05 - Optimization Barite Processing

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CICCU, R., CURRELI, L., GIULIANI, S., MANCA, P.P. and MASSACCI, G. Optimization of an integratedflowsheet for barite processing. APCOM 87. Proceedings of the Twentieth International Symposium on theApplication of Computers and Mathematics in the Mineral Industries. Volume 2: Metallurgy. Johannesburg,SAIMM, 1987. pp. 281- 293.

Optimization of an Integrated Flowsheet forBarite ProcessingR. CICCU, L. CURRELI, S. GIULIANI, P.P. MANCA and O. MASSACCI

Department of Mining and Minerals Engineering, University of Cagliari, Italy

This paper examine the optimization of a beneficiation plant for recoveringmarketable barites from crude ores of different characteristics. The plant,part of a mining complex in Sardinia, consists of a jig section integrated witha flotation line. The problem has been studied using a suitable model of theprocess, based upon experimental and field data pertaining to both thecharacteristics of the feed material and the performance of machinery. Datahave been automatically processed with the aid of a computer to find theoptimum setting of each section, in order to maximize profit for each kindof ore separately fed to the plant. Moreover, the advantages of blending thevarious concentrates - not all of them individually marketable - are alsodemonstrated.

The overall economic result can be improved provided suitable proport ionsof each kind of ore are fed to the plant. Such information is fundamentalfor the long-term planning of exploitation of available reserves, and providesguidelines for further prospecting.The paper illustrates the washability characteristics of the ores and describesin detail the model adopted. The results of data processing are then presentedin the form of computer graphs and discussed. Finally, conclusions are drawnregarding the advantages of resorting to Operations Research as an aid tomanagement.

IntroductionAt the Barega mine, in Sard in ia , ore r eser - se of considerable losses in the coarsev e ~ are conta ined in a number of orebodies waste (ore b, from Gianni s tope) .of varyi.ng ch a rac t e r i s t i c s . They ar,e mined The plan t cons i s t s of th r ee main sec t ions :e i th e r opencas t or underground, and the (a ) a t h ree -s t age crushing s ta t ion where thereSUlt ing run-of-mine can be dist inguished R.D.M. i s reduced from a top s i ze ofas fol lows, according to BaSD4 grade an d about 60 0 mm down to - 20 mm;in te rgrowth fea tures : (b) a two-s tage j igging sect ion with iIlt:e:L-la ) a crude ore eas i l y washable with grav i ty s tage gr inding whereby a grav i ty con-

methods y i e l d i ~ n g r e l a t i v e l y good recove- cent ra t e i s produced;r i e s (ore A, from Litopone s tope) ; (c ) a f l o t a t i o n l i n e for the recovery of Da-

(b) a crude ore of lower grade conta in ing r i t e values still conta ined in the f inef ine ly disseminated quar tz which yie lds f rac t ions discarded from the p r e c e ~ i n q a poor qual i ty concentra te a t the expen- sec t ion .

OPTIMIZA TION OF AN INTEGRATED FLOWSHEET FOR BARITE PROCESSING 281


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To Tailings Pond

jFlotationConcentrate

Preconcentrate

Concentrate

FIGURE 1. Flowsheet of the Barega plant

The f lowsheet of the plan t i s sketched in The r e j ec t of the sc reen-cont ro l l ed coneFigure 1. crusher i s col l ec ted in a 1200 tonnes bin a t

Each kind of ore i s stocked in d i f f e r en t the head of the upgrading p lan t .3tockpi les an d can be fed separate ly to t ~ h e Gravity t reatment i s car r ied out in tw oplan t . Crushing i s done with the same ma - s tages . In the f i r s t s tage the ore i s pre -chine se t t ing , i r r espect ive of the ore being concentrated in tw o para l l e l l ines , eachprocessed. cons i s t ing of a vibra t ing bed j ig with a282 METALLURGY: SIMULATION


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capac i ty of 60 t / h . The coarse waste i sseparated, screened and sold as an aggregatefor concrete . Th e f i n es t s i ze c l a ss ( -3 mm)may be su i tab le for f l o t a t i o n , provided itconta ins enough recoverable b a r i t e .

