57Fe Mössbauer spectroscopic studies of fly ash from coal-fired power plants and bottom ash from lignite-natural gas combustion

A series of four fly ashes, representing a variety of geological origins, and a bottom ash sample derived from the combustion of lignite-natural gas mixtures have been studied by ⁵⁷Fe Mössbauer spectroscopy. The ashes are separated into magnetic and non-magnetic fractions to facilitate a study of the chemical state of the iron contained in the ash. The bottom ash contains no magnetic fraction whereas the magnetic fractions of the fly ashes range from 1.1 to 7.3%. The magnetic fractions contained iron in the form of magnetite, Fe₃O₄. Iron in the non-magnetic fly ash fractions occur as Fe⁺¹ and Fe⁺² mullites, and Fe⁺³ and Fe⁺² silicates. Only Fe⁺³ silicates are found in the bottom ash.