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. The optimal Fe/Sch ratio for Fe(II)@Sch preparation was 120 mmol/g.Maximum Cr(VI) adsorption capacity of Fe(II)@Sch was 4.17 mmol/g at optimum pH 6.Adsorption of Cr(VI) on Fe(II)@Sch reached 81% of maximum adsorption within 1 min.Interaction between Fe(II)@Sch and Cr(VI) follows adsorption-reduction mechanism.