Solubility Of Calcium Sulfate Dihydrate Research Articles

Solubility and thermodynamic modeling of calcium sulfate dihydrate in three organic aqueous solutions (ethylene glycol, acetic acid, dimethyl sulfoxide) from 303.15 K to 348.15 K

In this work, for further study on solubility behaviors of calcium sulfate dihydrate (DH) in different organic aqueous solutions, solubility of calcium sulfate dihydrate (DH) in three binary solvents (water + ethylene glycol, acetic acid, dimethyl sulfoxide) was experimentally investigated by the dissolution equilibrium method at (303.15 to 348.15) K under 88.35 kPa. Solubility data of DH first increased and then decreased with the temperature increased while reduced with the increasing molality of organic solvents. Experimental solubility data was correlated by four thermodynamic models including Wilson, modified Apelblat-Jouyban-Acree, UNIQUAC and NRTL model, all of them can well correlate the solubility of DH. Besides, thermodynamic properties of mixing process (ΔmixG, ΔmixS, ΔmixH, H1E,∞ and lnγ1∞) were investigated based on solubility data and the Wilson equation.

Determination and Analysis of the Solubility of CaSO4·2H2O and α-CaSO4·0.5H2O in Formamide Aqueous Solutions at T = 303.15–363.15 K

The solubility of calcium sulfate dihydrate (DH) and α-calcium sulfate hemihydrate in formamide aqueous solutions with 0–13 m formamide at temperatures from 303.15 to 363.15 K was measured by the d...

Thermodynamic Models and Central Composite Design for Calcium Sulfate Dihydrate Solubility

AbstractThe solubility of calcium sulfate dihydrate (gypsum) was measured in HCl solutions in the presence of Cr3+ and Fe3+ ions at various temperatures. The results indicate that the solubility of gypsum is fairly dependent on the concentrations of HCl and impurities, i.e., Cr3+ and Fe3+ ions. The experimental data were analyzed by applying the Buchowski‐Kiazczak (λh) model and the modified Apelblat model. Some thermodynamic parameters, such as the standard molar dissolution enthalpy, the standard molar Gibbs energy, and the entropy of solutions, were calculated by Van't Hoff analysis and Gibbs equation. The influences of the concentrations of both HCl and impurities, i.e., Cr3+ and Fe3+ ions, and temperature on the gypsum solubility were examined by applying the central composite design.

Solubility and Physical Properties of Calcium Sulfate Dihydrate in NaCl and Glycerol Aqueous Solution at 303.15, 323.15, and 343.15 K

The solubility of calcium sulfate dihydrate (CaSO4·2H2O) was measured in NaCl and glycerol aqueous solution with the mass fraction of glycerol 0–80% and molality of NaCl 0–6 m in the temperature ra...

An efficient model for estimation of gypsum (calcium sulfate di-hydrate) solubility in aqueous electrolyte solutions over wide temperature ranges

Thermodynamic solubility of calcium sulfate di-hydrate (gypsum) plays a major role in many operations involved in oilfields and process industries. In this study, several solubility models were developed using the approaches including Multilayer Perceptron (MLP) networks, Radial Basis Function (RBF) networks, Least Squares Support Vector Machine (LSSVM), Adaptive Network-based Fuzzy Inference system (ANFIS), and Committee Machine Intelligent System (CMIS) for estimating the phase behavior of calcium sulfate dihydrate (or gypsum) in strong electrolyte solutions at high temperatures. The developed CMIS model was found to outperform all other modeling approaches indicating an excellent accordance with experimental data and yielding an overall correlation coefficient of (R2) 0.9968. The developed CMIS model was also found to outperform the ion interaction model of Pitzer providing superior predictability for gypsum solubility in aqueous electrolyte solutions. The results of this study indicate that gypsum solubility could be estimated by employing the CMIS approach with high accuracy in Na-Ca-Mg-Fe-Al-H-Cl-H2O system over temperatures ranging from 5 to 98 °C.

