioning, household appliances.
Typically,gadoliniumbasedalloyswithdysprosium,erbium,andothernon-REEsmaterials.
• Magnetooptics:Useoflaserstowrite,read,anderaseinformationonterbium-basedthinfilms(upto
50timeshigherstoragedensityversusmagneticharddisks).Yttriumisalsoused;
• Superconductors (YBCO [yttrium-barium-copper-oxide]): High-temperature conductors with
applicationsincircuitry,powergenerators,electricstorageunits,andelectricmotors.
2.4. Extractionandprocessing
NumerousminingandprocessingtechniquesareusedforthetransformationofREEs’bearingminerals,due
tothediversityofthesedeposits.Themajorityincludesthermaltreatmentoftheoreconcentrateinthepresence
ofacidicorcausticreagents.Thechoiceofthedecompositionmethodisdoneaccordingtotheoreconcentrate.
Ithastobenotedthat,sincerare-earthsarecommonlyexploitedasothermetals’by-products,thesewill
determinetheeconomicsoftheoperationsandtechniquesused.Forinstance,REEsextractedinChinaareaby-
productofironoreextraction.InRussiafromtitaniumextraction,whereasinCanadarare-earthswererecovered
fromuraniumexploitation.
An opinion article presented in the Le Monde exposed ignored problems to promote technological
innovation[27].
17
Regardingworkingconditions, labourhasbeenincreasinglyexportedtonationswithcheap[almostfree]
manpowerandminimaltonoregulationsasisthecaseofChinesemanufacturingsites.Moreover,althoughit
resultsincheaptechnology,productsarenotmadethatcheap,astheexampleofApple.
Secondly,therearesubstantialenvironmentalcostsconcerningtheprimaryexploitation.Onehastoextract
them,thenpurificationisneededandfinallythepureREEsareimplementedintotechproducts.
Theextractionprocessisratherunclean.Althoughthereareminingprocessesthatallowcleanmetalsthey
comeatagreatercost.Sincethecostisdemandedbythemanufactures,theminingindustryisforcedtoremain
dirtyandpollutant.Theextractionresultsinsubstantialpollutionintheminingsites:soillossanddegradation,
leachingintogroundwater,lakesriversand,asaresult,bioaccumulation.
Overall,theattainmentprocessofREEfromthemainoresischaracterizedbyfourmainsteps(Figure2.6):
• Extraction;
• Flotation (physical beneficiation process): there is the separation of the valuableminerals from the
wasteor“gangue”allowingtheattainmentofmineralconcentrate;
• Hydrometallurgy:solubilisationofthevaluableminerals;
• Separation:AmixtureofREOsresultsfromtheprocessabove,henceseparationisneededinorderto
obtainindividualrare-earthcompounds(oxides,carbonates,etc).
Figure2.6–GeneralextractionandprocessingofREEsores.TheoperationsdesignatedbySXmeansolventextraction:
amulti-stepprocess[28].
18
2.4.1. EnvironmentalImplications
Firstofall, likeotherextractiveoperations,theprimaryexploitationofREEsusessubstantialamountsof
energythatare,mostly,suppliedbycoalpowerstations[22].Thisaidstheincreaseofthemainenvironmental
concerns:climatechangeandincreasingcarbonemissions.
However,theuseofrare-earthsintechnologicalproductsallowsabetterenvironmentalfriendlyoutcome.
Theuseofnickel-lanthanumrechargeablebatteries,insteadofnickel-cadmiumones,reducescadmiumorlead
toxicityissues[sinceitdoesnotincludetheminthecomposition].Furthermore,theuseofREEsinfluorescent
lamps,aswellas inmagneticrefrigerationsignificantly increasesenergyefficiencyand,thereby,reduces𝐶𝑂,
emissions[22].
Anothercomplicationthatarisesfromprimaryobtainmentistheradioactivityofsomeores.Asmentioned
in 2.2.2, xenotime andmonazite are related to radioactive, and sometimesmineable, co-products. For this
reason,manyminesandplantswereclosed.
Ion adsorption clay deposits have lower radioactive element content. However, additional problems
develop:in-situminingtechniquesaremoreenvironmentallyfriendly,buttherearesomeconcernsaboutthe
injectionofstrongreagentsintotheground[29].
Concerningbastnäsite, itsdepositscarrysignificantdangersduetothechemicalsused intheprocessing.
Reports show that processing of bastnäsite has caused: water pollution, farmland destruction and human
poisoning.
OveralltherefiningofonetoneofREOscanproducetonsofwasteproductsandpollutants,ascanbeseen
inFigure2.7.
Figure2.7–Productsofrefining1toneofREOs[22].
19
2.4.2. HealthImpacts
Regarding the impacts in human health, some studies were done. One is aware that after human
interference, REEs can accumulate in mining areas due to its low mobility leading to soil and water
contamination,bioaccumulationand[chronic]toxicity[30].Bycomparingtoxicological literatureon inorganic
xenobiotics5,regardingREEslittleinformationisavailableabouthealtheffects,theexistingonefocusesonfew
elements [28, 29]. For instance, database is mostly confined to Ce and La with a total of 63 and 55
reports,correspondingly,withminor informationavailable forGd (21)andNd (16),andsparse for theother
REEs,especiallyforHREEs:Y(15),TbandYb(8)(Figure2.8).Onemustnotethatthisgroupissignificanttothe
developmentandfabricationofproductssuchasmagnetsandphosphors(asseenaheadin2.5),henceforthwith
trueeffectrelatedtowork-relatedandenvironmentalexposures[31].
SeveralstudieshavedemonstratedthatREEshavestimulatoryorprotectiveeffectsonlowquantities,and
adverseeffectsathigherlevels.AsummarizingtableconcerningthetoxicityoftheREEsispresentinAnnexII–
TableII.1.
Figure2.8–Publishedarticlesreportingoneithertoxic(■)orstimulatory(o)effectsofindividualREE[31].
On the vicinity of a large-scale mining area located in Hetian town of Changting County, Fujian
Province,SoutheastChina,theconcentrationofREEsincultivatedsoilandvegetableswasanalysed,aswellas
in human hair and blood [30]. More than 50 rare-earth mining sites are dispersed throughout Hentain,
moreover,the town has a vast agricultural production representing, approximately, 17% of Chinas’ total
production.
ItwasdeterminedthattheFarmlandsinthesurroundingsarecontaminatedseriouslyduetoREEsmining
production, leading to various accumulation levels of REEs amongst vegetable species, as well as elevated
concentration of REEs in human hair and blood. Despite the concentration values, it was determined that
vegetable consumption would not result in exceeding the safe values of estimate daily intake ( 100 −
5Foreignchemicalsubstancefoundwithinanorganismthatisnotnormallynaturallyproducedbyorexpectedtobepresentwithin.
20
110𝜇𝑔𝑘𝑔34𝑑34)[30].However,onenotesthatattentionshouldbepaidtomonitoringthehealthofthepeoples
inminingareasowingtolong-termexposuretohighdoseREEsfromsoilandfoodcontamination.
2.5. REEsspecificationsanduses
REEs have been recognised as useful due to their chemical and physical properties; they are becoming
increasinglyimportantinthetransitiontoagreeneconomy.Thevarietyofhigh-techapplicationsofrare-earth
elementshasflourished,especiallygreentechnologiesandarmourindustry/defenceweaponsystems[18].They
areusedinmetallurgy,inelectronics,inchemicalcatalysts,asfluorescentsubstancesforcomputermonitors,
lampsandtelevisions,aswellasincatalyticconverters[26].
In a more precise description, REEs, have a crucial role in applications like permanent magnets, lamp
phosphors, catalysts, rechargeable batteries, automotive catalytic converters, wind power generators,
phosphorsforflatscreens,lightemittingdiode(LED)andcompactfluorescentlight(CFL),highstrengthmagnets,
chemicalsandpetroleumrefiningcatalysts,pharmaceuticalsandmetallurgicaladditivesandalloys[1,2].
Forexample,Ce,thedominantREE,isusedincatalyticconvertersincars(autocatalysts),permittingthem
torideathightemperatures;Laisusedincameraandtelescopelensesasglassadditives;Ndisusedtomake
powerfulmagnetsused in computerharddrivesp.e,making themsmallerandeffective, aswell as ingreen
technologies (inwindturbinesandhybridcars).Pr isused inmetallurgytocreatedurablemetals for aircraft
engines;Gd isused inX-ray,magneticresonance imagescanningsystems,andalso intelevisionscreensasa
componentofphosphors(Figure2.9).
Figure2.9–REEsingreentechnology(adaptedfrom[28]).
Eu,TbandYareimportantinmakingscreensfordeviceswithvisualdisplays,astheyareusedinmaking
materialsthatgiveoffdifferentcolours[32].
Table2.3sumstheREEsusageinseveralapplications.
21
Table2.3–Rare-earthsusagebyapplicationinpercentage[33].Percentagesareroundedtothenearestdecimal.Values
maynotaddtototalsshownowningtoindependentrounding.–noconsumption.
REO Catalyst CeramicsGlass
IndustryMetallurgy
Battery
alloys
Neodymium
magnetsPhosphors Other
Ce 32.2 12.0 65.6 52.0 33.4 - 11.0 39.0
Dy - - - - - 5.0 - -
Eu - - - - - - 4.9
Gd - - - - - 2.0 1.8 1.0
La 66.4 17.0 28.3 26.0 50.0 - 8.5 19.0
Nd 0.83 12.0 1.3 16.5 10.0 69.4 - 15.0
Pr 0.57 6.0 2.5 5.5 3.3 23.4 - 4.0
Sm - - - 3.3 - - 2.0
Tb - - - - 0.2 4.6 -
Y 53.0 0.8 - - - 69.2 19.0
Other - 1.5 - - - - 1.0
Table2.4–DistributionofREOsconsumptionbymarketsectorin2008[33].ValuesareinmetrictonsofREOs.
REO Catalyst CeramicsGlass
IndustryMetallurgy
Battery
alloys
Neodymium
magnetsPhosphors Other Total
Ce 8820 840 18620 5980 4040 - 990 293042
200
Dy - - - - - 1310 - - 1310
Eu - - - - 441 441
Gd - - - 525 162 75 762
La 18180 1190 8050 2990 6050 - 765 143038
700
Nd 228 840 360 1900 1210 18200 - 113023
900
Pr 152 420 694 633 399 6140 - 300 8740
Sm - - - 399 - - 150 549
Tb - - - - 53 414 - 467
Y 3710 240 - - - 6230 143011
600
Other - 480 - - - - 75 555
Total 27400 7000 28400 11500 12100 26300 9002 7500129
000
22
According to the Congressional Research Service, REEs not only are critical elements, but also ofmajor
importanceduetotheiruseinavarietyofdefencerelatedapplications,suchas:“finactuatorsinmissileguidance
andcontrolsystems,controllingthedirectionofthemissile;diskdrivemotorsinstalledinaircraft,tanks,missile
systems,andcommandandcontrolcentres;lasersforenemyminedetection,interrogators,underwatermines,
andcountermeasures;satellitecommunications,radar,andsonaronsubmarinesandsurfaceships;andoptical
equipmentandspeakers.”[18](Table2.5).
ThisleadstoanextensiveandrisingexplorationaswellasevaluationofREEsdepositsaroundtheworld.At
the same time, there is international concern about the security of their future supply, their costs, and the
impactsthismighthave.
Table2.5–Useofrare-earthelementsinavarietyofdefence-relatedapplications[18].
Technology Selectedexamples REEsused
Compact/Powerful permanent
magnets for guidance and electric
controlofmotorsandactuators
Tomahawk cruise missile; Smart
bombs; Joint direct attack
munitions; Predator unmanned
aircraft
Nd,Pr,Sm,Dy,Tb
Energy storage, density
amplifications, capacitance for
electronic warfare and directed
energyweapons
Jamming devices; Area denial
system; Electromagetic railgun; Ni-
Mbatteries;
Numerous
Amplification of energy and
resolutions for targeting and
weapons
Laser targeting; Air based lasers;
Laseravenger;Saber-shotdisruptor;
Vehicleswithlaserweapons
Y,Eu,Tb
Compact and powerful permanent
magnetsforelectricdrivemotors
Integrated starter generator; Joint
Strikefighter;
Hubmountedelectrictractiondrive
Nd,Pr,Sm,Dy,Tb
Amplification (enhanced resolution
of signals) for radars, sonar,
radiationandchemicaldetection
Sonartransducers,radar,enhanced
𝜆rayradiationdetector;
Multipurpose integrated chemical
agentalarm(MICAD)
Nd,Y,La,Lu,Eu
23
Chapter3. RecyclingofEOLproductscontainingREEs3.1. Introduction
Asanoutcomeofthesupplyrestrictions,REEshavebeenlabelledascriticalmaterials.Thesupply-demand
balanceisgenerallycharacterisedbyanunder-supply.Asstatedin1.2.1,thefiveREEscharacterizedascritical
areNd,Eu,Tb,DyandYforwhichdemandisexpectedtogrowbyupto30%inthenextyears[16].
