Elucidation of sulfidation mechanisms of zinc ferrite in a reductive gas environment by in situ X-ray diffraction analysis and Mossbauer spectroscopy

A difference in reactivity of zinc and iron in zinc ferrite during sulfidation in a reductive gas environment is important to explain sulfur removal performance of the double oxide. We focused on their sulfidation characteristics under relatively lower sulfur concentration to determine the factors for a superior performance on sulfur removal. A series of sulfidation tests of the double oxide were performed in reductive gas environments at mainly 550 degrees C in an in situ X-ray diffraction instrument that identified products of reduction and sulfidation. Complementary information on valence and magnetic properties of iron in the products was obtained by Fe-57 Mossbauer spectroscopy analysis. Reduction products of zinc ferrite were wustite, partly zinc-bearing magnetite, and pure magnetite, depending on the strength of the reductive environment. Sulfidation of the reduced zinc ferrite yields sulfides of both zinc and iron, when the concentration of hydrogen sulfide was sufficiently high. Zinc sulfides, however, were predominantly produced in sufficiently low sulfur concentration, typically less than 80 ppm. The iron component at the low sulfur condition remained in the reduced chemical forms or as pure magnetite. These findings revealed that a higher performance during sulfur removal at lower sulfur concentration is maintained with zincite in the reduced zinc ferrite.