H2SO4 Mixed Media by

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Separation of Bi(III) and Sb(III) from Cu(II) HCl/H2SO4 Mixed Media by Supported Liquid Membranes Using Cyanex 921 as Carrier Luis A. Santiago-Santiago,† J. Antonio Reyes-Aguilera,*,§ M. P. Gonzalez,‡ Diana Cholico-Gonzalez,‡ and Mario Avila-Rodríguez‡ †

Universidad Politécnica de Tlaxcala, México Departamento de Ingenierías Química, Electrónica y Biomédica, Campus León, Universidad de Guanajuato, México ‡ Departamento de Química, Campus Guanajuato, Universidad de Guanajuato, México §

ABSTRACT: We present a systematic study of the separation of Bi(III) and Sb(III) contained in acidic HCl/H2SO4 aqueous solutions of Cu(II), by SLM, using Cyanex 921 as carrier. The transfer of Sb(III), Bi(III) and Cu(II) was evaluated in order to determine the efficiency and selectivity of the specific SLM developed. Using a polyvinylidene fluoride (PVDF) microporous membrane impregnated with Cyanex 921, as SLM, we studied the influence of the characteristics of the stripping solution and the effect of temperature on the membrane efficiency and stability. Recovery rates of Sb(III) and Bi(III) were close to 99%, while Cu(II) was barely transferred into the stripping solution.

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INTRODUCTION Refractory wastes (solid wastes) from industries are more common every day due to the characteristics both of feedstock and production processes. In some cases, these industrial wastes contain valuable materials. Leaching refractory wastes sometimes requires the use of a mixture of acids (for instance HCl/ H2SO4), resulting in complex aqueous solutions from which valuable materials must be recovered. The aim of this paper is to study the separation process of Sb(III) and Bi(III) from Cu(II) aqueous solutions using Supported Liquid Membranes (SLM). Copper is one of the most important commercial metals. Approximately 20% of all copper produced worldwide is obtained by leaching, liquid−liquid extraction, and electrolytic refining,1 the latter being the method used when high purity copper is required. Several authors have proposed the liquid− liquid extraction technique for removing some of the impurities from electrolyte solutions using neutral and acidic extractants. Dreisinger et al.2 have used tributyl phosphate (TBP), mono-2ethylhexylphosphoric acid (MEHPA), dibutylbutylphosphonate (DBBP), and dipentylpentylphosphonate (DPPP) to extract As, Sb, and Bi from electrolyte solutions with high Cu concentrations (35−45 g L−1). Wang et al.3 have reported the use of mixtures of octylphosphine oxides and sulfides (Cyanex 923 and Cyanex 925, respectively), di(2-ethylhexylphosphoric) acid (DEHPA), TBP, and primary amines for the liquid−liquid extraction of 3.5 g L−1 of As, 0.21 g L−1 of Sb, and 1.20 g L−1 of Bi from 190 g L−1 solutions of H2SO4, in the presence of Cu. Extraction rates under 61% were obtained when the Cyanex 923 was used as extractant. The authors show the extraction of Bi and Sb, from a mixed H2SO4/HCl media, has been improved significantly. For the extraction of As(V), Sb(III), and Bi(III), from real electrolyte cooper solutions, Cox et al.4 have proposed LIX 1104 SM, Cyanex 923, Cyanex 921, and Acorga SBX-50 as the extractants in the absence and presence of chlorides in a system carrying copper and impurities. The authors reported that Cyanex 923 can extract all three ions with good extraction percentages. Szymanowsky5 and Kim et al.6 © 2012 American Chemical Society

have studied the separation of Bi(III), Sb(III), and As(III) from Cu(II) using respectively Acorga SBX-50, TBP, DEHPA mono(iso-octadecyl) phosphoric acid (DS-5834), and LIX 1104, as extractants in chloride media. Gupta and Begum7 have proposed bis(2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex 301) for the removal of As(III) from Cu(II) solutions in the presence of Sb(III) and Bi(III). Finally, Kul and Cetinkaya8 have proposed LIX984N-C to recover copper in low concentrations (∼2.5 g L−1) in solutions from the washing stages of copper electro deposition processes. From this brief literature review, we can conclude that liquid−liquid extraction of Sb(III) and Bi(III) can be performed with acceptable results, especially when using the neutral extractants Cyanex 921 and Cyanex 923. However, the use of great quantities of solvents necessary in the liquid−liquid extraction system requires an important security system to avoid pollution problems. So it had been necessary to look for alternatives to reduce the use of organic solvents in the extraction processes for the removal of metal ions with at least as good performance as the liquid−liquid extraction. An interesting alternative is to employ Supported Liquid Membrane Systems (SLM). This technology has become increasingly important because of its advantages over solvent extraction, dramatically reducing the volume of organic phase used. Danessi,9 who conducted extensive studies, showed that the SLM technique offers advantages over liquid−liquid extraction such as the extraction and stripping processes are carried out simultaneously, and it is possible to perform it using highly selective and expensive extractants and low operating and capital costs. In the literature, the use of SLM has been reported for the recovery of Cu(II), when the Cu(II) concentrations are low, when it is an impurity, or when it is Received: Revised: Accepted: Published: 15184

