Fabrication of FeAl-LDH onto sponge for efficient chromium(VI) immobilization and reduction in soil remediation

Efficient remediation of Cr(VI)-contaminated soils is facilitated by materials possessing both high adsorption potential and reductive functionality. In this work, a novel composite, FeAl-LDH@PS, was synthesized by hydrothermally anchoring Fe-Al layered double hydroxides (LDHs) onto a porous, elastic polyurethane sponge (PS), serving as a recoverable support to enhance LDH dispersion, structural stability, and reusability. A Cr(VI) concentration of 1000 mg/kg was effectively treated by FeAl-LDH@PS, resulting in 74.97% immobilization within 60 minutes and a substantial decline in leachable Cr(VI) from 43.01 mg/L to 4.45 mg/L under varied environmental scenarios. Mechanism analysis indicated that Fe<sup>2+</sup> and Al<sup>3+</sup> were released from the FeAl-LDH@PS. The released Fe<sup>2+</sup> reduced Cr(VI) to Cr(III), while Al³⁺ underwent hydrolysis to form AlOOH. Subsequently, the newly generated Fe<sub>2</sub>O<sub>3</sub> and AlOOH co-precipitated or surface-adsorbed Cr species.The composite maintained high stability and remediation efficiency across a broad pH range and under repeated dry–wet and freeze–thaw cycles. Phytotoxicity assays further confirmed its low environmental risk and suitability for safe application in soil systems. Microbial community structure and predicted metabolic functions revealed that FeAl-LDH@PS remediation not only shifted the bacterial composition toward that of clean soil but also restored core metabolic pathways associated with carbon and nitrogen cycling.