RECOVERY SILVER AND GOLDBY DIRECT OXIDATIVE PRESSURE

CYANIDATION

by

Jose R. Parga and Jesus L. Valenzuela

3rd International Conference SDIMI

June 2007, Milos Island, Greece.

CYANIDE PROCESS CYANIDE PROCESS The McArthurThe McArthur--Forrest Process (1887)Forrest Process (1887)

Is a metallurgical technique for extracting gold Is a metallurgical technique for extracting gold from low grade ore by converting the gold to from low grade ore by converting the gold to water soluble aurocyanide metallic complex ionswater soluble aurocyanide metallic complex ions

Leaching Time

42 -72 hrs.

REFRACTING OREREFRACTING ORE(Recovery less than 60 %)(Recovery less than 60 %)

IMPROVED TREATMENT PROCESSES:IMPROVED TREATMENT PROCESSES:Fluid Bed RoastingFluid Bed RoastingWhole Ore RoastingWhole Ore RoastingPressure LeachingPressure LeachingBiological OxidationBiological Oxidation

Refractory Gold & Silver OresRefractory Gold & Silver Ores

Oxidative Pretreatment

Direct Leaching

Atmospheric Acid Leaching

Acid LeachingHigh Pressure

AlkalineCyanidation

High Pressure

Chemical Oxidation

Biological Oxidation

Whole OreRoasting

Leaching Gold & Silver

Carbon in Leach

Other LixiviantsThiourea,Thiosulfate

Alkaline Cyanidation &

OxigenHigh Pressure

Biological OxidationBiological Oxidation

Whole Ore RoastingWhole Ore Roasting

Pressure Oxidation of Refractory Gold OresPressure Oxidation of Refractory Gold Ores

Bulk Flotation GrindingDirect Oxidative

Pressure Cyanidation90 Minutes

Au(CN)-2

NEW TECHNOLOGY

PRESSURE LEACHING PROCESS

CHEMICAL AND MINERALOGICAL ANALYSISCHEMICAL AND MINERALOGICAL ANALYSISg/ton %

Au Ag Pb Zn Cu Fe As S

Concentrate 87.09 12320 2.6 3.8 0.5 29.2 0.15 32

Ore 4.12 289 0.5 0.4 0.04 3.67 0.1 3.7

THE MINERALOGICAL ANALYSIS ARE:- Silver Iron Sulfide- Argentite , Pyrite- Pyrrhotite, Arsenopyrite- Chalcopyrite, Covellite - Hematite and Magnetite- Quartz and Calcite

Schematic mechanism of gold and silver leaching60 minutes

GALENA

ARGENTITE

ARGENTITE

PYRITEPARTICLE

ARGENTITE

CN-

Ag(CN)2-

15O2 + 2H2O 2Fe(SO4)2 + 2H2SO4

GOLD

CN-

Au(CN)2-

SPHALERITE

Fe2(SO4)3

O2

CN-

Ag(CN)2-

Fe3+Zn2+

SIMULTANEOUSLY OXIDATIONSIMULTANEOUSLY OXIDATIONAND CYANIDATION LEACHINGAND CYANIDATION LEACHING

The primary reactions are:The primary reactions are:

2FeS2FeS2 2 + 7O+ 7O2 2 + 2H+ 2H22O = 2FeO = 2Fe2+2+ + 4SO+ 4SO4422-- + 4H+ 4H++ (1)(1)

FeSFeS22 + 2H+ 2H++ = Fe= Fe2+2+ + H+ H22S + SS + S00 (2)

Ferrous ions produced by reaction (1) and (2)Ferrous ions produced by reaction (1) and (2)are subsequently oxidized to ferric ions:are subsequently oxidized to ferric ions:

2Fe2Fe2+2+ + + 1/21/2OO22 + 2H+ 2H++ = 2Fe= 2Fe3+3+ + H+ H22O O

The ferric ions an also contribute to the oxidationThe ferric ions an also contribute to the oxidationof silver iron sulfide, argentite, pyrite, pyrrhotite,of silver iron sulfide, argentite, pyrite, pyrrhotite,

sphalerite and chalcopyrite:sphalerite and chalcopyrite:

