The solubility data of the MgF2–MnF2–MnSO4–H2O quaternary
system
and its subsystems are crucial for the removal of magnesium ions from
a MnSO4 aqueous solution as the MgF2 precipitate.
However, these data recorded at 298.15 K have not been reported, except
for the MnF2–MnSO4–H2O system. In this study, the solubility isotherms of the MgF2–MnF2–H2O, MgF2–MnSO4–H2O, and MgF2–MnF2–MnSO4–H2O systems at 298.15 K and MnF2 solubility in pure water
at various temperatures were systematically measured. The results
show that MgF2 solubility initially decreases sharply followed
by a gradual decrease as the MnF2 concentration increases.
MgF2 solubility rises with increasing MnSO4 concentration
in pure MnSO4 and the MnF2-saturated MnSO4 aqueous solution. MgF2 solubility in the MnF2-saturated MnSO4 aqueous solution decreases to
2.3–6.5% of its value in the pure MnSO4 aqueous
solution at a certain MnSO4 concentration. MnF2 solubility increases with increasing temperatures in the MnF2–H2O system. A Pitzer–Simonson–Clegg
model incorporated in the ISLEC software was used to simulate and
predict the solubility curves of the MgF2–MnF2–MnSO4–H2O quaternary
system and its subsystems. The model satisfactorily represented the
solubility data of the subbinary and subternary systems of the MgF2–MnF2–MnSO4–H2O quaternary system within the analysis error, except for
the solubility isotherms of the Mg(Mn)SO4·7H2O, Mg(Mn)SO4·4H2O, and Mg(Mn)SO4·H2O solid solutions. The predicted solubility data
of the MgF2–MnSO4–H2O system at 298.15 K agree well with the experimental data with a
slight deviation of the MgF2–MnF2–MnSO4–H2O system. Based on the established model,
the variation of MgF2 solubility curves with the addition
of anhydrous MnF2 in MnSO4 aqueous solutions
at different concentrations was predicted. The study provides theoretical
guidance for removing magnesium ions from a MnSO4 aqueous
solution via MgF2 precipitation.