Carbochlorination kinetics of tantalum and niobium pentoxides

The carbochlorination kinetics of pure Nb2O5 and Ta2O5 by gas mixture (Cl-2 + CO + N-2) between 380 and 1,000 degrees C is studied. A calculation of t he standard free energy of the carbochlorination reactions is made. A diagr am of the phases stability is drawn. The influence of the gas flow, tempera ture and the partial pressure of Cl-2 and CO at temperatures below 650 degr ees C on the reaction rate is studied. The apparent activation energy is ap proximately 75 and 110 kJ/mol for Nb2O5 and Ta2O5, respectively. At tempera tures above 650 degrees C the Arrhenius diagram presents an anomaly which m ay be attributed to the decomposition of the COCl2 formed in situ. The appa rent reaction order of the carbochlorination of these oxides against Cl-2+C O is approximately 2. The carbochlorination rates of these oxides are much greater than those of chlorination by Cl-2 + N-2. The carbochlorination kin etics of tin furnace slag leaching concentrates containing tantalum and nio bium compounds are also studied and compared with the carbochlorination kin etics of the pure oxides.