Multi-scale quantification of leaching performance using X-ray tomography

The performance of heap leaching is dictated by a large number of processes acting at a wide range of length scales. One important scale is that of the individual particles, where the interaction between the rate kinetics at the surfaces of the individual mineral grains and the mass transport through the particle combine to give the overall apparent particle scale kinetics. It has been recognised for a long time that variability in the mineralogy, size and spatial distribution of the mineral grains within the particle are likely to have a large effect on the leach performance and its variability and thus, ultimately, the performance of the heap. In this paper a new method for quantifying this behaviour and its variability at scales from the particle through to the grain and down to the surface kinetics is presented. This method is based on the use of a series of XMT (also called micro-CT) images of a column taken at regular intervals over 168 days of leaching. The key development in the analysis of this data is an algorithm that has allowed every single one of the hundreds of thousands of mineral grains within the column to be individually tracked across all the time points as they undergo dissolution. This has allowed the dependency of the mineral grain leach rate on its size and position in the particle to be decoupled from one another. It also meant that the variability in the surface kinetics of the grains could be assessed, with mineralogical variability being the key source of this variability. We demonstrate that understanding and quantifying this underlying kinetic variability is important as it has a major impact on the time evolution of the average kinetics of the leaching. (C) 2016 The Authors. Published by Elsevier B.V.