High purity alum (>99.9%) has been produced by the reaction of NH4Al(SO4)(2) derived from coal fly ash and ammonia in water at a controlled pH and then followed by the successive crystallization. The influence of heating source (conventional and microwave) on the decomposition of the alum and the characteristics of the resultant alumina was examined by means of XRD, TG/DTA, SEM and a laser scattering technique. The application of microwave heating for decomposition of the alum yielded finer alpha-Al2O3 powders with a higher specific surface area, when compared with conventional heating. (C) 2003 Elsevier B.V. All rights reserved.
Park, H. C., Park, Y. J., & Stevens, R. (2004). Synthesis of alumina from high purity alum derived from coal fly ash. Materials Science and Engineering A, 367(1-2), 166-170. https://doi.org/10.1016/j.msea.2003.09.093