Determination and correlation of the solubility of magnesium sulfate in ethanol solutions with different concentrations: Application to the removal of magnesium from zinc electrolytic waste solution

Abstract

In this study, the solubility of anhydrous magnesium sulfate (MgSO4) in ethanol solutions with concentrations ranging from 10 % to 50 % was determined at 15–50 °C. Next, the results were correlated by using the Apelblat model, polynomial empirical equation, ideal solution equation of state model, and Van’t Hoff–Jouyban–Acree model. The results indicated that all four models exhibited correlation coefficients greater than 97 %, and average relative deviations of 3.82 %, 4.24 %, 3.96 %, and 3.96 %, respectively. Notably, the Apelblat model was found to be more accurate and reliable in correlating the solubility of MgSO4 in ethanol solutions with different concentrations. Further, the Van’t Hoff equation was applied to determine the enthalpy and entropy of dissolution. Herein, a certain amount of anhydrous ethanol was added to the zinc (Zn) electrolytic waste solution (ZEWS) to crystallize Zn2+ and Mg2+ through the solvent crystallization method, with the precipitation rates reaching 20.13 % and 39.38 %, respectively. The concentration of Mg2+ reduced to below 15 g⋅L−1, meeting the quality standard of ZEWS. The XRD, TG, and SEM analyses of the output salt mix crystallization confirmed the primary components to be MgSO4·7H2O and ZnSO4·7H2O, with the morphological features primarily consisting of short rods and some crystal agglomerates. This study shows that the removal of Mg2+ from Zn smelting process can be effectively achieved by the proposed solvent crystallization method.