Electrochemical Processing of Metal Chalcogenides in Deep Eutectic Solvents
thesisposted on 17.01.2020 by Francesca Rose Bevan
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The increased need for metals in all aspects of life has resulted in attempts to make both primary extraction and secondary recycling of metals more efficient. This project investigates the use of DESs as an alternative to aqueous solutions for the dissolution of metal chalcogenides specifically, both in the form of minerals and synthetic semiconductors. The metals studied include silver, cadmium, zinc and lead with the biggest focus on copper. These compounds exhibit a wide range of properties and ultimate applications. Cd and Zn selenides and tellurides are important compounds in the ever-growing solar energy industry due to their small band gaps and high conductivities. Copper, in particular the sulphide minerals are an important source of Cu which is one of the most used metals worldwide.
This study has demonstrated a novel method of investigating the electrochemical properties of minerals in DESs using paint casting. The currents observed are semiquantitative for the metal content of the mineral. Signals for both the metal and the chalcogenide could be distinguished in the voltammetry and these were similar to those for the individual components. The electrochemical signals for the minerals were similar to those for the pure compounds.
Numerous sulfide, selenide and telluride compounds were studied in both the pure and mineral forms. It was found that during bulk electrolysis both components were solubilised, the speciation of the metals in solution were generally identified using UVVis spectroscopy coupled with EXAFS analysis. In most cases the metal speciation was dominated by the chloro-complexes and the chalcogenide was oxidised to an oxygen containing species. In all cases the solubilised metals could be recovered electrochemically by bulk electrolysis without cross contamination from the chalcogenide. The final part of the study showed that copper could be selectively won in a pure state from complex minerals like chalcopyrite.