Synthesis, Characterization and Application of Ferrous Iron-Embedded Schwertmannite for Cr(VI) Reduction–Adsorption from Aqueous Solutions

Previous studies have demonstrated that schwertmannite (Sch) exhibits good adsorption performance for Cr(VI). In order to further enhance the ability to remove Cr(VI), this study prepared a novel composite (Fe(II)@Sch) by embedding ferrous iron (Fe(II)) on Sch. The adsorption performance of Cr(VI) on Fe(II)@Sch was investigated by batch adsorption experiments, and a possible removal mechanism was proposed through characterization analysis. The results showed that the optimal Fe/Sch ratio for Fe(II)@Sch preparation was 120 mmol/g. Fe(II)@Sch enabled efficient and rapid adsorption of Cr(VI). The maximum Cr(VI) adsorption capacity of Fe(II)@Sch was 4.17 mmol/g at pH 6.0, which was 69% higher when compared to Sch, and 81% of the maximum adsorption could be achieved within 1 min. The embedding of Fe(II) led to a decrease in the particle size and an increase in the specific surface area (SSA) of Sch, which could be considered favorable for adsorption. After four repeated cycles 93.3% of the original Cr(VI) adsorption capacity was still maintained. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analysis showed that the interaction between Fe(II)@Sch and Cr(VI) followed an adsorption–reduction mechanism. The results demonstrated that Fe(II)@Sch could be used as an effective material for removing Cr(VI) from wastewater.