The role of organic acid in the abiogenic reduction of sulfate and the sulfur isotope effect

Abstract

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.