Development of solvents for Au(III) extraction in hydrochloric acid media based on ion solvation with reference to the Hansen solubility parameters: Success of dicyclohexylketone

Abstract

Ion solvation extraction using ethers and ketones is industrially applied for the extraction and separation of Au(III) from acidic chloride media. Although these have been in practical use since the 1970s, requirements for valid extractants (solvents) have not been systematically clarified. In this study, the relationship between Au(III) extractability using various organic solvents and their Hansen solubility parameters (HSPs) was investigated. The extractability of the solvents increases with the increase of the polar forces (δP) of the solvents, however, solvents with much higher δP values are water-miscible and unsuitable for solvent extraction. Hence a HSP sphere with center coordinates at δD = 17.73, δP = 7.82, δH = 2.48, where D, P and H represent dispersive, polar and hydrogen-bonding forces, was obtained from the results of extraction tests using 26 solvents, with the exclusion of HSPs for 25 water-miscible solvents. Twenty-four of the 26 solvents tested were properly classified as valid or invalid for the extraction of Au(III) using the Hansen sphere. The results suggest partial utility of the prediction of the extractability using HSPs. Dicyclohexylketone, which has HSPs within the sphere, was selected as a potential extractant: it showed sufficient extractability and selectivity for the extraction of Au(III).