Recovery of Lime, Sulfur, and Iron from Gypsum and Pyrite Wastes

Abstract

Currently, gypsum and pyrite, two major wastes generated by the coal combustion industry, have to be land-filled. The feasibility of a new approach of recovery of lime, iron, and sulfur products from these wastes is discussed in the present work. By thermal decomposition of pyrite, 42% of the sulfur is recovered and pyrrhotite is produced. A thermodynamic analysis shows that the recovery of iron and lime from pyrrhotite and gypsum in a single-stage process is not feasible. Instead, the process has to consist of two subsequent stages. The first is the reduction of pyrrhotite with carbon in the presence of lime to produce iron, calcium sulfide, and carbon monoxide, followed by reaction of calcium sulfide with gypsum to produce lime and a concentrated sulfur dioxide stream. The kinetics of the reactions involved in the two-stage process is studied using thermogravimetric analysis. The reaction rates are favorable above 950 °C and depend on initial reagent concentrations. The effectiveness of magnetic separat...