Kinetics and mechanism of the oxidation of aqueous hydrogen sulfide by peroxymonosulfate

Abstract

The stoichiometry and mechanism of the oxidation of aqueous S(-II) by HSO_5^-, is similar to the oxidation of S(-II) by H_2O_2, but the rate of oxidation by HSO_5^-; is 3-4 orders of magnitude faster than the corresponding reaction with H_2O_2. A two-term rate law of the following form is found to be valid for the pH range of 2.0-6.3: -d[S(-II)]/dt = k_1[H_2S][HSO_5^-] + k_2K_(a1)[H_2S][HSO_5^-]/[H^+], where k_1 = 1.98 X 10^1 M^(-1) s^(-1),k2 = 1.22 X 10^4 M^(-1) s^(-1), and K_(al) = [H^+][HS^-]/[H_2S] = 2.84 X 10^(-8) M at 4.9 °C, µ = 0.2 M, and [S(-II)] = [H_2S] + [HS^-] + [S^(2-). At high pH and high [HSO_5^-]/[S(-II)] ratios SO_4^(2-) and H^+ formation are favored, whereas at low pH and low [HSO_5^-]/[S(-II)] ratios elemental sulfur (S_8) is favored as the principal reaction product. Peroxymonosulfate is a monosubstituted derivative of hydrogen peroxide that is thermodynamically more powerful as an oxidant than H_2O_2 and kinetically more reactive. These properties make HSO_5^- a potentially important oxidant in natural systems such as remote tropospheric clouds and also a viable alternative to H_2O_2 for the control of malodorous sulfur compounds and for the control of sulfide-induced corrosion in concrete sewers.