Remediation of hexavalent chromium in contaminated soil by Fe(II)-Al layered double hydroxide

In this study, high-efficiency and low-cost Fe(II) and Al(III) layered double hydroxide (Fe-Al-LDH) was synthesized and used for the remediation of Cr(VI) contaminated soil. The Fe-Al-LDH characteristics were analyzed with different techniques. The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses revealed its highly crystalline structure with sheet morphology, and a Brunauer–Emmett–Teller (BET) surface area of 46.85 m2/g. In addition, the remediation tests indicated that adding 1 g/L of Fe-Al-LDH to a solution of Cr(VI)-contaminated soil, at a soil to solution ratio of 1 g: 5 mL, completely immobilized the pre-adsorbed Cr(VI) in the soil (2079.84 mg/kg). Additionally, the Fe-Al-LDH could be used in a wide range of pH conditions and no Cr(VI) was detected in the leaching solution. Based on the characterization of X-Ray Diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, inductively coupled plasma mass spectrometry (ICP-MS), and X-ray photoelectron spectroscopy (XPS) analysis, it is proposed that adsorption and reduction may be involved in the mechanism of Cr(VI) immobilization by Fe-Al-LDH. At the beginning of the reaction, Cr(VI) entered the layer structure of the LDH or was adsorbed on the surface of the LDH. Then, Fe(II) was involved in reducing the Cr(VI) to Cr(III) and was oxidized to Fe(III). Part of the Cr(VI) and Cr(III) were co-precipitated with Fe(III) and Al (III) during the formation of iron oxide or hydroxide.