The ability of nano-ZrO2 and modified nano-ZrO2 with humic acid (ZrO2-H) to remove Cd2+, Cu2+ and Ni2+ from aqueous media has been tested by batch sorption studies varying the contact time, initial metal concentration, initial solution pH, sorbent dosage and temperature to understand the adsorption behavior of these metals through adsorption kinetics and isotherms. The bare nanoparticles (NPs) and modified NPs (MNPs) were characterized using X-ray powder diffraction (XRD), SEM-EDX, FTIR to determine the phase, average grain size, morphology, surfacial elemental compounds and functional groups of NPs and MNPs. The pH of the solutions and the temperature controlled the adsorption of metal ions by NPs and MNPs as well as maximum uptake occurred in the first 120 min of reaction in almost all metals. The kinetics of adsorption followed a pseudo-second-order rate equation (R2>0.97) and the isotherms were well described by the Freundlich model in Cd2+ and Cu2+, but in Ni2+ isotherms were better described by Langmuir model. The adsorption of metals onto almost all NPs and MNPs were spontaneous and endothermic in nature. Among the three metals, Cd2+ showed more preference towards the sites on ZrO2 and ZrO2-H than Cu2+ and Ni2+. This study reveals that ZrO2 and ZrO2-H are effective adsorbents in removing Cd2+, Cu2+ and Ni2+ from the aqueous environment with an adsorptive capacity of 46.2, 59.7, 39.5, 29.7, 9.2 and 16.7 mg·g−1, respectively
