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Development of a Chemical Model for the Solubility of Calcium Sulphate in Zinc Processing Solutions
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.
... 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]. ...
In the process of scaling the measurement of oil production wastewater using the bottle test method, the deposition and attachment of scaling crystals on the bottle wall lead to a small measurement result and a large error compared to the actual measurement. The scaling amount of oil production wastewater is measured by adding quantitative clay and inducing adsorption, gathering, and deposition of scaling crystals onto the surface of clay particles. Comparing with the theoretical value, the determination result is more accurate than the result of the bottle test method. The comprehensive experimental design described in this paper applies various topics of colloid and interface chemistry, such as scale crystal growth, clay diffusion double electric layer, and micelle structure. We believe that this design will help students majoring in environmental engineering to master the measurement method of scaling the amount of oil production wastewater and strengthen their ability to solve practical problems.
... 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. ...
The growing concern of low-carbon economy and sustainable development has obliged the researchers to investigate green building materials through utilizing industrial by-products. In this study, the industrial waste material, flue gas desulfurization gypsum (FGDG), is incorporated into the magnesium oxysulfate cement (MOSC). The performance of FGDG-incorporated MOSC is evaluated by testing the setting time, compressive strength, density, water absorption, water resistance, volume stability and SO4²⁻ releasing. The hydration products are detected by X-ray diffraction, while microstructure is observed by optical microscope and scanning electron microscope. Increasing the proportion of FGDG retards the initial and final setting times of paste. Compressive strength for MOSC mixtures varies from 52.4 to 62.4 MPa at hydration age of 3 days. The water absorption and the release of SO4²⁻ increase when increasing the FGDG content. The FGDG-incorporated MOSC presents a superior water resistance and volume stability in contrast with the FGDG-free MOSC. The main hydration products of the paste are Mg(OH)2 and 5Mg(OH)2·MgSO4·7H2O (5·1·7) phase. The microstructure analysis is in agreement with the results of mechanical properties. Finally, the FGDG-incorporated MOSC is identified as a promising building material by the evaluation of economic and environmental sustainability.
... 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. ...
In a gypsum removal process, a solution which is saturated with calcium is cooled to lower temperature with solution cooling towers to precipitate calcium as gypsum (CaSO4 · 2H2O) and remove it before the next process step. In zinc
refineries, gypsum removal is part of the solution purification
step before electrowinning
. Gypsum removal after leaching
is important to control the maintenance load of the downstream equipment. Outotec gypsum removal plant was started in 2018 as a part of the zinc
Direct Leaching
plant in Torreón, Mexico. The plant utilizes Outotec cooling towers for solution cooling and Outotec high rate thickener for solid particle separation from the solution flow. First operation results are showing efficient gypsum removal from the solution flow. In this paper is presented the Outotec gypsum removal process and shows results from operation and discusses the importance of efficient operation and low emissions from the solution cooling.KeywordsGypsum removalCooling towerCooling efficiency
... 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]. ...
This paper reports a comprehensive thermodynamic treatment of the binary system ZnSO4–H2O including solution properties and phase equilibria involving various hydrates of zinc sulfate. Published thermodynamic data of ZnSO4(aq), solubilities of the hydrates of zinc sulfate and equilibrium data of the hydration–dehydration reactions have been collected and critically assessed. The more reliable solution properties were used to evaluate the parameters of an extended form of Pitzer's ion interaction model. With this model the activity coefficients and water activities of saturated ZnSO4 solutions have been calculated yielding, together with equilibrium data of hydration–dehydration reactions, the thermodynamic solubility products of the three stable phases, ZnSO4·7H2O (goslarite), ZnSO4·6H2O (bianchite), ZnSO4·H2O (gunningite), and the metastable, monoclinic ZnSO4·7H2O. Using these solubility products together with the ion interaction model, the predicted solubilities are in excellent agreement with the experimental data. The complete phase diagram of the system has been established in the temperature range (266–378) K.
Water-soluble ammonium polyphosphate (APP) as a promising high phosphorus fertilizer source in agricultural application can be used with ammonium dihydrogen phosphate (MAP) during fertilizer preparation and irrigation. In this work, the pH, density and solubility properties of the phase equilibrium of ternary APP-MAP-water system were systematically determined at the temperature of 278.2-313.2K. A new series of parameters of Simplified Apelblat model, empirical polynomials and Rational 2D function were used to express the solubility data of MAP, solution density and pH value, respectively. The maximum relative deviations of these three models were successively within 1.21%, 0.49%, and 0.54% and the corresponding model correlation coefficient R² was close to or greater than 0.9990, which indicating the accuracy and reliability. The experimental results were further verified by observing the effect of APP on MAP supersaturated solution in OptiMax 1001 reactor and through the online detection techniques of FBRM and PVM. With the addition of water-soluble APP can significantly improve the content of P2O5 when it was combined well with MAP into fertilizer application. Therefore, APP can be better used with MAP to improve the utilization rate of phosphorus during irrigation following the basic thermodynamic data and models established in this research.
