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 A, c = 17.681 A, 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.

中文翻译：

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硫酸铝铵溶液中氨铝石沉淀的热力学

摘要 研究了硫酸氢铵溶液浸出粉煤灰过程中氨铝石沉淀的热力学，发现在448 K以上的浸出系统中形成了氨铝石。此外，采用酸体系中的水热合成法制备了氨铝石，并通过X射线衍射（XRD）和场发射扫描电子显微镜（FESEM）研究了其性质。注意到升高反应温度有利于氨铝酸盐的形成。氨铝石具有规则的立方结构，属于六方晶系，晶格常数a=b=6.995A，c=17.681A，轴角α=β=90°，γ=120°。随着硫酸氢铵过量率的增加，氨铝石的转化率降低，氨铝石的形貌变为不规则颗粒。氨铝石溶于碱和α-Al2O3 是通过在1200 °C 下加热氨铝石获得的。