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 HNO 3, the reaction is first-order in Hg and Hg(II), respectively. The overall second-order rate constant is given by k 2 = 2.90 × 10 9 × exp(−1765/ T ). In 0.8 M HNO 3 with the addition of H 2 O 2, the reaction is first-order in Hg, H 2 O 2, and Hg(II), respectively. The overall third-order rate constant is given by k 3 = 2.13 × 10 23 × exp(−10110/ T ). The addition of Fe 2+ or Fe 3+ has no immediate effect on mercury removal. In 0.8 M HNO 3 with the addition of K 2 Cr 2 O 7, the reaction is first-order in Hg, Cr 2 O 7, and Hg(II), respectively. The overall third-order rate constant is 4.3 × 10 8 M - 2 s - 1 at 25 °C. For mercury absorption in Hg(II) obtained by HgCl 2 injection, the presence of HNO 3 greatly enhanced Hg absorption. H 2 SO 4 had a comparable positive effect while HCl had a negative effect. Succinic acid−NaOH buffer solution greatly enhanced Hg absorption in Hg(II), but NaHCO 3 −NaOH inhibited Hg absorption in Hg(II). MnSO 4 mildly enhanced Hg absorption in Hg(II). At MnSO 4 concentrations lower than 0.22 M, a constant overall third-order rate constant of 4.4 × 10 7 M - 2 s - 1 was obtained at 25 °C. NaCl, MgSO 4, FeCl 3, CaCl 2, and MgCl 2 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 NaHCO 3 /NaOH was present in the solution.