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) (CrVI) from aqueous solution. The adsorption of CrVI 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 CrVI onto MCh-Fe was an endothermic and spontaneous process. The loading capacity of CrVI on the adsorbent remained at a high level even after five cycles, showing that MCh-Fe can be used for repeated CrVI removal. Column adsorption results indicated that below 0.5 mg L–1 CrVI 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 CrVI, respectively. The CrVI removal mechanism of MCh-Fe was also investigated.