PARTⅠ PYROLYSISRECOVERY OF INDIUM FROM In2O3 AND LIQUID
CRYSTAL DISPLAY POWDER USINGDEHYDROCHLORINATION OF POLY (VINYL CHLORIDE)
Tomohito Kameda, Kye-Sung Park, Wakao Sato, Guido Grause, Toshiaki Yoshioka*
Graduate School of Environmental Studies, Tohoku University, 6-6-07 Aoba, Aramaki,
Aoba-ku, Sendai 980-8579, Japan
E-mail: yoshioka@env.che.tohoku.ac.jp
Abstract: Indium (In) was found to be recovered from In2O3 and LCD powder using poly(vinyl chloride) (PVC) as chlorination agent by chloride volatilization process. For In2O3, thedegree of In recovery increased with increasing the molar ratio of Cl in PVC to In in In2O3(Cl/In molar ratio) under the flow of N2 and air. Particularly, the degree of In recovery
increased notably with increasing temperature under the flow of N2. The degree of In recovery
from Liquid Crystal Display powder was lower than that from In2O3.
1. Introduction
Generally, the content of In in the ore is 10~20 ppm, and it exists more in the zinc
deposits (New Brunswick, 280ppm). Due to the small content of In in the ore and theby-product of primary metals (mainly Zn), In is hard to correspond to the rapid demandvariation [1-3]. In is used to fabricate ITO (Indium Tin Oxide) for transparent electrodes.
Particularly, about 84 % of In in worldwide is used to produce ITO due to the recent
development of LCD (Liquid Crystal Display) industry. The increase of In demand causes its
rapid price increase [4]. Waste In is mainly generated in the LCD panel process. In Japan in
2004, 470 t-In is used in ITO for transparent electrodes, out of which 220 t-In is dissipated or
potentially dissipated [5]. The dissipated In, which comes from sputtering (42.7 %), etching(10.5 %), assembling (4.1 %), recycling (36.3 %), is currently recovered and reused for theLCD panel process. However, the potential dissipated In (6.4 %), i.e., In in the LCD panel, is
not recycled but wasted. It is hereafter necessary to recover In from the waste LCD panel inorder to correspond to the increase of In demand. In this paper, the application of chloride
volatilization process for the recovery of In from the waste LCD panel has been examined.
The chloride volatilization process generates metal chloride through the reaction between
metal oxides and chlorination agent. The metal chloride is recovered in a gas phase, resulting
in the separation from the reactant. The metal chloride gases have different condensation
temperature, so it is possible to gain the selective recovery of target metal chlorides throughthe control of cooling temperature. The research for chlorination has been preceded mainly-1-The 5th ISFR (October 11-14, 2009, Chengdu, China)
for the recycling of the valuable metals in the waste resources or in the ore [6]. Furthermore,
PVC is examined as the chlorination agent for the effective use of waste PVC, because thethermal degradation of PVC generates HCl [7,8]. This study has investigated the recovery ofIn from In2O3 by chloride volatilization process. The effects of temperature and Cl/In molar
ratio on the recovery of In from In2O3 have been examined. Based on the obtained results, therecovery of In from LCD powder was examined.
2. Experimental procedures
The purity of In2O3 used in this study was 99.9 %. The LCD powder is composed of 75.6
wt% Al2O3, 12.0 wt% In2O3, 4.5 wt% Fe2O3, 1.6 wt% SnO2, and so on. The thermal
degradation of PVC was performed at 250 ºC. Under the flow of N2 and air at 50 ml/min, 0.1
g In2O3 or 0.5 g LCD powder was reacted with HCl from the PVC with the Cl/In molar ratioof 1-11 at 350-1000 ºC for 1 h. The products were identified by X-ray diffraction (XRD)
analysis using Cu Kα radiation. After the dissolution of the products in HNO3, In in thesample solutions were analyzed by inductively coupled plasma atomic emission spectrometry(ICP-AES) (SPS7800, Seiko Instruments Inc.).
3. Results and discussion
The chlorination of In2O3 results in the production of InCl3, as shown in Eq. (1):In2O3+6HCl→2InCl3 + 3 H2O (1)Since the Gibbs energy (ΔG) for the reaction (1), calculated from thermodynamic
databases [9,10], is negative at any temperature in the investigated temperature range (ΔG:–8.0 kJ mol–1 at 600 °C, –3.8 kJ mol–1 at 1000 °C), the reaction should proceed in theexpected way.
Fig.1 shows the effects of temperature and Cl/In molar ratio on In recovery from In2O3
under the flow of (a) N2 and (b) air. In both cases, the degree of In recovery increased withincreasing Cl/In molar ratio at any temperature. The degree of In recovery was 98.7 and96.6 % with Cl/In molar ratio of 11 at 350 ºC, respectively. For (a) N2, the degree of In
recovery was almost similar at 350-700 ºC at any Cl/In molar ratio. However, the degree of In
recovery increased with increasing temperature from 700 to 900 ºC at any Cl/In molar ratio,and the behavior of In recovery was almost similar at 900 and 1000 ºC. More than 95 % of In
recovery was obtained with Cl/In molar ratio of 3 at 900 and 1000 ºC and with the molar ratioof 6 at 800 ºC, although it was obtained with the molar ratio of 11 at 350-700 ºC. The increaseof temperature was found to result in the increase of degree of In recovery. In contrast, thebehavior of In recovery was almost similar at any temperature under the flow of (b) air.
Almost 100 % of In recovery was obtained with Cl/In molar ratio of 11 at any temperature.
The difference of behavior of In recovery between N2 and air is attributed to the difference ofproducts obtained by the chlorination of In2O3. From the XRD patterns of products obtainedby the chlorination of In2O3 under the flow of N2, InCl3 was observed to be produced at 500-2-