Alternativesupplysources,asefficientrecycling,notonlywouldreducethe“REEscrisis”,butalsowould
allow theattainingofREEsconcentrates freeofexportation fees, thusbalancing thepricevolatility,balance
problemsandradioactivity,sincewewouldobtaintheminhigherpercentageandtreated.Longtermavailability
wouldbeassured.Eventhoughtherearemanyinvestigatedmethodsofrecyclingthataresuitedandproven.Until2011less
than1%oftheREEsentertherecyclingloop[1].
The low percentage is due to inefficient collection, lack of infrastructure, technological problems, low
concentrationsinscrap,badecodesign(doesnotallowefficientrecoveryattheendoftheirlife)and,mainly,lack
ofincentives[1].
Regarding technological problems one knows that REEs are normally recycled using routine recycling
techniquesdesignedforstandardmetals,whicharenotonlyoutdatedbutalso,don’ttakeintoconsiderationthe
propertiesofthematerials[16].
ScopeforrecyclingisalsolimitedbythefactthatthelikelyfuturedemandforsomeREEsislargecompared
totheamountalreadyincirculation,andbythelonglifetimesofsomeoftheproductsinwhichtheyareutilized.
At present, Japan is the only significant centre for research into recycling techniques, with Hitachi, for
instance,aimingtorecycleelectricmotormagnetsby2016[2].
AdrasticimprovementintherecyclingofREEsis,therefore,anabsolutenecessity.Thiscanonlyberealized
bydevelopingefficient, fully integratedrecyclingroutes,whichcantakeadvantageoftherichREEsrecycling
literature.
Alternativesupplyingincludes:urbanmining(useofspentproductsbyextractingmetalfromit),reuseand
recyclingi.e.secondarysuppliesandstockpiling(Figure3.1).Substitutetechnologiesareaviablealternativeas
well.
Whereas, certain goods containing REEs have a somewhat long longevity, as well as content to create
secondary supplies aswind turbines and permanentmagnets, others contribute to the opposing. Electronic
deviceshaveagreatlycurterlifetimethereforeresultinginaconstantneedtoproducenewsubstituteproducts.
ThecorrespondingdemandforREEsisnotmetbyurbanmining[16].Tobemoredetailed,a1,5MWwindturbine
usedaround350kgofREEs,whereasloudspeakersofasmartphoneuses50mgofNdand10mgofPr[16].
24
Figure3.1–Alternativesupplying:directrecyclingofpre-consumerscraporresidues;urbanminingofEOLconsumer
goodsandotherproducts;landfillminingoflandfilledpre-consumerandpost-consumerwastestreams(adaptedfrom[2]).
Takingthisintoaccount,someproducts,suchasthoseusedincatalysis,glassesandalloys,arenotrecycled
due to their limited quantity of REEs as well as separation issues. Regarding ceramics, phosphors and
batteries,technologyisnowadaysavailable[16],itfollowsthelifecyclepresentedinFigure3.2,wheretheyare
ideallyprocessedinordertoobtainREOsandmetals.
Figure3.2–LifecycleofREEsinmajortechnologicalapplications(adaptedfrom[2]).
Shortandlong-termimprovementswouldcontributetooptimisingrecyclingtoprovideancillarysupplyof
REEs. Since recycling consumes less energy and chemicals than mining, it would also bring environmental
benefits.
Intheshortterm,thecollectionofspentproductscontainingREEsneedstobefurtherimprovedintermsof
quantities.Separatedepositsforconsumergoodswouldpreventlosingthispotentialresource.
25
A longer term action is to establish a recycling economy. This includes, in particular, creating products
consuming as few REEs as possible and allowing as much dismantling and recycling as possible, as well as
strengtheningexistingeco-designprovisions.
3.2. RecyclingofREEsinlampphosphors
Asmentionedinthesubchapterabove“regarding(…)phosphors(…),technology isnowadaysavailable”.
However,intheparticularcaseoflightningapplication,where9upto12tonsofREEsareused[6,33],phosphor
recyclingispracticallynullinthespecificcaseofPortugal.Inthewholecountry,thereare750lampcollection
sitesand,accordingtoAMB3E,around70%oflampsarestillnotbeingcollected[34].Furthermore,ecotaxes
decreased from 0.23€/lamp to 0.07€/lamp in 2015which does cover the recycling costs [35]. On the other
hand,Spainhasmore than12000 collectionpoints andeco taxes for fluorescent lampsof 0.20-0.30€/lamp
[36,37].
TherecyclingpotentialofREEsinlampphosphorsisfoundinTable3.1.Theauthorscalculatedthepresented
values starting fromthe in-used stocks in2007and furthermore, taking intoaccount thegrowth rateof the
lightingapplications[2].
Table3.1–RecyclingpotentialsforREEsfromphosphors[2].
Application
EstimatedREEs
stocksin2020
(tons)
Estimatedaverage
lifetime(years)
EstimatedREEsold
scrapin2020(tons)
RecycledREEsin2020(tons)
Pessimistic
scenario
Optimistic
scenario
Lamp
phosphors25000 6 4167 1333 2333
Fluorescentslamps,likeservicelamps,compactlamps,tubularlamps,areonegroupofseveralphosphors-
basedproducts(Figure3.3).Theyuseamixtureofphosphorsinordertoproducethedesiredlight,themajority
ofmodernlamps,alsoknownastri-bandlamps,usesamixtureof3phosphors,red,blueandgreen,togenerate
whitelight[38,39].
REEs-based phosphors are favoured over halophosphors since these last comprise a blend that is less
efficientthusproducingalowerqualitylight.Regardless,halophosphorsarestillusedsincetheyproducecheaper
whitelightlamps[38,40],constitutinganimpurityintherecyclingperspective6[39].
Even though the phosphors content varies, not only frommanufacture to manufacture, but also from
applicationtoapplication,astandardtrylamphasaphosphorcompositionof:55%red,35%greenand10%blue
[38,39].
6Thepresenceoflargeamountsofcalcium,originatingfromhalophosphors,posesproblemsduringleachingbyincreasingacidconsumptionandlimitingthesolidtoliquidratio.LeachingofcalciumwithacidicsolutionsoccurssignificantlyfasterthanREEs,leadingtofastconsumptionofprotons.
26
Themainphosphorsbeingcurrentlyusedintheproductionoffluorescentlightsareclassifiedthroughthe
followingacronyms,accordingtothechemicalcomposition[2],[38–40]:theredphosphor𝑌,𝑂8: 𝐸𝑢8<(YOX),the
green phosphors𝐿𝑎𝑃𝑂@: 𝐶𝑒8<, 𝑇𝑏8< (LAP),(𝐺𝑑,𝑀𝑔)𝐵J𝑂4K: 𝐶𝑒8<, 𝑇𝑏8< (CBT),(𝐶𝑒, 𝑇𝑏)𝑀𝑔𝐴𝑙44𝑂4N (CAT) and
thebluephosphors𝐵𝑎𝑀𝑔𝐴𝑙4K𝑂4O: 𝐸𝑢,<(BAM) and 𝑆𝑟, 𝐶𝑎, 𝐵𝑎,𝑀𝑔 J 𝑃𝑂@ 8𝐶𝑙: 𝐸𝑢,<which is less common.
One of the author refers to two green phosphors which are similar to CAT and
CBT,respectively:𝐶𝑒𝑀𝑔𝐴𝑙4K𝑂4O: 𝑇𝑏8<and(𝐶𝑒, 𝐺𝑑, 𝑇𝑏)𝐵J𝑂4K[39].
Figure3.3– Fluorescentlampdiagramwiththemainconstituents.
Regardingtherecovery,onemustunderstandthecompositionoftheproductinhands.Atypicalcompact
fluorescent light consists of glass, metals (Al, Fe-Ni alloy), plastic, phosphor powder and mercury 7
representing,in weight, 88%, 5%, 4%, 3% and 0.005%, respectively [40, 41]. In order to obtain phosphors’
powder,apre-treatmentisaprerequisitetoseparatethemfromothercomponents.Crushingistypicallyused
(asthecaseofthesamplesusedintheexperimentalworkofthisthesis)tobothreducethevolumeandpart
macro-fractions.Thefinefractionismorerichinphosphorpowder,butstillcontainsconsiderableamountsof
glass,thusresultinginsomedilutionofitsREEcontent[2].
Aftercrushingandsievingofthelamps,thephosphors’wetsludgecontains,typically,45%ofhalophosphate
phosphor,20to30%ofglassandsilica,12%ofaluminaand10to20%ofREEphosphors.Residualfractionare
alsopresentsintheorderof5%[40,41].Therelativelyhighcontentinbothsilicaandaluminaarisesfromthe
existingbarrierlayer[2,40].Thisbarrier,placedin-betweenthephosphorlayerandtheglasstube,protectsthe
7Althoughmercury is alsoametal, adistinction ispurposelymade since, in the caseof fluorescent lamp recycling,
mercuryisahazardousimpurity,unliketheothermetalspresent.
27
glassenvelopeagainstmercuryvapourpreventingHgOdepletion,improvingthelampefficiencybyreflectingUV
thatpassesintotheglasslayer[2,40].
Sincethereisalwaysmercuryintheseparatedfractions,adecontaminationistypicallycarriedoutthermally,
sinceitwasconsideredtobewaymoreefficientthanwetdecontaminationsanddoesnotcauseREEs’losses
[39].Itcanbeeitherdonepartly(400-600°Cinvacuum)ortotallybyusinghighertemperatures(800°C)[2].Its
presencecomprisesnotonlyahazard,sinceitistoxic,butalsoanimpurityforthesolventextractionoperations.
Even though regulations require amaximum of 3.5mg/lamp, old lamps are still being processedwhose
mercurycontentedvaries, inageneralperspective,between0.72mg/lampto115mg/lamp[2].Furthermore,
HgOtendstochemicallybondtothephosphorsparticlesgradually.ThusinanEOLlamptheamountofmercury
cancomeupto40timeshigherthaninanewlamp,comprisingmorethan85%ofthemercuryinthelamp.
Thelampphosphorscontainamaximumof,approximately,28%,inweight,ofREOsyetonly10%ofwhich
is truly recycled [2, 41]. In fact, in most countries, after the stabilization (or partial removal) of mercury,
phosphors’fractionsareeitherlandfilledorstoredincontainers.
TherearethreeroutesregardingtherecyclingofREEsfromphosphorsinfluorescentlamps[2,40],itcanbe
doneeitherby re-utilizationof theelements,or theREEscanbeseparated into individual rare-earthmetals
(REMs)forfurtherapplications:
1. Directre-use;
2. Separationofphosphormixtureintodifferentcomponentsbyphysicochemicalseparationmethodsfor
re-useinnewlamps;
3. RecoveryofREEscontentbychemicalattacks.
Second and third options use very similar hydrometallurgical processes to the primary extraction ones:
leaching,precipitationandsolventextraction.Leachingistheprocessofextractingconstituentsfromasolidby
dissolvingtheminaliquid,inthisparticularcaseisusedtoremovemetalsfromthesolidphaseintheformof
solublesalts.Precipitationconsistsonachemicalreactionbetweensolutionsresultingintheprecipitationasolid
(forexample,𝐴𝑔𝑁𝑂8 + 𝐾𝐶𝑙 → 𝐴𝑔𝐶𝑙 ↓ +𝐾𝑁𝑂8).Finally,thesolventextractionmethodallowstheseparation
ofcompoundsbasedonthesolubilityofthedifferentelementsintwoimmiscibleliquids,usuallywater(polar)
andanorganicsolvent(non-polar).
Nevertheless,thebehaviourofthedifferentphosphorstostrongacidchemicalattacksvariesbroadly.For
instance,YOXcanbedissolvedinmildacidic/dilutedsolutions,butLAP,CATandBAMaremoreresistantthus
needingadifferentapproach[2,39].Therefore,oneofthefocalchallengesisobtainingabsolutedissolutionof
theREEswhenleached[39].Somestudiesindicatethathydrochloricacidshowsbetterresultsintheleaching
process[42].
