THE PRODUCTS FROM THE OXIDATION OF H2S IN SEAWATER

The oxidation of sulfide in seawater is an overall second-order reaction, first-order with respect to both sulfide and oxygen. The major products formed from the oxidation of H2S with O2 have been measured in water and seawater as a function of pH (4-10), temperature (10-45-degrees-C), and salinity (0-36). The major products formed from the oxidation of H2S were SO32-, S2O32-, and SO42-. The pH dependence of the product distribution has been attributed to the effect of pH on the rate of the individual reaction steps. A kinetic model was developed to account for the distribution of the reactants and products. The model is based on the following overall reactions: H2S + O2 --> k1 Products (SO3), H2SO3 + O2 --> k2 Products (SO4), and H2S + H2SO3 + O2 --> k3 Products (S2O3). Rate constants were determined for the oxidation of HS- and formation of SO32- (k1), for the oxidation of SO32- and production of SO42- (k2) and for the formation of S2O32- from HS- and SO32- (k3). These values of k1, k2, and k3 as a function of pH, temperature, and salinity can predict the concentrations of the measured reactants and products within experimental error: The effect of metals (Fe3+, Fe2+, Mn2+, Cu2+, and Pb2+) and oxides (alpha-FeOOH and MnO2) on the product distribution has also been examined. The field measurements from the Framvaren Fjord (Norway) and Cariaco Trench (Venezuela) are in reasonable agreement with the laboratory results at the same concentration of Fe2+ as in the anoxic basins.