Synergistic heavy metal sequestration from acidic metallurgical wastewater: Unraveling critical chemical bond-mediated adsorption mechanisms in vanadium slag-derived hydroxyapatite

The removal of heavy metals from acidic metallurgical wastewater is critical due to their persistent toxicity and environmental hazards. Conventional methods often fail to effectively address multi-metal contamination. This study investigates the use of waste neutralizing slag (from the vanadium industry)-derived hydroxyapatite (Ns-HAP) for simultaneous removal of Cr(VI), Cu(II), Ni(II), and Cd(II) from acidic metallurgical wastewater. By repurposed industrial byproducts, this approach offers a cost-effective and sustainable solution. Batch adsorption experiments revealed that Ns-HAP exhibit maximum adsorption capacities of 62.61, 143.17, 45.92, and 144.73 mg·g−1 for Cr(VI), Cu(II), Ni(II), and Cd(II), respectively, in single-component systems. Competitive adsorption studies demonstrated reduced Ni(II) removal efficiency in multi-component systems, whereas Cd(II) and Cu(II) maintained high adsorption rates (>99 %). Kinetic and thermodynamic analyses confirmed chemisorption-dominated monolayer adsorption, with spontaneous characteristics. Post-adsorption characterization identified heavy metal deposition on Ns-HAP surfaces and highlighted the critical role of CO, PO, and phosphate groups in binding mechanisms. This research provides a scientific foundation and technical support for the development of efficient and cost-effective treatment technologies for acidic heavy metal wastewater, highlighting the potential of Ns-HAP as a promising adsorbent material in addressing complex heavy metal pollution issues.