Closed-loop fluorine sequestration via coordinated leaching-selective precipitation: Achieving zero-emission bastnaesite processing

• Establishes a simplified bastnaesite clean process: HCl coordinated leaching-thermal reductive precipitation. • Achieves 96.0% Ce and 97.6% non-Ce REEs leaching via Ce 4+ -F - coordination, prevents REF 3 formation. • Recovers >99.9% F as spherical (La,Ce)F 3 with only 5.1% non-Ce REEs loss. • Enables zero fluorine-containing wastewater discharge (F - < 2 mg/L) in closed-loop process. This study presents a sustainable hydrometallurgical process for refining bastnaesite, integrating oxidation roasting, HCl coordination leaching, and thermal reductive precipitation within a closed-loop system. By utilizing Ce 4+ -F - coordination chemistry, the process achieves leaching efficiencies of over 96% for cerium, 97.6% for non‑cerium REEs, and 66.6% for fluorine, effectively preventing REF 3 formation. Through Cl - ‑mediated reduction of the [CeF x ] 4-x complex at elevated temperatures, selective precipitation recovers 28.1% of cerium and >99.9% of fluorine as near‑spherical (La,Ce)F 3 powders (D 50 = 5.503 μm), with non‑cerium REEs loss limited to 5.1%. The resulting mother liquor contains <2 mg/L F - , achieving zero discharge of fluorine-containing wastewater. Compared with the conventional process, this strategy markedly cuts chemical consumption and avoids hazardous waste generation. Its simplified layout and efficient resource recovery underscore strong industrial scalability. This process establishes an eco‑efficient and technically feasible route for the simultaneous extraction of REEs and fluorine, with promising potential for application in sustainable mineral processing.