Rigorous modeling of gypsum solubility in Na–Ca–Mg–Fe–Al–H–Cl–H2O system at elevated temperatures

Precipitation and scaling of calcium sulfate have been known as major problems facing process industries and oilfield operations. Most scale prediction models are based on aqueous thermodynamics and solubility behavior of salts in aqueous electrolyte solutions. There is yet a huge interest in developing reliable, simple, and accurate solubility prediction models. In this study, a comprehensive model based on least-squares support vector machine (LS-SVM) is presented, which is mainly devoted to calcium sulfate dihydrate (or gypsum) solubility in aqueous solutions of mixed electrolytes covering wide temperature ranges. In this respect, an aggregate of 880 experimental data were gathered from the open literature in order to construct and evaluate the reliability of presented model. Solubility values predicted by LS-SVM model are in well accordance with the observed values yielding a squared correlation coefficient (R 2) of 0.994. Sensitivity of the model for some important parameters is also checked to ascertain whether the learning process has succeeded. At the end, outlier diagnosis was performed using the method of leverage value statistics to find and eliminate the falsely recorded measurements from assembled dataset. Results obtained from this study indicate that LS-SVM model can successfully be applied in predicting accurate solubility of calcium sulfate dihydrate in Na---Ca---Mg---Fe---Al---H---Cl---H2O system over temperatures ranging from 283.15 to 371.15 K.

Solubility of α-Calcium Sulfate Hemihydrate in Ca–Mg–K Chloride Salt Solution at (353.0 to 371.0) K

The solubility of α-calcium sulfate hemihydrate in CaCl2–MgCl2–KCl solution at temperatures from (353.0 to 371.0) K was measured by the dissolution equilibrium method. The investigated concentration ranges of CaCl2, MgCl2, and KCl were up to (6.01, 4.50, and 0.27) m, respectively. The calcium ion demonstrates the common ion effect, which results in the decreased solubility of α-calcium sulfate hemihydrate in CaCl2 solution. The solubility of α-calcium sulfate hemihydrate is augmented due to the association effect caused by the formation of stable MgSO40 in MgCl2 solution. Also it is shown that potassium chloride can increase the solubility of α-calcium sulfate hemihydrate slightly, which may be attributed to the salt effect. In the mixed salt solution, the solubility of α-calcium sulfate hemihydrate decreases because of the dominating action of the common ion effect. Compared with the solubility of calcium sulfate dihydrate in the mixed solution, the solubility of α-calcium sulfate hemihydrate is lower th...

Measurement and modelling of solubility for calcium sulfate dihydrate and calcium hydroxide in NaOH/KOH solutions

The solubility of calcium sulfate dihydrate (CaSO 4·2H 2O) and calcium hydroxide (Ca(OH) 2) in alkali solutions is essential to understand their desilication behavior from Bayer liquor. In this work, solubilities of calcium sulfate dihydrate and calcium hydroxide for the ternary systems of CaSO 4·2H 2O–NaOH–H 2O, CaSO 4·2H 2O–KOH–H 2O, and Ca(OH) 2–NaOH–H 2O were measured by using the classic isothermal dissolution method over the temperature range of 25–75 °C. The Pitzer model embedded in Aspen Plus platform was used to model the experimental solubility data for these systems. The experimental solubility data was employed to obtain the new binary interaction parameters for Ca(OH) +–OH −, Ca(OH) +–Ca 2+ and Ca(OH) +–K +, suggesting that the species Ca(OH) + is a dominant species in simulated solubility for alkali systems. Validation of the parameters was performed by predicting the solubility for the ternary systems of Ca(OH) 2–NaOH–H 2O, CaSO 4·2H 2O–NaOH–H 2O and CaSO 4·2H 2O–KOH–H 2O with the overall average relatively deviation (ARD) of 2.12%, 0.75% and 1.63%, respectively.

