Recovery of platinum using magnesium vapor
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Sachiko Yamamoto Department of Metallurgical Engineering, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino-City, Chiba, Japan 275-0016
Yoshihiro Kayanuma and Masafumi Maeda The Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, Japan 153-8505 (Received 3 February 2003; accepted 29 May 2003)
To develop an effective process for the recovery of precious metals from scrap, we investigated a new platinum extraction process using alloy formation by magnesium vapor and successive leaching with an aqueous solution. Pure platinum plates were reacted with magnesium vapor at constant temperatures ranging between 873 and 1173 K for 3 h, and Mg–Pt alloy samples were synthesized. The obtained Mg–Pt alloy was then dissolved in aqua regia or in an aqueous HCl solution at room temperature. Platinum was recovered from the leaching solution by conventional precipitation technique, and the platinum obtained by each process was analyzed chemically. It was found that 94% of the platinum was recovered by this process. After Mg vapor treatment, 100% of the platinum was dissolved when kept in aqua regia for 1 h, whereas only 25% of untreated pure platinum was dissolved when kept in aqua regia for 4 h.
I. INTRODUCTION
Platinum group metals (PGMs) are widely used in several applications such as catalytic substance, because these elements are corrosion and heat resistant and have various catalytic properties. Autocatalysts containing PGMs, which are used in the automobile industry, have become essential to compliance with environmental regulations, and the demand for PGMs is therefore increasing.1 Although PGMs are important elements for the industry, they are precious and rare elements, and large amounts of energy and other resources are required to extract them from mineral resources. Furthermore, a large amount of waste is generated during the processes of extracting and refining PGMs. To preserve our limited resources, it is extremely important to recover PGMs from scrap. In reality, however, this is economically difficult because most of the scrap containing PGMs has a complicated structure, and contains very small amounts of PGMs compared to other body materials. For example, PGMs in autocatalyst scrap exist in a ceramic substrate, which has a honeycomb structure with a large surface area.1
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J. Mater. Res., Vol. 18, No. 8, Aug 2003 Downloaded: 17 Mar 2015
As PGMs are chemically stable and do not react with most acids, it is difficult to extract them from scrap. Therefore, the whole body of scrap is smelted or dissolved in a large amount of strong acid to extract the PGMs.2 In the current acid leaching process, it takes very long for the scrap to dissolve, and a large amount of waste solution containing heavy metals and strong acid is generated. Therefore, it is important to develop an effective leaching process to recover PGMs from scrap. In the past, precious metals were
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