Magnetic Chitosan–Iron(III) Hydrogel as a Fast and Reusable Adsorbent for Chromium(VI) Removal

The magnetic chitosan–iron(III) hydrogel (MCh-Fe) was synthesized and characterized by SEM, TG, XRD, and FT-IR and used to remove toxic chromium(VI) (Cr VI ) from aqueous solution. The adsorption of Cr VI onto the MCh-Fe adsorbent was fast and could reach equilibrium in less than 30 min. The adsorption was well described by the pseudo-second-order rate model. The equilibrium isotherm was better matched with the Langmuir model. The adsorption of Cr VI onto MCh-Fe was an endothermic and spontaneous process. The loading capacity of Cr VI on the adsorbent remained at a high level even after five cycles, showing that MCh-Fe can be used for repeated Cr VI removal. Column adsorption results indicated that below 0.5 mg L –1 Cr VI was found in the effluent up to about 30 and 350 bed volumes for two wastewaters containing 115.0 and 5.6 mg L –1 Cr VI, respectively. The Cr VI removal mechanism of MCh-Fe was also investigated.