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Separation of Pt from hydrochloric acid leaching solution of spent catalysts by solvent extraction and ion exchange
Hydrometallurgy 110 (2011) 91–98
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Separation of Pt from hydrochloric acid leaching solution of spent catalysts by solvent extraction and ion exchange P.P. Sun, M.S. Lee ⁎ Department of Advanced Materials Science & Engineering, Mokpo National University, Chonnam 534-729, Republic of Korea
a r t i c l e
i n f o
Article history: Received 21 July 2011 Received in revised form 2 September 2011 Accepted 2 September 2011 Available online 10 September 2011 Keywords: Platinum(IV) Iron(III) Aluminum(III) Solvent extraction Ion exchange
a b s t r a c t Leaching of spent catalysts (Pt/Al2O3) with a mixture of HCl and H2O2 results in a mixed chloride solution containing Pt(IV), Fe(III), Al(III), Ni(II), and silicon. Separation of Pt(IV) from the synthetic chloride solution containing Fe(III) and Al(III) has been performed by solvent extraction and ion exchange. Effects of extraction and sorption conditions on the separation of Pt were investigated in the HCl concentration range from 1 to 9 M. In solvent extraction experiments, amines (Alamine304-1, Alamine308, Alamine336, Aliquat336), TBP and TOPO were tested, while AG1-x8 resin was employed in ion exchange experiments. Solvent extraction experiments indicated that it was difficult to separate Pt from Fe and Al by amines and solvating extractants in our tested range. In ion exchange by using AG1-x8 resin, only Pt was loaded from the synthetic solution when HCl concentration was lower than 1 M, while Fe and Al remained in the solution. Continuous experiments with AG1-x8 resin indicated that most of Pt was loaded onto the resin from 0.5 M HCl solution, leaving Fe and Al in the effluent and complete separation of Pt was possible. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Platinum along with some other platinum group metals (PGMs) is the main active ingredient of various catalysts for the automobile and petrochemical industries. Pt/Al2O3 catalysts are widely used in petrochemical industries for the catalytic reforming process (Baghalha et al., 2009) Substitution of Pt by other metals is difficult due to its special properties (Rao and Reddi, 2000). A large amount of spent catalysts is being generated from the petrochemical and automobile industries. Since the natural resources of PGMs are limited, recovery of PGMs from the spent catalysts is important from the viewpoint of economics as well as environment protection. In hydrometallurgical treatment of spent catalysts, PGMs together with other minor elements in the spent catalysts are dissolved by leaching with chloride based solutions at high temperature. In order to recover pure PGMs from the chloride based leaching solution of spent catalysts, various commercial amines have been tested in solvent extraction (Alam and Inoue, 1997; Benguerel et al., 1996; Bernardis et al., 2005; Charlesworth, 1981; Lee et al., 2008; Lee et al., 2009a; Lee et al., 2009b; Lee et al., 2010; Mhaske and Dhadke, 2001; Nowottny et al., 1997). Together with amines, solvating extractants, such as TBP and TOPO, have been widely used in the separation of PGMs from chloride solution (Benguerel et al., 1994) and in the refining of precious metals (Lewis et al., 1976; Zou et al., 1998). ⁎ Corresponding author. Fax: +82 61 450 2498. E-mail address: [email protected] (M.S. Lee). 0304-386X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2011.09.002
In our study on the recovery of Pt from the spent catalysts which have been used in the catalytic reforming process of petrochemical industries, leaching of the spent catalysts with a mixture of HCl and H2O2 resulted in a solution containing Pt(IV), Fe(III), Al(III), Ni(II), and silicon. The composition of the leaching solution was 0.00025 M Pt(IV), 0.0015 M Fe(III) and 0.1 M Al(III) together with negligible amount of Ni and Si. The chemical composition of the spent catalysts is shown in Table 1. Since the concentration of Ni and Si in the leaching solution was negligible, synthetic solution containing Pt(IV), Fe (III), and Al(III) was employed in this study. Platinum exists in HCl solution as PtCl62− (Lee et al., 2008). Ferric ion can form complexes with chloride ion, such as FeCl2+, FeCl2+, FeCl3aq, and FeCl4−(Lee, 2006), while Al is known to exist as Al3+ in HCl solution (Bjerrum et al., 1958). The difference in the nature of chemical complexes of Pt(IV), Fe(III), and Al(III) in chloride solution can be utilized to develop a process for the separation of these three metals. According to the literature on the extraction of PGMs from chloride solution, Aliquat336 is more suitable for separating PGMs at low concentration of HCl, while tertiary amine or solvating extractants are more suitable at high concentration of HCl (Kedari et al., 2005). In this work, solvent extraction and ion exchange experiments have been performed to find an optimum condition to separate Pt (IV) from Fe and Al in the HCl concentration range from 1 to 9 M. For this purpose, some tertiary amines, solvating extractants and anion exchange resin were employed and the extraction/loading behavior of the three metal ions with extraction/loading conditions is reported. Alamine304-1, Alamine308, Alamine336 and Aliquat336 were used as a tertiary amine and TBP and TOPO were used as a
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Table 1 The chemical composition of spent catalyst measured by XRF and ICP (Unit: wt.%).
Table 3 Chemical formula of extractants used in this study.
Pt
Al
Si
Fe
Ni
Extractant
Reagent class
Structure
0.08
10.15
0.85
0.28
0.005
Alamine304-1 Alamine308 Alamine336 Aliquat336 TBP TOPO DOS
Tertiary amine Tertiary amine Tertiary amine Aliphatic quaternary ammonium salt Tri-n-butyl phosphate Trioctylphosphine oxide Di-n-octyl sulfide
[CH3(CH2)11]3 N [(CH3)2CH(CH2)5]3 N [C8–C10 mixture]3 N [(C8H17) 3 N(CH3)]+Cl− [CH3(CH2)3O]3PO [CH3(CH2)7]3PO [CH3(CH2)7]2S
Minor elements: S, Cl, K, Ca, Sr, Zr, Sn.
solvating extractant. In ion exchange, AG1-x8 was employed in batch and continuous experiments. 2. Experimental 2.1. Materials Synthetic solutions were prepared by dissolving certain amount of PtCl4 (Aldrich, 98%), FeCl3·6H2O (Junsei Chem., 97%) and AlCl3 (Junsei Chem., 98%) in doubly distilled water. The composition of the synthetic solution was 0.00025 M Pt(IV), 0.0015 M Fe(III) and 0.1 M Al(III). The acidity of the solution was adjusted by adding HCl (Junsei Chem., 35%). Amines (Alamine304-1, Alamine308, Alamine336, and Aliquat336) were purchased from Cognis Corporation and used without further purification. Amine extractants except Alamine304-1 were pretreated with HCl to form salt. Alamine304-1 was used as received because it was solidified after the pretreatment with HCl solution. Amines and tributyl phosphate (TBP, Yakuri pure chemicals co., 99%) were diluted with toluene. Trioctylphosphine oxide (TOPO) solution was prepared by dissolving the necessary amount of TOPO powder (Aldrich, 90%) in toluene. The chemical formula of each extractant is shown in Table 3. The real leaching solution was obtained by leaching the spent catalyst with a mixture of HCl and H2O2. The leaching experimental conditions are shown in Table 2. Leaching experiments were carried out in a hermetic container (500 ml) under magnetic agitation (300 rpm) at 70 °C. One hundred ml of lixiviant was first filled in the hermetic container and the reaction temperature was adjusted to 70 °C by using digital magnetic stirrer. Then 5 g of spent catalyst with a particle size of 0.1–0.3 mm was filled in the reaction vessel. After 2 h reaction, the insoluble residue was separated immediately from the leaching solution by using ceramic filter under vacuum and the concentration of metals in the filtrate was measured by ICP-OES (Spectro Arcos). 2.2. Solvent extraction and ion exchange procedure In solvent extraction experiments, equal volume (20 ml) of aqueous and organic phase was mixed in a 100 ml screwed cap bottle and shaken for 30 min with a wrist action shaker. The aqueous phase was separated after settling the mixture. All the extraction experiments were carried out at ambient temperature. Batch ion exchange experiments were carried out in a shaking incubator (HB-201SF, Hanbaek Scientific Co.) using 100 ml screwed cap bottle. The temperature of the shaking incubator was controlled to 25 °C. Fifty ml of mixed chloride solutions were bottle rolled for 24 h after putting certain amount of resin. A commercial AG1-x8 resin (Bio-Rad) with particle size between 200 and 400 mesh was used and the resin had chloride form. In continuous experiments, 4 g of AG1-x8 resin was filled into the
