Ind. Eng. Chem. Res. 1997, 36, 4365-4368
4365
Recovery of Gallium(III) from Strongly Alkaline Media Using a Kelex-100-Loaded Ion-Exchange Resin Morio Nakayama*,† and Hiroaki Egawa‡ Faculty of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-Honmachi, Kumamoto 862, Japan, and Faculty of Engineering, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860, Japan
Kelex-100 [7-(4-ethyl-1-methyloctyl)-8-hydroxyquinoline] is an important liquid-chelating ion exchanger in hydrometallurgy and a highly selective extractant for gallium (Ga). In this study, Kelex-100-loaded ion-exchange resins were prepared for the recovery of Ga(III) from sodium aluminate solutions (Bayer solution) used in the Bayer process. When macroporous type ionexchange resins were used as polymer matrices for loading Kelex-100, the physical pore structure and the ion-exchange group significantly affected the adsorption of Ga(III) from strongly alkaline media on the Kelex-100-loaded resin. In particular, the Kelex-100-loaded carboxylic type resin having a macroporous structure showed a high capacity for Ga(III) in concentrated NaOH solution and effectively recovered Ga(III) from the Bayer solution containing large amounts of aluminum(III). Introduction Although gallium (Ga) is important in semiconductor manufacture, there is no ore bed that contains only Ga. At present, Ga is mainly obtained from sodium aluminate solutions (Bayer solution) used in the Bayer process. The Bayer solution is very strongly basic, and Ga is present in it as a trace amount of Ga(OH)4- with a large amount of Al(OH)4-. So, a material with a high affinity and selectivity for Ga(III) is required for the recovery of Ga(III) from the Bayer solution. The chemical structure of 7-(4-ethyl-1-methyloctyl)8-hydroxyquinoline (abbreviated as Kelex-100; Demopoulos and Distin, 1983) is given below:
Kelex-100 is an important liquid-chelating ion exchanger in hydrometallurgy and is known to be a highly selective extractant for Ga(III) (Obi et al., 1989; Matsuda and Ochi, 1990). It was reported that Kelex-100loaded organic adsorbents were effective for the separation and preconcentration of trace metals (Isshiki et al., 1987). However, these adsorbents were not always suitable for the recovery of trace amounts of metal in aqueous solution because of their hydrophobicity. In the present study, macroporous ion-exchange resins consisting of beads of a hydrophobic polymer to which hydrophilic ion-exchange groups had been attached were used as polymer matrices for loading Kelex-100, and the Kelex-100-loaded ion-exchange resin was applied to the recovery of gallium from the Bayer solution. Experimental Section Materials. Kelex-100 (Shering AC) was utilized without further purification. Metal standard solutions were prepared by dilution of 1000 mg/L (Merck) to obtain references. Ga(III) and Al(III) solutions were * Author to whom all correspondence should be addressed. Telephone: 81-96-371-4358. Fax: 81-96-372-7182. E-mail:
[email protected]. † Faculty of Pharmaceutical Sciences. ‡ Faculty of Engineering. S0888-5885(97)00027-4 CCC: $14.00
prepared by dissolving Ga(NO3)3 and Al(NO3)3. Macroporous styrene-divinylbenzene copolymer beads (RS5) were synthesized by suspension polymerization using 5 mol % of divinylbenzene in the presence of 2,2,4trimethylpentane (100 vol % per monomer) as the diluent (Egawa et al., 1984). The other resins were obtained from commercial sources. Other reagents were of analytical grade. Apparatus. The specific surface area was measured using a Yuasa surface area apparatus (BET method). Pore volumes and average pore radii were determined using a Carlo-Erba mercury pressure porosimeter (Model 220) in the range of pressure from 1 to 1600 kg/cm2. The concentrations of Ga(III) and Al(III) were measured using a Shimadzu atomic absorption spectrophotometer (Model AA640-13S). Preparation of a Kelex-100-Loaded Resin. Ionexchange resins and chelating ion-exchange