Rare earth extraction from bastnaesite concentrate by stepwise carbochlorination-chemical vapor transport-oxidation

Abstract

A stepwise carbochlorination-chemical vapor transport-oxidation process is developed for the green rare earth extraction from a bastnaesite concentrate using carbon as reductant, chlorine gas as chlorination agent, SiCl₄ gas as defluorination agent, AlCl₃ as vapor complex former, and (O₂+H₂O) mixed gas as oxidant. Between 500 °C and 800 °C, the apparent activation energy of the carbochlorination within 2 hours changed from 17 to 10 kJ/mole roughly for the initial 20 minutes and final 1.5 hours, respectively, in the absence of SiCl₄, but these values reduced to 15 and 5.9 kJ/mole under 10 kPa of SiCl₄ gas, while the rare earth chloride conversion for 2 hours was 43 to 81 mol pct in the absence of SiCl₄ and 55 to 99 mol pct under 10 kPa of SiCl₄ gas. After carbochlorination at 550 °C for 2 hours in the (Cl₂+SiCl₄) atmosphere for efficient rare earth extraction and thorium-free volatile by-product release, throium was removed by chemical vapor transport at 800 °C for 0.5 hours in the (Cl₂+SiCl₄+AlCl₃) atmosphere and alkaline earths were separated from rare earths by oxidation at 700 °C to 1000 °C in the (O₂+H₂O) atmosphere for 0.5 hours, followed by water leaching at room temperature. Their combination allows a clean and efficient rare earth extraction from the concentrate.