Article pubs.acs.org/jced
Solvent Extraction of Perrhenate Anion from Sulfuric Acid Aqueous System with N1923 Wei-jun Shan, Wei Yin, Ying Xiong, Da-wei Fang,* and Shu-liang Zang Key laboratory of Rare and Scattered Elements Liaoning Province, College of Chemistry, Liaoning University, Shenyang 110036, People’s Republic of China ABSTRACT: Perrhenate anion was extracted by extractant N1923 in sulfuric acid solution at ionic strength from (0.2 to 2.0) mol·kg−1. Molalities of perrhenate after extraction were measured in sulfuric acid aqueous system from (278.15 to 303.15) K. Standard extraction constants K0 were obtained by polynomial approximation method at various temperatures. Thermodynamic properties were investigated in the extraction process.
1. INTRODUCTION Rhenium is one kind of scattered metals, which associated with ferrous metal mineral.1−3 The main resource of rhenium is molybdenite and digenite. Rhenium in mineral was usually recovered from concentrates by pyrometallurgical and hydrometallurgical technology.4 Hydrometallurgy of rhenium is usually in sulfuric acid medium. So the separation of perrhenate from these systems became the focus of recent research, where solvent extraction method is used especially for separation of perrhenate from other components. The low-cost industrial material N1923 (one kind of primary amine), structure given in Figure 1b, is an extractant of the rhenium separation system. This study investigates the recovery of rhenium(VII) from sulfuric acid medium which simulates industry solution from molybdenum metallurgy, and the microcosmic phenomena in the extraction process was also discussed.
in the equilibrium aqueous phase was then determined using a spectrophotometer (type 722) for three replicate measurements. The results are shown in Table 1.
3. RESULTS AND DISCUSSION 3.1. Optimization Condition of Extraction. The remaining ReO4− concentration increased with increasing temperature and ionic strength, seen from Table 1. And the extraction efficiencies are all upon 96%, which indicated the extraction progress almost performed completely. Furthermore, the best extraction conditions were confirmed as 278.15 K with an extraction ratio of 99.77% at lower ionic strength. 3.2. Microcosmic Study. In the presence of excessive N1923, abbreviated as RNH2, the extraction reaction is RNH 2(org) + H+(aq) + ReO4 −(aq) = RNH3ReO4 (org) (1)
2. EXPERIMENTAL SECTION Aqueous solution was made with sulfuric acid, ammonium perrhenate, and sodium sulfate; all are AR (analytical reagent) grade 99.5% mass pure, as supporting electrolyte. The n-C7H16 used as diluent was of AR grade with density as ρ = 0.68·103 kg· m−3. The structure of extractant N1923 (one kind of primary amine) is given in Figure 1b. The organic phase was prepared by dissolving N1923 in n-C7H16, the initial molality of N1923 being kept constant (b = 0.02 mol·kg−1). The aqueous phase was prepared by dissolving NH4ReO4 in an aqueous solution of H2SO4 of constant molality. The initial molality of NH4ReO4 was a = 0.001 mol·kg−1, and the initial molality of the H2SO4 was c = 0.1 mol·kg−1. Na2SO4 was used as supporting electrolyte to adjust I (ionic strength) of the aqueous solution to (0.1 to 2.0) mol·kg−1. A volume (10 cm3) of the organic phase was brought into contact with the same volume of aqueous phase in an extraction bottle and shaken mechanically for 15 min. The extraction bottles were kept at different temperatures from (278.15 to 303.15) K, within ± 0.05 K. After standing for 15 min, the two phases were separated and the molality of ReO4− (mReO4−}) © 2015 American Chemical Society
where (org) and (aq) refer to the organic and aqueous phases, respectively, RNH2 is the extractant N1923, and RNH3ReO4 is the extraction complex. The standard equilibrium constant K° is given by log K ° = log[m{RNH3ReO4 }] − log[m{H+} m{ReO4−} m{RNH 2}] + log[γ {RNH3ReO4 }] − log[γ {H+} γ {ReO4−} γ {RNH 2}]
(2)
where m is the molality and γ is the activity coefficient. In the aqueous phase, the equilibrium molalities (m{i} for the species i) in the organic phase were calculated from the initial molalities a, b, and m{ ReO4−}: m{RNH3ReO4 } = [a − m{ReO4 −}]/ρ
(3)
m{NR3} = b − [a − m{ReO4 −}]/ρ
(4)
where ρ is the density of the organic phase. Received: September 11, 2014 Accepted: February 25, 2015 Published: March 17, 2015 1006
DOI: 10.1021/je500759q J. Chem. Eng. Data 2015, 60, 1006−1009
Journal of Chemical & Engineering Data
Article
Figure 1. Structures of the extractants: a, N235; b, N1923; c, NN503.
