Effects of Aliphatic Alcohols on Solubility, Physicochemical Properties

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Effects of Aliphatic Alcohols on Solubility, Physicochemical Properties, and Morphology of Calcium Sulfate Dihydrate (Gypsum) in Aqueous Sodium Chloride Solution at 35 °C Jignesh Shukla, Mohit J. Mehta, and Arvind Kumar* Salt and Marine Chemicals Division, CSIR-Central Salt and Marine Chemicals Research Institute, Council of Scientific and Industrial Research, G. B. Marg Bhavnagar-364002, India

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S Supporting Information *

ABSTRACT: The effect of addition of aliphatic alcohols (methanol, ethanol, and isopropyl alcohol) on the dissolution characteristics of calcium sulfate dihydrate (gypsum, CaSO4·2H2O) in brines has been studied at 35 °C. Addition of alcohols decreased the dissolution of CaSO4·2H2O in aqueous NaCl solutions significantly and also shifted its solubility maximum toward a lower concentration of NaCl. We have also recorded the density (ρ) and speed of sound (u) for the quaternary systems (CaSO4·2H2O + NaCl + alcohols + H2O) at 35 °C. Using primary data, we derived the isentropic compressibility (κS) of the solutions. The experimentally determined physical and derived properties have been correlated using polynomial or linear fits using the method of least-squares. The crystal growth behavior and morphology of gypsum cocrystallized with NaCl crystals from different solutions has also been examined. Alcohol additives seem to be an environmentally friendly, low-cost additive to decrease the solubility of gypsum in aqueous systems with or without NaCl. the inorganic salts start depositing over the membrane surface.14 Calcium sulfate is usually the first to precipitate when brackish water undergoes reverse osmosis.15 Once the membrane surface is covered with inorganic salt, the membrane loses its efficiency. A cleaning step is required to reuse it. Therefore, it is essential to prevent precipitation either by doing pretreatment using organic and inorganic additives or using retardants.16−20 Extensive research has been carried out on CaSO4·2H2O solubility in aqueous or aqueous salt solutions.4−11 In the case of sodium chloride solutions (brines), the solubility of CaSO4· 2H2O increases up to a certain concentration, attains a maximum value, and then decreases with a further increase in concentration. The effects of inorganic salts or organic additives on CaSO4·2H2O dissolution in aqueous or aqueous NaCl solutions have also been investigated by several researchers.21−28 Aliphatic alcohols are well-known for their antisolvent crystallization activity. Kan et al.27 have reported the dissolution behavior of gypsum in methanol (0−91.4 wt % as cosolvent), whereas Gomis et al.28 have studied the effect of ethanol (0−50 wt % as cosolvent) on the solubility of gypsum in the presence of different concentrations of sodium chloride in the solution. However, a systematic study on the effect of aliphatic alcohols on gypsum solubility in sodium chloride solutions is not performed and compared. Further, the data on the physical− chemical solution properties (density and speed of sound) of

1. INTRODUCTION Gypsum (calcium sulfate dihydrate, CaSO4·2H2O) is the most common naturally occurring hydrated sulfate of calcium and is among the most abundant minerals found in nature.1 It is principally found as a sedimentary evaporate and rock-forming mineral on a worldwide scale.2 Calcium sulfate, when in contact with water, grows in three different forms: gypsum (dihydrate); CaSO4·2H2O, bassanite (hemihydrate); CaSO4·0.5H2O and anhydrite (anhydrous); CaSO4. Apart from this, gypsum is crystallized as selenite, massive as alabaster, or fibrous as satin spar.3 CaSO4·2H2O is a sparingly soluble salt. The nature of the solvent, temperature, pH, and ionic concentration are some of the factors responsible for gypsum solubility.4−7 The solubility of CaSO4·2H2O slightly increases with an increase of temperature, attains a maximum, and then decreases with a further increase in temperature.8,9 Because of very low solubility, several times CaSO4·2H2O precipitates out and deposits on the surfaces of equipment wherein brine solution containing calcium and sulfate ions is processed. These deposits (scale) reduce the efficiency of industrial processes and affect the life of equipment severely.10 Such deposits or scale are hard, adherent, almost insoluble in common solvents, and difficult to remove mechanically and thus create an obstacle for flowing fluid.11 One of the most useful methods to desalinate saline water is reverse osmosis (RO). Over 80% of the desalination plants all over the world are RO membrane plants.12,13 In RO, less saline or potable water is recovered from seawater. The salt concentration in the feedwater is increased up to the point where the solubility limit of CaSO4·2H2O could be reached, and once it exceeds the limit, © XXXX American Chemical Society

