Solubility phenomena involving CaSO4 in hydrometallurgical processes concerning heavy metals

Abstract

Deposit of CaSO 4 in hydrometallurgical processes involving heavy metals usually decreases production quality and harms the production process. To avoid its formation at false time and sites, a sound understanding of the solubility behavior of CaSO 4 in the quaternary systems CaSO 4 + H 2 SO 4 + (heavy metal)SO 4 + H 2 O over large ranges of temperature and concentration is a prerequisite. Up to now, although a large amount of solubility data has been reported in these systems, little information is available on the solubility of anhydrite, especially at salt concentrations near saturation points. In this paper, we introduce the effect of CaSO 4 in hydrometallurgical processes involving heavy metals, review published solubility data of calcium sulfate and its hydrate in relevant systems, and report our newly determined solubility results involving anhydrite in the quaternary systems CaSO 4 + H 2 SO 4 + MSO 4 + H 2 O (M = Cu,Zn,Mn) at 348.1 and 363.1 K. Based on the newly obtained data some application examples were given. On account of the complexity of the solubility phase diagram of these quaternary systems, where the calcium sulfate solubility is a function of its crystal type, temperature, compositions of sulfuric acid, and heavy metal sulfate, a complete solubility phase diagram is not available until some basic data measurement, for instance, water activity at temperatures higher than 298 K, and final modeling has been finished.

Solubility Measurement of the Systems MF2 (M = Ca, Mg, Zn) + ZnSO4 + H2O and MF2 (M = Ca, Mg) + ZnF2 + H2O at 298.15 K

“…The impurities Ca 2+ , Mg 2+ , and F – in electrolyte solution of zinc hydrometallurgy will cause serious damage to the production process. For instance, CaSO 4 ·2H 2 O or CaSO 4 can block the pipeline and filter cloth by scaling on them, − and MgSO 4 accumulates constantly in the aqueous solution and can occupy the site for ZnSO 4 and finally result in the increase of electric resistance of bath and energy consumption of zinc electrowinning. , The F – ion can corrode the electrodes and interfere with the adhesion of zinc on cathodes and affect deposit morphology . To remove these impurities from electrolyte solution, researchers have developed a lot of approaches, among which precipitating the impurities as hardly or slightly soluble salts is a prospective for its process simplicity and low cost.…”

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

“…The solubility of gypsum in the MSO 4 (M = Mn, Co, Ni, Cu, Zn) aqueous solution at various temperatures was measured by several researchers. , The solubility of anhydrite in the MSO 4 (M = Mn, Cu, Zn) aqueous solution was measured at higher temperatures in our previous work . In this work, we continued to determine the anhydrite solubility in MSO 4 (M = Co, Ni) at 348.1 K and 363.1 K. All of the experimental solubility data formed a basis for determining the solubility phase diagram of the studied systems.…”

“…4,19 The solubility of anhydrite in the MSO 4 (M = Mn, Cu, Zn) aqueous solution was measured at higher temperatures in our previous work. 11 In this work, we continued to determine the anhydrite solubility in MSO 4 (M = Co, Ni) at 348.1 K and 363.1 K. All of the experimental solubility data formed a basis for…”

“…Previously, a considerable amount of experimental work has been conducted to study gypsum solubility under atmospheric pressure at 298.15 K in water or in MSO 4 solutions (M = Mn, Co, Ni, Cu, Zn). − Several experimental studies have also examined the solubility of gypsum and anhydrite in MSO 4 (M = Mn, Ni, Cu, Zn) aqueous solutions at higher temperatures, as described in our previous work . However, the literature contained no data for either anhydrite in NiSO 4 and CoSO 4 aqueous solutions or for hemihydrate in MSO 4 (M = Mn, Co, Ni, Cu, Zn) aqueous solutions over a wide temperature range, particularly at elevated temperatures.…”

“…3−10 Several experimental studies have also examined the solubility of gypsum and anhydrite in MSO 4 (M = Mn, Ni, Cu, Zn) aqueous solutions at higher temperatures, as described in our previous work. 11 However, the literature contained no data for either anhydrite in NiSO 4 and CoSO 4 aqueous solutions or for hemihydrate in MSO 4 (M = Mn, Co, Ni, Cu, Zn) aqueous solutions over a wide temperature range, particularly at elevated temperatures. Azimi 4,10 1 shows the chemicals used in this work.…”