Nanoscale iron oxides loaded granular activated carbon (GAC-NSIO) for cadmium removal

Abstract

A new hybrid material was prepared by loading the nanoscale iron oxide particles within the pores of granular activated carbon (GAC-NSIO) and used as adsorbent to remove Cd(II) in aqueous phase. The new material is characterized by the pHpzc, TEM, XRD, BET, and XPS analytical techniques to deduce the potential adsorptive mechanism, and further it along with GAC were assessed in the removal of Cd(II) from aqueous solution for various physico-chemical factors iron-loaded content, pH, humic acid, isotherm, kinetics, and thermodynamics, under the batch reactor studies and rapid small-scale column tests also appended dealing with the breakthrough volume. Characterization of adsorbent indicated that the amorphous nanoscale iron oxides were successfully immobilized on GAC. Adsorption mechanism mainly included surface complexation, Donnan membrane effect, and electrostatic attraction. The optimum iron-loaded content of GAC-NSIO was 17%. The adsorption process was more favorable at high pH, and iron oxide was almost no leaching (<0.25%) in the pH range of 3–6. Adsorption isotherm fitted well with Langmuir and Freundlich models. And adsorption kinetics fitted well with pseudo-second-order and intraparticle diffusion models. Results indicated that loaded nanoscale iron oxides significantly increased adsorption capacity of Cd(II) though the adsorption rate declined slightly and the adsorption process was endothermic. The maximum adsorptive capacity of GAC-NSIO (7.84 mg/g) increased by 700%, compared to that of GAC (0.98 mg/g). The presence of humic acid could greatly impact Cd(II) adsorption which promoted adsorption at low concentrations (1–10 mg/L) and inhibited adsorption at high concentrations (10–300 mg/L). Rapid small-scale column tests were conducted to obtain Cd(II) breakthrough profile. The results corresponded well with those from batch tests. Results demonstrate that the GAC-NSIO is a promising adsorbent for the removal of Cd(II) in contaminated water environment.