RECOVERY SILVER AND GOLD BY DIRECT OXIDATIVE PRESSURE CYANIDATION

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1 3rd International Conference SDIMI RECOVERY SILVER AND GOLD BY DIRECT OXIDATIVE PRESSURE CYANIDATION by Jose R. Parga and Jesus L. Valenzuela June 2007, Milos Island, Greece.

2 CYANIDE PROCESS The McArthur-Forrest Process (1887) Is a metallurgical technique for extracting gold from low grade ore by converting the gold to water soluble aurocyanide metallic complex ions Leaching Time hrs.

3 REFRACTING ORE (Recovery less than 60 %) IMPROVED TREATMENT PROCESSES: Fluid Bed Roasting Whole Ore Roasting Pressure Leaching Biological Oxidation

4 Refractory Gold & Silver Ores Leaching Gold & Silver Oxidative Pretreatment Direct Leaching Whole Ore Roasting Chemical Oxidation Biological Oxidation Atmospheric Acid Leaching Acid Leaching High Pressure Alkaline Cyanidation High Pressure Carbon in Leach Alkaline Cyanidation & Oxigen High Pressure Other Lixiviants Thiourea, Thiosulfate

5 Biological Oxidation

6 Whole Ore Roasting

7 Pressure Oxidation of Refractory Gold Ores

8 PRESSURE LEACHING PROCESS NEW TECHNOLOGY Au(CN) - 2 Bulk Flotation Grinding Direct Oxidative Pressure Cyanidation 90 Minutes

9 CHEMICAL AND MINERALOGICAL ANALYSIS g/ton % Au Ag Pb Zn Cu Fe As S Concentrate Ore THE MINERALOGICAL ANALYSIS ARE: - Silver Iron Sulfide - Argentite, Pyrite - Pyrrhotite, Arsenopyrite - Chalcopyrite, Covellite - Hematite and Magnetite -Quartz and Calcite

10 Schematic mechanism of gold and silver leaching 60 minutes Fe 3+ Zn 2+ CN - Ag(CN) 2 - SPHALERITE ARGENTITE PYRITE PARTICLE ARGENTITE CN - CN - O 2 GALENA GOLD ARGENTITE Fe 2 (SO 4 ) 3 Ag(CN) 2 - Au(CN) 2-15O 2 + 2H 2 O 2Fe(SO 4 ) 2 + 2H 2 SO 4

11 SIMULTANEOUSLY OXIDATION AND CYANIDATION LEACHING The primary reactions are: 2FeS 2 + 7O 2 + 2H 2 O = 2Fe SO H + (1) FeS 2 + 2H + = Fe 2+ + H 2 S + S 0 (2) Ferrous ions produced by reaction (1) and (2) are subsequently oxidized to ferric ions: 2Fe /2O 2 + 2H + = 2Fe 3+ + H 2 O

12 The ferric ions an also contribute to the oxidation of silver iron sulfide, argentite, pyrite, pyrrhotite, sphalerite and chalcopyrite: AgFe 2 S 3 + Fe 3+ = Ag Fe S S 0 Ag 2 S + 2Fe 3+ = 2Ag + + 2Fe 2+ + S 0 ZnS + 2Fe 3+ = Zn Fe 2+ + S 0 CuFeS 2 + 4Fe 3+ = Cu Fe S 0

13 Then, elemental sulfur may also be further oxidized to sulfate by oxygen or by ferric sulfate: 2S 0 + 3O = 4H + + 2SO 2-4 S 0 + 6Fe H 2 O = 6Fe H + + SO 2-4 This results in the formation of a porous,but nonprotective, elemental sulfur layer, thus allowing cyanide and dissolved oxygen to access to the previously locked gold, silver and electrum Ag 2 S + 4CN - = 2Ag(CN) S 2-4 Au + 8CN - + O 2 + H 2 O = 4Au(CN) OH -

