Ashing temperature of lignite and mineral transition sequence

To investigate the effect of non-mineral inorganics on the degree of ashing and determine the minerals in lignite, we performed selective leaching of amorphous materials in coal. Three kinds of lignite ash samples were prepared at <200 °C, 500 °C and 815 °C, and the minerals and ash products were analyzed by X-ray diffraction, ash composition analysis and statistical modelling. The results suggest that the mineral types of the main coal seams of three sags in the Erlian Basin mainly comprise of clay minerals and quartz, of which clay minerals are mainly kaolinite, followed by mixed illite/smectite and illite. The increase in ashing temperature below 500 °C was found to not affect the mineral species, but it damages the clay minerals to various degrees, mainly kaolinite. Based on principal component analysis and multiple regression analysis, a prediction model was established for medium-temperature ash to obtain the low-temperature ash mineral composition. Erlian Basin lignite contains a large amount of alkali or alkaline earth elements (AAEMS), among which Ca, Na, and Mg cations react with organic oxygen-containing functional groups or other organic functional groups, whereas K is mainly hosted in clay minerals. The positive effect of AAEMS in non-mineral inorganics on the ash yield is higher than the negative effect of the increase in ashing temperature. Ca is an important element that controls the degree of ashing in low-temperature ashing below 500 °C. The effect of Mg on the degree of ashing is enhanced with increasing ashing temperature, but does not exceed that of Ca.