Efficient preparation and characterization of LDH/GCN based 3D foam for sustainable continuous column removal of U<SUP>6+</SUP> and Cd<SUP>2+</SUP> from water: mechanistic insights and application feasibility

Abstract

Industrial effluents discharge uranium (U6+) and cadmium (Cd2+) into water bodies, posing serious environmental risks. We investigated using a magnesium iron layered double hydroxide intercalated with carbon nitride (LDH/g-C3N4) foam for removing U6+ and Cd2+ from aqueous solutions. The adsorbent was characterized using advanced spectroscopic techniques, revealing carbonyl, metal-oxygen, C-N=C, and N-O groups, with a BET surface area of 48.21 m(2) g(-1) and pore volume of 0.108 cm(3) g(-1). Maximum adsorption capacities were 238.43 mg g(-1) for U6+ at pH 4 and 184.39 mg g(-1) for Cd2+ at pH 6 and 293 K. Adsorption followed pseudo-second order kinetics and Langmuir isotherms, with favorable thermodynamic parameters indicating spontaneous adsorption. The metal ions adsorption process involves co-ordination covalent and electrostatic (non-covalent) interactions between metal ions and LDH/g-C3N4 surfaces, enhanced by functional groups. Importantly, the foam retained substantial removal efficiency (>75%) even after three regeneration cycles using EDTA, showcasing excellent stability and reusability. