KINETICS AND MECHANISM OF PYRITE FORMATION AT LOW TEMPERATURES.

Abstract

The kinetics of pyrite formation in the reaction between FeS, sulfur, and hydrogen sulfide in aqueous solution have been investigated between 20 degree and 50 degree C and at 1 atm pressure. The kinetics were followed by timed analyses of pyrite concentrations for a series of experimental runs with varying initial reactant concentrations. The kinetics are consistent with a mechanism involving the dissolution of both elemental sulfur and ferrous sulfide. Elemental sulfur dissolves in sulfide solutions producing polysulfide ions, and ferrous sulfide dissolves to form aqueous ferrous ions and sulfide species. Pyrite is formed directly through the reaction between aqueous ferrous ions and polysulfide ions. The rate of pyrite formation in this chemically-controlled reaction is considerably greater than observed rates in natural sediments, which are probably transport-controlled. Refs.