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

Abstract

LaF 3(s) with extremely low solubility in pure water is the most promising compound to remove F − from heavy-metal sulfate aqueous solutions. However, LaF 3(s) solubility data in sulfate aqueous solutions of heavy metals have never been reported in any literature up to now. First, the LaF 3(s) solubility in pure water was measured in this work. The obtained results show that the LaF 3(s) solubility in pure water at 298.15 and 348.15 K is determined to be lower than 1.7 × 10 −6 mol•kg −1 by the fluoride ion-selective electrode (FISE) and lower than 1.4 × 10 −7 mol•kg −1 by inductively coupled plasma optical emission spectroscopy (ICP-OES), which are the lower detection limits of each analysis method. Second, the LaF 3(s) solubility in MSO 4 (M = Zn, Mn, Mg) aqueous solutions at 298.15 and 348.15 K was measured by ICP-OES. The experimental results show that the LaF 3(s) solubility increases with an increasing MSO 4 (M = Zn, Mn, Mg) concentration at both temperatures. At each temperature, the salting-in effect of LaF 3(s) is continuously enhanced in the order ZnSO 4 < MnSO 4 < MgSO 4 at a certain salt concentration. For example, the LaF 3(s) solubility in a 3.583 mol•kg −1 MgSO 4 aqueous solution at 348.15 K is 1.59 × 10 −3 mol•kg −1 , tens of thousands of times higher than that in pure water. Furthermore, the LaF 3(s) solubility at 348.15 K is about 2.1−6.2 times that at 298.15 K in MSO 4 (M = Zn, Mn, Mg) aqueous solutions of the same concentration, indicating that a lower temperature is more favorable to remove fluoride ions from MSO 4 (M = Zn, Mn, Mg) aqueous solutions by LaF 3(s) .

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

“…The sampling method was the same as detailed in our previous work. 12 The sample was analyzed using the corresponding analysis method. Afterward, the solid was removed using a spoon, and the solution attached to the solid was dried by blotting it with a filter paper before immediate analysis by XRD.…”

“…At the end of each experiment, the magnetic stirring was stopped, and the solid–liquid mixture was kept static for 3 days. The sampling method was the same as detailed in our previous work . The sample was analyzed using the corresponding analysis method.…”

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

“…The mixtures were allowed to stand for 3 days after reaching equilibrium. The sampling method was consistent with our previous work . The solution composition was analyzed using an appropriate analytical method, while the moist solid was analyzed via XRD.…”