The influence of anionic additives on the microwave dehydration process of lignite

Different anionic additives were added to lignite to enhance the effect of microwave heating on the dehydration and upgrading processes. The dehydration kinetics and moisture diffusion coefficient as well as the physical and chemical properties of solid and liquid products were studied in detail. During the microwave heating process, the enhancement effect of each additive was in the order of Na2CO3 < Na2SO4 < NaCl < NaNO3. The dehydration process of lignite was well fitted by the logarithmic model. For the solid products, as the promotion effect on the dehydration process of lignite increased, the structure tended to be stable, the content of harmful gas released by combustion was reduced, and the surface hydrophobicity was enhanced. At the same time, for the liquid products, the total organic carbon, chemical oxygen demand, and electrical conductivity increased, the pH decreased and the surface tension increased first and then decreased. With an increasing additive enhancement effect, moisture loss was supplemented by the loss of inorganics and then organics.