Received: August 16, 2018 Accepted: January 23, 2019

A

DOI: 10.1021/acs.jced.8b00723 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Table 1. Compounds with Their Source, Mass Fraction Purity, Purification Method, and Analysis chemical name

source

mass fraction puritya

purification method

analysis method

methanol ethanol 2-propanol NaCl CaSO4·2H2O

RANKEM RANKEM HiMedia SD Fine Chemical SD Fine Chemical

0.999 0.995 0.995 0.999 0.980

used as received used as received used as received used as received used as received

none none none none none

a

Purity as stated by the supplier.

Table 2. Solubility of CaSO4·2H2O in Aqueous NaCl Solutions in the Presence of Alcohols, Solution Density ρ, and Speed of Sound u at 35 °C at Pressure P = 0.1 MPaa NaCl (mol·kg−1)

CaSO4 (mol·kg−1)

0.0000 0.5079 0.9962 1.4845 1.9533 2.4221 2.9691 3.4378 3.8285 4.4536 4.8833

5% MeOH 0.0040 0.0231 0.0354 0.0411 0.0447 0.0455 0.0452 0.0431 0.0409 0.0390 0.0373 15% MeOH 0.0025 0.0130 0.0184 0.0217 0.0251 0.0252 0.0255 0.0261 0.0267 0.0261 0.0282 10% EtOH 0.0063 0.0165 0.0244 0.0286 0.0301 0.0328 0.0332 0.0330 0.0332 0.0325 0.0309 5% IPA 0.0097 0.0243 0.0315 0.0363 0.0387 0.0400 0.0400 0.0394 0.0369 0.0374 0.0352

0.0000 0.4688 0.9083

0.0058 0.0168 0.0223

0 0.5436 1.0299 1.5639 2.1170 2.4794 2.7655 3.5475 3.9289 4.2722 4.8063 0 0.4101 0.8487 1.2016 1.6975 2.0789 2.4794 2.9372 3.2042 3.6238 3.9289 0.0000 0.5079 0.8985 1.4650 1.7775 2.3049 2.7347 3.1839 3.6722 4.1410 4.4926

ρ (g·cm−3)

u (m·s−1)

NaCl (mol·kg−1)

