Selective Recovery of Rare Metals From Secondary Resources by Chlorination

In order to obtain fundamental data for developing an efficient recovery process of rare metals from grinding powder of optical glass as secondary resources, release behavior of Nb, Ta, La, Gd and coexisting elements was investigated in Cl2 gas stream. The release extents of Zn, Nb, Ti and La drastically increased above 700°C and attained to almost 100% at 1000°C, while that of Zr attained to 10% above 800°C. Carbon addition accelerated the volatilization of elements and the release extents reached 100% by 1000°C except for La and Gd. The release of La and Gd were only 2-3# in the temperature from 800 to 1000°C. When the samples were heated at 700°C for 120 min, Ta and Nb were selectively volatilized from solid phase without the releasing of La and Gd.

   To separate and recover the rare metals from the optical glass, three-step chlorination with carbon addition was carried out. As the first-step chlorination at 500°C, the coexisting elements, Ti, Zr, and Zn were selectively volatilized. Ta and Nb could be obtained as the volatile in the second chlorination at 700°C with the holding time of 120 min. In the third-step chlorination at 1000°C with 120 min, La and Gd were recovered as the volatile and residue, respectively.