The solubility of gypsum (CaSO4·2H2O) in ammonium solutions plays a significant role to prevent gypsum scaling on the heater and tower in the treatment of ammonium-N wastewater bearing sulfate ions by the steam stripping process. In this work solubilities of calcium sulfate dihydrate in NH4Cl, NH4NO3, and mixed NH4Cl and (NH4)2SO4 solutions up to 343.15 K were measured using the classic isothermal dissolution method. The investigated concentration (at ambient temperature) is up to 1.50 mol·dm–3 for both NH4Cl and NH4NO3. The solubility of CaSO4·2H2O was found to increase sharply with either NH4Cl or NH4NO3 concentration, whereas the temperature has a limited effect. The XRD analysis of equilibrated solids for these systems shows that CaSO4·2H2O is stable in all cases over the temperature range (298.15 to 343.15) K. The electrolyte nonrandom two-liquid (the electrolyte NRTL) model embedded in AspenPlus was applied to model the solubility of CaSO4·2H2O in the above systems. The newly obtained model parameters were used to well estimate the solubility of CaSO4·2H2O in all cases with a relative deviation of 1.52 %.
A theoretical and experimental investigation of the solubility of gypsum and anhydrite in simulated laterite pressure acid leach (PAL) solutions containing 0–0.3mol/L NiSO4, 0–0.4mol/L H2SO4, 0–0.3mol/L MgSO4 and 0.005mol/L Al2(SO4)3 was conducted in the temperature range of 25–250°C. High temperature experiments were carried out using a batch titanium autoclave equipped with a dip tube for sample withdrawal through an in-situ porous titanium filter. The solubility values obtained at high temperatures were one order of magnitude smaller than those obtained at temperatures below 100°C because gypsum (CaSO4·2H2O) transforms to anhydrite (CaSO4) at higher temperatures. A recently developed thermodynamic database for the Mixed Solvent Electrolyte (MSE) model was extended to predict the calcium sulphate phase equilibria in the systems studied. The model was successfully tested against the measured experimental data for both solids over wide ranges of composition and temperature. The use of the model developed made it possible to assess the solubility of calcium sulphate hydrates in complex aqueous pressure acid leach solutions over wide ranges of conditions.
A chemical model for the solubility of Friedel’s salt (FS, 3CaO·Al2O3·CaCl2·10H2O) was developed. The model was built with the help of the OLI platform via regression of experimental solubility data for FS in the Na−OH−Cl−NO3−H2O systems. The solubility of FS in water was measured using a batch nickel autoclave over the temperature range of 20−200 °C, and the solubility product of FS (log10 Ksp) was obtained. It was found that the solubility of FS in water shows a maximum value as a function of temperature. The solubility of FS in 0−5 mol/L NaOH and 0−2.5 mol/L NaCl solutions was found to decrease with increasing NaOH and NaCl concentrations, because of the common ion effect; however, in 0−2.5 mol/L NaNO3 solutions, it was found to increase because of complexation. During the regression analysis, it was found that CaOH+ plays an important role in solubility modeling, and its dissociation constant was determined by an empirical equation. New Bromley−Zemaitis activity coefficient model parameters for the Ca2+−OH−, CaOH+−OH−, and CaCl+−OH− ion pairs were also regressed, using the experimental solubility data generated in the present study. The new model was shown to successfully predict the solubility of FS in mixed NaOH + NaNO3 solutions not used in model parametrization. With the aid of the newly developed model, the concentration and temperature effects on calcium species distribution were analyzed.
A thermodynamic model is here developed to describe the solubility of calcium sulphate in salt water. A system of equations based on the ionic atmosphere theory of Debye and Hückel, Born model contribution, and local compositions of the nonrandom two-liquid (NRTL) model is used to describe isothermal activity coefficients for aqueous multicomponent solutions of partially or completely dissociated electrolytes. This approach is an extension of the model of Cruz and Renon for binary electrolyte solutions.Unlike previously published models, where the solubility behaviour of CaSO4 depends only on the total dissolved solid (TDS) content, our model takes into account the nature and the amount of each ion which is present in the aqueous solution.Using only binary parameters, good agreement is obtained between the experimental and predicted values of calcium sulphate solubility in sea water and in natural and synthetic water (brackish brines), at 25 °C.By letting a limited set of binary parameters to be adjusted in the multicomponent case, we are able to calculate more accurately than previously the solubility behaviour of CaSO4 over a wider range of salt compositions, including sea-water brines with magnesium augmentation.
