Thermodynamics of solvent extraction of perrhenate with tertiary isooctyl amine

Fluid Phase Equilibria 300 (2011) 116–119

Contents lists available at ScienceDirect

Fluid Phase Equilibria journal homepage: www.elsevier.com/locate/fluid

Thermodynamics of solvent extraction of perrhenate with tertiary isooctyl amine Da-wei Fang ∗ , Han Wang, Ying Xiong, Xue-jun Gu, Shu-liang Zang Research Institute of Rare and Scattered Element, College of Chemistry, Liaoning University, Shenyang 110036, China

a r t i c l e

i n f o

Article history: Received 7 January 2010 Received in revised form 29 September 2010 Accepted 25 October 2010 Available online 3 November 2010

a b s t r a c t In the solvent extraction system, the equilibrium molalities of ReO4 − were measured at ionic strength from 0.2 to 2.0 mol kg−1 in the aqueous phase containing NH4 Cl as supporting electrolyte at temperatures from 278.15 K to 303.15 K. The standard extraction constants K0 at various temperatures were obtained by methods of Debye–Hückel extrapolation and Pitzer polynomial approximation. Thermodynamic properties for the extraction process were calculated. © 2010 Elsevier B.V. All rights reserved.

Keywords: Extraction Perrhenate TiOA

by

1. Introduction Owing to the application on chemical industry, martial materials, catalyzer and dystectic metals, research on rhenium has attracted more attention. Rhenium is one of the rare elements on earth, which accompanies with other fertility elements. Solvent extraction is one of the main methods of separation and enrichment of rhenium from non ferrous metals mine tailings[1]. Thermodynamic extraction equilibrium constant and thermodynamic parameters are the basis of research on extraction process technics and best design [2]. In this paper, we measured concentration of rheniumate in aqueous phase at different ionic strength in hydrochloric acid system. The standard extraction constants K0 are obtained by methods of extrapolation and polynomial approximation [3–5]. Thermodynamic quantities for the extraction process are calculated. In the presence of excessive extractant tertiary isooctyl amine (TiOA), the extraction reaction is R 3 N(org) + H+ (aq) + ReO4 − (aq) = H+ ·NR 3 ·ReO4 − (org)

(1)

where (aq) and (org) refer to the aqueous and organic phase, respectively, R3 N is the extractant TiOA, and NR3 ·H+ ·ReO4 − is the extraction complex. The standard equilibrium constant K0 is given

∗ Corresponding author. Tel.: +86 24 62202006. E-mail address: davidfi[email protected] (D.-w. Fang). 0378-3812/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2010.10.019

lg K 0 = lg[m{H+ · NR3 · ReO4 − }] − lg[m{H+ } · m{ReO4 − } · m{NR3 }] + lg[{H+ · NR3 · ReO4 − }] − lg[{H+ } · {ReO4 − } · {NR3 }] (2) where  is the activity coefficient in the molality scale, and m is the molality. 2. Experimental The water used was doubly deionized and its conductance was 1.5 × 10−4 −1 m−1 ( is ohm). The thallium sulphate was of GR (Guarantee Reagent) grade, the sulphuric acid was of AR (analytical reagent) grade (99% mass pure), and the ammonium chloride was of AR grade. The n-C7 H16 used as diluent was of AR grade. All initial solutions to be measured were freshly prepared. The aqueous phase was prepared by dissolving NH4 ReO4 in an aqueous solution of HCl of constant molality. The initial molality of the NH4 ReO4 was a = 0.001 mol kg−1 , and the initial molality of the HCl was c = 0.1 mol kg−1 . The supporting electrolyte (NH4 Cl) was used to adjust the total ionic strength I of the aqueous solution to 0.2–2.0 mol kg−1 . The organic phase was prepared by dissolving TiOA in n-C7 H16 , the initial molality of TiOA being kept constant (b = 0.02 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 the two-phase mixture was shaken mechanically for 15 min. The extraction bottles were kept at different temperatures: 278.15, 283.15, 288.15, 293.15, 298.15 and 303.15 K, within ±0.05 K. After

D.-w. Fang et al. / Fluid Phase Equilibria 300 (2011) 116–119 Table 1 Values of lg Km and effective ionic strength I at temperatures in the range 278.15–303.15 K. T/K