resins were immersed in 1 M HCl and rinsed with distilled water until the pH of the washing solution reached 5-6 (acid treatment). Next, the resins were immersed in 1 M NaOH and washed with distilled water until the pH of the washing solution reached 8-9 (alkali treatment). This operation was repeated three times. Finally, the resins were dried in vacuo at 40 °C. MP62 dried after alkali or acid treatment was abbreviated to MP62-OH or MP62-Cl, respectively. To 5 g of Kelex-100 was added 1 g of each resin. The mixtures were shaken for 24 h at 30 °C. After shaking, the resin beads were filtered, washed with MeOH, and dried in air. Finally, the resulting resins were treated with 2 M NaOH and 1 M HCl, washed with distilled water until the wash out became neutral, and dried in vacuo. Adsorption of Ga(III) and Al(III). Batch Method. Kelex-100-loaded resins (0.1 g) were immersed in 50 mL of Ga(III) and Al(III) (20 or 100 mg/L) at various concentrations of NaOH. The mixtures were shaken for 15 h at 30 °C. After filtration, the concentrations of Ga(III) and Al(III) in the filtrate were determined using an atomic absorption spectrophotometer. Column Method. Kelex-100-loaded ATP202 (32-60 mesh) was immersed in 5 M NaOH for 24 h, and 4 mL of the resin was then packed into a glass column equipped with a water jacket (resin bed: 10 mm φ × 51 mm). The Ga(III) (100 mg/L) solution was then passed through the column at a constant flow rate of two bed © 1997 American Chemical Society
4366 Ind. Eng. Chem. Res., Vol. 36, No. 10, 1997 Table 1. Properties of Resin Matrix polymer matrix
commercial name
functional group
total ion-exchange capacityd (equiv/L of wet resin)
SP120 (Lewatit) SP112 (Lewatit) ATP202 (Lewatit) WK10 (Diaion) CNP80 (Lewatit) CG400 (Amberlite) IRA911 (Amberlite) MP62-OH (Lewatit)a MP62-Cl (Lewatit)b CS346 (Duolite) CR10 (Diaion) HP 21 (Diaion) RS-5c
-SO3H -SO3H -COOH -COOH -COOH -N(CH3)3Cl -N(CH3)2(C2H4OH)Cl -N(CH3)2
1.4 1.8 2.4 2.5> 4.7 1.4 0.9 1.8
a
-C(NH2)NOH -C(CH2COONa)2
OH type. b Cl type. c Synthesized in our laboratory.
d
Kelex-100-loaded resin specific surface area (m2/g)
pore volume (mL/g)
average pore radius (nm)
adsorption of Ga(III) in 0.1 M NaOH (%)
26.3 3.1 35.7 1.2 0.0 0.0 45.7 38.1 0.0 24.4 0.0 513.0 37.9
0.560 0.015 0.159 0.428
43.5 15.3 27.3 551.7
0.330 0.646
16.3 23.8
0.423
24.9
0.500 0.804
16.9 33.3
70.8 8.0 74.5 62.0 0.0 1.2 42.9 51.3 0.0 53.4 0.0 11.0 15.0
According to manufacturer’s data.
volumes per hour (SV 2 h-1) at 30 or 60 °C. The effluent was fractionated into portions of 4 mL, and the Ga(III) in each fraction was determined. The column was washed with deionized water (200 mL, SV 2 h-1), and 0.1 M HCl was passed through the column for neutralization. The Ga adsorbed on the resin was eluted using 10 L of 1.0 M HCl/L of resin and was washed with deionized water (200 mL, SV 2 h-1). Recovery of Ga(III) from the Bayer Solution. The concentrations of Ga(III) and Al(III) in the Bayer solution used in this study were 120 and 12 800 mg/L, respectively. The Kelex-100-loaded ATP202 was immersed in 5 M NaOH for 24 h, and 4 mL of the resin was packed into the glass column equipped with a water jacket (resin bed: 10 mm φ × 51 mm). The Bayer solution was then continuously supplied to the column at a constant flow rate (SV 2 h-1) at 60 °C. The effluent was fractionated into portions of 4 mL, and the amounts of Ga(III) and Al(III) in each fraction were determined by atomic absorption spectrophotometry. After washing with deionized water (200 mL, SV 2 h-1), 0.1 M HCl was passed through the column for neutralization. The Ga and Al adsorbed on the resin were eluted using 10 L of 1.0 M HCl/L of resin. After the resins were washed with deionized water, the sorption-elution procedure was repeated. Results and Discussion Ionic-exchange resins with various chemical and physical properties were employed as polymer matrices for loading Kelex-100. The total ion-exchange capacity and the