The effect of 2-propanol, ferrous sulfate and copper chloride on the solubility and physicochemical properties of acidic copper sulfate solutions at 298.15 K

The effect of 2-propanol, ferrous sulfate and copper chloride on the solubility and physicochemical properties of acidic copper sulfate solutions at 298.15 K

Fluid Phase Equilibria 391 (2015) 78–84 Contents lists available at ScienceDirect Fluid Phase Equilibria j o u r n a l h o m e p a g e : w w w . e l...

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Fluid Phase Equilibria 391 (2015) 78–84

Contents lists available at ScienceDirect

Fluid Phase Equilibria j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / fl u i d

The effect of 2-propanol, ferrous sulfate and copper chloride on the solubility and physicochemical properties of acidic copper sulfate solutions at 298.15 K M.E. Taboada a,b, * , M. Claros a , E.K. Flores b , T.A. Graber a,b , Silvia Bolado c a

Departamento de Ingeniería Química, CICITEM, Universidad de Antofagasta, Av. Angamos 601, Antofagasta, Chile Centro de Investigación Científico y Tecnológico para la Minería (CICITEM R10C1004), Antofagasta, Chile Departamento de Ingeniería Química y Tecnología del Medio Ambiente, Escuela de Ingenierías Industriales, Universidad de Valladolid, Dr. Mergelina s/n, 47005 Valladolid, Spain b c

A R T I C L E I N F O

A B S T R A C T

Article history: Received 22 October 2014 Received in revised form 20 January 2015 Accepted 29 January 2015 Available online 30 January 2015

Solubility, density and the refractive index were determined for saturated solutions of the systems CuSO4 + H2SO4 + (2-propanol + H2O), CuSO4 + H2SO4 + (FeSO4 + H2O) and CuSO4 + CuCl2 + (H2SO4 + H2O). The experimental study was carried out at 298.15 K, and for different mass ratios of 0.04 of 2-propanol/ water, 0.02 and 0.002 of ferrous sulfate/water and 0.1 of sulfuric acid/water, respectively. 2-Propanol has a drowning-out effect, decreasing copper sulphate solubility. No remarkable effect was found when adding FeSO4. With the experimental results obtained, the phase diagrams and their regions were determined. The most important precipitated salt for all the analyzed systems is copper sulfate pentahydrate. The experimental data on solubility and physical properties of the copper sulphate as a function of the sulfuric acid concentration were correlated with empirical equations for all the systems. ã 2015 Elsevier B.V. All rights reserved.

Keywords: CuSO4 Solubility H2SO4 Physical properties 2-Propanol FeSO4 CuCl2

1. Introduction Copper sulfate has a great variety of applications in different areas, such as agriculture [1], environment, industry and metallurgy [2]. There are several methods for obtaining copper sulfate pentahydrate crystals (CuSO45H2O), crystallization by cooling [3,4] or evaporating [5,6], both of which involve high energy requirements that raise operational costs. One of the methods to be explored is the addition of a third compound in the water–copper sulfate system, known as drowning-out crystallization [7], which decreases the solubility of the desired salt and causes copper sulfate crystallization. The first step for this alternative is to determine the solubility isotherms with the addition of a co-solvent. One of the most common co-solvents used is sulfuric acid. The solubility isotherm for this system can be obtained from Linke and Seidell [8]. De Juan et al. [9] determined the solubility of copper sulfate at different acid concentrations and temperatures. As was expected, the solubility of the salt decreases with the addition of

* Corresponding author. Tel.: +5655 637313; fax: +5655 240152. E-mail address: [email protected] (M.E. Taboada). http://dx.doi.org/10.1016/j.fluid.2015.01.023 0378-3812/ ã 2015 Elsevier B.V. All rights reserved.

sulfuric acid at low temperatures. However, it is known that the quantity and quality of the crystal depends on the amount of acid present in the solution, as well as the temperature. The addition of sulfuric acid leads to the formation of finer crystals with fewer hydration water molecules [4]. Consequently, it is necessary at the industrial level to re-crystallize the CuSO4 obtained, from which CuSO45H2O crystals are obtained with commercial purity and size. An alternative to the conventional process is to carry out only one crystallization stage by adding another solvent that decreases the solubility of copper sulphate and facilitates its crystallization as CuSO45H2O. This technique has been used to crystallize numerous salts, especially using alcohols as solvents to modify the phase equilibrium, among them, ethanol to crystallize LiOH [10] and CuSO4 [11], 2-propanol for K2SO4 [12], and methanol and 2-propanol to crystallize CaSO4 [13]. Graber et al. [10] determined the behavior of crystals of LiOHH2O obtained by evaporation and drowning out with ethanol. They found that crystals obtained by a simple evaporation differed in morphology and solubility from those precipitated by the addition of ethanol as a co-solvent. Polymorphic behavior of the crystals was evidenced from X-ray diffraction patterns. Aktas [11] studied the technology of adding a second solvent, 1-propanol, to aqueous solutions of potassium sulfate in an automated reactor–crystallizer. The results show that the