Table 2 Leaching condition of spent catalysts. Pretreatment temperature Composition of leaching solution Particle size Reaction temperature Reaction time Pulp density
800 °C 10% HCl + 1%H2O2 0.1–0.3 mm 70 °C 2h 50 g/L
glass column (250×10 mm). The volume of 4 g resin in the column was 5.7 ml. The temperature of the column in continuous experiments was controlled to 25 °C by using water circulator bath (Scientific Co., Vs1902WF). Flow rate of the feed solution was adjusted by using pump (FMI lab pump, QG20) to ensure that 6 ml of effluent was collected every 3.5 to 4.min. The concentration of metal in the aqueous phase was measured by ICP-OES (Spectro arcos). The concentration of metal in the organic phase and resin was obtained by the following mass balance equation. Corg Vorg ¼ Cinitial Vinitial −Caq Vaq mon
resin
¼ mfeed −meffluent :
ð1Þ ð2Þ
In the above equation, C, V, and m represent the concentration, volume and mass. The subscript, org, initial, aq represent the organic solution, initial solution and aqueous solution, and mon resin , mfeed , meffluent represent the mass of metal absorbed on the resin, contained in feed solution and remained in the effluent. 3. Results and discussion 3.1. Solvent extraction of Pt from mixed solution Effects of extraction conditions on the separation of Pt(IV) from Fe (III) and Al(III) were investigated from the synthetic solution. In these experiments, the concentration of amines was varied from 0.1 to 0.7 M and HCl concentration was adjusted from 1 to 9 M. The composition of the synthetic chloride solution was 0.00025 M Pt(IV), 0.0015 M Fe(III) and 0.1 M Al(III). Figs. 1 to 2 show the results obtained from the extraction with Alamine336 and Aliquat336, respectively. The extraction behavior of the metals with Alamine304-1 and Alamine308 was similar to that with Alamine336 and Aliquat336. In the HCl concentration range from 1 to 9 M, most of Pt was extracted irrespective of the nature of amine whereas the extraction percentage of Al was zero throughout our experimental conditions. In the case of Fe, most of Fe was extracted in the HCl concentration range from 1 to 9 M when the concentration of amine was higher than 0.1 M. When the concentration of amine was 0.1 M, the extraction percentage of Fe increased with the increase of HCl concentration. Solvent extraction results with amines indicated that most of Pt and Fe were extracted into amines and Al remained in the aqueous phase. Thus it may be concluded that it is difficult to separate Pt from Fe and Al by solvent extraction with amine in the HCl concentration range from 1 to 9 M. Tertiary amines belong to strong-base extractant. Since the strong bases of tertiary amines are readily protonated, tertiary amines can behave as ion-exchanger at relatively low acid concentrations. The difference in the extraction characteristics of tertiary amines is due to the basicity of R (the tertiary amine is represented as R3N) (Charlesworth, 1981). Solvent extraction of Pt and Fe from the synthetic chloride solution by using amines follows ion exchange mechanism. The high extraction percentage of Pt and Fe by amines might be due to their high capacity
Extraction percentage Extraction percentage Extraction percentage of Al of Fe of Pt
P.P. Sun, M.S. Lee / Hydrometallurgy 110 (2011) 91–98
93
100 80
[Alamine336] 0.1 M 0.3 M 0.5 M 0.7 M
60 40 20 0
1
2
3
4
5
6
7
100 80
9
[Alamine336] 0.1 M 0.3 M 0.5 M 0.7 M
60 40 20 0
8
1
2
3
4
5
6
7
100 80 60 40 20 0
8
9
[Alamine336] 0.1 M 0.3 M 0.5 M 0.7 M
1
2
3
4
5
6
7
8
9
HCl concentration (M) Fig. 1. Effect of HCl concentration on the extraction of Pt(IV), Fe(III) and Al(III) at different concentration of Alamine336.
of Pt and Fe. The extraction reaction of Pt and Fe by amine can be represented as (Reddy et al., 2010) 2−
PtCl6 þ 2R3 NHClorg ¼ PtCl6 ðR3 NHÞ2 ;org þ2Cl
−
FeCl4 þ R3 NHClorg ¼ FeCl4 ðR3 NHÞorg þ Cl
−
ð3Þ
−
ð4Þ
Extraction percentage Extraction percentage Extraction percentage of Al of Fe of Pt
Separation experiments of Pt from Fe and Al were also performed by using TBP and TOPO. The concentration of HCl in the solution was
100 80 60 40 20 0 100 80 60 40 20 0
varied from 1 to 9 M. The concentration of TBP and TOPO was fixed at 1 M, and the results are shown in Fig. 3. This figure shows that most of Pt and Fe were extracted by 1 M TOPO in the HCl concentration range from 1 to 9 M and it was impossible to separate Pt from Fe and Al by extraction with 1 M TOPO. In the extraction with 1 M TBP, the extraction percentage of Fe and Pt depended on HCl concentration. When HCl concentration was 1 M, the extraction percentage of Pt and Fe was zero. Extraction percentage of Fe rapidly increased with the increase of HCl concentration and reached 99% when HCl concentration was higher than 5 M.
[Aliquat336] 0.1 M 0.3 M 0.5 M 0.7 M
0
2
4
6
8
10
[Aliquat336] 0.1 0.3 0.5 0.7
0
2
4
6
100 80 60 40 20 0
8
10
[Aliquat336] 0.1 M 0.3 M 0.5 M 0.7 M
0
2
4
6
8
10
HCl concentration (M) Fig. 2. Effect of HCl concentration on the extraction of Pt(IV), Fe(III) and Al(III) at different concentration of Aliquat 336.
P.P. Sun, M.S. Lee / Hydrometallurgy 110 (2011) 91–98
Extraction percentage Extraction percentage Extraction percentage of Al of Fe of Pt
94
100 80 60 40 20 0 100 80 60 40 20 0
TBP TOPO
0
2
4
6
8
10
TBP TOPO
0
2
4
6
100 80 60 40 20 0
8
10
TBP TOPO
0
2
4
6
8
10
HCl concentration (M) Fig. 3. Effect of HCl concentration on the extraction of Pt(IV), Fe(III) and Al(III) with TBP and TOPO. ([TBP] = [TOPO] = 1 M).
Extraction percentage Extraction percentage Extraction percentage of Al of Fe of Pt
Extraction percentage of Pt increased with HCl concentration and reached a maximum of 43% at 7 M HCl. Extraction percentage of Al by 1 M TBP and 1 M TOPO was zero in our experimental range. The difference in the extraction abilities between TBP and TOPO might be related with the donor ability of phosphoryl oxygen in them (Reddy et al., 2007). The phosphoryl oxygen of TOPO was affected by three electron donation groups [ CH3(CH2)7− ], while that of TBP was affected by three electron withdrawing groups [CH3
(CH2)3O− ]. Therefore, donor ability of phosphoryl oxygen follows the order: TOPO N TBP. The extraction behavior of metals by TBP was further investigated by varying TBP concentration from 0.5 to 2.0 M and the results are shown in Fig. 4. According to Fig. 4, extraction percentage of Pt and Fe increased with the increase of HCl concentration when the TBP concentration was fixed. When HCl concentration was higher than 5 M, most of Fe was extracted irrespective of TBP concentration,
100 80 60 40
[TBP] 0.5 M 1.0 M 1.5 M 2.0 M
20 0 0 100 80 60 40 20 0 0 100 80 60 40 20 0 0
2
4
6
8
10
[TBP] 0.5 M 1.0 M 1.5 M 2.0 M
2
4
6
8
10
[TBP] 0.5 M 1.0 M 1.5 M 2.0 M
2
4
6
8
10
HCl concentration (M) Fig. 4. Effect of HCl concentration on the extraction of Pt(IV), Fe(III) and Al(III) at different concentration of TBP.
