Thermodynamic modelling of magnesium fluoride precipitation in concentrated zinc sulphate environment

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

“…attributed to increasing ion strength and multiple associations. 5,13 Generally speaking, the increasing ion strength has limited impact on the solubility of salts. For example, CaF 2(s) solubility in 0.72 mol•kg −1 NaCl aqueous solution could increase to 0.000447 mol•kg −1 , about twice its solubility in pure water.…”

“…As discussed above, all salts MF 2(s) (M = Ca, Mg, Zn) exhibit a salting-in effect in relatively concentrated ZnSO 4 aqueous solution. The salting-in effects can be commonly attributed to increasing ion strength and multiple associations. , Generally speaking, the increasing ion strength has limited impact on the solubility of salts. For example, CaF 2(s) solubility in 0.72 mol·kg –1 NaCl aqueous solution could increase to 0.000447 mol·kg –1 , about twice its solubility in pure water .…”

“…ZnSO 4 impacts a stronger salting-in effect on CaF 2(s) than on MgF 2(s) . While both salting-in effects can be commonly attributed to increasing ion strength and multiple associations, , the difference of the association extent may lead to the difference of the salting-in effect. As shown in Table , slightly stronger association of SO 4 2– with Ca 2+ than with Mg 2+ (judged by an association constant) may result in a slightly stronger salting-in effect of ZnSO 4 on CaF 2 .…”

“…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.…”

Magnesium removal in the electrolytic zinc industry

“…3.2Thermodynamic modelling of magnesium fluoride precipitation in concentrated zinc sulphate environment (Section 3.2 is largely adopted from a publication in Minerals Engineering [44] )…”