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

Abstract

Abstract The effect of various chemical oxidants on inhibition of sulfide (S 2‐ ) in a previously reduced soil was studied. Oxygen, KNO 3 , MnO 2 , ferricitrophosphate, and FePO 4 · 2H 2 O at rates equivalent to 1,000 ppm O 2 (O 2 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 (SO 4 2‐ ) reduction to S 2‐ . The soluble oxidants (KNO 3 and ferricitrophosphate) delayed S 2‐ production by 17 and 9 days, respectively. The less soluble compounds (MnO 2 and FePO 4 · 2H 2 O) 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 KNO 3 and the least effect from MnO 2 . 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 SO 4 2‐ reduction and S 2‐ oxidation both appeared to commence at potentials in the vicinity of −100 mV.