Oxidation of H2S with H2O2in Natural Waters

Abstract

■ The oxidation of H2S with H2O2has been studied as a function of pH (2–13), temperature (5–45 °C), and ionic strength (0–6 m) in seawater and NaCl solutions. The rate constant, k (min–1 M–1), for the oxidation d[H2S]T/dt = –k[H2S]T[H2O2] at pH = 8 was found to be given by log k = 8.60 – 2052/T+ 0.084I1/2 in seawater and NaCl solutions (σ = 0.07). The energy of activation (ΔE* = 39 ± 2 kJ mol–1) for the reaction was independent of ionic strength. The rate increased from pH = 2 to 8 due to the increased rate of oxidation of HS– compared to H2S. The rate constant for the oxidation of H2S was found to be zero at every temperature. The rate constant for the oxidation of HS– was found to be 12.0 ± 0.5, 36.2 ± 0.4, and 211 ± 5 min–1 M–1, respectively, at 5, 25, and 45 °C. The energy of activation (ΔE1* = 51 ± 3 kJ) for HS– was higher than the ΔE* for the overall reaction due to the effect of temperature on K1, the dissociation constant of H2S. Above pH = 8.0, the rate slowly decreased in a near linear manner. The formation of HO2–, which does not react easily with HS–, could be part of the cause of this decrease. © 1989, American Chemical Society. All rights reserved.