Recovering Indium from the Liquid Crystal Display of Discarded Cellular Phones by Means of Chloride-Induced Vaporization
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INTRODUCTION
IN recent years, much progress has been made in mobile telecommunication and, therefore, the number of new subscribers using this service is increasing. For instance, in Japan, the number of new subscribers reached about 95 million in 2006. In turn, the number of discarded cellular phones is rising sharply. Every year about 15 million cellular phones are discarded, and only 15 pct of this amount has been collected for recycling purpose. Considering the average weight of a cellular phone (about 100 g), it is estimated that the total weight of discarded cellular phones is approximately 1500 tonnes per year. Figure 1 shows the composition of a cellular phone. It can be seen that the liquid crystal display (LCD) is about 4.4 pct of the entire telephone’s weight, if organic materials (for example, film) are removed. Moreover, the LCD of a cellular phone contains several electroconductive electrodes, which are sandwiched between two glass planes. These electrodes are made mainly of indium tin oxide (ITO), also known as tindoped indium oxide. The ITO is a mixture of indium(III) KUNIHIKO TAKAHASHI, GJERGJ DODBIBA, and JUN SADAKI, Doctors, and TOYOHISA FUJITA, Professor, are with the Department of Systems Innovation, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. Contact e-mail: [email protected] ATSUSHI SASAKI is with the Yokohama Metal Co., Ltd., 3-5-2 Hashimotodai, Sagamiharashi, Kanagawa 229-1132, Japan. NOBUAKI SATO, Doctor, is with the Research Center for Sustainable Materials Engineering, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan. Manuscript submitted September 22, 2008. Article published online February 20, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
oxide (In2O3) and tin(IV) oxide (SnO2), typically 80 to 90 pct In2O3 and 10 to 20 pct SnO2 by weight.[1,2] The LCD contains approximately 1400 g/t indium (In), if the parts made of organic material are removed in advance. Thus, considering the average weight of a cellular phone, it can be found that one cellular phone contains about 6.2 mg indium. Table I gives the content of indium in various parts of a cellular phone. Generally speaking, indium is extracted from natural resources primarily as a by-product of zinc ores. For instance, the indium content in zinc ores varies from 10 to 20 g/t, which is much smaller than its content in the LCD of discarded cellular phones after all the parts made of organic materials are removed (Table I). In other words, end-of-life cellular phones are a valuable resource for the extraction of indium, indicating the need for the recycling of indium metal from such devices in order to save natural resources and protect the environment. The demand for indium metal is increasing sharply since the production of LCDs is expanding. In 1999, the world consumption of indium was approximately 230 tonnes per year, with 50 pct of it is consumed in Japan.[3] It has been estimated that
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