Construction of FeS/MgAl-carboxylate layered double hydroxide functional materials using steel slag for Cr(VI) removal

Significant progress has been observed in steel slag recycling. However, advanced approaches for minimizing metal-element-abundant residues have rarely been adopted. In this work, we present a facile strategy to tailor steel slag surface and use various metal components of steel slag to construct MgAl-carbonate layered double hydroxide (LDH)-supported iron sulfide nanocomposites (FeS-LDH-CO₃) using a filtrate rich in Fe³⁺, Mg²⁺, and Al³⁺ ions after steel slag dissolution. Two-dimensional intercalated FeS-LDH-RCOO nanosheets were then obtained by exchanging carboxylate anions derived from acetic, chloroacetic, dichloroacetic, n-propionic, or acrylic acids with carbonate anions within the FeS-LDH-CO₃ structure. The FeS-LDH-RCOO nanocomposites were characterized via X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, thermogravimetry–derivative thermogravimetry, the Brunauer–Emmett–Teller method, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results revealed that poorly crystalline FeS was uniformly dispersed on LDH nanosheets, leading to FeS-LDH-RCOO nanocomposites with a high specific surface area and special composite structure. In addition, FeS-LDH-RCOO exhibited outstanding Cr(VI) detoxification performance in designed case studies. Acetate-intercalated FeS-LDH (FeS-LDH-CH₃COO) exhibited a Cr(VI) adsorption capacity of 36.1 mg/g resulting from the synergy of the simultaneous immobilization of Cr(VI) on LDH nanosheets and reduction of Cr(VI) to Cr(III) on FeS. The fabricated FeS-LDH-RCOO composite not only utilizes various components of steel slag while minimizing metal element-abundant residues but also possesses good Cr(VI) cleaning ability because of the integration of FeS and MgAl-carboxylate LDH. Thus, this study provides a new method for the reasonable and extensive utilization of steel slag in environmental cleaning applications, transforming a waste material into a valuable resource.