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Fig. 1. Phase diagram for the CuSO4 + H2SO4 + (0.04 2-propanol + H2O) system at 298.15 K, in mass fraction, (&) experimental equilibrium data, (—) solubility curve (Eq. (1) and Table 5), (—) last value obtained.

drowning-out of potassium sulfate using 1-propanol is an alternative to crystallization by cooling, delivering a similar basic crystal quality, but with greater agglomeration. In particular, isopropyl alcohol has been used to electrochemically crystallize CuSO4 in aqueous solutions [14], ethanol has been used to determine changes in the solubility of copper sulfate in the system CuSO4 + water + ethanol at different temperatures [15] and ethanol has also been used to selectively crystallize CuSO4 [11]. The selective crystallization of copper sulfate was performed by adding ethanol, leaving impurities in the solution and obtaining an analytical grade product with several precipitations. Evaluation of different parameters indicated that selective separation is possible, since, there is no precipitation of salts at low concentrations. The presence of ethanol decreases the thermodynamic activity of water and the dielectric constant of the medium and makes water less available as a ligand for Cu2+ and SO42. In the case of pH, the precipitation efficiency increases with higher pH, which was attributed to the appearance of HSO4 assuming that it interferes with the formation of the Cu—SO4 bond. The effect of adding ethanol was also studied at an ethanol/aqueous solution ratio of 4 and the precipitation efficiency at nearly 100%. With this simple

Fig. 2. Solubility curves for the CuSO4 + H2SO4 + H2O system at 298.15 K, in mass fraction with and without 2-propanol. The range of each solid phase is indicated with perpendicular lines. (—) solubility curve with 2-propanol, (—) solubility curve without 2-propanol obtained from [8].

Fig. 3. Diffractogram (a). Black line represent the experimental sample and red line the copper sulphate pentahydrate pattern from databases and thermogravimetric curve (b) of copper sulfate pentahydrate. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

process, the authors obtained high quality copper sulfate pentahydrate crystals. However, the study did not involve the size and shape of the product, which could be affected by the addition of ethanol. Rocha et al. [16] studied the solid–liquid equilibrium of the CuSO4 + NaCl + (H2O or H2SO4/H2O) system at 298.15 K by the wet residue method. The density and refractive index of saturated solutions were also measured. The addition of NaCl has a clear effect on the solid–liquid equilibrium, promoting the formation of solid phases. In the phase equilibrium diagram that includes sulfuric acid, pH affects the solubility curve. Using the information Table 1 Experimental data refractive index and densities of the saturated solutions of the CuSO4 (1) + H2SO4 (2) + (0.04 2-propanol + H2O) ternary system at 298.15 K, w1, CuSO4,w2, H2SO4 and w3, H2O 1 atm. w1

w2

w3

r/g cm3

nD

Solid phase

0.1357 0.1159 0.0929 0.0484 0.0213 0.0235 0.0202 0.0230 0.0179 0.0079 0.0038 0.0037 0.0023 0.0015 0.0012 0.0012 0.0020 0.0026 0.0010

0.0000 0.0751 0.1384 0.2662 0.4404 0.4800 0.4983 0.5286 0.5917 0.6385 0.6579 0.6841 0.7556 0.7930 0.8293 0.8205 0.8897 0.8941 0.9423

0.8311 0.7779 0.7391 0.6590 0.5176 0.4774 0.4630 0.4312 0.3754 0.3400 0.3253 0.3002 0.2328 0.1976 0.1630 0.1714 0.1041 0.0993 0.0545

1.1419 1.1687 1.1881 1.2336 1.3361 1.3721 1.3868 1.4185 1.4840 1.5115 1.5152 1.5641 1.6306 1.6614 1.7195 1.7237 1.7850 1.8005 1.8191

