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.
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 42-72 hrs.
REFRACTING ORE (Recovery less than 60 %) IMPROVED TREATMENT PROCESSES: Fluid Bed Roasting Whole Ore Roasting Pressure Leaching Biological Oxidation
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
Biological Oxidation
Whole Ore Roasting
Pressure Oxidation of Refractory Gold Ores
PRESSURE LEACHING PROCESS NEW TECHNOLOGY Au(CN) - 2 Bulk Flotation Grinding Direct Oxidative Pressure Cyanidation 90 Minutes
CHEMICAL AND MINERALOGICAL ANALYSIS g/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 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
SIMULTANEOUSLY OXIDATION AND CYANIDATION LEACHING The primary reactions are: 2FeS 2 + 7O 2 + 2H 2 O = 2Fe 2+ + 4SO 2-4 + 4H + (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 2+ + 1/2O 2 + 2H + = 2Fe 3+ + H 2 O
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 + + 3 Fe 2+ + 2S 2 - + S 0 Ag 2 S + 2Fe 3+ = 2Ag + + 2Fe 2+ + S 0 ZnS + 2Fe 3+ = Zn 2+ + 2Fe 2+ + S 0 CuFeS 2 + 4Fe 3+ = Cu 2+ + 5Fe 2+ + 2S 0
Then, elemental sulfur may also be further oxidized to sulfate by oxygen or by ferric sulfate: 2S 0 + 3O 2 + 2 = 4H + + 2SO 2-4 S 0 + 6Fe 3+ + 4H 2 O = 6Fe 2+ + 8H + + 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) - 2 + S 2-4 Au + 8CN - + O 2 + H 2 O = 4Au(CN) - 2 + 4OH -
Comparison of silver extraction at ambient conditions and high pressure EXTRACTION, % 100 80 60 40 20 0 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 0 50 100 150 200 250 300 350 TIME (min)
Comparison of gold extraction at ambient conditions and high pressure EXTRACTION, % 100 80 60 40 20 0 GOLD 80 psi 80 o C GOLD (1 atm) 25 ο C 0 30 60 90 120 150 180 210 240 270 300 TIME (min)
Effect of autoclave retention time on gold and silver extraction 100 EXTRACTION, % 95 90 85 CONDITIONS %S o lids = 20 ph = 11.7 P ressure = 80psi rpm = 300 Te mp. = 80 C GOLD SILVER 15 30 45 60 75 90 105 120 AUTOCLAVE RETENTION TIME (minutes)
Effect of the cyanide concentration on gold and silver extraction EXTRACTION, % 100 90 80 70 60 50 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, %
Effect of temperature on gold and silver extraction EXTRACTION. % 100 80 60 40 20 0 SILVER CONDITIONS % S o lids = 20 ph = 11.2 P ressure = 80 psi rpm = 300 leach time = 60 min. GOLD 50 100 150 200 250 TEMPERATURE, o C
Effect of ph on gold and silver extraction 100 EXTRACTION, % 98 96 94 92 90 CONDITIONS % Solids = 20 Temp. = 80 o C P ressure = 80 psi rpm = 300 NaCN = 1% leach time = 60 min. SILVER 10 10,5 11 11,5 12 12,5 13 13,5 ph GOLD
100 Effect of percent solids in the extraction of gold and silver EXTRACTION, % 80 60 40 20 0 CONDITIONS Temp. = 80 o C ph = 11.2 P ressure = 80 psi rpm = 300 NaCN = 1 % leach time = 60 min. 0 5 10 15 20 25 30 35 % SOLIDS SILVER GOLD
Results of continuous plant operation EXTRACTION, % 99 98 97 96 95 94 93 SILVER GOLD 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
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.
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%.
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.
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
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