AgFeAgFe22SS33 + Fe+ Fe3+3+ == AgAg++ + 3 Fe+ 3 Fe2+2+ + 2S+ 2S22-- + S+ S00

AgAg22S + 2FeS + 2Fe3+3+ = 2Ag= 2Ag++ + 2Fe+ 2Fe2+2+ + S+ S00

ZnS + 2FeZnS + 2Fe3+3+ = Zn= Zn2+2+ + 2Fe+ 2Fe2+2+ + S+ S00

CuFeSCuFeS22 + 4Fe+ 4Fe3+3+ = Cu= Cu2+2+ + 5Fe+ 5Fe2+2+ + 2S+ 2S00

Then, elemental sulfur may also be further oxidized to Then, elemental sulfur may also be further oxidized to sulfate by oxygen or by ferric sulfate:sulfate by oxygen or by ferric sulfate:

2S2S00 + 3O+ 3O22 + 2 = 4H+ 2 = 4H++ + 2SO+ 2SO4422--

SS00 + 6Fe+ 6Fe3+3+ + 4H+ 4H22O = 6FeO = 6Fe2+2+ + 8H+ 8H++ + SO+ SO4422--

This results in the formation of a porous,but nonprotective, eleThis results in the formation of a porous,but nonprotective, elemental mental sulfur layer, thus allowing cyanide and dissolved oxygen to accesulfur layer, thus allowing cyanide and dissolved oxygen to access to ss to the previously locked gold, silver and electrumthe previously locked gold, silver and electrum

AgAg22S + 4CNS + 4CN-- = 2Ag(CN)= 2Ag(CN)--22 + S+ S22--

4 4 Au + 8CNAu + 8CN-- + O+ O22 + H+ H22O = 4Au(CN)O = 4Au(CN)--22 + 4OH+ 4OH--

Comparison of silver extraction at ambient conditions and high pressure

0

20

40

60

80

100

0 50 100 150 200 250 300 350

TIME (min)

EXTR

ACT

ION

, %

S ILVER 80 C(80 psi)

S ILVER (N.C.)

C ON D ITION S%S olids = 20pH= 11.0P re ssure = 80 psi

rpm = 300

Te mp. = 80 oC

Comparison of gold extraction at ambient Comparison of gold extraction at ambient conditions and high pressureconditions and high pressure

0

20

40

60

80

100

0 30 60 90 120 150 180 210 240 270 300

TIME (min)

EXTR

ACT

ION

, % GOLD 80 p s i80 oC GOLD (1 atm)

25 οC

Effect of autoclave retention time on gold and Effect of autoclave retention time on gold and silver extractionsilver extraction

85

90

95

100

15 30 45 60 75 90 105 120

AUTOCLAVE RETENTION TIME (minutes)

EXTR

ACT

ION

, % GOLD

SILVER

C ON D ITION S%So lids = 20pH = 11.7P res s ure = 80ps irpm = 300Temp. = 80 C

Effect of the cyanide concentration on gold and Effect of the cyanide concentration on gold and silver extractionsilver extraction

50

60

70

80

90

100

0,4 0,6 0,8 1 1,2

CYANIDE CONCENTRATION, %

EXTR

ACT

ION

, %

GOLD

SILVER

C ON D ITION S% So lids = 20pH = 11.7Temp. = 80oCP res s ure = 80 ps irpm = 300leach time = 60 min.

Effect of temperature on gold Effect of temperature on gold and silver extractionand silver extraction

0

20

40

60

80

100

50 100 150 200 250TEMPERATURE, oC

EXTR

ACT

ION

. % GOLDSILVER

C ON D ITION S% So lids = 20pH = 11.2P res s ure = 80 ps irpm = 300leach time = 60 min.

Effect of pH on gold and silver extractionEffect of pH on gold and silver extraction

90

92

94

96

98

100

10 10,5 11 11,5 12 12,5 13 13,5

pH

EXTR

ACT

ION

, %

GOLD

SILVER

C ON D ITION S% So lids = 20Temp. = 80 oCP res s ure = 80 ps irpm = 300NaCN = 1%leach time = 60 min.

