Article pubs.acs.org/jced
Thermodynamics Study of Rhenium Solvent Extraction Process from Sulfuric Acid Medium Shu-liang Zang, Guo-sheng Zhao, Hui-min Zhao, Jun Li, and Da-wei Fang* Key Laboratory of Rare and Scattered Elements, College of Chemistry, Liaoning University, Shenyang 110036, China ABSTRACT: In the rhenium solvent extraction process, molalities of perrhenate after extraction were measured from 278.15 to 303.15 K at impurity ionic strength from 0.2 to 2.0 mol·kg−1 in aqueous phase. Optimization condition of extraction was determined in this sulfuric acid medium. The standard extraction constants K0 at various temperatures were obtained by method of polynomial approximation. Thermodynamic quantities for the solvent extraction process were calculated.
1. INTRODUCTION Rhenium is one kind of scattered metals without solo mine. In copper and molybdenum mineral exploitation and metallurgy, the rhenium(VII) was separated as ash and immerged into the acid waste aqueous solution. So the removal of perrhenate ion from wastewater and residual becomes of great significance.1 In the hydrometallurgy process, most rhenium occurs as rheniite (ReS2) together with molybdenite (MoS2) in porphyry copper minerals. During processing, the Re value follows Mo and Cu and is recovered together with Cu or Mo sulfide concentrate. Typically, copper or molybdenum sulfide concentrates recovered from flotation circuits contain 50−100 g/t (ppm) Re. Rhenium then deports during Cu smelting or molybdenite roasting mainly in slimes, flue dusts, or wet scrubbing acid solutions. Among the available methodologies for the separation and enrichment of rhenium from aqueous media, solvent extraction has the advantage of being effective in delivering a high-purity product. Hydrometallurgy of copper and molybdenum are usually in sulfuric acid medium. So the separation of perrhenate from these systems became the focus of recent research. The purpose of this study is to investigate the recovery of rhenium(VII) by N503 (N,N′-di(1-methyl-heptyl)-acetamide) from sulfuric acid medium which simulated waste aqueous solution from metallurgy and also research the physicochemical properties in the extraction process.
Table 1. Sources and Purity of the Materials mass fraction purity sulfuric acid ≥0.98 sodium sulfate ≥0.995 ammonium rhenate ≥0.99 N-heptane ≥0.99 N,N′-di(1-methyl-heptyl)−acetamide ≥0.95
Shanghai Reagent Co. Ltd. Shanghai Reagent Co. Ltd. Jiangxi Copper Co. Ltd. Shanghai Reagent Co. Ltd. Shenyang Organ. Chem. Institute.
NH4ReO4 in an aqueous solution of H2SO4 at constant molality. The initial molality of the NH4ReO4 was a = 0.001 mol kg−1, and initial molality of the H2SO4 was c = 0.1 mol kg−1. The organic phase was prepared by dissolving N503 in nC7H16, the initial molality of N503 being kept constant (b = 0.02 mol kg−1). Na2SO4 was used to adjust the ionic strength (I) of the aqueous solution to 0.1−2.0 mol kg−1. A volume (10 cm3) of the organic phase was brought into the same volume of aqueous phase in an extraction bottle and the two-phase mixture was shaken mechanically for 15 min. It was then kept for 15 min at different temperatures of 278.15, 283.15, 288.15, 293.15, 298.15, and 303.15 K within ±0.05 K. The two phases were separated and the molality of ReO4− (m{ReO4−}) in the equilibrium aqueous phase was determined using a 722 spectrophotometer with an accuracy ±0.01 for three replicate measurements. The results are shown in Table 2 and Figure 1.
