Ferrate(VI) Oxidation of Hydrogen Sulfide

The rates of oxidation of hydrogen sulfide with Fe(VI) were made anaerobically as a function of pH (7−12) and temperature (5−15 °C). The reaction was found to be first order for each reactant. The rates decrease with an increase in pH. The energy of activation was found to be 30.1 ± 4.9 kJ mol-1 at pH = 12. When the concentrations of [H2S]T ([H2S] + [HS-]) are in excess, the ratio of [H2S]T consumed to [Fe(VI)] consumed was 1.51 ± 0.14 at pH = 7.0 and 2.50 ± 0.13 at pH = 9.0 and 11.3. Thiosulfate was the main product at pH = 7.0; sulfite, thiosulfate, and sulfate were identified as the products of the reactions at pH = 9.0 and 11.3. In an excess of [Fe(VI)] over [H2S]T, the hydrogen sulfide is fully oxidized to sulfate. A mechanism in which Fe(VI) oxidizes H2S by a one-electron process is proposed. Experiments were conducted to test the Fe(VI) removal efficiency of sulfide in groundwater and wastewater. The results indicate that Fe(VI) can be used as an effective oxidant to remove hydrogen sulfide from wastewaters.