Effect of Seawater on the Solubility and Physicochemical Properties of

Article pubs.acs.org/jced

Effect of Seawater on the Solubility and Physicochemical Properties of Acidic Copper Sulfate Solutions Pía C. Hernández, Héctor R. Galleguillos, Teófilo A. Graber, Elsa K. Flores,† and María E. Taboada* Departamento de Ingeniería Química, Facultad de Ingeniería, Universidad de Antofagasta, Av. Angamos 601, Antofagasta, Chile ABSTRACT: Seawater is an alternative to freshwater, which is scarce for copper mining in northern Chile, but it has components that may be problematic for hydrometallurgical processes. This work determines the influence of seawater on the solid−liquid equilibrium for acid solutions of CuSO4 at different temperatures, (298.15 to 323.15) K, and its effect on physical properties (density, refractive index, ionic conductivity, and viscosity). The measured properties show an average difference between CuSO4 in seawater and CuSO4 in freshwater of 1.42 % for solubility, 1 % for density, 0.29 % for refractive index, 24.61 % for ionic conductivity, and 5.61 % for viscosity. In addition, the physical properties of unsaturated solutions composed of CuSO4 in acidic seawater at different temperatures, (298.15 to 323.15) K, and molalities, (0.1 to 1.8) m, were measured. The experimental data for the physical properties were correlated using Othmer’s rule. This equation yields a good fit and predicts saturation data with the exception of ionic conductivity, where the Casteel−Amis equation is recommended. The solubilities and properties for both systems (acidic seawater and freshwater) are similar. This observation suggests that seawater may be appropriate for leaching with no major short-term effects. (Bester-Rogac,16 Taboada et al.,17 Christov,18 De Juan et al.,19 Giulietti et al.,20 Giulietti et al.,21 Ishii and Fujita,22 Linke and Seidell23). Certain researchers have studied copper equilibrium in chloride solutions and estimated its properties (Lundström et al.,24 Senanayake,25 Plyasunova et al.,26 Wang et al.,27,28 Nila and González,29 Winand,30 Berger and Winand31). In addition, differences between ions, density and viscosity of desalinated water and seawater in the mining process have been reported (Philippe et al.32). An industrial process using seawater in a copper−molybdenum plant has been described (Moreno et al.33). This work studies the effects of seawater (3.5 % salinity) on the solid−liquid equilibrium of copper sulfate in acid solutions at different temperatures, (298.15 to 323.15) K, for possible industrial applications. This paper provides data on solubilities and physical properties (density, refractive index, ionic conductivity and viscosity) for CuSO4 in seawater at pH 2. This pH was used because it is similar to the pH levels in copper mining operations. Data for solubility and density of the CuSO4 in H2O system at different temperatures have been reported in the literature (Linke and Seidell23). These values were used as a reference to determine the effect of acidic seawater. For this system, refractive index, ionic conductivity, and viscosity data were obtained through experimental measurements. Moreover, physical properties (density, refractive index, ionic conductivity, and viscosity) were measured for unsaturated solutions of the CuSO4 in acidic seawater system. These experimental data were fit using Othmer’s rule, and the Casteel− Amis equation was used for conductivity.

1. INTRODUCTION Water is important to copper hydrometallurgy. Currently, there is a worldwide shortage of available water. Therefore, mining industries are developing new methods to optimize water use. In northern Chile, for example, certain mining companies are using raw seawater in their production processes. In a mine, the solid−liquid equilibrium and physical properties of solutions change upon seawater incorporation into the process (especially the density and viscosity used in pipe-sizing and pumping calculations). These properties are related to the cost of energy required to bring seawater to mining operations (usually farther than 120 km). Seawater contains a high concentration of ions,1 especially Cl− and Na+. High ion concentrations can precipitate salt during the process. Therefore, it is important to know the saturation concentrations for solutions used in copper leaching to avoid salt precipitation and for operation design (stream of recycling or purges). No data in the literature are available for behavior of the copper sulfate in a seawater system. However, investigations have estimated such seawater properties as density, heat capacity, entropy, and equations of state (Feistel,2 Millero and Huang,3 Sun et al.,4 Feistel and Marion,5 Voigt6). Equilibrium studies have been performed for aqueous systems with inorganic salts in seawater, which have generated data for properties with similar salinities to seawater (Deng and Wang,7 Zhang and Han,8 Fabuss et al.,9 Korosi and Fabuss,10 Fabuss et al.11) as well as the behaviors of copper in seawater and copper-chlorine using an Eh-pH diagram (González-Dávila et al.,12 Glasby and Schulz,13 Beverskog and Puigdomenech,14 Bianchi and Longhi15). Copper sulfate in distilled water solutions has been investigated for crystallization, supersaturation, equilibrium, and properties © 2012 American Chemical Society