P.P. Sun, M.S. Lee / Hydrometallurgy 110 (2011) 91–98
while the highest extraction percentage of Pt was 80% with 2.0 M TBP at 7 M HCl. None of Al was extracted by TBP in our experiment condition. The extraction percentage of Pt and Fe by 0.5 M TBP was 10 and 85% at 5 M HCl, which seems to be the best condition to separate Fe from Pt by TBP. The extraction reaction of Pt and Fe by TBP might be expressed as (Lee and Lee, 2005; Lee et al., 2004; Reddy and Bhaskara Sarma, 1996; Seyed and George, 1995; Specker and Cremer, 1959): þ
2−
ð5Þ
−
ð6Þ
2H þ PtCl6 þ 2TBPorg ¼ 2TBP·H2 PtC16 ;org
3þ
Fe
þ
þ 3Cl þ 3TBP ¼ FeCl3 ·3TBP
−
H þ FeCl4 þ 2TBP ¼ HFeCl4 ·2TBP
ð7Þ
In strong HCl solution of 6–9 M, ferric ion is extracted by Eq. (5), while Eq. (4) is responsible for the extraction of ferric ion in the lower HCl concentration. Among the amines and solvating extractants tested in this study, extraction with TBP resulted in the best condition to separate Pt from Fe and Al. Since extraction percentage of Fe was higher than that of Pt in the extraction with TBP, another extraction step is necessary to recover Pt from the remaining solution after extraction with TBP. The stripping of Pt and Fe from the loaded TBP was investigated by using dilute HCl solution. The concentration of HCl was varied from 0.01 to 0.5 M, and the results are shown in Fig. 5. Most of Fe was stripped from the loaded TBP in our stripping conditions. The stripping percentage of Pt was 71% by 0.01 M HCl and decreased with the increase of HCl concentration.
95
3.2. Solvent extraction of Pt from the real leaching solution As observed in the solvent extraction of synthetic solution by using different solvent extractants, the possible extractant to separate Pt from other metals was TBP. So 1.5 M TBP was used in the solvent extraction of metals from the real leaching solution. The other variable was kept at the same. The results showed that the extraction percentage of Pt, Fe, Al, were 98%, 97%, 0.5%, and nil for Ni and Si. Since the stripping selectivity of Pt and Fe from loaded TBP was low, it is difficult to separate Pt from the other impurity metals by solvent extraction using TBP.
3.3. Ion exchange of Pt from the synthetic solution Ion exchange experiments with AG1-x8 were performed to separate Pt from Fe and Al. Effects of the concentration of HCl and the amount of resin were investigated. In order to obtain equilibrium loading isotherm of Pt, loading experiments were done from the pure PtCl4 solution of 5 M HCl and the results are shown in Fig. 6. The loading capacity of AG1-x8 for Pt(VI) was about 50 mg/g of resin at 5 M HCl. In the batch experiments, the amount of AG1-x8 resin was varied from 0.025 to 0.2 g. The effect of HCl concentration was investigated by varying HCl concentration from 1 to 5 M and the results are shown in Fig. 7. This figure shows that the loading of Pt and Fe depended on the sorption conditions while the loading percentage of Al was zero in our experimental condition. When HCl concentration was 1 M, only Pt was loaded onto the resin and the loading percentage of Fe was negligible. Most of Pt was loaded onto AG1x-8 from 3 M HCl solution when the amount of resin was higher than 0.05 g. However, the loading percentage of Fe increased to 18% at 3 M HCl. When HCl concentration was 5 M, the loading percentage of Pt decreased compared to that at 1 and 3 M HCl, whereas the loading percentage of Fe increased linearly with the increase in the amount of resin. The increase in the loading percentage of Fe with the increase
100
60
90 50
70 60 50
Pt Fe
40 30
Equilibrium resin loading (mg/g)
Stripping percentage of metals
80
40
Pt [HCl]=5 M
30
20
20 10 10 0
0.0
0.1
0.2
0.3
0.4
0.5
HCl concentration (M)
0
0
10
20
30
40
50
Equilibrium concentration in solution (mg/L) Fig. 5. Effect of HCl concentration on the stripping of Pt and Fe from 1.5 M TBP loaded organic phase.
Fig. 6. Equilibrium loading of Pt in 5 M HCl solution.
P.P. Sun, M.S. Lee / Hydrometallurgy 110 (2011) 91–98
Adsorption percentage Adsorption percentage Adsorption percentage of metals of metals of metals
96
100 80 60 40 20 0 0.00 100 80 60 40 20 0 0.00 100 80 60 40 20 0 0.00
[HCl]=1 M Pt Fe Al
0.05
0.10
0.15
0.20
[HCl]=3 M Pt Fe Al
0.05
0.10
0.15
0.20
[HCl]=5 M Pt Fe Al
0.25
0.50
0.75
1.00
Amount of resin (g)
Fig. 7. The effect of amount of AG1-x8 resin on the adsorption of metals with different concentration of HCl.
3.4. Continuous experiments Batch experiments with AG1-x8 indicate that it is possible to separate Pt from Fe and Al by adjusting HCl concentration of the synthetic solution. Therefore, continuous experiments were done by employing glass column. In these continuous experiments, the amount of resin was fixed at 4 g. The change in the concentration of metals in the effluent was represented by using concentration fraction which is defined as Eq. (8). Concentration fraction ¼
the concentration of metal in the effluent : initial concentration of metal in the solution ð8Þ
According to Fig. 7, the loading percentage of Fe decreased with the decrease of HCl concentration and was 1.7% at 1 M HCl. In the next continuous experiments, HCl concentration in the feed was adjusted to 0.5 M, keeping the other experimental conditions the same
100 90 80
Adsorption percentage of metals (%)
of HCl concentration is related with the formation of FeCl4− at higher concentration of HCl (Lee and Lee, 2005). Fig. 7 indicates that it is possible to separate Pt from Fe and Al by using AG1-x8 and the control of HCl concentration is the most important step in achieving complete separation of Pt from Fe and Al. In order to investigate the effect of HCl concentration on the loading of Fe, sorption experiments were done by varying HCl concentration from 1 to 3 M at the interval of 0.5. In these experiments, the amount of AG1-x8 was fixed at 0.2 g, and the results are shown in Fig. 8. This figure indicates that loading percentage of Fe decreased rapidly with the decrease of HCl concentration while there was not much difference in the loading percentage of Pt in our tested range. When HCl concentration was 1 M, the loading percentage of Pt and Fe was 95 and 1.7%, respectively.
Pt Al Fe
70 60 50 40 30 20 10
Fig. 9 shows the results which was obtained from the continuous experiments with the synthetic solution of 3 M HCl. Most of Pt in the feed solution was loaded onto AG1-x8 resin, while Al remained in the effluent. Iron was loaded until 10 bed volume, and after this bed volume the loading of Fe decreased slowly with the increase of bed volume. The results shown in Fig. 9 indicate that it is difficult to separate Pt from Fe and Al in one step from 3 M HCl solution.
0 1.0
1.5
2.0
2.5
3.0
Concentration of HCl (M) Fig. 8. The effect of concentration of HCl on the adsorption of metals by 4 g/L AG1-x8 resin.
P.P. Sun, M.S. Lee / Hydrometallurgy 110 (2011) 91–98
100
1.0 0.8 0.6 0.4 0.2 0.0 0
5
10
15
20
25
30
Pt Al Fe Si Ni
80
Fe Al Pt [HCl]=3 M
35
Bed volume Fig. 9. Loading condition of metals from mixed solution by using 4 g AG1-x8 resin.
Adsorption percentage of metals (%)
Concentration fraction
97
60
40
20 and the results are shown in Fig. 10. This figure shows that after 3 bed volume, most of Pt was loaded onto AG1-x8 resin, while most of Al and Fe in the feed remained in the effluent. Therefore, it might be concluded that Pt could be separated from Fe and Al in 0.5 M HCl solution by using AG1-x8 resin.
0 0.00
0.05
0.10
0.15
0.20
Amount of resin (g) 3.5. Ion exchange of Pt from the real leaching solution The effect of amount of AG1-x8 resin on the loading of metals from the real leaching solution of the spent catalysts was investigated by varying the amount of resin from 0.01 g to 1 g in each batch experiment. The chemical compositions of the real leaching solution were 0.00025 M Pt, 0.0015 M Fe, 0.1 M Al, 0.0008 M Si, and 0.00002 M Ni. The concentration of HCl in this leaching solution was 3.2 M and the results are shown in Fig. 11. Most of Pt in the leaching solution was loaded onto the resin while the loading percentage of Ni, Si and Al was nearly zero. In the case of Fe, the loading percentage of Fe increased linearly with the increase in the amount of resin. In the batch and continuous experiments with the synthetic solution, it was difficult to separate Pt and Fe when the concentration of HCl in the synthetic solution was 3 M. Since the concentration of HCl in the real leaching solution of the spent catalysts was 3.2 M, 4–14% of iron was loaded onto the resin together with Pt when the amount of resin was from 0.025 to 0.2 g. From the batch experiments with the real leaching solution, it was observed that there was little difference
Concentration fraction
in the loading behavior of Pt, Fe, and Al from the synthetic and real leaching solution. The difference in the loading percentage of Pt, Fe Al was within 5%, 4.5%, and 0.2%, respectively. Moreover, the loading of Ni and Si onto AG1-x8 was nil. Therefore, decrease of HCl concentration is very important in separating Pt from the real leaching solution of the spent catalysts. Vacuum distillation is one of the methods to reduce the concentration of HCl from 3.2 M to 0.5 M. Elution of Pt from the resin is necessary to regenerate the resin. Several agents were tried to regenerate the resin, and the results are shown in Table 4. The maximum of elution percentage of Pt was 41% by using 2 M Na2CO3. Further work on the continuous experiments with real leaching solution and on the elution of Pt from the resin needs to be done.