Effect of percent solids in the extractionEffect of percent solids in the extractionof gold and silverof gold and silver

0

20

40

60

80

100

0 5 10 15 20 25 30 35

% SOLIDS

EXTR

ACT

ION

, % GOLD

SILVER

CONDITIONSTemp. = 80 oCpH = 11.2P ressure = 80 ps irpm = 300NaCN = 1 %leach time = 60 min.

Results of continuous plant operationResults of continuous plant operation

9394

9596

9798

99

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

DAYS

EXTR

ACT

ION

, %

SILVER GOLD

CONCLUSIONSCONCLUSIONS

The present study shows that, gold and silver values are The present study shows that, gold and silver values are associated with silver iron sulfide, argentite, pyrite, associated with silver iron sulfide, argentite, pyrite, pyrrhotitepyrrhotite, , sphaleritesphalerite and chalcopyrite in the and chalcopyrite in the BacBacííssconcentrate.concentrate.

The dissolution of gold and silver are due to the strong The dissolution of gold and silver are due to the strong complexingcomplexing capabilities of cyanide anions combined with capabilities of cyanide anions combined with the oxidizing properties of the dissolved molecular oxygenthe oxidizing properties of the dissolved molecular oxygen..

The kinetics of the direct pressure oxidation/The kinetics of the direct pressure oxidation/cyanidationcyanidation was was found to be strongly dependent on particle size, found to be strongly dependent on particle size, concentration of sodium cyanide, temperature and pH.concentration of sodium cyanide, temperature and pH.

Single stage direct pressure oxidation/Single stage direct pressure oxidation/cyanidationcyanidation, has , has proven to be effective in treating pyrite refractory gold and proven to be effective in treating pyrite refractory gold and silver concentrates from silver concentrates from BacBacííss mining, for both gold and mining, for both gold and silver it was found that the precious metals recovery silver it was found that the precious metals recovery exceeded 96%.exceeded 96%.

The relatively mild operating conditions of 80 The relatively mild operating conditions of 80 °°C and 80 C and 80 psipsioxygen pressure offer distinct advantages. oxygen pressure offer distinct advantages. For example, low cost materials of construction can be For example, low cost materials of construction can be utilized for the autoclaveutilized for the autoclave..

Finally in this process, there is obviously lower gold and Finally in this process, there is obviously lower gold and silver inventorysilver inventory..

JesJesúús L. Valenzuelas L. ValenzuelaDept. Chemical Engng. & Metallurgy,Dept. Chemical Engng. & Metallurgy,University of Sonora, University of Sonora, Hermosillo, Sonora, MexicoHermosillo, Sonora, Mexicojvalen@iq.uson.mxjvalen@iq.uson.mx

JosJoséé R. PargaR. PargaDept. of Metallurgy and Mater. Sci.,Dept. of Metallurgy and Mater. Sci.,Institute Technology of Saltillo, Institute Technology of Saltillo, Saltillo, Coahuila MexicoSaltillo, Coahuila Mexico

HHééctor Moreno and David L. Cockector Moreno and David L. CockeDept. Chemistry, Lamar University, Dept. Chemistry, Lamar University, Beaumont, Texas, USBeaumont, Texas, US

Thank you for your attention

PRINCIPALES CENTROS MINEROS EN EL ESTADO DE SONORA

POTENCIAL DE CRECIMIENTO

10 nuevos proyectos mineros en operaciónen el período 2004-2009

PROYECTO EL CHANATEO r o

PROYECTO CERRO COLORADO

O r o PROYECTO LLUVIA DE OROO r o

PROYECTO MILPILLASCobre

PROYECTO MARIQUITA

Cobre

PROYECTO BACADEHUACHI

Sulfato de Sodio

PROYECTO MULATOSO r o

PROYECTO SAN ANTONIOO r o, Cobre

PROYECTO PIEDRAS VERDES

Cobre PROYECTO ALAMO DORADO

P l a t a