Release Behavior of Tantalum and Niobium from Refractory Metal Scrap during Chlorination

In order to develop a selective recovery process of tantalum and niobium from tungsten and cobalt extracted residue (WCR), the release of rare metals during chlorination in a chlorine stream in a fixed bed reactor was investigated. The chemical forms of niobium in the sample were estimated to be CrNbO4 and (Ti, Nb, Fe, Ta) O-2. During chlorination at 573-1273 K, release of tantalum reached 15-46%, and that of niobium 74-97%. In the presence of added carbon, niobium originating from CrNbO4 was released in the temperature range of 273-773 K, and niobium and tantalum originating from (Ti, Nb, Fe, Ta) O-2 were rapidly released into the gas phase at above 773 K. The carbochlorination enabled all niobium and tantalum in the solid phase to be released at the temperature of 873 K by changing their chemical forms to chlorides via oxychlorides. Two-step chlorination consisting of chlorination and carbochlorination was carried out for selective separation of niobium and tantalum from coexisting elements. During chlorination in the first step, 96% of niobium and 26% of tantalum were recovered from WCR. All of the tantalum in the residue of the first step could be released into the gas phase by addition of carbon, and a volatile composed of 80% of tantalum was obtained in the second step.