The feasibility of pyrite dissolution in the deep eutectic solvent ethaline: experimental and theoretical study

Teimouri, Samaneh ORCID: https://orcid.org/0000-0003-2511-8040, Potgieter, Johannes Herman ORCID: https://orcid.org/0000-0003-2833-7986, Billing, Caren ORCID: https://orcid.org/0000-0001-5462-1150 and Conradie, Jeanet ORCID: https://orcid.org/0000-0002-8120-6830 (2023) The feasibility of pyrite dissolution in the deep eutectic solvent ethaline: experimental and theoretical study. Journal of Molecular Liquids, 392. 123468. ISSN 0167-7322

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Abstract

Environmental concerns about the traditional gold extraction process, and the potential volume of encapsulated gold in sulfidic minerals i.e. pyrite, have motivated researchers to find effective, efficient and ecologically benign ways to expose the enclosed gold for improved extraction. Neoteric deep eutectic solvents (DESs) are an analogue of ionic liquids (ILs) which are gaining more attention as eco-friendly solvents. This study examined the viability of pyrite dissolution in a DES comprised of choline chloride (ChCl) and ethylene glycol (EG), called Ethaline. The pH of the ethaline solvent mixed with hydrogen peroxide oxidant, and different solid-to-liquid ratios were examined. Ethaline solution with pH 8 provided the desired condition at which EG is deprotonated to [C2H4O2]2−, a favourable ligand for Fe complexation and thus pyrite dissolution. A solid-to-liquid ratio of 1/20 was optimal and achieved 23.6% Fe extraction as an indication of pyrite dissolution. Density functional theory (DFT) was applied to determine which of the two ligands provided by ethaline (Cl– and/or [C2H4O2]2−) can form the most stable complex with Fe2+ and/or Fe3+. As a result, the tetrahedral complex [Fe(C2H4O2)2]− with the ligand [C2H4O2]2− through O-donor chelating with Fe3+ was found to be the most probable and stable complex. However, the ethaline solvent did not deliver adequate Fe extraction compared to commonly used reagents/solvents like mineral acids, to fully break down pyrite and expose any encapsulated gold.