Chlorination methods applied to recover refractory metals from tin slags

Cassiterite, the principal ore of tin, contains a considerable amount of niobium and tantalum, which are rejected in the tin smelter slag. Therefore, the tin slag should be considered as an important source of niobium and tantalum, particularly when the reserves of the principal ores of these two metals, are very limited in nature. Because of the increasing demand and very high value of these two metals, it has been necessary to develop a suitable process to recover niobium and tantalum from tin smelting slag. In view of certain advantages of chloride metallurgy, the authors have carried out some studies on chlorination of tin slag by gaseous chlorine in presence of carbon, hydrochloric acid leaching and chlorination by carbon tetrachloride vapor, at a comparatively low temperature and partial pressure, to recover the metal values, particularly niobium and tantalum. In this paper, based on thermodynamics and kinetics of these chlorination processes, the recovery of Nb and Ta and some associated metals has been briefly described and discussed. Based on the findings of the chlorination studies made, some further investigations for recovering niobium and tantalum from tin slags have been suggested.