Sustainable synthesis and application of green deep eutectic solvent in chalcopyrite leaching: A combined experimental and molecular dynamic simulation approach

Abstract

In this study, the chemical dissolution of chalcopyrite in a deep eutectic solvent (DES) solvent with a combination of choline chloride (ChCl) and maleic acid (MA) was investigated. Using the Taguchi experimental design, three parameters were optimized: leaching time (2–24 h), leaching temperature (100–200 °C), and the mol ratio of ChCl to MA (1:2, 1:1, and 2:1). The results of the Taguchi design showed that increasing temperature and time enhances copper recovery. Under optimal conditions for dissolving chalcopyrite at a ChCl:MA ratio of 1:1, with a leaching temperature of 150 °C and a leaching time of 24 h, copper recovery was approximately calculated as about 49.2 %, which is relatively consistent with experiment results showing 52.6 %. Under optimal conditions, XRD and SEM-EDS analyses of leaching residues show no sulfur film formation on chalcopyrite surfaces. Instead, they indicate elevated levels of SiO₂, FeS₂, and CuS, suggesting these phases have limited solubility in DES. Combining ChCl and MA forms a DES with altered infrared spectra due to hydrogen bonding, allowing for stable reuse after metal separation via precipitation or electrolysis methods. Cyclic voltammetry (CV) results show that chalcopyrite dissolution in DES is a chemical process, occurring without oxidation reactions. Molecular dynamic (MD) simulations explored interactions in an MA and ChCl DES. Radial distribution function (RDF) analysis revealed strong interactions between MA's hydroxyl hydrogens as well as ChCl's chloride, and intramolecular hydrogen bonds within MA. Simulations also showed Cu²⁺ and Fe²⁺ ions interact strongly with chloride ions of ChCl and oxygen atoms of MA, with low diffusion coefficients suggesting a 3D hydrogen bond network.