4. Conclusions Solvent extraction and ion exchange experiments have been performed to separate Pt(IV) from the leaching solution of the spent catalysts for the catalytic reforming process in the petrochemical industries. Synthetic chloride solution containing Pt(IV), Fe(III) and Al(III) was used as a feed solution in this work. Extraction and loading experiments were done in the HCl concentration range from 1 to 9 M. In solvent extraction, Alamine336, Alamine304-1, Alamine308, Aliquat336, TBP and TOPO were tested. The extraction behavior of the three metals by amines
1.0 0.8
Fe Al Pt [HCl]=0.5 M
0.6
Fig. 11. The effect of amount of resin on the adsorption of metals from the real leaching liquor solution.
0.4
Table 4 Results of the elution of Pt from the loaded AG1-x8 resin.
0.2 0.0 0
5
10
15
20
25
30
35
Bed volume Fig. 10. Loading condition of metals from mixed solution by using 4 g AG1-x8 resin.
Elution regent
Elution percentage %
0.1 M HCl 1 M NaOH 5 M NaOH 1 M NaCl 2 M Na2CO3 0.1 M thiourea
b 0.1 0.2 14 nil 41 25.3
98
P.P. Sun, M.S. Lee / Hydrometallurgy 110 (2011) 91–98
was similar to each other. Most of Pt was extracted into amine irrespective of HCl concentration. Extraction of iron depended on extraction conditions and most of Fe was extracted into amine when HCl concentration was higher than 5 M. TOPO extracted most of Pt and Fe irrespective of HCl concentration. In the extraction with TBP, the extraction percentage of iron was higher than that of platinum. None of Al was extracted by amines, TOPO and TBP in our experimental conditions. It was difficult to separate Pt from Fe and Al by solvent extraction with amines, TBP, and TOPO. Batch sorption experiments with AG1-x8 indicated that separation of Pt from Fe and Al was possible by adjusting HCl concentration of the synthetic solution. When HCl concentration was 1 M, most of Pt was loaded onto the resin, while the loading of Fe and Al was negligible at this HCl concentration. Continuous experiments with glass column led to complete separation of Pt from Fe and Al from the feed of 0.5 M HCl. In the batch experiments with the real leaching solution of spent catalysts, most of Pt together with a small amount of Fe was loaded onto the resin, leaving Si, Ni and Al in the solution. Our results could be utilized in developing a separation process to recover Pt from the chloride leaching solution of the spent catalysts containing Fe, Al, Si and Ni. Acknowledgments This work was supported by a grant operated by KEITI of the Ministry of Environment of Korea. The authors would like to thank for the financial support. References Alam, M.S., Inoue, K., 1997. Extraction of rhodium from other platinum group metals with Kelex100 from chloride media containing tin. Hydrometallurgy 46, 373–382. Baghalha, M., Khosravian Gh., H., Mortaheb, H.R., 2009. Kinetics of platinum extraction from spent reforming catalysts in aqua-regia solutions. Hydrometallurgy 95, 247–253. Benguerel, E., Demopoulos, G.P., Cote, G., Bauer, D., 1994. An investigation on the extraction of rhodium from aqueous chloride solutions with 7 substituted 8 hydroxyquinolines. Solvent Extr. Ion Exch. 12, 497–516. Benguerel, E., Demopoulos, G.P., Harris, G.B., 1996. Speciation and separation of rhodium(III) from chloride solutions : a critical review. Hydrometallurgy 40, 135–152. Bernardis, F.L., Grant, R.A., Sherrington, D.C., 2005. A review of methods of separation of the platinum-group metals through their chloro-complexes. React. Funct. Polym. 65, 205–217. Bjerrum, J., Schwarzenbach, G., Sillén, L.G., 1958. Stability Constants of Metal-Ion Complexes with Solubility Products of Inorganic Substances, Part II Inorganic Ligands. The Chemical Society, London, p. 105.
Charlesworth, P., 1981. Separating the platinum group metals by liquid-liquid extraction. Platinum Met. Rev. 25, 106–112. Kedari, C.S., Coll, M.T., Fortuny, A., Goralska, E., Sastre, A.M., 2005. Liquid-liquid extraction of Ir, Ru and Rh from chloride solutions and their separation using different commercially available solvent extraction reagents. Sep. Sci. Technol. 40, 1927–1946. Lee, M.S., 2006. Use of the Bromley equation for the analysis of ionic equilibria in mixed ferric and ferrous chloride solutions at 25 °C. Metall. Mater. Trans. 37 B, 173–179. Lee, M.S., Lee, K.J., 2005. Separation of iron and nickel from a spent FeCl3 etching solution by solvent extraction. Hydrometallurgy 80, 163–169. Lee, M.S., Lee, G.S., Sohn, K.Y., 2004. Solvent extraction equilibria of FeCl3 with TBP. Mater. Trans. 45, 1859–1863. Lee, M.S., Lee, J.Y., Kumar, R.J., Kim, J.S., Sohn, J.S., 2008. Solvent extraction of PtCl4 from hydrochloric acid solution using Alamine336. Mater. Trans. 49, 2823–2828. Lee, J.Y., Kumar, J.R., Kim, J.S., Park, H.K., Yoon, H.S., 2009a. Liquid-liquid extraction/separation of platinum(IV) and rhodium(III) from acidic chloride solutions using triiso-octylamine. J. Hazard. Mater. 168, 424–429. Lee, J.Y., Kumar, J.R., Kim, J.S., Kim, D.J., Yoon, H.S., 2009b. Extraction and separation of Pt(IV)/Rh(III) from acidic chloride solution using Aliquat 336. J. Ind. Eng. Chem. 15, 359–364. Lee, J.Y., Raju, B., Kumar, B.N., Kumar, J.R., Park, H.K., Reddy, B.R., 2010. Solvent extraction separation and recovery of palladium and platinum from chloride leach liquors of spent automobile catalyst. Sep. Purif. Technol. 73, 213–218. Lewis, P.A., Morris, D.F.C., Short, E.L., Waters, D.N., 1976. Application of solvent extraction to the refining of precious metals IV. Practical and structural aspects of the separation of rhodium, palladium, iridium and platinum with organic sulphoxides. J. Less-Common Met. 45, 193–214. Mhaske, A.A., Dhadke, P.M., 2001. Extraction separation studies of Rh, Pt and Pd using Cyanex 921 in toluene — a possible application to recovery from spent catalyst. Hydrometallurgy 61, 143–150. Nowottny, C., Halwachs, W., Schugerl, K., 1997. Recovery of platinum, palladium and rhodium from industrial process leaching solutions by reactive extraction. Sep. Purif. Technol. 12, 135–144. Rao, C.R.M., Reddi, G.S., 2000. Platinum group metals(PGM); occurrence, use and recent trends in their determination. Trends Anal. Chem. 19, 565–586. Reddy, B.R., Bhaskara Sarma, P.V.R., 1996. Extraction of iron(III) at macro-level concentrations using TBP, MIBK and their mixtures. Hydrometallurgy 43, 299–306. Reddy, K.J., Reddy, A.V., Shaibu, B.S., Reddy, M.L.P., 2007. Enhanced extraction and separation of zirconium(IV) and hafnium(IV) with 3-phenyl-4-benzoyl-5-isoxazolone in presence of various neutral organophosphorus extractants. Radiochim. Acta 95, 289–295. Reddy, B.R., Raju, B., Lee, J.Y., Park, H.K., 2010. Process for the separation and recovery of palladium and platinum from spent automobile catalyst leach liquor using LIX 84I and Alamine 336. J. Hazard. Mater. 180, 253–258. Seyed, N.A., George, P.D., 1995. Formation of W/O microemulsions in the extraction system Rh(III)–HCl–Kelex 100 and its impact on Rh(III) distribution. J. Colloid Interface Sci. 173, 448–459. Specker, H., Cremer, M.Z., 1959. Liquid-liquid extraction of iron(III) with tributylphosphate: separation from mixtures. Anal. Chem. 167, 110. Zou, L.H., Chen, J., Pan, X.J., 1998. Solvent extraction of rhodium from aqueous solution of Rh(III)–Sn(III)–Cl system by TBP. Hydrometallurgy 50, 193–203.
