Solvent Extraction of Perrhenate from Sulfuric Acid Medium by

Article pubs.acs.org/jced

Solvent Extraction of Perrhenate from Sulfuric Acid Medium by Triisooctylamine Wei-jun Shan, Peng Cheng, Jun Li, 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, P. R. China ABSTRACT: In sulfuric acid medium, triisooctylamine was used as extractant to separate perrhenate from the aqueous phase. Molalites of perrhenate in the aqueous phase were measured from 278.15 K to 303.15 K at impurity ionic strength from 0.2 to 2.0 mol·kg−1. Standard extraction equilibrium constants K0 at different temperatures were calculated by polynomial approximation method. Some microcosmic property values in the process were investigated and obtained by Pitzer’s theory, which indicated enthalpy and entropy were both dominant thermodynamic factors.

1. INTRODUCTION The demand of rhenium is growing, owing to the increasing production of superalloys, which are used in the fabrication of high temperature turbine blades found in jet engines.1 In nature, most rhenium is associated with molybdenum or copper in minerals. Typically 50−100 g/t (ppm) rhenium can be recovered from copper or molybdenum sulfide concentrates.2 Rhenium is recovered mainly from slimes, flue dusts generated in Cu smelting or Mo roasting, or the wet scrubbing acid solutions.3−7 Thus, the separation of perrhenate from these systems became a focus of recent research. The solvent extraction method is most widely used for the separation of rhenium from other components, such as tungsten, arsenic, or molybdenum.8,9 Especially for rhenium extraction, pyridine, bis-isododecylamine, tri-n-octylamine, Aliquat336, trioctylphosphine oxide, tributyl phosphate, cyklohexanon, mesityloxide, and ethyl xanthate are used. In industry, the most widely used system of extracting rhenium consists of a sulfuric acid medium. After extraction, in the stripping process from the organic phase, both alkali solutions and acid solutions were used, that is, ammonium solutions (for ammonium perrhenate separation) or aqueous solutions of KOH and NaOH, and aqueous H2SO4, HCl.10−13 The objective of this research was rhenium separation from sulfuric acid medium, containing perrhenate and some impurities, by the solvent extraction method using triisooctylamine (TiOA) as extractant.

The organic phase was prepared by mixing TiOA into nC7H16, for which the initial molality of TiOA was kept constant (b = 0.02 mol kg−1). The aqueous phase was prepared by dissolving NH4ReO4 in H2SO4 solution of constant molality. Na2SO4 was used to adjust the ionic strength I from 0.2 mol kg−1 to 2.0 mol kg−1 in aqueous solution. The molality of NH4ReO4 was a = 0.001 mol kg−1, and the molality of the sulfuric acid was c = 0.1 mol kg−1. A 10 cm3 sample of extractant was added to 10 cm3 aqueous solution, and the mixture was then shaken mechanically for 15 min. The system was kept from 278.15 K to 303.15 K, within ±0.05 K. After equilibrium for 15 min, two phases were allowed to separate. The aqueous phase was analyzed to determine the molality of ReO4− (m{ReO4−}) by using a spectrophotometer (type 722) for three replicate measurements. The results are listed in Table 1.

3. RESULTS AND DISCUSSION 3.1. Optimization Condition of Extraction. Shown from Table 1, with the increasing of ionic strength, acidity of the extraction system decreased, which indicated the usage amount of acid was increasing when there were more impurities. The ReO4− molality increased with the increasing of temperature, which revealed that low temperature was advantageous to the extraction. The extraction ratio was almost over 99 %, which shown the extraction progress performed completely. Molalities of perrhenate remained in queous phase are little at low ionic strength and low temperature, which indicated that the best extraction conditions was at 278.15 K, where extraction ratio was

2. EXPERIMENTAL SECTION An aqueous solution was composed of ammonium perrhenate, sulfuric acid, and sodium sulfate as an impurity, according to real industry concentrates. n-C7H16, analytical reagent (AR) grade, was used as diluent; the density is ρ = 0.68·103 kg/m3. Ammonium perrhenate, sodium sulfate, and H2SO4 (99 % mass pure) were also AR grade. © XXXX American Chemical Society

Received: March 4, 2015 Accepted: September 14, 2015

A

DOI: 10.1021/acs.jced.5b00188 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Values of Perrhenate Molality and pH at Temperatures from 278.15 K to 303.15 Ka T/K =

278.15

283.15

pH m ReO4− (10−6) log Km

1.19 0.745 5.3282

1.12 0.869 5.2611


1.23 0.869 5.2611

1.14 0.993 5.2031


1.25 0.993 5.2031

1.42 1.80 4.9445


1.30 1.06 5.1769

1.51 2.42 4.8155


1.38 1.12 5.1517

1.42 1.99 4.9015


1.31 1.24 5.1060

1.50 2.61 4.7831


1.40 1.37 5.0646

1.54 2.73 4.7629


1.44 1.55 5.0090

1.52 2.79 4.7531


1.50 1.99 4.9015

1.60 3.42 4.6657


1.57 2.36 4.8268

1.57 3.66 4.6351


1.62 2.61 4.7831

1.68 3.79 4.6206


1.66 2.79 4.7531

1.75 4.59 4.5363

288.15 I = 0.2 1.39 3.23 4.6902 I = 0.4 1.40 3.48 4.6578 I = 0.5 1.42 3.73 4.6278 I = 0.6 1.45 4.10 4.5862 I = 0.8 1.41 4.35 4.5605 I = 1.0 1.45 4.47 4.5483 I = 1.2 1.54 5.46 4.4607 I = 1.4 1.56 7.08 4.3474 I = 1.5 1.68 7.45 4.3250 I = 1.6 1.63 7.82 4.3036 I′ = 1.8 1.65 8.07 4.2899 I = 2.0 1.73 8.20 4.2833

