Abstract: In a cyclic hydrogen sulfide oxidation-catalyst regeneration process using an aqueous chelated polyvalent metal catalyst solution, excessive degradation of the aminopolycarboxylic acid chelating agent is prevented by incorporating in the solution an effective amount of a stabilizing agent capable of retarding or preventing rupture of nitrogen-carbon bonds in the chelating agent during oxidative regeneration of the catalyst solution. Alkaline thiosulfates are the preferred stabilizing agents. Particularly good results are obtained using an alkaline thiosulfate stabilizer in a catalyst solution comprising the dimer form of the NTA-iron complex.

Abstract: An aqueous oxidation-reduction composition and method for removing hydrogen sulfide gas from a fluid stream by liquid phase oxidation of the hydrogen sulfide to elemental sulfur with a chelated polyvalent metal catalyst, such as iron, wherein the composition is stabilized against rapid loss of chelated polyvalent catalyst caused by contamination of the aqueous composition with micro-organisms, such as bacteria. The aqueous composition is stabilized by incorporating in the aqueous composition and adding throughout the normal usage thereof a broad spectrum biocide in an amount which acts as a bacteriostat to prevent rapid growth of bacteria in the aqueous composition and when the bacteria concentration rises above about 1.times.10.sup.6 colonies per ml.