<p>To address the dual challenges of ammonia–nitrogen pollution and high operational costs in conventional rare-earth separation processes, this study has developed a novel P507-unsaponifiable buffered extraction system using maleic acid for sustainable and efficient rare earth recovery. Through systematic optimization of maleic acid concentration (0.2–0.5 mol&#xa0;L⁻¹), aqueous phase pH (2.0–3.5), and rare earth loading (0.2–0.5 mol&#xa0;L⁻¹), combined with slope method analysis (to determine extraction stoichiometry) and FTIR, the extraction mechanism was clarified. Under optimal conditions (0.5 mol&#xa0;L⁻¹ maleic acid, 0.5 mol&#xa0;L⁻¹ rare earth concentration, pH = 3.5), the single-stage extraction capacity of Nd³⁺ reached 0.228 mol&#xa0;L⁻¹, 75% higher than the traditional P507-kerosene system (0.130 mol&#xa0;L⁻¹). Significant improvements were achieved in the separation coefficient for light/medium rare earths (<i>β</i>_Sm/Nd = 12.82), while the heavy rare-earth separation performance remained comparable to conventional systems. Slope analysis and FTIR spectroscopy confirmed that maleic acid acts solely as a buffer without organic-phase coordination. The system completely eliminated ammonia–nitrogen wastewater, reducing treatment costs by 60%, and demonstrated stable performance even at high rare-earth concentrations. This work provides an efficient and industrially scalable solution for green rare-earth separation, aligning with environmental sustainability goals.</p>