Improved inter-particle flow models for predicting heap leaching hydrodynamics

Heap leaching is one of the most important hydrometallurgical techniques for the extraction of valuable metals from low grade ores due to the relatively low capital costs and limited comminution requirements. However, it is typically affected by low recoveries, compared to conventional mineral extraction techniques such as froth flotation followed by smelting. These low recoveries indicate that there is still significant scope for the improvement of the process performance. This overall process performance is governed by chemical kinetics, mass transport and hydrodynamic effects, with hydrodynamics being particularly not completely understood at the heap scale. The authors have previously presented a model for the hydrodynamics which accounts for both liquid holdup hysteresis and the influence of particle porosity on the fluid flow. In this previous work the model form was only validated for narrowly sized particles. This shortcoming is addressed in this paper, with the validation of the models being extended to cover a range of more complex size distributions representative of those encountered in industrial heap leaching. In this work load cell based gravimetric measurements of liquid holdup values were complimented with electrical capacitance tomography (ECT) measurements, which gave not only the average holdup, but also the liquid distribution within the columns. This study demonstrates that these new hydrodynamic models remain applicable for more realistic particle size distributions, with the need to distinguish between the behaviour of the liquid held within the particle porosity compared to that flowing around the particles being critical to accurate prediction of the hydrodynamics.