Solubility Phase Equilibrium of the Quaternary Reciprocal System Ca²⁺, Mn²⁺//F^–, SO₄^2– + H₂O at 298.15 K

Abstract

Solubility data for the reciprocal system Ca2+, Mn2+//F–, SO4 2– + H2O is very important for the removal of fluoride or calcium ions from the MnSO4 aqueous solution by CaF2(s) precipitation; however, these data have not been reported in literature to date. In this work, the solubility data for the ternary systems CaF2 + MnSO4 + H2O, CaF2 + MnF2 + H2O, and MnF2 + MnSO4 + H2O and the quaternary systems CaF2 + CaSO4 + MnSO4 + H2O and CaF2 + MnF2 + MnSO4 + H2O were measured in detail at 298.15 K. The results showed that CaF2(s) solubility increases monotonically with increasing MnSO4 concentration in the CaF2 + MnSO4 + H2O system, and MnSO4 produces a stronger salting-in effect on CaF2(s) than ZnSO4. CaF2(s) solubility decreases with the increase in the MnF2 concentration and increases again after reaching the minimum value. In the MnF2 + MnSO4 + H2O system, the addition of MnSO4 results first in a decrease and then in an increase of the MnF2(s) solubility, similar to the MgF2(s) solubility behavior in the MgF2 + MgSO4 + H2O system. In the CaSO4·2H2O(s)-saturated solution, CaF2(s) solubility increases with increasing MnSO4 concentration but is generally lower than that in the pure MnSO4 aqueous solution. In the MnF2(s)-saturated solution, CaF2(s) solubility increases with increasing MnSO4 concentration but is remarkably lower than that in the pure MnSO4 aqueous solution. The reciprocal system Ca2+, Mn2+//F–, SO4 2– + H2O exhibits cosaturated phase fields of CaSO4·2H2O(s)-CaF2(s)-MnSO4·H2O(s), CaF2(s)-MnSO4·H2O(s), and CaF2(s)-MnSO4·H2O(s)-MnF2(s).

LaF3 Solubility in Pure Water and in MSO4 (M = Zn, Mn, Mg) Aqueous Solutions at T = 298.15 and 348.15 K

“…All of the factors result in the decrease of the F – ion activity and consequently the increase of the LaF 3(s) solubility. Similar phenomena have been observed for CaF 2 and MgF 2 in our previous work, − as shown in Figure .…”

“…Among all defluorination methods, precipitating F – ions as sparingly soluble salts is the most simple, effective, and economical method. Theoretically, CaF 2 and/or MgF 2 solubility is low enough to remove fluoride ions; however, their solubilities in the ZnSO 4 electrolyte solution are much higher than those in pure water because of the strong salting-in effect. − This makes the requirement (F – content: 2 × 10 –3 mol·kg –1 ) hard to achieve by precipitating CaF 2(s) or MgF 2(s) solely.…”

CaF2(s) Solubility Isotherm in the CaF2–CaSO4–MSO4–H2O (M = Zn, Mn, Mg) Quaternary Systems and Their Subsystems at Various Temperatures

“…However, it is reported that the fluoride content in the zinc hydrometallurgical system (e.g., a CaSO 4 ·2H 2 O(s)-saturated ZnSO 4 aqueous solution containing the impurities of MnSO 4 and MgSO 4 ) is still >5.26 mol·L –1 , which is far higher than the CaF 2 (s) solubility in pure water . To understand this behavior, we investigated CaF 2 (s) solubility in MSO 4 (M = Zn, Mn) aqueous solutions at 298.15 K. , The zinc hydrometallurgical process was performed over a wide temperature range of 313–368 K. , With increasing temperature, the CaSO 4 (s) solubility in pure water decreases, while the CaF 2 (s) solubility in pure water increases. , Additionally, CaSO 4 (s) solubility in MSO 4 (M = Zn, Mn, Mg) aqueous solution decreases with increasing temperature. , However, to the best of our knowledge, it is unknown if CaF 2 (s) solubility in MSO 4 (M = Zn, Mn, Mg) aqueous solutions decreases with increasing temperature as CaSO 4 (s) solubility does. Herein, we systematically measured the CaF 2 (s) solubility isotherms in the CaF 2 –CaSO 4 –MSO 4 –H 2 O (M = Zn, Mn, Mg) quaternary systems and its subsystems CaF 2 –MSO 4 –H 2 O (M = Zn, Mn, Mg) at 348.15 K and the CaF 2 –CaSO 4 –MSO 4 –H 2 O (M = Zn, Mg) quaternary systems and the CaF 2 –MgSO 4 –H 2 O ternary system at 298.15 K. These data will contribute to an essential understanding of the simultaneous existence of fluoride corrosion and CaSO 4 ·2H 2 O(s) scaling in MSO 4 (M = Zn, Mn, Mg) aqueous solutions and provide theoretical guidance for removing calcium and fluoride from the zinc hydrometallurgical system.…”

“…However, it is reported that the fluoride content in the zinc hydrometallurgical system (e.g., a CaSO 4 •2H 2 O(s)-saturated ZnSO 4 aqueous solution containing the impurities of MnSO 4 and MgSO 4 ) is still >5.26 mol•L −1 , 5 which is far higher than the CaF 2 (s) solubility in pure water. 3 To understand this behavior, we investigated CaF 2 (s) solubility in MSO 4 (M = Zn, Mn) aqueous solutions at 298.15 K. 6,7 The zinc hydrometallurgical process was performed over a wide temperature range of 313− 368 K. 1,8 With increasing temperature, the CaSO 4 (s) solubility in pure water decreases, while the CaF 2 (s) solubility in pure water increases. 3,9 Additionally, CaSO 4 (s) solubility in MSO 4 (M = Zn, Mn, Mg) aqueous solution decreases with increasing temperature.…”

Solubility Experiments and Thermodynamic Modeling for the Quaternary System MgF2–MnF2–MnSO4–H2O and Its Subsystems at 298.15 K

“…The solubility behavior of MgF 2 in MnSO 4 aqueous solution and the influence of the common-ion effect are crucial factors for this separation. The reported solubility data of anhydrous MnF 2 in the MnF 2 –MnSO 4 –H 2 O system at 298.15 K are insufficient. Herein, we systematically measured the MgF 2 solubility isotherms in the MgF 2 –MnF 2 –H 2 O, MgF 2 –MnSO 4 –H 2 O, and MgF 2 –MnF 2 –MnSO 4 –H 2 O systems at 298.15 K. We also analyzed the anhydrous MnF 2 solubility in pure water at different temperatures.…”