Received: March 23, 2012 Accepted: August 15, 2012 Published: August 29, 2012 2430

dx.doi.org/10.1021/je300444r | J. Chem. Eng. Data 2012, 57, 2430−2436

Journal of Chemical & Engineering Data

Article

Table 1. Individual Ions in Seawater from Bahiá San Jorge, Chile (mg·L−1) Na+

Mg+2

Ca+2

K+

B+3

Cu2+

Cl−

SO4−2

HCO3−

NO3−

9480

1190

386

374

4.6

0.072

18765

2771

142

2.05

refractometer with ± 1·10−4 resolution. Before taking measurements, both instruments were calibrated at atmospheric pressure using air and distilled deionized water (reference substances).36 The ionic conductivities were measured using an Orion model 170 conductivity meter, which has ≤ 0.5 % precision and was calibrated using a standard KCl solution. The kinematic viscosities were measured using a calibrated microOstwalt viscometer with a Schott-Gerate automatic measuring unit (model AVS 310), which was equipped with a thermostat (Schott-Gerate, model CT 52) for temperature regulation within ± 0.05 K. The absolute viscosities were measured by multiplying kinematic viscosity and corresponding density with ± 5·10−3 mPa·s precision for viscosity measurements. pH was measured using an Accumet pH meter 50 with a measurement range from −2 to 20 between (268.15 and 378.15) K as well as ± 0.002 precision. 2.3. Procedures. 2.3.1. Saturation Solutions. The known masses for copper(II) sulfate pentahydrate in a solution (seawater at pH 2) were measured using an analytical balance using solubility data for copper(II) sulfate pentahydrate in water (Linke and Seidell23). To ensure saturation of the solution, excess copper(II) sulfate pentahydrate was added. Acidic seawater was prepared before each measurement by adding sulfuric acid to seawater and magnetically stirring the solution until it reached a constant pH of 2. The solutions were placed in closed glass flasks and immersed in a rotary water bath at different temperatures (a range of (298.15 to 323.15) K). These flasks were mechanically shaken for 2 h until equilibrium. The time to equilibrium was measured in preliminary tests. The rotation was then stopped, and the solutions in the flasks were decanted for 1 h while maintaining the work temperature. Using a syringe filter at a slightly elevated temperature (to prevent salt precipitation at lower temperatures), the solutions (without solid) were obtained for each equilibrium. The physical properties were measured for each solution, and their concentrations were determined. CuSO4 solubility was obtained by stoichiometry from a copper concentration determined by volumetric oxide reduction. The solubilities were measured in triplicate. CuSO4 in freshwater solubility and density values were acquired from the literature (Linke and Seidell23). Additional

This work is part of a broader research strategy; the results from there may be useful for mining companies that use seawater in the leaching process (Taboada et al.34).

2. MATERIALS AND METHODS 2.1. Reagents. Analytical grade reagents were used without purification (copper(II) sulfate pentahydrate, Merck, 99 %; sulfuric acid, Merck, (95 to 97) %, absolute). All of the tests were performed using natural seawater. The seawater was obtained from San Jorge Bay, Antofagasta, Chile and was filtered in a quartz sand filter (50 μm) and a mechanical polyethylene filter (1 μm). Table 1 shows the composition of the seawater used in this paper, which was obtained by chemical analysis. The individual ions in seawater are similar to the ions reported by Luning Prak and O’Sullivan.35 Table 2 shows the physical properties Table 2. Experimentally Derived Physical Properties of Seawater at Different Temperatures system

T/K

ρ/g·cm−3

nD

κ/mS·cm−1

η/mPa·s

seawater

298.15 303.15 308.15 313.15 318.15 323.15

1.02302 1.02125 1.01938 1.01764 1.01538 1.01295

1.3387 1.3381 1.3373 1.3366 1.3358 1.3350

49.75 54.77 59.50 64.70 70.00 75.50

0.9640 0.8536 0.7725 0.7026 0.6424 0.5909

measured for the seawater. Ultrapure water was generated through a Millipore Co. “Ultrapure Cartridge Kit” with conductivity less than 0.05 μS·cm−1. 2.2. Apparatus. The solutions were prepared by mass using an analytical balance (0.07 mg precision, Mettler Toledo Co. model AX204). To generate phase equilibrium data at different temperatures, a rotary thermostatic water bath (to ± 0.1 K, 50 rpm) with a rack for ten 90 mL glass flasks was used. The densities were measured using a Mettler Toledo model DE-50 vibrating tube density meter with ± 5·10−2 kg·m−3 precision. For temperature control, the density meter had self-contained Peltier systems with ± 0.01 K precision. The refractive indices were determined using a Mettler Toledo Co. model RE-40