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16 Comparison of silver extraction at ambient conditions and high pressure EXTRACTION, % S ILVER 80 C (80 psi) SILVER (N.C.) CONDITIONS %S olids = 20 rpm = 300 ph= 11.0 Te mp. = 80 o C Pressure = 80 psi TIME (min)

17 Comparison of gold extraction at ambient conditions and high pressure EXTRACTION, % GOLD 80 psi 80 o C GOLD (1 atm) 25 ο C TIME (min)

18 Effect of autoclave retention time on gold and silver extraction 100 EXTRACTION, % CONDITIONS %S o lids = 20 ph = 11.7 P ressure = 80psi rpm = 300 Te mp. = 80 C GOLD SILVER AUTOCLAVE RETENTION TIME (minutes)

19 Effect of the cyanide concentration on gold and silver extraction EXTRACTION, % SILVER GOLD C O N D IT IO N S % S o lids = 20 ph = 11.7 Temp. = 80 o C Pressure = 80 psi rpm = 300 leach time = 60 min. 0,4 0,6 0,8 1 1,2 CYANIDE CONCENTRATION, %

20 Effect of temperature on gold and silver extraction EXTRACTION. % SILVER CONDITIONS % S o lids = 20 ph = 11.2 P ressure = 80 psi rpm = 300 leach time = 60 min. GOLD TEMPERATURE, o C

21 Effect of ph on gold and silver extraction 100 EXTRACTION, % CONDITIONS % Solids = 20 Temp. = 80 o C P ressure = 80 psi rpm = 300 NaCN = 1% leach time = 60 min. SILVER 10 10, , , ,5 ph GOLD

22 100 Effect of percent solids in the extraction of gold and silver EXTRACTION, % CONDITIONS Temp. = 80 o C ph = 11.2 P ressure = 80 psi rpm = 300 NaCN = 1 % leach time = 60 min % SOLIDS SILVER GOLD

23 Results of continuous plant operation EXTRACTION, % SILVER GOLD DAYS

24 CONCLUSIONS The present study shows that, gold and silver values are associated with silver iron sulfide, argentite, pyrite, pyrrhotite, sphalerite and chalcopyrite in the Bacís concentrate. The dissolution of gold and silver are due to the strong complexing capabilities of cyanide anions combined with the oxidizing properties of the dissolved molecular oxygen.

25 The kinetics of the direct pressure oxidation/cyanidation was found to be strongly dependent on particle size, concentration of sodium cyanide, temperature and ph. Single stage direct pressure oxidation/cyanidation cyanidation,, has proven to be effective in treating pyrite refractory gold and silver concentrates from Bacís mining, for both gold and silver it was found that the precious metals recovery exceeded 96%.

26 The relatively mild operating conditions of 80 C C and 80 psi oxygen pressure offer distinct advantages. For example, low cost materials of construction can be utilized for the autoclave. Finally in this process, there is obviously lower gold and silver inventory.

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28 Thank you for your attention Jesús s L. Valenzuela Dept. Chemical Engng. & Metallurgy, University of Sonora, Hermosillo, Sonora, Mexico jvalen@iq.uson.mx José R. Parga Dept. of Metallurgy and Mater. Sci., Institute Technology of Saltillo, Saltillo, Coahuila Mexico Héctor Moreno and David L. Cocke Dept. Chemistry, Lamar University, Beaumont, Texas, US

29 PRINCIPALES CENTROS MINEROS EN EL ESTADO DE SONORA

30 POTENCIAL DE CRECIMIENTO 10 nuevos proyectos mineros en operación en el período PROYECTO EL CHANATE O r o PROYECTO CERRO COLORADO O r o PROYECTO SAN ANTONIO O r o, Cobre PROYECTO MILPILLAS Cobre PROYECTO MARIQUITA Cobre PROYECTO LLUVIA DE ORO O r o PROYECTO BACADEHUACHI Sulfato de Sodio PROYECTO MULATOS O r o PROYECTO PIEDRAS VERDES Cobre PROYECTO ALAMO DORADO P l a t a