The solubility of gypsum in different salt solutions containing Ca, Mg, Na, Cl, and SO4 was determined experimentally at 298[degrees] K. Sixteen subprograms were developed by using five methods of calculating the single ion activity coefficient and four combinations of ion pairs. Statistical analysis of the difference between the experimentally determined solubility of gypsum (average of seven data sets) and the solubilities predicted with the sixteen subprograms was used to determine the subprogram that best predicts the experimental data. Results showed that acceptable predicted values within the experimental error of measurement can be obtained by considering only CaSO4 and MgSO4 ion pairs. The values for the dissociation constant at 298[degrees] K for CaSO4 and MgSO4 ion pairs of the best subprogram were 4.9 * 10-3 and 5.9 * 10-3.5, respectively. The best agreement between experimental and predicted solubility was found when a constant "1.3" was used instead of the value of the effective diameter of the hydrated ions "[alpha]i" multiplied by the coefficient "[beta]" which involves universal constants, dielectric constant, and temperature in the Debye-Huckel theory for calculating the single ion activity coefficient.
Phase-transition diagrams of three CaSO4 phases, namely, dihydrate, hemihydrate, and anhydrate, in the HCl−CaCl2−H2O system are successfully constructed making use of a recently developed OLI-based chemical model. After initial validation of the model by comparison to experimentally determined CaSO4 phase-transition points in H2O or pure HCl solutions, the phase-transition border between dihydrate and anhydrite and that between dihydrate and hemihydrate was obtained by calculating the solution supersaturation (or scaling tendency according to OLI). The constructed phase-transition diagrams show three main regions, namely, regions I, II, and III. In region I, dihydrate is stable, while anhydrite is stable in regions II and III. Dihydrate is metastable in region II, while hemihydrate is metastable in region III. An increase in HCl and/or CaCl2 concentration causes the metastable region of HH to expand at the expense of DH. This has the result of lowering the corresponding transition temperatures.
A comprehensive model has been developed for the calculation of speciation, phase equilibria, enthalpies, heat capacities and densities in mixed-solvent electrolyte systems. The model incorporates chemical equilibria to account for chemical speciation in multiphase, multicomponent systems. For this purpose, the model combines standard-state thermochemical properties of solution species with an expression for the excess Gibbs energy. The excess Gibbs energy model incorporates a long-range electrostatic interaction term expressed by a Pitzer–Debye–Hückel equation, a short-range interaction term expressed by the UNIQUAC model and a middle-range, second virial coefficient-type term for the remaining ionic interactions. The standard-state properties are calculated by using the Helgeson–Kirkham–Flowers equation of state for species at infinite dilution in water and by constraining the model to reproduce the Gibbs energy of transfer between various solvents. The model is capable of accurately reproducing various types of experimental data for systems including aqueous electrolyte solutions ranging from infinite dilution to fused salts, electrolytes in organic or mixed, water+organic, solvents up to the solubility limit and acid–water mixtures in the full concentration range.
A comprehensive mixed-solvent electrolyte model has been extended to calculate liquid – liquid equilibria in water – organic salt systems. Also, it has been applied to calculate phase equilibria and speciation in strongly associating systems such as sulfuric acid/oleum (H 2 SO 4 +SO 3 +H 2 O) in the entire concentration range. The model combines an excess Gibbs energy model with detailed speciation calculations. The excess Gibbs energy model consists of a long-range interaction contribution represented by the Pitzer – Debye – Hü ckel expression, a short-range term expressed by the UNIQUAC model and a middle-range term of a second-virial-coefficient type for specific ionic interactions. The model accurately represents the thermodynamic behavior of systems ranging from infinite dilution in water to pure acids and beyond, e.g. in mixtures of H 2 SO 4 and SO 3 . In particular, the model has been shown to predict speciation that is consistent with spectroscopic measurements for the H 2 SO 4 +H 2 O system. In addition, vapor – liquid and liquid – liquid equilibria can be accurately reproduced in mixtures that show complex phase behavior. D 2005 Elsevier B.V. All rights reserved.
Solubilities of calcium sulfate hemihydrate in the low-concentration range from (0 to 3.5) mol·kg-1 (equivalent to mol·kg-1 H2O) of sulfuric acid solutions at 100 °C (373 K) were measured. The measured solubilities were compared with available literature studies and simulated with empirical equations.