The preconcentra te and the f ines f i l t e r edthrough the j ig bed are dewatered in a sp i -ra l c la s s i f i e r : the overf low i s sent to aDorr th ickener whereas the coarse f r ac t ionis screened a t 8 mm, which i s the l i b e r a t i o ns i ze for the f i n a l grav i ty concent r a t ion . Ashor t -head cone crusher reduces the screenr e j ec t to below t h a t s i ze . The crushed pre -concentra te i s s p l i t and s tored in fourbins , each feeding a sta t ionary-bed j ig witha capac i ty of 7 t /h fo r f i n a l c lean ing . Bothconcentra te and middl ings are dewatered;overf low f ines are thickened and sent tof lo ta t ion toge ther with preconcent r a t ionf ines while middlings fol low the same routeas the preconcentra t ion waste.

Se t t l ed pulp from the Dorr th ickener i sfed to the f l o t a t i o n l i n e . The mater ia l i sf i r s t cycloned; t h i s opera t ion genera l lyproduces a 10 to 15 BaS04 poin ts inc rease inthe underflow grade with to lerab le bar i t el osses . This underf low i s ground to - 0.5 mmin a b a l l mil l in c losed c i r cu i t with a rakec la s s i f i e r ; a f t e r condit ioning with Na -Cethylsu l f a te , the r e j ec t i s processed v iaf lo ta t ion with tw o cleaning s tages obtaininga commercial f i l t e r cake assaying 94 - 95%BaS04 su i t ab le for barium chemicals .

The optimization problemThe b ar i t e market i s today undergoing aworldwide slump. In f ac t ,cent f a l l in o i l p r i ces ,

owing to the re the demand fo r

dr i l l i ng ~ u d s appl i ca t ions , by f a r the l a r -g e s t o u t l e t for bar i t e concent r a tes ,suddenly diminished. 2

has

Consequently , the market s t r u c tu r e has un-dergone a major change c o ~ p a r e d to the pre vious per iod. This chief ly concerns the mores t r ingen t qua l i ty requirements fo r the di f -fe ren t u t i l i za t i o n s : o i l se rv ice companies,in addi t ion to OCMA (Oil Companies l1ater ia lsAssociation) s tandards , tend now to refuseblends wi th products containing f lo ta t ionr eagents , whereas manufacturers o f bariumsa l t s accept only high-grade concent r a teswi th very lo w p o l l u t a n t s . 110reover, over thel a s t fe w years market pr ices have f a l lenconsiderably in r e a l terms.

Under these circumstances,schedule had to be adjus ted ;

the product ionpresen t ly , the

p l a n t output cons i s t s of the following products :(a ) a high-grade , lo w s i l i c a grav i ty concen-

t r a t e for barium chemicals ;(b) a 4.20 S.G. j ig concentra te su i tab le as

weighing agent fo r dr i l l i ng mudsgrinding) or heavy concrete ;

( af ter

(c ) a f l o t a t i o n f i l t e r cake fo r barium chem-i ca l s ;

(d ) c lass i f i ed aggregates fo r common concrete s or road cons t ruc t ion

Therefore the ~ a i n problem i s how to opt i mize the production schedule in order toachieve the maximum p ro f i t while sa t i s fy ingmarket demand.

As regards the ore , the bas ic da ta to beinc luded in the process model are the washab i l i t y ch a r ac t e r i s t i c s and the propor t ion ofeach kind of ore being benef i c i a t ed . Thispropor t ion must be cons i s t en t with the l e v e l

OPTIMIZA TION OF AN INTEGRATED FLOWSHEET FOR BARITE PROCESSING 283


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TABLE 1. Washability characteristics of crude ore A, by size

SIZE CLASS DENSITY2.56 2.60 2.65 2.71 2.78 2.91 3.00 3.10 3.20 3.70 4.20 4.30 4.40 4.45

-20.000 +7.925- 7.925 +4.699- 4.699 +2.362- 2.362 +1.168- 1. 168

-20.000 +7.925- 7.925 +4.699- 4.699 +2.362- 2.362 +1.168- 1. 168

JRE GRADE = .3810

MASS.0289 .0520 .0748 .1178 .0632 .0245 .0146 .0087 .0233 .0291 .0146 .0437 .0874.0071 .0089 .0108 .0226 .0059 .0004 .0002 .0005 .0010 .0017 .0015 .0103 .0340.0067 .0077 .0137 .0168 .0061 .0019 .0014 .0001 .0035 .0038 .0037 .0119 .0106.0062 .0034 .0087 .0120 .0038 .0020 .0010 .0007 .0007 .0010 .0012 .0065 .0206.1567