1.3616 1.3650 1.3675 1.3743 1.3889 1.3933 1.3962 1.3992 1.4071 1.4104 1.4108 1.4166 1.4242 1.4274 1.4330 1.4334 1.4362 1.4359 1.4325

CuSO45H2O CuSO45H2O CuSO45H2O CuSO45H2O CuSO45H2O CuSO45H2O CuSO45H2O + CuSO43H2Oa CuSO43H2O CuSO43H2O CuSO43H2O CuSO43H2O + CuSO4H2Oa CuSO4H2O CuSO4H2O CuSO4H2O CuSO4H2O CuSO4H2O CuSO4H2O CuSO4H2O CuSO4H2O

The average standard deviation, ASD was 0.0003, 0.001 and 0.0006 for concentrations, density, and refractive index, respectively. a Invariant points.

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Table 2 Experimental data refractive index and densities of the saturated solutions of the CuSO4 + H2SO4 + (0.002 g FeSO4/g H2O) ternary system at 298.15 K, w1, CuSO4, w2, H2SO4 and w3, H2O 1 atm. w1

w2

w3

r/g cm3

nD

Solid phase

0.1802 0.1149 0.0596 0.0236 0.0245 0.0246 0.0298 0.0212 0.0205 0.0043 0.0083 0.0039 0.0015 0.0013 0.0011 0.0026

0.0000 0.1327 0.2643 0.4404 0.4535 0.5244 0.5366 0.5694 0.6033 0.6834 0.6991 0.7109 0.7755 0.8253 0.8577 0.9297

0.8182 0.7509 0.6748 0.5349 0.5210 0.4501 0.4327 0.4086 0.3754 0.3117 0.2920 0.2846 0.2226 0.1731 0.1409 0.0676

1.2100 1.2199 1.2532 1.3564 1.3665 1.4282 1.4528 1.4738 1.5170 1.5728 1.5770 1.5826 1.6753 1.7428 1.7665 1.8040

1.3691 1.3696 1.3746 1.3890 1.3904 1.3944 1.4000 1.4044 1.4098 1.4166 1.4172 1.4177 1.4282 1.4343 1.4357 1.4357

CuSO45H2O CuSO45H2O CuSO45H2O CuSO4 5H2O CuSO45H2O CuSO45H2O CuSO45H2O + CuSO43H2Oa CuSO43H2O CuSO43H2O CuSO43H2O CuSO43H2O + CuSO4H2Oa CuSO4H2O CuSO4H2O CuSO4H2O CuSO4H2O CuSO4H2O

The average standard deviation, ASD was 0.0002, 0.0013 and 0.0005 for concentrations, density, and refractive index, respectively. a Invariant points.

equilibrium of copper sulphate aqueous acid systems is an interesting research subject. In order to investigate the effect of other co-solvents and the presence of certain impurities, such as ferrous sulfate or copper chloride in aqueous acid systems, this work has determined the solubility curves and crystallization areas of four systems: CuSO4 + H2SO4 + (2-propanol + H2O, mass ratio 0.04), CuSO4 + H2SO4 + (FeSO4 + H2O, mass ratio 0.02 and 0.002) and CuSO4 + CuCl2 + (H2SO4 + H2O, mass ratio 0.1), at 298.15 K. Density and refractive index of saturated solutions have been also determined. 2. Experimental 2.1. Chemicals All the reagents were used without purification and were obtained from Merck, copper sulfate pentahydrate, 99%; sulfuric acid, 96–97%; ferrous sulfate heptahydrate, 99.5%; 2-propanol, 99.7% and copper chloride dihydrate 99%. Ultrapure water was used for all the solutions obtained with a Millipore Co. “Ultrapure Cartridge Kit” with conductivity of 0.054 mS cm1. 2.2. Apparatus and procedure

of the new phase diagrams, six simulation cases, varying the NaCl content and the addition of sulfuric acid in the feed, were evaluated in terms of mass and energy balance. Contrary to what might be expected, the yields for the cases that include sulfuric acid were lower. The best results were obtained using a 50% NaCl pulp, which produced the lowest total flux and a high yield of 75.6%. In the present work, 2-propanol was used to modify the phase equilibrium of the system CuSO4 + H2SO4 + H2O at 298.15 K. 2-propanol has peculiar characteristics when compared with other alcohols like 1-propanol and ethanol, in terms of vapor– liquid equilibrium behavior with water and physicochemical properties like moment dipole. Sulphuric acid is widely used in industrial applications given that copper is lixiviated with sulphuric acid in hydrometallurgic processes, yielding a solution of CuSO4 dissolved in H2O + H2SO4. This solution also has other dissolved cations, the most important being iron, with concentrations between 2 and 5 g/L. These solutions sometimes contain chloride, with concentrations between 0 and 10 g/L. Therefore, the effect of iron sulphate and copper chloride in the phase