There were six ionic species (H+, NH4+, Na+, HSO4−, SO42−, and ReO4−) in the equilibrium aqueous phase. The molalities and activity coefficients are m{H+}, m{NH4+}, m{Na+}, m1, m2, and m{ReO4−} and γ{H+}, γ{ NH4+ }, γ{ Na+}, γ1, γ2, and γ{ReO4−}, respectively. The effective ionic strength I′ in the equilibrium aqueous phase can then be calculated as
ln γX = z X 2F +
c
+
∑ (ma /m0)(2ΦMa + ∑ (mc /m0)ψcXa) a
+
∑ ∑ (mc /m )(mc ′/m )ψcc ′ X
−
+
+ m{Na } + 4m2)
+
(5)
HSO4 − = H+ + SO4 2 −
(1) (1) + 2(m2 /m0)βH2 + 2(m2 /m0)βH2 y1
+ (m{Na +}/m0)(m2 /m0)C H2
K2 is the second dissociation constant:
(0) (1) + 2(m{Na +}/m0)(βNa2 − βNa1 )
The temperature dependence of K2 between (0 and 55) °C has been given by Pitzer et al.5 as
(1) (1) + 2(m{Na +}/m0)y1(βNa2 − βNa1 )
+ (m{Na +}/m0)2 (C Na2 − C Na1)
(8)
+ (m{Na +}/m0)(m2 /m0)C Na2)
Consequently, m1 and m2 vary with temperature as well as with the total ionic strength of the solution. With respect to mass equilibrium, m1 + m2 = c + d
log K ° = log K m + pH + (log γ {RNH3ReO4 })/(log γ {RNH 2}) − log γ {ReO4 −}
where d is the initial molality of Na2SO4 used as the supporting electrolyte. The values of m1 and m2 can be obtained from eqs 5 to 9 using an iterative method, where
K m = m{RNH3ReO4 }/[m{ReO4 −} m{RNH 2}]
∑ (ma /m0)(2BMa + zCMa) a
F = fr +
∑ (mc /m0)(2ΦMc + ∑ (ma /m0)ψMca) ∑ ∑ (ma /m )(ma′/m )ψMaa′
∑ ∑ (mc /m0)(mc ′/m0)Φ′cc ′
+
∑ ∑ (ma /m0)(ma′/m0)Φ′aa′
c
a
(11)
a
1007
c
+
a′
c
∑ ∑ (ma /m0)(mc /m0)B′ca a
a 0
+ |z M| ∑ ∑ (mc /m0)(ma /m0)Cca
(16)
The molalities of the extraction complex and the extractant in the equilibrium organic phase are both small; it could be assumed that γ{ RNH3ReO4−}/γ{ RNH2} ≈ 1, as activity coefficient γ{ReO4−} in the equilibrium aqueous phase might be proportional to the effective ionic strength, which can be expressed by Pitzer’s equations. In eqs 11 to 14, where
According to Pitzer’s theory, the activity coefficients γM and γX of the cation M and the anion X in a multicomponent electrolyte solution are given by5−7
0
(15)
and Km is the equilibrium concentration product, defined as
(10)
c
(14)
3.3. Polynomial Approximation To Determine K°. Then eq 2 could be expressed as
(9)
m{H+} = 10−pH /γ {H+}
(13)
(1) ln(γ2/γ1) = 3f r + 3(m{Na +}/m0)(m2 /m0)βNa2 y2
(7)
ln K 2 = −14.0321 + 2825.2/T
(12)
(1) ln γ {H+} = f r + (m{Na +}/m0)(m2 /m0)(βH2 y2 + C Na2)
(6)
K 2 = [a{H+}(m2 /m1)][γ2/γ1]
a
In estimating activity coefficients, γ1, γ2, and γ{H+}, all of the mixed parameters are neglected, so
The second dissociation of sulfuric acid is
a
c′
c
+
= (1/2)(m{ReO4 } + m{NH4 } + m{Cl } + m{H }
+
0
+ |z X| ∑ ∑ (mc /m0)(ma /m0)Cca
−
+
c 0
c
I ′ = (1/2) ∑ mizi 2
ln γM = z M 2F +
∑ (mc /m0)(2Bc X + zCcX)
c′
a′
(17)
DOI: 10.1021/je500759q J. Chem. Eng. Data 2015, 60, 1006−1009
Journal of Chemical & Engineering Data
Article
where the subscripts “c” and “a” represent cations and anions, respectively, z is the charge of the ion (m0 = 1 mol·kg−1), Bca and Cca are the second and third virial coefficients for the electrolyte, 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, Φ′ij is the derivative of Φij with respect to I/m0, AP is the Debye−Hückel coefficient of the osmotic function (given by Bradley and Pitzer8 for a wide range of temperatures and pressures). According to Pitzer and Kim,9