293.15

298.15

303.15

1.42 7.84 4.3027

1.21 7.08 4.3474

1.12 13.5 4.0640

1.55 8.07 4.2899

1.36 12.7 4.0919

1.45 26.3 3.7689

1.58 10.1 4.1933

14.8 13.4 4.0669

1.53 32.9 3.6677

1.80 15.0 4.0169

1.52 16.4 3.9783

1.55 35.8 3.6295

1.82 15.3 4.0096

1.50 16.9 3.9651

1.59 39.3 3.5875

1.74 12.0 4.1166

1.63 21.5 3.8572

1.62 43.5 3.5411

1.69 12.0 4.1166

1.61 22.1 5.8458

1.65 45.9 3.5171

1.68 11.6 4.1326

1.72 30.0 3.7094

1.65 48.8 3.4888

1.55 12.6 4.0943

1.79 33.9 3.6543

1.68 51.6 3.4633

1.71 13.0 4.0792

1.86 39.9 3.5811

1.71 55.8 3.4276

1.74 14.2 4.0429

1.85 40.7 3.5720

1.71 57.4 3.4143

1.77 15.8 3.9954

1.89 44.5 3.5308

1.73 60.0 3.3933

m is the molar concentration (mol·kg−1), T is Kelvin temperature, I is ionic strength (molar concentration, (mol·kg−1). Standard uncertainties u are u(T) = ± 0.05 K, u(p) = ± 10 kPa, and the combined expanded uncertainty Uc is Uc(ρ) = ± 5·10−7 mol kg−1 (0.95 level of confidence).

a

ReO4− is the extraction complex. The standard extraction

99.77 %. In industry, the system should be kept at low temperature in high acidity with little impurities. 3.2. Activity Coefficient Study. In the presence of excessive TiOA (NR3), the extraction reaction is

equilibrium constant K0 is given by log K 0 = log[m{H+· NR3·ReO4 −}]

R3N(org) + H+(aq) + ReO4 −(aq) = H+·NR3·ReO4 −(org)

− log[m{H+} ·m{ReO4 −} ·m{NR3}]

(1)

+ log[γ {H+·NR3·ReO4 −}]

where (org) and (aq) refer to the organic and aqueous phase, respectively, NR3 is the extractant triisooctylamine, and NR3·H+·

− log[γ {H+} ·γ {ReO4 −} ·γ {NR3}] B

(2)

DOI: 10.1021/acs.jced.5b00188 J. Chem. Eng. Data XXXX, XXX, XXX−XXX


Article

where m is molality and γ is the activity coefficient. In the aqueous phase, molalities (m{i} for the species i) in the organic phase were calculated from the initial molalities a, b, and m{ReO4−}: m{H+· NR3· ReO4 −} = [a − m{ReO4 −}]/ρ

ln γX = z X 2F +

c

+

∑ (ma /m0)(2ΦMa + ∑ (mc /m0)(ψcXa a

+

(3)

c

∑ ∑ (mc /m )(mc ′/m )ψcc ′ X 0

+ |Z X | ∑ ∑ (mc /m0)(ma /m0)Cca

(4)

c

where ρ is the density of the organic phase. There were six ionic species (H+, NH4+, Na+, HSO4−, SO42−, and ReO4−) in the balanced aqueous phase. The activity coefficients and molalities are γ{H+}, γ{ NH4+ }, γ{ Na+}, γ1, γ2, and γ{ReO4−}, m{H+}, m{NH4+}, m{Na+}, m1, m2, and m{ReO4−}, respectively. The effective ionic strength I′ in the equilibrium aqueous phase could be calculated as

In estimating the activity coefficient, γ1, γ2, and γ{H }, in the solution, mixed parameters are all neglected, therefore, (1) ln γ {H+} = f r + (m{Na +}/m0)(m2 /m0)(βH2 y2 + C Na2) (1) (1) + 2(m2 /m0)βH2 + 2(m2 /m0)βH2 y1

+ (m{Na +}/m0)(m2 /m0)C H2

+ m{Na +} + 4m2)

(0) (1) + 2(m{Na +}/m0)(βNa2 − βNa1 ) (1) (1) + 2(m{Na +}/m0)γ1(βNa2 − βNa1 )

(5)

+ (m{Na +}/m0)2 (C Na2 − C Na1)

The second dissociation of sulfuric acid is +

HSO4 = H + SO4

+ (m{Na +}/m0)(m2 /m0)C Na2)

