Adsorption/reduction of Hg(II) and Pb(II) from aqueous solutions by using bone ash/nZVI composite: effects of aging time, Fe loading quantity and co-existing ions

Abstract

In this research, a versatile and highly efficient method for the stabilization of nanoscale zerovalent iron particles (nZVI) on the surface of ostrich bone ash (OBA) was presented as a novel inorganic adsorbent (OBA/nZVI) for the removal of Hg(II) and Pb(II) ions from aqueous solutions, even after 1 year of storage under room conditions. The removal behavior of the OBA/nZVI was assessed as a function of the initial pH, contact time, initial pollutants concentration, temperature, amount of adsorbent, effect of competitive metal ions, and ionic strength. The synthesized adsorbent was characterized by several techniques including N₂ adsorption at − 196 °C, FT-IR spectroscopy, scanning electron microscopy, X-ray diffraction, and zeta potential. The results confirmed that the OBA is a good candidate as support of nZVI. The maxima adsorption capacity for Hg(II) and Pb(II) ions found from experimental results were 170 and 160 mg g⁻¹, when the loading quantities of Fe were 20%. The equilibrium sorption data obeyed a Langmuir–Freundlich isotherm type model. The kinetic data of the adsorption followed the mechanism of the pseudo-second-order model. The thermodynamic experiments indicated that the removal of metal ions were feasible, endothermic, and spontaneous. It can be found that fresh and aged OBA/nZVI maintained its usability even after five cycles in the order: fresh (OBA/nZVI)-Hg(II) > fresh (OBA/nZVI)-Pb(II) > aged (OBA/nZVI)-Hg(II) > aged (OBA/nZVI)-Pb(II), which indicate that OBA/nZVI can be regenerated as adsorbent. The existence of Fe in the OBA/nZVI was proved by SEM-EDX results and X-ray diffraction analysis also confirmed adsorption/reduction of some of the Hg(II) to Hg⁰ and Pb(II) to Pb⁰.