to the copper adsorption reaction below), followed by activation with sulphuric acid (similar to the cyanide elution reaction below). This is a one-off treatment during commissioning. Fresh, unconditioned resin added to the metal adsorption circuit, will adsorb the cyanide metal complexes, including gold:
R-SO 4 2- + Cu(CN) 3 2- R-Cu(CN) 3 2- + SO 4 2-
Copper adsorption:
•
R-SO 4 2- + 2Au(CN) 2 - R-2Au(CN) 2 - + SO 4 2-
Gold adsorption:
•
Elution steps reverse the above reactions:
+ 2 NaCl R-2Cl -
+
2-
2-
+ Cu(CN) 3
+ 2 Na
Copper elution :
R-Cu(CN) 3
•
R-2Au(CN) 2 -
R-Zn(CN) 4 2-
+ 2Au(CN) 2 -
+ Zn(CN) 4 2-
Gold elution:
•
R-Zn(CN) 4 2- + 2H 2 SO 4 R-SO 4 2- + ZnSO 4 + 4HCN
Gold Regeneration:
•
Conditioned resin is added to the cyanide adsorption circuit:
R-Cu(CN) 3 2-
Cyanide adsorption:
R-CuCN + 2CN -
•
• R-CuCN + 2HCN + SO 4 2- The above are the predominant reactions of interest and represent the mechanism to demonstrate the adsorption and elution processes. More detail can be found in the many excellent papers showing the reactions for adsorption and elution (4) . Cyanide elution: R-Cu(CN) 3 2- + H 2 SO 4
CAPITAL AND OPERATING COST
Capital Cost An equivalent capital cost comparison to a CIP/Gold Room/Detox plant is not strictly valid due to the additional benefit of cyanide and copper recovery in the ReCYN plant. There are potential cost savings with CIL vs. CIP, but for the ReCYN process, the preferred flowsheet is for a separate leach and therefore compared to CIP. The Mount Morgan tailings project uses an RIL circuit for metal recovery as it is found to give improved gold recovery compared to carbon. Excluding the copper recovery section, the following circuit differences are noted as contributing to a reduced cost for the ReCYN process. • The ReCYN adsorption circuit is co-current with low residence times, thus saving on interstage screening, counter-current pumping, and the use of smaller adsorption tanks. • No regeneration kiln is required, but ReCYN includes an additional recovery stage for zinc. • Gold elution is carried out at 60 O c using an in-tank electric heater negating the need for a high- temperature heat exchanger circuit. The ReCYN circuit capital cost would be 10% to 20% lower than the "equivalent" carbon circuit assuming a “greenfields” project. As noted above, the comparison does not take into account the additional economic benefit of the ReCYN plant such as exclusion of a detox circuit. Operating Cost Fixed costs for the ReCYN plant would be similar to those for a carbon circuit in terms of labour and slightly less for maintenance. The significant variable operating costs are related to reagent usage, primarily sulphuric acid and sodium chloride. As with capital, the operating cost cannot be directly compared to carbon without taking into account the benefit side of the equation.
ALTA 2020 Gold-PM Proceedings
7
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