Calcium sulphate solubilities in simulated zinc processing solutions, as well as the densities of the corresponding saturated solutions, were determined on heating and cooling in a series of experiments carried out from 20 to 95 °C. In dilute ZnSO4 media, increasing H2SO4 concentrations in the range of 0.0–0.6 M H2SO4 strongly increase the solubility of calcium sulphate, but have little additional effect for acid concentrations >0.6 M H2SO4. In more concentrated zinc sulphate solutions, however, increasing acid concentrations in the range from 0.0 to 2.0 M H2SO4 slightly decrease the solubility of calcium sulphate. In dilute H2SO4 media, the solubility of calcium sulphate decreases with increasing ZnSO4 concentrations, and the decrease is most pronounced for concentrations in the range 0.0–0.2 M ZnSO4. Higher ZnSO4 concentrations further depress the solubility at temperatures below 70 °C, but have a complex effect at higher temperatures. Increasing ferric sulphate concentrations to 1.0 M Fe(SO4)1.5 in 0.3 M H2SO4–1.15 M ZnSO4 media depress the solubility of calcium sulphate to a modest extent. The addition of up to 1.25 M MgSO4 also decreases the solubility of calcium sulphate in 0.3 M H2SO4–1.15 M ZnSO4 media. In contrast, the solubility of calcium sulphate in 2.5 M ZnSO4–0.4 M MgSO4–0.18 M MnSO4 solutions, at pH values ranging from 3.6 to 4.6, is not significantly affected by the presence of up to 0.25 M Na2SO4 or up to 0.09 M (NH4)2SO4. Supporting mineralogical studies showed that the solubility depends strongly on whether the saturating solid phase is gypsum (CaSO4·2H2O) or anhydrite (CaSO4). The transition from gypsum to anhydrite was found to depend on the temperature, the H2SO4 concentration and the total sulphate concentration of the solution. Unlike the solubilities, which varied in a complex manner, the densities of the calcium sulphate-saturated solutions increased systematically with increasing concentrations of any of the solution species and decreased slightly with increasing temperature.
Values for second dissociation quotients and constants of H2SO4 were determined from extensive solubility measurements of CaSO4 and its hydrates in aqueous sulfuric acid from 0 to 1.0 m (4.8 m below 50°) at temperatures from 25 to 350°. It was shown that the dissociation quotients could be described over the entire range of temperature to very high ionic strengths by the use of the one extended Debye-Hückel term, √I/(l + bå√I), which contained only the "ion-size" parameter, å. The ion size varied from 2.8 A at 25° to a maximum of 4.2 A at 200°. The pK value for the second dissociation constant increased from 1.99 at 25° to 6.42 at 350°. This study is believed to be one of the first comprehensive investigations of this type to obtain an acid constant over such an extreme range of temperature and ionic strength. Whereas additional parameters were necessary to describe the dissociation quotients at 25-43° at the highest ionic strengths (0.5-4.8 m), these terms were unnecessary at higher temperatures, thus further supporting the contention that aqueous electrolyte solutions in general behave more simply at temperatures above 100°.
The chemistry of several calcium sulphate systems was successfully modelled in multi-component acid-containing sulphate solutions using the mixed solvent electrolyte (MSE) model for calculating the mean activity coefficients of the electrolyte species. The modelling involved the fitting of binary mean activity, heat capacity and solubility data, as well as ternary solubility data. The developed model was shown to accurately predict the solubility of calcium sulphate from 25 to 95 °C in simulated zinc sulphate processing solutions containing MgSO4, MnSO4, Fe2(SO4)3, Na2SO4, (NH4)2SO4 and H2SO4. The addition of H2SO4 results in a significant increase in the calcium sulphate solubility compared to that in water. By increasing the acid concentration, gypsum, which is a metastable phase above 40 °C, dehydrates to anhydrite, and the conversion results in a decrease in the solubility of calcium sulphate. In ZnSO4–H2SO4 solutions, it was found that increasing MgSO4, Na2SO4, Fe2(SO4)3 and (NH4)2SO4 concentrations do not have a pronounced effect on the solubility of calcium sulphate. From a practical perspective, the model is valuable tool for assessing calcium sulphate solubilities over abroad temperature range and for dilute to concentrated multi-component solutions.
A comprehensive mixed-solvent electrolyte model has been applied to calculate phase equilibria and other thermodynamic properties of multicomponent solutions containing salts, acids and bases in wide concentration ranges. The model combines an excess Gibbs energy model with detailed speciation calculations. The excess Gibbs energy model consists of a long-range interaction contribution represented by the Pitzer–Debye–Hückel expression, a short-range term expressed by the UNIQUAC model and a middle-range term of a second-virial-coefficient type for specific ionic interactions. The model accurately represents the thermodynamic behavior of systems ranging from infinite dilution in water to molten salts or pure acids at temperatures from the freezing point to 300 • C. It has been determined that a physically realistic treatment of speciation is important for the simultaneous representation of vapor–liquid equilibria, osmotic coefficients, solid–liquid equilibria, pH, enthalpies of dilution and heat capacities.