Article pubs.acs.org/jced
Solvent Extraction of Rhenium(VII) from Aqueous Solution Assisted by Hydrophobic Ionic Liquid Da-wei Fang, Zong-ren Song, Si-cai Zhang, Jun Li,* and Shu-liang Zang Institute of Rare and Scattered Elements, College of Chemistry, Liaoning University, No. 66 Chongshan Middle Road, Huanggu District, Shenyang, Liaoning Province 110036, China ABSTRACT: The solvent extraction of rhenium using TiOA as extractant assisted by ionic liquids from aqueous solutions was investigated. The molalities of ReO4− after extraction were measured at impurity ionic strength from 0.2 to 2.0 mol·kg−1 at temperatures from 293.15 to 318.15 K in the aqueous phase. Standard extraction constants K0 at different temperatures were obtained by the Pitzer polynomial approximation method. Thermodynamic properties for the extraction procedure were also calculated.
NR3(org) + H+(aq) + ReO4 −(aq) = H+·NR3·ReO4 −(org)
1. INTRODUCTION
(1)
Rhenium is scattered metal that is not solely mined. Molybdenite of copper mine concentrate and flue dust from molybdenite of copper mine roasters are the only source for rhenium. Most rhenium occurs with molybdenum in porphyry copper minerals. Rhenium is widely used in petro-chemical, aviation, power plant, electronics, medicine, and metallurgical industries. Solvent extraction is the main manner of purification and acquisition of rhenium from mine tailings. Some important thermodynamic properties are the basis of the processes.1,2 Ionic liquids (ILs) have attracted significant attention over the past decade because of their unique properties, such as high ionic conductivity, recyclability, negligible vapor pressure, designable structures, and excellent thermal and chemical stability.3 In our study, we propose a simple, fast, and sustainable strategy for rhenium extraction by means of liquid−liquid extraction using TiOA (tertiary isooctyl amine) diluted in [C5mim][PF6] (1-pentyl-3-methyl-imidazolium hexafluorophosphate), which is the first time ionic liquids have been used as a diluent in the history of liquid−liquid extraction. We adopted the [C5mim][PF6] because of low cost, it is simple and easy to use, and it is hydrophobic, making its application widespread. In particular, the ionic liquid can be recycled by evaporation for further use. As a continuation of our previous work,4−6 we measured perrhenate concentration in a hydrochloric acid system at different ionic strengths. The standard extraction constants K0 are calculated by the polynomial approximation method.7−9 Thermodynamic properties for the process are obtained. In the presence of excessive extractant TiOA, abbreviated as NR3, the extraction reaction is © 2017 American Chemical Society
where NR3 is the extractant TiOA, (org) and (aq) refer to the organic and aqueous phase, respectively, and H+·NR3·ReO4− is the extraction complex. The standard equilibrium constant K0 is given by 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.
2. EXPERIMENTAL SECTION Water used in the extraction system was of high purity, and its conductivity was 1.5 × 10−4 Ω−1·m−1 (Ω is ohm) by a DDSJ318 conductivity meter (Shanghai Leici instrument Co., LTD) . The [C5mim][PF6], 99% mass pure, used as the diluent was purchased from Lanzhou Institute of Chemical Physics. The HCl was guarantee reagent grade, and the ammonium chloride was AR grade. The organic phase was prepared by dissolving TiOA in ionic liquid [C5mim][PF6], the initial molality of TiOA was kept constant (b = 0.02 mol·kg−1). The aqueous phase was prepared by dissolving NH4ReO4 in aqueous solution with HCl at constant molality. The initial Received: October 27, 2016 Accepted: February 9, 2017 Published: February 23, 2017 1094
DOI: 10.1021/acs.jced.6b00909 J. Chem. Eng. Data 2017, 62, 1094−1098
Journal of Chemical & Engineering Data
Article
molality of the HCl was c = 0.1 mol·kg−1, and the initial molality of the NH4ReO4 was a = 0.001 mol·kg−1. NH4Cl was used to adjust ionic strength I of solution to 0.2−2.0 mol·kg−1. A 10 cm3 organic phase and aqueous phase were placed into the extraction bottle, and make them fully mixed magnetic stirring for 25 min. The bottles were kept at different temperature points: 293.15, 298.15, 303.15, 308.15, 313.15, and 318.15 K, within ±0.05 K, using a superthermostatic waterbath (Shanghai ShunYu scientific instrument Co., LTD, type DC-0506), adding self-make secondary temperature control device, to keep the temperatures. After being static for 15 min, the two phases were separated. Molality of ReO4− (m{ReO4−}) in aqueous phase was measured using a 722 type spectrophotometer within uncertainty ±0.01 for three replicate measurements, where results were listed in Table 1 and shown in Figure 1. Molalities in the organic phase were calculated by initial molalities a, b and m{ ReO4− } in the aqueous phase: m{H+·NR3·ReO4 −} = [a − m{ReO4 −}]/ρ
(3)
m{NR3} = b − [a − m{ReO4 −}]/ρ
(4)
Table 1. Values of pH and Perrhenate Concentration at the Temperatures 293.15−318.15 Ka T/K
where ρ is density of the organic phase.