Table 3. Solubility (s), Density (ρ), Refractive Index (nD), Ionic Conductivity (κ), and Viscosity (η) for Saturated Solutions of Copper Sulfate in the Freshwater and Acidic Seawater Systems at Various Temperatures system CuSO4 + freshwater

CuSO4 + acidic seawater

a

T/K

s/g·(100 g solution)−1

ρ/g·cm−3

nD

κ/mS·cm−1

η/mPa·s

298.15 303.15 308.15 313.15 318.15 323.15 298.15 303.15 308.15 313.15 318.15 323.15

18.20a 19.40 20.74 22.30 23.95 25.30 18.06 19.22 20.64 21.88 23.33 24.83

1.21110a 1.23200 1.24980 1.26200 1.27400 1.29900 1.22705 1.24028 1.25869 1.27345 1.29296 1.31120

1.3688 1.3712 1.3734 1.3756 1.3782 1.3808 1.3731 1.3748 1.3772 1.3802 1.3821 1.3847

52.90 60.69 68.92 76.86 85.29 93.92 71.38 79.07 86.12 94.08 101.53 108.97

2.2153 2.1163 2.0306 1.9680 1.9322 1.9047 2.3166 2.2125 2.1351 2.1050 2.0551 2.0206

The solubilities and densities of CuSO4 in freshwater are literature values.23 2431



Article

Due to seawater salinity (presence of salts), density values for the copper sulfate in acidic seawater system are slightly higher (with an approximate average difference of 1 %) than the copper sulfate in the freshwater system (see Figure 2). Moreover, the density of the saturated solutions increased with temperature for both systems studied because the salt concentration is higher. The refractive indices for the saturated solutions comprising copper sulfate in acidic seawater are slightly higher (with an approximate average difference of 0.29 %) than for a copper sulfate in freshwater system; the indices are directly related to temperature (see Figure 3).

properties (refractive index, conductivity, and viscosity) were measured at concentration values for the reported solubility data (Table 3). 2.3.2. Unsaturated Solutions. Various molalities of copper sulfate in seawater at pH 2 below saturation were prepared by weighing know masses, which ranged from (0.1 to 1.8) mol·kg−1 with precisions less than 0.07 mg for the six temperatures studied. The physical property measurements were performed in triplicate for each solution in the saturated and unsaturated systems at the specified temperatures.

3. RESULTS AND DISCUSSION 3.1. Experimental Results. The solubilities, densities, refractive index, ionic conductivities, and viscosities are shown in Table 3 for both systems studied at different temperatures. The uncertainties are 0.093 % for solubility, 0.0011 g·cm−3 for density, 0.0003 for the refractive index, 0.24 mS·cm−1 for ionic conductivity, and 0.023 mPa·s for viscosity. The two systems have similar solubility values. The solubility values for the copper sulfate in freshwater system are 1.42 % higher than the copper sulfate in seawater system at pH 2. Figure 1

Figure 3. Refractive index for the saturated solutions: ◆, CuSO4 + freshwater; ▲, CuSO4 + seawater (pH 2); , linear trend added to guide the eye.

The ionic conductivity values increase with temperature for both systems studied. Moreover, the ionic conductivity values for the saturated solutions comprising copper sulfate in acidic seawater are higher than for freshwater (24.61 % average difference). The seawater system values are greater because of the salts therein (see Figure 4).

Figure 1. Solubility for the saturated solutions: ◆, CuSO4 + freshwater (values of ref 23); ▲, CuSO4 + seawater (pH 2); , linear trend added to guide the eye.

shows the solubility values for saturated solutions of copper sulfate in seawater compared with copper sulfate in freshwater (literature data) as a function of temperature. A slight increase in temperature increases the solubility values. Figures 2 through 5 show a comparison of the different physical property values for saturated solutions of copper sulfate in

Figure 4. Ionic conductivity for the saturated solutions: ◆, CuSO4 + freshwater; ▲, CuSO4 + seawater (pH 2); , linear trend added to guide the eye.