2−

(6)

+

K 2 = [a{H } ·m2 /m1]·[γ2/γ1]

log K 0 = log

(7)

Relationship of K2 between 0 and 55 °C can be given as14 ln K 2 = −14.0321 + 2825.2/T

= log K m + pH + log

K m = m{H+· NR3· ReO4 −}/[m{ReO4 −}·m{NR3}]

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 by14−16

F = fr +

a

c

0

(mc ′/m )Φ′cc ′ +

∑ (mc /m )(2ΦMc + ∑ (ma /m )(ψMca ∑ ∑ (ma /m0)(ma′/m0)ψMaa′

Z=

a′

c

∑ (mc /m0)|Zc| = ∑ (ma /m0)|Za| c

a

a′

+(2/1.2) ln[1 + 1.2(I /m0)1/2 ]

a

+ |Z M| ∑ ∑ (ma /m )(ma /m )Cca

∑ ∑ (ma /m )(ma′/m )Φ′aa′ 0

(17)

f r = −AP[(I /m0)1/2 /[1 + 1.2(I /m0)1/2 ]

0

0

c′

c 0

a

∑ (ma /m )(2BMa + ZCMa) a

a

∑ ∑ (ma /m0)(mc /m0)Bca′ + ∑ ∑ (mc /m0)

0

c

(16)

The molalities of the extractant in the equilibrium organic phase and the extraction complex are both small, which could be assumed that γ{ H+·NR3·ReO4−}/γ{ NR3} ≈ 1. In this system, activity coefficient γ{ReO4−} in the equilibrium aqueous can be expressed by Pitzer’s theory. In eq 11 to 14, where

(10)

0

(15)

and equilibrium concentration product, Km was defined as

(9)

m{H+} = 10−pH /γ {H+}

γ[H+NR3ReO−4 ] γ[NR3]

− log γ[ReO−4 ]

the initial molality of the Na2SO4, d, was used as the supporting electrolyte. m1 and m2 values can be obtained from eqs 5 to 9 using the iterative method. To our knowledge

+

γ[H+NR3ReO−4 ] γ[ReO−4 ] × γ[NR3]

+ log

Thus, m1 and m2 vary with temperature, also they vary with ionic strength of the aqueous solution. In the system

+

m[H+NR3ReO−4 ] − log(a[H+]) m[ReO−4 ] × m[NR3]

(8)

m1 + m2 = c + d

(14)

3.3. Polynomial Approximation Method to Determine K0. Equation 2 can now be expressed as

K2 is the second dissociation constant:

ln γM = z M F +

(13)

(1) ln(γ2/γ1) = 3f r + 3(m{Na +}/m0)(m2 /m0)βNa2 y2

= 1/2 × (m{ReO4 −} + m{NH4 +} + m{Cl−} + m{H+}

2

(12)

a +

I ′ = 1/2ΣmiZi 2

−

0

c′

c

m{NR3} = b − [a − m{ReO4 −}]/ρ

∑ (mc /m0)(2BCX + ZCcX)

a

(18)

(19)

0

CijP = CijP /2(|zizj|)1/2

(11) C

(20) DOI: 10.1021/acs.jced.5b00188 J. Chem. Eng. Data XXXX, XXX, XXX−XXX


Article

Table 2. Values of log K0 and Standard Molar Thermodynamic Quantities in the Extraction Process at Temperature from 278.15 K to 303.15 K ΔrGm0

T 0

K

log K

s

278.15 283.15 288.15 293.15 298.15 303.15

5.913 5.475 5.175 4.877 4.515 4.333

0.089 0.025 0.032 0.049 0.069 0.012

kJ mol

ΔrHm0

−1

−1

kJ mol

−136.8 −129.6 −123.3 −117.8 −113.0 −109.1

where the subscripts “a” and “c” represent anions and cations, respectively, AP is Debye−Hückel coefficient of the osmotic function,17 z is the charge of ion (m0 = 1 mol kg−1). Bca ′ is the first derivative of Bca with respect to I/m0, Bca and Cca are the second and third virial coefficients for the electrolyte, Φij is the second virial coefficient representing the difference between the averaged interactions, Φij′ is the derivative of Φij with respect to I/m0. According to Pitzer,18

Bca = βcs(0) + βca(1)y1

(21)

′ = βca(1)y2 Bca

(22)

- 555.6 −510.7 −465.0 −418.5 −371.2 −323.1

(24)

0

In determination of K , according to our previous word and the advice of Pitzer and Mayorga,15,16 ψMca, is considered to be independent of ionic strength; therefore, all the mixed parameters (Φij, Φ′ij and ψijk) are neglected in estimating γ{ReO4−} and γ{H+}. The pertinent combination of activity coefficients could then be written as

+ 2(vX /v)ΦXa ] + (vX /v) ∑ mc[2BCx + ZCCx c

∑ ∑ mcmav−1[2vM ZMCCa a

■

∑ ∑ mcmc ′(vX /v)ψcc ′ X + c

Solvent Extraction of Perrhenate from Sulfuric Acid Medium by

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