0.9886 1.0123 1.0294 1.0511 1.0691 1.0818 1.0947 1.1238 1.1402 1.1527 1.1623

1533.2 1561.6 1587.4 1617.7 1643.9 1668.3 1684.0 1718.4 1742.4 1764.9 1789.8

0 0.4959 0.9059 1.3541 1.7547 2.4031 2.8990 3.2805 3.3949 4.0815 4.5774

0.9710 0.9901 1.0101 1.0239 1.0420 1.0570 1.0728 1.0910 1.0955 1.1146 1.1240

1566.7 1588.2 1614.1 1633.0 1655.0 1674.2 1695.2 1720.5 1729.4 1752.0 1767.0

0.0000 0.5274 0.9181 1.6017 2.1975 2.6175 3.3206 3.7894 3.9848 4.8442 5.3912

0.9828 0.9990 1.0152 1.0359 1.0491 1.0677 1.0863 1.1009 1.1160 1.1322 1.1426

1559.2 1586.4 1604.3 1627.5 1655.1 1677.1 1700.1 1721.3 1739.9 1765.1 1784.1

0.0000 0.3907 0.8009 1.1915 1.5920 2.0315 2.3440 2.8323 3.1253 3.5160 4.0434

0.9931 1.0137 1.0334 1.0521 1.0685 1.0855 1.1084 1.1250 1.1391 1.1598 1.1745

1551.7 1579.6 1606.7 1631.1 1657.1 1682.3 1704.5 1725.8 1744.4 1773.8 1797.0

0.0000 0.5079 0.9376 1.4064 1.8166 2.3831 2.8519 3.2425 3.6722 4.2973 4.4731

0.9876 1.0082 1.0279

1569.7 1592.6 1616.7

CaSO4 (mol·kg−1) 10% MeOH 0.0075 0.0204 0.0265 0.0295 0.0323 0.0355 0.0347 0.0342 0.0350 0.0332 0.0326 5% EtOH 0.0025 0.0220 0.0310 0.0409 0.0451 0.0456 0.0449 0.0431 0.0424 0.0386 0.0372 15% EtOH 0.0038 0.0110 0.0154 0.0186 0.0206 0.0230 0.0236 0.0235 0.0241 0.0240 0.0228 7.5% IPA 0.0067 0.0207 0.0267 0.0307 0.0340 0.0350 0.0360 0.0352 0.0346 0.0345 0.0328

ρ (g·cm−3)

u (m·s−1)

0.9806 1.0017 1.0186 1.0361 1.0515 1.0740 1.0920 1.1051 1.1099 1.1342 1.1460

1543.5 1568.1 1592.8 1617.1 1641.0 1673.7 1698.8 1718.7 1726.1 1761.5 1784.4

0.9906 1.0090 1.0250 1.0520 1.0750 1.0898 1.1136 1.1279 1.1351 1.1637 1.1797

1542.9 1574.9 1597.1 1623.2 1653.2 1676.4 1715.9 1740.2 1749.0 1795.4 1825.8

0.9717 0.9887 1.0043 1.0187 1.0360 1.0478 1.0622 1.0769 1.0916 1.1024 1.1244

1590.4 1607.8 1626.0 1644.3 1661.7 1678.3 1693.6 1712.1 1727.9 1747.6 1775. 5

0.9918 1.0098 1.0262 1.0446 1.0610 1.0821 1.0990 1.1156 1.1305 1.1492 1.1541

1566.2 1590.0 1612.9 1637.6 1661.2 1689.1 1710.7 1725.7 1747.9 1775.0 1786.1

10% IPA

B

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Table 2. continued NaCl (mol·kg−1)

CaSO4 (mol·kg−1)

ρ (g·cm−3)

u (m·s−1)

1.3478 1.7971 2.2268 2.6956 3.1644 3.5550 4.0629

0.0263 0.0289 0.0311 0.0325 0.0315 0.0312 0.0314

1.0476 1.0631 1.0817 1.1039 1.1140 1.1284 1.1543

1641.1 1667.1 1685.3 1710.5 1728.8 1748.4 1770.8

NaCl (mol·kg−1)

CaSO4 (mol·kg−1)

ρ (g·cm−3)

u (m·s−1)

10% IPA

Standard uncertainties u are u(m) = 0.002 mol·kg−1, u(T) = 0.01 °C, and u(P) = 10 kPa; the expanded uncertainties U are U(ρ) = 0.010 g·cm−3, U(u) = 0.5 m·s −1, and Ur(w) = 0.05 for alcohol content in solution (0.95 level of confidence, k = 2).

a

Figure 1. Solubility behavior of CaSO4·2H2O at various concentrations of alcohol aqueous solution with varying NaCl. Alcohols are (A) methanol, (B) ethanol, and (C) isopropyl alcohol (A, B: ▼, Milli-Q; ■, 5%; ●, 10%; ◆, 15%. C: ▼, Milii-Q; ■, 5%; ●, 7.5%; ◆, 10%). Lines are a polynomial fit to the experimental data.

