Mercury Absorption in Aqueous Oxidants Catalyzed by Mercury(II)

Abstract

The absorption of elemental Hg vapor into aqueous solution containing Hg(II) was measured in a stirred cell contactor at 25 and 55 °C. In 0.8 M HNO3, the reaction is first-order in Hg and Hg(II), respectively. The overall second-order rate constant is given by k2 = 2.90 × 109 × exp(−1765/T). In 0.8 M HNO3 with the addition of H2O2, the reaction is first-order in Hg, H2O2, and Hg(II), respectively. The overall third-order rate constant is given by k3 = 2.13 × 1023 × exp(−10110/T). The addition of Fe2+ or Fe3+ has no immediate effect on mercury removal. In 0.8 M HNO3 with the addition of K2Cr2O7, the reaction is first-order in Hg, Cr2O7, and Hg(II), respectively. The overall third-order rate constant is 4.3 × 108 M-2 s-1 at 25 °C. For mercury absorption in Hg(II) obtained by HgCl2 injection, the presence of HNO3 greatly enhanced Hg absorption. H2SO4 had a comparable positive effect while HCl had a negative effect. Succinic acid−NaOH buffer solution greatly enhanced Hg absorption in Hg(II), but NaHCO3−NaOH inhibited Hg absorption in Hg(II). MnSO4 mildly enhanced Hg absorption in Hg(II). At MnSO4 concentrations lower than 0.22 M, a constant overall third-order rate constant of 4.4 × 107 M-2 s-1 was obtained at 25 °C. NaCl, MgSO4, FeCl3, CaCl2, and MgCl2 all inhibited Hg absorption in Hg(II). Under most conditions, oxygen in the gas phase did not have any effect on Hg absorption in Hg(II). However, oxygen had a positive effect on Hg absorption in Hg(II) when HCl or NaHCO3/NaOH was present in the solution.