Table 1. Values of pH and Anion Strength at Temperatures in the Range of (278.15 to 303.15) Ka T/K = 278.15
T/K = 283.15
pH m ReO4− (10−5)
1.30 1.91
1.25 2.12
pH m ReO4− (10−5)
1.23 1.93
T/K = 288.15
T/K = 293.15
T/K = 298.15
T/K = 303.15
I= 0.2 1.15 2.45
1.10 2.76
1.03 3.00
1.00 3.66
1.24 2.14
I= 0.4 1.15 2.37
1.08 2.79
1.02 3.03
0.99 3.66
1.08 2.82
1.01 3.06
0.98 3.70
pH m ReO4− (10−5)
1.23 1.95
1.23 2.15
I= 0.5 1.14 2.38
pH m ReO4− (10−5)
1.22 1.97
1.22 2.18
I = 0.6 1.13 2.41
1.07 2.84
1.00 3.07
0.97 3.67
pH m ReO4− (10−5)
1.22 2.01
1.21 2.20
I = 0.8 1.12 2.43
1.06 2.85
1.00 3.10
0.96 3.70
pH m ReO4− (10−5)
1.21 2.05
1.20 2.22
I = 1.0 1.11 2.45
1.06 2.88
0.99 3.13
0.95 3.73
pH m ReO4− (10−5)
1.20 2.08
1.20 2.24
I = 1.2 1.11 2.48
1.05 2.91
0.98 3.15
0.95 3.75
pH m ReO4− (10−5)
1.19 2.10
1.19 2.27
I = 1.4 1.10 2.51
1.05 2.93
0.97 3.17
0.94 3.77
1.04 2.96
0.95 3.19
0.92 3.78
1.03 2.99
0.95 3.21
0.91 3.81
pH m ReO4− (10−5)
1.18 2.14
1.18 2.29
I = 1.5 1.09 2.53
pH m ReO4− (10−5)
1.18 2.17
1.17 2.33
I = 1.6 1.08 2.56
1.17 2.37
I′ = 1.8 1.08 2.59
1.15 2.38
I = 2.0 1.07 2.62
pH m ReO4− (10−5)
1.17 2.19
pH m ReO4− (10−5)
1.15 2.22
(23)
y2 = 2[− 1 + (1 + α{I /m0}1/2 + α 2{I /m0}/2) exp(− α{I /m0}1/2 )] /(α 2{I /m0}2)
(24)
In determination of K°, 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; (3) following the advice of Pitzer et al.,5,6 ψMca, is considered to be independent of ionic strength. In estimating γ{ReO4−} and γ{H+}, all of the mixed parameters (Φij, Φ′ij, and ψijk) are neglected; the pertinent combination of activity coefficients could be written as ln γMX = |z Mz X|F + (vM /v) ∑ ma [2BMa + zCMa + 2(vX /v)ΦXa ] a
+ (vX /v) ∑ mc[2BcX + zCcX + 2(vM /v)ΦMc] c
+
∑ ∑ mcmav−1[2vMZ MCca + vMψMca′ + vXψcaX ′]
+
∑ ∑ mcmc′(vX /v)ψcc′ X ′ + ∑ ∑ mama′(vM/v)ψMaa′
c
a
c N503. It led to the recognition of the difference originating from the extraction mechanism and extractant molecular structures. When combining the H+, their formula exhibited a different structure; see Figure 1. According to our knowledge of organic chemistry, the ability of absorbing electron was deduced as N235 > N1923 > N503, which is caused by the steric effect. So N235 has the best extraction results, and N503 implemented poorly.
4. CONCLUSION The negative experimental association Gibbs free energy, ΔGM° < 0, means that the reaction can occur spontaneously under the conditions of constant temperature and pressure. As is wellknown, Gibbs energy includes two factors, that is ΔGM° = ΔHM° − TΔSM°, which leads us to conclude that enthalpy and entropy are both the dominant thermodynamic factors. The extractant has satisfactory extraction effect of 99%, which indicated the extraction progress performed completely. So in industry, the system should be kept as little ionic strength at low temperature.
■
REFERENCES
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AUTHOR INFORMATION
Corresponding Author
*E-mail: davidfi
[email protected]. 1009
DOI: 10.1021/je500759q J. Chem. Eng. Data 2015, 60, 1006−1009
