Towards fundamentally based heap leaching scale-up

Abstract

A procedure is proposed for the extrapolation of laboratory column leaching kinetics for commercial heap leaching design. It employs previously published models based on dual-porosity hydrology and chemical reactions occurring during diffusion via the regions holding immobile solution. Case studies were analysed for which both the column leaching and heap leaching performance had been recorded on acid-soluble copper, sulphide-copper and gold ores. Theoretical relationships were developed for the manner in which bulk density and dripper spacing were expected to affect the diffusional path length via the immobile solution of the column/heap. The resulting correlations were fitted to the case study data by means of a single empirical constant, p, to which an average value of 4.5 (a dimensionless value) could be assigned. The magnitude of p suggests that densification, i.e. compaction of the ore particle bed, results in a slight increase in the spacing of solution flow channels but a large increase of the tortuosity of diffusion pathways. In the case of narrow dripper spacing, the decrease in leaching kinetics upon scale-up can be attributed to the increase in bulk density. The proposed method identifies the maximum dripper spacing that can be used before the width of the dripper spacing has a stronger effect on the diffusional path length than the increase in bulk density. The effect of dripper spacing on the asymptotic extractions (extrapolated to time infinity) of the case studies was quantified. Confidence in the reliability of the method can be further improved if more case study data can be accessed.