In this study, novel polyaniline-3-amino-4-methoxybenzoic acid (PANI–AMB) copolymers were prepared and used as adsorbents for the separation and recovery of Pd(II) from a mixed solution containing Pt, Pd, and Rh. Batch sorption studies were carried out, and the main adsorption parameters were systematically investigated. Furthermore, the relevant thermodynamic parameters, isotherms, and kinetic models were also evaluated. Results revealed a high adsorption capacity of 278.5 mg g⁻¹ for Pd(II). Separation factors β_Pd/Pt and β_Pd/Rh were 4.3 × 10³ and 5.3 × 10³, respectively. Results obtained from scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-vis), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) measurements indicated that the sorption of Pd(II) occurs mainly by chelation between Pd(II) and –NH–/–N/–COOH/–OCH₃ and is accompanied by a redox mechanism involving the reduction of Pd(II) to Pd(0). The new PANI–AMB adsorbent showed efficient adsorption and separation of palladium from the leaching liquor of spent automotive catalysts, as well as good stability and reusability.