June 2, 2012 October 23, 2012 October 23, 2012 October 23, 2012 dx.doi.org/10.1021/ie301447x | Ind. Eng. Chem. Res. 2012, 51, 15184−15192

Industrial & Engineering Chemistry Research

Article

Sb2O3 (Sigma-Aldrich), and CuSO4·5H2O (Karal), dissolved in an HCl/H2SO4 mineral acid mixture (Karal) with the acids previously diluted in deionized water to obtain a concentration of 0.5 mol L−1/2 mol L−1. The stripping solutions were prepared by dilution of concentrated H2SO4 to a concentration of 0.2 mol L−1 and by dissolution in deionized water of the adequate mass of NaCl, Na2SO4 (Industrial Kem), or tartaric acid (Karal) to obtain their respective solutions at the desired concentration. The metal ion-Cyanex 921 solvate stoichiometry was determined by using the liquid−liquid extraction technique applying the slope method, and the chloride/M(III) ratio was determined by titration of total chlorides transported through the SLM to the stripping solution (transport of the complex M(III)-Cl− + HCl transport). Both experimental procedures have been described in detail elsewhere.11

found in the wash effluents of copper plating processes.10 In a previous paper,11 we reported the transfer of Bi(III) using SLM with Cyanex 921 as extractant diluted in kerosene and supported on hydrophobic polyvinylidenefluoride (PVDF), with good recovery rates. In the same study, we showed that the SLM was stable for working periods exceeding 12 h, which allowed bismuth to be recovered form acidic solutions with efficiencies above 90%. We did not find in the literature, any studies for the recovery of Sb(III) and the separation of Bi(III) and Sb(III) from Cu(II) aqueous solutions using SLM. Thus, in this paper, we report the separation of bismuth(III) and antimony(III) from mixed media HCl/H2SO4 solutions of copper(II) by SLM, evaluating the performance of the separation system considering the characteristics of the stripping solution and the temperature and their effect over the transfer process of both metal ions and the stability of the supported liquid membrane.

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RESULTS AND DISCUSSION Extraction of Sb(III) and Bi(III) by SLM. Figure 2 shows the transfer of Sb(III) and Bi(III) by SLM, in four steps: 1)

EXPERIMENTAL SECTION The extractant used to prepare the SLM was tri-noctylphosphine oxide, commercially known as Cyanex 921, which was kindly provided by Cytec Canada Inc., with a purity of 93%, used without any purification. The organic phase used in the impregnation of the SLM was made with Cyanex 921 diluted in kerosene (Aldrich, US), with a boiling point at 448.15−588.15 K, and with low aromatic content. As a support we used hydrophobic polyvinylidenedifluoride (PVDF) Millipore brand, with a porosity of 75%, thickness of 125 μm, and average pore size of 0.22 μm. The SLM was prepared by immersing the membrane for two hours in the organic solution containing 0.3 mol L−1 Cyanex 921 diluted in kerosene and removing the excess by allowing it to drip off for 10 min. Once ready, it was placed in a circular window of cells 1 and 2 (Figure 1), and the system was assembled. The feed and stripping

Figure 2. Schematic diagram for M(III) transfer process through SLM using Cyanex 921 as extractant. M(III) = Sb(III) or Bi(III).

formation of neutral species of metal ions in the feed phase; 2) solvation of these species by the action of Cyanex 921 at the feed-SLM interface; 3) diffusion of the metal solvates M(III)Cyanex 921 formed through the SLM; and 4) release of metal ion M(III) from the SLM to the stripping solution. Hence the hydrodynamic and chemical conditions of both, feed and stripping phases, play an important role in the transfer efficiency. Permeability of the SLM System. Preliminary Bi(III) and Sb(III) liquid−liquid extraction studies with Cyanex 921 have shown that the extraction of these metal ions from HCl aqueous media is possible. On the other hand, when the extraction is conducted form sulfuric acid aqueous media, the transfer to the organic phase of both metal ions is negligible. Hence, the transfer efficiency of Bi(III) and Sb(III) through the SLM was studied for each metal ion separately. We used H2SO4/HCl mixed media in the feed solution and H2SO4 as the stripping solution. Considering that the SLM system reaches a steady state and that the concentrations of chemical species transferred are much lower than the extractant concentrations, the transfer efficiency can be obtained as a function of the SLM permeability calculated by9

Figure 1. Lateral view of unit used in mass transfer of Sb(III), Bi(III), and Cu(II).