GRADE.0239 .0267 .0259 .0208 .1053 .1314 .1866 .2447 .4190 .7095 .8838 .9419 .9855.0346 .0282 .0313 .0296 .1318 .1572 .2107 .2671 .4362 .7181 .8872 .9436 .9859.0440 .0243 .0331 .0304 .1076 .1337 .1887 .2467 .4205 .7103 .8841 .9421 .9855.0251 .0226 .0331 .0246 .1445 .1695 .2223 .2778 .4445 .7222 .8889 .9444 .9861.4982

FEED GRADE (FINES EXCLUDED) .3593

TABLE 2. Washability characteristics of crude ore B, by size

SIZE CLASS DE NSITY2.56 2.60 2.65 2.71 2.78 2.91 3.00 3.10 3.20 3.70 4.00 4.20 4.30 4.40

-20.000 +7.925- 7.925 +4.699- 4.699 +2.362- 2.362 +1.168

- 1.168

-20.000 +7.925- 7.925 +4.699- 4.699 +2.362- 2.362 +1.168- 1. 168

ORE GRADE = .2293

MASS.0293 .0454 .1134 .0792 .1765 .0412 .0203 .0102 .0190 .0319 .0305 .0475 .0339.0065 .0074 .0223 .0185 .0212 .0020 .OG09 .0011 .0020 .0034 .0018 .0053 .0122.0050 .0085 .0150 .0101 .0151 .0039 .0021 .0005 .. 0010 .0007 .0021 .0066 .0058.0062 .0043 .0071 .0053 .0071 .0024 .0016 .0007 .0005 .0005 .0007 .0032 .0064

.0894

GRADE.0195 .0207 .0153 .0369 .0473 .0751 .1339 .1958 .3814 .6288 .7835 .8763 .9381.0227 .0198 .0141 .0279 .0336 .0618 .1215 .1842 .3725 .6235 .7804 .8745 .9372.0273 .0152 .0129 .0277 .0448 .0727 .1316 .1937 .3797 .6278 .7829 .8759 .9380.0196 .0137 .0100 .0261 .0435 .0714 .1305 .1926 .3789 .6273 .7826 .8758 .9379.3680

FEED GRADE (FINES EXCLUDED) .2157284 METALLURGY: SIMULATION


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of known re se rves ava i l ab le a t the mine.Washabil i ty charac te r i s t i cs have been d e t e r -mined by s i nk- f l oa t analysis using heavyl iqu ids or FeSi suspens ions in TBE ( t e t r a -bromoethane) fo r the higher d en s i t i e s . 3

The resul t s o f thE' experimental inves t iga-t ion are summarized in Tables 1 and 2 and bythe graphs of Figure 2.

As regards the fea tures of the p lan t , thebas ic in format ion on machinery performancehas been co l l ec t ed a f t e r ca re fu l l y samplingthe mate r ia l passing through the va r ioussec t ions of the i ndus t r i a l opera t ions, an dln pa r t i cu l a r the feed and r e j ec t of thej i gs . Accordingly, the following da ta havebeen assumed:(a ) imperfect ion of primary j i gs : 0.15;

1 0 0 + ' ~ - - ~ - - ~ - + - - + - - - 4 ~ ~ - - + - - + - - ~ 1 0 0 ~

::w::: 80zCl)UJ 60>

40...J:::l:E 20:::l( )

2.50 I2.90

(L1TOPONE)2

I I


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( imperfect ion parameters fo r th e preconcent r a t i on and f i n a l c lean ing s t ages , p l an tcapac i ty , average da i ly throughput) .

Th e main s e t t i n g parameters o f th e processa re the values of the sepa ra t ion d e n s i t i e sd l and d 2 a t which the p reconcen t ra t ion a n ~ f i n a l upgrading j i gs a re ad jus ted .

with re fe rence to one tonne o f crude orefed to th e p l a n t , th e model developed al lowsto obta in , fo r each combinat ion o f d l and d 2within the ass igned f i e l ds , th e fol lowingr e s u l t s :(a ) th e ore mass c i r cu l a t i n g through th e

var ious p l a n t sec t ions and th e cor re s -ponding opera t ing cos t s , fo r t h a t p a r tpropor t iona l to th e amount of oret rea ted (va r iab le cost ) . In f ac t , asa l ready mentioned, only t h i s p a r t o f th eprocess ing cos t , given th e average da i lyfeed r a t e , i s re l evan t fo r optimum regul a t i o n of th e p l a n t ;

