Comparative assessment of heap leach production data – 1. A procedure for deriving the batch leach curve

Abstract

A method is provided for deriving the average macro-scale batch leaching kinetics of ore on a commercial heap on which portions of the heap (or cells) possess a range of leaching ages due to irrigation commencing while stacking is still in progress. It has been designed to require as only inputs the average ore grade, daily amount of ore stacked and the rate of metal extraction to a common drainage collection point for all cells.A comparison of the batch curve, thus derived, with the batch curve upon which the design of the pad footprint was based provides an early indication of the likelihood of reaching the desired rate of metal production. Furthermore, any attempt to fit the performance of a leaching model to that of a commercial heap requires the description of heap leaching kinetics in the form of a batch curve, since leaching models typically produce batch curves as simulation outputs.The procedure relies on the selection of a functional form, denoted Xi(t), to describe the macro-kinetic batch extraction curve from a single cell (or part thereof) on a heap. Summation over time of the contributions to production from all cells stacked up to time t, assuming each cell leaches according to Xi(t), yields a calculated production graph. The parameters of the function Xi(t) are adjusted to minimise the sum of squared residuals between observed and calculated production graphs. Xi(t) thus found defines the batch curve sought. The procedure can be implemented on a spreadsheet and can be applied to both the rate of valuable target metal extraction and the rate of reagent consumption.In a subsequent paper the application of the method on commercial heap leaching production data will be demonstrated. From the optimised parameters in Xi(t) conclusions can be drawn about the efficiency of wetting of the ore, the relative rate of leaching and the diffusional restriction to reagent supply to the mineral surface.