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Separation of Pt from hydrochloric acid leaching solution of spent catalysts by solvent extraction and ion exchange P.P. Sun, M.S. Lee ⁎ Department of Advanced Materials Science & Engineering, Mokpo National University, Chonnam 534-729, Republic of Korea
a r t i c l e
i n f o
Article history: Received 21 July 2011 Received in revised form 2 September 2011 Accepted 2 September 2011 Available online 10 September 2011 Keywords: Platinum(IV) Iron(III) Aluminum(III) Solvent extraction Ion exchange
a b s t r a c t Leaching of spent catalysts (Pt/Al2O3) with a mixture of HCl and H2O2 results in a mixed chloride solution containing Pt(IV), Fe(III), Al(III), Ni(II), and silicon. Separation of Pt(IV) from the synthetic chloride solution containing Fe(III) and Al(III) has been performed by solvent extraction and ion exchange. Effects of extraction and sorption conditions on the separation of Pt were investigated in the HCl concentration range from 1 to 9 M. In solvent extraction experiments, amines (Alamine304-1, Alamine308, Alamine336, Aliquat336), TBP and TOPO were tested, while AG1-x8 resin was employed in ion exchange experiments. Solvent extraction experiments indicated that it was difficult to separate Pt from Fe and Al by amines and solvating extractants in our tested range. In ion exchange by using AG1-x8 resin, only Pt was loaded from the synthetic solution when HCl concentration was lower than 1 M, while Fe and Al remained in the solution. Continuous experiments with AG1-x8 resin indicated that most of Pt was loaded onto the resin from 0.5 M HCl solution, leaving Fe and Al in the effluent and complete separation of Pt was possible. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Platinum along with some other platinum group metals (PGMs) is the main active ingredient of various catalysts for the automobile and petrochemical industries. Pt/Al2O3 catalysts are widely used in petrochemical industries for the catalytic reforming process (Baghalha et al., 2009) Substitution of Pt by other metals is difficult due to its special properties (Rao and Reddi, 2000). A large amount of spent catalysts is being generated from the petrochemical and automobile industries. Since the natural resources of PGMs are limited, recovery of PGMs from the spent catalysts is important from the viewpoint of economics as well as environment protection. In hydrometallurgical treatment of spent catalysts, PGMs together with other minor elements in the spent catalysts are dissolved by leaching with chloride based solutions at high temperature. In order to recover pure PGMs from the chloride based leaching solution of spent catalysts, various commercial amines have been tested in solvent extraction (Alam and Inoue, 1997; Benguerel et al., 1996; Bernardis et al., 2005; Charlesworth, 1981; Lee et al., 2008; Lee et al., 2009a; Lee et al., 2009b; Lee et al., 2010; Mhaske and Dhadke, 2001; Nowottny et al., 1997). Together with amines, solvating extractants, such as TBP and TOPO, have been widely used in the separation of PGMs from chloride solution (Benguerel et al., 1994) and in the refining of precious metals (Lewis et al., 1976; Zou et al., 1998). ⁎ Corresponding author. Fax: +82 61 450 2498. E-mail address: [email protected] (M.S. Lee). 0304-386X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2011.09.002
In our study on the recovery of Pt from the spent catalysts which have been used in the catalytic reforming process of petrochemical industries, leaching of the spent catalysts with a mixture of HCl and H2O2 resulted in a solution containing Pt(IV), Fe(III), Al(III), Ni(II), and silicon. The composition of the leaching solution was 0.00025 M Pt(IV), 0.0015 M Fe(III) and 0.1 M Al(III) together with negligible amount of Ni and Si. The chemical composition of the spent catalysts is shown in Table 1. Since the concentration of Ni and Si in the leaching solution was negligible, synthetic solution containing Pt(IV), Fe (III), and Al(III) was employed in this study. Platinum exists in HCl solution as PtCl62− (Lee et al., 2008). Ferric ion can form complexes with chloride ion, such as FeCl2+, FeCl2+, FeCl3aq, and FeCl4−(Lee, 2006), while Al is known to exist as Al3+ in HCl solution (Bjerrum et al., 1958). The difference in the nature of chemical complexes of Pt(IV), Fe(III), and Al(III) in chloride solution can be utilized to develop a process for the separation of these three metals. According to the literature on the extraction of PGMs from chloride solution, Aliquat336 is more suitable for separating PGMs at low concentration of HCl, while tertiary amine or solvating extractants are more suitable at high concentration of HCl (Kedari et al., 2005). In this work, solvent extraction and ion exchange experiments have been performed to find an optimum condition to separate Pt (IV) from Fe and Al in the HCl concentration range from 1 to 9 M. For this purpose, some tertiary amines, solvating extractants and anion exchange resin were employed and the extraction/loading behavior of the three metal ions with extraction/loading conditions is reported. Alamine304-1, Alamine308, Alamine336 and Aliquat336 were used as a tertiary amine and TBP and TOPO were used as a
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Table 1 The chemical composition of spent catalyst measured by XRF and ICP (Unit: wt.%).
Table 3 Chemical formula of extractants used in this study.
Pt
Al
Si
Fe
Ni
Extractant
Reagent class
Structure
0.08
10.15
0.85
0.28
0.005
Alamine304-1 Alamine308 Alamine336 Aliquat336 TBP TOPO DOS
Tertiary amine Tertiary amine Tertiary amine Aliphatic quaternary ammonium salt Tri-n-butyl phosphate Trioctylphosphine oxide Di-n-octyl sulfide
[CH3(CH2)11]3 N [(CH3)2CH(CH2)5]3 N [C8–C10 mixture]3 N [(C8H17) 3 N(CH3)]+Cl− [CH3(CH2)3O]3PO [CH3(CH2)7]3PO [CH3(CH2)7]2S
Minor elements: S, Cl, K, Ca, Sr, Zr, Sn.
solvating extractant. In ion exchange, AG1-x8 was employed in batch and continuous experiments. 2. Experimental 2.1. Materials Synthetic solutions were prepared by dissolving certain amount of PtCl4 (Aldrich, 98%), FeCl3·6H2O (Junsei Chem., 97%) and AlCl3 (Junsei Chem., 98%) in doubly distilled water. The composition of the synthetic solution was 0.00025 M Pt(IV), 0.0015 M Fe(III) and 0.1 M Al(III). The acidity of the solution was adjusted by adding HCl (Junsei Chem., 35%). Amines (Alamine304-1, Alamine308, Alamine336, and Aliquat336) were purchased from Cognis Corporation and used without further purification. Amine extractants except Alamine304-1 were pretreated with HCl to form salt. Alamine304-1 was used as received because it was solidified after the pretreatment with HCl solution. Amines and tributyl phosphate (TBP, Yakuri pure chemicals co., 99%) were diluted with toluene. Trioctylphosphine oxide (TOPO) solution was prepared by dissolving the necessary amount of TOPO powder (Aldrich, 90%) in toluene. The chemical formula of each extractant is shown in Table 3. The real leaching solution was obtained by leaching the spent catalyst with a mixture of HCl and H2O2. The leaching experimental conditions are shown in Table 2. Leaching experiments were carried out in a hermetic container (500 ml) under magnetic agitation (300 rpm) at 70 °C. One hundred ml of lixiviant was first filled in the hermetic container and the reaction temperature was adjusted to 70 °C by using digital magnetic stirrer. Then 5 g of spent catalyst with a particle size of 0.1–0.3 mm was filled in the reaction vessel. After 2 h reaction, the insoluble residue was separated immediately from the leaching solution by using ceramic filter under vacuum and the concentration of metals in the filtrate was measured by ICP-OES (Spectro Arcos). 2.2. Solvent extraction and ion exchange procedure In solvent extraction experiments, equal volume (20 ml) of aqueous and organic phase was mixed in a 100 ml screwed cap bottle and shaken for 30 min with a wrist action shaker. The aqueous phase was separated after settling the mixture. All the extraction experiments were carried out at ambient temperature. Batch ion exchange experiments were carried out in a shaking incubator (HB-201SF, Hanbaek Scientific Co.) using 100 ml screwed cap bottle. The temperature of the shaking incubator was controlled to 25 °C. Fifty ml of mixed chloride solutions were bottle rolled for 24 h after putting certain amount of resin. A commercial AG1-x8 resin (Bio-Rad) with particle size between 200 and 400 mesh was used and the resin had chloride form. In continuous experiments, 4 g of AG1-x8 resin was filled into the