(b) th e t o t a l var i ab le cos t o f the wholeprocess per tonne of o re ;

(c ) th e yie ld , recovery and grade fo r thevar ious f i n a l products ; the cha rac te r i s t i c s o f th e mate r i a l s en te r ing o rl eav ing the in te rmedia te s tages of theprocess a re a l so s imulated ;

(d) th e overa l l product ion and market valueof th e commercial products which can beso ld a t maximum p r o f i t , t h e i r optimummix and th e t o t a l sa l e s income;

(e ) th e r e su l t i n g margin of con t r ibu t ion ofthe p rocess ing p lan t .

The peak value of t h i s l a t t e r parametercorresponds to th e most advantageous adjus tment , i . e . th e optimum combination o f d l286

and d 2 .The computer program cons i s t s o f a Qain

prograQ and f ive su b ro u t in es wri t t en ln agenera l i zed form,s imi l a r cases .

su i t ab le fo r a v a r i e ty of

Th e ch a rac t e r i s t i c s o f ch e f l o a t and s inkproducts reSUl t ing from th e f i r s t j igg ings tage (p reconcen t ra t ion) a re given in mat r ixform by a su i t ab le su b ro u t in e ; fo r each s i zec l a s s , th e f rac t ions of th e u n i t mass r e l a t i ng to each dens i ty range a re obtained byass igning to th e corresponding mass of th efeed th e co l lec t ive ~ r o b a b i l i t i e s a and(1 - a ) to belong to e i t h e r a l t e rn a t i v e p r o -duct of th e opera t ion , re spec t ive ly . Th evalue of these p ro b ab i l i t i e s i s ca lcu la t edaccord ing to the log-normal d i s t r i b u t i o n la was a funct ion of th e sepa ra t ion dens i ty(d-l) r e l a t i v e to the d e n s i t y o f water ,given the imperfect ion parameter 11log-normal d i s t r i b u t i o n has been approx i mated by a 5th degree po lynomial .

Owing to th e non- l inea r i ty of th e curve,a s u f f i c i en t degree o f accuracy in th e ca l cula t ion i s ach ieved by reducing th e widthof the elementary in te rva l s (0.01 kg.dm- 3 )by which th e var i ab le dens i ty i s increasedfrom t h a t o f th e l i gh t e s t ganguekg dm- 3 ) up to t h a t of pure ba r i t ekg dm- 3 )

(2 .60(4.45

Th e mass o f th e feed ass igned to each u n i ti n t e rv a l i s ca lcu la ted by l i n ea r i n t e rp o l a t ion o f th e ava i l ab le exper imenta l d a t a . Th escreen ing o f th e preconcentra te which pre cedes th e i n t e r s t age gr ind ing i s regu la . tedby th e mesh s i z e . However, in t h e case a thand t:,e r,1odel does not imply any dec i s ion

METALLURGY: SIMULATION


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s ince both ores are s u f f i c i en t l y l i be ra tedbelow about 8 mm. Actua l ly , an imperfec t ionfac tor a f f ec t s the disper s ion of the Gaussprobabi l i ty d i s t r i b u t io n la w which descr ibessc reen performance; bu t fo r the sake ofs impl ic i ty and on account of the f ac t t h a tsc reening i s wet, a p e r f e c t s i ze c l a s s i f i ca -t ion was assumed, with negl ig ib le los s ofaccuracy.

Pr ior to the f i n a l concent r a t ion s tage ,overs ize i s coarsely ground in a shor t -headcone crusher , with the d ischarge aper ture

s e t a t around 8 mm. This opera t ion producesa propor t ion of f ines below 1 .168 mm, weigh-ing on average one- ten th of the feed to thecrusher ; In prac t i ce t h i s f igure va r iess l i g h t l y with the preconcent r a te s ince thewaste rock (Cambrian l imestone) i s tougherthan b ar i t e ; however, the s impl i f i ca t ionadopted can be considered to have a negl i -g ib le e i f ec t .

It i s a lso assumec t h a t no SUbstant ia lconcentra t ion of b ar i t e in the f ines takesplace . This hypothes is i s corrobora ted bysome ' s p o t ' l abora tory t e s t s using a crush-ing machine of performance comparable tot h a t i n s t a l l ed in the p lan t .

