Hydrodynamics of unsaturated particle beds pertaining to heap leaching

Heap leaching is a method for extracting metals from ores and is particularly applicable to low grade deposits due to its low operating and capital costs. The main drawback of heap leaching is the lower recoveries than more traditional techniques, such as flotation followed by smelting. The major contributing factors are inefficiencies in the liquid addition and mass transport. This thesis describes a combined experimental and theoretical modelling approach for better understanding the behaviour of these complex multiphase systems. The first major finding was that these systems exhibit hysteresis in the liquid holdup as the flow rate is varied. This means that the commonly used approach of directly correlating the flow rate and holdup is not entirely appropriate. A novel experimental and analysis procedure was used to demonstrate that the main reason for the hysteresis was an increase in the number of flow paths as the liquid flow was increased, but no subsequent decrease in the flow paths as the flow is decreased. This work developed a theoretical liquid holdup model to describe the flow behaviour in between the particles by performing liquid flow experiments in a non-porous model glass bead system and slightly porous ore system in a way that it accounts for liquid content hysteresis in both systems. The experimental results showed the effect of inter- and intra-particle porosity on heap flow behaviour. If the inter-particle liquid content is separated from the liquid held within the ore particles, it was shown that both systems follow a similar square relationship between the two model parameters and the only difference is the pre-factor in the flow model. This demonstrated the importance of separating these two contributions to the liquid holdup when trying to make accurate predictions. The transient flow behaviour of the packed bed systems was described both experimentally and using simulations in order to both validate the flow models and to study the behaviour during start-up and shutdown. The salt tracer tests and Positron Emission Particle Tracking (PEPT) are independent techniques to measure the dispersion behaviour in packed beds and column leaching. It was shown that the results from these two methods are very similar, but that the PEPT results also provide more details as to the mechanisms involved