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Sulfate Reduction and Sulfide Oxidation in Flooded Soil as Affected by Chemical Oxidants¹

ABSTRACT

The effect of various chemical oxidants on inhibition of sulfide (S^2-) in a previously reduced soil was studied. Oxygen, KNO₃, MnO₂, ferricitrophosphate, and FePO₄ · 2H₂O at rates equivalent to 1,000 ppm O₂ (O₂ added at rates of either 300 or 500 ppm) were both added prior to flooding and after soil reduction had reached a maximum. The results indicate that the more soluble oxidants had the greatest effects in maintaining more positive redox potentials and in delaying sulfate (SO₄^2-) reduction to S^2-. The soluble oxidants (KNO₃ and ferricitrophosphate) delayed S^2- production by 17 and 9 days, respectively. The less soluble compounds (MnO₂ and FePO₄ · 2H₂O) were less effective in delaying S^2- production but persisted longer in preventing maximum S^2- buildup.

Adding the oxidants after maximum S^2- accumulation showed the most pronounced effect on S^2- oxidation from KNO₃ and the least effect from MnO₂. Oxygen at the rate of 500 ppm was also a very effective oxidant. Sulfate reduction to S^2- and S^2- oxidation were apparently controlled by, or at best related to the redox potential since SO₄^2- reduction and S^2- oxidation both appeared to commence at potentials in the vicinity of –100 mV.

¹ Contribution from the Agronomy Dep., Louisiana State Univ., Baton Rouge, La. 70803. This study was supported in part by National Science Foundation Project NSF GB-8653.

² Associate and Professor, respectively. The senior author is currently Research Soil Scientist, Dep. of Army, Corps of Engineers, Waterways Exp. Sta., Office of Dredged Material Research, Vicksburg, Ms. 39180.

Received for publication March 3, 1973. Accepted for publication May 31, 1973.