Figure 2. Density (ρ) of CaSO4·2H2O at various concentrations of alcohol aqueous solution with varying NaCl. Alcohols are (A) methanol, (B) ethanol, and (C) isopropyl alcohol (A, B: ▼, Milli-Q; ■, 5%; ●, 10%; ◆, 15%. C: ▼, Milli-Q; ■, 5%; ●, 7.5%; ◆, 10%). Lines are a polynomial fit to the experimental data. C

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Table 3. Parameters Ai and Standard Deviations σ of eq 1 for the Systems CaSO4·2H2O−NaCl−Water−Alcohols at 35 °C additive

A0

5% MeOH 10% MeOH 15% MeOH 5% EtOH 10% EtOH 15% EtOH 5% IPA 7.5% IPA 10% IPA

0.0044 0.0083 0.0030 0.0033 0.0065 0.0043 0.0105 0.0075 0.0063

5% MeOH 10% MeOH 15% MeOH 5% EtOH 10% EtOH 15% EtOH 5% IPA 7.5% IPA 10% IPA

0.9914 0.9850 0.9768 0.9935 0.9832 0.9739 0.9956 0.9926 0.9874

5% MeOH 10% MeOH 15% MeOH 5% EtOH 10% EtOH 15% EtOH 5% IPA 7.5% IPA 10% IPA

1532.92 1544.60 1569.08 1544.00 1560.47 1589.62 1556.47 1568.08 1572.22

5% MeOH 10% MeOH 15% MeOH 5% EtOH 10% EtOH 15% EtOH 5% IPA 7.5% IPA 10% IPA

429.94 428.56 419.56 422.99 418.72 406.94 418.37 411.76 411.51

A1

A2

Solubility (mol·kg−1) 0.0403 −0.0123 0.0256 −0.0078 0.0257 −0.0096 0.0389 −0.0110 0.0236 −0.0067 0.0172 −0.0049 0.0288 −0.0087 0.0273 −0.0084 0.0235 −0.0071 Density, ρ (g·cm−3) 0.0370 0.0361 0.0383 0.0354 0.0362 0.0371 0.0372 0.0369 0.0368 Velocity of Sound, u (m·s−1) 53.58 53.09 50.66 51.73 49.83 44.78 49.48 48.99 49.87 Isentropic Compressibility, κS·1012 (Pa−1) −46.20 2.90 −49.71 4.45 −50.37 6.17 −44.77 3.43 −47.61 3.76 −42.05 5.11 −48.06 4.88 −42.51 2.43 −42.58 2.17

σ

A3 0.0011 0.0007 0.0012 0.0009 0.0006 0.0004 0.0008 0.0008 0.0007

5.94 × 10−4 1.17 × 10−4 1.36 × 10−4 4.64 × 10−4 7.87 × 10−4 5.54 × 10−4 1.00 × 10−4 1.25 × 10−4 1.32 × 10−4 0.0018 0.0016 0.0015 0.0005 0.0005 0.0004 0.0003 0.0005 0.0004 0.4924 0.4125 0.4705 0.5897 0.7350 0.5914 0.6364 0.5894 0.7987

−0.07 −0.22 −0.64 −0.17 −0.12 −0.58 −0.31 0.02 0.11

0.16 0.13 0.23 0.01 0.16 0.16 0.64 0.77 0.81

2. EXPERIMENTAL SECTION Materials. All materials used in this study are mentioned in Table 1. Preparation of Solutions. Solutions were prepared by weight, using an analytical balance with a precision of ±0.0001 g (Denver Instrument APX-200) in Millipore grade water. Stock solutions of the different amounts of alcohols + saturated NaCl were prepared by adding NaCl to the respective aqueous alcohol solution. A range of solutions were then prepared and analyzed as described in our earlier paper.24,25 Analysis of samples indicated an error of EtOH > MeOH. The solubility maximum at a concentration of 10 wt % organic solvent in the solution was 0.0325, 0.0332, and 0.0355 mol·kg−1 for IPA, EtOH, and MeOH, respectively. Water molecules can form a strong hydrogen bond with small alcohols. Due to this H-bonding, the availability of free water molecules decreases and results in a decreased solubility of CaSO4·2H2O. Moreover, the number of void spaces also decreases due to H-bonding in the system and hence lesser accommodation of Ca2+ and SO42− ions. Density