Figure 5 shows the viscosity values. The viscosities for saturated copper sulfate in acidic seawater are higher than for freshwater (5.61 % average difference) due to the different ions dissolved in seawater. The viscosity of a solution is always expected to be higher in solutions with high ion concentrations. The viscosities of both systems decrease with a temperature increase. The properties change linearly with temperature except for viscosity, which exhibits polynomial behavior in the range for the variables studied herein. Values for the physical properties of CuSO4 and acidic seawater (Table 3) as well as raw seawater (Table 2) are compared. The uncertainties for the values in Table 2 are

Figure 2. Density for the saturated solutions: ◆, CuSO4 + freshwater (values of ref 23); ▲, CuSO4 + seawater (pH 2); , linear trend added to guide the eye.

acidic seawater and freshwater as a function of temperature. The properties of copper sulfate in acidic seawater measured herein have higher values than copper sulfate in the freshwater system. Figures 2 through 5 show the same trends for the two systems (parallel curves). 2432



Article

copper sulfate behaves differently for both properties; these property values increase with temperature. Viscosity and conductivity for the systems studied herein exhibit reverse behaviors; an increase in temperature decreases viscosity and increases ionic conductivity. Table 4 shows the experimental values for the physical properties measured in the unsaturated aqueous solutions composed of copper sulfate in acidic seawater at different molalities and temperatures. The uncertainties for the values measured are 0.00002 g·cm−3 for density, 0.00004 for the refractive index, 0.00027 mS·cm−1 for ionic conductivity, and 0.337 mPa·s for viscosity. 3.2. Correlations. Using eq 1, which is Othmer’s rule (Korosi and Fabuss10), the experimental values of the physical properties for the unsaturated solutions composed of copper sulfate in acidic seawater were correlated.

Figure 5. Viscosity for the saturated solutions: ◆, CuSO4 + freshwater; ▲, CuSO4 + seawater (pH 2); , linear trend added to guide the eye.

0.00001 g·cm−3 for density, 0.00001 for refractive index, 0.03 mS·cm−1 for ionic conductivity, and 0.0001 mPa·s for viscosity. The property values increase upon addition of CuSO4. The property values for copper sulfate and acidic seawater are 19.60 %, 3.03 %, 30.82 %, and 64.96 % higher than raw seawater for density, refractive index, ionic conductivity, and viscosity values, respectively. The densities and refractive indices in seawater are nearly temperature-independent with a slight downward trend as temperature increases. However, the acidic seawater-saturated

log YR = A 0 + B0 ·log YH2O

(1)

YR represents the ratio between the experimental value of the physical property Y (in this case, density, refractive index, ionic conductivity, or viscosity) and the physical properties of water (YH2O) at the same temperature. The units for density, ionic conductivity, and viscosity used in this equation are in g·cm−3, mS·cm−1, and mPa·s, respectively. The parameters A0 and B0 are in function of the copper sulfate ionic strength and are

Table 4. Density (ρ), Refractive Index (nD), Ionic Conductivity (κ), and Viscosity (η) for the Unsaturated Copper Sulfate and Acidic Seawater System at Various Molalities and Temperatures m/mol·kg−1

ρ/g·cm−3

0.10 0.25 0.40 0.55 0.70 0.85 1.00 1.15

1.03923 1.06270 1.08574 1.10845 1.13082 1.15299 1.17480 1.19639

0.10 0.25 0.40 0.55 0.70 0.85 1.00 1.15 1.35

1.03753 1.06086 1.08396 1.10642 1.12863 1.15069 1.17247 1.19395 1.22320

0.10 0.25 0.40 0.55 0.70 0.85 1.00 1.15 1.35

1.03568 1.05888 1.08176 1.10423 1.12639 1.14831 1.17002 1.19143 1.22073

0.10 0.25 0.40

1.03363 1.05674 1.07958

nD 298.15 K 1.3418 1.3458 1.3497 1.3536 1.3574 1.3611 1.3647 1.3683 303.15 K 1.3412 1.3451 1.3491 1.3529 1.3567 1.3603 1.3642 1.3674 1.3723 308.15 K 1.3407 1.3445 1.3485 1.3522 1.3561 1.3597 1.3634 1.3668 1.3713 313.15 K 1.3398 1.3437 1.3475

κ/mS·cm−1

m/mol·kg−1

η/mPa·s

55.10 59.65 62.85 65.40 67.35 69.60 70.80 71.30

1.0428 1.1326 1.2503 1.3503 1.4832 1.6308 1.8028 1.9933

61.25 65.25 68.75 71.60 74.20 76.40 78.05 78.50 78.95

0.9277 1.0228 1.1000 1.2298 1.3444 1.4686 1.6262 1.7809 2.0066

67.05 70.85 74.40 78.40 81.15 83.10 84.60 85.35 85.45

0.8387 0.9061 1.0053 1.1005 1.2049 1.3164 1.4314 1.5934 1.7911

72.75 76.95 80.80

0.7673 0.8222 0.9153 2433

ρ/g·cm−3

0.55 0.70 0.85 1.00 1.15 1.35 1.50

1.10190 1.12433 1.14578 1.16742 1.18876 1.21832 1.23951

0.10 0.25 0.40 0.55 0.70 0.85 1.00 1.15 1.35 1.50 1.65

1.03150 1.05453 1.07724 1.09955 1.12176 1.14329 1.16489 1.18613 1.21553 1.23714 1.25948