278.15

283.15

288.15

293.15

298.15

303.15

I = 0.2 I ReO4 − (×10−5 ) pH

0.189 1.260 1.39

0.196 1.502 1.30

0.203 1.589 1.22

0.216 2.055 1.11

0.212 2.353 1.18

0.206 2.769 1.20

I = 0.4 I ReO4 − (×10−5 ) pH

0.385 1.850 1.5

0.401 1.850 1.28

0.406 1.881 1.23

0.425 2.477 1.08

0.411 2.409 1.20

0.417 2.794 1.14

I = 0.5 I ReO4 − (×10−5 ) pH

0.483 2.328 1.54

0.503 1.943 1.27

0.511 1.943 1.20

0.519 2.403 1.14

0.510 2.508 1.22

0.521 2.732 1.13

I = 0.6 I ReO4 − (×10−5 ) pH

0.587 1.726 1.49

0.606 2.024 1.25

0.616 2.148 1.17

0.618 2.396 1.16

0.623 2.365 1.14

0.609 2.527 1.23

I = 0.8 I ReO4 − (×10−5 ) pH

0.795 1.881 1.39

0.811 2.105 1.23

0.816 2.210 1.19

0.831 2.353 1.09

0.824 2.415 1.15

0.846 2.726 1.01

I = 1.0 I ReO4 − (×10−5 ) pH

0.987 2.154 1.52

0.992 2.117 1.45

1.022 2.161 1.16

1.035 2.477 1.08

1.033 2.452 1.10

1.041 2.738 1.05

1.191 2.210 1.46

1.219 2.235 1.19

1.228 2.235 1.13

1.217 2.496 1.21

1.235 2.390 1.10

1.247 2.788 1.03

I = 1.4 I ReO4 − (×10−5 ) pH

1.389 2.279 1.51

1.426 2.328 1.15

1.434 2.322 1.10

1.438 2.577 1.08

1.441 2.446 1.07

1.449 2.800 1.03

I = 1.5 I ReO4 − (×10−5 ) pH

1.495 2.365 1.43

1.522 2.396 1.18

1.532 2.471 1. 12

1.535 2.657 1.10

1.552 2.496 1.02

1.556 2.906 1.00

I = 1.6 I ReO4 − (×10−5 ) pH

1.589 2.471 1.51

1.626 2.438 1.16

1.629 2.521 1.14

1.660 2.701 0.98

1.647 2.496 1.05

1.653 2.930 1.02

I = 1.8 I ReO4 − (×10−5 ) pH

1.793 2.527 1.47

1.804 2.552 1.34

1. 821 2.477 1.20

1.872 2.769 0.94

1.857 2.955 1.01

1.859 2.608 1.00

I = 2.0 I ReO4 − (×10−5 ) pH

1.997 2.552 1.42

2.005 2.645 1.34

2.022 2.564 1.20

2.037 2.775 1.11

2.006 3.017 1.04

2.051 3.048 1.04

standing for 15 min, the two phases were separated and the molality of ReO4 − (m{ReO4 − }) in the equilibrium aqueous phase was determined using a 722 spectrophotometer. 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 · ReO− 4} =

m{NR3 } =

Table 2 Values of lg K0 over the temperature range 278.15–303.15 K obtained using the two methods. T (K)

lg K0 (D–H)

a0 (A)

lg K0 (P)

303.15 298.15 293.15 288.15 283.15 278.15

6.6087 6.7889 6.8335 7.0731 7.2173 7.4211

1.90 1.60 1.80 1.60 1.50 1.30

3.2431 3.2773 3.3497 3.5404 3.563 3.6382

3. Results and discussion The values of pH measured at the various temperatures (in the range 278.15–303.15 K) for several total ionic strengths in the range 0.2–2.0 mol kg−1 are listed in Table 1, where each value of pH is the mean of three replicate measurements. 3.1. Extrapolation to determine the value of K0 There were four ionic species (H+ , NH4 + , ReO4 − and Cl− ) in the equilibrium aqueous phase. Their molalities and activity coefficients are m{H+ }, m{NH4 + }, m{ReO4 − } and m{Cl− }, and {H+ }, {NH4 + }, {ReO4 − } and {Cl− }, respectively. The effective ionic strength I in the equilibrium aqueous phase can then be calculated as I =

I = 1.2 I ReO4 − (×10−5 ) pH

[a − m{ReO− 4 }] 

b − [a − m{ReO− 4 }] 

where  is the density of the organic phase.

