REDUCTION OF SULFATE SULFUR UNDER HYDROTHERMAL CONDITIONS: AN EXPERIMENTAL STUDY

Abstract

The reduction of sulfate ion by oil was studied experimentally within a temperature range of 250-380°C in neutral and acid environments. It was shown that this reaction passes through various intermediate compounds depending on physicochemical conditions. The main intermediate product at temperatures below 350°C, is elemental sulfur in acid media. In neutral and alkalic media the sulfite ion and, sometimes, the formation of thiosulfate are also possible. The kinetic characteristics of the process are controlled by reactions with these compounds. Introduction of a precipitator of sulfate sulfur (cadmium acetate) to the reaction system suppresses reactions between sulfide sulfur species and intermediate products of the reaction, thereby resulting in more thorough sulfate reduction. The results demonstrate that the most appropriate geochemical environment for the reduction of sulfate sulfur is an oxidation-reduction front, which forms when oxygen-bearing water moves through reduced rocks. Under other geochemical conditions, the realization of sulfate reduction requires the removal of generated sulfide sulfur from the reaction zone.