technology known as the GreenGold ReCYN Process. Initially promoted as a cyanide recovery and detox process, it has the added ability to provide an answer to the problem of cyanide soluble copper.
The basis of the technology was first described in 1956 in South Africa by Eric Goldblatt (7). The road since that time has certainly been long, including the involvement of the author and others in developing the technology for the last 30 years.
THE CHALLENGE
A major challenge with gold/copper ore types has been to first quantify the problem. Simply assaying for total copper is only the first step; the real challenge is quantifying the soluble copper throughout an ore body. Often the distribution of soluble copper is not consistent, with variations occurring not just with oxidation level, but often with more complex geology and mineralisation confusing the spatial distribution. Sometimes a relationship between copper head grade and CNsolCu is described by a formula, but with varying success. A common approach is to apply a cyanide leach test (BLEG or Leachwell) to each drill core interval of ore and apply that result as a modifying factor in the Resource estimate, influencing the cut-off- grade. The results are then related to a mining schedule that theoretically allows the resultant impact to be predicted and costed. The complexity of gold/copper ore bodies makes this assessment process risky and is why so much effort has been dedicated to understanding and trying to quantify the impact of soluble copper in a gold project.
THE ANSWER
Elegance is born of simplicity.
The ReCYN process has been promoted for use in gold/silver cyanidation projects to support cyanide’s continued use as the preferred solvent. It reduces operating costs, improves project economics and has significant environmental benefits.
There is now an added benefit; it provides a universal answer to the problem of cyanide soluble copper.
Cyanide soluble copper can now be effectively ignored from a cost standpoint; it is no longer a distraction or project killer. The focus is directed to the main revenue stream, gold.
Insoluble copper is considered separately and economically justified in its own right, independent of the gold project. If it is shown to be economically viable and justifies the capital and operating cost of the additional flotation and concentrate handling circuits, these circuits can then be added to the flowsheet. It cannot be assumed that the non-soluble copper is worth recovering, especially if a proportion of the copper has been removed in cyanidation.
QUANTIFYING THE BENEFIT
The ReCYN process treats the CIL tails to recover Free Cyanide and WAD cyanide-metal complexes. The Free cyanide is recovered and recycled to the leach plant. The WAD cyanide consists of the complexed metal cyanides, mainly copper. The cyanide associated with the complexed metal cyanides is recovered and recycled to the leach plant, and the associated metals recovered for sale. The cyanide consumption specific to copper is approximately 3kg NaCN for 1kg CNsolCu, i.e., a ratio of 3:1, matching the theoretical complex of Cu(CN) 4 3- . This ratio approximates to an equal dollar value for copper and cyanide, i.e. copper consumes its’ own value in cyanide. The minimum cost impact due to cyanide consumption is, therefore, $6/kg of CNsolCu.
For a 2Mtpa gold project and an average CNsolCu of 0.1%, the additional operating cost is $12M/a. The full impact is more than doubled when the loss of copper and detox costs are considered.
By contrast, the ReCYN process is cost-neutral.
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