The new f ines produced are combined withthe f ines separa ted dur ing the preconcentra-t ion s tage and sen t to the gr ind ing mil l forf l o t a t i o n .

Th e f i n a l j igg ing opera t ion i s simUlatedworking on the washabi l i ty ch a r ac t e r i s t i c sa t t r i b u t ed to the ground preconcentra tea f t e r removal of f ines , combined with thoseof the sc reen unders ize , given by the simu-l a t i o n of the preconcent r a t ion s tage .

The washabi l i ty curve of the ground pre -concentra te i s cons t ruc ted by means of amathemat ica l a lgor i thm; the r e s u l t s obta inedagree f a i r l y well with the corresponding

3opera t ion da t a .To check the above assumption, spot sam-

pIes have been t aken from the b e l t feederan d the d ischarge chutes of the preconcen-t r a t i o n j i g . Th e -20 +8 mm an d the -8 +1.168mm s i ze f rac t ions of the feed sample havebeen analyzed wi th heavy l i qu ids up to4.20 kg.dm- 3 ; the washabi l i ty curve of theground preconcent r a te ca lcu la ted with themodel i s repor ted in Figure 3 toge ther withthe exper imenta l poin ts o f the d i r ec t ana ly-s is of the ac tua l preconcentra te sample,ground to -8 mm. As it can be observed, theagreement i s f a i r l y s a t i s f ac to r y .

It has been assumed t h a t the washabi l i tych a r ac t e r i s t i c s of the ground produc t a res imi la r to those o f the same s i ze c l a ss -8+1.2 mm of the ore fed to the p l a n t , ex-per imental ly s tud ied by heavy l i qu id ana ly-

. 3 , 5S l S .Accordingly,

w:::4I-


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screening o f f the -1.168 mm f ines , wil lconta in , in the intermediate dens i ty rangeof the washabi l i ty curve; the same propor-t ion of in tergrown middlings as the cor re -sponding f r ac t ion of the feed, i. e. the tw ocurves have the same grad ien t .

This assuQption i s j u s t i f i ed in the casebeing examined, s ince crude ore A cons i s t sof tw o preva i l ing components (ba r i t e an dl imestone , with Qinor assoc ia t ions of o t he rgangue minera l s ) suf f i c ien t ly l ibera ted a ts i zes below 8 mm, whereas in the case of oreB the pol lu t ing gangue (quartz) i s evenlyintergrown with the bar i t e matr ix in theform of f ine assoc ia t ions or disseminat ions .However, the tw o products have d i f f e r en tBaS04 grades, general ly higher in the pre -concentra te . Therefore su i t ab le adjus tmentsmust be in t roduced as regards the ma.3S ofdens i ty f rac t ions outs ide the 'w iddl ings '

range, i. e . l i g h t e r than 3.20 kg.dQ-3 orheavier tl1an 3.80 kg.dm- 3 . In f ac t it hasbeen observed t h a t within t h i s range thewashabi l i ty curves o f the Barega ore arealmost f l a t ,with miniwuQ constant s lope.

According to the model, the amount of massto be subt r ac ted from the l igh ter and addedto the heavie r f rac t ions i s kept propor-t ional to the mass conta ined in the cor -responding dens i ty f r ac t ion of the -8 +1.2mm s i ze c l a ss of the feed.

The fo l lowing formulas have been used:

288

m ( i)y

for 1 i .::: nl

HY m ( i )Y

where mz{i) and my(i) are the shares o f theu n i t mass contained in the i - th dens i tyf rac t ions of the ground preconcent r a te andof the ' r e fe rence ' feed, r e sp e c t i v e l y . Then l - t h and n ~ - t h dens i ty f r ac t ions c o r r e s p o n ~ to the extremes of the 'w iddl ings ' rangewhereas the n 3- t h i s bound by t he dens i ty ofthe I leavier mineral component. In our casethe nl - th f rac t ion i s t h a t j u s t above 3.20,the n2- th lS t h a t j u s t below 3.80 and then 3- th i s t h a t j u s t below 4.45 kg.dm- 3 (vo-lu,"e r.lass of b a r i te) .

The amount o f mass to be ca lcu la ted fromthe above formulas depends on the value ofthe parameter q which i s determined underthe cons t ra in t t h a t the grade t z o f theproduct leaving the crusher i s exact ly thesame as the grade tx of the screen undersizeenter ing it .