117

1 × ˙mi Zi 2 2

(5)

The calculated values of I are listed in Table 1. Then Eq. (2) could be expressed as lg K 0 = lg

m[H+ NR3 ReO− 4]

− lg(a[H+ ]) + lg

m[ReO− 4 ] × m[NR3 ]

= lg Km + pH + lg

[H+ NR3 ReO− 4] [NR3 ]

[H+ NR3 ReO− 4]

[ReO− 4 ] × [NR3 ]

− lg [ReO− 4]

(6)

and Km is equilibrium concentration product, defined as Km =

m{H+ · NR3 · ReO− 4}

(7)

[m{ReO− 4 } · m{NR3 }]

Because the molalities of the extraction complex and the extractant in the equilibrium organic phase are very small, it can be assumed that {H+ ·NR3 ·ReO4 − }/{NR3 } ≈ 1. As {ReO4 − } in the equilibrium aqueous phase might be proportional to the effective ionic strength, it can be expressed by the extended Debye–Hückel equation, the working equation to determine K0 by extrapolation is



lg K  = lg Km + pH+

A

I

1 + Ba0



I

= lg K 0 + bI 

(8)

where lg K’ is an extrapolation function, which can be calculated from experimental results. a0 is the ion-size parameter, b is an empirical parameter, A, B are the Debye–Hückel parameters. Using a least-squares method, a linear regression of lg K vs. I yielded values of lg K0 . These are given in Table 2 as lg K0 (D–H) together with the standard deviations. 3.2. Polynomial approximation to determine K0

(3)

Eq. (2) could be expressed as − + lg K 0 = lg[m{H+ · NR3 · ReO− 4 }] − lg[m{H } · m{ReO4 } · m{NR3 }]

(4)

− lg[{H+ } · {ReO− 4 }]

(9)

The activity coefficients {H+ } and {ReO4 − } in Eq. (9) can be estimated using Pitzer’s equations. According to Pitzer’s theory, the

118

D.-w. Fang et al. / Fluid Phase Equilibria 300 (2011) 116–119

Table 3 The standard molar thermodynamic properties for the extraction process in the temperature range 278.15–303.15 K. T (K)

0 r GM (kJ mol−1 )

0 r HM (kJ mol−1 )

0 r SM (J (K mol)−1 )

0 r CP,M (J (K mol)−1 )

303.15 298.15 293.15 288.15 283.15 278.15

−18.67 −18.87 −19.05 −19.20 −19.33 −19.43

−31.52 −30.08 −28.66 −27.27 −25.90 −24.55

−42.39 −37.59 −32.80 −28.01 −23.21 −18.42

−291 −286 −281 −276 −271 −267

activity coefficients  M and  X of the cation M and the anion X in a multicomponent electrolyte solution are given by [6]: ln M = zM 2 F +

  ma  m0

a

+

+



  mc 

2˚Mc

m0

c

m0

a

m0

c

ln X = zX 2 F +

a

  mc  m0

c

2˚Ma +

m0

a

c

m0

a

c

m0

a

 f = −Ap

m0

[1 + 1.2(I/m0 )

  mc  m0

|Zc | =

CijP 2(|zi Zj |)1/2

1/2



m0

)exp(−˛{I/m0 }

2

+

(11)

   mc   mc  m0

m0

+

+ ˛ {I/m }/2) exp(−˛{I/m }

+

  M 

  X



+

1.2

|Za |

(18)

0 2

2

)]/(˛ {I/m } )



ln 1 + 1.2

a

mc 2BCx + ZCCx + 2

 

(19)

  M



˚Mc

  X



a

 

mc mc

 

ma ma





  X



cc X ,

  M



Maa

 mn (M nm + X nX )

+2

m0

˚Xa

mc ma −I [2M ZM CCa + M Mca + X CaX ]

a
 I 1/2



ma × 2BMa + ZCMa + 2

c

c

˚cc

(12)



]/(˛2 {I/m0 }) 0 1/2

0

c
 2 

1/2

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; (3) following the advice of Pitzer and Mayorga [10,11]. In estimating {ReO4 − } and {H+ }, all the mixed parameters (˚ij , ˚ij

ln MX = |ZM ZX |F +

c

1/2

and ijk ) are neglected, so that the pertinent combination of activity coefficients may be written as

cXa

(13)

  ma  a

(10)

˚aa

]

(1)

y2 = 2[−1 + (1 + ˛{I/m }

c

+

(17)

y1 = 2[1 − (1 + ˛{I/m0 }

Cca

 Bca +

1/2

I/m0

r

CijP =

m0

   ma   ma  a

c

m0

 Bca =

(0)

cc X M

m0

   ma   mc 

F = fr +

Z=

m0

a

(16)

(1) ˇca y2

where ˇca and ˇca are characteristic parameters of the electrolyte, and y1 and y2 are defined as

Cca

m0

   mc   ma  c

+

m0

(1)

Bca = ˇcs + ˇca y1

0 1/2

  mc  c

+ |ZX | where

m0

   mc   mc  c

Mca

(2BCX + ZCcX )



  ma 



Maa

   mc   ma  m0

(0)



m0

a

+ |ZM |

+

 ma

   ma   ma  a

+

(2BMa + ZCMa )

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 Kim [9]:



n

(20)