0.10 0.25 0.40 0.55 0.70 0.85 1.00 1.15 1.35 1.50 1.65 1.80

1.02945 1.05208 1.07470 1.09688 1.11895 1.14051 1.16194 1.18333 1.21269 1.23446 1.25584 1.27300

nD 313.15 K 1.3515 1.3552 1.3590 1.3626 1.3661 1.3707 1.3740 318.15 K 1.3390 1.3428 1.3469 1.3507 1.3545 1.3582 1.3617 1.3652 1.3696 1.3732 1.3768 323.15 K 1.3383 1.3424 1.3459 1.3498 1.3538 1.3578 1.3610 1.3645 1.3690 1.3725 1.3759 1.3790

κ/mS·cm−1

η/mPa·s

84.80 88.10 90.40 92.50 93.25 94.15 95.30

0.9884 1.0897 1.1928 1.2861 1.4345 1.6302 1.7563

78.70 82.90 87.20 91.70 95.05 97.10 99.55 100.80 101.65 102.80 103.45

0.6851 0.7490 0.8246 0.9061 0.9910 1.0753 1.1666 1.2869 1.4490 1.6067 1.7551

83.80 88.65 93.40 97.25 100.95 103.80 106.25 107.80 110.00 111.05 111.45 111.80

0.6382 0.6922 0.7465 0.8224 0.9024 0.9780 1.0695 1.1670 1.3075 1.4422 1.5766 1.7083



Article

Table 5. Equations 2 and 3 Parameter Values for Density, Refractive Index, Ionic Conductivity, and Viscosity in the Unsaturated Copper Sulfate in Acidic Seawater System eq 2 property −3

ρ/g·cm nD κ/mS·cm−1 η/mPa·s a

eq 3

A1

A2

A3

B1

B2

B3

AADa

0.014700 −0.004637 0.209209 0.076370

0.000377 0.003872 −0.071011 −0.004364

−0.000079 −0.000307 0.006853 0.000606

0.301624 0.055215 −0.071222 0.031678

−0.134641 −0.031231 0.031434 −0.012952

0.014860 0.002446 −0.003293 0.002182

0.0004 0.0002 0.6866 0.0095

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

Table 6. Casteel−Amis Parameters for Conductivity in Equation 4

a

T/K

μ/mol·kg−1

α

β·10−4

κmax/mS·cm−1

AADa

298.15 303.15 308.15 313.15 318.15 323.15

1.230035 1.293895 1.24117 1.41272 1.448106 1.68568

0.030458 0.008102 −0.01209 −0.00315 −0.015416 0.01906

−0.164831 −0.169161 −0.20286 −0.15803 −0.168948 −0.09918

71.385623 78.992560 85.65181 95.00693 104.150466 111.46559

0.1325 0.0875 0.1304 0.2684 0.4051 0.1700


Figure 6. Experimental values of density in unsaturated CuSO4 + seawater (pH 2) solutions at ◊, 298.15 K and ∗, 323.15 K; , correlations with eq 1.

Figure 8. Experimental values for the ionic conductivities in the unsaturated CuSO4 and seawater (pH 2) solutions at ◊, 298.15 K; ◆, 303.15 K; ▲, 308.15 K; ●, 313.15 K; ■, 318.15 K; and ∗, 323.15 K; , correlations with eq 4.

Figure 7. Experimental values for the refractive index in the unsaturated CuSO4 and seawater (pH 2) solutions at ◊, 298.15 K; ▲, 308.15 K; and ■, 318.15 K; , correlations with eq 1.