2. EXPERIMENTAL SECTION The aqueous solution consisted of sulfuric acid, ammonium perrhenate, and sodium sulfate. The H2SO4 was of AR (analytical reagent) grade (99% mass pure), and the sodium sulfate was of AR grade. The n-C7H16 used as diluent was of AR grade with density of ρ = 0.68 × 103 kg/m3. All the sources are listed in Table 1. The aqueous phase was prepared by dissolving © 2016 American Chemical Society
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Received: November 18, 2015 Accepted: March 1, 2016 Published: March 15, 2016 1592
DOI: 10.1021/acs.jced.5b00976 J. Chem. Eng. Data 2016, 61, 1592−1596
Journal of Chemical & Engineering Data
Article
Table 2. Values of pH and Perrhenate Molality at Temperatures in the Range 278.15−303.15Ka T/K
278.15
283.15
pH m{ReO4−} (10−5)
1.09 2.68
1.05 4.14
pH m{ReO4−} (10−5)
1.08 2.74
1.04 4.25
pH m{ReO4−} (10−5)
1.07 2.76
1.03 4.36
pH m{ReO4−} (10−5)
1.07 2.78
1.03 4.45
pH m{ReO4−} (10−5)
1.05 2.79
1.02 4.69
pH m{ReO4−} (10−5)
1.04 2.80
1.00 4.82
pH m{ReO4−} (10−5)
1.03 2.81
0.98 5.04
pH m{ReO4−} (10−5)
1.03 2.84
0.98 5.17
pH m{ReO4−} (10−5)
1.02 2.88
0.97 5.28
pH m{ReO4−} (10−5)
1.01 2.90
0.95 5.39
pH m{ReO4−} (10−5)
1.00 2.91
0.94 5.51
pH mReO4− (10−5)
1.00 2.92
0.94 5.62
288.15 I = 0.2 1.03 5.16 I = 0.4 1.03 5.20 I = 0.5 1.02 5.26 I = 0.6 1.02 5.37 I = 0.8 1.01 5.49 I = 1.0 1.00 5.61 I = 1.2 0.98 5.82 I = 1.4 0.98 5.95 I = 1.5 0.96 6.17 I = 1.6 0.95 6.38 I = 1.8 0.94 6.59 I = 2.0 0.94 6.82
293.15
298.15 303.15
0.99 6.18
0.93 7.61
0.88 8.86
0.99 6.20
0.93 7.72
0.87 8.99
0.98 6.32
0.92 7.83
0.88 9.10
0.98 6.48
0.92 7.94
0.86 9.19
0.97 6.64
0.91 8.16
0.85 9.34
0.95 6.75
0.90 8.28
0.84 9.45
0.93 6.98
0.88 8.41
0.83 9.58
0.92 7.10
0.87 8.53
0.81 9.69
0.90 7.31
0.87 8.65
0.80 9.76
0.88 7.43
0.85 8.76
0.80 9.83
0.87 7.64
0.84 8.78
0.78 9.95
0.87 7.67
0.82 8.89
0.78 9.99
Figure 1. Extraction ratio at various temperatures: black square, 278.15 K; red circle, 283.15 K; green triangle, 288.15 K; blue inverted triangle, 293.15 K; teal diamond, 298.15 K; magenta left-pointing triangle, 303.15 K.
Table 3. Extraction Ratio for the Extraction Process in the Temperature Range 278.15−303.15 K T/K I
278.15
283.15
288.15
293.15
298.15
303.15
0.2 0.4 0.5 0.6 0.8 1.0 1.2 1.4 1.5 1.6 1.8 2.0
97.32 97.26 97.24 97.22 97.21 97.20 97.19 97.16 97.12 97.10 97.09 97.08
95.86 95.75 95.64 95.55 95.31 95.18 94.96 94.83 94.72 94.61 94.49 94.38
94.84 94.80 94.74 94.63 94.51 94.39 94.18 94.05 93.83 93.62 93.41 93.18
93.82 93.80 93.68 93.52 93.36 93.25 93.02 92.90 92.69 92.57 92.36 92.33
92.39 92.28 92.17 92.06 91.84 91.72 91.59 91.47 91.35 91.24 91.22 91.11
91.14 91.01 90.90 90.81 90.66 90.55 90.42 90.31 90.24 90.17 90.05 90.02
R3N (org) + H+ (aq) + ReO4 − (aq) = H+· NR3· ReO4 − (org)
a
m is the molality, T is Kelvin temperature, and I is ionic strength (molar concentration). Standard uncertainties u are u(T) = 0.05 K, u(p) = 10 kPa, and the expanded uncertainty is U(m) = 5 × 10−7 mol kg−1, U(pH) = 0.01 (0.95 level of confidence).
