regeneration stages do not require to be matched to the elution rate. The capital cost therefore increases by only 60 per cent instead of doubling, as might perhaps be expected from simple application of the relative cost data given in Figure 1 .
are given due consideration in the technical and economic evaluations.
By carrying out appropriate testwork and using a proven modelling technique it can be demonstrated that CIP is more often a preferable option for high silver ores than Merrill- Crowe. GreenGold have recently been involved in the conversion of a hybrid Merrill-Crowe plant to a full CIL circuit simply with the addition of electro-winning capacity. Silver grades for this plant range up to 150g/t.
Operating Costs
The differences which apply to operating costs are more significant than those for capital costs and benefit the CIP treatment route for high silver ore. Figure 2 and Figure 3 illustrate the operating cost distribution for the two cases of treating gold ore and high silver ore at the same ore treatment rate. These results translate to 60 per cent increase in the annual operating cost for the high silver ore recovery plant instead of a pro-rata 200 per cent increase. This obviously has a major influence on any cost comparison study. There are many other factors that need to be considered when undertaking a comparative study of two processes and this paper does not address what are often case-specific factors. The intention is simply to point out some additional major factors that should be addressed when designing plants for high silver ores.
References
1. S.A.I.M.M. monograph series M.T. The Extractive Metallurgy of Gold in South Africa. Editor G.G. Stanley: 1987.
2. Menne D.M., Predicting and assessing Carbon-in-Pulp circuit performance: XIV International Mineral Processing Conference, 1982.
Conclusions
The above assessment does not give a specific comparison of Merrill-Crowe versus CIP but instead indicates the fundamental considerations when assessing the applicability of a carbon system for the treatment of high silver ores.
Testwork must be specifically designed to measure the carbon parameters for silver.
Each process area for the carbon plant should be assessed separately and not simply matched to the elution rate.
The latest process system should be included, such as the AARL elution system and in·situ cleaning, high efficiency electrowinning cells. There is no limiting silver/gold ratio that naturally precludes the use of carbon, and many more high silver ore projects would select the carbon route if the methods described above
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