Figure 9. Experimental values of viscosities for the unsaturated CuSO4 + seawater solutions (pH 2) at: ◊, 298.15 K; ◆, 303.15 K; ▲, 308.15 K; ●, 313.15 K; ■, 318.15 K; ∗, 323.15 K; , correlations with eq 1.

independent of temperature; the equations for these parameters are as follows. A 0 = A1·I + A 2 ·I 2 + A3 ·I 3

(2)

B0 = B1·I + B2 ·I 2 + B3 ·I 3

(3)

For eqs 2 and 3, only CuSO4 ionic strength was considered. I is equal to 4·m because CuSO4 is a 2−2 electrolyte. The parameter values for the four properties measured are shown in Table 5; the absolute average deviations (AAD) for the fit are also presented in this table. These equations fit satisfactorily with AAD of 0.0004 g·cm−3, 0.0002, 0.6866 mS·cm−1,

In this case, the ionic strength of seawater was not considered because it did not change throughout the experiments. 2434



Article

Table 7. Experimental and Calculated Values for Density (ρ), Refractive Index (nD), and Viscosity (η) for eq 1 and Ionic Conductivity (κ) for Equations 1 and 4 in the Saturated Copper Sulfate and Acidic Seawater System at Various Temperatures ρ/g·cm−3 T/K 298.15 303.15 308.15 313.15 318.15 323.15 AADa a

m/mol·kg 1.3808 1.4910 1.6293 1.7545 1.9069 2.0698

−1

κ/mS·cm−1

nD

η/mPa·s

exptl

eq 1, calcd

exptl

eq 1, calcd

exptl

eq 1, calcd

eq 4, calcd

exptl

eq 1, calcd

1.22705 1.24028 1.25869 1.27345 1.29296 1.31120

1.22983 1.24419 1.26247 1.27838 1.29587 1.31120 0.00305

1.3731 1.3748 1.3772 1.3802 1.3821 1.3847

1.3730 1.3749 1.3773 1.3794 1.3821 1.3848 0.0002

71.38 79.07 86.12 94.08 101.53 108.97

72.25 80.36 88.46 97.19 106.22 115.09 3.07

71.10 78.47 83.12 93.28 100.58 109.80 1.08

2.317 2.212 2.135 2.105 2.055 2.021

2.358 2.223 2.182 2.115 2.078 2.036 0.025


The physical property values for the saturated system composed of copper sulfate in seawater are greater than those of the saturated system composed of copper sulfate in freshwater. Both systems (seawater and freshwater) maintain the same trend for the measured physical property values as a function of temperature; thus the graphs for these trends yield parallel curves. Density, refractive index, and ionic conductivity change linearly as a function of temperature change, while viscosity shows polynomial behavior. Conductivity and viscosity deviate the most between saturated CuSO4 systems in freshwater and seawater (24.61 and 5.61 %, respectively). The solubility and density differences are low (1.42 and 1 %, respectively), and the refractive index varies by less than 1 %. Using Othmer’s rule, the experimental values for the physical properties in the unsaturated concentrations of CuSO4 in seawater correlate satisfactorily with absolute average deviation for density, refractive index, ionic conductivity, and viscosity at 0.0004 g·cm−3, 0.0002, 0.6866 mS·cm−1 and 0.0095 mPa·s, respectively. Extrapolation of ionic conductivity data using Othmer’s rule is not recommended. The Casteel−Amis equation generates superior predictions for values of this property under saturation conditions.

and 0.0095 mPa·s for the density, refractive index, ionic conductivity, and viscosity experimental values, respectively. Furthermore, using eq 4, which is the Casteel−Amis equation (Bester-Rogac16), the experimental conductivity values for the unsaturated system composed of copper sulfate in acidic seawater were correlated as follows. κ κ max

⎡ ⎛ m ⎞α m − μ⎤ = ⎜ ⎟ ·exp⎢β ·(m − μ)2 − α · ⎥ ⎣ μ ⎦ ⎝ μ⎠

(4)

κ represents the specific conductivity as a function of molality m, κmax is the maximum specific conductivity at molality μ, and parameters α and β have no physical meaning. These parameters are adjusted using experimental data. The values for each parameter as a function of temperature are shown in Table 6. This equation fits satisfactorily for each temperature with 0.1990 mS·cm−1 AAD. The physical property values measured for unsaturated solutions composed of copper sulfate in acidic seawater (symbols) as well as the correlations (through eqs 1 to 4 (line)) are shown in Figures 6 to 9. For better visualization of the graph, Figures 6 and 7 only show two and three temperatures. The physical property values measured herein at a saturated concentration were extrapolated using the solubility value from the Othmer and Casteel−Amis equations (see Table 7). These extrapolated values were compared with experimental values (shown in Table 3). The physical properties have a direct relationship with the molal concentration of copper sulfate at a particular temperature (see Figures 6 to 9). Moreover, the curves show a clear trend toward the saturation point. The ionic conductivity reaches a maximum value and then decreases in value until saturation. This behavior is common for ionic conductivity over incremental ion concentrations because ion mobility in the system decreases. For a fixed concentration of copper sulfate, density, refractive index, and viscosity values decrease with an increase in temperature, which is in contrast with ionic conductivity. The calculated values using eqs 1 and 4 are shown in Figures 6 to 9 as full lines. These lines demonstrate a good fit with the experimental values. Equation 1 can be used to extrapolate data for saturated solutions in the ranges studied (see Table 7) with the exception of ionic conductivity, where it is preferable to use eq 4.

