PARTICULATE PYRITE FORMATION BY THE FE3+ HS- REACTION IN AQUEOUS-SOLUTIONS - EFFECTS OF SOLUTION COMPOSITION/

Microsize particles of pyrite were synthesized by reaction of ferric i ons with sulfide ions in aqueous solutions. The reaction products of t he synthesis experiments were characterized by X-ray diffraction and e lectron-optical techniques. The formation of pyrite was affected stron gly by the pH and redox potential (E(h)) of the working solutions, Pyr ite, with a mean particle diameter of 1.5 mu m, formed in the pH range 3.6-5.7 at E(h) values of approximate to 0 V(-0.05-0.01 V). The inter mediate products of elemental sulfur and FeS (or Fe(HS)(+)) were ident ified as essential precursors for pyrite formation. E(h)-pH diagrams f or the S-H2O and Fe-S-H2O systems indicated that the solid species FeS (or the soluble complex Fe(HS)+) and elemental sulfur are both thermo dynamically stable under the conditions where pyrite forms. The inabil ity to form pyrite below approximate to pH 3.6 is attributed to unders aturation of FeS or the absence of Fe(HS)(+). In contrast, the inhibit ion of pyrite formation above pH approximate to 5.7 is ascribed to the corresponding E(h) conditions which make FeS unstable relative to FeO OH. In addition, it was demonstrated that nanoparticles of pyrite coul d be obtained by lowering the concentrations of Fe3+ and HS- in the ea rly stages of the reaction.