Study On The Leaching Process Of CFB Ash With Hydrochloric Acid

Circulating Fluidized bed boiler (CFB) ash is a by-product collected from combustion process of low heat value coal in a fluidized bed. It is one of coal fly ash largely piled in China, which leads to land occupation and potential environmental pollution. The average weight percent of AI2O3in CFB ash is very high in China due to the character of geological structure. CFB ash is hence becoming an alternative resource of bauxite. Alumina extraction process plays an important role in the aluminum recovery from CFB ash. This research proposed operation parameters and theoretical guidance for industrial application after investigating the acid leaching kinetics of CFB ash. The selection of reactor and stirrer were also investigated in this research.Through online temperature testing it is found that the reaction between hydrochloric acid and CFB ash is a strong exothermic process and the tested reaction heat is765kJ/kg CFB ash. The value of reaction heat calculated from thermodynamic data of minerals in CFB ash is in accordance with the measured one, which shows that the exothermic heat of acid leaching process resulted from the chemical reaction.The key factors affecting the reaction process are temperature and the concentration of hydrochloric acid after investigating the influence of stir speed, liquid to solid ratio, concentration of hydrochloric acid and activation temperature on the leaching of aluminum, iron and calcium. The Avrima dissolution model is suitable for the leaching process of CFB ash and corresponding kinetics equations were inferred.The acid leaching reactors suitable for batch and continuous operation are also designed according to experimental results.