Kinetics of carbothermal and carbon monoxide reduction of calcium molybdate

Kinetic investigations have been carried out on the carbothermal and carbon monoxide reduction of synthetic calcium molybdate (CaMoO4) powder in the temperature range 1173 - 1298 K using a thermogravimetric set-up. Phase identification studies, by XRD, on the typical reacted products, reveal that whereas elemental Mo forms in carbothermy, both reduction and carburisation take place in the CO treatment of the molybdate resulting in molycarbide (Mo2C) formation. An unreduced intermediate Ca3MoO6 phase has also been detected in the products of the CaMoO4 + CO reaction. Carbon reduction of the molybdate has been found to proceed in accordance with the Jander's linear rate law with an activation energy of 179 kJ mol(-1) On the other hand, results of the reduction-carburisation of CaMoO4 by carbon monoxide have been found to fit into parabolic kinetics with a relatively high activation energy (194 kJ mol(-1)). The mechanisms of carbon and carbon monoxide reductions of the molybdate seem to be entirely different, Further, whereas carbothermy of CaMoO4 appears suitable for molybdenum metal preparation, the utility of CaMoO4 + CO reaction seems limited even for preparing molycarbide.