A 3D dual pore-system leaching model. Part 1: Study on fluid flow

Two scale pore networks are retrieved from computerised tomographic (CT) images of a leaching column based on the detected dual pore-size distribution. The 'macro-pore' network is comprised of the void space between ore particles, where the liquid is allowed to flow as in free channels, while the 'micro-pore' network resides in the ore particles, through which the flow path can only be achieved by percolation. The dual pore system refers to the porous ore stack, where both macro- and micro-pore networks exist and two different flow patterns prevail. The characterisation of pore networks is carried out firstly by generating finite element geometries and meshes and simultaneously estimating the porosity; the anisotropic intrinsic permeability of both pore networks is calculated by free flow simulation (using Navier-Stokes equations) within the pore networks based on Darcy's definition of permeability. The dual pore-system is then derived by integrating the micro-pore characteristics into the macro-pore ore stack. Subsequently, with Navier-Stokes equations governing the free flow in the macro-pore network and Brinkman's equations governing the seepage in the micro-pore network, the flow in the dual pore-system model is established and solved. Ultimately, a comparison of the fluid velocity among the uniform flow model, the single pore scale model, and the dual pore-system model is made, and the preferential flow pathways in the heterogeneous models are analysed, suggesting that it is necessary to adopt a dual pore-system model to capture the flow behaviour within a leaching system.