Presented by Thom Seal, Ph.D., PE. Co-Authors: C. L. Bolin

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Presentation transcript:

OPEN PIT & STOCKPILE ORE CONTROL FOR CYANIDE HEAP LEACHING to PREVENT A SOUR PAD Presented by Thom Seal, Ph.D., PE. Co-Authors: C. L. Bolin SME – Salt Lake City March 1, 2000 Knight Piesold – ARD Conference – Elko, NV. March 15, 2012

ORE CONTROL Cyanide Leachable - Mill & Heap Leach Refractory Waste Mill {Roaster - Autoclave - Flotation} Grade Leach {Biooxidation - ATS} Grade Waste General (Non Acid Generating) Acid Generating (PAG)

METALLURGICAL CHARACTERISTICS Cyanide Gold Extraction CN Shake Test - AA for [Au] = AUCN Fire Assay AA/FA - Theoretical CN Gold Extraction Preg. Rob Spike w/Au CN Shake Test Determine [Au] Absorbed by Ore PRV = (AUCN + 0.1) - AUPR Fuel Value = 1.3 (OrgC) + SS - Target 2.5

MINERAL CHARACTERISTICS Sulfides Pyrite - FeS2 GQ - 10 microns (um) + Arsenopyrite - FeAsS GQ - 1-2 microns (um) Carbonates Calcite - CaCO3 Dolomite - CaMg(CO3)2 Siderite - FeCO3 Carbonaceous Material

ANALYTICAL LECO Total Sulfur & Carbon Sulfur as a Percent % Sulfate Sulfur = SRO % Sulfide Sulfur - Roast {% SS} = STOT - SRO Carbon as a Percent % Organic Carbon = CAI = OrgC % Carbonate Carbon - Leach HCl {% CC} % CC = CTOT - CAI

AGP Acid Generating Potential - AGP Sample Equation: Equal to - 1.37 * % SS Sample Equation: 2 FeS2 + 7 O2 + 2 H2O  2 FeSO4 + 4 H+ + 2 SO42- Leads to Acid Rock Drainage

ANP Acid Neutralization Potential - ANP Sample Equation: Equal to 3.67 * % CC Sample Equation: CaCO3 + 2 H+ + SO42-  CaSO4 + H2O + CO2

NCV Net Carbonate Value - NCV Equal to ANP + AGP NCV = 3.67 * % CC - 1.37 * % SS

EQUATIONS Cyanide Hydrolyses at pH < 10 CN- + H2O  HCN + OH- Cyanide Reaction with Sulfides 2 FeS + 12 CN- + 5 O2 + 2 H2O  2 Fe(CN)64- + 2 SO42- + 4 OH- Lime Hydrolyses CaO + H2O  Ca(OH)2

LIME USE MODEL Net Reaction Regression Model 4 FeS2 + 8 CaO + 15 O2 + 6 H2O  4 Fe(OH)3 + 8 CaSO4 Regression Model Lime (pounds/ton) = 5.066 - 2.6874 * NCV Multiply by Safety Factor: Using S.F. = 2 for NA Stockpiles

LIME USE AND COLUMN TESTS

CYANIDE USE MODEL

GOLD EXTRACTION AND NCV

BLAST HOLE INFORMATION

GOLD QUARRY PIT - POLYGON

LIME USE MODEL Net Reaction Regression Model – Oxide Ore 4 FeS2 + 8 CaO + 15 O2 + 6 H2O  4 Fe(OH)3 + 8 CaSO4 Regression Model – Oxide Ore Lime (pounds/ton) = 5.066 - 2.6874 * NCV Multiply by Safety Factor: Using S.F. = 2 for NA Stockpiles

LIME USE MODEL Regression Model – ARD Stockpile Ore Lime (pounds/ton) = 6.68 – 7.68 * CC1.01 + 45.7 * SRO1.09 CC = % Carbonate Carbon SRO = % S as SO4 (Sulfate Sulfur)

Lime Model for ARD Stockpiles

NAL Gold Production

NAL Solution Grade

Gold Quarry Results 2.6 million stockpile tons 2.5 million mines tons 85,000 recovered Au oz. Net Revenue $ 18,000,000 1996 - 1999

CONCLUSIONS Reagent Utilization is Ore Dependant Run of Mine Ore to have + NCV Value Biooxidation of Ores with NCV Values less than - 2.0 Caustic Cost is 7.5 times higher than Lime Cyanide Cost is 22 times higher than Lime Ore Destination by Grade, AA/FA, Preg. Rob and NCV Value