The effects of leaching and floatation on the ash fusion temperatures of three selected lignites

Experiments have been conducted with Huolinhe (HLH), Xiaolongtan (XLT), and Ethiopian (ET) lignites to investigate the effects of washing with water, acid-leaching, and floatation on their ash fusion temperatures (AFTs). The results show that the AFTs of XLT and ET are elevated by washing with water and floatation, but the AFT of HLH is decreased. The AFTs of all three lignites are increased markedly by acid leaching. A decrease in the total basic composition in ash increases its AFT, and vice versa. Changes in the mineral contents of the coals after treatment contribute to the variations in their AFTs. After washing with water, the lower AFT of HLH is brought about by the increases in the amounts of cordierite and anhydrite, whereas the higher AFT of XLT is caused by the decreases in the amounts of anhydrite and calcite. For the floatation treatment, the decrease of AFT for HLH is due to the reduction in the amount of kaolinite, but the elevation of AFT for XLT or ET is caused by the decrease in the amount of pyrite and the reductions in the amounts of gypsum and xanthoxenite, respectively. For the acid-leaching treatment, a decrease in the amount of pyrite and an increase in the amount of kaolinite result in increases in AFTs for HLH and XLT. Increases in the amounts of kaolinite and cristobalite in FET (ET after floatation), WET (ET after washing with water), and AET (ET after acid-leaching) lead to corresponding increases in the AFTs.