Liquid-Liquid Extraction of Mercury(2) from Hydrochloric Acid Solutions by Dihexyl-Sulphide and -Sulphoxide

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The extraction of mercury(2) from hydrochloric acid solutions by dihexyl sulphide (DHS, R2S) and dihexyl sulphoxide (DHSO, R2SO) in benzene has been investigated under different conditions. The organic extracts were examined by infrared, Raman and nuclear magnetic resonance spectroscopies. As a result, it was found that with increasing the concentration of aqueous hydrochloric acid solutions, the distribution coefficient for DHS decreases below 1 mol dm-3 acid and its decrease becomes gentle above this acidity；the distribution coefficient for DHSO decreases up to a minimum at 2 mol dm-3 acid and then rises above this acidity. At low aqueous acidity, the behaviour and efficiency for the extraction of mercury(2) by DHS were analogous to those by DHSO and at higher acidities the extraction efficiency of mercury(2) by DHSO is higher than that by DHS. Consequently the following equilibrium equations are proposed for the extraction of mercury(2) from hydrochloric acid solutions：by DHS, HgCl2(aq) + 2R2S(org) →← HgCl2·2R2S(org), and with increasing the loading of mercury(2) HgCl2(aq) + R2S(org) →← HgCl2·R2S(org)；by DHSO , HgCl2(aq) + 2R2SO(org) →← HgCl2·2R2SO(org), HgCl3-(aq) + H+(aq) + 3R2SO(org) →← HHgCl3·3R2SO(org) and HgCl42-(aq) + 2H+(aq) + 2R2SO(org) →← H2HgCl4·2R2SO(org), and when mercury loading increases HgCl2(aq) + R2SO(org) →← HgCl2·R2SO(org).