Changes of Iron-Sulfur Compounds in the Process of Coal Microwave Desulfurization

The total sulfur in Donglin (D) and Yutianbao (Y) coals can be removed above 20% by irradiation with 2.45 GHz microwave for a duration of about 100 s without leachant in nitrogen atmosphere (containing approximately 1% oxygen). The percentage sulfur removal may be increased to 68% after the irradiated coals were further treated with 5% hydrochloric acid. It was shown by Mssbauer spectroscopy that pyrite and ferrous sulfate were both present in the coals, and a little jarosite existed in Donglin coal. Microwave exposure converted pyrite to pyrrhotite and/or troilite, and ferrous sulfate to other phases. The extent of conversion was changed with varying desulfurization level, and pyrrhotite and troilite can be removed rather completely from the coals by treatment with dilute hydrochloric acid. Therefore, microwave irradiation combined with acid washing will be an effective method of disulfurization.