Highly efficient competitive removal of Pb(II) and Ni(II) by chitosan/diatomaceous earth composite

A novel adsorbent for an effective removing of Pb(II) and Ni(II) from aqueous systems in both noncompetitive and competitive modes was prepared by dispersion chitosan onto the diatomaceous earth (CSDE), and then was synthesized into a spherical shape by using a drop-wise method. Its chemical composition, microstructure morphology, and metal-binding mechanism were characterized by dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) techniques. Batch adsorption studies were utilized to evaluate the potential suitability of the prepared CSDE beads and to examine the impact of major adsorption parameters such as solution-pH, initial metal concentration, and contact time on the Pb(II) and Ni(II) adsorption. Under optimal conditions, the maximal adsorption capacities of the CSDE beads based on the Langmuir isotherm model were 175.22 mg/g for Pb(II) and 149.64 mg/g for Ni(II) for noncompetitive adsorption and 234.8 mg/g for both metals in competitive adsorption. The common foreign ions such as Na+, Mg2+, and Ca2+ had insignificant effect on the Pb(II) adsorption while Mg-2 and Ca-2 affected on Ni(II) adsorption. Adsorption kinetics of both metals followed a pseudo-second order model better than pseudo-first-order model. The prepared CSDE beads could be reused at least ten consecutive adsorption-desorption cycles with marginal decrease in the total adsorption capacity of both metals.