The solutions were prepared by mass using an analytical balance (0.07 mg precision, Mettler Toledo Co., model AX204). A stock solution was used to ensure the same ratio of 2-propanol and water in all experiments. Known masses of sulphuric acid and copper(II) sulfate pentahydrate were added in excess to reach slight oversaturation to the system CuSO4 + H2SO4 + (2-propanol + H2O) at a known quantity of a mixture of 2-propanol plus water at a ratio (0.04 g/g H2O) to reach slight oversaturation. In the second system CuSO4 + H2SO4 + (FeSO4 + H2O), different known concentrations of iron sulphate plus water in a ratio (0.002 and 0.02 g/g H2O) are mixed with known quantities of sulphuric acid and copper sulphate is added in excess to ensure its presence in the solid phase. In the third system CuSO4 + CuCl2 + (H2SO4 + H2O), the acid/ water mass ratio is maintained at 0.1. Known quantities of copper chloride and copper sulphate are added in excess. To estimate the mass of copper sulphate sufficient to ensure slight oversaturation, the data from ternary systems published by Linke and Seidell [8] are used as a baseline. The excess used was

Table 3 Experimental data refractive index and densities of the saturated solutions of the CuSO4 + H2SO4 + (0.02 g FeSO4/g H2O) ternary system at 298.15 K, w1, CuSO4, w2, H2SO4 and w3, H2O at 1 atm. w1

w2

w3

r/g cm3

nD

Solid phase

0.1734 0.1485 0.1061 0.0828 0.0516 0.0407 0.0254 0.0300 0.0298 0.0229 0.0217 0.0061 0.0083 0.0053 0.0026 0.0014 0.0018 0.0019

0.0000 0.0577 0.1279 0.1828 0.2563 0.3322 0.4387 0.4710 0.4996 0.5407 0.5697 0.6318 0.6360 0.6691 0.7263 0.7766 0.8657 0.8717

0.8104 0.7782 0.7510 0.7200 0.6785 0.6148 0.5254 0.4892 0.4614 0.4278 0.4006 0.3550 0.3487 0.3192 0.2658 0.2176 0.1299 0.1239

1.2243 1.2175 1.2304 1.2431 1.2652 1.2975 1.3626 1.4215 1.4325 1.4499 1.4710 1.5391 1.5505 1.5575 1.6130 1.6836 1.7863 1.7877

1.3713 1.3701 1.3711 1.3730 1.3763 1.3811 1.3900 1.3977 1.3986 1.4013 1.4040 1.4123 1.4142 1.4147 1.4212 1.4291 1.4363 1.4362

CuSO45H2O CuSO45H2O CuSO45H2O CuSO45H2O CuSO45H2O CuSO45H2O CuSO4 5H2O CuSO45H2O CuSO45H2O + CuSO43H2Oa CuSO43H2O CuSO43H2O CuSO43H2O CuSO43H2O + CuSO4H2Oa CuSO4H2O CuSO4 H2O CuSO4H2O CuSO4H2O CuSO4H2O

The average standard deviation (ASD) was 0.0011, 0.0018 and 0.0002 for concentrations, density and refractive index, respectively. a Invariant points.

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Table 4 Experimental data refractive index and densities of the saturated solutions of the CuSO4 + CuCl2 + (0.1 g H2SO4/g H2O) ternary system at 298.15 K, w1, CuSO4, w2, CuCl2 and w3, H2O 1 atm. w1

w2

w3

r/g cm3

nD

Solid phase

0.1497 0.0753 0.0211 0.0026 0.0097 0.0020

0.0000 0.0988 0.2612 0.3557 0.3820 0.3820

0.8419 0.8177 0.7106 0.6353 0.6023 0.6099

1.2127 1.2346 1.3583 1.4508 1.4809 1.5940

1.3685 1.3794 1.4127 1.4352 1.4455 1.4450

CuSO45H2O CuSO45H2O CuSO45H2O CuSO45H2O + CuSO4 4H2Oa CuSO44H2O + CuCl22H2Oa CuCl22H2O

The average standard deviation (ASD) was 0.0002, 0.0014 and 0.0003 for concentrations, density and refractive index, respectively. a Invariant points.