Therefore :n3

q1.'i= l

n1-11 2: m.( i ) t (i)Ly i= l Y x

where m x ( i ~ an d tx ( i ) a re the mass and thegrade of the i - t h dens i ty f r ac t ion o f themate r i a l to be ground, re spec t ive ly .

In p r ac t i ce , s a t i s f ac to r y r e s u l t s areeas i l y me t if the 'middl ings ' i n t e r v a l i sreasonably l imi ted .

The ch a r ac t e r i s t i c s of the ground productare given by a subrout ine in v ec to r i a l forms ince the subdivis ion o f the masses intos ize classes i s no longer necessary norusefu l for the subsequent development o f the



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model.Fina l ly . the l a s t subrout ine enables the

ch a r ac t e r i s t i c s of the mate r i a l feeding thej igs to be ca lcu la ted by appropria te ly com-bining the unders ize with the ground pro-duct obta ined from the comminution of over-s i ze .

The f i n a l cleaning s tage i s simulatedusing procedures s imi la r to those followedfo r the preconcent r a t ion s imula t ion .

The product of t h i s opera t ion i s a bar i t econcentra te an d middlings to be sen t to f lo -

t a t ion toge ther with the primary f ines andthe f ines obta ined a f t e r in ter s tage cowainu-t ion. fljoreover, the model makes allowancefor sending to f lo ta t ion the f rac t ion -3 .0+1.168 mm screened from the preconcent r a t ionr e j ec t . For th i s purpose th e computer pro-gram v e r i f i e s whether the recoverable va luesstill conta ined t he re in are a t l e a s t equalto the marginal cos t s o f f lo ta t ion .

The above-descr ibed procedures are repea t -cd fo r each p a i r of d en s i t i e s , d l an d d 2within the programmed f i e ld s of var ia t ion .

The data base genera ted i s su i tab le fo rautomatic p lo t t i n g and fo r fu r ther proces -s ing.

Blending opera t ions a re s imula ted ~ h r o u g h the l a s t subrout ine: t h i s al lows i d en t i f i ca -t i on of the s e t of admissib le so lu t ions forvar iab les tA ' tB an d A (mutual propor t ion ofores A an d B) a t which marketable productscan be obta ined .

DiscussionFi r s t of a l l , the t r ea tment of each kind ofore i nd iv idua l ly fed to the p l a n t has beens imula ted . The se t t ing parameters fo r the

grav i ty sec t ion are the separat ion d en s i t i e s01 and d2 o f preconcentra t ion an d f i n a lc lean ing , re spec t ive ly .

In t h i s case the objec t ive to be pursuedwas t h a t of achieving from each ore themaximum margin of cont r ibu t ion , i . e . thel a r g es t di f f e r ence between the marke t valueof a l l the sa leab le products obta inable fromone tonne of ore (gravi ty and f lo ta t ionconcent r a tes , c lass i f i ed aggregates) and thecorresponding uni t va r i ab le process ing cos t .The exis tence of a peak value of the marginof cont r ibu t ion for varying combinations ofthe separa t ion dens i t i e s i s highl ighted bythe curves of Figure 4. The upper fami ly o f

2 7 + - - - - - + - - - - - r - - - ~ - - - - _ + - - - - _ + - - - - _ + ......

....I

zQ 24I -:::>00c::I Zot> 21LLoZ(!jc::c:(::E 18

15

120

~ 0 . 8 9 0.91~ 0 . 8 7

0.85

GIANNI

10

LlTOPONE

: : : : ; ; ; ; .890.870.85

20 30PRECONCENTRATION LOSS, %

FIGURE 4. Processing margin of contribution (M.O.C.) forores A (Litopone tope) and B (Gianni stope) atvarying level of barite loss in coarsepreconcentration waste. The parameter is theBaSO grade of final jog concentrate

OPTIMIZATION OF AN INTEGRATED FLOWSHEET FOR BARITE PROCESSING 289


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curves r e f e r s to ore A, which i s of h igherq u a l i t y and eas i ly washable, the lower fami-ly to ore B, which i s l eaner and l e ss amena-b le to t reatment .

