Abstract
The extraction of mercury (II) from hydrochloric and nitric acid solutions by trioctyl phosphine oxide (TOPO) in benzene has been investigated under different conditions. The organic extracts were examined by infrared, Raman and nuclear magnetic resonance spectroscopies. As the results, it was found that with increasing the concentration of aqueous hydrochloric acid solutions, the distribution coefficient for TOPO decreased below 1 mol dm-3 HCl and rised to a maximum at about 4 mol dm-3 HCl and then fell. The distribution behavior for the extraction of mercury (II) by TOPO from nitric acid solutions was analogous to that from hydrochloric acid solutions, while their extraction efficiencies were in the order of extraction systems HCl > HNO3. Consequently the following equilibrium equations are proposed for the extraction of mercury (II) from hydrochloric and nitric acid solutions by TOPO : for HCl extraction system, HgCl2 (a) + 2TOPO (o) ⇔ HgCl2·2TOPO (o), HgCl42- (a) + 2H+ (a) + 2TOPO (o) ⇔ H2HgCl4 · 2TOPO (o) and when mercury loading increases HgCl2 (a) + TOPO (o) ⇔ HgCl2·TOPO (o) ; for HNO3 extraction system, Hg (NO3)2 (a) + 2TOPO (o) ⇔ Hg (NO3)2·2TOPO (o) and Hg (NO3)42- (a) + 2H+ (a) + 2TOPO (o) ⇔ H2Hg (NO3)4·2TOPO (o).
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