(1)
where (aq) and (org) refer to the aqueous and organic phase, respectively, R3N is the extractant N503, and NR3·H+·ReO4− is the extraction complex. The standard equilibrium constant K0 is given by
3. RESULTS AND DISCUSSION 3.1. Optimization Condition of Extraction. It is shown from Table 2 that the acidity of the solvent extraction system decreased with the increasing of ionic strength, which indicated low ionic strength benefits the system. The remaining ReO4− increased with the increase in temperature, which revealed the extraction was inclined to low temperature. The extractant has satisfactory extraction effect at various temperatures of the experiment, see Table 3. The extraction efficiency is almost above 90%, which indicated the extraction progress performed well. Furthermore, molalities of the remaining ReO 4− in aqueous phase are small at low temperature and low ionic strength, which indicates the best extraction conditions. In industry, the system should be kept at high acidity and low ionic strength at low temperature. 3.2. Microcosmic View of the Extraction System. In the presence of excessive N503, the extraction reaction is2
log K 0 = log[m{H+·NR3·ReO4−}] − log[m{H+}·m{ReO4−}·m{NR3}] + log[γ {H+· NR3·ReO4−}] − log[γ {H+}·γ {ReO4−}·γ {NR3}]
(2)
where γ is the activity coefficient in the molality scale, and m is the molality. The equilibrium molalities (m{i} for the species i) in the organic phase were calculated from the initial molalities a, b, and m{ ReO4− } in the aqueous phase m{H+· NR3·ReO4 −} = m{NR3} = b −
[a − m{ReO4 −}] ρ
[a − m{ReO4 −}] ρ
(3)
(4)
where ρ is the density of the organic phase. 1593
DOI: 10.1021/acs.jced.5b00976 J. Chem. Eng. Data 2016, 61, 1592−1596
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There were six ionic species (H+, Na+, NH4+, HSO4−, SO42−, and ReO4−) in the equilibrium aqueous phase. Their molalities and activity coefficients are m{H+}, m{Na+}, m{NH4+}, m1, m2, and m{ReO4−}, and γ{H+}, γ{Na+}, γ{NH4+}, γ1, γ2, and γ{ReO4−}, respectively. The effective ionic strength I′ in the equilibrium aqueous phase can then be calculated as
⎛γ ⎞ ⎛ m{Na +} ⎞ (0) ⎛ m{Na +} ⎞⎛ m2 ⎞ (1) (1) ln⎜⎜ 2 ⎟⎟ = 3f r + 3⎜ ) ⎟(β − βNa1 ⎟⎜ 0 ⎟βNa2y2 + 2⎜ 0 ⎝ ⎠ ⎝ m0 ⎠ Na2 ⎠ m ⎝ m ⎝ γ1 ⎠ ⎛ m{Na +} ⎞2 ⎛ m{Na +} ⎞ (1) (1) y ( ) + 2⎜ β − β + ⎟ (C Na2 − C Na1) ⎜ ⎟ Na1 ⎝ m0 ⎠ ⎝ m0 ⎠ 1 Na2 ⎛ m{Na +} ⎞⎛ m2 ⎞ +⎜ ⎟⎜ ⎟C Na2) ⎝ m0 ⎠⎝ m0 ⎠
1 ΣmiZi 2 2 1 = (m{ReO4−} + m{NH4 +} + m{Cl−} + m{H+} + m{Na +} + 4m2) 2
In eqs 11−14, where
I′ =
F = fr +
⎡ ⎢ ⎢ f r = −AP⎢ ⎡ ⎢ ⎢1 + 1.2 ⎣⎣
