Relevance of hydro-mechanical-chemical processes involved in the construction and operation of copper heap leach pads

Abstract

Heap leaching in the mining industry had become a fairly sophisticated practice at least 500 years ago. It is defined as a mineral processing technology whereby large piles of crushed Run-of–Mine (ROM) rock are leached with various chemical solutions to extract the valuable minerals. The main goal of this work is to contribute to the understanding of the behavior of a heap leach pad by using coupled Hydro-Mechanical-Chemical (HMC) simulations and optimize its design by improving the pad stability and the ore recovery efficiency. The methodology of the work has been the following. First, an exhaustive review of the state of the art of heap leach pad construction is included, describing the coupled equations of the involved physical and chemical phenomena. Then, the implementation of numerical methods to solve the complete system of equations is described. The commercial Finite Element (FE) code COMSOL Multiphysics has been used as a numerical tool. Afterwards, several benchmark examples involving the different physics are solved to check the proper implementation of these numerical tools. Finally, a simulation of a general heap leach pad with a complete system of equations is performed. The numerical tool used in this work is able to solve simultaneously unsaturated flow, soil mechanics and reactive transport in porous media. The changes in porosity, permeability due to mineral dissolution/precipitation and irrigation time affect significantly the hydromechanical behavior of the heap leach pad. The stability of the pad and the ore recovery efficiency improves because the variable saturation and the mechanical deformation are considered during the construction and operation process.