Menthol-Based eutectic solvent for indium and thallium partition from hydrochloric acid media

Abstract

Eutectic mixtures have been considered as alternative green solvents due to having characteristics similar to ionic liquids. Some of these solvents were reported to be hydrophobic and were able to extract metal ions from aqueous media through a liquid–liquid extraction process. In this work, the ability of a hydrophobic eutectic mixture composed of DL-menthol and lauric acid (ES-MLA) to extract In(III) and Tl(I, III) from hydrochloric acid media was investigated. The most promising results were obtained for Tl(III). The addition of bis(2-ethylhexyl)phosphoric acid (HDEHP) into ES-MLA was able to improve the extraction yields of In(III) and Tl(I) significantly, particularly at low acidity, but had a minor effect on Tl(III) extraction. Metal extraction decreases in the orderTl(III) > Tl(I) > In(III) for the entire HCl range studied in the case of pure ES-MLA and above 1 M HCl for the HDEHP + ES-MLA systems. A mathematical model to explain the metal extraction is presented. When added HDEHP diluents, the effect of the ES-MLA eutectic mixture and the conventional solvent kerosene on In(III) and Tl(III) extraction was also studied. It was observed that the kerosene-containing system was able to improve In(III) extraction at low acidity by two orders of magnitude while Tl(III) behavior in this acidity range was not affected. However, at high acid concentrations, the eutectic-based system shows advantageous behavior.