Abstract

VAN STADEN, P.J.  and  PETERSEN, J.. First-order exchange and spherical diffusion models of heap leaching in PhreeqC. J. S. Afr. Inst. Min. Metall. [online]. 2018, vol.118, n.7, pp.681-694. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/2018/v118n7a2.

PhreeqC is an open-source software designed to perform geochemical calculations. It offers a feature for modelling heap leaching according to the most modern 'dual-porosity' visualization, as well as an extensive database of reactions and equilibria. It should represent an attractive option for modelling the chemical heap leaching of oxidized ores since it requires only the entering of the system characteristics and a minimal amount of coding to formulate kinetic expressions and output parameters. Both first-order exchange and spherical diffusion PhreeqC models are compared to published short-term pulse-test data (over a few days) and model fits to it. The former is simpler and more convenient to use, but the latter yields more realistic results over longer periods of leaching. Comparisons are also made between PhreeqC and HeapSim, the latter having been acclaimed as the most comprehensive heap leaching model to date. The two models were found to yield very similar results. The observed differences are ascribed to subtle differences in the methods of allocation of reagents to competing reactions and in the methods of advancing the liquid phase between time steps. PhreeqC is slower to execute than HeapSim, but is more rigorous with regard to solution speciation and permits spatial variation of physical and chemical kinetic parameters. The latter feature makes it well suited to the modelling of the effects of segregation and stratification, which have been identified by a number of authors as phenomena that impact on heap leaching performance but which have not yet been systematically studied.

Keywords : heap leaching; modelling; first-order exchange; spherical diffusion.

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