<p>To address issues such as high energy consumption in traditional processes for bastnaesite, this study investigated the selective roasting of bastnaesite using ammonium chloride. By analyzing the Gibbs free energy of chemical reactions for major mineral phases across different temperature ranges, the feasibility of each reaction was verified. Chlorination experiments revealed the influence of factors such as ammonium chloride dosage, roasting temperature, roasting time, and raw material particle size on rare-earth leaching efficiency. The reaction washed residue was characterized and analyzed using methods such as XRD, SEM–EDS, and TG–DTG, and the optimized process conditions for selective roasting of bastnaesite with ammonium chloride were established. A low-to-medium temperature roasting environment reduces fluorine volatilization pollution, while byproduct alkaline earth metal chlorides serve dual roles as chlorinating and fluorine-fixing agents, promoting the reaction process. By examining the impact of various factors on rare-earth leaching efficiency, an 88% rare-earth chlorination rate was achieved under optimal reaction conditions. Finally, the reaction mechanism for the selective recovery of rare-earth elements from bastnaesite via chlorination was elucidated.</p>