properties of physical pore structure (specific surface area, pore volume, and average pore radius) are listed in Table 1. The macroporous organic adsorbents which have no ion-exchange groups, HP21 and RS5, were used for comparison with the ion-exchange groups. Since the cation-exchange resins had a sulfonic acid group or carboxylic acid group which dissociated in alkaline solution, the Kelex-100-loaded resin was also expected to retain its hydrophilicity. In fact, all of the Kelex-100-loaded cation-exchange resins examined easily settled in a 0.1 M NaOH solution. CNP80, which is sold as a macroporous resin, changed to a transparent resin after alkali or acid treatment and drying, and the specific surface area was almost zero. Consequently, the Kelex-100-loaded CNP80 hardly adsorbed Ga(III) in a 0.1 M NaOH solution. The specific surface area and pore volume of SP112 were low, and the Kelex-100loaded SP112 also showed low adsorption of Ga(III). On
the other hand, Kelex-100-loaded SP120, ATP202, and WK-10 which had large specific surface areas or pore volumes showed more than 60% adsorption of Ga(III). Since the five cation-exchange resins did not contain nitrogen atoms, the amounts of Kelex-100 loaded on the resins were determined from their nitrogen contents. The contents of Kelex-100 loaded were as follows: SP120 (0.56 mmol/g), SP112 (0.23 mmol/g), ATP202 (0.96 mmol/g), WK10 (0.52 mmol/g), CNP80 (0.41 mmol/ g). The Kelex-100 contents did not correspond to the adsorption of Ga(III). These results indicated that the physical pore structure of the polymer matrix had an important role in the adsorption of Ga(III). Strongly basic and weakly acidic anion-exchange resins generally have a quaternized amino group and a tertiary amino group, respectively. In this study, IRA911 was used as a strongly basic anion-exchange resin of which the physical pore structure was comparable with that of the gel-type resin CG400. The weakly basic type anion-exchange resin MP62-OH had a physical pore structure, while MP62-Cl after acid treatment was opaque and the specific surface area was very small. Although the contents of Kelex-100 loaded on the anionexchange resins were not calculated from nitrogen contents, desorption indicated that more than 0.3 mmol/g of Kelex-100 was loaded on each resin. Accordingly, the high and low adsorption of Ga(III) on the Kelex-100-loaded IRA911 and the CG400, respectively, suggested that the physical pore structure of the polymer matrix was important for Ga(III) adsorption on the Kelex-100-loaded anion-exchange resins. MP62OH and MP62-Cl have the same chemical structure and their physical pore structures changed following pretreatment. Although no differences were observed in the Kelex-100 contents of both resins, there were marked differences in Ga(III) adsorption between these resins. These results indicated that Kelex-100 could permeate into the polymer chain, while a large internal surface area was essential for effective binding of 8-hydroxyquinolino groups with Ga(III). In the case of chelating ion-exchange resins, macroporous resin containing amidoxime groups, CS346, showed high Ga(III) adsorption. The styrene-divinylbenzene copolymer beads without ion-exchange groups, HP21 and RS-5, were compared with the ion-exchange resins as a polymer matrix. Both resins had high specific surface areas and pore volumes, and the Kelex-100 contents of HP21 and RS5 were 1.84 and 0.74 mmol/g of resin, respectively. However, the adsorption of Ga(III) onto these resins was not very
Ind. Eng. Chem. Res., Vol. 36, No. 10, 1997 4367
Figure 2. Ga(III) adsorbed on the Kelex-100-loaded ion-exchange resin from alkaline solution. Resin loaded with Kelex-100: 0.1 g. Ga(III) solution (100 mg/L): 50 mL. Shaking: 15 h at 30 °C.
Figure 3. Time courses for the adsorption of Ga(III) from alkaline solution at 30 and 60 °C. Resin loaded with Kelex-100: 0.25 g. Ga(III) solution (100 mg/L): 50 mL (5 M NaOH).