Table 2 Leaching condition of spent catalysts. Pretreatment temperature Composition of leaching solution Particle size Reaction temperature Reaction time Pulp density
800 °C 10% HCl + 1%H2O2 0.1–0.3 mm 70 °C 2h 50 g/L
glass column (250×10 mm). The volume of 4 g resin in the column was 5.7 ml. The temperature of the column in continuous experiments was controlled to 25 °C by using water circulator bath (Scientific Co., Vs1902WF). Flow rate of the feed solution was adjusted by using pump (FMI lab pump, QG20) to ensure that 6 ml of effluent was collected every 3.5 to 4.min. The concentration of metal in the aqueous phase was measured by ICP-OES (Spectro arcos). The concentration of metal in the organic phase and resin was obtained by the following mass balance equation. Corg Vorg ¼ Cinitial Vinitial −Caq Vaq mon
resin
¼ mfeed −meffluent :
ð1Þ ð2Þ
In the above equation, C, V, and m represent the concentration, volume and mass. The subscript, org, initial, aq represent the organic solution, initial solution and aqueous solution, and mon resin , mfeed , meffluent represent the mass of metal absorbed on the resin, contained in feed solution and remained in the effluent. 3. Results and discussion 3.1. Solvent extraction of Pt from mixed solution Effects of extraction conditions on the separation of Pt(IV) from Fe (III) and Al(III) were investigated from the synthetic solution. In these experiments, the concentration of amines was varied from 0.1 to 0.7 M and HCl concentration was adjusted from 1 to 9 M. The composition of the synthetic chloride solution was 0.00025 M Pt(IV), 0.0015 M Fe(III) and 0.1 M Al(III). Figs. 1 to 2 show the results obtained from the extraction with Alamine336 and Aliquat336, respectively. The extraction behavior of the metals with Alamine304-1 and Alamine308 was similar to that with Alamine336 and Aliquat336. In the HCl concentration range from 1 to 9 M, most of Pt was extracted irrespective of the nature of amine whereas the extraction percentage of Al was zero throughout our experimental conditions. In the case of Fe, most of Fe was extracted in the HCl concentration range from 1 to 9 M when the concentration of amine was higher than 0.1 M. When the concentration of amine was 0.1 M, the extraction percentage of Fe increased with the increase of HCl concentration. Solvent extraction results with amines indicated that most of Pt and Fe were extracted into amines and Al remained in the aqueous phase. Thus it may be concluded that it is difficult to separate Pt from Fe and Al by solvent extraction with amine in the HCl concentration range from 1 to 9 M. Tertiary amines belong to strong-base extractant. Since the strong bases of tertiary amines are readily protonated, tertiary amines can behave as ion-exchanger at relatively low acid concentrations. The difference in the extraction characteristics of tertiary amines is due to the basicity of R (the tertiary amine is represented as R3N) (Charlesworth, 1981). Solvent extraction of Pt and Fe from the synthetic chloride solution by using amines follows ion exchange mechanism. The high extraction percentage of Pt and Fe by amines might be due to their high capacity
Extraction percentage Extraction percentage Extraction percentage of Al of Fe of Pt
P.P. Sun, M.S. Lee / Hydrometallurgy 110 (2011) 91–98
93
100 80
[Alamine336] 0.1 M 0.3 M 0.5 M 0.7 M
60 40 20 0
1
2
3
4
5
6
7
100 80
9
[Alamine336] 0.1 M 0.3 M 0.5 M 0.7 M
60 40 20 0
8
1
2
3
4
5
6
7
100 80 60 40 20 0
8
9
[Alamine336] 0.1 M 0.3 M 0.5 M 0.7 M
1
2
3
4
5
6
7
8
9
HCl concentration (M) Fig. 1. Effect of HCl concentration on the extraction of Pt(IV), Fe(III) and Al(III) at different concentration of Alamine336.
of Pt and Fe. The extraction reaction of Pt and Fe by amine can be represented as (Reddy et al., 2010) 2−
PtCl6 þ 2R3 NHClorg ¼ PtCl6 ðR3 NHÞ2 ;org þ2Cl
−
FeCl4 þ R3 NHClorg ¼ FeCl4 ðR3 NHÞorg þ Cl
−
ð3Þ
−
ð4Þ
Extraction percentage Extraction percentage Extraction percentage of Al of Fe of Pt
Separation experiments of Pt from Fe and Al were also performed by using TBP and TOPO. The concentration of HCl in the solution was
100 80 60 40 20 0 100 80 60 40 20 0
varied from 1 to 9 M. The concentration of TBP and TOPO was fixed at 1 M, and the results are shown in Fig. 3. This figure shows that most of Pt and Fe were extracted by 1 M TOPO in the HCl concentration range from 1 to 9 M and it was impossible to separate Pt from Fe and Al by extraction with 1 M TOPO. In the extraction with 1 M TBP, the extraction percentage of Fe and Pt depended on HCl concentration. When HCl concentration was 1 M, the extraction percentage of Pt and Fe was zero. Extraction percentage of Fe rapidly increased with the increase of HCl concentration and reached 99% when HCl concentration was higher than 5 M.
[Aliquat336] 0.1 M 0.3 M 0.5 M 0.7 M
0
2
4
6
8
10
[Aliquat336] 0.1 0.3 0.5 0.7
0
2
4
6
100 80 60 40 20 0
8
10
[Aliquat336] 0.1 M 0.3 M 0.5 M 0.7 M
0
2
4
6
8
10
HCl concentration (M) Fig. 2. Effect of HCl concentration on the extraction of Pt(IV), Fe(III) and Al(III) at different concentration of Aliquat 336.
P.P. Sun, M.S. Lee / Hydrometallurgy 110 (2011) 91–98
Extraction percentage Extraction percentage Extraction percentage of Al of Fe of Pt
94
100 80 60 40 20 0 100 80 60 40 20 0
TBP TOPO
0
2
4
6
8
10
TBP TOPO
0
2
4
6
100 80 60 40 20 0
8
10
TBP TOPO
0
2
4
6
8
10
HCl concentration (M) Fig. 3. Effect of HCl concentration on the extraction of Pt(IV), Fe(III) and Al(III) with TBP and TOPO. ([TBP] = [TOPO] = 1 M).
Extraction percentage Extraction percentage Extraction percentage of Al of Fe of Pt
Extraction percentage of Pt increased with HCl concentration and reached a maximum of 43% at 7 M HCl. Extraction percentage of Al by 1 M TBP and 1 M TOPO was zero in our experimental range. The difference in the extraction abilities between TBP and TOPO might be related with the donor ability of phosphoryl oxygen in them (Reddy et al., 2007). The phosphoryl oxygen of TOPO was affected by three electron donation groups [ CH3(CH2)7− ], while that of TBP was affected by three electron withdrawing groups [CH3
(CH2)3O− ]. Therefore, donor ability of phosphoryl oxygen follows the order: TOPO N TBP. The extraction behavior of metals by TBP was further investigated by varying TBP concentration from 0.5 to 2.0 M and the results are shown in Fig. 4. According to Fig. 4, extraction percentage of Pt and Fe increased with the increase of HCl concentration when the TBP concentration was fixed. When HCl concentration was higher than 5 M, most of Fe was extracted irrespective of TBP concentration,
100 80 60 40
[TBP] 0.5 M 1.0 M 1.5 M 2.0 M
20 0 0 100 80 60 40 20 0 0 100 80 60 40 20 0 0
2
4
6
8
10
[TBP] 0.5 M 1.0 M 1.5 M 2.0 M
2
4
6
8
10
[TBP] 0.5 M 1.0 M 1.5 M 2.0 M
2
4
6
8
10
HCl concentration (M) Fig. 4. Effect of HCl concentration on the extraction of Pt(IV), Fe(III) and Al(III) at different concentration of TBP.
