A clean and efficient one-step process for rare earth extraction: Carbochlorination of mixed rare earth concentrate in a chlorine-rich environment

• Proposed a new one-step carbochlorination-washing process for mixed rare earth ores. • Achieved collaborative recovery of multiple elements from rare earth ores. • Realized "zero discharge" of acidic wastewater throughout the entire process. In addressing the critical scientific challenges of the low synergistic chlorination efficiency of multiple elements, including rare earth elements, calcium (Ca), barium (Ba), and iron (Fe), in rare earth mixed ores, as well as the unclear reaction mechanism, this study systematically conducted a comprehensive thermodynamic analysis and experimental verification of the carbochlorination process. A thermodynamic model was constructed to calculate the Gibbs free energy of reactions within the temperature range of 200 °C to 1200 °C. The results indicated that nearly all chlorination reactions could proceed spontaneously in the forward direction, thereby providing robust theoretical support for the feasibility of this process. Subsequently, experimental investigations demonstrated that under the optimized conditions, namely a chlorination temperature of 800 °C, a reaction time of 60 min, a chlorine flow rate of 10 L/min, a carbon-to-rare earth oxide molar ratio [n(C)/n(RE 2 O 3 )] of 4.2, and a raw material particle size of 250 mesh, the chlorination rates of rare earth elements, Ca, Ba, and Fe reached 93 %, 99 %, 95 %, and 99 %, respectively. These findings signify the successful achievement of efficient conversion of multiple elements. Furthermore, by integrating X-ray diffraction (XRD) phase analysis, scanning electron microscopy (SEM) microscopic morphology observation, and Fourier transform infrared spectroscopy (FTIR) functional group characterization, the reaction mechanism of each phase during the carbochlorination process of the mixed ore was elucidated. The obtained results provide a solid theoretical foundation and valuable references for process parameters, which are essential for the clean and efficient extraction of rare earth mixed ores.