Someexamplesofprocessesareshowninthefollowingtables(Table3.2andTable3.3).Othershavealso
beendeveloped,asmentionedinliterature[2,38,39],andevenpatented[43,44].
Notwithstandingthenumberofpapersandstudies,pilot-scaletestsareinfrequent.Likewise,aredeveloped
atlab-scaleand,sometimes,withartificialand/orpurephosphormixtures.
28
Table3.2–PublicationsregardingtheleachingofREEsfromlampphosphors(adaptedfrom[38]).
Table3.3–PublicationsdealingwithseparationsofREEsfromlampphosphorsbysolventextraction(adaptedfrom[38]).
Material ExtractionSystem Extractionconditions Efficiency(%) Reference
Powde
rfrom
fluorescentlamps
TBPcomplexeswithHNO3
Patm;50℃;
120min.
37.4(Y)36.8(Eu)
<3(La,Ce,Tb)[51]Supercritical
CO2;60℃;15MPa
99.7(Y)99.8(Eu)
<7(La,Ce,Tb)
Real
fluorescent
lampwaste
leacha
tes
Trimethyl-benzylammoniumchloride 80℃ 98.8(Y)96.5(Eu) [46]
Lamp
phosph
ors
leacha
tes
N,N-dioctyldiglyocolamicacidintheionicliquid1-butyl-3-
methylimidazoliumbis(trifluoromethylsulfonylimide)
Batchtests:pH3
Declineinextractionabilityafterfiveextractioncycles.
[49]
Material
LeachingConditions Leachingefficiency(%)
ReferenceReagents T
℃t(h)
S:Lratio Eu Y La Ce Tb Gd
Fluo
rescen
tlam
pwaste
fractio
ns 25%v/vCH3COOH 20 168 1:10 50 75 2-10
[45]0,5M,1M,2M,4MHCl0,5M,1M,2M,4M
HNO320 168 1:10 >95 >97
Phosph
orsfromEOL
fluorescentlamps 3M+5MHCl 60 4+3 1:10 97.38 99.06 98.22 98.15 [42]
MixedHNO3+H2SO4(4Meach) 125 4 92.8 96.4 [46]
2MH2SO4 37 8 1:50 71.5 75.3 61.1 66.9 [47]2MH2SO4 90 3 1:5 90 [48]
Variousacidicsolutions 70 6 1:20 >85 >91 [49]
4MHCl 60 1 1:10 96.28 [50]
29
Chapter4. ExperimentalA representative 18L sample of REE richmud, resulting from the physical-chemical treatment of spent
fluorescentlamps,wascollectedfromAMBICAREINDUSTRIAL–TratamentodeResíduosS.A.facility,locatedin
ParqueIndustrialdeMitrena,Setúbal,Portugal.ThesamplewaskeptinaPVCtank.AMBICAREprocessesvarious
typesoffluorescentlampsinlargebatches(500kg),simultaneously.Crushingiscarriedoutinawatersolution
and a rotary screener is used to separate macro-fractions (glass and steel fragments) from a fine fraction
containingthepowderphosphors,increasingtheREEscontent.
A strong oxidation product is utilized during the crushing in order to oxidize elementalmercury and to
stabilizeit.Duetothenatureoftheprocess,separationofpurephosphorspowderisnotpossible.
Theresultantphosphorwetsludge(approx.30wt%moisture)comprises,typically,45%ofhalophosphate
phosphor,20to30%ofglassandsilica,12%ofaluminaand10to20%ofREEsphosphors
Thepurposeofthisworkisto:
• Characterize (physically, chemically, structurally and morphologically) the lamp waste fraction by-
productinordertofinditspossibleapplications;
• Assess the applicability of a recovery, via physical-chemical processes of REEs from the waste at
laboratoryscale,usingacidleachingoperations.
TheoverallexperimentalworkgoesasexplicatedinFlowchart4.1:
Flowchart4.1–Setupfortheexperimentalworkfortreatmentoflampwaste.LettersA-D,redirecttootherflowcharts
explainingeachstepoftheexperimentalprocedure.
The initial phase of the experimental work process consists on obtaining several types of samples by
samplingthe18Lsludgeinordertoobtainbothdryandwetsamplesforfurthercharacterization,analysisand
processing.ThesamplingprocessgoesaccordingtoFlowchart4.2.
30
Flowchart4.2–Samplingandphysicalprocessing.
31
Inthesamplingprocesstwowayswereconsideredsince,oncethetankwasopened,therewasaseparation
betweenapulpandaliquid.Foreachphasedifferentmethodologiesweretakenintoconsideration.
Forthesupernatantliquidthefollowingstepsweremade:
1. FilterthesupernatantliquidwithaBüchnerfunnel;
2. Measurethevolumeandmassofthefilteredliquid;
3. Prepare3sampleswiththeliquidforfurtheranalysis(SL.Xsamples):
a. pHdetermination;
b. densitycalculation.
4. Weightthesupernatantpulp,resultingfromfiltration–SPsample;
5. Dry in the oven at 50°C the SP sample until constantweight is obtained, for the determination of
humidity.
6. RemovalofthetoplayerofdriedSPsample–TL.Xsamples;
7. SievingofdriedSPsample,separately,witha0.315mmsieve–IS.Xsamples;
8. Homogenizationandseparationofinfra0.315powdersintherotationalsampler–P.Xsamples;
Theremainingproductinthetanksufferedadifferentprocess,asfollowing:
1. Sieving(3.15mmsieve)thewetsludgewhilstpouringintotherotationalmoulding–IL3.15;
2. Homogenization and separation in the rotational sampler: divide into the eight flasks and pour in
containers,repeatedlyuntiltheallsampleisdivided–Lsamples;
BothwetanddrysampleswillbeobtainedfromLsamples.Regardingtheattainmentofthedrysamples
onemustfollowthesamestepsastookinwiththeSPsamples:
3. Drying in the oven at 50°C of samples L1, L12 and L19, until constant weight is obtained, for the
determinationofhumidity;
4. Removalofthetoplayerofeachdriedsample–TPsamples;
5. Sievingofeachdriedsample,separately,witha0.315mmsieve–IS.Xsamples;
6. Homogenizationandseparationofinfra0.315powdersintherotationalsampler–P.Xsamples;
7. Mixtureofca.70gofeachP.X.sample;
8. Homogenizationandseparationofsamples’mixtureintherotationalsampler–PGsamples;
Forthesmallerwetsamples,onemust:
9. MixtureofsamplesL2,L11andL20;
10. Sievethewetsludgewhilstpouringintotherotationalsampler(0.315mmsieve)–IL0.315samples;
11. Homogenizationandseparationintherotationalsampler–LG.1sample;
12. Homogenization and separation in the rotational sampler of one wet global sample type 1 – LG.2
sample;
32
Itcanbepointedoutthatseveralsampleswereproduced.Inordertofacilitatethereaders’interpretation,
thelettersusedtonamethesamplesareacronymsofthesamplestype/nature,asexplainedahead.
Thefiltrationofthesupernatantliquidresultedinafilteredsupernatantliquidandinpulp,thusproducing
3SL.XsampleswhereX=1,2,3,aswellasoneSPsample.Fromtheseparationofthewetsludge24samples
wereproduced:L.Xsamples,whereX=1,2,…,24.Inthesievingoperations,supramaterialworksasimpurities
hencecreatingtheIsamples.Whensievingadriedsolidmaterial,thenIS.Xisusedtonameit.Ifthesampleisa
wetsludgethenisnamedILfollowedbythesievemeshsize,p.eIL3.15ifa3.15mmsieveisused.Thedryingof
L1,L12,L19andSP,resultedintoplayersamples(TL.Xsamples),powdersamples,P.XsampleswhereX=1,12,
19andSPinbothcases,aswellasdryglobalsamples(PGsamples).Wetglobalsampleswereproduced,named,
LG.1andLG.2samples,werethelatestismorehomogenized.
Theresumeoftheseveralsampledesignations,fromthesamplingprocess,arepresentinTable4.1.
Table4.1–TypesofSamples.The“X”codeimpliesthereareseveralsampleswithinagroup.Furthermore,thevaluetaken
bytheXsisrelatedtotheLsamplesifX=number,ortothepulpifX=SP.
Nameofthesample Designatedmaincode DesignatedXcode
FilteredSupernatantLiquid SL.X X=1,2,3
SupernatantPulp SP –
ImpuritiesPulpsievedsample
Supra3.15mm IL3.15 –
Supra0.315mm IL0.315 –
Drysolidsievedsample Supra0.315mm IS.X X=1,12,19,SP
“Liquid”-Sluge L.X X=1,2,…,24
“Liquid”GlobalType1 LG.1 –
“Liquid”GlobalType2 LG.2 –
TopLayers TL.X X=1,12,19,SP
DryPowder P.X X=1,12,19,SP
DryPowderGlobal PG –
SamplesP.X(allfour)andPGwerefurtherdividedinto8smallplasticbags(usingtherotationalsampler),to
facilitate the use of the powders in the following steps. However, a code was not created for each of the
bags,beingnamed1st,2nd,….,8thinthetablesahead(Table5.3andTable5.5).
Somesampleswereproducedwithoutadetermineduse:supraimpurities,top-layersandthesupernatant
liquid. Supra samples were produced since thematerial presented numerous impurities (glass, caps, wires,
amongst others). The top-layers were removed since, when the material was dried, the surface became
extremelydarkerthantherest.Finally,thesupernatantliquidwasfilteredandputaside.
All these sampleswere supposed to be further characterized, otherweighing and/or pHdetermination,
however,duetotimecomplications,itwaspostponedtoafuturework.
33
Asimplifiedschemewasmadeinordertoillustratehowthemainsamples(theonescharacterized)were
collected,regardingtheinitial18Lsample(Figure4.1).
Figure4.1– Simplifiedsamplingdiagram.
Characterizationoccursnextforbothwetanddrysamples:
• Granulometryanalysisinthelaserdiffractiongranulometer(CILAS1064)ofsamples:P.1,P.12,P.19,
PG,L3,L13,L21andLG.1(performedinLNEG);
• StructuralcharacterizationbyX-RayPowderDiffraction(XRPD)(PanalyticalX´PERTPRO)ofsamples
P.SP,P.1,P.12,P.19andPG(performedinLAMPIST);
Thediffractogramswereobtainedbyapplyingthefollowingparameters:
• Position4.9751≤ 2𝜃 ≤79.9751,withstepsize2𝜃=0.0500;
• ScanStepTime[s]=99.4293;
• RadiationK-Alpha1[Å]=1.54060fromaCuampoule(anodematerial);
• GeneratorSettings=35mA,40kV.
• Morphologicalcharacterizationby:
a. StereoZoomMicroscope(OlympusSZ61withmicroscopecameraMOTICAM10Mp)ofP.SP,
P.1,P.12,P.19andPG(performedinLAMPIST);
b. Scanning Electron Microscope/Energy Dispersive Spectroscopy (SEM/EDS) (FEG-SEM: JEOL
7001F)ofsamplesP.SP,P.12andPG(performedinMicroLab).Eachonewasmetalizedusing
goldandpalladiumfilm(15nmthick),inordertomakethesamplesconductive,andthenplaced
inaaluminiumsampleholder;
• ChemicalelementalanalysisbyInductivelyCoupledPlasma–AtomicEmissionSpectrometer
(ICP-AES)(JYULTIMA)ofliquorsamples(directanalysisafterdilution)andofSLsample(performed
inRequimte).Forsolidsamplesanalysis,apreviousdigestioninaquaregiawasmadetosolubilise
themetalsinsolution(samplesAR1andAR2).Thedigestionprocedurewascarriedoutbeattackof
1gofpowderwith40mLofaquaregia(1:3ofnitrictohydrochloricacid)at80°C,for3h;
Thefollowingstepoftheexperimentalprocedureistheleachingprocessthatgoesintwoseriesoftests,as
follows(Flowchart4.3andFlowchart4.4).
34
Flowchart4.3– Firstseriesofleachingexperiments(1and2)todetermineparametersthatallowmorerecoverypercentage
Inthefirstseries(experiments1and2)severalcombinationsofconditionswereconsidered(Table4.1),in
ordertodeterminefurtherconditionstoexplore.HClwasalwaysusedasleachant.
