Desulphurization of high-sulfur coking coal by microwave irradiation assisted with alkali solution

Abstract

A desulfurization method that by using microwave radiation assisted with alkali solution was applied to a high-sulfur coking coal collected from Shanxi Province, north of China. First, the single factor experiments were involved to get the optimal microwave desulfurization conditions. Then, several methods including X-ray photoelectron spectroscopy (XPS), sulfur K-edge X-ray absorption near edge spectroscopy (XANES) and Fourier transform infrared spectroscopy (FTIR) were used to investigate the changes in the relative contents of sulfur forms and main organic groups in coal before and after desulfurization process. The single-factor experiment results showed that the optimal microwave desulfurization conditions were: particle size of -0.074 mm, additive concentration of 6 mol/L, microwave power of 900 W, irradiation time of 8 min and solid-to-liquid ratio of 1:4. And the total desulfurization rate was 25.23% under the optimum experimental conditions. XPS and XANES analysis showed the decline of mercapten (sulfother), thiophene and sulfides, while the contents of sulfone, sulfoxide and sulfates increased. The FTIR spectra demonstrated that the overall organic structure of coal hardly got destruction after microwave desulfurization. In addition, the caking index (G) declined from 76 to 62, which suggested the microwave radiation combined with NaOH solution weakened the cokability of coking coal slightly.