An Alternative Technique for the Extraction of Valuable Elements from Fly Ash: the Carbochlorination Method

The extraction of valuable elements from high-alumina fly ash was carried out using two methods, the carbochlorination method and the carbothermic method. The carbochlorination experiments were conducted to investigate the impacts of the factors of reaction time, temperature, and carbon content. The carbochlorination of fly ash at a carbon: alumina molar ratio of 4.5 : 1 yielded extractions of Al2O3, SiO2, CaO, and TiO2 of 84.3 72.7, 68.9, and 87.3%, respectively, at 1000°C for 60 min of reaction time with a pellet diameter of 8 mm and a chlorine gas flow of 0.35 L/min. By comparing the decomposition behavior between the carbochlorination and the carbothermic treatment, the carbochlorination mechanism of fly ash was elucidated. Alumina was preferentially chlorinated from mullite in the fly ash. The carbochlorination method provides the potential for the efficient and clean extraction of valuable elements from fly ash.