10% more than the value obtained from literature for all the systems. For the phase equilibrium determination at 298.15 K, a rotary thermostatic water bath (to 0.1 K, 50 rpm) was used with a rack for ten 90 mL glass flasks. The solutions were placed in closed glass flasks and immersed in the rotary water bath at 298.15 K. The flasks were mechanically shaken for 72 h until reaching equilibrium. The time to equilibrium was determined in preliminary tests. The rotation was then stopped, and the solutions in the flasks were decanted for 12 h at work temperature. Sample of the solutions were obtained for each equilibrium point using a syringe filter at a slightly elevated temperature (to prevent salt precipitation at lower temperatures), additionally the room temperature was 25  C using air conditioning system. In the saturated solutions, copper and iron were analyzed by atomic absorption (AA) and sulphate by gravimetric analysis. The composition of the solids was determined by the wet residue method [17]. The remainder of the solution is decanted and the wet residue of crystals is analyzed as a whole. The wet residue was weighted, dissolved in a known volume of water, and copper, iron and sulphate were analyzed in the resulting solution. Straight lines joining compositions of liquid and wet residue phases provided the solid phase in equilibrium. The solid phase was verified by X-ray diffraction and thermogravimetric analysis. Density and refractive index were measured for triplicate for each solution. The densities were measured using a Mettler Toledo, model DE-50 vibrating tube densimeter with 5  102 kg m3 precision. For temperature control, the densimeter has selfcontained Peltier systems with 0.01 K precision. The refractive index was measured using a Mettler Toledo Co., model RE-40 refractometer with 1 104 resolution. The instruments were calibrated with a certified standard liquid of 2,4-dichlorotoluene from Mettler Toledo.

Fig. 4. Phase diagram for the CuSO4 + H2SO4 + (0.002 g FeSO4/g H2O) system at 298.15 K, in mass fraction, (&) experimental equilibrium data, (—) solubility curve (Eq. (1) and, Table 5), (—) last value obtained.

4. Results and discussion 4.1. Phase diagrams and properties The experimental solubility data obtained to the system CuSO4 + H2SO4 + (2-propanol + H2O) to 298.15 K can be seen in Fig. 1. In this diagram, three hydrates of copper sulphate are formed with five, three and one water molecules, where the largest area corresponds to the CuSO45H2O crystallization zone. The experimental data does not allow the invariant for the monohydrate sulphate and anhydrous mixture, therefore, the final line has been drawn in dashes given that it corresponds to the last tie line obtained within the crystallization field of copper sulphate monohydrate. Fig. 2 compares the copper sulphate solubility in 2-propanol + H2SO4 + H2O system obtained in this work with solubility data in H2SO4 + H2O from the literature [8]. A difference in the solubility curve of copper sulphate pentahydrated can be appreciated. Solubility expressed as grams of copper sulphate in 100 g of solution decreases from 18.47% (binary solubility CuSO4 + H2O) to 13.57% (pseudo-binary solubility CuSO4 + 2-propanol/H2O) and consequently the unsaturated liquid area decreased when adding 2-propanol. Fig. 3 shows a diffractogram and a thermogravimetric curve for a solid sample in the crystallization field of copper sulphate pentahydrate as a sample of purity of the obtained solid phase. As well, the displacement and increase in the crystallization field of copper sulphate trihydrate and copper sulphate monohydrate in the system with 2-propanol was verified. Tables 1–4 present the physical properties determined for the saturated solutions. The values of the invariant points are detached in bold.

Fig. 5. Phase diagram for the CuSO4 + H2SO4 + (0.02 g FeSO4/g H2O) system at 298.15 K, in mass fraction, (&) experimental equilibrium data, (—) solubility curve (Eq. (1) and Table 5), (——) last tie-line obtained.

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Fig. 6. Phase diagram for the CuSO4 + CuCl2 + (0.1 g H2SO4/g H2O) system at 298.15 K, in mass fraction, (&) experimental equilibrium data, (—) solubility curve (Eq. (1) and Table 5).