solutions, both 300 mL, were added to cells 1 and 2, respectively. Both cells were covered, and the system was stirred at 1850 rpm (30.8 Hz). Aliquots were taken from both cells at different transfer times, and Bi(III), Sb(III), and Cu(II) contents were determined by the flame atomic absorption technique, with a Perkin-Elmer AAnalyst 200 spectrophotometer. All reagents were analytical grade. The feed solutions with Bi(III), Sb(III), and Cu(II) were respectively prepared from BiOCO3 (Aldrich),

ln 15185

[M(III)]t Q = −P t [M(III)]t ,0 V

(1)

dx.doi.org/10.1021/ie301447x | Ind. Eng. Chem. Res. 2012, 51, 15184−15192


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Figure 3. Variation of ln [M(III)0/[M (III)]t in the feed solution during the transfer of M(III) through SLM. Feed solution: a): [Sb(III)] = 100 mg L−1 in: ⧫ 2 mol L−1 H2SO4/2.5 mol L−1HCl, ■ 1 mol L−1 H2SO4/1 mol L−1HCl, ▲ 2 mol L−1 H2SO4/0.5 mol L−1 HCl; b): [Bi(III)] = 100 mg L−1 in: ⧫ 2 mol L−1 H2SO4/0.2 mol L−1 HCl, ■ 2 mol L−1 H2SO4/0.5 mol L−1 HCl, ▲ 2 mol L−1 H2SO4/1 mol L−1 HCl. Stripping solution: 0.2 mol L−1 H2SO4.

Table 1. Cl−/Sb(III) and Cl−/Bi(III) Ratio for Sb(III) and Bi(III) Transfer with SLMa Sb(III) transfer

Bi(III) transfer

transfer time (min)

Sb(III) transfer stripping (10−5 mol)

Cl− transfer stripping (10−5 mol)

nCl−/nSb(III) ratio stripping

Bi(III) transfer stripping (10−5 mol)

Cl− transfer stripping (10−5 mol)

nCl−/nBi(III) ratio stripping

0 15 30 60 120 180 240 300

1.71 3.83 7.13 12.1 15.2 17.0 18.0

5.52 13.5 25.4 46.4 61.9 71.4 79.0

3.23 3.54 3.56 3.85 4.07 4.20 4.39

0.575 1.38 3.03 5.95 8.69 11.0 11.9

1.87 4.63 9.15 18.0 31.1 39.7 52.3

3.25 3.37 3.02 3.03 3.58 3.62 4.38

Feed: [Sb(III)] = 87.23 mg L−1, [Bi(III)] = 109.5 mg L−1 in 2 mol L−1 H2SO4 /0.5 mol L−1 HCl; Stirring 30.8 Hz. Stripping: H2SO4 0.2 mol L−1; SLM: Hydrophobic PVDF support impregnated with 0.3 mol L−1 Cyanex 921 in kerosene.

a

metal ions transfer. We quantified the Cl− ions transferred into the stripping solution, and we found a relation to the mass (moles) of Sb(III) and Bi(III) found in the stripping phase. The results in Table 1 show that the Cl−/Sb(III) ratio increases from 3.23 to 3.56 for the first 60 min of transfer; from 3.56 to 3.85 for a transfer time of 60 to 120 min, and finally it increases to 4.39 for a time of 300 min. In the case of Bi(III), the ratio between Cl− ions and Bi(III) is just over 3 for transfer times of 15 to 120 min. From 120 to 240 min, the ratio Cl−/Bi(III) increases slightly to 3.62, and, finally, it reaches 4.4 for a transfer time of 300 min. In both cases the quantity of Cl− ions into the stripping solution increased with the time and reaches a Cl−/ M(III) ratio of 4.4. It is possible to explain this phenomenon if we consider that the solvating extractants (like Cyanex 921) have the capacity to extract mineral acids, among them the HCl as Alguacil and Lopez12 proposed. In order to confirm this fact, we studied the HCl extraction with Cyanex 921 (see Figure 4). It is possible to conclude that the extraction of HCl occurs simultaneously during the transfer of Sb(III) or Bi(III) into the organic phase. Considering that the extraction of metal ions by Cyanex 921 requires the neutral form, with the results shown in the Table 1, it is possible to confirm that the transfer of Sb(III) and Bi(III) is conducted through the formation of neutral complexes with the chloride ions. The study of the liquid− liquid extraction of Bi(III) and Sb(III) by the slope method confirms these assumptions.

where P is the permeability of the SLM; [M(III)]t and [M(III)]t,0 are the metal ion concentration at time t and at time t = 0, respectively; Q, V, and t are respectively the effective SLM contact area in cm2, the feed solution volume in cm3, and time in minutes. Figure 3 shows the permeabilities obtained for Sb(III) and Bi(III). In the case of Sb(III) extraction, the permeability decreases when the HCl concentration increases getting permeability values of 0.1966 cm min−1, 0.1835 cm min−1, and 0.0828 cm min−1 for 0.5 mol L−1, 1 mol L−1, and 2.5 mol L−1 HCl concentrations, respectively. This means that the SLM efficiency diminishes with the HCl concentration in the feed solution. On the other hand, Bi(III) permeabilities have a mixed behavior with values of 0.2060 cm min−1, 0.2479 cm min−1, and 0.2351 cm min−1 for 0.2 mol L−1, 0.5 mol L−1, and 1 mol L−1 HCl concentration, respectively. These differences in transfer behavior for Sb(III) and Bi(III) are related to the extraction reactions involving the presence of H+ and Cl− ions in the aqueous phase, as it will be seen later. Employing a mixed media composed of 2 mol L−1 H2SO4/ HCl 0.5 mol L−1 as feed phase gives the best mass transfer for both metal ions, so these same conditions will be used for the next transfer studies by SLM. During the transfer process of metal ions, it was observed that chloride ions were transferred through the SLM from the feed solution to the stripping solution, accompanying both 15186



