Changes in sulfur form during coal desulfurization with microwave: Effect on coal properties

The changes in sulfur form in coal were analyzed by sulfur K-XANES (K-edge X-ray absorption near edge structures) spectra before and after the coal microwave desulfurization in a NaOH solution. After the desulfurization, the pyritic sulfur content of coal decreased significantly from 53.6% to 39.2%, while the sulfate sulfur content increased from 17.3% to 34.6%. Only a small amount of thiophene sulfur (20.1–16.1%) was removed. Some sulfur-containing components were oxidized to sulfate sulfur. Under the optimum conditions, the ash content decreased, while the volatile content increased. The calorific value of coal slightly decreased with a slight variation in the amplitudes. The overall structure of coal did not change significantly based on Fourier transform infrared (FTIR) spectral analyses. Thus, the desulfurization of coal with microwave irradiation in a NaOH solution did not significantly change the properties of coal.