Figure 1. Adsorption of Ga(III) on Kelex-100-loaded resins. Resin loaded with Kelex-100: 0.1 g. (a) Cation-exchange resin. (b) Anionexchange resin. (c) Chelating ion-exchange resin. (d) Organic adsorbent. Ga(III) solution (20 mg/L): 50 mL. Shaking: 15 h at 30 °C.
high. Since HP21 and RS5 did not have ion-exchange groups, Kelex-100-loaded HP21 and RS5 showed low hydrophilicity and these resins floated during 15 h of shaking. These results indicated that not only the macroporous structure but also the ion-exchange group in the polymer matrix was important to effectively adsorb Ga(III) in the alkaline solution. The adsorption of Ga(III) from 0.5 and 1.0 M NaOH solutions was investigated using the Kelex-100-loaded resins that showed over 10% adsorption of Ga(III). The adsorption of Ga(III) is shown in Figure 1. In the 0.11.0 M NaOH solutions, Kelex-100-loaded SP120, ATP202, WK10, MP62, IRA911, and CS346 showed almost constant and comparatively high adsorption of Ga(III). In Kelex-100-loaded HP21 and RS5, the adsorption increased slightly with increases in the concentration of NaOH. This increase may have been attributable to the improvement of hydrophilicity based on the dissociation of phenolic -OH in Kelex-100. However, the hydrophilicities of these resins were lower than those of the Kelex-100-loaded ionic-exchange resins, and these resins did not settle in the NaOH solution. Therefore, Kelex-100-loaded organic adsorbents were not suitable for use in the column. Next, the adsorption capacities of Kelex-100-loaded SP120, ATP202, WK10, MP62, IRA911, and CS346 for Ga(III) in 0.1-5.0 M NaOH were investigated (Figure 2). Kelex-100 loaded ATP202 and SP120 showed little decrease in the capacity for Ga(III) adsorption even if
the concentration of NaOH was increased. Although the adsorption capacity of Kelex-100-loaded MP62-OH for Ga(III) was 0.135 mmol/g of resin in 0.1 M NaOH, the capacity of the resin showed a tendency to decrease with increasing concentration of NaOH. Since Kelex-100loaded MP62(OH) floated at NaOH concentrations above 3 M, the decrease in the adsorption capacity may have been caused by the decrease in hydrophilicity based on a tertiary amino group as a weak anionexchange group. Since the capacity of Kelex-100-loaded IRA911 did not decrease markedly, it seemed possible to use this resin at higher concentrations of NaOH. However, the quaternized amino group was not highly stable and it was not suitable for repeated use in the concentrated NaOH solution or acidic solution for desorption of Ga. CS346 containing an amidoxime group shows high adsorption of Ga(III) by itself. Accordingly, the capacity of Kelex-100-loaded CS346 showed a total capacity based on the amidoxime group and Kelex-100. For these reasons, SP120 and ATP202 were used as polymer matrices in the following investigations concerning the recovery of Ga(III). Figure 3 shows the effects of temperature on the adsorption rate of Ga(III). The time required for the adsorption of 1/2 Ga(III) capacity was 1 h. The adsorption rate was increased slightly at 60 °C compared to that at 30 °C. The Kelex-100-loaded ATP202 recovered Ga(III) more effectively from alkaline solution than Kelex-100-loaded SP120. It was concluded that the difference between the Kelex-100-loaded ATP202 and SP120 was not based on the ion-exchange groups but the physical pore structure. In the following experiment, the Kelex-100-loaded ATP202 was utilized as the typical Kelex-100 loaded cation-exchange resin. Figure 4 shows the breakthrough curves of the Kelex100-loaded ATP202 for Ga(III) in 5 M NaOH using a
4368 Ind. Eng. Chem. Res., Vol. 36, No. 10, 1997
Figure 4. Breakthrough curves for Ga(III) in alkaline solution. Resin bed: Kelex-100-loaded ATP202; 10 mm φ × 51 mm. Loading solution: 100 mg/L of Ga(III) in 5 M NaOH. Flow rate: SV 2 h-1. Temperature: 60 °C. C ) concentration of Ga(III) in effluent. Co ) concentration of Ga(III) in loading solution. Elution: 1 M HCl, 10 L/L of resin. Recycle at 30 °C: O, 1; b, 2; 4, 3. Recycle at 60 °C: 0, 4.