P.P. Sun, M.S. Lee / Hydrometallurgy 110 (2011) 91–98
while the highest extraction percentage of Pt was 80% with 2.0 M TBP at 7 M HCl. None of Al was extracted by TBP in our experiment condition. The extraction percentage of Pt and Fe by 0.5 M TBP was 10 and 85% at 5 M HCl, which seems to be the best condition to separate Fe from Pt by TBP. The extraction reaction of Pt and Fe by TBP might be expressed as (Lee and Lee, 2005; Lee et al., 2004; Reddy and Bhaskara Sarma, 1996; Seyed and George, 1995; Specker and Cremer, 1959): þ
2−
ð5Þ
−
ð6Þ
2H þ PtCl6 þ 2TBPorg ¼ 2TBP·H2 PtC16 ;org
3þ
Fe
þ
þ 3Cl þ 3TBP ¼ FeCl3 ·3TBP
−
H þ FeCl4 þ 2TBP ¼ HFeCl4 ·2TBP
ð7Þ
In strong HCl solution of 6–9 M, ferric ion is extracted by Eq. (5), while Eq. (4) is responsible for the extraction of ferric ion in the lower HCl concentration. Among the amines and solvating extractants tested in this study, extraction with TBP resulted in the best condition to separate Pt from Fe and Al. Since extraction percentage of Fe was higher than that of Pt in the extraction with TBP, another extraction step is necessary to recover Pt from the remaining solution after extraction with TBP. The stripping of Pt and Fe from the loaded TBP was investigated by using dilute HCl solution. The concentration of HCl was varied from 0.01 to 0.5 M, and the results are shown in Fig. 5. Most of Fe was stripped from the loaded TBP in our stripping conditions. The stripping percentage of Pt was 71% by 0.01 M HCl and decreased with the increase of HCl concentration.
95
3.2. Solvent extraction of Pt from the real leaching solution As observed in the solvent extraction of synthetic solution by using different solvent extractants, the possible extractant to separate Pt from other metals was TBP. So 1.5 M TBP was used in the solvent extraction of metals from the real leaching solution. The other variable was kept at the same. The results showed that the extraction percentage of Pt, Fe, Al, were 98%, 97%, 0.5%, and nil for Ni and Si. Since the stripping selectivity of Pt and Fe from loaded TBP was low, it is difficult to separate Pt from the other impurity metals by solvent extraction using TBP.
3.3. Ion exchange of Pt from the synthetic solution Ion exchange experiments with AG1-x8 were performed to separate Pt from Fe and Al. Effects of the concentration of HCl and the amount of resin were investigated. In order to obtain equilibrium loading isotherm of Pt, loading experiments were done from the pure PtCl4 solution of 5 M HCl and the results are shown in Fig. 6. The loading capacity of AG1-x8 for Pt(VI) was about 50 mg/g of resin at 5 M HCl. In the batch experiments, the amount of AG1-x8 resin was varied from 0.025 to 0.2 g. The effect of HCl concentration was investigated by varying HCl concentration from 1 to 5 M and the results are shown in Fig. 7. This figure shows that the loading of Pt and Fe depended on the sorption conditions while the loading percentage of Al was zero in our experimental condition. When HCl concentration was 1 M, only Pt was loaded onto the resin and the loading percentage of Fe was negligible. Most of Pt was loaded onto AG1x-8 from 3 M HCl solution when the amount of resin was higher than 0.05 g. However, the loading percentage of Fe increased to 18% at 3 M HCl. When HCl concentration was 5 M, the loading percentage of Pt decreased compared to that at 1 and 3 M HCl, whereas the loading percentage of Fe increased linearly with the increase in the amount of resin. The increase in the loading percentage of Fe with the increase
100
60
90 50
70 60 50
Pt Fe
40 30
Equilibrium resin loading (mg/g)
Stripping percentage of metals
80
40
Pt [HCl]=5 M
30
20
20 10 10 0
0.0
0.1
0.2
0.3
0.4
0.5
HCl concentration (M)
0
0
10
20
30
40
50
Equilibrium concentration in solution (mg/L) Fig. 5. Effect of HCl concentration on the stripping of Pt and Fe from 1.5 M TBP loaded organic phase.
Fig. 6. Equilibrium loading of Pt in 5 M HCl solution.
P.P. Sun, M.S. Lee / Hydrometallurgy 110 (2011) 91–98
Adsorption percentage Adsorption percentage Adsorption percentage of metals of metals of metals
96
100 80 60 40 20 0 0.00 100 80 60 40 20 0 0.00 100 80 60 40 20 0 0.00
[HCl]=1 M Pt Fe Al
0.05
0.10
0.15
0.20
[HCl]=3 M Pt Fe Al
0.05
0.10
0.15
0.20
[HCl]=5 M Pt Fe Al
0.25
0.50
0.75
1.00
Amount of resin (g)
Fig. 7. The effect of amount of AG1-x8 resin on the adsorption of metals with different concentration of HCl.
3.4. Continuous experiments Batch experiments with AG1-x8 indicate that it is possible to separate Pt from Fe and Al by adjusting HCl concentration of the synthetic solution. Therefore, continuous experiments were done by employing glass column. In these continuous experiments, the amount of resin was fixed at 4 g. The change in the concentration of metals in the effluent was represented by using concentration fraction which is defined as Eq. (8). Concentration fraction ¼
the concentration of metal in the effluent : initial concentration of metal in the solution ð8Þ
According to Fig. 7, the loading percentage of Fe decreased with the decrease of HCl concentration and was 1.7% at 1 M HCl. In the next continuous experiments, HCl concentration in the feed was adjusted to 0.5 M, keeping the other experimental conditions the same
100 90 80
Adsorption percentage of metals (%)
of HCl concentration is related with the formation of FeCl4− at higher concentration of HCl (Lee and Lee, 2005). Fig. 7 indicates that it is possible to separate Pt from Fe and Al by using AG1-x8 and the control of HCl concentration is the most important step in achieving complete separation of Pt from Fe and Al. In order to investigate the effect of HCl concentration on the loading of Fe, sorption experiments were done by varying HCl concentration from 1 to 3 M at the interval of 0.5. In these experiments, the amount of AG1-x8 was fixed at 0.2 g, and the results are shown in Fig. 8. This figure indicates that loading percentage of Fe decreased rapidly with the decrease of HCl concentration while there was not much difference in the loading percentage of Pt in our tested range. When HCl concentration was 1 M, the loading percentage of Pt and Fe was 95 and 1.7%, respectively.
Pt Al Fe
70 60 50 40 30 20 10
Fig. 9 shows the results which was obtained from the continuous experiments with the synthetic solution of 3 M HCl. Most of Pt in the feed solution was loaded onto AG1-x8 resin, while Al remained in the effluent. Iron was loaded until 10 bed volume, and after this bed volume the loading of Fe decreased slowly with the increase of bed volume. The results shown in Fig. 9 indicate that it is difficult to separate Pt from Fe and Al in one step from 3 M HCl solution.
0 1.0
1.5
2.0
2.5
3.0
Concentration of HCl (M) Fig. 8. The effect of concentration of HCl on the adsorption of metals by 4 g/L AG1-x8 resin.
P.P. Sun, M.S. Lee / Hydrometallurgy 110 (2011) 91–98
100
1.0 0.8 0.6 0.4 0.2 0.0 0
5
10
15
20
25
30
Pt Al Fe Si Ni
80
Fe Al Pt [HCl]=3 M
35
Bed volume Fig. 9. Loading condition of metals from mixed solution by using 4 g AG1-x8 resin.
Adsorption percentage of metals (%)
Concentration fraction
97
60
40
20 and the results are shown in Fig. 10. This figure shows that after 3 bed volume, most of Pt was loaded onto AG1-x8 resin, while most of Al and Fe in the feed remained in the effluent. Therefore, it might be concluded that Pt could be separated from Fe and Al in 0.5 M HCl solution by using AG1-x8 resin.
0 0.00
0.05
0.10
0.15
0.20
Amount of resin (g) 3.5. Ion exchange of Pt from the real leaching solution The effect of amount of AG1-x8 resin on the loading of metals from the real leaching solution of the spent catalysts was investigated by varying the amount of resin from 0.01 g to 1 g in each batch experiment. The chemical compositions of the real leaching solution were 0.00025 M Pt, 0.0015 M Fe, 0.1 M Al, 0.0008 M Si, and 0.00002 M Ni. The concentration of HCl in this leaching solution was 3.2 M and the results are shown in Fig. 11. Most of Pt in the leaching solution was loaded onto the resin while the loading percentage of Ni, Si and Al was nearly zero. In the case of Fe, the loading percentage of Fe increased linearly with the increase in the amount of resin. In the batch and continuous experiments with the synthetic solution, it was difficult to separate Pt and Fe when the concentration of HCl in the synthetic solution was 3 M. Since the concentration of HCl in the real leaching solution of the spent catalysts was 3.2 M, 4–14% of iron was loaded onto the resin together with Pt when the amount of resin was from 0.025 to 0.2 g. From the batch experiments with the real leaching solution, it was observed that there was little difference
Concentration fraction
in the loading behavior of Pt, Fe, and Al from the synthetic and real leaching solution. The difference in the loading percentage of Pt, Fe Al was within 5%, 4.5%, and 0.2%, respectively. Moreover, the loading of Ni and Si onto AG1-x8 was nil. Therefore, decrease of HCl concentration is very important in separating Pt from the real leaching solution of the spent catalysts. Vacuum distillation is one of the methods to reduce the concentration of HCl from 3.2 M to 0.5 M. Elution of Pt from the resin is necessary to regenerate the resin. Several agents were tried to regenerate the resin, and the results are shown in Table 4. The maximum of elution percentage of Pt was 41% by using 2 M Na2CO3. Further work on the continuous experiments with real leaching solution and on the elution of Pt from the resin needs to be done.
