Sustainable Utilization of K-Humate Coal Residue into Bead Adsorbents for Cu(II) Removal

The increasing discharge of heavy metals, particularly copper (Cu), into soil and water systems poses significant environmental and health risks due to their toxicity, persistence, and potential for bioaccumulation.In this study, coal residue, a solid byproduct derived from potassium humate (K-humate) production, was sustainably converted into composite chitosan beads and evaluated as an adsorbent for the removal of Cu(II) from aqueous solutions.The coal residue was pretreated with HCl, sieved, and incorporated into chitosan gel, followed by crosslinking with sodium tripolyphosphate to form stable beads.Batch adsorption experiments were performed to investigate the effects of pH (4-7), adsorbent dosage (0.1-0.4 g in 25 mL solution), and temperature (30-50 C) on Cu(II) removal efficiency at an initial concentration of 67.46 mg L.The results consistently demonstrated high removal efficiencies (>92%) under all tested conditions, with optimal performance observed at a slightly acidic pH (4), higher adsorbent dosages, and elevated temperatures, indicating an endothermic adsorption process.The coalchitosan composite beads showed stable performance across varying conditions, highlighting the synergistic role of chitosan as a matrix for residue immobilization and improved reusability.This work not only presents a low-cost and sustainable route for valorizing coal residue but also introduces an effective adsorbent for Cu(II) remediation in wastewater treatment applications.