Figure 5. Al(III) adsorbed on the Kelex-100-loaded ATP202 from alkaline solution. Kelex-100-loaded ATP202: 0.1 g. Al(III) solution (100 mg/L): 25 mL. Shaking: 15 h at 30 °C. Table 2. Adsorption of Ga(III) from the Mixture of Ga(III) and Al(III) concentration of Al(III) (mg/L)
Al(III)/Ga(III) added
Ga(III) adsorbed (mmol/g of resin)
0 1000 5000 10000
0 10 50 100
0.20 0.15 0.12 0.10
column packed with 4 mL of the resin. The adsorption and elution procedure was repeated four times. In the first to third adsorption procedures, the Ga(III) solution was passed through the column at 30 °C. Only the fourth adsorption procedure was carried out at 60 °C. Elution of Ga(III) on the resin was possible using 1 M HCl. The amounts of Ga(III) recovered in the first, second, and third recycles were 3.38, 3.22, and 3.36 g/L of resin, respectively. The Ga(III) recovered in the final recycle was 3.20 g/L of resin. Repeated use did not cause a decrease in the recovery of Ga(III) or the desorption of Kelex-100 from the resin matrix. The adsorption behavior of Kelex-100-loaded ATP202 for Al(III) was investigated to assess the adsorption of Ga(III) in the presence of a large amount of Al(III). Figure 5 shows the adsorption capacity of the Kelex100-loaded ATP202 for Al(III) in 0.1-5.0 M NaOH. These resins also had a high capacity for Al(III) in solutions with low NaOH concentration. However, the adsorption of Al(III) on the resins showed a tendency to decrease with increasing NaOH concentration. Table 2 shows the adsorption of Ga(III) in the presence of Al(III). Although the capacity of Ga(III) decreased with increases in the concentration of Al(III), these resins still adsorbed 0.1 mmol/g of resin Ga(III) when the ratio of Al(III) to Ga(III) was 100. Figure 6 shows the breakthrough curves of the Kelex100-loaded ATP202 for Ga(III) and Al(III) in the Bayer
Figure 6. Breakthrough curves for Ga(III) and Al(III) in the Bayer solution. Kelex-100-loaded ATP202: 10 mm φ × 51 mm. Bayer solution: Ga(III), 120 mg/L; Al(III), 12800 mg/L. Flowrate: SV 2 h-1. Temperature: 60 °C. C ) concentration of Ga(III) in effluent. Co ) concentration of Ga(III) in loading solution. Elution: 1 M HCl, 10 L/L of resin. Recycle for Ga(III): -O-, 1; -4-, 2; -0-, 3. Recycle for Al(III): - -b- -, 1; - -2- -, 2; - -9- -, 3.
solution when the adsorption of Ga(III) and Al(III) and recycling were carried out with the column packed with 4 mL of resin. The Bayer solution was passed at a flow rate of SV 2 h-1 at 60 °C. These results indicated that the resin selectively adsorbed and concentrated Ga(III). Ga(III) adsorbed during the first recycle was 1.94 g/L of resin, that during the second recycle was 2.02 g/L of resin, and that during the third recycle was 1.85 g/L of resin. The recovery of Ga(III) using Kelex-100-loaded ATP202 was about 43 mg/g of Kelex-100. On the other hand, when the solvent extraction of Ga(III) from the Bayer solution was carried out using 10% Kelex-100 in kerosene, the extraction of Ga(III) was 2.5 mg/g of Kelex100. These results demonstrated that this method had a high efficiency for the recovery of Ga(III) in the Bayer solution and the physical pore structure and cationexchange group of the resin matrix contributed to the recovery of Ga(III) from strongly alkaline solution using Kelex-100-loaded resin. Literature Cited Demopoulos, G. P.; Distin, P. A. On the Structure and Composition of Kekex 100. Hydrometallurgy 1983, 11, 389. Egawa, H.; Nonaka, T.; Ikari, M. Preparation of Macroreticular Chelating Resins Containing Dihydroxyphosphino and/or Phosphono Groups and their Adsorption Ability for Uranium. J. Appl. Polym. Sci. 1984, 29, 2045. Isshiki, K.; Tsuji, F.; Kuwamoto, T. Preconcentration of Trace Metals from Seawater with 7-Dodecenyl-8-quinolinol Impregnated Macroporous Resin. Anal. Chem. 1987, 59, 2491. Matsuda, M.; Ochi, K. The Recovery of Gallium from Bayer Solution by Solvent Extraction. Nippon Kagaku Kaishi 1990, 415. Obi, H.; Segawa, T.; Yotsuyanagi, T. Ion-Associate Solvent Extraction of Ga(III) from Aqueous Sodium Hydroxide Solution. Chem. Lett. 1989, 547.
Received for review January 2, 1997 Revised manuscript received June 11, 1997 Accepted June 11, 1997X IE9700270
Abstract published in Advance ACS Abstracts, August 1, 1997. X