4. Conclusions Solvent extraction and ion exchange experiments have been performed to separate Pt(IV) from the leaching solution of the spent catalysts for the catalytic reforming process in the petrochemical industries. Synthetic chloride solution containing Pt(IV), Fe(III) and Al(III) was used as a feed solution in this work. Extraction and loading experiments were done in the HCl concentration range from 1 to 9 M. In solvent extraction, Alamine336, Alamine304-1, Alamine308, Aliquat336, TBP and TOPO were tested. The extraction behavior of the three metals by amines
1.0 0.8
Fe Al Pt [HCl]=0.5 M
0.6
Fig. 11. The effect of amount of resin on the adsorption of metals from the real leaching liquor solution.
0.4
Table 4 Results of the elution of Pt from the loaded AG1-x8 resin.
0.2 0.0 0
5
10
15
20
25
30
35
Bed volume Fig. 10. Loading condition of metals from mixed solution by using 4 g AG1-x8 resin.
Elution regent
Elution percentage %
0.1 M HCl 1 M NaOH 5 M NaOH 1 M NaCl 2 M Na2CO3 0.1 M thiourea
b 0.1 0.2 14 nil 41 25.3
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P.P. Sun, M.S. Lee / Hydrometallurgy 110 (2011) 91–98
was similar to each other. Most of Pt was extracted into amine irrespective of HCl concentration. Extraction of iron depended on extraction conditions and most of Fe was extracted into amine when HCl concentration was higher than 5 M. TOPO extracted most of Pt and Fe irrespective of HCl concentration. In the extraction with TBP, the extraction percentage of iron was higher than that of platinum. None of Al was extracted by amines, TOPO and TBP in our experimental conditions. It was difficult to separate Pt from Fe and Al by solvent extraction with amines, TBP, and TOPO. Batch sorption experiments with AG1-x8 indicated that separation of Pt from Fe and Al was possible by adjusting HCl concentration of the synthetic solution. When HCl concentration was 1 M, most of Pt was loaded onto the resin, while the loading of Fe and Al was negligible at this HCl concentration. Continuous experiments with glass column led to complete separation of Pt from Fe and Al from the feed of 0.5 M HCl. In the batch experiments with the real leaching solution of spent catalysts, most of Pt together with a small amount of Fe was loaded onto the resin, leaving Si, Ni and Al in the solution. Our results could be utilized in developing a separation process to recover Pt from the chloride leaching solution of the spent catalysts containing Fe, Al, Si and Ni. Acknowledgments This work was supported by a grant operated by KEITI of the Ministry of Environment of Korea. The authors would like to thank for the financial support. References Alam, M.S., Inoue, K., 1997. Extraction of rhodium from other platinum group metals with Kelex100 from chloride media containing tin. Hydrometallurgy 46, 373–382. Baghalha, M., Khosravian Gh., H., Mortaheb, H.R., 2009. Kinetics of platinum extraction from spent reforming catalysts in aqua-regia solutions. Hydrometallurgy 95, 247–253. Benguerel, E., Demopoulos, G.P., Cote, G., Bauer, D., 1994. An investigation on the extraction of rhodium from aqueous chloride solutions with 7 substituted 8 hydroxyquinolines. Solvent Extr. Ion Exch. 12, 497–516. Benguerel, E., Demopoulos, G.P., Harris, G.B., 1996. Speciation and separation of rhodium(III) from chloride solutions : a critical review. Hydrometallurgy 40, 135–152. Bernardis, F.L., Grant, R.A., Sherrington, D.C., 2005. A review of methods of separation of the platinum-group metals through their chloro-complexes. React. Funct. Polym. 65, 205–217. Bjerrum, J., Schwarzenbach, G., Sillén, L.G., 1958. Stability Constants of Metal-Ion Complexes with Solubility Products of Inorganic Substances, Part II Inorganic Ligands. The Chemical Society, London, p. 105.
Charlesworth, P., 1981. Separating the platinum group metals by liquid-liquid extraction. Platinum Met. Rev. 25, 106–112. Kedari, C.S., Coll, M.T., Fortuny, A., Goralska, E., Sastre, A.M., 2005. Liquid-liquid extraction of Ir, Ru and Rh from chloride solutions and their separation using different commercially available solvent extraction reagents. Sep. Sci. Technol. 40, 1927–1946. Lee, M.S., 2006. Use of the Bromley equation for the analysis of ionic equilibria in mixed ferric and ferrous chloride solutions at 25 °C. Metall. Mater. Trans. 37 B, 173–179. Lee, M.S., Lee, K.J., 2005. Separation of iron and nickel from a spent FeCl3 etching solution by solvent extraction. Hydrometallurgy 80, 163–169. Lee, M.S., Lee, G.S., Sohn, K.Y., 2004. Solvent extraction equilibria of FeCl3 with TBP. Mater. Trans. 45, 1859–1863. Lee, M.S., Lee, J.Y., Kumar, R.J., Kim, J.S., Sohn, J.S., 2008. Solvent extraction of PtCl4 from hydrochloric acid solution using Alamine336. Mater. Trans. 49, 2823–2828. Lee, J.Y., Kumar, J.R., Kim, J.S., Park, H.K., Yoon, H.S., 2009a. Liquid-liquid extraction/separation of platinum(IV) and rhodium(III) from acidic chloride solutions using triiso-octylamine. J. Hazard. Mater. 168, 424–429. Lee, J.Y., Kumar, J.R., Kim, J.S., Kim, D.J., Yoon, H.S., 2009b. Extraction and separation of Pt(IV)/Rh(III) from acidic chloride solution using Aliquat 336. J. Ind. Eng. Chem. 15, 359–364. Lee, J.Y., Raju, B., Kumar, B.N., Kumar, J.R., Park, H.K., Reddy, B.R., 2010. Solvent extraction separation and recovery of palladium and platinum from chloride leach liquors of spent automobile catalyst. Sep. Purif. Technol. 73, 213–218. Lewis, P.A., Morris, D.F.C., Short, E.L., Waters, D.N., 1976. Application of solvent extraction to the refining of precious metals IV. Practical and structural aspects of the separation of rhodium, palladium, iridium and platinum with organic sulphoxides. J. Less-Common Met. 45, 193–214. Mhaske, A.A., Dhadke, P.M., 2001. Extraction separation studies of Rh, Pt and Pd using Cyanex 921 in toluene — a possible application to recovery from spent catalyst. Hydrometallurgy 61, 143–150. Nowottny, C., Halwachs, W., Schugerl, K., 1997. Recovery of platinum, palladium and rhodium from industrial process leaching solutions by reactive extraction. Sep. Purif. Technol. 12, 135–144. Rao, C.R.M., Reddi, G.S., 2000. Platinum group metals(PGM); occurrence, use and recent trends in their determination. Trends Anal. Chem. 19, 565–586. Reddy, B.R., Bhaskara Sarma, P.V.R., 1996. Extraction of iron(III) at macro-level concentrations using TBP, MIBK and their mixtures. Hydrometallurgy 43, 299–306. Reddy, K.J., Reddy, A.V., Shaibu, B.S., Reddy, M.L.P., 2007. Enhanced extraction and separation of zirconium(IV) and hafnium(IV) with 3-phenyl-4-benzoyl-5-isoxazolone in presence of various neutral organophosphorus extractants. Radiochim. Acta 95, 289–295. Reddy, B.R., Raju, B., Lee, J.Y., Park, H.K., 2010. Process for the separation and recovery of palladium and platinum from spent automobile catalyst leach liquor using LIX 84I and Alamine 336. J. Hazard. Mater. 180, 253–258. Seyed, N.A., George, P.D., 1995. Formation of W/O microemulsions in the extraction system Rh(III)–HCl–Kelex 100 and its impact on Rh(III) distribution. J. Colloid Interface Sci. 173, 448–459. Specker, H., Cremer, M.Z., 1959. Liquid-liquid extraction of iron(III) with tributylphosphate: separation from mixtures. Anal. Chem. 167, 110. Zou, L.H., Chen, J., Pan, X.J., 1998. Solvent extraction of rhodium from aqueous solution of Rh(III)–Sn(III)–Cl system by TBP. Hydrometallurgy 50, 193–203.