Thermodynamics of ammonioalunite precipitation in ammonium aluminum sulfate solution

Abstract

The thermodynamics of ammonioalunite precipitation during the leaching of coal fly ash by ammonium hydrogen sulfate solution was studied, and it was found that ammonioalunite was formed above 448 K in the leaching system. Moreover, ammonioalunite was prepared by the hydrothermal synthesis method in an acid system, and its properties were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). It was noticed that the increasing reaction temperature was beneficial to the formation of ammonioalunite. Ammonioalunite possessed a regular cubic structure and belonged to the hexagonal crystal system with the lattice constants of a = b = 6.995 Å, c = 17.681 Å, and the axis angles of α = β = 90°, γ = 120°. The conversion rate of ammonioalunite decreased with the increase of the ammonium hydrogen sulfate excessive rate, and the morphology of ammonioalunite changed to irregular particles. Ammonioalunite dissolved in alkali and α-Al2O3 was obtained by heating ammonioalunite at 1200 °C.