Screening of sustainable binders for alkali roasted mixed rare earth concentrate pellets: Mechanistic study of xanthan gum for pelletization, kiln skin inhibition and closed-loop resource recovery

Addressing kiln skin formation during traditional alkali roasting of Bayan Obo Mixed Rare Earth Concentrate (MREC), this study incorporated sintered pellet technology into the MREC alkaline decomposition system and systematically evaluated organic polymer binders under highly alkaline conditions. Comparative experiments demonstrated that xanthan gum (XG) exhibits excellent adhesion stability at pH > 14, with interfacial bond strength surpassing other polymers. At 0.5–1 % XG addition, composite pellets achieved compressive strengths up to 153 N pre-roasting and 283 N post-roasting, with rare earth recovery rates reaching 90 %. Comprehensive testing confirmed that XG-MREC bonding follows a multistage synergistic mechanism comprising charge absorption, chemical adsorption, mechanical bonding, and solid-phase interdiffusion bonding, in which chemical adsorption driven by the functional groups of XG (–OH, –CH₃, and COO^–) predominates. Key MREC elements (C, O, F, Ce) serve as primary adsorption sites. Additionally, a synergistic evaporation-crystallization-glass preparation method was developed by repurposing crystallized alkaline wastewater salts into glass raw materials. This approach enabled resource utilization of hazardous wastewater components (e.g., F^-, PO3- 4, Na⁺) and established a closed-loop green process. The integrated technology demonstrates efficient, clean extraction potential for complex rare-earth ores, offering significant implications for sustainable industrial-scale processing.