Biosorption of chromium(VI) ions from aqueous solutions by iron oxide-impregnated alginate nanocomposites: batch and column studies

This study evaluates the feasibility of using iron-oxide-impregnated nanoparticles of alginate (FeO-Alg) in removing hexavalent chromium ions from aqueous solutions by batch and continuous (fixed bed) column adsorption methods. In the batch mode experiments, the influence of contact time, chromium(VI) concentration, pH, and adsorbent were studied while in the fixed-bed column mode, bed height, flow rate, and initial metal ions concentration on the adsorption profiles of the metal ions employing FeO-Alg as nanoadsorbents (0.02 g 20 mL(-1)) were investigated. The maximum adsorption was observed at 2.3 pH for an initial metal ion concentration of 10 mg L-1. The results suggest that adsorption is due to electrostatic attraction between chromate ions (HCrO4-) and protonated surface (FeOH2+) groups. At a bed height of 0.82 cm and a flow rate of 0.5 mL min(-1), the metal removal capacity of FeO-alginate for chromium(VI) was found to be 85%. The bed depth service time (BDST) model was used to analyze the data of the column mode experiments. Sorption capacity per unit bed volume and rate constant of adsorption were calculated to be 17 mg L-1 and 0.6 L mg(-1) min(-1), respectively. In the flow rate experiments, the results confirmed that the metal uptake capacity and the metal removal efficiency decreased with increasing flow rate. The characterization of the prepared nanoparticles has been accomplished by Fourier transform infrared spectrocopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and zeta-potential measurements. The sorption equilibrium and kinetic data could be well fitted to the Freundlich, Langmuir, and Lagergren models. FeO-alginate nanoparticles are effective adsorbent for chromium(VI) removal from water samples.