From Table 1, an increase can be noted in density and the refractive index of the saturated solutions with increases in the concentration of sulphuric acid. As well, it can be appreciated a change in the density values tendency at each invariant point. Similar tendency changes are observed in copper sulphate solubility curve in Fig. 1, with two invariant points. To study the effect of the concentration of iron sulphate, two concentrations were used (0.02 and 0.002 g FeSO4/g H2O) in the system CuSO4 + H2SO4 + (FeSO4 + H2O). These concentrations of ferrous sulfate are common in industrial solutions from copper lixiviation. The experimental solubility data obtained for the two systems are shown in Figs. 4 and 5. Comparing Figs. 4 and 5 with the diagram of the ternary system CuSO4 + H2SO4 + H2O described by Linke and Seidell [8], iron sulphate has a minor effect in the copper sulphate solubility curve. The solubility expressed as grams of copper sulphate in 100 g of solution decreases from 18.47% (solubility of the binary CuSO4 + H2O) to 18.02% (solubility of the pseudo-binary CuSO4 + 0.002 g FeSO4/g H2O) and to 17.34% (CuSO4 + 0.02 g FeSO4/g H2O), respectively. The new CuSO45H2O field crystallization areas can be calculated using solubility data from Tables 2 and 3. Results of these calculations show an 11% decrease in the crystallization field of copper sulphate pentahydrate when increasing the iron sulphate concentration from 0.002 to 0.02 g FeSO4/g H2O. Minor variations in the crystallization field areas of copper sulphate trihydrate and monohydrate were found.

Fig. 8. Phase diagram for the CuSO4 + NaCl + (0.1 g H2SO4/g H2O) system at 298.15 K, (&) experimental equilibrium data, (—) solubility curve, in mass fraction, both from [16].

The physical properties determined for the saturated solutions are shown in Tables 2 and 3. Tables 2 and 3 show very similar values with an increase in density and the refractive index of the saturated solutions with the sulphuric acid mass fraction. The increase is slightly greater in the system with less iron. Comparing the invariant points obtained in Tables 2 and 3, although the increase in the concentration of FeSO4 from 0.002 to 0.02 g FeSO4/g H2O does not produce changes in the concentration of copper sulphate, the properties decrease slightly by the slightly lower concentration of sulphuric acid. Fig. 6 shows the phase equilibrium diagrams obtained for the system CuSO4 + CuCl2 + (0.1 g H2SO4/g H2O) at 298.15 K and for the effects of comparison, Fig. 7 shows the diagram for the acidless ternary system CuSO4 + CuCl2 + H2O a 298.15 K obtained from Druzhinin and Kosyakina [18]. By comparing Figs. 6 and 7, it can be appreciated that, adding sulphuric acid, the crystallization field of copper sulphate pentahydrate increased, the crystallization field of copper sulphate tetrahydrate decreased and copper sulphate trihydrate disappeared. The presence of sulphuric acid decreases the solubility of copper sulphate from 19% for the water–copper sulphate system to 16% for the ternary system and consequently the unsaturated liquid zone decreases. This difference, expressed with respect to water, changes from 23.5 to 21.4 g CuSO4/100 g H2O. Because of the effect of the common ion, the higher sulphate concentration facilitates the precipitation of copper sulphate. Something similar occurs with the concentration of copper, which favors the crystallization of copper sulphate. Fig. 8 shows the previously published phase equilibrium diagram for the system CuSO4 + NaCl + (0.1 g H2SO4/g H2O) at 298.15 K [16]. In this previous work, Rocha et al. found that adding NaCl has a clear effect on the solid–liquid equilibrium, promoting the formation of solid Table 5 Values of fitted parameters for solubility.

Fig. 7. Phase diagram for the CuSO4 + CuCl2 + H2O system at 298.15 K in mass fraction, from [18].

With 0.04 2propanol With 0.02 FeSO4 With 0.002 FeSO4 a

AAD = |

c

a

1.5646

1.34E-3

w0 (mass fraction)

a

0.1357

0.2359 0.7465

0.1734 0.1802

0.5577 0.2235 0.5524 2.17E-3 0.5054 0.0231 0.8249 7.67E-4

b

AAD

P (sexp  scal)/n|, where n is the number of experimental points.