F(Q ) = A 0 + A1(m NaCl) + A 2 (m NaCl)2 + A3(m NaCl)3

(1)

where Q represents the experimentally determined property or a derived function and m is the molality (mol·kg−1) of NaCl in the solution. The method of least-squares with all points equally weighted was used to evaluate A0, A1, A2, and A3. Fitting parameters can be correlated with concentration to generate the appropriate model for a measured physical property. A0, A1, A2, and A3 values and standard deviations are provided in Table 3. Figure 1 depicts the effects of MeOH, EtOH (concentration: 5.0, 10.0, and 15.0% w/v), and IPA (concentration: 5.0, 7.5, and 10.0% w/v) on dissolution of CaSO4·2H2O in aqueous NaCl solutions up to ∼5 mol·kg−1. In the case of solutions without any additive, the solubility of CaSO4·2H2O increases with an increase in NaCl concentration, reaches a maximum (0.051 mol·kg−1) around 2.5 mol·kg−1 NaCl concentration, and then starts decreasing. F

DOI: 10.1021/acs.jced.8b00723 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Figure 6. Real time crystal growth in aqueous solutions of CaSO4·2H2O + NaCl + IPA (10 wt %).

10 wt % MeOH, EtOH, or IPA), whereas Figure 5E−G shows crystals of CaSO4·2H2O grown in aqueous NaCl−alcohol solutions (containing 10 wt % MeOH, EtOH, or IPA) where CaSO4·2H2O has maximum solubility at 35 °C. SEM images of CaSO4·2H2O crystals grown in aqueous NaCl−alcohol solutions (different alcohol contents) are provided in the Supporting Information (Figures S1 and S2, Supporting Information). All crystals are rigid, and alcohol additives do not exhibit any significant effect on the morphology or elemental composition (EDX spectra, Figures S3 and S4 and Tables TS1 and TS2, Supporting Information). It has been observed that some gypsum crystals are thicker than the others which can be due to the surface adsorption. Figure 5H−M shows elemental mapping for crystals grown from a representative solution containing NaCl and IPA (7.5 wt %) wherein it has been clearly seen that NaCl is cocrystallizing over CaSO4·2H2O crystals, indicating that gypsum is crystallizing prior to sodium chloride. This is quite obvious, as gypsum has very low solubility as compared to NaCl. It has also been reported that sodium ions become partially incorporated into the gypsum structure when these are crystallized from aqueous NaCl solutions.32 We have also captured real time crystal growth images of precipitation of CaSO4·2H2O from various aqueous NaCl−alcohol solutions. Representative real time crystal growth images of CaSO4·2H2O from aqueous NaCl−IPA (wt %) solution is provided in Figure 6, and for other alcohol solutions (methanol and ethanol), the images are provided as Supporting Information (Figures S5 and S6).

(ρ) and speed of sound (u) values for the quaternary systems CaSO4·2H2O + NaCl + EtOH/MeOH/IPA + H2O at 35 °C of varying alcohol content in the solutions as a function of NaCl concentration are plotted in Figures 2 and 3. Both ρ and u increase linearly as the concentration of CaSO4·2H2O and NaCl increases. Moreover, the density of the system decreases with increasing alcohol concentration in the system. The significant reduction in the density is observed for thhe 10% w/v IPA system which is likely due to the salting out effect. It is also reported that breaking of the hydrogen bonding network in the isopropanol−water solutions results in an enhancement of the entropy of mixing due to inhomogeneous mixing at the microscopic level.34 This may be another reason for the decreased density of IPA containing solutions. The isentropic compressibility (κS) of the solutions was derived from ρ and u using the Newton−Laplace equation. κS = 1/u 2ρ

(2)