Inthesecondexperiment,eventhoughtheleachingparametersaresimilar(Table4.2)calcination8isdone
primarily,untilconstantweight,sinceitmightresultinthebreakageofthephosphates(LAPandhalophosphate
phosphors)intooxides,thusfacilitating/increasingtheleachingefficiency.
Table4.2–Determinedleachingconditionsforexperiments1and2.
Experiment LeachingConditions
1 𝑡\]\^_=6h
T=90°C4MHCl
0.5MHCl
T=25°C4MHCl
0.5MHCl
2 𝑡\]\^_=6h T=90°C 4MHCl
The following experiments (3 to 6) (Flowchart 4.4) were performed, after the results of the preceding
ones,andaimedattestingalternativeleachants(HNO3andH2SO4)orcombinationsofthem.Hydrochloricacid
waschosen toperformthe firstacid leaching (inexperiments3,4,5), since it showsbetter leaching results,
accordingtoliterature[42].SeveralauthorsexploredtheuseofHNO3andH2SO4.However,thelatestisused
highquantities(18M).InsteadofleachingaconcentratedH2SO4digestion9,wasthought,wherelessvolumeof
acid is used, as well as higher temperatures. In this case, a subsequent water leaching operation was
implementedinordertosolubilizethemetalsthatweretransformedtosulphatesduringthedigestion.
8Calcination isasathermaltreatmentprocess intheabsenceor limitedsupplyofairoroxygentobringaboutathermaldecomposition.Normally isperformedwithtemperaturesin-between500and1000°C,howeveranauthordemonstratedgoodrecuperationresultsbyusinganaidingcalcinationwith200°C.Hence,theoptionwastested.9Thechoiceofacidresultsfromthefactthattheotherstudiedacidsarenotstableathightemperaturesanditismoresecuretoworkwiththemdissolvedinsteadofconcentrated.Thisprocessworksinthesamebasesoftheleachingprocess.
35
Inleachingprocesses,samplesweretakenafteroneandsixhoursofreaction,inordertodoso,3mLare
centrifugedandthen2mLofwhicharediluted10timesandsentforanalysis.
Allreagentswereofanalyticalgrade.Demineralizedwaterwasusedtopreparesolutionsfortheleaching
testsandforallanalyticalprocedures.Theleachingbehaviourofmetalswasstudiedusingalwaysasolid-liquid
ratio(S:L)of10%w/vi.e.foreach5gofsolid50mLofliquidneedtobeused.
Table 4.3 presents the process conditions for the second set of experiments. The samples from all the
experimentsarenotnamed,sinceitdoesnotinfluencethediscussion.
Flowchart4.4–Secondseriesofleachingexperiments,withalternativeacidcombinations.
Table4.3–Determinedleachingconditionsforexperimentsthreetosix.
Experiment ProcessConditions
3Leaching 𝑡\]\^_=6h T=90°C 4MHCl
Calcination 𝑡\]\^_=3h T=200°C
4 Leaching𝑡\]\^_=6h T=90°C 4MHCl
𝑡\]\^_=6h T=90°C 5MHNO3
5
Leaching 𝑡\]\^_=6h T=90°C 4MHCl
Digestion𝑡\]\^_=3h T=90°C 1.1mLH2SO4/g
𝑡\]\^_=6h T=40°C 1MH20
6 Digestion𝑡\]\^_=3h T=90°C 1.1mLH2SO4/g
𝑡\]\^_=6h T=40°C 1MH20
36
Chapter5. ResultsHereafter the various series of tests that had been performed are related and the results obtained are
presented.
5.1. SamplingandPhysicalProcessing
Fromthefiltrationofsupernatantwereobtained680mLofliquid(whichwasdividedinto3SLsamples)and
1052.6gofwetsludgethatwasthendried.Theseresultsdonotrepresentthe2Lofafloatsincepartoftheliquid
samplewas returned to the initial vessel, given the consistency of the pulp in the bottom and difficulty in
removingit.
𝑉ab = 680𝑚𝐿 = 680𝑐𝑚8;𝑚ab = 679.1𝑔 → 𝜌ab = 0.9987𝑔𝑐𝑚8 ; 𝑝𝐻 = 9.92
𝑚al = 1052.6𝑔
Regardingtheremainingmudinthetank,whenthehomogenizationwasperformed,a3.15mmwasused
sincethesamplehasseveralimpurities(Figure5.1).Theimpuritiesarecrushedmetal,glassandplasticpartsthat
passedtherotationalsieve.
𝑚nb8.4J = 57.2𝑔
Figure5.1–IL3.15sample.
Aftersuccessivedivisionsthroughtheeightvialsofthesampler,thehomogenizedandsievedpulpwassplit
intwenty-foursamples(numberedfrom1to24)placedintoindividualcontainers(L.Xsamples).
Thefirsttestsaimedatthecalculationofmoistureinthewetpulps.Foursampleswereused:oneresulting
fromthefiltrationofthesupernatantliquid,i.e.SPsample,andthreefromthehomogenizedandsievedpulp
from the tank (L1, L12, L19). Samples 1, 12 and 19 representing the top,middle and lower part of the 18L
container.Theirinitialweight(priortodryingprocess)where:
𝑚b4 =1688.7g;
𝑚b4, =1497.7g;
𝑚b4N =741.7g.
37
Allsampleswereweighedintwosituations:freshfromtheovenintheoriginalcontainerandafteronehour
ofbeinginadesiccator,afterbeingtransferredtotwogobletseach.Thereasonofthetwoweightsarisesfrom
thefactthattheoriginalcontainersdidnotfitthedesiccator,sowhenthetransfersisdone,masslosswould
arise.Thecoolinginalowhumidityenvironmentpreventshumiditytoenterthesamples.
ThecalculationsforthemoisturecontentofsamplesSP,L1,L12andL19arepresentedinAnnexIII.Onlythe
finalmoisturecontentsarepresentedinthissub-chapter,aswellasthemassbalancethroughoutthesampling
andphysicalprocessing.
Fromtheobtainedmoisturecontentonecaninferthatthepercentageofwaterisapprox.30%(Table5.1).
Itwasexpectedthatthesampleswillhavelesswatercontentastheyareremovedfromtop-downfromthe
sampletank.Howeversomeincreasesinvaluewereobserved.TheincreaseinmoisturecontentfromsampleSP
toL1probablyarisesfromsurfacedisturbance;theaugmentationfromL12toL19isduetotheadditionofwater
madeforbettersludgehandling.
Table5.1–MoisturecontentofsamplesSP,L1,L12andL19.
Sample MoistureContent(%)
SP 31.27
L1 32.1
L12 28.3
L19 29.1
Sincetheoriginaldrysampleswereseparatedintogoblets,themakingoftheP.Xsampleswasmadewith
onlypartofthetotaldrymass,regardingonlyonegoblet(whichmassispresentedinthecolumn“Goblet”in
Table5.2).
Table5.2presentstheevolutionoftheweightofthesamplesintheproductionofthedrysamples,untilthe
attainingoftheinfra0.315mmpowders.
Table5.2–Masslossintheproductionofthedrysamples.Massisexpressedisgrams(g).
Samples WetweightDryweight Masslost
(fortotaldrymass)IS.X TL.X Infra0.315mmpowder
Total Goblet
SP 1052.6 723.5 165.7 329.1 4.3 9.6 145.9
1 1688.7 1143.9 604.1 544.8 7.7 17 564.9
12 1407.7 1008.8 470.5 399.7 8.4 14.9 335.7
19 741.7 525.5 254.7 216.2 10.9 9.7 233.6
Aftertheremovalofthetoppartandsupra0.315mm,theinfra0.315mmpartsweredividedintotheeight
P.X samples each (Table 5.3). Afterwards, all type P.X samples numberedwith number 1, originated the PG
samples.
38
Theuseoftherotationalsamplerresultsinmasslosses,sincethemachinecannotbeproperlycleaned.In
betweentheP.Xsamples,themachinewasbrushed,aspartofthemassthatwasabletobereleased,itwas
addedtothepreparationoftheglobalsample.
Table5.3–Weightofthe32P.Xsamples,togetherwiththemasslossoftheprocess.Massisexpressedisgrams(g).
Sample 1st 2nd 3rd 4th 5th 6th 7th 8th Total InputMass
loss
P.SP 18.7 17.9 18.1 18.2 18.2 17.5 17.7 17.3 143.6 145.9 2.3
P.1 70.7 72.1 69.1 72.8 69.2 69 71.4 69.5 563.8 564.9 1.1
P.12 41.9 40.5 41.2 41.5 40.8 41.3 41.3 40.7 329.2 335.7 6.5
P.19 28.3 28.6 28 30 28 28.4 28.6 29.7 229.6 233.6 4
PG 20.4 20.8 20.3 20.4 20.7 20.7 19.9 21.2 164.4 159.6 -4.8
ForthepreparationoftheLGsamples,theprocessstartedwithtypeLsamplesclosetotheonesusedto
producethedrysamples(numbers2,11and20).Somemasswaslostwhilepouringintotherotationalsampler,
andagainwhenproducingbothwetglobalsamples(i.e.pouringfromtherotationalsampler’sflaskintothefinal
container).
Table5.4–MasslossintheproductionoftheLGsamples.Massisexpressedisgrams(g).
Samples Lsamplemass VolumeofsupernatantliquidinLsample Pouredmass Masslost
2 1753.7 53 1743.1 10.6
11 1475.4 52 1457.2 18.2
20 752.7 29 739.4 13.3
Total 3981.8 134 3939.7 42.1
LG.1sample isobtainedfromthemixtureof thethreeLsamples,summinga totalof3939.7g (as initial
weight).TheLG.1encodedwithnumber1wasusedtoproduceLG.2,asmentionedin0.
Table5.5–WeightoftheLGsamples,togetherwiththemasslossoftheprocess.
Sample 1st(g) 2nd(g) 3rd(g) 4th(g) 5th(g) 6th(g) 7th(g) 8th(g)Total
(g)
Input Mass
loss
LG.1(sampler’sflask) 437.1 436.8 459.5 462.9 457.4 424.1 452.5 444.4 3574.7 3939.7 365
LG.1(finalsample) 426.3 424 444 450.1 441.8 411.8 440.9 429.5 3468.4 3574.7 106.3
LG.2(sampler’sflask) 67.6 66.2 63.9 60.3 64.6 65.4 70.7 67.7 526.4 426.3 -100.1
LG.2(finalsample) 57.2 57.2 55.1 50.1 54.7 54.9 57.3 53.1 439.6 526.4 86.8
39
ThemasslossinthepreparationofLG.1samplesresultsnotonlyfromthemassretainedinthe1.12mm10
sieve(𝑚opqr^4.4, = 2.6𝑔),butalsofromthemassthatwasentrappedintherotationalsampler,aswellasthe
lossfrompouringfromthesampler’sflasksintothefinalflaks(106.3g).
Itisnoticeable,oncemore,thatwhilepreparingthelastgroupof8samples,therewasanincreaseinmass,
eventhoughwhilstpouringintothefinalsamplecontainerthereisalossof86.8g.Unlikethepreparationofthe
PGsamples,thesamplerwasnotcleanedinbetweenPG.1andPG.2,sincetheybothcomprisedamixture.So
partoftheentrappedmasshasfallenintothesampler’sflaks,100.1gtobeprecise.
5.2. Characterization
5.2.1. GrainsizemeasurementbyLaserDiffraction
Ithastobenoted,first,thatthetechniqueusedhasanabilitytomeasurefineparticles(0.04–500.00𝜇𝑚).
ThetestedsampleswereP.1,P.12,P.19,PG,L3,L13,L21andLG.1.
Thepulpsamples(L3,L13andL21)wereobtainedbyseparatingtheinitialsample(with18L),whichpassed
througha3.15mmsieve, into24samples.Assuch, inthecaseofthesesamples, theyareknowntocontain
particlessmallerthan3150𝜇𝑚(orinfra3.15mm).Onanothernote,theoverallwetsample(LG)wasmadefrom
pulpwhichwasfurtherpassedthrougha1.12mmsieve(asmentionedinthefooterabove),thereforeonecan
infer that, the particles present, are smaller than 1 120𝜇𝑚,which almost fits in the resolution of the laser
equipmentused.Finally,whenthepowdersampleswereprepared,thedriedpulpwassievedthrougha0.315
mmscreen,sotheparticlesareinfra315𝜇𝑚,thusfittingtheresolutionoftheequipment.