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we observe a greater amount of SbOCl on the membrane. At the same time the extraction of Bi(III) into the stripping solution is reduced to 52%. However after 480 min (Figure 5b) the concentrations of both metal ions increases again. This behavior can be explained if one considers that the concentration of Cl− in the stripping solution (at these stages) is high enough to redissolve the precipitate due to the formation of soluble complexes between the Sb(III) ions and the chloride ions. The transfer of Cu(II) (24.22 g L−1) through the SLM and its influence on the transfer process of Bi(III) and Sb(III) is shown in Figure 6. This figure shows the variation of Bi(III), Sb(III), and Cu(II) concentrations in the feed and in the stripping solutions, as a function of time, by the SLM, when Cu(II) has been added to the feed solution. The analysis of these figures reveals that the presence of Cu(II) does not significantly affect the extraction behavior of the two metals. We can also see that the SLM has a low affinity for Cu(II), with only 17.3 mg L−1 transferred in 720 min, which equals a transfer rate of 0.07%. These results demonstrate the feasibility of separating Bi(III) and Sb(III) from solutions with high Cu(II) content. This selectivity behavior by the SLM is according to that observed in the case of liquid−liquid extraction of Bi(III), Sb(III), and Cu(II), where the copper ion extraction is neglectable.2,3 However, we note, as in the previous case, the formation of a precipitate on the SLMstripping solution interface, which has a negative influence on the transfer process of Bi(III) and Sb(III) by the SLM. Then, it is necessary to find a solution that allows the stripping of the metal ions from the SLM, capable of maintaining, in aqueous solution, the entire amount of metal ions transferred by the SLM. Table 2 shows the different stripping solutions used in the transfer of Bi(III) and Sb(III) by the SLM and the percentage extracted to the membrane as well as the percentage recovered in the stripping solution. We observe that in using a 2 mol L−1 NaCl as a stripping solution, transfer is lower than the obtained by using H2SO4; in addition, only a fraction of the amount extracted to the SLM is recovered in the stripping solution. When using the 0.8 mol L−1 Na2SO4/0.2 mol L−1 H2SO4 mixture as stripping solution, we were able to transfer, to the SLM, the entire amount of both metal ions, Sb(III) and Bi(III), contained in the feed solution.

Figure 4. Variation of DHCl as a function of [Cyanex 921]. Aqueous phase: HCl 0.5 mol L−1; Organic phase: Cyanex 921 in Kerosene; Vorg/Vaq = 1; Temperature = 298.15 K.

Extraction of Bi(III)/Sb(III) Mixtures by SLM. Figure 5 shows the concentrations of Bi(III) and Sb(III) as a function of time both for the feed (Figure 5a) and the stripping solutions (Figure 5b), when the feed solution was composed by HCl 0.5 mol L−1/H2SO4 2.0 mol L−1 and the stripping solution by H2SO4 0.2 mol L−1. We observe that the extraction to of both metal ions the SLM occurs simultaneously, and it is practically quantitative after 660 min of the transfer process. It is important to note that in the stripping solution, we only recover 90% and 59% of Bi(III) and Sb(III), respectively, from that is extracted in the SLM (Figure 5b). This difference is explained by the formation of a precipitate, which is deposited in the SLM-stripping solution interface beginning at 240 min of transfer, and which affects the final mass balance. The SbOCl is the main component of the precipitate, and its presence affects the transfer of Bi(III) as in the following reaction: SbCl3 + H 2O ⇌ SbOCl + 2HCl

(2)

The formation of precipitate SbOCl increases with increasing Sb(III) in the feed solution, and it affects the performance of the SLM for the transfer of both ions. On increasing concentration to 300 mg L−1 of Sb(III) in the feed solution,

Figure 5. Variation in the concentration of Bi(III) and Sb(III) in the a) feed solution and b) stripping solution in the SLM transfer process at 298.15 K. Feed: [Bi(III)], [Sb(III)] 100 mg L−1 in 2 mol L−1 H2SO4/0.5 mol L−1 HCl, Stirring 30.8 Hz (1850 rev min−1). Stripping: 0.2 mol L−1 H2SO4; Stirring 30.8 Hz (1850 rev min−1). SLM: 0.3 mol L−1 Cyanex 921 in kerosene supported in hydrophobic PVDF. 15187



