Evaluating the electrochemical properties and behaviour of copper/cobalt minerals

Abstract

Mining projects around the world face a significant challenge to reduce their footprint and be more environmentally friendly. Research has shown that mineral processing is of major influence, due to the use of heavy chemicals that are both expensive and polluting. Currently, electrowinning (the electrodeposition of metals) is only used in the last purification step of the process. So far, the majority of the studies on cobalt have focused on non-electrowinning possibilities. Therefore, it is of interest to investigate the electrochemical behaviour within different environments to obtain more information and gain a better understanding. This thesis focuses on the electrochemical behaviour and deposition of cobalt-bearing minerals, which will be evaluated with the help of cyclic voltammetry (CV) and the electrochemical quartz crystal microbalance (EQCM). These techniques use the help of multiple variable input parameters, which will be investigated and compared to gain the optimised condition to perform the experiments. Furthermore, the sensitivity of the techniques to different input parameters and different solutions will be investigated. This is done to investigate what the origins are for the differences in the electrochemical behaviour of copper-cobalt minerals in aqueous solutions using analytical, synthetic and real ores, and to find a correlation between the obtained results using the graphs generated using CV and EQCM-techniques. This is done to investigate to possibilities using selective electrowinning, meaning the electrodeposition of multiple elements within the same electrolyte solution. Based on a review of the literature, the experimental setup used for the experiments will be discussed to gain better understanding of the specialised equipment and corresponding software. Cobalt chloride, cobalt sulphate and copper sulfate solution will be evaluated first, after which two synthetic cobalt-bearing minerals containing iron will be tested. With the help of CV, the electrochemical behaviour, e.g. redox- reactions, can be analysed. Using the EQCM, accurate measurements of the mass change per unit area of the electroplated cobalt will be recorded. Synthetic minerals will be used to discover how much can be recovered using this technique. Finally, six samples from the Democratic Republic of Congo (DRC) will be evaluated to obtain the same data as for the synthetic minerals. For this QEMSCAN data is used to evaluate the mineral composition. Analysis of the results demonstrated that under different circumstances in different environments, similar electrochemical behaviour and the occurrence of copper, iron and/or cobalt deposition is observed. However, for special cases these reactions do not occur. This difference can be explained by a varying mineralogy, where bornite and chalcopyrite have a positive effect on the electrochemical activity. Regarding the shape of the voltammogram, the number of electrons involved in the reaction has the largest influence. Furthermore, alkaline conditions have a positive effect on the electrodeposition of cobalt. No overall correlation has been found between the samples. For all experiments similar reactions and electrochemical activity is observed regarding the peak potentials and within the same environment, correlations can be found. Recommendations for further research are to investigate the influence of changes to parameters such as temperature, magnetic field and impurities on the electrochemical behaviour of the reaction and changes in the yield of electrodeposited material, to generate more data to validate and calibrate the characteristic potentials that can be used for selective electrowinning and to gather more data of the selective electrowinning experiments in terms of additional (rare) elements, such as lithium.