First-order exchange and spherical diffusion models of heap leaching in PhreeqC

Abstract

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. heap leaching, modelling, first-order exchange, spherical diffusion.* Mintek, South Africa.

Copper Mineral Leaching Mathematical Models—A Review

“…In Van Staten and Petersen [ 117 ], a first-order exchange model (see Equation (29)) and spherical diffusion (see Equation (30)) [ 60 ] are compared with published short-term pulse test data, concluding that the former is simpler and more convenient to use, but the latter produced more realistic results over longer leaching periods. While in Hashemzadeh et al [ 118 , 119 ], chalcocite leaching kinetics using a variable order kinetic model are modeled, which were already successfully applied in the literature [ 56 , 120 ], and whose formulation are provided in Equation (79).…”

Numerical modelling of column experiments to investigate in-situ bioleaching as an alternative mining technology

“…It is to be considered as an artefact of discretisation, because the continuous exchange between the outer rim and the core of the grains is approximated by only two zones mixed with a first order exchange coefficient. An improved description of mass transfer kinetics, for example through a finite difference diffusional model [Parkhurst and Appelo, 1999;Van Staden and Petersen, 2018] or a multi-rate model that considers a higher number of exchanging zones [Haggerty and Gorelick, 1995], should improve these results.…”