Inter-particle liquid spread pertaining to heap leaching using UV fluorescence based image analysis

Abstract The visualisation of individual flow paths in a porous media and how they relate to the overall hydrodynamics is crucial to improving our understanding of a number of systems. Unsaturated flow through larger particles (order of millimetres and a few centimetres) in heap leaching systems where both gravity and capillarity play an important role in the structure of the flow paths is complex and still not fully understood. A variety of laboratory methods have been employed for this purpose, with UV light being used in several studies. Flow studies have typically involved millimetre and sub-millimetre scale particles and the flow is typically capillary-dominated. This paper instead concentrates on gravity-dominated flows pertaining to heap leaching and is particularly focused on developing methods for using the UV fluorescence to obtain quantitative measurements of liquid spreading, such as average lateral liquid spread for a point source liquid addition. This study uses a pseudo2-D system with larger ore particles than in previous UV flow studies. The UV fluorescence results were analysed using image analysis to determine the overall liquid spreading and the locations of the flow paths. Both narrowly sized and realistic ore systems were investigated to understand the effect of length scale on flow paths and dynamics of liquid spreading through the gravity-dominated ore beds. It was shown that both ore systems experience distinct flow channelling compared to the more uniform flow profiles observed in capillary-dominated systems. Lateral liquid spreading coefficients were calculated, with the narrowly sized ore system showing higher values, probably due to the larger effective length scale of the inter-particle spaces.