(6)
⎡ m ⎤⎡ γ ⎤ K 2 = ⎢a{H+} 2 ⎥⎢ 2 ⎥ m1 ⎦⎢⎣ γ1 ⎥⎦ ⎣
(7)
ln K 2 = −14.0321 + 2825.2/T
Z=
m1 + m2 = c + d
c
CijP =
where d is the initial molality of the Na2SO4 used as the supporting electrolyte. The values of m1 and m2 can be obtained from eqs 5−9 using the iterative method where
(10)
According to Pitzer’s electrolyte solution theory, the activity coefficients γM and γX of the cation M and the anion X in a multicomponent electrolyte solution are given by3−5 ⎛ ma ⎞ ⎟(2B Ma + ZC Ma) m0 ⎠
∑ ⎜⎝
⎛ mc ⎞ ⎟(2Φ Mc + m0 ⎠
∑ ⎜⎝ c
⎛ ma ⎞ ⎟ψ )+ m0 ⎠ Mca
∑ ⎜⎝ a
⎛ ma ⎞⎛ ma′ ⎞ ⎟⎜ ⎟ψ m0 ⎠⎝ m0 ⎠ Maa ′
∑ ∑ ⎜⎝ a
a′
⎛ m ⎞⎛ m ⎞ + |Z M| ∑ ∑ ⎜ c0 ⎟⎜ a0 ⎟Cca ⎝ m ⎠⎝ m ⎠ c a
ln γX = z X 2F + +
a
⎛ mc ⎞ ⎟ψ ) + m0 ⎠ c Xa
∑ ⎝⎜ c
⎤ ⎥ ⎥ 1/2 ⎤ ⎥ ⎥⎥ ⎦⎦
c′
⎛ mc ⎞⎛ mc′ ⎞ ⎟⎜ ⎟ψ m0 ⎠⎝ m0 ⎠ cc ′ X
(12)
⎛ ma ⎞ ⎟| Z | a m0 ⎠
∑ ⎜⎝ a
(17)
(18)
Bca = βcs(0) + βca(1)y1
(19)
B′ca = βca(1)y2
(20)
β(1) ca
⎡ ⎛ ⎢ ⎜1 + α 1 − + ⎢ ⎜ ⎝ ⎢ y2 = 2⎢ ⎢ ⎢ ⎢⎣
In estimating γ1, γ2, and γ{H+}, all the mixed parameters are neglected so that ⎛ m{Na +} ⎞⎛ m2 ⎞ (1) ⎛ m ⎞ (1) ln γ {H+} = f r + ⎜ ⎟⎜ ⎟(β y + C Na2) + 2⎜ 20 ⎟βH2 ⎝m ⎠ ⎝ m0 ⎠⎝ m0 ⎠ H2 2 + ⎛ m{Na } ⎞⎛ m2 ⎞ ⎛ m ⎞ (1) y1 + ⎜ + 2⎜ 20 ⎟βH2 ⎟⎜ ⎟C H2 ⎝m ⎠ ⎝ m0 ⎠⎝ m0 ⎠
I m0
2 1.2
2(|zizj|)1/2
⎡ ⎛ ⎢ 1 − ⎜1 + α ⎝ y1 = 2⎢ ⎢ ⎢ ⎣
∑ ⎝⎜
⎛ m ⎞⎛ m ⎞ + |Z X | ∑ ∑ ⎜ c0 ⎟⎜ a0 ⎟Cca ⎝ m ⎠⎝ m ⎠ c a
I 1/2 m0
where and are characteristic parameters of the electrolyte, and y1 and y2 are defined as
(11)
⎛ mc ⎞ ⎟(2B CX + ZCc X ) m0 ⎠
⎛ ma ⎞ ⎟(2Φ Ma + m0 ⎠
∑ ⎜⎝
I 1/2 m0
CijP
β(0) ca
∑ ⎜⎝ c
(15)
where the subscripts “c” and “a” represent cations and anions, respectively, z is the charge of the ion (m0 = 1 mol kg−1), AP is the Debye−Hückel coefficient of the osmotic function (this is given by Bradley and Pitzer6 for a wide range of temperatures and pressures), Bca and Cca are the second and third virial coefficients for the electrolyte, repsectively, B′ca is the first derivative of Bca with respect to I/m0, Φij is the second virial coefficient representing the difference between the averaged interactions between unlike ions with charges of the same sign and between like ions, Φ′ij is the derivative of Φij with respect to I/m0 and is the third virial coefficient similarly defined but for three ions with charges not all of the same sign. According to Pitzer and Kim7
(9)
10−pH γ {H+}
⎛ mc ⎞ ⎟| Z | = c m0 ⎠
∑ ⎜⎝
(8)
Consequently, m1 and m2 vary with temperature as well as with the total ionic strength of the solution. In terms of mass equilibrium
+
c′
(16)
The temperature dependence of K2 between 0 and 55 °C has been given by Pitzer et al.2−6 as