■

AUTHOR INFORMATION

Corresponding Author

*Phone: 56-55-637313. Fax: 56-55-637109. E-mail: mtaboada@ uantof.cl. Present Address

́ Centro de Investigación Cientifico y Tecnológico para la Mineria,́ (CICITEM) R10C1004, Av. José Miguel Carrera 1701, 4° piso, Antofagasta, Chile. †

Funding

The authors are grateful for the financial support provided by CONICYT through Fondecyt Project No. 1100685 and CICITEM R04I1001. Notes

The authors declare no competing financial interest.

■

4. CONCLUSIONS The solubility of the CuSO4 in acidic seawater system is similar to that of the CuSO4 in freshwater system, but the differences increase at higher temperatures.

REFERENCES

(1) Gianguzza, A.; Pelizzetti, E.; Sammartano, S. Chemistry of Marine Water and Sediments; Springer-Verlag: Berlin, 2002. (2) Feistel, R. Extended equation of state for seawater at elevated temperature and salinity. Desalination 2010, 250, 14−18.

2435



Article

(3) Millero, F.; Huang, F. The density of seawater as a function of salinity (5 to 70 g kg−1) and temperature (0 to 90 °C). OceanSci. Discuss. 2009, 6, 153−169. (4) Sun, H.; Feistel, R.; Koch, M.; Markoe, A. New equations for density, entropy, heat capacity, and potential temperature of a saline thermal fluid. Deep-Sea Res. Part I 2008, 55, 1304−1310. (5) Feistel, R.; Marion, G. A Gibbs-Pitzer function for high-salinity seawater thermodynamics. Prog. Oceanogr. 2007, 74, 515−539. (6) Voigt, W. Solubility equilibria in multicomponent oceanic salt systems from t = 0 to 200 °C. Model parameterization and databases. Pure Appl. Chem. 2001, 73, 831−844. (7) Deng, T.; Wang, S. Metastable phase equilibrium in the reciprocal quaternary system (NaCl + MgCl2 + Na2SO4 + MgSO4 + H2O) at 273.15 K. J. Chem. Eng. Data 2008, 53, 2723−2727. (8) Zhang, H.; Han, S. Viscosity and density of water + sodium chloride + potassium chloride solutions at 298.15 K. J. Chem. Eng. Data 1996, 41, 516−520. (9) Fabuss, B.; Korosi, A.; Othmer, D. Viscosities of aqueous solutions of several electrolytes present in sea water. J. Chem. Eng. Data 1969, 14, 192−197. (10) Korosi, A.; Fabuss, B. Viscosities of binary aqueous solutions of NaCl, KCl, Na2SO4, and MgSO4 at concentrations and temperatures of interest in desalination processes. J. Chem. Eng. Data 1968, 13, 548−552. (11) Fabuss, B.; Korosi, A.; Shamsul, A. Densities of binary and ternary aqueous solutions of NaCl, Na2SO4, and MgSO4, of sea water concentrates. J. Chem. Eng. Data 1966, 11, 325−331. (12) González-Dávila, M.; Santana-Casiano, J.; González, A.; Pérez, N.; Millero, F. Oxidation of copper (I) in seawater at nanomolar levels. Mar. Chem. 2009, 115, 118−124. (13) Glasby, G.; Schulz, H. Eh, pH Diagrams for Mn, Fe, Co, Ni, Cu and As under seawater conditions: application of two new types of Eh, pH diagrams to the study of specific problems in marine geochemistry. Aquat. Geochem. 1999, 5, 227−248. (14) Beverskog, B.; Puigdomenech, I. Pourbaix Diagrams for the System Copper-Chlorine at 5−100 °C. SKI Report 98:19, Swedish Nuclear Power Inspectorate, Stockholm, 1998, 18 p + app. 16 p. (15) Bianchi, G.; Longhi, P. Copper in seawater, potential−pH diagrams. Corros. Sci. 1973, 13, 853−864. (16) Bester-Rogac, M. Electrical conductivity of concentrated aqueous solutions of divalent metal sulfates. J. Chem. Eng. Data 2008, 53, 1355−1359. (17) Taboada, M.; Schilling, F.; Flores, E.; Graber, T. Investigación del nacimiento de cristales de sulfato de cobre en soluciones de alimentación a electroobtención en minera Escondida. Innovación 2003, 15, 7−13. (18) Christov, C. Thermodynamic study of the Na-Cu-Cl-SO4-H2O system at the temperature 298.15 K. J. Chem. Thermodyn. 2000, 32, 285−295. (19) De Juan, D.; Meseguer, V.; Lozano, L. Una contribución al estudio de la solubilidad del CuSO4·5H2O en medio acuoso. Rev. Metal. Madrid 1999, 35, 47−52. (20) Giulietti, M.; Seckler, M.; Derenzo, S.; Schiavon, J.; Valarelli, J.; Nývlt, J. Effect of selected parameters on crystallization of copper sulfate pentahydrate. Cryst. Res. Tech. 1999, 34, 959−967. (21) Giulietti, M.; Derenzo, S.; Nývlt, J.; Ishida, L. Crystallization of copper sulfate. Cryst. Res. Tech. 1995, 30, 177−183. (22) Ishii, T.; Fujita, S. Crystallization from supersaturated cupric sulfate solutions in a batchwise stirred tank. Chem. Eng. J. 1981, 21, 255−260. (23) Linke, W.; Seidell, A. Solubilities of Inorganic and Metal Organic Compounds, 4th ed.; American Chemical Society: Washington, DC, 1965; Vols. 1 and 2. (24) Lundström, M.; Aromaa, J.; Forsén, O. Redox potential characteristics of cupric chloride solutions. Hydrometallurgy 2009, 95, 285−289. (25) Senanayake, G. Review of theory and practice measuring proton activity and pH in concentrated chloride solutions and application to oxide leaching. Miner. Eng. 2007, 20, 634−645.

