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Selective Recovery of Tantalum from Refractory Metal Scrap by Chlorination

Risehiro Nonaka and Katsuyasu Sugawara. Faculty of Engineering and Resource Science, Akita University, 1-1 Tegata Gakuen-cho, Akita, 010-8502, Japan

As a secondary rare metal resource, WCR (W and Co extracted residue) produced from a recycling process of refractory metal scrap contains various rare metals such as tantalum, niobium, titanium etc. To develop an efficient recovery process of rare metals from refractory metal scrap, release behavior of tantalum and niobium from WCR was investigated in a chlorine gas stream with the addition of solid carbon. The sample was dried at 373 K and classified into 200 + 250 mesh. Carbon powder derived from phenolphthalein was used as a chlorination accelerating agent. The WCR or carbon mixed sample were heated up to the terminal temperatures ranging from 573 to 1273 K in a chlorine atmosphere with a fixed bed reactor. The treated sample was cooled in a nitrogen stream. 56 % of tantalum was volatilized at 1273 K for 3 h while niobium was completely volatilized from WCR. The carbon addition was effective for accelerating the chlorination reaction, and lowered the starting temperature of tantalum and niobium release from 1273 K to 573 K. Volatilization of tantalum and niobium completed by 873 K. Based on above results, two step chlorination of WCR was carried out for selective separation of tantalum from other metals. In the first step, the WCR sample was heated in a chlorine stream at 1273 K to volatilize tungsten, niobium and titanium. In the second step, the sample was chlorinated again in the presence of carbon. 74 % of tantalum was recovered successfully as a chloride.