Abstract: The microwave/magnetic desulfurization is an attractive, novel and efficient physical method for coal cleaning. The Mössbauer spectrum of the coal sample after microwave irradiation shows that high-frequenoy selective heating of coal has transformed more than 50% nonmagnetic pyrite FeS₂ into moderately magnetic pyrrhotite Fe_1-xS (0 < x ≤ 0.125) which will enhance effectively magnetic separation of inorganic sulfur in coal, and into antiferro-magnetic troilite FeS. The ferrous sulfate FeSO₄ of weathered products derived from FeS₂ is probably oxidized first and then sulfidized. There are no traces of iron oxide in the spectrum.
The magnetization enhancement of coal after microwave exposure is clear. Mössbauer spectra of magnetic separa ted samples show that there are no Fe_1-xS, FeS and FeSO₄ in the non-magnetic fraction, but there is a little of pyrite. Consequently, a majority of inorganic sulfur in the run-of-mine coal has already been removed significantly.
Calculations from the spectra of the abovementioned samples indicate that a 24% reduction of inorganic sulfur in coal after microwave treatment and a 91% reduction after microwave irradiation/magnetic separation treatment have been obtained, respectively.