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.
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