Thermochimica Acta 493 (2009) 105–108
Thermochimica Acta
journal homepage: www.elsevier.com/locate/tca
Short communication
Recovery of indium from In O and liquid crystal display
2
3
powder via a chloride volatilization process using
polyvinyl chloride
∗
Kye-Sung Park, Wakao Sato, Guido Grause, Tomohito Kameda, Toshiaki Yoshioka
Graduate School of Environmental Studies, Tohoku University, 6-6-07 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
2 3
Indium(In)was recoveredfrom indium oxide(In O ) and liquid crystal display (LCD) powder via a chloride
Received 4 December 2008
Received in revised form 25 February 2009
Accepted 7 March 2009
volatilization process using polyvinyl chloride (PVC) as the chlorination agent. The recovery of In from
In2O3 increased with an increasing molar Cl/In ratio in N2 and air atmospheres. The degree of In recovery
◦
at a Cl/In molar ratio of 11 and a temperature of 350 C was 98.7% and 96.6%, for N2 and air, respectively. The
Available online 19 March 2009
In recovery also increased notably with increasing temperature in N2 atmosphere. In both atmospheres,
the In recovery increased with an increasing degradation temperature of PVC. However, the In recovery
from LCD powder was lower than that from In2O3. For LCD powder, the degree of In recovery at a Cl/In
Keywords:
Chlorination
Indium
◦
molar ratio of 11 and a temperature of 350 C was 66.7% and 54.1%, for N2 and air, respectively.
©
2009 Elsevier B.V. All rights reserved.
In2O3
PVC
Recovery
Liquid crystal display
1
. Introduction
thermodynamically favored. Volatile metal chlorides can be sepa-
rated from nonvolatile oxides and chlorides and are obtained after
condensation. However, besides In, other metals form volatile chlo-
rides with different vapor pressures, making it possible to separate
them by choosing an adequate condensation temperature. Thermal
halogenation was mainly investigated for the recovery of valuable
metals from waste materials or ores [5–10].
Indium (In), a rare element present only in a few natural miner-
als, is obtained mainly from zinc minerals whose In content varies
from 10 to 20 ppm. Due to its rising demands and difficulties in
exploitation, a shortage of In and rising prices are expected for
the future [1–3]. The rising demand is mainly due to the use of
indium tin oxide (ITO) for transparent electrodes. About 84% of the
worldwide indium consumption is used for the production of liquid
crystal displays (LCDs). In 2004, the consumption of In used for ITO
was about 470 t in Japan. An estimated 220 t of In were released as
waste. In has been recovered from sputtering (42%), etching (11%),
assembling (4.1%), and recycling (36%), but it has not yet recovered
from used LCDs (6.4%) [4].
Developing a new process for an effective end of life utilization in
both metal and plastic waste is necessary. We propose a combined
recycling process composed of the thermal treatment of PVC and
the simultaneous separation of the metal-containing waste. In this
study, we investigated the applicability of a recovery process for In
from LCDs using hydrochloric acid released during the degradation
Furthermore, waste PVC is a problematic material due to
its chlorine (Cl) content. The thermal degradation and stabi-
lization of PVC has been investigated for about half a century
[11–13]. Recently, the degradation behavior of PVC using coupled
thermogravimetry–mass spectrometry (TG–MS) was examined by
our research group to improve the dehydrochlorination process
during feedstock recycling of plastic waste [14]. The dehydrochlo-
◦
rination of PVC at 650 C in helium (He) is divided into three
degradation stages, two dehydrochlorination steps, and a polyene-
aromatic network breakdown. In addition, the effect of temperature
on the dehydrochlorination of PVC in N2 atmosphere during
isothermal degradation has also been examined [15]. The degree of
dehydrochlorination of PVC is nearly 100% at temperatures above
◦
260 C, and PVC is almost completely dehydrochlorinated at mod-
3
ally, metal chlorides are known to be easily formed since they are
erate temperatures.
This study has investigated the recovery of In from In O by chlo-
2
3
ride volatilization process. PVC was examined as the chlorination
agent for the effective use of waste PVC. The effects of temperature
and the molar Cl/In ratio on the recovery of In from In2O3 were
∗ Corresponding author. Tel.: +81 22 795 7211; fax: +81 22 795 7211.
0
040-6031/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2009.03.003