Serpentine-modified biochar from dual wastes for enhanced copper removal: Performance and mechanism

Widespread copper (Cu²⁺) pollution from mining and industrial activities demands effective, low-cost remediation solutions. This study developed a novel adsorbent fabricated through a simple one-step co-pyrolysis of magnesium-rich serpentine jade waste (SJ) and rice straw biochar (BC) at an optimal SJ:BC mass ratio of 1:5, denoted as SJBC. The composite achieved a maximum Cu²⁺ adsorption capacity of 131.91 mg g^-1, significantly surpassing that of pristine BC (46.67 mg g^-1) and thermally treated SJ (100.75 mg g^-1). Comprehensive characterization using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) confirmed the successful integration of SJ into the carbon matrix, resulting in enhanced surface roughness, increased oxygen-containing functional groups, and the formation of active MgO sites. Adsorption isotherms were best fitted by the Freundlich model, while kinetics followed the Elovich model, indicating a chemisorption-dominated process on a heterogeneous surface. The removal mechanism involved synergistic effects of Mg²⁺-facilitated ion exchange, surface precipitation of Cu(OH)₂, complexation with oxygen functional groups, and potential Cu²⁺-π interactions. The composite exhibited excellent pH adaptability, maintaining high removal efficiency (>95%) in the environmentally relevant pH range of 4-6, and demonstrated effective performance in real copper-laden wastewater. This work presents a sustainable strategy for dual waste valorization, transforming industrial and agricultural residues into a high-performance, low-cost material for copper remediation in water, with promising potential for soil stabilization applications.