In short, the granulometry only measures the fine component of samples L3, L13, L21 and LG.1, but
comprises100%oftheparticlesintheremainingsamples.
Onecannotethatthereisfewdifferencein-betweenthefinestofparticles(Table5.6).
ThevaluesofD10indicatethat10%ofthevolume(ormass)ofthepowderfractionhasvalueslowerthanthe
onepresentedinthetable,whereasD90indicatesthat90%ofthemass’averagemaximumdiameter.Regarding
thetopoftheinterval,thereismorevariationinsize,asitcanbeseenbythedeviationvaluesi.e.SD.
Inaverage, the fractionconsistsofparticleswith𝜙 < 45.37 ± 13.80𝜇𝑚ifweregardonlythesludgeor
with𝜙 < 73.46 ± 16.21𝜇𝑚consideringonlythepowdersamples.So,onageneraloverview,theparticlesare
finer in thewet samples than in thepowder samples.A reason for thisbehaviourcanbe relatedwith some
agglomerationoftheparticlesduringthedryingprocess.Itcanalsobepointedoutthatthedeviationsfoundin
theD90diameterareclearlyhigherthanfortheothercharacteristicdiameters,sincelargeparticlescontained
someamountofimpuritiessuchasglassfragmentswhichgivesmoreheterogeneitytothosecoursefractions.
Furthermore,thelowervaluesintheliquidsamplesarisefromthefactthatthesupernatantliquidwasusedfor
themeasurement.Sothebiggest,thusheavierparticleshavealreadybeenprecipitated.
10In0,theexperimentalstatesthatthepreparationofLG.1sampleswasobtainedbysievingthewetsludge,whilstpouringintothe
rotationalsampler,througha0.315mmsieve.However,theprocesswasratherslow,soa1.12mmsievewasusedinstead.
40
Table5.6–ParticleSizeDistribution-D10,D50&D90-SieveAnalysis.AM–arithmeticmean;SD–standarddeviation.
5.2.2. X-RayPowderDiffraction
Onlythedrysamples(P.SP,P.1,P.12,P.19,PG)wereanalysedbyX-RayPowderDiffraction(XRPD).
XRPDisatechniqueusedfordeterminingthestructureofcrystallinephasespresent.AnincidentX-Raybeam
diffracts,duetothecrystallineatoms/molecules,intomanyspecificdirections.Theangleandintensityofthe
beamsisthencorrelatedtoaspecificstructure.
However,differentmaterial canhave the same lattice system, crystal familyor crystal structure. Lattice
substitutionscanalsochangetheanglewheresomereflexionsoccurduetothevariations in the interplanar
spacings.Forinstance,diamond,α-germanium,havebothadiamondcubiccrystalstructureAnnexI–TableI.1
presents several structureswhere solid substitutionsoccurs, namely: allanite,bastnäsite, loparite,monazite,
parisiteandsynchysite.
Theprecisechemicalcompositionofthephasesisnotpossibletodo,duetotheextensivesolidsubstitution.
Nevertheless, as mentioned EOL fluorescent lamps are a source of HREEs i.e. the lamp phosphor fraction
contains:La,Ce,Eu,Gd,TbandY.Therewillbealso,inlargeconcentration,Al,Si,P,Caandinsmallerquantities
Ba,Sr,Mg,Mn,Sb,Cl,F,Hg,PbandCd[2],[38].
Sample D10(𝜇𝑚) D50(𝜇𝑚) D90(𝜇𝑚)
P.1 1.98 11.04 55.40
P.12 2.48 13.55 91.21
P.19 2.63 13.14 82.18
PG 1.83 11.22 65.03
AM 2.23 12.24 73.46
SD 0.39 1.29 16.21
L3 0.96 6.95 28.16
L13 1.59 9.99 46.70
L21 1.45 10.44 61.90
LG.1 1.44 9.90 44.73
AM 1.36 9.32 45.37
SD 0.28 1.60 13.80
41
Figure5.2–XRPDpatterns(Intensityvs2𝜃)forthedrysamplesanalysed.Fromtoptobottomorder:P.SP,P1,P12,P19and
PG.
It can be concluded from Figure 5.2 that the same set of crystal structures are present in all the
samples,sincethesamepeakpatternispresent.
Themaingraphic,withtheanalysedview,obtainedisfeaturedinFigure5.3andthestructuresidentifiedin
thepatternlistinTable5.7.
Table5.7–NameofthecompoundsidentifiedbytheXRPDtechnique11.
Ref.Code Score CompoundName Displacement[°2Th.] ScaleFactor ChemicalFormula
00-005-0574 57 YttriumOxide -0.056 0.979 Y2O3
00-009-0432 48 Hydroxyapatite,syn 0.078 0.347 Ca5(PO4)3(OH)
00-004-0612 22 Monazite -0.060 0.065 (Ce,La,Y,Th)PO4
00-032-0199 31 Monazite-(Ce),syn -0.009 0.225 CePO4
00-042-1468 19 Alumina 0.030 0.189 Al2O3
11Thescalefactorisanarbitraryvalueusedtoadjusttherelativecontributionofindividualphasestotheoveralldiffractionpattern.
Thescorerepresentsthenumberofpeaksassociatedwiththeidentifiedstructure.
42
Figure5.3–XRPDpattern(Intensityvs2𝜃),with40 < 2𝜃 < 60.Thephase(s)ofthecompoundscorrespondenttothepeak
is(are)identifiedbythesymbols:p-YOX;¿-Monazite;�-Hydroxylapatiteand¢-Alumina.
Figure5.4–XRPDpattern(Intensityvs2𝜃),with60 < 2𝜃 < 80.Thephase(s)ofthecompoundscorrespondenttothe
peakis(are)identifiedbythesymbols:p-YOX;¿-Monazite;�-Hydroxyapatiteand¢-Alumina.
Correlatingtheidentifiedphaseswiththeknowphosphorsused,onecansaythattheexistenceofyttrium
oxideimpliestheexistenceofYOXphosphor(𝑌,𝑂8);thestructureofhydroxyapatitecanberelatedtotheblue
43
phosphor 𝑆𝑟, 𝐶𝑎, 𝐵𝑎,𝑀𝑔 J 𝑃𝑂@ 8𝐶𝑙 since both are part of the apatite group, the 𝑂𝐻3 ion(in the
hydroxyapatite)canbereplacedbychloride,producingchlorapatite,i.e.thereferredphosphor.Themonazite
structure,whichcanalsohavesubstitutingelementsinthestructuresuchasCeinsteadofLa,comprisestheLAP
greenphosphors(𝐿𝑎𝑃𝑂@).Thepresenceofaluminaisexpected,asmentionedin3.2,duetothebarrierlayerin
thelamp.
Othercrystallinephasesshouldberecognisedbythetechnique.Thenon-identificationsuggeststhatmaybe
theyareinmuchlowerconcentration.
5.2.3. ScanningElectronMicroscopy
Thedrysampleswerealsocharacterizedbyscanningelectronmicroscopy.Inthiscase,onlysamplesP.SP,
P.12andPGwereanalysed.
Thesamplesareratherheterogeneousbothinparticleshapeandparticlesize;phosphors,inparticular,seem
toformaggregatesofseveralparticles(Figure5.5,Figure5.6andFigure5.7).
Figure5.5–SEMmicrographofP.12sample(200x).
Figure5.6–SEMmicrographofPGsample(200x).
SampleP.SPwasanalysedbyEDS,inordertodeterminetheconstituentsofeightselectedparticles(Figure
5.7).Lanthanumandterbiumwereonlydenotedinthissample.Thisfactdoesnotinferthattheyarenotpresent
intheremainingsamples.Onemustnote,again,thatthesamplesareveryheterogeneous,andonlyaverysmall
areawasanalysed.
Moreover,amapwasmadeoftheelementspresentthroughoutthescanofthePGsamplethusallowinga
moreaccurateidentificationofthenatureofeachparticleintheselectedarea(Table5.8).
44
Figure5.7–SEMmicrographofP.SPsample(1500x),withtheeightstudiedparticles.
Table5.8–Atomicpercentageoftheelementsconstitutingeachparticle(P.SPsample,particlenumbersarethosefrom
Figure5.7)andmaininferredchemicalcompounds.
Particle 1 2 3 4 5 6 7 8
C 4.75 34.08 31.21 28.30
O 67.97 49.00 54.50 56.76 69.06 71.35 67.08 62.80
Mg 1.98 0.70
Al 21.97 8.79 7.07 6.38 1.38 2.74 1.71 3.57
Si 0.54 0.92 2.30 3.06
P 0.78 0.66 1.07 1.30 2.97 2.40 12.12
Ca 0.42 0.64 1.09 2.24 1.93 0.76 19.08 0.74
V 0.93
Mn 0.68 0.62
Fe 0.22 0.35 29.83
Y 4.96 3.29 2.12 23.98 21.20
Ba 0.76 0.23
La 0.29
Ce 1.07 0.12
Eu 0.41 0.10 0.13
Tb 0.53
Inferred
chemical
composition
CAT
Alumina
YOX
BAM
YOX
LAPorCa
halophosphate
YOX
Ca
halophosphate
YOX YOXCa
halophosphate
Fe
Alumina
SiO2
45
TheresultspresentinTable5.8leadtotheinferenceofcertainphasesforeachparticle,whencomparedto
theliterature.Halfoftheparticleshavecarbonwithin,whichisanon-expectedresult,sinceitwasnotusedto
prepareorhold the sample. It canbeattributed toorganic substancesadded in thebathof themechanical
processingusedbythecompany.Infact,thepulphadastrongodour,butnoinformationwasobtainedabout
thecompositionofthesolution,forconfidentialityreasons.Oxygenatomiccontentisalsohighwhencompared
withthemetalscontent,aswasdeterminedfromstoichiometriccalculationsbasedontheexpectedquantities
ofeachphosphorphase.However,theidentificationofthemainphaseswassuccessfullyachieved,aspresented
inthenextparagraphs.
Onparticle1,theexistenceofMg,Ce,TbandespeciallyAlandOinhighquantitiessuggeststhattheparticle
ismadeofCATorceriummagnesiumaluminate,terbiumdoped.Someamountofceriumphosphate(LAP-Ce
type)isalsoprobable.Thepresenceofsilicon,eventhoughbeingsmall,liketheliteraturesuggested,mustbean
impurityfromtheglassand/orbarrierlayeri.e.silica.PandCaarealsoexistent,whatcouldindicatethatthere
ispartofcalciumhalophosphatephosphor,asanimpurityaswell.Alispracticallyexplainedbytheatomicratio
betweenMg/AlinCATformula,andso,someeventualaluminapresentisvestigial.
InthesecondparticleanalysedthereisevidenceofthepresenceofYOX.BAMisalsopresentintheparticle
duetothe,practically,equalpercentageofBaandMg.ThepresentaluminiumismainlyfromtheBAMphosphor,
leavingresidualaluminaintheparticle.ThepresenceofEuisjustifiedbyitsuseasdopantinbothYOXandBAM
phosphors.SincethereisalsoPandCa,anequaldeductionismade,asintheparticle1case.
Thethirdandfourthparticleshaveresidualsilicapresentalso.BothseemtobemainlyconstitutedbyYOX
phosphor.EuisalsoidentifiedasYOXdopant.TheamountsofLa,CaandPinthethirdparticlealsoindicatethe
presenceofLAPandcalciumhalophosphate.InthefourththerelationbetweenpercentagesofCaandPsuggests
thereiscalciumhalophosphate,butalsosomeCephosphate.BothparticleshavealsoAlcontentsthatmustbe
attributedtoalumina.
ThefifthandsixthparticlesareYOXphosphortogetherwithsmalltracesofaluminaandhalophosphorparts;
MnandVareconsideredimpurities.Particle7compositionsuggeststhatitismadeofcalciumhalophosphate
sinceitismainlyconstitutedbyP,CaandO.
Finally,thelastparticleanalysedisconstitutedbyoxides,namelyironoxide,aluminaandsilica.Ironisalso
probablyacontaminantfromthelampofthetreatmentprocess.
ThemappingofthePGsampleresultedintheidentificationofthephasesillustratedinFigure5.8.Onemust
notethattheparticleswereidentifiedbythemajorcomponent.Duetothecrushing,thereareelementsspread
overthesample.