Then, substitution of Eq. (20) into Eq. (9), yields a working equation: lg K  = lg Km − lg m{H+ } − ln[{H+ } · {ReO4 − }]/ln 10

(14)

= lg K 0 + 2/ln 10 · mNH4 + 2/ln 10 · y1 mNH4 +2/ln 10 · ZmNH4 CNH4 ReO4

(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 Pitzer [7,8] for a wide range of temperatures and pressures), Bca and Cca are the second and third virial coefficients for the  is the first derivative of B with respect to I/m0 , ˚ electrolyte, Bca ca ij 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, ˚ij is the derivative of ˚ij with

(21)

Using a least-squares method, regression of the extrapolation function (lg K ) calculated from the experimental results against (0) (1) ˇNH ·ReO , y1 ˇNH ReO , and 1/2ZCNH4 ReO4 yielded the value of lg K0 4

4

4

4

which are here denoted by lg K0 (P) and are given in Table 2. 3.3. Thermodynamic properties for the extraction process The values of lg K0 obtained at various temperatures obtained by Pitzer’s equation were fitted to the following equation [12–14]: lg K 0 = A1 + A2 /T + A3 T

(22)

D.-w. Fang et al. / Fluid Phase Equilibria 300 (2011) 116–119

The values of parameters Ai are: A1 = 12.97, A2 = −654.74 and A3 = −2.50 × 10−2 with a standard deviation of s = 4.895 × 10−2 . 0 ,  H0 , The standard molar thermodynamic properties r GM r M 0 ,  C0 r SM for the extraction process are simply related to the r P,M parameters in Eq. (22):

119

Acknowledgements This project was supported by NSFC (Nos. 21003068 and 21071073), National Science Foundation of China, and Foundation of Education Bureau of Liaoning Province (Nos. 2008S103 and 2009S041).

0 r GM = −(R ln 10) (A1 T + A2 + A3 T 2 )

(23)

0 r HM

= (R ln 10)(A3 T − A2 )

(24)

References

0 r SM = (R ln 10)(A1 + 2A3 T )

(25)

0 r CP,M = (R ln 10)(2A3 T )

(26)

[1] L.Z. Zhou, S.C. Chen, Separation and Metallurgy of Rare and Scattered Metals [M], vol. 11, Metallurgy Industry Press, Beijing, 2008 (in Chinese). [2] X.Z. Liu, Y.C. Ge, Y.L. Song, Chem. J. Chin. Univ. 12 (1991) 1007 (in Chinese). [3] K.Y. Song, J.Z. Yang, Y.L. Song, X.P. Wang, J. Chem. Thermodyn. 22 (1990) 695–707. [4] X.Z. Liu, J.-Z. Yang, Y.L. Song, Y.-H. Kang, Acta Chim. Sinica 50 (1992) 789–795 (in Chinese). [5] J.Z. Yang, X.Z. Liu, Y.H. Kang, K.Y. Song, Fluid Phase Equilib. 786 (1992) 249–260. [6] K.S. Pitzer, An interaction approach: theory and data correlation, in: K.S. Pitzer (Ed.), Activity Coefficients in Electrolyte solutions, 2nd ed., CRC Press, Boca Raton, FL, 1991. [7] K.S. Pitzer, in: R.M. Pytkowicz (Ed.), Activity Coefficients in Electrolyte Solutions, vol. 157, CRC Press, Florida, 1979. [8] D.J. Bradley, K.S. Pitzer, J. Phys. Chem. 83 (1979) 1599. [9] K.S. Pitzer, J. Kim, J. Am. Chem. Soc. 96 (1974) 5701. [10] K.S. Pitzer, R.N. Roy, L.F. Silvester, J. Am. Chem. Soc. 99 (1977) 4930. [11] K.S. Pitzer, G. Mayorga, J. Phys. Chem. 77 (1973) 2300. [12] J.Z. Yang, P.-S. Song, D.-B. Wang, J. Chem. Thermodyn. 29 (1997) 1343–1351. [13] J.Z. Yang, B. Sun, P.-S. Song, Thermochim. Acta 352 (2000) 69–74. [14] J.Z. Yang, R.-B. Zhang, H. Xue, P. Tian, J. Chem. Thermodyn. 34 (2002) 401–407.

2

where R is the gas constant. The thermodynamic quantities calculated from Eq. (23) to (26) are listed in Table 3. 4. Conclusions The extractant has satisfactory extraction effect at various temperatures of the experiment. r G0 and K0 increase with decrease of experimental temperatures, which indicates low temperature benefits extraction. The negative experimental association Gibbs 0 < 0 means that the ionic association reaction can energy. GM occur spontaneously under the conditions of constant temperature and pressure. And the enthalpy is the dominant thermodynamic factor [12–14].