The lij.O. C. (I1argin of Contr ibut ion) i srepresented as a func t ion of the percentl oss of bar i t e in the coarse preconcentra-t i on waste, which i s the most s ig n i f i can tvar iab le of t h i s opera t ion . The parameter ofthe curves i s the BaS04 grade of the f i n a lgrav i ty concent r a te .~ h e peak l1. 0. C. fo r ore A i s reachec a t

very lo w l o s se s , between 5 and 10%. Everypercent p o i n t l o s t in preconcentra te A re -covery e n t a i l s g r e a t e r economic c isadvan-tages than for ore B fo r which l osses ashigh as 15 - 20% are still t o l e r ab l e . As canbe observed, the optimum M.O.C. i s obta inedfo r a concentra te g r ~ d e of 89%: a t in -creas ing values above th i s l e v e l t he h ighe rmarket pr ice paid by the chemical indus t ryi s neut ra l i zed by th e d e t e r i o r a t i o n of theovera l l y i e l d .

The peak M.O.C. i s a func t ion of f ina l j igconcentra te grade , as c lea r ly shown by thecurves of Figure 5, upper p ar t . The t e rmina lpo i n t of each curve r epresen ts the highes tBaS04 grade t echnica l ly achievable with thepresen t p lan t , given the gr inding s i ze : con-cent ra t ion o f ore A can be pushed to 96%,whereas t h a t of ore B i s l imi ted a t 89%.Correspondingly, optimum concent r a te yie ldsvary according to th e curves o f Figure 5,lower p a r t . Gravi ty yie ld deter io ra tes gra -dua l ly with cons tan t g r ad ien t up to 92% fo rore A and 86% for ore E, then drops sharp lywith asynpto t ic values of 96% and 89%, r e s -290

pe c t i ve l y . Flo ta t ion y ie ld inc reases almostsymmetr ica l ly .

The most s ig n i f i can t conc lusion i s t h a toptimum j ig concentra te grade lS 89% forboth ores , under the c o n s t r a i n t t h a t each i sind iv idua l ly so ld on the narke t . In f ac t ,89% BaS04 i s the lowes t acceptable l i m i t fore i th e r d r i l l i n g or chemical use ; below th i sthe mater ia l i s re j ec ted or heavi ly pen-

3 0 + - ~ - r ~ - - ~ + - ~ - + ~ - - l - - + - - b - + - + I ~

25 fLlTOPONE !1i 5! GIANNI f~ ~ ! ~ - - ~ + I - 4 ~ + - 4 - ~ ~ I - - ~ . ~ + - - ~ 70 80 90 100CONCENTRATE GRADE, %

o 5 0 + - + - + - + - + - + - + - ~ ~ ~ - + - + - + - + - + - + i ' '0"-ou:: 40> LJCw

30Cl:::I -ZwU 20zoU10

70 80 90 100CONCENTRATE GRADE, %

FIGURE 5. Above: Processing margin of contribution as afunction of jig concentrate grade for ores A(Litopone stope) and B (Gianni stope). Below:Jigging and flotation' yields of ore A (LJC andLFC, respectively) and ore B (HJC and GFC,respectively) versus jig concentrate gradeMETALLURGY: SIMULATION


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a l i zed .The fac t t h a t j igg ing yie ld of ore B pro-

gress ive ly d e te r io r a t e s wel l before reachingthe s a l eab i l i t y l im i t sugges ts t h a t con-s i s t en t economic advantages may be achievedby re sor t ing to blending .

After th i s approach to the problem ofoptimu,c1 benef i c i a t ion of the whole R.O. l1 . ,upgrading of ore A can be pushed fu r the r ,an d t h a t of ore B somewhat di rJ inished, tothe exten t t h a t a blended concentra te i s ob-

6ta ined which meets market speci f ica t ions .The outcome of computer s imulat ion i s shownIn Figure 6, where the di f fe rence between

....

...... 60 0...,...J Ic.i T0 400:E 0...JI-Z 200wc:::w 0.I..L.I.. '\9Cl 0

tA

-200

- 400t to00 20 40 60 80 100

PROPORTION OF ORE All, %

the 1'i. O. C. a f t e r blending an d the optimumU.O.C. without blending i s p lo t t ed aga ins tpercent propor t ion of ores A an d B fed tothe plan t (with r espec t to the t o t a l ) . The

parameters of the curves are the grades tAand tB of j ig concentra tes A an d B, respec-t ive ly .