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Figure 6. Variation of Bi(III) and Sb(III) in the a) feed solution and b) stripping solution in the SLM transfer process in the presence of Cu(II). Feed: [Bi(III)] 84.4 mg L−1, [Sb(III)] 97.3 mg L−1, [Cu(II)] 22,220 mg L−1 in 2 mol L−1 H2SO4/0.5 mol L−1 HCl; Stirring 30.8 Hz. Stripping: 0.2 mol L−1 H2SO4; Stirring 30.8 Hz. SLM: 0.3 mol L−1 Cyanex 921 in kerosene supported on hydrophobic PVDF.

achieved (see Figure 7) were similar to those obtained using 0.8 mol L−1 Na2SO4/0.2 mol L−1 H2SO4, and the entire amount of Sb(III) and Bi(III) extracted by the SLM was recovered in the stripping solution. This phenomenon can be explained by considering that the complex formation constants of Sb(III)tartrate and Bi(III)-tartrate are high13 (KBi(III)‑Tartrate = 107.56 and KSb(III)‑Tartrate = 1010.16) which enables the dislodging of Cyanex 921 from the solvate that it forms with these metal ions. Reactions Involved in the Mass Transfer of Bi(III) and Sb(III) through the SLM. The first stage of the mass transfer process by the SLM is the complex formation between the metal ion and the Cyanex 921 at the interphase feed solution/ SLM. The characteristics of the complex, extracted into the organic phase (at the SLM), could be determined through the slope method. The extraction of M(III) by Cyanex 921 as extractant is accomplished through a solvation mechanism that can be expressed by the following general equation

Table 2. Transfer of Bi(III) and Sb(III) by SLM As a Function of the Stripping Solution Useda [M]Feed initial, mg L−1

[M]Feed final, mg L−1

[M]stripping final, mg L−1

2 mol L−1NaCl (transfer 380 min) Bi(III) 106.7 80.8 Sb(III) 284.1 193.7 0.8 mol L−1 Na2SO4/0.2 mol L−1 H2SO4 Bi(III) 110 0.2 Sb(III) 299 1.4 0.5 w/v tartaric acid (transfer 625 min) Bi(III) 92.4 2.6 Sb(III) 258 12

% extracted

25.2 24.3 36.9 31.8 (transfer 720 min) 58.1 99.8 205 99.5 90.1 248.2

97.2 95.4

% recovered 97.2 40.8 53 69 100 100

a Feed: Bi(III), Sb(III) in 2 mol L−1 H2SO4/ 0.5 mol L−1 HCl; Stirring 30.8 Hz; SLM: 0.3 mol L−1 Cyanex 921 in kerosene supported in hydrophobic PVDF.

M3 + + mCl − + nH + + pCyanex 921

However, only 52% and 68% of Bi(III) and Sb(III), respectively, were recovered in the stripping solution. The remaining amount of both metals was found as a precipitate in the bulk of the stripping solution. When tartaric acid was used as stripping solution, the transfer rates of Sb(III) and Bi(III)

⇔ HnMClm·pCyanex 921

(3)

where the species with over bars are those found in the organic phase.

Figure 7. Variation in the concentration of Bi(III) and Sb(III) in the a) feed solution and b) stripping solution in the SLM transfer process at 298.15 K. Feed: [Sb(III)] = 258 mg L−1, [Bi(III)] = 92.4 mg L−1 in 2 mol L−1 H2SO4/0.5 mol L−1 HCl; Stirring 30.8 Hz. Stripping: 0.5% w/v tartaric acid, Stirring 30.8 Hz; SLM: Hydrophobic PVDF support impregnated with 0.3 mol L−1 Cyanex 921 in kerosene. 15188



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Figure 8. Species distribution diagram of M(III) at H2SO4 2 mol L−1 as a function of the chlorides concentration. a) Sb(III) and b) Bi(III).

Figure 9. Variation of Bi(III) and Sb(III) in the a) feed solution and b) stripping solution in the SLM transfer process in the presence of Cu(II) at 331.15 K. Feed: [Sb(III)] = 265.1 mg L−1, [Bi(III)] = 97.4 mg L−1, [Cu(II)] = 36000 mg L−1 in 2 mol L−1 H2SO4/0.5 mol L−1 HCl. Stripping: 0.5% w/v tartaric acid; Stirring 30.8 Hz. SLM: 0.3 mol L−1 Cyanex 921 in kerosene supported on hydrophobic PVDF.

determined by carrying out the extraction of Sb(III) and Bi(III) using variable concentrations of Cyanex 921, through the procedure described by Reyes-Aguilera et al.11 For both metals, the experimental points conform to the behavior of a straight line. In the case of Sb(III), the slope of the straight line is close to 1 (1.18; R = 0.990). This slope indicates that it is possible to have a predominant solvate Sb(III): Cyanex 921 with a 1:1 ratio. The same situation is observed with Bi(III), with a slope in this case close to 2 (2.25; R = 0.997). This slope value indicates that the solvate with a Bi(III):Cyanex 921 ratio of 1:2 prevails under the conditions of this study. Due to the characteristics of the extractant used (Cyanex 921), the extraction process is carried out by a solvation mechanism. It is therefore necessary that the final form of the metal ion, on passing to the organic phase, neutralizes its charge by forming neutral species or ion pairs. Figure 8, that shows the species distribution diagram (Sb(III)-Cl− and Bi(III)-Cl− formation constants taken from Dean and Lange14), let us see that Bi(III) and Sb(III) form neutral chloride complexes (MCl3). An analysis of the results obtained from the transfer of Bi(III) as a function of HCl concentration on feed solution in Figure 3 and Figure 9 indicates that, on increasing the concentration of HCl from 0.2 mol L−1 to 0.5 mol L−1, the fraction of the species BiCl3 increases from 0.23 to 0.25 and the fraction of species HBiCl4 increases from 0.18 to 0.5,

