Determination and modeling of the solubilities of NH4Al(SO4)2·12H2O in the NH4+-Al3+-H3O+-HSO4−-SO42−-H2O system at different H2SO4 molalities and temperatures

• Solubility of ammonium alum in NH4+-Al3+-H3O+-HSO4−-SO42−-H2O system is measured.
• The experimental data are successfully correlated with electrolyte NRTL model.
• Solubility of ammonium alum can be predicted precisely at different conditions.

Solubilities of NH4Al(SO4)2·12H2O in the NH4+-Al3+-H3O+-HSO4−-SO42−-H2O system, as well as the densities of the saturated solution were measured at the temperature range from 293.15 to 323.15 K and at the H2SO4 molalities varying from 0.6 to 3.6 mol/kg. At the same temperature and H2SO4 molality, the solubilities of (NH4)2SO4 sharply deceased with the addition of Al2(SO4)3 from 0 to a turning point at first and then slightly decreased. The electrolyte NRTL model embedded in Aspen plus was applied to model the solubilities of NH4Al(SO4)2·12H2O in the NH4+-Al3+-H3O+-HSO4−-SO42−-H2O system. The model parameters were obtained via regressing the experimental results and the total relative average deviation of temperature is 1.04%, indicating that the calculation values are good with experiment data. With the newly obtained model parameters, the fundamental solubilities of NH4Al(SO4)2·12H2O in the NH4+-Al3+-H3O+-HSO4−-SO42−-H2O system can be calculated precisely for its crystallization process.