The mine has a significant resource with increasing copper levels with depth. The resource cannot be converted to reserve below a certain depth due to the higher copper levels; this would mean consuming excessive cyanide, leading to negative economics. Using the RECYN process, the copper can be economically recovered potentially leading to a substantial increase in reserves. APPLICATION Each project is unique and has a specific solution depending on the ore type and environmental compliance conditions. The economics will vary with plant size, free cyanide levels, and solution chemistry. There is no simple answer, but our experience of the last 30 years has shown that most projects can be accommodated using the RECYN Process for cyanide recovery and tailings detox. There are three parts to the evaluation process: free cyanide recovery, detoxification, and metal recovery: ● Cyanide recovery is simply an economical consideration, although often it will overlap with detox requirements. The two commercial applications in Indonesia are based on free cyanide recovery; but they find this also satisfies detox requirements, resulting in substantial cost savings and recovery benefits. The capital cost is easily justified and usually results in payback periods of less than one year. Economics are more favorable for larger projects and higher cyanide levels. ● Detox is a more complex evaluation because it involves detailed solution chemistry and compliance requirements. The same adsorption plant can be used for detox, but a metal recovery section must be added. The detox evaluation generally splits into two areas, compliance for tailings dams and compliance for river discharge. Either level can be accommodated with the RECYN process. The cyanide code level of <50mg/l WAD cyanide for discharge to tailings dams is easily achieved, usually just by free cyanide recovery. For river discharge, the levels are more country specific, but can also be accommodated with the RECYN process, usually by including a metal recovery stage. ● Metal recovery is sometimes required for the detox of tailings, but can be assessed on a stand-alone economic basis if there is no detox requirement. For the recovery of copper a positive economic result can usually be achieved. A preliminary evaluation requires a few basic details to be inputted to an evaluation model that gives capital and operating costs and cost benefit information. The assumption is that no capital benefit is derived from existing plant equipment. The GreenGold website has a template for preliminary assessment. www.greengoldengineering.com TECHNICAL PERFORMANCE The RECYN process has proven through laboratory, piloting, and commercial application that it can satisfy both requirements of:
● Economically recovering free cyanide for recycle, and ● Detoxifying tailings streams to compliance levels.
The resin bead has proven to be robust in an industrial application, particularly in a pulp application where it is subject to contamination, wide pH swings, large scale pumping, screening and general process plant operator abuse. For a purely cyanide recovery role the solution chemistry is less critical than the mechanical design. Large volumes of resin are moved through the adsorption and elution stages, which requires special design considerations. Slurry mixing, pumping, screening and continuous elution processes are critical design areas that differ from conventional carbon circuit designs.
ALTA 2017 Gold-PM Proceedings
6
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