The κS data are fitted to polynomial eq 1. A nonlinear decrease in κS of solution with an increase in alcohol content as well as with the increase in total salt concentration is observed, Figure 4. κS is reflecting the disruption of the water hydrogen bonding network, resulting in a more rigid solution structure. The surface morphology of gypsum crystals obtained from aqueous solutions of alcohols was studied through FE-SEM. Figure 5A−D shows the comparison of crystals of CaSO4·2H2O crystallized from water and aqueous alcohol solutions (containing G

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(2) Cornelis, K.; Cornelius, S. H., Jr. Manual of Mineralogy, 20th ed.; John Wiley: 1985; pp 352−353. (3) Gypsum mineral in http://webmineral.com/data/Gypsum.shtml. (4) Bock, E. On the solubility of anhydrous calcium sulphate and of gypsum in concentrated solutions of sodium chloride at 25, 30, 35, 40, 45, and 50°C. Can. J. Chem. 1961, 39, 1746−1751. (5) Shukla, J.; Mohandas, V. P.; Kumar, A. Effect of pH on the Solubility of CaSO 4 ·2H 2 O in Aqueous NaCl solutions and Physicochemical Solution Properties at 35 °C. J. Chem. Eng. Data 2008, 53, 2797−2800. (6) Raju, U. G. K.; Atkinson, G. The Thermodynamics of “Scale” Mineral Solubilities. 3. Calcium Sulfate in Aqueous NaCl. J. Chem. Eng. Data 1990, 35, 361−367. (7) Kumar, A.; Sanghavi, R.; Mohandas, V. P. Solubility Pattern of CaSO42H2O in the System NaCl + CaCl2 + H2O and Solution Densities at 35°C: Non ideality and Ion Pairing. J. Chem. Eng. Data 2007, 52, 902−905. (8) Hill, A. E.; Yanick, N. S. Ternary Systems. XX. Calcium Sulfate, Ammonium Sulfate and Water. J. Am. Chem. Soc. 1935, 57, 645−651. (9) Dutrizac, J. E. Calcium sulphate solubilities in simulated zinc processing solutions. Hydrometallurgy 2002, 65, 109−135. (10) Hasson, D. Precipitation fouling. In Fouling of Heat Transfer Equipment; Somerscales, E., Knudsen, J., Eds.; Hemisphere: Washington, DC, 1981; pp 527−568. (11) Hill, A. E.; Wills, J. H. Ternary Systems. XXIV. Calcium Sulfate, Sodium Sulfate and Water. J. Am. Chem. Soc. 1938, 60, 1647−1655. (12) Macedonio, E.; Drioli, G. A. A.; Bardow, A.; Semiatf, R.; Kurihara, M. Efficient technologies for worldwide clean water supply. Chem. Eng. Process. 2012, 51, 2−17. (13) Frenkel, V. S. Sea vs. Bay Water Desalination: Which One is for You? World Environmental and Water Resources Congress 2010, 3542− 3551. (14) Bader, M. S. Methods to produce sulfate free saline water and gypsum. US Patent 7,392,848, 2008. (15) Macedonio, F.; Drioli, E.; Gusev, A. A.; Bardow, A.; Semiat, R.; Kurihara, M. Efficient technologies for worldwide clean water supply. Chem. Eng. Process. 2012, 51, 2−17. (16) Bacchin, P.; Si-Hassen, D.; Starov, V.; Clifton, M. J.; Aimar, P. A unifying model for concentration polarization, gel-layer formation and particle deposition in cross-flow membrane filtration of colloidal suspensions. Chem. Eng. Sci. 2002, 57, 77−91. (17) Koyuncu, I.; Wiesner, M. R. Morphological variations of precipitated salts on NF and RO membranes. Environ. Eng. Sci. 2007, 24, 602−614. (18) McCartney, E. R.; Alexander, A. E. The effect of additives upon the process of crystallization, I. Crystallization of calcium sulphate. J. Colloid Sci. 1958, 13, 383−396. (19) Kuntze, R. A. Retardation of the crystallization of calcium sulphate dehydrate. Nature 1966, 211, 406−407. (20) Jones, L. W. Development of a Mineral Scale Inhibitor. Corrosion 1961, 17, 232t−236t. (21) Amjad, Z. Applications of antiscalants to control calcium sulfate scaling in reverse osmosis systems. Desalination 1985, 54, 263−276. (22) Li, Z.; Demopoulos, G. P. Effect of NaCl, MgCl2FeCl2FeCl3 and AlCl3 on Solubility of CaSO4 Phases in Aqueous HCl or HCl + CaCl2 Solutions at 298 to 353 K. J. Chem. Eng. Data 2006, 51, 569−576. (23) Kumar, A.; Shukla, J.; Dangar, Y.; Mohandas, V. P. Effect of MgCl2 on the Solubility of CaSO4·2H2O in the Aqueous NaCl System and Physicochemical Solution Properties at 35°C. J. Chem. Eng. Data 2010, 55, 1675−1678. (24) Trivedi, T. J.; Pandya, P.; Kumar, A. Effect of Organic Additives on the Solubility Behavior and Morphology of Calcium Sulfate Dihydrate (Gypsum) in the Aqueous Sodium Chloride System and Physicochemical Solution Properties at 35 °C. J. Chem. Eng. Data 2013, 58, 773−779. (25) Kaur, M.; Srinivasa Rao, K.; Singh, T.; Mohandas, V. P.; Kumar, A. Effect of Ethylene Glycol and Its Derivatives on the Solubility Behavior of CaSO4·2H2O in the Aqueous NaCl System and

