Solubility Isotherms of Gypsum, Hemihydrate, and Anhydrite in the Ternary Systems CaSO₄ + MSO₄ + H₂O (M = Mn, Co, Ni, Cu, Zn) at T = 298.1 K to 373.1 K

Abstract

The solubilities of anhydrite in the ternary systems CaSO 4 + MSO 4 + H 2 O (M = Co, Ni) were determined through isothermal solution saturation at 348.1 K and 363.1 K. At low bivalent metal sulfate concentrations, anhydrite solubility decreases until it eventually reaches a minimum. Anhydrite solubility subsequently increases with the amount of heavy metal sulfate to a maximum. At this point, further increases in the concentration of metal sulfate decreases the solubility of anhydrite until saturation of the added bivalent metal sulfate. A Pitzer thermodynamic model was selected to predict isopiestic data including calcium sulfate solubilities of the ternary systems CaSO 4 + MSO 4 + H 2 O (M = Mn, Co, Ni, Cu, Zn) from 298.1 K to 373.1 K. The functional dependencies of the MSO 4 (M = Ni, Cu, Zn) ion interaction parameters with temperature were determined, and the third virial parameters were given. The calculated solubilities are in agreement with the available experimental data. Using the Pitzer model and parameters, the solubility isotherms of metastable solid-phase hemihydrate, as well as gypsum and anhydrite, in the CaSO 4 + MSO 4 + H 2 O (M = Mn, Co, Ni, Cu, Zn) systems were predicted over a wide range of temperatures and concentrations.

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

“…Conversely, at medium (1.123–1.502 mol·kg –1 ) and high (>2.55 mol·kg –1 ) concentrations of MgSO 4 , CaF 2 (s) + CaSO 4 ·2H 2 O(s) + MgF 2 (s) and CaSO 4 ·2H 2 O(s) + MgF 2 (s) were the detected equilibrium solid phases, respectively, which can be attributed to the reaction MgSO 4 (aq) + CaF 2 (s) + 2H 2 O ⇌ CaSO 4 ·2H 2 O(s) + MgF 2 (s). Although CaSO 4 (s) should generally be a stable phase in high temperature ( T > 315 K, in pure water) and high salt (MgSO 4 , in this case) concentrations thermodynamically, ,, CaSO 4 ·2H 2 O(s) seems easy to form dynamically. Hence, the equilibrium data of CaSO 4 ·2H 2 O(s) at 348.15 K in Table should be metastable.…”

“…The CaSO 4 (s) and CaSO 4 •2H 2 O(s) were synthesized by CaCO 3 (purity in mass fraction >0.9995, Shanghai Lingjin Fine Chemical Co., Ltd., China) and H 2 SO 4 (G.R., Sinopharm Chemical Reagent Co., Ltd., China), and the preparing processes are the same as the literature. 9,10 The above synthesis compounds were also verified by X-ray diffraction (XRD, Rigaku, Model D/Max-2500, Japan) and inductively coupled plasma emission spectroscopy (ICP-OES, Avio 500, PerkinElmer). Doubled distilled water with conductively less than 1.2 × 10 −4 S•m −1 was used for phase equilibrium experiments and chemical analysis.…”

“…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.…”

“…3,9 Additionally, CaSO 4 (s) solubility in MSO 4 (M = Zn, Mn, Mg) aqueous solution decreases with increasing temperature. 10,11 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 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.…”

Weathering alteration in the Antarctic environment as seen in the Miller Range (MIL) 090030 Martian meteorite

“…There are different types of calcium sulfates depending on the water proportion in their structure. These minerals include gypsum (CaSO 4 ⋅2H 2 O), bassanite (CaSO 4 ⋅0.5H 2 O) and anhydrite (CaSO 4 ) (Wang and others, 2015). The stability of these phases depends on the environmental conditions.…”