Extraction Equilibria of Mercury(II) from Hydrochloric Acid with Trialkylphosphine Sulfides

Abstract

Abstract The extraction of mercury(II) from hydrochloric acid was compared using five kinds of sulfur-containing extractants. Mercury(II) was extracted most effectively by trialkylphosphine sulfides. Subsequently, the distribution equilibria of mercury(II) from hydrochloric acid with triisobutylphosphine sulfide (TIBPS=\barS) and trioctylphosphine sulfide (TOPS=\barS) in toluene have been measured at 303 K in order to clarify the concentration dependencies of the reactant species. It was found that mercury(II) is extracted according to the solvation reaction by TIBPS or TOPS as a mercury(II): extractant 1:2 complex, HgCl2S2, in the range of low loading ratio of mercury(II) to the extractants, and as a 1:1 binuclear complex, (HgCl2)2S2, in the region of high loading ratios, as follows: HgCl2+2\barS\ightleftharpoons‾HgCl2S2 Ke 2HgCl2+2\barS\ightleftharpoons‾(HgCl2)2S2 Ke′ The extraction equilibrium constants, Ke and Ke′, were evaluated as Ke=4.0×105 (dm3 mol−1)2 and Ke′=2.0×108 (dm3 mol−1)3 for TIBPS and as Ke=7.2×106 (dm3 mol−1)2 for TOPS.