Multicomponent transport modelling of enhanced metal leaching using synthetic ligands

Abstract

Two multicomponent transport formulations are illustrated with metal leaching in a simple soil analog, i.e., the direct combination of the chemical algebraic equations with the partial differential equations for transport, as well as the separate evaluation of these sets of equations. Exemplary calculations for enhanced metal leaching using a synthetic ligand were done with a general chemical equilibrium program, as a subroutine to the “mixing cell” transport formulation known from systems analysis. A simple criterion for space and time discretization following from numerical dispersion consideration is given. For a non-adsorbing species (ligand) the numerical solution was compared to an analytical solution, to evaluate the accuracy of the program. By appropriate scaling, the numerically obtained approximations for the metal-ligand complexes could also be understood upon comparison with the analytical solution. In order to predict the effect of different feed solution ligand concentrations, a simple analytical approximation was given that showed that time may be scaled linearly with the total ligand concentration. Constraints of this analytical approximation underline the intrinsic multicomponent nature of solute chemistry and transport in soil.