46
Figure5.8–SEMmicrographofPGsample(1500x).Particlesare:p–Calciumhalophosphate;u–YOX;À–BAM;l
–CAT;n–strontiumhalophosphate;–particlerichinFe.
5.2.4. ElementalanalysisbyICP-AESofinitialsamples
AsmentionedanICP-AESchemicalanalysiswasmadetosamplestreatedwithaquaregia,namedAR1and
AR2.Thepurposeistodeterminethetotalcontentofrare-earthsandothermetalsinthephosphorsampleas
wellastoevaluatethesolublepartofthosemetalsintheliquid.
Table5.9–Elementalcompositionofseveralmetalsinwastefractions(wt.%).AM–arithmeticmean;SD–standarddeviation.
Sample Al Ba Ca Ce Eu Gd Hg La Mg P Sr Tb Y MetalContent
REEcontent
AR.1 1.38 1.040 13.1 0.690 0.840 0.320 0.040 0.890 0.220 6.49 0.630 0.280 15.5 34.93 18.52
AR.2 1.27 1.050 12.9 0.480 0.840 0.320 0.038 0.540 0.210 6.28 0.620 0.210 14.6 33.08 16.99
AM 1.32 1.045 13.0 0.585 0.840 0.320 0.039 0.715 0.215 6.39 0.625 0.245 15.1 34.00 17.76
SD 0.08 0.007 0.14 0.148 0.000 0.000 0.001 0.247 0.007 0.15 0.007 0.049 0.64 1.31 1.08
Table5.9showsthattheREEcontentis17.76%drywt.(bysummingalltheREEs)inaverage,whichindicates
thatthefractionshaveinterestregardingurbanmining.
ThemainmetalimpuritieswerestudiedaccordingtopreliminarySEM/EDSresults.Calciumcontentisthe
mostpresent,followedbyaluminium,barium,strontium,magnesiumandmercury.
ThechemicalanalysisagreeswiththeresultsobtainedbyXRPDanalysisandSEMmicroscopy,thatthereis
mainlyYOXandcalciumhalophosphate inthewaste,asexpected;yttriumoxidecomprising15%ofthetotal
sample.SmallpercentagesofCBT,CAT,BAMandLAParepresent.
47
5.3. Leachingofphosphormaterials
5.3.1. LeachingwithHClsolutions
Thefirstseriesofleachingexperimentsaimedtotestseveralconditions(temperature,concentration,time)
usingHClasleachant,inordertoevaluatetheleachingyieldsofthemainelementssuchasLa,Ce,Eu,Gd,Tb,Y,
Ca,Al,asstatedinFlowchart4.3.InTable5.10arepresenttheleachingyieldsobtainedfromICPanalysisofthe
leachates,fortheexperimentsoneandtwo.
Table5.10–LeachingyieldsofREEsafterleachinginHClaccordingtoconditionsinTable4.2.Resultsin%.
Experiment Al Ca Ce Eu Gd La Tb Y
Experimentswithoutcalcination
0.5MHCl,90°C,1h 16.80 42.30 0.90 5.60 1.90 0.50 0.50 6.00
0.5MHCl,90°C,6h 2.30 44.70 2.30 24.80 6.90 0.60 1.70 22.80
4MHCl,90°C,1h 64.80 91.00 12.60 27.90 57.10 1.70 19.50 74.40
4MHCl,90°C,6h 95.30 102.30 19.30 27.90 88.70 2.20 28.90 85.10
0.5MHCl,25°C,1h 12.30 39.20 0.50 4.00 0.90 0.60 0.70 3.70
0.5MHCl,25°C,6h 16.50 40.80 0.70 11.30 1.90 0.80 1.20 10.00
4MHCl,25°C,1h 16.70 94.80 0.90 16.20 2.90 1.00 1.80 14.00
4MHCl,25°C,6h 23.60 99.60 1.90 27.90 7.60 1.30 3.40 67.10
Experimentswithcalcination
4MHCl,90°C,1h 68.70 95.40 15.30 27.90 72.80 1.70 22.80 78.30
4MHCl,90°C,6h 95.60 94.50 19.70 27.90 85.60 2.40 27.80 82.00
Inanoverallviewoftheresults,testscarriedoutathighervaluesoftemperatureandacidconcentration
weretheoneswherehighyieldsarose.Someelementswerealsoefficientlyleachedwhenusingthehigheracid
concentration, suchasCaandY.Therefore,onecanstate that theHCl leachingprocess resulted inselective
leachingofsomeREEs.ThechemicalprocessforleachingofREMsfromtheircorrespondingphosphorsusingan
acidicsolutioncanbewrittenasthefollowingsimplifiedequations,consideringthatvirtuallyallthemetalscould
bedissolved(whichdoesnotalwaysoccur):
1. Redphosphor:𝑌,𝑂8: 𝐸𝑢8< + 6𝐻< ↔ 2𝑌8<(+𝐸𝑢8<) + 3𝐻,𝑂;
2. Greenphosphors:𝐿𝑎𝑃𝑂@: 𝐶𝑒8<, 𝑇𝑏8< + 3𝐻< ↔ 𝐿𝑎8<(+𝐶𝑒8<, 𝑇𝑏8<) + 𝐻8𝑃𝑂@;
𝐺𝑑,𝑀𝑔 𝐵J𝑂4K: 𝐶𝑒8<, 𝑇𝑏8< + 18/17𝐻< ↔ 𝐺𝑑8<,𝑀𝑔,<(+𝐶𝑒8<, 𝑇𝑏8<) + 5/2𝐵,𝑂8 + 10𝐻,𝑂;
𝐶𝑒, 𝑇𝑏 𝑀𝑔𝐴𝑙44𝑂4N + 38𝐻< ↔ 𝐶𝑒8<, 𝑇𝑏8< + 𝑀𝑔,< + 11𝐴𝑙8< + 19𝐻,𝑂;
3. Bluephosphors:𝐵𝑎𝑀𝑔𝐴𝑙4K𝑂4O: 𝐸𝑢,< + 34𝐻< ↔ 𝐵𝑎,< + 𝑀𝑔,<(+𝐸𝑢8<) + 10𝐴𝑙8< + 17𝐻,𝑂;
𝑆𝑟, 𝐶𝑎, 𝐵𝑎,𝑀𝑔 J 𝑃𝑂@ 8𝐶𝑙: 𝐸𝑢,< + 10𝐻< ↔ 5 𝑆𝑟,<, 𝐶𝑎,<, 𝐵𝑎,<,𝑀𝑔,< +𝐸𝑢,< + 3 𝐻8𝑃𝑂@ + 𝐻𝐶𝑙.
48
Consumptionofprotonsoccursmakingacidconcentrationanimportantparameterintheleachingprocess.
Itwasindeednotedthathigheracidconcentration,i.e.higherprotonconcentrationresultedinmorequantity
ofleachedmetal.ThisparameterhoweverbarelyinfluencedLaleachingbehaviour.
Hydrochloricacidrevealedtobeaneffectiveleachantforaluminium,calcium,gadoliniumandyttrium.It
wasexpectedthateuropiumfollowedthetendency,howeveritssolidcontentwasonlyapprox.28%(with4M
at90°C).
Temperature increase influenced, significantly the leaching of Y, Al, Ce, Gd and Tb (Table 5.10). Higher
quantitiesofmetalsarecomingintothesolutionbyincreasingtemperaturefrom25°Cto90°C.Thetreatment
bycalcinationaffectedslightlytheleachingbehaviourofAl,Ce,Gd,La,TbandY.
ThemassbalancethroughouttheexperimentsispresentinTable5.11.
Table5.11–MassbalanceandvolumeofsolutionusedinexperimentsE1andE2.Samplesbythesameorderas.Table5.10.
Exp.1stLeaching 2ndStep(Calcination,Digestion) 2ndLeaching Massloss
m(g) Vtotal(mL) mf(g) m(g) Vacid(mL) mf(g) m(g) Vtotal(mL) mf(g) (%)
E1
0.590°C 5 50 3.98 20.4
0.525°C 5 50 1.88 24.4
4M90°C 5 50 3.78 62.4
4M25°C 5 50 2.12 57.6
E2 6 5.91 5.91 60 1.86 69.0
5.3.2. Evaluationofseveralacidleachatesandmultistepleaching
Since the leaching behaviour of the several REEs, contained in different phosphormaterials, was quite
diverse, several optional processes were proposed and tested, involving in some cases multistep leaching
operations and other complementary treatments. The aim was essentially to evaluate the possibility of
recoveringdifferentelementsindifferentsteps,thusimprovingtheselectivityofthetreatmentandsimplifying
thesubsequentseparationandrecoveryoperations.
Accordingwiththepreviousstatement,severaltreatmentoptionswereproposedforcomparisonandtested
experimentally:
• SingleleachingwithHCl(alreadytestedinprevioussection)–allowsefficientrecoveryofYandGd,but
notforLa,Ce,Tb,Eu;
• Two-stepleaching,bothwithHCl,withacalcinationoperation(atlowtemperature)includedbetween
thetwoleachingsteps(Exp.3)–tryingtoimprovetherecoveryofalltherare-earthsinthesecondstep
throughathermalactivationoftherespectivebearingphases;
• Two-stepleaching,thefirstwithHClandthesecondwithHNO3.(Exp.4)–tryingtoimprovetherecovery
ofalltherare-earthsbyadifferentleachingagent;
• Two-stepreaction,thefirstconsistingonHClleachingandthesecondbeingadigestionwithH2SO4(Exp.
5)–alsotryingtoimprovetherecoveryofalltherare-earthsbyadifferentacidagentandapproach
(digestioninsteadofleaching);
49
• SingleH2SO4 digestion (Exp. 6) – alternative chemical treatmentwith another acid rather thanHCl;
allowscomparisonwiththesingleHClleaching;
ThemassbalancethroughouttheexperimentsispresentinTable5.12.
Onemustnotethat,theseexperimentsaremulti-stepthushavingseveralsuccessivereactionsstepsand
alongwithitbothglobalandindividualefficiencyvalues.
Table5.12–MassbalanceandvolumeofsolutionusedineachexperimentE3-E6.
Exp.1stLeaching 2ndStep(Calcination,Digestion) 2ndLeaching Massloss
m(g) Vtotal(mL) mf(g) m(g) Vacid(mL) mf(g) m(g) Vtotal(mL) mf(g) (%)
E3 6 50 2.32 2.32 2.22 2.22 22 2,06 58.8
E4 6 50 2.36 2.36 25 2,03 66.17
E5 6 50 2.31 2.31 2.54 2.06 2.06 23 1,46 75.7
E6 5 5.5 4.32 4.32 50 2,77 53.8
Whentheefficiencycalculationswerebeingmade,itwasnoticeablethatintheprocessesinvolvingH2SO4,
moremetalswereobtainedinsolution,thanthepredictedinitially(forLa,CeandTb).Whatsuggeststhatthe
aqua-regiaattacks,inwhichtheinitialcompositionofthepowderwasdefined,maynothavebeencompleted.
Therefore,theinitialvalues(Table5.9)werecorrectedaccordingtothetotaldissolved.
TheleachingefficiencyisgivenbothinTable5.13andTable5.14,thefirstonepresentsrecoveryvaluesfor
theindividualsteps,whereasthesecondpresentstheaccumulatedvaluesattheendofeachexperiment.The
recovery percentage is also shown in the set of graphs below (Graph 5.1). However, unlike Table 5.13, the
percentages presented in the graphs are the percentages referring to the initial metal content, and not
percentagesofrecoveryofthematerialleftinthesolidbythepreviousstep.
Table5.13–OverviewoftheleachingbehaviourofREEs(valuesofextractionpercentageforeachstep,notaccumulated).
Elements
Recoveryefficiencyperprocedure
1stacidleaching
(E2,E3,E4andE5)
2ndStep+2ndleaching
E3 E4 E5 E6
REEs
Ce 10.20 56.09 81.85 93.68 99.18
Eu 27.93 0,00 0.00 1.58 67.67
Gd 88.69 0,00 0.00 0,00 94.60
La 1.11 58.42 89.42 94.71 99.86
Tb 14.18 58.36 84.30 96.93 99.40
Y 85.10 3.39 2.54 8.46 73.31
OthermetalsAl 70.38 7.70 8.70 95.62 85.22
Ca 98.54 15.28 15.38 15.19 8.71
50
Table5.14–Overallleachingyieldsattainedaftereachtreatmentprocess(6hofresidencetime).