The apparent equilibrium constant of this reaction is Kext =

[HnMClm·pCyanex 921] [M3 +]aClm−a Hn +[Cyanex 921]p

(4)

If there is only one solvate in the organic phase, the distribution coefficient of M(III), DM(III), is defined by DM(III ) =

[HnMClm·pCyanex 921] [M(III)]

(5)

Total concentration of M(III) corresponds to the metal ion concentration in all chemical forms in the aqueous phase. Substituting eq 5 into 4, we can express the distribution coefficient of M(III), DM(III), in its logarithmic form: log DM(III ) = log Kext + m log aCl− + n log a H + + p log[Cyanex 921] +

(6) −

If concentration of the ions H and Cl remains constant in the system, eq 6 can be simplified as log DM(III ) = log k + p log[Cyanex 921]

(7)

where log k = log Kext + m log aCl− + n log aH+. Equation 7 has the form of a straight line with slope ″p″ and an intercept of ″log k″. The M(III)-Cyanex 921 ratio can be 15189



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respectively, while the permeability increases from 0.2351 cm min−1 to 0.2479 cm min−1. When HCl in the feed solution increases its concentration from 0.5 to 1.0 mol L−1, it is observed that the fraction of BiCl3 decreases from 0.25 to 0.18 and the fraction of HBiCl4 increases from 0.5 to 0.73, while the permeability decreases from 0.2479 cm min−1 to 0.2060 cm min−1. This indicates that the extraction of BiCl3 prevails over the extraction of HBiCl4. A similar situation is observed for Sb(III). When HCl concentration increases from 0.5 to 2.5 mol L−1, the molar fraction of SbCl3 decreases, and the fraction of HSbCl4 increases over the entire range of HCl concentrations, while the value of permeability decreases. This fact confirms that the extraction of specie SbCl3 predominates as it is suggested by results shown in Table 1. As such, the extraction reactions from the feed solution to the SLM could be represented as BiCl3 + 2Cyanex 921 ⇔ BiCl3·2Cyanex 921

Table 3. Transfer of Bi(III) and Sb(III) through SLM at Different Temperaturesa [M]Feed initial, mg L−1 298.15 K Bi(III) Sb(III) 331.15 K Bi(III) Sb(III) Cu(II) 339.15 K Bi(III) Sb(III) 347.15 K Bi(III) Sb(III)

(8)

(9)

Once the complex is at the interface SLM/stripping solution, the stripping reaction involves the formation of a complex between the metal ion and the tartaric ion. The stripping reaction can be represented as

(10)

and

% recovered

92.4 258

2.6 11.9

89.2 246

97.2 95.4

100 100

625

97.4 265.1 36000

2.5 10.6 -----

95.4 250.1 21.2

97.4 96.8 0.06

100 97.3 ----

570

95.8 274.6

2.1 8.9

94.8 263.8

97.9 96.8

100 100

482

102.3 268.3

2.9 7.7

101.2 255.7

97.2 97.1

100 99.0

400

JM(III) = P[M(III)]t = 0

SbCl3·Cyanex 921 + (Tartrate)2 − ⇔ Sb(tartrate)+ + 3Cl − + Cyanex 921

% transport

t transfer min

21.2 mg L−1 of this metal ion is transferred. This indicates that the extractant is highly selective for Sb(III) and Bi(III) and can be used in real samples. Enthalpy of Extraction Reaction of Sb(III) and Bi(III) into the SLM. The permeability was determined as a function of temperature according to eq 1. Once calculated, the molar flux JM(III) could be calculated as9

BiCl3·2Cyanex 921 + (Tartrate)2 − ⇔ Bi(tartrate)+ + 3Cl − + 2Cyanex 921

[M]Strip final, mg L−1

a Feed: Bi(III), Sb(III) in 2 mol L−1 H2SO4/0.5 mol L−1 HCl; Stripping: 0.5% w/v tartaric acid. Stirring 30.8 Hz; SLM: Hydrophobic PVDF support impregnated with 0.3 mol L−1 Cyanex 921 in kerosene.

and SbCl3 + Cyanex 921 ⇔ SbCl3·Cyanex 921

[M]Feed final, mg L−1

(12)

where P is the membrane permeability and [M(III)]t=0 is the initial metal ion concentration. According to Van’t Hoff’s equation, it is possible to evaluate the variation of the flux through the membrane as a function of temperature according to

