Effects of intermittent liquid addition on heap hydrodynamics

Heap leaching is a well-known mineral processing technique, whereby crushed low grade ore is used for valuable metal extraction. The technique is typically used to extract precious and base metals, however, the metal extraction efficiency is relatively low. Even though reaction kinetics are extensively studied in heap leaching, the detailed hydrodynamic studies are still required to understand the underlying flow aspects. Heap hydrodynamics plays an important role in the transport of both leaching reagents and dissolved metal species and thus uniform liquid distribution through the ore mass is required. However, liquid channelling within the heaps has been identified as one of the main contributing factors for non-uniform liquid distribution. Since liquid channelling is supposed to be an inherent property in heap leaching systems, this work was primarily designed to explore the suitable techniques to improve liquid distribution and minimise liquid channelling in heaps. Intermittent liquid addition is employed and its effect on liquid channelling is studied, which has not been reported in the literature despite the application of it in industrial heaps. Both narrowly sized ore (16-20 cm) and realistic ore mixtures (2.36-25 cm) were studied in a pseudo 2-D Perspex column and the effect of rest period in intermittent leaching on liquid channelling was studied using out-flow liquid distribution measurements. The experimental results showed improved out-flow liquid distribution profiles and less channelling flow features in intermittent liquid addition conditions. The liquid out-flow profiles in both the packed bed systems were improved by resulting more flow paths through the particles and reduced features of liquid channelling. The narrowly sized fraction formed a near-Gaussian liquid distribution, which is the expected continuous probability based theoretical flow profile with drip emitter based liquid addition in heaps.