Kinetics of the carbochlorination of columbite

The chlorination of the niobium- and tantalum-bearing mineral columbite in the presence of carbon-carbochlorination-was studied by thermogravimetry, s canning-electron microscopy, energy-dispersive Xray spectroscopy, X-ray dif fraction analysis and X-ray fluorescence analysis. The effect of reaction t emperature on the carbochlorination kinetics was studied between 450 and 95 0 degrees C and the microstructural evolution of reacting solids was invest igated as a function of conversion. Layers of MnCl2 formed on the columbite and carbon particles during the carbochlorination reaction at moderate tem peratures (630 degrees C). The carbochlorination of columbite proceeded in two stages: first, preferential carbochlorination of Fe, Mn and Nb left a r esidue rich in beta-Ta2O5 having an orthorhombic structure, and this was ca rbochlorinated in the second stage to TaCl5.