Figure 6 cons i s t s of tw o graphs , one foreach blending scheme. The f i r s t r e f l ec t s thecase where the j ig concentra tes are blendedin t h e i r en t i r e ty ; the second r e f e r s to thecase w:,ere blencling with the whole concen-t r a t e B i s l imi ted to t h a t p ar t of concen-t r a t e A in excess of the chemical indust ry

.......... 600 r...,...J t.)ci 40 tE...JI-z 200wc:::WL.I..L.I..Cl 0

-2000CO t

-400 t0 20 40 60 80 100

PROPORTION OF ORE All, %FIGURE 6. Additional economic advantage achievable through blending operations of concentrates A andB of varying quality with respect to the weighed M.O.C. for the single ores at optimum plant

setting. Abscissa represents the proportion of ore A in the overall feed. Left side: Blendingof concentrates A and B in their entirety. Right side: Blending of whole concentrate B withthat part of concentrate A in excess of chemical industry demand.

OPTIMIZATION OF AN INTEGRATED FLOWSHEET FOR BARITE PROCESSING 291


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demand. Flo ta t ion concentra te i s not u t i l -ized in e i t h e r case .

It i s worthwhile not ing t h a t blending i salways advantageous , except fo r the extremecases when tA i s too high , l e t us say above

and tB i s i nve rse ly too smal l , around80% or l e s s . Blending i s aga in economical lyadvantageous even fo r the h i ghe s t values of

provided t h a t tB i s increased to al e v e l such t h a t smaller propor t ions of concent ra t e A are required fo r o f f s e t t i n g i t spoor q u a l i t y .

Concerning the f i r s t scheme, the advan tageof blending inc reases a t :1igher tB whileadapt ing e i th e r th e grade or the r e l a t i v epropor t ion of concentra te A, o r both . Theabsolu te peak value of the envelope curvei nd ica tes t h a t blending i s most convenientwhen ore A i s upgraded to 93,5 and ore B to87% BaS04 ' the propor t ion of ore A beingaround 20% of the t o t a l . This , of -:ourse,does no t ir.1ply t h a t the plan t shoulo. be s e ta t t he se condi t ions .

Obviously the l a r g e r the amount of ore Athe higher the p ro f i t s . Th e optimum process -ing 11.0 . C. fo r ore A alone i s about 25.5k L i t / t whereas t h a t for ore B i s s l i g h t l yabove 14.2 ; the u n i t cos t s o f mining andhaulage are almost th e same in both cases .

The propor t ion of the tw o ores i s dic ta t edby the s i t u a t i o n of the reserves and by themining c o n s t r a i n t s . Given t h i s propor t ion ,which may vary with t ime, the produc t ionscheGule should be s e t a t the cor respondingpo i n t on the envelope curve . Simi la r con-s i d e r a t i o n s a lso holo. for the ~ l e n d i n g scheme B, except t h a t presen t ly the curves292

are displaced towards higher propor t ions ofore A.

Scheme A i s more advantageous, excep t whenore A preva i l s by f a r over ore B; In t h i scase the tw o envelope curves a lmost over lap.

ConclusionsThe advantages of applying Opera t ions Research ano. in p ar t i cu l a r computer s imulat ionfo r i den t i fy ing optimum opera t ing condi t ionsof a process ing p l a n t a re widely r ecogni zed. 7 The case d i sc usse d in t h i s paper fu r t h e r suppor ts t h i s assumpt ion .

In p ar t i cu l a r , the l ike l ihooo. of the m o ~ e l here proposed fo r mul t i - s t age j igg ingp l a n t s , eventua l ly i n t egra ted with f l o t a -"cion, seems reasonably v er i f i ed , a t l e a s tfo r ores o f s imple composi t ion.

Fina l ly , the advantage of blending h igh-qua l i ty concentra tes with poorer ones obt a ined from l e ss amenable ores in order tomake the l a t t e r marketable , are a l so shown.In the case here i l l us t r a t ed an addi t iona lp ro f i t of the order of 50 0 I t a l i an Lire pertonne of ore can be achieved by r e so r t i n g tobleno.ing techniques , a lso tak ing i n to ac-coun t the cos t of handl ing .

References1. CARBINI, P. ano. CICCD, R. Confronto

t ecn ico e economico per due p o s s i b i l idiagrammi o. i arr icchimento gravimetr icod i un minera le d i b ar i t e . Resoc. Ass.Min, Sarda. vo l . 88, n 1 , 1983. pp. 75-99 .

2. CICCD, R. s i tuaz ione e prospe t t ive d e lcomparto de l ba r io in Sardegna. Att i



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05 - Optimization Barite Processing