THE ROLE OF ORGANIC-ACID IN THE ABIOGENIC REDUCTION OF SULFATE AND THE SULFUR ISOTOPE EFFECT

Abiogenic reduction of sulfate by acetic acid has been conducted at temperatures ranging from 241 to 340°C, The sulfides produced and the remaining sulfates have been chemically and isotopically quan-tified. The reaction of the aqueous sulfate reduction obey first-order kinetics. The rate constants are strongly dependent on temperature. The temperature dependence of the reaction rate (min-1) is given by the following rate law: logk=-10.3 xl0Vr+15.L The activation energy for the reaction of sulfate reduction is 208 kJ mol-1. The remaining sulfates display distinct sulfur isotopic variations under a closed system due to the kinetic isotope effect. The kinetic isotope fractionation factor can be expressed as: 103(a-l) = 3-32x 10Vr2-4.19. The kinetic isotope effects during abiogenic reduction of the sulfate may depend on the atomic hydrogen produced, independent of the reducing agents. © 1990, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.