Preparation of α-FeOOH loaded chitosan composite and its efficient removal for Cr(VI)

FeOOH has a large specific surface area and numerous active binding sites for Cr(VI), but it usually exists in the form of powder, being agglomerate easily and difficult for recycling after use. In this study, the in-situ generation of alpha-FeOOH and the shaping of CS spheres simultaneously happened in the mixed solution of 2 mol/L NaOH and 1 wt% of PEI, and then the rusultant spheres were crosslinked in 3 % glutaraldehyde solution to obtain the alpha-FeOOH loaded chitosan composite (alpha-FeOOH-PEI-CS). It had a connected three-dimensional reticular structuree, being easily separated. Under the optimal adsorption conditions (pH = 2.5, reaction temperature of 35 degrees C and adsorbent dosage of 0.5 g/L), the maximum adsorption capacity of the alpha-FeOOH-PEI-CS for Cr(VI) reached 250.63 mg/g. The adsorption process was consistent with the pseudo-second-order kinetic model, and intraparticle diffusion was the main rate-limiting step. In addition, the alpha-FeOOH-PEI-CS had good anti-interference and reusability. Coexisting anions and cations except SO42- had no significant effect on the adsorption of Cr (VI), and the removal rate still maintained above 97 % after 5 cycles. The adsorption mechanism included electrostatic attraction, reduction of Cr(VI) to Cr(III) and chelation of Cr(III) by amino and carboxyl groups.