3. RESULTS AND DISCUSSION The pH values were determined at the various temperature from 293.15 K to 318.15 K, for the ionic strengths as listed in Table 1. Each pH value is the mean of three replicate determination within the uncertainty ±0.01. 3.1. Optimization Extraction Condition. The acidity of the system decreased with the increasing ionic strength, which showed that low ionic strength benefits the system, as seen from Table 1 and Figure 1. The remaining perrhenate increased with the increase of temperature, which meant that the solvent extraction was improved at lower temperatures. The extraction efficiencies are mostly over 99%, which indicated that the extraction performed completely. Furthermore, perrhenate molalities in the aqueous phase are small at lower temperatures and lower ionic strengths. The best extraction condition with a extraction ratio of 99.63% is at 293.15 K. So in industry, the extraction system should be kept at a high acidity with little impurities at low temperatures. It could be seen from refs 4 and 5 that the extractant TOA had better extraction efficiency than TiOA over the entire temperature and ionic strength ranges. The perrhenate concentration remaining in the aqueous phase was 10−6 grade in the TOA system, but 10−5 grade in the TiOA system. As shown in this work, the ionic liquid [C5mim][PF6] has enhanced the ability of extractant TiOA in the same extraction system. The perrhenate concentration remaining in the aqueous phase has achieved 10−6 grade in TiOA system, which is very inspiring. As is concluded, the extraction process is an ion exchange procedure, and the ionic liquid can accelerate the exchange rate through the organic phase, as compared with tradition organic reagents, which demonstrates a higher extraction efficiency. 3.2. Polynomial Approximation to Determine K0. There are four ionic species (ReO4−, H+, NH4+, and Cl−) in the aqueous phase. Molalities and activity coefficients are m{ReO4−}, m{NH4+}, m{H+}, and m{ Cl−}, and γ{H+}, γ{NH4+}, γ{ReO4−}, and γ{Cl−}, respectively. The I′ (effective ionic strength) in the aqueous phase can then be calculated as
293.15
I′ pH m{ReO4−}(10−6)
0.196 1.29 3.735
I′ pH m{ReO4−}(10−6)
0.400 1.28 3.884
I′ PH m{ReO4−}(10−6)
0.503 1.26 4.014
I′ pH m{ReO4−}(10−6)
0.602 1.27 4.163
I′ pH m{ReO4−}(10−6)
0.806 1.25 4.349