M.E. Taboada et al. / Fluid Phase Equilibria 391 (2015) 78–84 Table 6 Parameters for density empirical equations.

r0/ g cm3

a

a

C

AAD

0.37972 0.54681 1.55795 5.17E-4 0.13881 1.21804 0.21179 5.69E-3 0.15777 1.33593 0.46102 4.29E-3

With 0.04 2-propanol 1.14190 With 0.02 FeSO4 1.22428 With 0.002 FeSO4 1.21000 a

b

The density and refractive index for the sulphate pentahydrate crystallization were adjusted to empirical Eqs. (2) and (3), respectively. The parameters adjusted for the three systems can be seen in Tables 6 and 7, where ru and hny indicate density and the refractive index for the solutions without sulphuric acid.

r ¼ r0 þ a  w2 þ b  w22 þ c  w32

(2)

hn ¼ hny þ a  w2 þ b  w22 þ c  w32

(3)

P AAD = | (sexp  scal)/n|, where n is the number of experimental points.

Table 7 Parameter for refractive index empirical equations.

Table 8 presents the data adjustment for concentration and properties of the experimental system CuSO4 + CuCl2 + (0.1 g H2SO4/g H2O) at 298.15 K, using Eqs. (1)–(3) for the copper sulphate pentahydrate crystallization field.

Refractive index parameters a

b

C

a

0.0483 0.0291 0.0010

0.0543 1.1412 0.0456

0.1942 0.0529 0.1108

1.05E-4 6.74E-3 9.18E-4

AAD

hn y With 0.04 2-propanol With 0.02 FeSO4 with 0.002 FeSO4 a

83

1.3616 1.3713 1.3691

P AAD = | (sexp  scal)/n|, where n is the number of experimental points.

phases. Comparing Figs. 7 and 8, it can be appreciated that by changing the cation from copper, which is a common cation, to sodium, major changes occur such as a significant decrease in the area of crystallization of copper sulphate pentahydrate. The tetrahydrate and trihydrate copper sulphate crystallization fields disappear when working with NaCl. As established by Rocha et al., the presence of the sodium ion favors the formation of solid solutions and the double salt CuSO4Na2SO42H2O, a product of the system being part of the reciprocal saline pair: 2NaCl + CuSO4 = CuCl2 + Na2SO4 In Table 4, because the sulphuric acid concentration remains constant with respect to the water, the increase in density is related to the concentration of copper chloride. The same effect can be appreciated in the refractive index. 4.2. Correlation of solubility and properties For the system CuSO4 (1) + H2SO4 (2) + (0.04 g 2-propanol/g H2O) the experimental solubility values of the systems for the copper sulphate pentahydrate crystallization field correlate adequately through Eq. (1), non-linear in function of the mass fraction of sulphuric acid where parameter w0 indicates the pseudo-binary solubility in this study. The adjustment parameters are shown in Table 5. w1 ¼ w0 þ aw2 þ bw22 þ cw32

5. Conclusions The presence of 2-propanol in a ratio of 2-propanol/ H2O = 0.04 in the ternary system of CuSO4 + H2SO4 + H2O decreases the solubility of copper sulphate, making the drowning-out effect with which the copper sulphate pentahydrate and trihydrate crystallization fields increase. In system CuSO4 + H2SO4 + H2O, the presence of FeSO4, in a ratio of FeSO4/H2O equal to 0.002 and 0.02 respectively, do not show significant changes for the iron concentrations used, except for displacements in the invariants. In the studied systems in the presence of 2-propanol or iron sulphate, three solid phases are observed: copper sulphate pentahydrate, copper sulphate trihydrate and copper sulphate monohydrate. These systems do not present the formation of double salts. The experimental solubility values of copper sulphate of the systems under study correlates adequately in function of the mass fraction of H2SO4 through Eq. (1) and the experimental density and refractive index values through Eqs. (2) and (3). The presence of sulphuric acid in the system CuSO4 + CuCl2 + H2O decreases the solubility of copper sulphate, increase the sulphate pentahydrate crystallization field, reduces the tetrahydrate field and causes trihydrate to disappear. Acknowledgments The authors are grateful for the financial support provided by CONICYT through Fondecyt Project no. 1140169 and CICITEMR04I1001.

(1) References

Table 8 Fitted parameters for the solubility of the system CuSO4 + CuCl2 + (0.1 g H2SO4/g H2O).

Solubility parameters Density parameters Refractive index parameters a

Parameter without CuCl2 Mass fraction for solubility and g cm

a

0.1497

0.7851

b

0.6461

C

a

1.1202

4.16E-3

AAD

1.21270

0.57554 1.02423 3.62122 7.27E-3

1.3685

0.1322

0.0857

0.2145

1.01E-3

P AAD = | (sexp  scal)/n|, where n is the number of experimental points.

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