RECOVERY OF INDIUM FROM SPENT FLAT PANEL DISPLAY WITH SOLVENT-IMPREGNATED RESINS. K. Inoue, M. Nishiura, H. Kawakita, K.Ohto, and H.

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1 RECOVERY OF INDIUM FROM SPENT FLAT PANEL DISPLAY WITH SOLVENT-IMPREGNATED RESINS K. Inoue, M. Nishiura, H. Kawakita, K.Ohto, and H. Harada Department of Applied Chemistry, Saga University, Honjo 1, Saga , Japan. Corresponding author address: ABSTRACT An effective recovery process for indium(iii) from waste liquid crystal display panels was developed using porous resins impregnated with each of Cyanex 923 and Aliquat 336. Total dissolution of the powdered sample of the waste in aqua regia suggests the metal contents (mg/l) as follows: Al 230, In 205, Ba 175, Si 105, Ca 95, Fe 60, Zn 39.5, Cr 29, Sn 24, Mg 10. The powdered sample was leached with 3 M HCl and extracted metals can be mutually separated and recovered by passing through the column packed with the resin impregnated with Aliquat 336 followed by that with Cyanex 923. The former column recovered Sn, Fe and Zn while the latter column only In. The metal ions trapped in these columns were eluted with 0.1 M H 2 SO 4 concentrated more than about 10 times. INTRODUCTION Due to the rapid spread of liquid crystal television (TV) and plasma TV in recent years, the demands for indium is now increasing as the feed material for indium tin oxide (ITO) transparent electrode, produced by means of sputtering. Since indium is contained in sphalerite in small amount, it is produced as a byproduct in the smelting of zinc. The resources of indium are limited on the earth and the countries or areas which can provide indium are also limited, which resulted in the rapid increase in the price of indium in recent years. Although big efforts have been devoted to the development of the new technology for substituting indium with common metals such as zinc, it is expected to take a long time for its commercialization. Consequently, only one choice to avoid the shortage of indium is its effective recovery from various indium-containing wastes and its recycle. Although spent target generated in the production of ITO transparent electrode by sputtering is now fully recycled, indium contained in flat panel display (FPD) of liquid crystal TV and plasma TV has not been attempted to be recovered for recycling yet. In the present work, we conducted a fundamental investigation of the hydrometallurgical recovery process of indium from waste FPD. Materials and Reagents EXPERIMENTAL

2 The actual waste sample of FPD produced by Samsung Electronics Co. Ltd. was supplied from Shimada Shokai Co. Ltd. The sample of the solvent extraction reagent, Cyanex 923, which is a mixture of 4 kinds of trialkylphosphine oxides with different alkyl radicals, and produced and marketed by CYTEC Industries Inc., Canada, was kindly donated by Fujitec Co., Japan. That of Aliquat 336, the main component of which is trioctylmethylammonium chloride, was purchased from Cognis Corp.. In the experiments of solvent extraction using these reagents, reagent grade toluene was employed as a diluent. The sample of Amberlite XAD-7, the porous spherical beads of acrylic ester resin, was purchased from ORGANO Corp.. Preparation of Solvent-Impregnated Resins (SIR) Two types of SIR were prepared: i.e., that impregnated with Cyanex 923 and that with Aliquat 336. In both cases, 2.0 g XAD-7 beads was put in 20 ml acetone containing 2.0 g reagent to be shaken for 12 h, after which the beads were taken by filtration and vacuum dried to remove acetone. The contents of the impregnated reagent in the beads were 1.29 and 1.23 mol/kg for the former and latter resins, respectively. Leaching Test of Indium from Spent FPD Actual sample of spent FPD was crushed by hammer into small particles. One g of particles was mixed with 10 ml of aqua regia, 3 M (M = mol/l) hydrochloric acid, sulfuric acid and nitric acid to be shaken for a required time, after which the sample acid solution was taken for the analysis of metal concentration by using Shimadzu model ICPS-8100 ICP/AES spectrometer. Solvent Extraction and Adsorption Tests In order to examine the solvent extraction behaviors of some extraction reagents for In(III), 10 ml of toluene solution containing 80 mm of the reagent was shaken together with 10 ml of varying concentration of hydrochloric acid containing 4 mm In(III) at 303 K for 3 h. Batchwise adsorption tests were carried out using the resin impregnated with Cyanex 923 to examine the adsorption isotherm of In(III) at first by shaking 30 mg resin together with 15 ml of 3 M hydrochloric acid containing varying concentration of In(III) at 303 K for 12 h. Similar batchwise adsorption tests were carried out using the two types of impregnated resins by shaking 30 mg resin together with 15 ml of varying concentration of hydrochloric acid containing 0.2 mm of all metal ions mentioned above to examine the adsorption behaviors of these impregnated resins. On the basis of the results of the batchwise adsorption tests mentioned above, continuous adsorption test using two columns packed with 0.60 g of each of two types of impregnated resins connected in series as shown in Figure 1 was carried out. In this continuous adsorption test, synthetic test solution of 3 M hydrochloric acid containing

3 the same concentration of each metal ion measured in the leaching test was fed to the columns at the feed rate of 5.0 ml/h with a peristaltic pump. Figure 1. Experimental set up for the continuous adsorption test for the selective recovery of indium. Leaching of Spent FPD RESULTS AND DISCUSSION Figure 2 shows the relationship between the concentration of In(III) in the various leach liquors and the leaching time. From this figure, In(III) is the most effectively leached with aqua regia; however, nearly the same leaching behavior was observed with 3 M hydrochloric acid while effective leaching was not observed with 3 M nitric acid and sulfuric acid. On the other hand, total dissolution of the powdered sample in aqua regia suggested the metal contents (mg/l) as follows: Al 230, In 205, Ba 175, Si 105, Ca 95, Fe 60, Zn 39.5, Cr 29, Sn 24, Mg 10. Figure 2. Leaching of indium from powder of crushed spent FPD with various acids.

