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The chlorination process utilizing ammonium chloride as chlorination reagent has been employed for the recovery of elements with emphasis on indium from bearing alloy through vaporization of the chlorides. It was found that the chlorination took place by the heating of the model sample in the presence of ammonium chloride. The influence of the process parameters, such as reaction temperature and gas flow rate, has been investigated. The addition of activated carbon resulted in the adsorption of chloride on the carbon surface. The present result indicates the possibility of the recovery process through transport of the target element from the sample to pores of activated carbon. (doi:10.2320/matertrans.M2013206) The development of recovery process of valuable metals from wastes is of great importance in the view of resource securities. Conventional processes are based on the technique of hydrometallurgy, where target elements are dissolved in e.g., acid and enriched by various types of extracting reagent, which have been developed in the past decades. As for the pyrometallurgical processes, the chlorination metallurgy is one of the attractive methods for the extraction of target elements, as it enables the spatial separation of the elements in a single step according to the difference in the vapor pressure of the chlorides. So far, series of basic studies have been reported in literature, 1­8) in which chlorine or hydrogen chloride gases are mostly used as chlorination reagent. In the view of the practical application of the processes, however, one has to pay special attention for the handling of the corrosive gases. Ammonium chloride is an alternative chlorination reagent, which is utilized, for instance, in the laboratory-scale synthesis of rare earth chlorides. 9) The handling is much easier than the gaseous reagents, so that the utilization of ammonium chloride is an attractive way. Recently, Itoh et al. demonstrated that neodymium in Nd­Fe­B magnet scrap could be selectively chlorinated. 10) In our previous studies 11,12) we have reported the results of the pyrometallur- gical chlorination treatment utilizing ammonium chloride for the recovery of indium from wastes. It has been demonstrated that indium can be recovered from dental metal recycling sludge as well as indium tin oxide, transparent conductor, deposited on glass surface. The reaction is apparently described as In2O3ðs Þþ 6NH4ClðsÞ ! 2InCl3ðg Þþ 6NH3ðg Þþ 3H2Oðg Þð 1Þ One of the advantages of the proposed process is that the chemicals used in the reaction can be considerably reduced when the position of the target element is known: the chlorination reagent is directly put onto the sample specimen where the target element exists, e.g., glass surface in the case of ITO-deposited glass. In contrary, the entire sample should be immersed in treatment bath in conventional hydro- metallurgical processes, which may lead to higher cost in case that very small amount of the target element exists in the sample, e.g., in the form of thin film. In the present paper, we address the chlorination treatment of bearing alloy made of lead, indium and tin, which is plated on substrate metal for the improvement of tribological property. The influence of the process parameters has been studied and discussed. 2. Experimental Procedure 2.1 Materials As for the material for the chlorination treatment, model samples were kindly supplied from Daido metal Co., Ltd. A sample specimen has iron substrate (20mm © 50mm © 2mm) above which copper, then nickel intermediate layer and finally Pb­In­Sn alloy (Pb:In:Sn = 8:1:1 in mass%) are plated. The nickel layer is plated in order to avoid the diffusion of the elements of the upper layer into the inner copper layer. The average contents of Pb, Sn and In in a sample specimen were 21, 2.7 and 2.7mg, respectively. Given amount of ammonium chloride (99.5%, Wako pure chem. Co., Ltd.) was put onto the sample surface. Typical composition of NH4Cl, defined as 100  mNH4Cl=mSample, where mNH4Cl and mSample are the mass of ammonium chloride and sample specimen, respectively, was 6mass%. In order to ensure the sufficient contact between NH4Cl and alloy surface, small amount of ethanol was poured on the surface, which was then dried.

Indium Recovery from Bearing Alloy via Pyrometallurgical Chlorination Process Utilizing Ammonium Chloride