CFD modelling of chalcopyrite heap leaching

Abstract

Heap leaching is widely applied to recover metals from ore. The behaviour of the fluid and chemical species inside heaps, which involves many coupled physico-chemical phenomena, are highly variable and complex. Computational Fluid Dynamics (CFD) simulation can provide an efficient approach to investigate these phenomena and offer guidelines to improve heap design.

Stagnant zones exist in the packed bed with multiphase flow, however, the conventional advection-dispersion model (ADE) failed to capture this phenomenon, therefore, the mobile immobile model (MIM) is employed to model the mass transport and heat transfer instead of the conventional ADE. For predicting the mineral dissolution in heap leaching, we developed a new semi-empirical model which is an alternative to the traditional shrinking core model (SCM), but is more flexible in ability to fit with various dissolution kinetics profiles. The key assumption of this semi-empirical model is validated, and it is calibrated with experiments for chalcopyrite leaching.

The software Fluidity, which is an unstructured mesh based finite element/control finite volume modelling, is further developed to implement the reactive mass transport and heat transfer simulation for heap leaching. The numerical schemes for multiphase flow models are control volume finite element method (CVFEM) for spacial discretization and the implicit pressure explicit saturation algorithm (IMPES) for temporal discretization. The mass transport and heat transfer equations are solved implicitly by using the control volume method.\

Before the implementation of various heap leaching simulations, the MIM is validated by experiments and the liquid-solid phase heat transfer models are verified by method of manufactured solution (MMS). Then the reactive transport model for chalcopyrite leaching, which includes the semi-empirical model for predictions of mineral dissolution, is validated by three separate experiments.

Various heap leaching simulations are implemented to analyse the leaching performance and efficiency. Four groups of 1D simulations are implemented to evaluate the effects of the bacterial activity, the form of the mass transport model, solution temperature, 〖Fe〗^(3+) concentrations and solution pH on the leaching system. The large scale 2D simulations for leaching with a heap of trapezoid shape were implemented to evaluate the effects of oblique walls on the leaching performance. There different wall slopes, which are 30℃, 45℃ and 60℃, are investigated in the 2D simulations.

The main contribution of this project is that a new semi-empirical model and the mobile immobile model are developed and integrated into a chalcopyrite leaching simulator, the simulation results of those models approach to the real physical world better than the conventional models. In conclusion, an improved numerical scheme is provided in this project to investigate and optimise the process of chalcopyrite leaching for industrial purpose.