Abstract
In this work, a systematic study of the reaction between xenotime, chlorine, and carbon has been performed. The kinetics of carbochlorination of xenotime raw material (rare-earth elements in phosphate form, REPO4) has been studied over a temperature range from 600 °C to 950 °C. The influences of temperature, partial pressure of chlorine, carbon content, and particle size on the rate of conversion of xenotime to RECl3 were investigated. The results showed that the process follows the unreacted core-shrinking model with formation of a porous product layer. Powder X-ray diffraction (XRD) corroborated this model, showing clearly the patterns related to the formation of yttrium oxychloride (YOCl), indicating that the reaction mechanism involves the presence of an intermediate step before the formation of lanthanide chloride. A global rate equation which includes these parameters has been developed: $$1 - (1 - X)^{{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3}} = k_{appt} = 2.8 \times 10^{ - 4} d_0^{ - 0.4} P_{Cl_2 }^{0.9} \exp \left( { - \frac{{9057}}{T}} \right)t$$
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