Solubility of Calcium Sulfate Dihydrate in Ca−Mg−K Chloride Salt Solution in the Range of (348.15 to 371.15) K

Solubility data are given for calcium sulfate dihydrate in the system CaCl2−MgCl2−KCl at the temperature range of (348.15 to 371.15) K and in ranges of concentrations up to 3.86 m CaCl2, 1.17 m MgCl2, 0.27 m KCl, and their admixture by using a dissolution method. The calcium ion exhibits the common ion effect on the solubility of calcium sulfate dihydrate. The magnesium ion augments the solubility of calcium sulfate dihydrate in the investigated concentrations by stable MgSO4° ion pair formation. Potassium influences on the solubility of calcium sulfate dihydrate are found to be a salt effect by changing the activity coefficients of the calcium ion and sulfate ion. The temperature has a positive effect on the solubility both in magnesium chloride and potassium chloride solutions. There are two sharp falls. One is between (359.15 and 363.15) K in calcium chloride solution, and the other is at a potassium ion concentration of 0.108 mol·kg−1 in its solution. The common ion effect is the main factor on the so...

Solubility of Calcium Sulfate Dihydrate in Nitric Acid at 20°C

The solubility of gypsum in 0-30 wt % nitric acid solutions at 20°C was studied. The data were compared with the results obtained at 60°C.

The Nucleation Kinetics of Calcium Sulfate Dihydrate in NaCl Solutions up to 6 m and 90°C

Induction periods for the nucleation of calcium sulfate dihydrate were experimentally determined as a function of supersaturation in NaCl solutions from 0 to 6 m at 25°C and in 3.0 m NaCl solutions at temperatures from 25 to 90°C. Using classic nucleation theory, the interfacial tension between gypsum and 3.0-m NaCl solution was estimated to be about 39 mJ/m 2 at 25°C and increases with increasing temperature (to 63 mJ/m 2 at 90°C). It was observed that the induction period decreases with increasing NaCl concentrations up to 3 m and then starts to increase slightly at a given temperature and saturation state. The electrolyte effect on nucleation was proportional to the enhanced solubility of calcium sulfate dihydrate in NaCl solutions. This phenomenon may result from decreased crystal-solution interfacial tensions caused by increased gypsum solubility in electrolyte solutions. Although anhydrite is the thermodynamically stable phase at elevated temperatures and in concentrated solutions, only gypsum was nucleated.

Solubility of calcium sulfate dihydrate in nitric acid solutions containing calcium nitrate and phosphoric acid

Les solubilites du gypse dans des solutions d'acide nitrique contenant differentes concentrations de nitrate de calcium, d'acide phosphorique et d'acide sulfurique sont determinees a 25°C. Les equilibres impliques dans le systeme etudie sont consideres. Presentation des equations decrivant la solubilite

Calcium sulfate solubility in brackish water concentrates and applications to reverse osmosis processes; polyphosphate additives

The solubility of calcium sulfate dihydrate, which by precipitation can impede reverse osmosis (RO) processes, was determined at 25°C in three typical brackish water compositions and their concentrates. These waters corresponded to those used in U.S. Office of Saline Water (OSW) RO plants at Gillette, Wyoming, and Webster, South Dakota, and that of a post-irrigation water from the Wellton-Mohawk Canal in Arizona. Sodium hexametaphosphate was shown, when added in small amounts, to produce an apparent increase in the saturation concentration of CaSO 4. Later, this concentration decreased to the solubility in the absence of the additive. Calculations of maximum water recoveries and other parameters of direct application to RO processes are presented.

Solubility of calcium sulfate dihydrate and association equilibriums in several aqueous mixed electrolyte salt systems at 25.deg.

The solubility and association behavior of calcium sulfate dihydrate (gypsum) in several aqueous 3-component systems at 25$C have been presented and show excellent, systematic behavior when treated separately in the several systems. The attempt to correlate the solubility behavior among the different systems proves difficult to achieve. From the discussion, it is clear that several factors, some competitive, determine the solubility behavior of calcium sulfate dihydrate in a given electrolyte solution. Even though no attempt was made to list all the factors involved, it is apparent from a few considered that there is insufficient information at present to evaluate the relationship among such quantities as association quotients and the different hydration numbers of the many solute species.

Calcium electrode method for measuring dissociation and solubility of calcium sulfate dihydrate

Calcium electrode method for measuring dissociation and solubility of calcium sulfate dihydrate

Solubility of Calcium Sulfate Dihydrate in the System NaCl-MgCl2-H2O from 28° to 70° C.

Solubility of Calcium Sulfate Dihydrate in the System NaCl-MgCl₂-H₂O from 28° to 70° C.