Abstract: A stepwise carbochlorinationchemical vapor transport (SC-CVT) technique is proposed for separation of thorium from mixed bastnaesitemonazite concentrate. Mixed bastnaesitemonazite concentrate is first isothermally carbochlorinated for 2 h in a Cl₂ atmosphere with activated carbon as a reductant and SiCl₄ as a fluorine scavenger at a temperature as low as 500 ℃, only about 1 percent of the total thorium contained in the bastnaesitemonazite concentrate is evaporated. CVT processing is then undertaken at 800 ℃ for 0.5 h in a Cl₂-SiCl₄-AlCl₃ atmosphere. During this stage thorium is converted to a volatile complex ThAlCl₇, and is driven to transport to a temperaturegradient collection system, where thorium is deposited around 600 ℃, while FeCl₃ and AlCl₃ are deposited in the range of 200~350 ℃ and at even lower temperature(＜200 ℃), respectively. By using this technique the pollution caused by thorium radioactivity could be significantly alleviated.