ElementsLeachingyields(%)(accumulated,forallsteps)
E2 E3 E4 E5 E6
REEs
Ce 10.20 60.60 80.50 94.80 99.18
Eu 27.93 27.90 27.90 29.10 67.67
Gd 88.69 88.70 88.70 88.70 94.60
La 1.11 58.90 85.70 94.80 99.86
Tb 14.18 64.30 83.40 97.40 99.40
Y 85.10 85.60 85.40 86.30 73.31
OthermetalsAl 70.38 72.70 72.80 98.70 85.22
Ca 98.54 98.80 98.80 98.80 8.71
Asstatedbefore,thesinglestepleachingonlyallowsa,ratherhigh,Y,Al,CaandGdrecoveryhencethe
developmentofnewexperimentalprocedures.InexperimentE3,thecalcinationandsecondHClleachingmust
have,infact,thermallyactivatedthebearingphases,sinceitresultedintheincreaseofleachedLaandTbto
approx.58%andapprox.56%ofCe(Table5.13).EventhoughE3allowedandoverall recuperationofall the
identifiedmetals,mainlyGd,Y,CaandAl,values,apartfromCaandY,werethelowest(Table5.14).
InE4andE5,the2ndstepplus2ndleachingincreasedseverelytheCe,LaandTbextraction.E5alsoresulted
into further Al extraction (Table 5.13) eventually leading to the highest values for Al leaching (Table 5.14).
However,AlinsolutionwouldbeacontaminantforsubsequentREEsseparation.
ThevaluesforCarecoveryarehandtohandthroughouttheexperimentsapartfromthelastone.Itcanalso
bedenotedthatfromexperimentthreeuptofive,thereis[practically]noEuandGdandfewY.Thefactthata
“0.00”appearsdoesnotmeanthattherewerenoelementstoanalyseinsolutionbutonlythattheywerepresent
inaquantitylowerthanthedetectionlimitoftheequipment.(estimatedas<50ppb).
InE6thevaluesaremuchhigher(Table5.13),thisexperimenthasthehighestextractionefficiencyforCe,
Eu,Gd,LaandTb,butthelowestforCaandY.Theseresultssuggestthatthedigestionwithsulphuricacidseems
to be the most efficient process; it seems that metals reactivity with sulphuric acid is higher than with
hydrochloricornitricacid.ThecalciumleachingefficiencyattainedinE6,clearlylowerthantheobtainedinthe
otherexperiments,isrelatedtothelowersolubilityofthiselementinsulphatemedia(theoreticalsolubilityof
calciumsulphateisabout0.54-0.90gL-1,dependingonthetypeofcalciumsulphateformed).
Whencomparingvaluesfromtheliteraturetothefinalresultsobtained(Table5.15),onecannoticefirstly,
thatinthepublishedworkGd,LaandTbextractionwasnottestedor,regardlesstheexperimentalprocedure
chosen the valueswere too low;on theotherhand someexperimental protocols focusedonlyonEuandY
recoveryfromtheYOXphosphorwhichwasattainedatdifferentlevels,dependingontheleachingconditions.
51
Table5.15–ComparisonofREEsrecoverybetweenliteraturedataandpresentwork.“–”meanstheelementwasnotstudied.
Comparingelementbyelement,eventhoughsimilartechniqueswereused,theYOX’sREEs(EuandY),the
recoveryinthepresentworkwasnotsogoodsince,themajorityofthepublisheddataisover90%.E6wasmade
toallowcomparisontoasingleHClleaching,howevertheCeandTbobtainedvalueswerequitecomparable12
totheliterature’sandpresentworkdoubleHClleaching.Valuesfromexperimentsfourandfivewerebetterthan
the values found in the remaining bibliography. Furthermore,most of the published results are referred to
phosphors materials taken from lamps and not from the waste sludge fractions from treatment plants,
consequently,don’thaveasmanyimpuritiesassludge.
Comparingtheoverallresults,onepositiveoutcomeisthatallREEsinthefluorescentlampswereabletobe
leachedinexperimentsonetosix.Terbium,lanthanumandgadolinium,asmentioned,werenotstudiedin[most
of]theavailablepublishedbibliography,howeverhighpercentageswereobtained,especiallyinE5andE6.
12From95%thevaluesareallverysimilar,sincetheexperimentalerrorsofthistypeoftestscanbe3-5%.
Material Experiment
Leachingefficiency(%)
ReferenceEu Y La Ce Tb Gd
Fluo
res
cent
lamp
waste
fractio
ns 25%v/vCH3COOH 50 75 2-10 – –
[45]0,5M,1M,2M,4MHCl0,5M,1M,2M,4MHNO3
>95 >97 – – – –
Phosph
orsfromEOL
fluorescentlamps DoubleHCLleaching(3M,then5M) 97.38 99.06 98.22 98.15 – [42]
HNO3+H2SO4(4Meach) 92.8 96.4 – – – – [46]
2MH2SO4 71.5 75.3 – 61.1 66.9 – [47]2MH2SO4 – 90 – – – – [48]
5MHNO3+H2SO4+HCl >85 >91 – – – – [49]4MHCl – 96.28 – – – – [50]
Fluo
rescen
tlampwaste
fractio
ns
Presentwork
E3 27.90 85.60 58.90 60.60 64.30 88.70
E4 27.90 85.40 85.70 80.50 83.40 88.70
E5 29.10 86.30 94.80 94.80 97.80 88.70
E6 67.67 73.31 99.86 99.18 99.40 94.60
52
Graph5.1–Leachingyields,fortheseveralmetals,ineachtreatmentprocess,specifyingthecontributionofeachstep¢-1st
acidleaching;¢-2ndStep+2ndleaching.Theresultsonthebottomrefertothe1stacidleachingwhereastheonesontop
refertothe2ndStep+2ndleaching.
10.20 10.2 10.2 10.2 00
50.37
70.33
84.1299.2
0
20
40
60
80
100
E2 E3 E4 E5 E6
Cerecovery(%)
27.93 27.9 27.9 27.9 0
0 0.00 0.00 1.14
67.7
0
20
40
60
80
100
E2 E3 E4 E5 E6
Eurecovery(%)
88.69 88.7 88.7 88.7 0
0 0.00 0.00 0.0094.6
0
20
40
60
80
100
E2 E3 E4 E5 E6
Gdrecovery(%)
1.11 1.1 1.1 1.1 0.00
57.77
84.62
93.6699.9
0
20
40
60
80
100
E2 E3 E4 E5 E6
Larecovery(%)
14.18 14.2 14.2 14.2 0
0
50.09
69.23
83.18 99.4
0
20
40
60
80
100
E2 E3 E4 E5 E6
Tbrecovery(%)
85.1 85.1 85.1 85.1 0
0 0.51 0.36 1.26
73.3
0
20
40
60
80
100
E2 E3 E4 E5 E6
Yrecovery(%)
70.38 70.4 70.4 70.4 0
0 2.28 2.46
28.32
85.2
0
20
40
60
80
100
E2 E3 E4 E5 E6
Alleached(%)
98.54 98.5 98.5 98.5 0
0 0.22 0.21 0.22
8.7
0
20
40
60
80
100
E2 E3 E4 E5 E6
Caleached(%)
53
Chapter6. ConclusionandFutureWorkEndoflifefluorescentlampsareavaluablesourceofthreeoutofthefivemostcriticalrare-earthelements
i.e.europium,terbiumandyttrium;alsocontainingcerium,gadoliniumandlanthanum.
Therecoveryofrare-earthelementsfromlampphosphors’,unlikeotherrecyclingapproaches,leadstovery
pureendproducts.
In thiswork,multi-step leachingandseveralacid leachantswereevaluated inorder to recover theREEs
present if real fluorescent lamp waste fractions. Thematerial contained large amounts of impurities, most
notablyglass,butalsometallicandplasticpartsanddirtduetotherecyclingprocess.
Cerium, europium, gadolinium, lanthanum, terbium, and yttrium were the RE elements
identified,comprisingapprox.18%(drywt.)ofthesample,beingyttriumclearlypredominantwithabout15%.
Hydrochloricacidrevealeditselftobeaneffectiveleachantforaluminium,calciumbutalsoforgadolinium
andyttrium.Itwasexpectedthateuropiumfollowedthetendency,howeveritssolidcontentwasonlyapprox.
28%(with4Mat90°C).
Temperature increase influenced, significantly the leaching of yttrium, cerium, gadolinium and terbium.
Higherquantitiesofmetalsarebeingbroughtintothesolutionbyincreasingthetemperaturefrom25°Cto90°C.
Accordingtotheresults,onecanchoosetheprocedureaccordingtotheprioritizedelements.
Iftheleachingofyttriumisthemainfocus,thenthebestleachingconditionsare;leachingwithhydrochloric
acid(4M)for6hat90°C(85.10%ofYleached),orasulphuricaciddigestionfor3hat150°Cwithawaterleaching
(1M)for6hat40°C(73.31%ofYleached).
IfbothREEs inYOX’sphosphorsarethepriority,thenasulphuricdigestionprocess(1.1mLg-1,3h,150°C)
togetherwithwaterleachingisthebestsolution.However,thusincreasingtheeuropiumleachingyield(from
27.93%to67.67%)itreducestheyttrium’sto73.31%.Furthermore,thisprocessalsoledtoaleachingyieldof
over99%forlanthanum,ceriumandterbium,andaround95%ofgadolinium.
The digestion step (present in experiments five and six) resulted in the best results attained in this
work,consequently,itsuggeststhattheREMsinphosphorsaremorereactivewhenusingsulphuricacidthan
withhydrochloricornitricacids.Thisworkalsodemonstratedthepossibilityofatwo-stepleachingapproachto
allowselectivereactionofdifferentrare-earths,namelyYandGdinafirstHClleachingstep,andtheremaining
REEs(La,Ce,Tb,Eu)inasecondstepusingsulphuricaciddigestion.
Unlikemoststudiesperformed,whereYOXisthemainfocus,terbium,lanthanumandgadoliniumleaching
wasnotassuccessfulornotstudied,thepresentworkresulted inthe leachingofallsix identifiedrareearth
elements.
Futureworkconcernsadeeperanalysisofrare-earthsrecoveryandrecycling.
Methods to separate lamp fractions into individual lamp components need further improvements: the
resultant sludge contains a large amount of impurities, hence causing the need for a continuous/repetitive
sievingthroughouttheexperimentalwork.TofurtherimproveREErecyclingrate,logisticsinthebringingtheRE
scraps,shouldbeimproved.
54
Whenthesamplesweredried,toplayerandsuprasampleswereproduced,sincethesurfacebecameway
darkerthantheremainingsample.However,noanalysiswasdonetothesesamples.Thesamehappenstothe
supernatantliquid.Itshouldbeinterestingtofigureoutwhatthecompositioninbothcasesis.
It couldbe interesting to furtherexplore thedigestionprocedure insteadof leachingprocesses,asmost
literaturespoint.
ExtractionoftheretrievedREEswasnotperformed,asmentioned,sinceitgoesoutoftheworkcontext:this
thesis focused both in characterization and recovery via physical-chemical processes. Therefore, extraction
mechanismsshouldbetested.
55
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58
59
AnnexI. RareEarthbearingmineralsTableI.1–Selectedrare-earthmineralsbearingeitherLREEand/orHREE.
