Iron Sulfides Formed from Aqueous Solution at Low Temperatures and Atmospheric Pressure

Abstract

Several different iron sulfides have been synthesized from aqueous sulfide solutions at low temperatures (20°-90° C.) and atmospheric pressure and identified by means of X-ray diffraction and/or chemical analysis. These are tetragonal FeS, pyrite, marcasite, a magnetic cubic iron sulfide of the spinel structure type, pyrrhotite, and an X-ray amorphous precipitated iron sulfide of composition approximating FeS. The nature of the resulting iron sulfide depends upon many factors, the most important of which are pH, temperature, the presence of specific oxidizing agents, and the type of iron source material used as a reactant. Tetragonal FeS was formed over a wide range of conditions and was the iron sulfide most commonly encountered in this study. It results from the reaction of hydrogen sulfide with fine-grained goethite under conditions simulating those in natural marine sediments. The substance described as hydrotroilite in many sedimentary occurrences is believed to be, at least in part, poorly crystallized tetragonal FeS. Tetragonal FeS has been found in the sediments of the Mystic River, Boston, Massachusetts, and in an iron sulfide concretion from the sediments of the Black Sea. The initial corrosion product of metallic iron in , which has been called kansite, is tetragonal FeS. The material originally denoted as melnikovite by Doss (1912) is believed to have been a mixture of phases containing one or more of several known magnetic iron sulfides. The substance called melnikovite by Volkov (1961) from the Black Sea concretion is shown to be the magnetic cubic iron sulfide synthesized in the present study.