(26) Plyasunova, N.; Wang, M.; Zhang, Y.; Muhammed, M. Critical evaluation of thermodynamics of complex formation of metal ions in aqueous solutions II. Hydrolisis and hydroxo-complexes of Cu2+ at 298.15 K. Hydrometallurgy 1997, 45, 37−51. (27) Wang, M.; Zhang, Y.; Muhammed, M. Critical evaluation of thermodynamics of complex formation of metal ions in aqueous solutions I. A description of evaluation methods. Hydrometallurgy 1997, 45, 21−36. (28) Wang, M.; Zhang, Y.; Muhammed, M. Critical evaluation of thermodynamics of complex formation of metal ions in aqueous solutions III. The system Cu(I)(II)-Cl–e at 298.15 K. Hydrometallurgy 1997, 45, 53−72. (29) Nila, C.; González, I. Thermodynamics of Cu-H2SO4-Cl−-H2O and Cu-NH4Cl−-H2O based on predominance-existence diagrams and Pourbaix-type diagrams. Hydrometallurgy 1996, 42, 63−82. (30) Winand, R. Chloride hydrometallurgy. Hydrometallurgy 1991, 27, 285−316. (31) Berger, J.; Winand, R. Solubilities, densities and electrical conductivities of aqueous copper(I) and copper(II) chlorides in solutions containing other chlorides such as iron, zinc, sodium and hydrogen chlorides. Hydrometallurgy 1984, 12, 61−81. (32) Philippe, R.; Dixon, R.; DalPozzo, S. Sal or Desal: Sea Water Supply Options for the Mining Industry; WIM2010 Proceeding of the 2nd International Congress on Water Management in the Mining Industry, Santiago, Chile, 2010; pp 13−20. (33) Moreno, P.; Aral, H.; Cuevas, J.; Monardes, A.; Adaro, M.; Norgate, T.; Bruckard, W. The use of seawater as process water at Las Luces copper-molybdenum beneficiation plant in Taltal (Chile). Miner. Eng. 2011, 24, 852−858. (34) Taboada, M.; Hernández, P.; Galleguillos, H.; Flores, E.; Graber, T. Behavior of sodium nitrate and caliche mineral in seawater: solubility and physicochemical properties at different temperatures and concentrations. Hydrometallurgy 2012, 113−114, 160−166. (35) Luning Prak, D.; O’Sullivan, D. Solubility of 4-nitrotoluene, 2,6dinitrotoluene, 2,3-dinitrotoluene, and 1,3,5-trinitrobenzene in pure water and seawater. J. Chem. Eng. Data 2007, 52, 2446−2450. (36) Majer, V.; Pádua, A. Measurement of density with vibrating bodies. In Measurement of the thermodynamic properties of single phases; Goodwin, A. R. H., Marsh, K. N., Wakeham, W. A., Eds.; Elsevier Science: Amsterdam, 2003; Vol. 6, pp 149−168.

2436


Effect of Seawater on the Solubility and Physicochemical Properties of

Recommend Documents