REALIZING OREBODY VALUE THROUGH IMPROVED PROCESSING MODELLING

Abstract

The mining industry faces much uncertainty stemming from price volatility and challenges in terms of decreasing ore grade and escalating costs. In response, the mining industry seeks to minimise the environmental impact of its operations by increasing the efficiency of extraction and promoting sustainable and environmentally-friendly practices. During initial reconnaissance of a deposit, an optimised extraction plan is designed using a strategic geometallurgical approach. Once extraction commences, continuous improvement is pursued by implementing a tactical geometallurgical approach. The prime objective of geometallurgy is to encourage investment in the mining sector by reducing risk and uncertainty. The scientific objective of this thesis is to identify ways to make gold extraction more sustainable, environmentally-friendly, and economically viable. This thesis explores the application of geometallurgy through a case study of the Ad Duwayhi gold mine in Saudi Arabia. All stages of the beneficiation of gold ore are investigated, including simulation of the Carbon-In-Leach (CIL) process. The Carbon-In-Leach (CIL) unit was modelled using METSIM, HSC Sim, and JKSimMet software. While these packages do not consider the kinetics of gold leaching by cyanide, a separate study into the kinetics of gold leaching by cyanide was made. Kinetic models by Schubert et al. (1993), Ling et al. (1996), de Andrade Lima and Hodouin (2005a), and Wadnerkar et al. (2015) were used to model the carbon in leach plant of Ad Duwayhi. Rate constants (k) of the models were modified to provide a better description of leaching at Ad Duwayhi. It was found that the model proposed by Schubert et al. (1993) best describes the leaching process. Results show that, as more variables are included and combined in the rate constant (k), the better the model describes an ongoing onsite leaching operation. Experimental data and simulations of gold leaching at Ad Duwayhi show that most of the gold is leached by cyanide in the first four tanks (out of eight). This suggests that either there is less gold than expected or the relatively long retention time ensures that possible fluctuations in the feed gold grade can be absorbed by the process without loss of recovery. Addition of cyanide in the carbon in leach tanks was studied, revealing that increasing the dosage of cyanide only leads to a small increase the leaching of gold. It is questionable whether there is an economic case for increasing the cyanide dosage at Ad Duwayhi. Adsorption of gold into carbon was investigated using models by de Andrade Lima and Hodouin (2005a) and Wadnerkar et al. (2015). Results show that the model by de Andrade Lima and Hodouin (2005a) provides the best description of the adsorption process of gold. Although the Wadnerkar model contains more parameters, these do not appear to support the modelling of the physical adsorption of the gold at Ad Duwayhi. Alternative leaching agents to cyanide for the leaching of gold were reviewed and their performance was investigated. Although several alternative leaching agents show potential, further research is requirement to assess the viability of replacing cyanide. The role of a geometallurgist was analysed. It is postulated that such a person could provide solutions by communicating across departments, implementing a geometallurgical plan, and identifying opportunities for optimisation through tactical geometallurgy. To achieve better mineral stewardship, resource modelling needs to include geometallurgical attributes such as mineralogical composition and hardness. A geometallurgically-informed block model is a starting point for optimisation of mining and processing operations within the context of production targets. To improve the environmental impact of gold processing, a new feed path in the processing plant was identified which improves equipment utilisation. To improve energy efficiency, it is suggested to install a closed system to stabilise the temperature of the leaching tanks during day-night cycles. In addition, it is recommended to install solar panels above the leaching tanks to reduce the tank temperature and generate electricity for the process during the daytime.