SelectedMinerals LREE HREE
A
Aeschenite(Nd)-
(Nd,Ce,Ca)(Ti,Nb)2(O,OH)6Neodymium
Allanite(Ce)-
(Ca,Ce)(Al2,Fe+2)(Si2O7)(SiO4)O(OH)
Cerium,Praseodymium,Neodymium,
Samarium,Europium
Allanite(Y)-
(Ca,Ce)(Al2,Fe+2)(Si2O7)(SiO4)O(OH)
Terbium;Erbium
Ancylite(Ce)-SrCe(CO3)2(OH)•H2O Samarium,Europium,Gadolinium
Åskagenite(Nd)-
(Mn2+,Nd)(Al2,Fe3+)(Si2O7)(SiO4)O2
Neodymium
B
Bastnäsite(Ce,La,Nd,Pr)(CO3)F
Cerium,Praseodymium,Neodymium,
Samarium,Europium,Gadolinium,
Lanthanium
Dysprosium
Bastnäsite(Nd)(Nd,Ce,La,Pr)(CO3)F Neodymium
Bazzite:Be3Sc2(Si6O18) Scandium
C
Cerite-(Ce)
(Ca,Ce)9(Fe,Mg)(SiO4)3(HSiO4)(OH)3Cerium,Praseodymium Terbium,Erbium
Clays:Y-enrichedlateric Europium
Ytrium,Terbium,Dysprosium,
Erbium,Thulium,Ytterbium,
Lutetium
Clays:Ionadsorptionlateric Europium
Ytrium,Terbium,Dysprosium,
Erbium,Thulium,Ytterbium,
Lutetium
E
Euxenite-(Y)(Y,Ca,Ce,U,Th)(Nb,Ti,Ta)2O6 Terbium,Erbium
Eudialyte-(Y)
Na4(Ca,Ce)2(Fe2+,Mn,Y)ZrSi8O22(OH,Cl)2
Yttrium,Terbium,Dysprosium,
Holmium,Erbium,Ytterbium,
Lutetium
F
Fergusonite-(Nd)(Nd,Ce)(Nb,Ti)O4 Neodymium
Florencite-(Nd)(Nd,La,Ce)Al3(PO4)2(OH)6 Neodymium
G
60
Gadolinite-(Y)Y2Fe2+Be2(Si2O10) Gadolinium
Terbium,Dysprosium,Holmium,
Erbium,Thulium,Ytterbium,
Lutetium,Yttrium
I
Iimoriite-(Y)Y2(SiO4)(CO3) Terbium,Erbium
Sc-Ixiolite:(Nb,Ta,Ti,Sc,Fe,Mn)4O8 Scandium
L
Lanthanite-(Nd)(Nd,La)2(CO3)3•8H2O Neodymium
Loparite-(Ce)
(Ce,Na,Ca,Sr,Th)(Ti,Nb,Ta,Fe+3)O3
Cerium,Praseodymium,Neodymium,
Saramarium,Europium,GadoliniumErbium,Ytterbium
Loparite(Ce,Na,Sr,Ca)(Ti,Nb,Ta,Fe+3)O3 Lanthanum
M
Magbasite:KBa(Al,Sc)Fe2+Mg5F2Si6O20 Scandium
Monazite(Ce,La,Nd,Th)(PO4)Lanthanum,Neodymium,Samarium,
Europium,Gadolinium
Yttrium,Terbium,Erbium,
Ytterbium
Monazite-(Nd)(Nd,Ce,La,Th)(PO4) Neodymium Ytterbium
MosandriteNa2Ca4(REE)(Si2O7)2OF3 Terbium,Dysprosium,Erbium,
Thulium,Ytterbium,Lutetium.
P
Parisite-(Ce)Ca(Ce,La)2(CO3)3F2 Neodymium,Europium
Parisite-(Nd)Ca(Nd,Ce,La)2(CO3)3F2 Neodymium
Perrierite:(Ce,Ca,
Th)4(Fe2+,Sc)Fe2
3+(Ti,Fe3+)2(Si2O7)2O8 Scandium
R
Rhabdophane-(Nd)(Nd,Ce,La)(PO4)•H2O Neodymium
S
Samarakite-(Y)
(Y,Fe+3,Fe+3,U,Th,Ca)2(Nb,Ta)2O8Samarium,Gadolinium
Synchysite-(Nd)Ca(Nd,Y,Gd)(CO3)2F Neodymium
Synchysite-(Y)Ca(Y,Ce)(CO3)2F
Yttrium,Terbium,Dysprosium,
Holmium,Erbium,Thulium,
Ytterbium,Lutetium
T
Thortveitite:(ScY)2Si2O7 Scandium
U
Uraninite Promethium
X
61
XenotimeY(PO4)
Yttrium,Terbium,Dysprosium,
Holmium,Erbium,Thulium,
Ytterbium,Lutetium
TheorderisaccordingtoREEatomicnumber
62
63
AnnexII. Rare-earthToxicologicalInformationTableII.1–Summaryoftoxicologicalinformationwithrare-earths[32].
Z13
Symbol Name CASNo. ToxicologicalInformation14
21 Sc Scandium 7440-20-2
Elemental scandium is considerednon-toxic, and little animal testing of
scandiumcompoundshasbeendone.Thehalflethaldose(LD50)levelsfor
scandium (III) chloride for rats have been determined as 4mg/kg for
intraperitoneal,and755mg/kgfororaladministration.
39 Y Yttrium 7440-65-5
Watersolublecompoundsofyttriumareconsideredmildlytoxic,whileits
insoluble compounds are non-toxic. In experiments on animals, yttrium
and its compounds caused lung and liver damage. In rats, inhalation of
yttriumcitratecausedpulmonaryedemaanddyspnea,whileinhalationof
yttrium chloride caused liver edema, pleural effusions, and pulmonary
hyperemia. Exposure to yttrium compounds in humansmay cause lung
disease.
57 La Lanthanum 7439-91-0
Inanimals,theinjectionoflanthanumsolutionsproduceshyperglycaemia,
lowbloodpressure,degenerationof the spleenandhepaticalterations.
Lanthanum oxide (1312-81-8) LD50 in rat oral (> 8 500mg/kg), mouse
intraperitoneal(i.p.)(530mg/kg).
58 Ce Cerium 7440-45-1
Ceriumisastrongreducingagent,andignitesspontaneouslyinairat65°C
to 80°C. Fumes from cerium fires are toxic. Animals injectedwith large
dosesofceriumhavediedduetocardiovascularcollapse.Cerium(IV)oxide
is a powerful oxidizing agent at high temperatures, and will react with
combustible organic materials. Ceric oxide (1306-38-3) LD50 in rat oral
(5000mg/kg),dermal(1000-2000mg/kg),inhalationdust(5.05mg/L).
59 Pr Praseodymium 7440-10-0 Praseodymiumisoflowtomoderatetoxicity.
60 Nd Neodymium 7440-00-8
Neodymium compounds are of low to moderate toxicity; however, its
toxicityhasnotbeenthoroughlyinvestigated.Neodymiumdustandsalts
arevery irritating to theeyesandmucousmembranes, andmoderately
irritating to the skin. Neodymium oxide (1313-97-9) LD50 in rat oral (>
5000mg/kg), mouse i.p. (86mg/kg), and Nd2O3was investigated as a
mutagen.
61 Pm Promethium 7440-12-2
It is not known what human organs are affected by interaction with
promethium; apossible candidate is thebone tissue.Nodangers, aside
fromtheradioactivity,havebeenshown.
13Z:atomicnumber.14 Mostly referred from National Toxicology Program database search application
(http://tools.niehs.nih.gov/ntp_tox/index.cfm) and material safety data sheets information in KOSHANET(http://www.kosha.or.kr/bridge?menuId=69). Searches were conducted using keywords chemical name AND/OR CASnumber
64
62 Sm Samarium 7440-19-9
Thetotalamountofsamariuminadultsisabout50μg,mostlyinliverand
kidneys,andwithabout8μg/Lbeingdissolvedintheblood.Insolublesalts
of samarium are nontoxic, and the soluble ones are only slightly toxic.
Wheningested,onlyabout0.05%ofsamariumsaltsisabsorbedintothe
bloodstream,andtheremainderisexcreted.
Fromtheblood,about45%goestotheliver,and45%isdepositedonthe
surfaceofthebones,whereitremainsforabout10years;thebalanceof
10%isexcreted.
63 Eu Europium 7440-53-1
Therearenoclearindicationsthateuropiumisparticularlytoxiccompared
to other heavymetals. Europium chloride nitrate and oxide have been
testedfortoxicity:europiumchlorideshowsanacutei.p.LD50toxicityof
550mg/kg, and the acute oral LD50 toxicity is 5 000mg/kg. Europium
nitrateshowsaslightlyhigheri.p.LD50toxicityof320mg/kg,whiletheoral
toxicityisabove5000mg/kg.
64 Gd Gadolinium 7440-54-2
Asafreeion,gadoliniumishighlytoxic,butmagneticresonanceimaging
contrastagentsarechelatedcompounds,andareconsideredsafeenough
tobeusedinmostpersons.Thetoxicitydependsonthestrengthofthe
chelating agent. Anaphylactoid reactions are rare, occurring in
approximately0.03-0.1%.
65 Tb Terbium 7440-27-9Aswiththeotherlanthanides,terbiumcompoundsareoflowtomoderate
toxicity,althoughtheirtoxicityhasnotbeeninvestigatedindetail.
66 Dy Dysprosium 7429-91-6
Soluble dysprosium salts, such as dysprosium chloride and dysprosium
nitrate,aremildlytoxicwheningested.Theinsolublesalts,however,are
non-toxic. Based on the toxicity of dysprosium chloride to mice, it is
estimatedthattheingestionof500gormorecouldbefataltoahuman.
67 Ho Holmium 7440-60-0The element, aswith other RE, appears to have a low degree of acute
toxicity.
68 Er Erbium 7440-52-0Erbiumcompoundsareoflowtomoderatetoxicity,althoughtheirtoxicity
hasnotbeeninvestigatedindetail.
69 Tm Thulium 7440-30-4
Soluble thulium salts are regarded as slightly toxic if taken in large
amounts,buttheinsolublesaltsarenon-toxic.Thuliumisnottakenupby
plantrootstoanyextent,andthusdoesnotgetintothehumanfoodchain.
70 Yb Ytterbium 7440-64-4
Allcompoundsofytterbiumshouldbetreatedashighlytoxic,becauseitis
known to cause irritation to the skin and eye, and some might be
teratogenic.
71 Lu Lutetium 7439-94-3
Lutetium is regarded as having a low degree of toxicity: for example,
lutetiumfluorideinhalationisdangerousandthecompoundirritatesskin.
Lutetium oxide powder is toxic as well if inhaled or ingested. Soluble
lutetiumsaltsaremildlytoxic,butinsolubleonesarenot.
65
AnnexIII. MoistureContentCalculationsForthesupernatantpulpwithinitialmassof𝑚oq = 1052.6𝑔,afterdryingonehas:
𝑚al 𝑑𝑟𝑦y]\ = 1708.0 − 984.5𝑔 = 723.5𝑔,
were1708.0𝑔isthetotalmassand984.5𝑔themassoftheoriginalcontainer.
𝑚al 𝑑𝑟𝑦z]_{ = 𝐺4b = 775.0 − 217.2 = 557.8𝐺,b = 268.4 − 102.7 = 165.7 → = 723.5𝑔
Giventheformationofblocks,whenthemasswastransferredfortwogoblets,therewasnolossofmass.
Hencethedrycakemasswas723.5𝑔,whichresultsinamassloss:Δ𝑚 = 1052.6 − 723.5 = 329.1.
Sothelossofmassrepresentsapercentageofmoistureof:
%~]�o\pr� =329.1×1001052.6
≈ 31.27%
Forsample1:
𝑚4 𝑑𝑟𝑦y]\ = 1146.2𝑔
𝑚4 𝑑𝑟𝑦z]_{ =𝐺4.4 = 604.1𝐺4., = 539.8 → = 1143.9𝑔
Itisverifiedthatwhenthemassistransferredintothegobletstherewerelossesof2.3g.Giventheproximity
ofthevalues,andtakingintoaccount,comparativelyothersamples,wherethelossofmassfromhottocoldhas
beenpracticallynil,themassofdrycakewillbeconsidered1146.2𝑔.
SoΔ𝑚 = 542.5,andtherefore%~]�o\pr�o ≈ 32.1%.
Forsample12:
𝑚4, 𝑑𝑟𝑦y]\ = 1008.9𝑔
𝑚4, 𝑑𝑟𝑦z]_{ = 𝐺4,.4 = 470.5𝐺4,., = 537.5 → = 1008.0𝑔
As seen themass lossdue to the transferof recipients is smaller than1𝑔. Like theabovecases, for the
calculationofthemoisturecontentoneconsidersthatthemassofthedrycakeis:1008.9𝑔.
SoΔ𝑚 = 398.8,andtherefore%~]�o\pr�o ≈ 28.3%.
Forsample19,eventhoughitIsexpectedthepercentageofmoisturetodiminish,asnoted,partoftheafloat
liquidwasaddedatthispointowingtothehighconsistencyofthesludge.
𝑚4N 𝑑𝑟𝑦y]\ = 525.9𝑔
𝑚4N 𝑑𝑟𝑦z]_{ =𝐺4,.4 = 270.8𝐺4,., = 254.7 → = 525.5𝑔
Consideringthatthefinalmassis525.9𝑔,onehasΔ𝑚 = 215.8𝑔andtherefore%~]�o\pr�o ≈ 29.1%.