4 Solvent Extraction of Indium Figure 3 (left). % extraction of In(III) with some sovent extraction reagents in toluene from varying concentration of hydrochloric acid. Figure 4 (right). % extraction of In(III) with Cyanex 923 in toluene from hydrochloric acid and sulfuric acid. Figure 3 shows the plot of % extraction of In(III) from varying concentrations of hydrochloric acid with some solvent extraction reagents in toluene. From this figure, it is seen that Cyanex 923, the mixture of 4 kinds of trialkylphosphine oxides with different alkyl radicals, exhibits the highest extraction though TOPO also exhibits the similar extraction behavior. On the other hand, TBP exhibited no extraction of In(III) over the whole concentration region of hydrochloric acid. Figure 4 shows the % extraction of In(III) with Cyanex 923 in toluene from varying concentrations of hydrochloric acid and sulfuric acid as well as that containing 0.2 M ammonium chloride. It is seen that although In(III) is not extracted from sulfuric acid the addition of some amount of chloride improves the extraction similar to hydrochloric acid, suggesting that chloride ion plays an important role in this extraction system and that sulfuric acid can be employed as stripping agent for In(III). Adsorption of Metal Ions on Solvent-Impregnated Resins From the test of adsorption isotherm of In(III) from 3 M hydrochloric acid on the resin impregnated with Cyanex 923, it was found that the adsorption takes place according to the Langmuir adsorption mechanism and the maximum adsorption capacity for In(III) was evaluated as 0.45 mol/kg-resin.

5 Batchwise Adsorption of Various Metal Ions on the Two Types of Solvent- Impregnated Resins Figures 5 and 6 show the % adsorption of all metal ions existing in the leach liquor from varying concentration of hydrochloric acid on the resins impregnated with Cyanex 923 and Aliquat 336, respectively. From Figure 5, it is seen that although In(III) is effectively adsorbed on the Cyanex 923 impregnated resin at 3 M hydrochloric acid, Sn(IV), Zn(II) and Fe(III) are more selectively adsorbed over In(III), suggesting these impurity metal ions should be removed prior to the recovery of In(III). Figure 6 indicates that although % adsorption of these three impurity metal ions is higher than 90 %, that of In(III) is less than 20 % at 3 M hydrochloric acid in the case of Aliquat 336 impregnated resin, suggesting that this resin is suitable for selectively removing these impurity metal ions from In(III). On the other hand, adsorption of other metal ions, Al(III), Mg(II), Si(IV), Ca(II), and Ba(II), are only negligible on both of these resins. Figure 5 (left). % adsorption of all metal ions existing in the leach liquor of the spent FPD from varying concentration of hydrochloric acid on the Cyanex 923 impregnated resin. Figure 6 (right). % adsorption of all metal ions existing in the leach liquor of the spent FPD from varying concentration of hydrochloric acid on the Aliquat 336 impregnated resin. Adsorptive Recovery and Purification of Indium from Model Leach Liquor by Means of Continuous Operation Using Columns Packed with Two Types of Impregnated Resins Figure 7 shows the breakthrough profiles of all metal ions tested from the first column shown in Figure 1 packed with the resin impregnated with Aliquat 336. Although Fe(III), Zn(II) and Sn(IV) were not detected in the effluent from the column even after 100 bed volumes (B.V.), Al(III), Mg(II), Si(IV), Ca(II), Ba(II), and Cr(VI) were immediately broken through just after the initiation of the feed. On the other hand, In(III)

6 was gradually broken through until 50 B.V., suggesting that some amount of In(III) is retained in this column. Figure 8 shows the breakthrough profiles from the second column packed with Cyanex 923 impregnated resin together with the elution profile of In(III) (after 50 B.V.) from the same column. All of Al(III), Mg(II), Si(IV), Ca(II), Ba(II), and Cr(VI) which had passed through the first column without being adsorbed were immediately broken through just after the initiation of the feed also in the second column. On the other hand, In(III) was not detected at all in the effluent from the second column up to 50 B.V., suggesting that In(III) is successfully purified free from the contamination of other metal ions. As mentioned earlier, after the 50 B.V., the second column was washed by water and, subsequently, with 0.1 M sulfuric acid. As seen from the elution profile of In(III) in Figure 8, all In(III) adsorbed in the second column is eluted enriched more than 10 times compared to the feed solution. Figure 7 (left). Breakthrough profiles of all metal ions tested from the first column packed with Aliquat 336 impregnated resin. Figure 8 (right). Breakthrough profiles (up to 50 B.V.) from the second column packed with Cyanex 923 impregnated resin and the elution profile of In(III) (after 50 B.V.) from the same column. Symbols: In (III), *Cr(VI), Fe(III), Zn(II), Sn(VI), Al(III), Mg(II), Si(IV), Ca(II), Ba(II). CONCLUSIONS From the present work, it can be concluded that small amounts of indium can be effectively extracted with 3 M hydrochloric acid from crushed spent FPD and can be purified and enriched by passing through the columns packed with porous resins impregnated with Aliquat 336 and Cyanex 923. ACKNOWLEDGEMENTS The present work was financially supported in part by the 2007 research project of Kyushu Recycle and Environmental Industry Plaza (K-RIP). The authors are also deeply indebted to Fujitec Co. for the kind supply of the samples of Cyanex 923 and TOPO.

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Ion Exchange Letters 2 (2009) 22-26 iel.vscht.cz Selective Recovery of Indium from Acid Sulfate Media with Solvent Impregnated Resin of Bis(4-cyclohexylcyclohexyl)phosphoric Acid as an Extractant T. Nakamura,