PARTⅠ PYROLYSISºC. This confirms that In recovery from In2O3 by the chlorination is due to the production ofInCl3. At 900 ºC, InCl was produced in addition to InCl3. Therefore, the high degree of In
recovery at high temperature with low Cl/In molar ratio is considered to be caused by theproduction of InCl. For air, in contrast, InOCl was produced in addition to InCl3 at 500 and900 ºC. The similar products at any temperature probably results in the similar degree of In
recovery with any Cl/In molar ratio.
The In recovery from LCD powder by the chlorination for Cl/In molar ratio of 11 at 350ºC was 66.7 % for N2 and 54.1 % for air. In both atmospheres, the degree of In recovery fromLCD powder was lower than that from In2O3. The LCD powder contains Al2O3, FeO, andSnO2, in addition to In2O3, leading to the less chance to contact of In2O3 with HCl.
Furthermore, HCl is probably consumed by the reaction with other metal oxides, resulting in
the prevention of production of InCl3.
4. Conclusions
In was found to be recovered from In2O3 and LCD powder using PVC as chlorination
agent by chloride volatilization process. For In2O3, the degree of In recovery increased withincreasing the Cl/In molar ratio under the flow of N2 and air. Particularly, the degree of In
recovery increased notably with increasing temperature under the flow of N2. The differenceof behavior of In recovery between N2 and air is attributed to the difference of products
obtained by the chlorination of In2O3, i.e., the production of InCl3 and InCl for N2, and InCl3and InOCl for air. The degree of In recovery from LCD powder was lower than that fromIn2O3. The LCD powder contains Al2O3, FeO, and SnO2, in addition to In2O3, leading to theless chance to contact of In2O3 with HCl. Furthermore, HCl is probably consumed by thereaction with other metal oxides, resulting in the prevention of production of InCl3.
100100(a)(b)
80In recovery/%In recovery/%

806040350 ºC
600 ºC
700 ºC

20002468Cl/In molar ratio

800 ºC
900 ºC
1000 ºC

106040350 ºC
600 ºC
700 ºC

2012002468Cl/In molar ratio

800 ºC
900 ºC
1000 ºC

1012Fig.1 Effects of the temperature and the molar Cl/In ratio on the In recovery
from In2O3 under(a)N2 and (b) air atmosphere[1]-3-The 5th ISFR (October 11-14, 2009, Chengdu, China)
Acknowledgements
This manuscript has some contents of the paper accepted in the journal ofThermochimica Acta.
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