Real time crystal growth analysis revealed an indirect kinetics (where the microscopes can be used to observe or count the number of crystals which already grow into a big size) of CaSO4· 2H2O and NaCl crystallization in the presence of alcohols. As we can see, the crystallization starts after ∼10 min and lasts about ∼60 min, and after a certain period, already formed crystals grow in size instead of forming new crystals which is a common phenomenon in crystal growth. Crystal growth behavior is almost similar in the presence of different alcohols except that, with increasing chain length of alcohol, the crystals are slightly forming earlier. This is in correlation with the fact that the solubility of gypsum is decreasing with increasing alcohol chain length.

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CONCLUSIONS The solubility behavior of CaSO4·2H2O in brines has been determined in the presence of methanol, ethanol, and isopropyl alcohol. It has been found that all of the alcohols lead to antisolvent crystallization and reduce the solubility of CaSO4·2H2O significantly. The solubility maximum of CaSO4·2H2O also shifts toward a lower concentration of NaCl in the aqueous alcohol solutions. Solutions become less dense with an increase in alcohol content. Solution compressibility decreases with an increase of alcohol content as well as with an increase in total salt concentration, indicating the disruption of the water hydrogen bonding network. The morphology of CaSO4·2H2O when crystallized from aqueous or aqueous NaCl solutions containing alcohols is not altered significantly. The crystal growth behavior of CaSO4·2H2O is also nearly similar for all of the investigated alcohols. The solution property data generated in this report can be effectively used in industrial applications where alcohols are used as antisolvents for gypsum precipitation from brines.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.8b00723.

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FE-SEM images of crystals, EDX spectra of crystals, and real time crystal growth (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +91-278-2567039. Fax: +91-278-2567562. ORCID

Arvind Kumar: 0000-0001-9236-532X Funding

CSIR India is gratefully acknowledged for supporting the research as part of an in-house project. M.J.M. acknowledges UGC for MANF-JRF (MANF-2017-18-GUJ-73741). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The analytical division of CSIR-CSMCRI is acknowledged for sample characterization. REFERENCES

(1) Deer, W. A.; Howie, R. A.; Zussman, J. An Introduction to the Rock Forming Minerals; Longman: London, 1966; p 469. H

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DOI: 10.1021/acs.jced.8b00723 J. Chem. Eng. Data XXXX, XXX, XXX−XXX