Insight into Cu Extraction Using Deep Eutectic Solvent: Reaction Mechanism

Abstract

Metal extraction by the use of deep eutectic solvent (DES) is also called as Solvatometallurgy i.e. metal extraction from minerals and secondaries by using DES as prime solvent. Solvatometallurgical extraction is highly futuristic in the study as it involves nontoxic and ecofriendly solvents and comparatively more economic process flowsheet using lower water content. In this study, Cu was extracted from two different resources Cu spent catalyst and Cu concentrate by using DES. The DES mixture was obtained by mixing Choline Chloride (Quaternary Ammonium salt) with ethylene glycol (EG) at 80 degrees C. The leaching reaction takes place with the as obtained DES in a glass reactor. Elemental analyses of the leach liquor were carried out with an Atomic Absorption Spectrophotometer after it reacted with aqua regia to break metal-ligand complex so that metal ion will be perfectly detected by the instrument. The maximum extraction of Cu was 81.6 and 99.9 pct in 72 hour for Cu catalyst and 24 hour for Cu concentrate. Parametric variations were performed such as variation of time, temperature, ratio of EG:Choline chloride and pulp density to obtain the optimized condition for the leaching reaction. The extracted Cu from DES is taken into an aqueous system via solvent extraction with LIX. DEHPHA and Na-DEHPHA. Here the solvent extraction is organic vs organic but they are separated easily because of their density difference. The stripping of 63.63 pct was recorded for 10 pct LIX-84 and the stripping of 66.6 pct was reported for 10 pct H2SO4. The advantage of DES extraction is that it is selective towards the metal of interest and generates no effluent or sludge thus making the downstream simple and cost effective. Efforts are given to establish the reaction mechanism of the DES and the Cu containing solid phases like Cu concentrate and spent catalyst sample with the help of the result analyses of NIR and NMR. One reaction mechanism is also proposed schematically to represent the reaction mechanism.