I′ pH m{ReO4−}(10−6)
1.008 1.23 4.424
I′ pH m{ReO4−}(10−6)
1.208 1.24 4.666
I′ pH m{ReO4−}(10−6)
1.411 1.22 4.647
I′ pH m{ReO4−}(10−6)
1.512 1.21 4.852
I′ pH m{ReO4−}(10−6)
1.612 1.21 5.020
I′ pH m{ReO4−}(10−6)
1.815 1.19 5.187
I′ pH m{ReO4−}(10−6)
2.014 1.20 5.355
298.15
303.15
I= 0.197 1.28 4.200 I= 0.401 1.27 4.349 I= 0.503 1.26 4.517 I= 0.603 1.26 4.685 I= 0.807 1.24 4.834 I= 1.006 1.25 5.057 I= 1.209 1.23 5.020 I= 1.411 1.22 5.262 I= 1.513 1.21 5.430 I= 1.615 1.19 5.597 I= 1.817 1.18 5.765 I= 2.017 1.18 5.932
0.2 0.199 1.26 4.424 0.4 0.403 1.25 4.536 0.5 0.503 1.26 4.647 0.6 0.607 1.23 4.796 0.8 0.807 1.24 4.945 1.0 1.010 1.22 5.113 1.2 1.212 1.21 5.355 1.4 1.413 1.21 5.336 1.5 1.516 1.19 5.616 1.6 1.618 1.17 5.746 1.8 1.817 1.18 5.914 2.0 2.019 1.17 6.119
308.15
313.15
318.15
0.198 1.27 4.908
0.204 1.25 5.318
0.202 1.23 5.932
0.402 1.26 5.057
0.406 1.24 5.448
0.408 1.21 6.063
0.505 1.24 5.225
0.507 1.24 5.597
0.508 1.22 6.212
0.605 1.25 5.299
0.612 1.21 5.765
0.611 1.20 6.435
0.808 1.23 5.523
0.812 1.22 5.988
0.814 1.19 6.640
1.011 1.21 5.727
1.013 1.21 6.137
1.016 1.18 6.845
1.211 1.22 5.951
1.218 1.18 6.342
1.220 1.16 7.068
1.414 1.20 6.174
1.420 1.17 6.547
1.419 1.17 7.292
1.516 1.19 6.435
1.523 1.15 6.789
1.523 1.15 7.609
1.617 1.18 6.696
1.622 1.16 7.050
1.626 1.13 7.571
1.818 1.18 6.975
1.825 1.14 7.292
1.828 1.12 7.832
2.021 1.16 7.236
1.988 1.15 7.534
2.034 1.09 8.037
a
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).
I′ =
1 1 ΣmiZi 2 = (m{ReO4 −} + m{NH4 +} 2 2
+ m{Cl−} + m{H+})
(5)
where 1095
DOI: 10.1021/acs.jced.6b00909 J. Chem. Eng. Data 2017, 62, 1094−1098
Journal of Chemical & Engineering Data
Article
F = fr +
∑ ∑ (ma /m0)(mc /m0)Bca′ a
+
∑ ∑ (mc /m0)(mc ′/m0)Φ′cc ′ c
+
c
c′
∑ ∑ (ma /m0)(ma′/m0)Φ′aa′ a
a′
f r = −AP[(I /m0)1/2 /[1 + 1.2(I /m0)1/2 ] 2 + ln[1 + 1.2(I /m0)1/2 ] 1.2
Z=
∑ (mc /m0)|Zc| = ∑ (ma /m0)|Za| c
a
CijP = CijP/2(|zizj|)1/2
(6)
m{Cl−} = m{NH4Cl} + c
(7)
and [H+] was obtained by pH values. The calculated I′ values are listed in Table 1. Equation 2 can be expressed as log K 0 = log[m{H+· NR3·ReO4 −}]
(16)
β(1) ca
exp( −α{I /m0}1/2 )]/(α 2{I /m0}2 )
ln γMX = |z Mz X|F + (vM /v) ∑ ma[2BMa + ZC Ma a
a
+ 2(vX /v)ΦXa ] + (vX /v) ∑ mc[2BCx + ZCCx
∑ ∑ (ma /m )(ma′/m )ψMaa′ 0
0
c
a′
+ |Z M| ∑ ∑ (mc /m0)(ma /m0)Cca c
a
+ 2(vM /v)ΦMc] +
a
∑ ∑ mcmc ′(vX /v)ψcc ′ X c
