Effect of alkali treatment on the pore structure of lignite

Abstract：To lower its hydroscopicity, the lignite was treated with different concentrations of sodium hydroxide. Nitrogen adsorption method and scanning electron microscope （SEM） were used to study the effect of treatment conditions on pore structure of Xilinhaot lignite. The re- sults show that the surface areas of treated sample increased compared with that of raw coal when the sodium hydroxide concentration is less than 0.05 mol/L, and the surface areas de- creased when the concentration increase continuously. The total pore volumes decreased when alkali concentrations of 0.01--0. 5 tool/L, and increased slightly when alkali concentrations are less than 0.01 mol/L. With the increasing of sodium hydroxide concentration between 0.01 and 0.5 mol/L, both the mesoporous and mieroporous amount were gradually reduced, and the macroporous increased correspondingly. The adsorption-desorption loops imply the appearing of opening holes with smaller size and crack-shaped when alkali concentrations of 0.1--1 mol/ L, but less effect happened when alkali concentrations of 0. 001--0.05 mol/L.