Recent Advances in Copper Heap Leach Analysis
Abstract
The analysis of heap leach test and operating results has been advanced by the use of techniques developed in the last few years. Application of these techniques has shown that the actual field leaching of all projects studied is a diffusion controlled situation. This is despite the copper mineralogy covering the range from carbonate to chalcocite.
The correlation between fines and clay content and a reduced leaching rate has been established for a number of projects where the proportion of fines is variable. The use of diffusion controlled modelling allows the calculation of leaching rates that can be compared between operations and provide an absolute characterisation from fast to very slow. This is a significant improvement on previous methods where the leach rate was not strictly comparable between operations.
The analysis method also allows the identification of fundamental changes in leaching behaviour. It can show the change from agglomerate leaching kinetics to ore particle leaching kinetics. This knowledge is useful in scale up where high recoveries may take extremely long times to achieve.
The new methods also provide a means of understanding the interaction between the leaching time and the acid consumption. The rate of consumption is related to the acid concentration and this can be modelled to allow consideration of alternate acid concentration profiles to minimise overall consumption.
Heap placement parameters such as lift height and bulk density can be used to alter the overall leach time and help to reduce the acid consumption. The interaction of lift height and the end of economic leaching can be used to maximise recovery at the same time as minimising acid consumption.
Bulk density can be used as a predictive tool in considering the leach rates of material in the lower parts of a lift or in underlying lifts. Ores with a high degree of fines and clay show plastic characteristics which have the combined effects of reducing the inter-agglomerate voidage and increasing the effective size of ‘meta particles’ formed in the heap. This combination can lead to reductions in leach rate of 1/10th to 1/150th of the unconsolidated material.
A new suit of models have been developed to allow assessment of the effects of the various variables on leach rate, economic recovery limits, acid consumption, grade, PLS grade and leach time.
Author
Graeme Miller
Sinclair Knight Merz