Abstract <p>In this study, polyethylene glycol-stabilized nanoscale zero-valent iron (PEG-nFe⁰) was loaded on sludge biochar (SBC) via a liquid-phase reduction method for the removal of Cd(II) from aqueous solutions, where nFe⁰ is the Fe⁰-FeO/FeOOH mixture. The morphology, functional groups, and crystal structure of the resulting PEG-nFe⁰@SBC composites were characterized using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) techniques. The incorporation of PEG introduced numerous –OH functional groups, which facilitated the dispersion of nFe⁰ as smaller particle size on the SBC surface. Kinetic studies revealed that the Cd(II) removal process by PEG-nFe⁰@SBC adhered to a pseudo-second-order kinetic model. The Freundlich isotherm model provided the best fit for describing the adsorption process. Thermodynamic analysis indicated that the removal of Cd(II) by PEG-nFe⁰@SBC was a spontaneous endothermic reaction. Under the initial conditions of 200 mg/L Cd(II), 1 g/L of PEG-nFe⁰@SBC, pH 5.0, and a temperature of 298 K, more than 85.8% of Cd(II) was removed within 24 h. The presence of PEG significantly enhanced the oxidation resistance of nFe⁰ in air. The adsorption capacity of PEG-nFe⁰@SBC for Cd(II) remained stable at 123.60 mg/g even after 90 days of air exposure, compared to 73.87 mg/g for nFe⁰@SBC. Typical macroscopic composition of natural water (Ca(II), Mg(II), humic acid (HA)) had minimal impact on Cd(II) removal by PEG-nFe⁰@SBC. Mechanistic analysis suggested that the primary removal mechanisms for Cd(II) by PEG-nFe⁰@SBC involved precipitation/co-precipitation and complex formation.</p>