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Relationship between particle size distribution and porosity in dump leaching Zhang, Shuo


Fluid flow is a critical process involved in the valuable metals extraction from low grade ore in heap and dump leaching as well as the release of harmful substances from waste rock piles. The mechanisms by which fluids move through the porous media depend on the fluid properties and the intrinsic properties of the porous media, with permeability being one critical factor. Particle size distribution is a key factor that affects permeability by forming pores of different structure and size. The objective of this research was to assess the particle size distribution in heterogeneous packed ore/rock beds and quantify the effect of particle size distribution on porosity. In the studied mine site, the particle size distribution in the dump leach pad was determined by analyzing aerial images of multiple dump faces taken by a drone. Particles spanned a wide range in size from less than 2 cm in diameter to larger than 2 m in diameter, with a P80 to be 2 m. The spatial segregation of fine particles and coarse particles along the dump faces was observed, which may contribute to the formation of preferential flow. The effect of particle size distribution on porosity was quantified by two methods: the bulk density and CT-imaging techniques. Porosities under three particle sorting conditions were studied: narrow-sized particles, poorly sorted particles and well sorted particles. For narrow-sized particles, the porosity measured by the bulk density method decreased as the particle size was increased up to 0.151 mm after which the porosity remained constant in the range tested. The influence of the particle size on the porosity for the well sorted particles was similar to that of the narrow-sized particles from both of the methods. For poorly sorted particles, in both methods, porosity decreased as the fraction of the fine particles added was increased to a certain value, after which the porosity started to increase as the fraction of fine particles was further increased. The results have important implications for metal extraction from run of mine ores using dump leaching and release of contaminants from waste rock piles by influencing fluid flow properties.

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