Kinetics of extracting alumina by leaching coal fly ash with ammonium hydrogen sulfate solution

Abstract

A newly developed technology for extracting alumina from coal fly ash with ammonium hydrogen sulfate was studied in this paper. Kinetics of extracting alumina was determined using a reduced timescale method. Coal fly ash and leaching residue were characterized by X-ray diffraction and field emission scanning electron microscopy. The results show that the extraction efficiency of alumina increases with the increase of leaching temperature and time. Compared with 240 min of leaching time, the extraction efficiency of alumina at 180 °C decreases by 1.4% for 300 min. Aluminum ions, sulfate and ammonium ions dissolve in solution and interact with water to form ammonioalunite (NH4Al3(SO4)2(OH)6) precipitate, which is the key factor causing the decrease of extraction efficiency of alumina. The apparent activation energy is 40.95 kJ/mol. The chemical reaction is a rate-controlling step for extracting alumina from coal fly ash with ammonium hydrogen sulfate solution.