a
c
( ) ( ) ⎤⎦+( )ln⎡⎣1 + 1.2( )
K2 is the second dissociation constant
ln γM = z M 2F +
c
⎛ mc ⎞⎛ mc′ ⎞ ⎟⎜ ⎟Φ′ cc ′ m0 ⎠⎝ m0 ⎠
∑ ∑ ⎝⎜
⎛ m ⎞⎛ m ⎞ + ∑ ∑ ⎜ a0 ⎟⎜ a0′ ⎟Φ′aa ′ ⎝ m ⎠⎝ m ⎠ a a′
The second dissociation of sulfuric acid is
m{H+} =
⎛ ma ⎞⎛ mc ⎞ ⎟⎜ ⎟B′ + ca m0 ⎠⎝ m0 ⎠
∑ ∑ ⎜⎝ a
(5)
HSO4 − = H+ + SO4 2 −
(14)
(13) 1594
1/2 ⎞ ⎛ ⎟exp⎜ − α
{ } I m0
⎠
⎝
1/2 ⎞ ⎤ ⎟⎥
{ } I m0
(α { }) I m0
2
1/2
{ } I
m0
⎛ ⎝
⎠⎥ ⎥ ⎥ ⎦
{ } ⎞⎟exp⎛⎜−α I
+ α2
⎜α
2
m0
2
2⎞
{ }⎠ I
m0
⎟
⎟ ⎠
⎝
(21)
m0
⎤⎤ ⎥ ⎟⎥ ⎥ ⎠⎥ ⎦⎥ ⎥ ⎥ ⎥ ⎥⎦ (22)
1/2 ⎞
{ } I
DOI: 10.1021/acs.jced.5b00976 J. Chem. Eng. Data 2016, 61, 1592−1596
Journal of Chemical & Engineering Data
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3.3. Polynomial Approximation to Determine K0. Then eq 2 could be expressed as
3.4. Thermodynamic Quantities for the Extraction Process. The values of log K0 obtained at different temperatures were fitted to following equation8,9
m[H+NR3ReO‐4 ] − log(a[H+]) m[ReO−4 ] × m[NR3]
log K 0 = log
⎛ ⎞ A log K 0 = ⎜A1 + 2 + A3T ⎟ ⎝ ⎠ T
+
+ log
γ[H NR3ReO−4 ] γ[ReO−4 ] × γ[NR3] +
γ[H NR3ReO−4 ] = log K m + pH + log − log γ[ReO‐4 ] γ[NR3]
The following values of parameters Ai were obtained: A1 = −264, A2 = 4.06 × 105 and A3= 0.440 with a standard deviation of s = 0.90. The standard molar thermodynamic quantities ΔrGm0, ΔrHm0, ΔrSm0, ΔrCP,m0 for the extraction process are simply related to the parameters in eq 24
(23)
and Km is equilibrium concentration product, defined as Km =
m{H+· NR3·ReO4 −} [m{ReO4 −} ·m{NR3}]
(24)
Because the molalities of the extraction complex and the extractant in the equilibrium organic phase are small, it can be assumed that γ{ H+NR3ReO4−}/γ{ NR3} ≈ 1. As γ{ReO4−} in the equilibrium aqueous phase might be proportional to the effective ionic strength, it can be expressed by Pitzer’s equations. In using Pitzer’s equations to determine K0, it is assumed that (1) the effective ionic strength is regarded as the total ionic strength in the aqueous phase; (2) interactions between ions can be regarded as those between ReO4−, H+, and the ions of the supporting electrolyte; and (3) following the advice of Pitzer and Mayorga,3,4 ψMca, is considered to be independent of ionic strength. In estimating γ{ReO4−} and γ{H+}, all the mixed parameters (Φij, Φ′ij and ψijk) are neglected, so that the pertinent combination of activity coefficients may be written as ln γMX = |z Mz X|F +
a
⎛ vM ⎞ ⎟Φ ]+ Mc v ⎠
∑ ∑ mcmav−1[2vMZ MCCa + vMψMcaψCa X] a
+
⎛ vX ⎞ ⎟ψ v ⎠ cc ′ X
∑ ∑ mcmc′⎜⎝
c
