THE CARBOTHERMIC REDUCTION OF NIOBIUM PENTOXIDE AND PYROCHLORE IN THE PRESENCE OF IRON IN A TRANSFERRED ARC ARGON PLASMA

The kinetics of the carbothermic reduction of niobium pentoxide and pyrochlore concentrate are studied in the presence of iron in the temperature ranges 1575-2440 K and 1430-2125 K, respectively, in an argon transferred arc plasma. Influences of time, temperature, carbon and iron concentrations as well as graphite and pyrochlore particle size on the reaction rate are examined. The main reaction products are NbC and CO. The overall reaction rates are represented by the same logarithmic expression used previously for the carbothermic reductions without the presence of iron. The reaction rates are almost independent of reactant particle size but are dependent on the Fe/C weight ratio. The average activation energy for niobium pentoxide reduction is 142.5 +/- 33.2 kJ mol-1, while for pyrochlore reduction, it is 96.3 +/- 14.5 kJ mol-1. The presence of iron enhanced the reaction rates. With niobium pentoxide, the reaction rates are significantly higher as the quantity of iron increased. This is attributed to the reduction reaction taking place between the dissolved carbon in the iron and the niobium pentoxide. With pyrochlore there appears to be an optimum Fe/C ratio which gives the maximum reduction rate.