Recent measurements on the oxidation of H2S in the Black Sea yielded rates that were ten times faster than expected. To determine if this increase was due to trace metals, measurements have been made on the oxidation of H2S in seawater with added transition metals. Below a concentration level of 100 nM, none of the metals except Fe2+ affect the rate of oxidation. At higher concentrations the rates increase for all the metals except Zn2+. The increase in the rates followed the order. The increase in the rates below sulfide precipitation appears to be related to the formation of MHS+ ion pairs that have a higher rate of oxidation than HS−. Only Fe2+ and Mn2+ have concentrations high enough to be effective in influencing the rate of oxidation of H2S in the waters of anoxic basins and sediments. The estimated rates of oxidation of H2S in the Black Sea using the laboratory measurements were found to be in reasonable agreement with the measured values. Since CuHS+ has a higher rate of oxidation than HS−, it cannot be used to explain the stability of H2S in oxic seawaters. A more likely choice is ZnHS+.
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)