Transforming industrial residues and ZnO nanoparticles into hybrid adsorbents for enhanced heavy metal removal

This study explores the modification of power plant residues (PPR) with ZnO nanoparticles (ZnO-NPs) to improve adsorption of As(III), Cd(II), Pb(II), and Cr(VI). Batch experiments identified a 3% w/w impregnation ratio as optimal, creating PPR@ZnO3%. Maximum adsorption occurred at pH 7 for As(III), pH 8 for Cd(II), pH 3 for Pb(II), and pH 3 for Cr(VI), with capacities in the order of Pb(II) > Cd(II) > As(III) > Cr(VI). The pseudo-second-order model best fit the adsorption kinetics, with equilibrium capacities of 40.93 mg/g for As(III), 39.64 mg/g for Cd(II), 43.59 mg/g for Pb(II), and 19.27 mg/g for Cr(VI). The Redlich-Peterson model indicated homogeneous monolayer adsorption driven by cation exchange and surface precipitation.