(11)

Effect of Temperature on Transfer of Bi(III) and Sb(III) by the SLM. One of the major drawbacks of the SLMs is their stability in continuous processes and at high temperatures. For this reason, their application in industrial processes has not seen the expected growth in spite of their high efficiency, savings, and wide scope of applicability. Although the SLMs prepared for this study are quite stable with operating times of 12 h or even more, it is necessary to study the stability of these membranes at temperatures used in the electrolytic cells where copper is refined, which vary from 343.15 to 363.15 K.15 Thus, we studied the efficiency and stability of the SLMs in the transfer of Sb(III), Bi(III), and Cu(II) at 298.15, 331.15, 339.15, and 347.15 K. Results are shown in Table 3. The results shown in Table 3 indicate that on increasing operating temperature, the SLM used requires less time to obtain similar transfer rates. This can be explained if we consider that transfer is established by two factors: extraction of the metal ion to the SLM (feed solution) and diffusion through the SLM of the solvate formed. The increase in temperature decreases the viscosity of the organic phase, enabling faster diffusion and, consequently, faster transfer of the metal ion. In virtually all cases, the total Sb(III) and Bi(III) extracted by the SLM is recovered in the stripping solution. Figure 9 shows the profiles obtained for concentration of the metal ion in the feed and stripping solutions for Sb(III) and Bi(III), respectively, where we used the Bi(III)/Sb(III)/Cu(II) mixture shown in Table 3 with a corresponding temperature of 331.15 K. It is important to note that in the case of Cu(II), of an initial total in the feed solution of 36000 mg L−1, at 331.15 K, only

log JM(III) =

−ΔH ° + Cte 2.303RT

(13)

where JM(III) is the molar flux of the extracted species, R is the universal gas constant (R = 8.3144 J mol−1 K−1), and T is the absolute temperature (K). In the graph of log JM(III) vs T−1 (Figure 10), we obtain a straight line with a slope equal to −ΔH°/2.303R. Table 4 shows the values obtained from the permeabilities, the molar flux and the change in enthalpy for the transfer of Sb(III) and Bi(III). It could be seen that both the membrane permeability and the molar flux rise with the increase in the transfer temperature. This is due to the fact that the rise in temperature promotes both a reduction in the viscosity of the organic phase contained at the membrane and the diffusion of the extracted species. With an increment of 298.15 to 322.15 K, the values of the molar flux of both Sb(III) and Bi(III) are duplicated. The enthalpy value obtained for Sb(III) is 22.6 kJ mol−1 and 27.8 kJ mol−1 for Bi(III), this being more sensitive to the change in temperature. This enthalpy value could be due to the change in the viscosity of the organic phase into the SLM given a rise in temperature. Based on data reported by Perry 16 and Wohlfarth,17 the viscosity of the organic phase (Cyanex 921 and kerosene) was calculated as a function of the temperature according to the concentration used. The activation energy 15190



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ACKNOWLEDGMENTS

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REFERENCES

Article

The authors wish to thank CONACYT for the financial support given to this study (Project 44768-Q).

