Ash removal from inferior coal via ammonium fluoride roasting and simultaneous yield of white carbon black

Abstract

The quality upgrading and deashing of inferior coal by chemical method still faces great challenges. The dangers of strong acid, strong alkali, waste water and exhaust gas as well as high cost limit its industrial production. This paper systematically investigates the ash reduction and desilicification of two typical inferior coal utilizing ammonium fluoride roasting method. Under the optimal conditions, for fat coal and gas coal, the deashing rates are 69.02% and 54.13%, and the desilicification rates are 92.64% and 90.27%, respectively. The molar dosage of ammonium fluoride remains consistent for both coals; however, the gas coal, characterized by a lower ash and silica content (less than half that of the fat coal), achieves optimum deashing effect at a reduced time and temperature. The majority of silicon in coal transforms into gaseous ammonium fluorosilicate, subsequently preparing nanoscale amorphous silica with a purity of 99.90% through ammonia precipitation. Most of the fluorine in deashed coal are assigned in inorganic minerals, suggesting the possibility of further fluorine and ash removal via flotation. This research provides a green and facile route to deash inferior coal and produce nano-scale white carbon black simultaneously.