Magnetically recoverable fly ash-based adsorbents for high-efficiency Pb(ii) removal: performance and mechanism

Abstract

This study employed a combined alkaline and magnetic modification on three materials for the removal of Pb(II) ions from aqueous solutions and systematically compared their adsorption performance. Although the adsorption capacity of fly ash, magnetic beads, and tailings for water pollutants has been studied, no systematic research has been conducted, and the separation and recovery of these powdered adsorbents are challenging. Results demonstrated that the three adsorbents exhibited excellent lead adsorption efficiency and magnetic recyclability after the sorption. The magnetization intensities of modified fly ash, modified magnetic beads, and modified tailings were 0.6, 1.27, and 0.8 emu g⁻¹, respectively. The adsorption of Pb(II) onto the three adsorbents achieved equilibrium within 60 minutes, with highly efficient Pb(II) removal rates of 98.58%–99.49%. Compared with the modified magnetic beads, the modified tailings and modified fly ash showed higher Pb(II) adsorption efficiencies under the same conditions due to their higher specific surface areas and greater pore volumes. The adsorption of Pb(II) onto the adsorbents followed the Langmuir isotherm and the pseudo-second-order kinetic model, indicating monolayer chemical adsorption. The maximum adsorption capacities for Pb(II) adsorption onto modified fly ash, modified magnetic beads, and modified tailings were 115.34 mg g⁻¹, 97.94 mg g⁻¹ and 129.70 mg g⁻¹, respectively. The adsorption of Pb(II) was primarily performed by electrostatic attraction, surface complexation, ion exchange, and chemical precipitation. Regeneration studies demonstrated satisfactory reusability of the three modified adsorbents. This study presents modified fly ash-based adsorbents as low-cost, effective, and magnetically recyclable adsorbents for Pb(II) removal, providing a promising practical application for lead-containing wastewater treatment and the high-value utilization of fly ash.