Article

Development of a Chemical Model for the Solubility of Calcium Sulphate in Zinc Processing Solutions

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Abstract

A new model capable of predicting the solubility of calcium sulphate solid phases in zinc sulphate processing solutions from 25 to 95°C was developed. The model uses the Mixed Solvent Electrolyte (MSE) model of the OLI systems software to calculate the activity coefficients of the electrolyte species. The model was tested using recently developed experimental measurements. It was shown to accurately predict the solubility behaviour of calcium sulphate in multi-component zinc processing solutions containing ZnSO4, H2SO4, MgSO4, MnSO4, Fe2 (SO4)3, Na2SO4 and (NH4)2SO4. The model can also explain the complex effect of coexisting metal sulphates on the solubility of the CaSO4 phases. The model is a practical tool for assessing the process chemistry of a wide variety of complex aqueous processing streams. Résumé On a développé un nouveau modèle capable de prédire la solubilité de phases solides de sulfate de calcium dans des solutions de traitement du sulfate de zinc, de 25 à 95°C. Le modèle est basé sur le modèle d'Électrolyte à Solvants Mixtes (MSE) du logiciel des systèmes OLI pour calculer les coefficients d'activité des espèces d'électrolytes. On a fait l'essai du modèle en utilisant des measures expérimentales développées récemment. On a montré qu'il prédisait avec précision le comportement de solubilité du sulfate de calcium dans des solutions de traitement du zinc à plusieurs composantes, contenant du ZnSO4, du H2SO4, du MgSO4, du MnSO4, du Fe2 (SO4)3, du Na2SO4 et du (NH4)2SO4. Le modèle peut également expliquer l'effet complexe de sulfates de métal en coexistence sur la solubilité des phases de CaSO4. Le modèle est un outil pratique pour établir la chimie de traitement d'une grande variété de méthodes complexes de traitement aqueux.

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... In this chapter, a new database for the Mixed Solvent Electrolyte (MSE) model of the OLI ® software (Wang et al., , 2004(Wang et al., , 2006 (Dutrizac, 2002). The details of the procedures followed are described in the next section and are also available in the literature (Azimi et al., 2007(Azimi et al., , 2010. ...
... The more recently developed Mixed Solvent Electrolyte (MSE) model (Wang et al., , 2004(Wang et al., , 2006) is capable of accurately calculating the thermodynamic properties of electrolyte solutions in water and/or organic solvent(s) over the entire concentration range from infinite dilution to pure fused salt electrolytes. The application of the MSE model within the OLI ® software platform for hydrometallurgical processes has already proven its efficiency and accuracy in predicting the properties of multicomponent solutions (Liu et al., 2005;Liu and Papangelakis, 2006;Azimi et al., 2006Azimi et al., , 2007Azimi et al., , 2010. ...
... In Chapters 2 and 3, a new database for the Mixed Solvent Electrolyte (MSE) model of the OLI software was developed to predict calcium sulphate solubilities in multicomponent sulphatechloride electrolyte solutions (Azimi et al., 2007(Azimi et al., , 2008. The model was shown to accurately predict gypsum and anhydrite solubility data in various industrial solutions including the nickel sulphate-chloride processing solutions of the Voisey's Bay plant (Azimi et al., 2008) and the neutralized zinc sulphate leach solutions (Azimi et al., 2010) for which the experimental data were measured by Dutrizac and Kuiper (2006) and Dutrizac (2002), respectively. ...
... At the third stage, the CaSO4 scaling crystal nucleus is in the colloidal state on the surface of the clay particles, the CaSO4 scaling crystal particles are adsorbed on the surface by excess Ca 2+ ions, the structure is [(CaSO4)m•nCa 2+ •2(n-x)Cl -]2x + •2xCl -, the colloid outer shell is electronegative, and SO4 2will replace Clin the supersaturated solution, combine with Ca 2+ , and promote scaling crystal growth, so that the scaling crystals are angled along the crystal nucleus monolayer growth, growing up gradually. This is the growth stage of the CaSO4 scaling crystal in the deposition process on the surface of the clay particles [3,[17][18][19][20][21]. ...
... As seen in Table 3, increasing gypsum content in the mixture leads to the increase of SO 4 2À concentration. The concentration of MgSO 4 will have a negative effect on the solubility of CaSO 4 because of the common ion effect (Zimi et al., 2010). So the concentration of SO 4 2À reaches a steady rate when the dosage of FGDG increases. ...
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... The article by Azimi et al. [7] was made using a solution with slightly lower concentration of zinc, 120 g/l, but still close to the actual process conditions and can be utilized as a reference. The internal Outotec values have been measured on site to give reference for the calcium solubility. ...
... The production of metallic zinc via the hydrometallurgical process is based on acidic zinc sulfate solutions [3,4]. The optimization of these processes requires precise knowledge of the binary phase diagram ZnSO 4 -H 2 O as well as the ternary systems with sulfuric acid and impurities, such as calcium and magnesium [5]. ...
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