(1) Fuentes, G.; Viñals, J.; Herreros, O. Hydrothermal purification and enrichment of Chilean copper concentrates. Part 2: The behavior of the bulk concentrates. Hydrometallurgy 2009, 95 (1−2), 113−120. (2) Dreisinger, D. B.; Leong, B. J. Y.; Balint, B. J.; Beyad, M. H.; Logsdail, D. H.; Slater, J. In The solvent extraction of As, Sb and Bi from copper refining electrolytes using organophosphorus reagents, Internations Solvent Extraction Conference, York, UK, 1993; Logsdail, D. H., Slater, M. J., Eds.; SCI UK: York, UK, 1993; pp 1271−1278. (3) Wang, C. W. K. J. D. L. H. In Purification of copper electrolyte with Cyanex 923, International Solvent Extraction Conference, Johannesburg, South Africa, Sole, K., Cole, P. M., Preston, J. S., Robinson, D. J., Eds.; Chris van Rensburg Publications: Johannesburg, South Africa, 2002; pp 1039−1044. (4) Cox, V. M.; Flett, D. S.; Velea, T.; Vasiliu, C. In Impurity removal from copper tankhouse liquors by solvent extraction, International Solvent Extraction Conference, South Africa, Sole, K., Cole, P. M., Preston, J. S., Robinson, D. J., Eds.; Chris van Rensburg Publications: South Africa, 2002; pp 995−1000. (5) Szymanowksi, J. Removal of toxic elements from copper electrolyte by solvent extraction. Miner. Process. Extr. Metall. Rev. 1998, 18 (3−4), 389−418. (6) Kim, D. K.; Leese, T. A.; Neild, M. P.; Saito, B. R.; Young, S. K.; Weidner, C. J. In Use of solvent extraction to remove bismuth and antimony from copper electrolyte at the San Manuel refinery, EPD Congress San Antonio, USA, Mishra, B., Ed.; TMS Warrendale PA: USA, 1998; pp 301−315. (7) Gupta, B.; Begum, I. Z. Separation and removal of arsenic from metallurgical solutions using bis(2,4,4-trimethylpentyl)dithiophosphinic acid as extractant. Sep. Purif. Technol. 2008, 63 (1), 77−85. (8) Kul, M.; Ç etinkaya, Ü . Recovery of copper by LIX 984N-C from electroplating rinse bath solution. Hydrometallurgy 2009, 98 (1−2), 86−91. (9) Danesi, P. R. Separation of metal species by supported liquid membranes. Sep. Sci. Technol. 1984, 19 (11−12), 857−894. (10) (a) Vander Linden, J.; De Ketelaere, R. F. Selective recuperation of copper by supported liquid membrane (SLM) extraction. J. Membr. Sci. 1998, 139 (1), 125−135. (b) Sarangi, K.; Das, R. P. Separation of copper and zinc by supported liquid membrane using TOPS-99 as mobile carrier. Hydrometallurgy 2004, 71 (3−4), 335−342. (c) Wojciechowski, K.; Kucharek, M.; Buffle, J. Mechanism of Cu(II) transport through permeation liquid membranes using azacrown ether and fatty acid as carrier. J. Membr. Sci. 2008, 314 (1−2), 152−162. (11) Reyes-Aguilera, J. A.; Gonzalez, M. P.; Navarro, R.; Saucedo, T. I.; Avila-Rodriguez, M. Supported liquid membranes (SLM) for recovery of bismuth from aqueous solutions. J. Membr. Sci. 2008, 310 (1−2), 13−19. (12) Alguacil, F. J.; López, F. A. The extraction of mineral acids by the phosphine oxide Cyanex 923. Hydrometallurgy 1996, 42 (2), 245− 255. (13) Perrin, D. D.; Sillén, L. G. Stability constants of metal-ion complexes, part B: organic ligands; Pergamon Press: Oxford, New York, 1979. (14) Dean, J. A. Lange’s Handbook of Chemistry, 15th ed.; McGrawHill: 1999; p 8.83. (15) (a) Moats, M. S.; Hiskey, J. B.; Collins, D. W. The effect of copper, acid, and temperature on the diffusion coefficient of cupric ions in simulated electrorefining electrolytes. Hydrometallurgy 2000, 56 (3), 255−268. (b) Morales, A.; Hevia, J. F.; Santis, D.; Cifuentes, G. Anodic electrolytic dissolution of copper sulphides precipitated from ammoniacal leaching media. J. Chil. Chem. Soc. 2009, 54, 119−122. (16) Green, D. W.; Perry, R. H. Perry’s Chemical Engineers’ Handbook, 7th ed.; McGraw-Hill: United States of America, 1999.

Figure 10. Variation of molar flux of Sb(III) and Bi(III) as a function of temperature.

Table 4. Permeabilities (P) and Molar Flux for Sb(III) and Bi(III) Transfer at Various Temperatures

Sb(III)

Bi(III)

temperature (K)

P (cm min‑1)

J•10‑7 (mol cm‑2 min‑1)

ΔH° (kJ mol‑1)

298.15 306.15 314.15 322.15 298.15 306.15 314.15 322.15

0.1061 0.1260 0.1557 0.2003 0.0971 0.1346 0.1675 0.2071

2.25 2.74 3.51 4.41 0.45 0.62 0.77 1.01

22.6

27.8

value obtained for the viscous flow was 25.2 kJ mol−1, which matches the enthalpy obtained from the experiments as function of temperature using eq 4. It is possible to say that an increase in the molar flux of Sb(III) and Bi(III) observed when the temperature rises is due to the reduction in the viscosity of the organic phase.

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CONCLUSIONS The results of this work show that the use of SLM is adequate for separating Bi(III) and Sb(III) from mixed HCl/H2SO4 media with high concentrations (24 g L−1) of Cu(II). The best separation conditions are the following: 0.5 mol L−1 HCl/2 mol L−1 H2SO4 as feed solution and hydrophobic PVDF support impregnated with Cyanex 921 diluted in kerosene at 347.15 K. The recovery values for both metal ions are over 99% for a transfer time of 400 min, for concentrations of 100 mg L−1 of Bi (III) and 250 mg L−1 of Sb(III). The use of 0.5% w/v tartaric acid as stripping solution allows the recovery of virtually all the Sb(III) and Bi(III) extracted to the SLM, regardless of the presence of Cu(II), which is not transferred. Finally, the chosen SLM showed high stability, even at transfer times of over 12 h and at temperatures of 347.15 K.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: jareyes@fisica.ugto.mx. Notes

The authors declare no competing financial interest. 15191



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(17) Wohlfarth, C.; Wohlfahrt, B. 2 Pure Compounds: References. In Pure Organometallic and Organononmetallic Liquids, Binary Liquid Mixtures; Lechner, M. D., Ed.; Springer: Berlin, Heidelberg, 2001; Vol. 18A, pp 144−149.

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H2SO4 Mixed Media by

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