Comparative assessment of heap leach production data – 2. Heap leaching kinetics of Kipoi HMS floats material, laboratory vs. commercial scale

Abstract

At the Kipoi copper/cobalt operation in the Democratic Republic of the Congo, the coarse fraction of the floating product from a heavy media separation (HMS) plant is being heap leached. The macro-scale performance observed in laboratory columns is compared to that of the first three commercial heaps to ascertain the efficiency of the commercial operation, and to present a case study in heap leaching scale-up.This paper draws on a method published in part 1 of the series for deriving batch curves for copper extraction and for gangue acid consumption (GAC) from the commercial heap Production Graphs, for the case where irrigation commences while stacking is still in progress, so that the commercial Production Graph does not represent a batch leach curve. This facilitates quantitative comparisons of the performance of the commercial heaps against the laboratory column batch curves, based on the parameters describing the fitted batch curve expression Xi(t). It further provides an early indication of the ultimate extent of extraction towards which the operation is tending, while such information cannot be gauged directly from the commercial Production Graph in the case where irrigation commenced while stacking was still in progress. The function Xi(t) is based on a previously published form and the fitting of batch curves to it relies on adjustment of the parameters of Xi(t) such as to minimise the sum of squared residuals between the commercial production data and the theoretical rate of production calculated from an integration of Xi(t).The parameter group κxκw occurring in Xi(t) represents the product of (a) mass fraction of liberated non-refractory mineral and (b) mass fraction of mineral effectively in contact with leach solution. The values of this parameter group that fitted the commercial production data of Kipoi indicated that the very wide dripper spacing applied to the first part of heap 3-1 (which was also the tallest of the three heaps) did not merely lead to slower leaching, but actually increased the proportion of the ore that remained inaccessible to leach solution. The trends observed in parameter κ0 suggest that the rate of copper extraction could still be accelerated in both columns and commercial heaps through increased supply of acid. A comparison of the κ1 values of the columns with that of the heaps indicate that there exists notably greater diffusional restriction in the heaps than in the columns.By analysing a number of case studies in this way, a history can be built of how key parameters fitting laboratory column leaching data correlate to the parameters fitting commercial heap leaching data, thereby providing a more fundamental basis for the extrapolation of laboratory column leaching kinetic data to commercial heap leaching design.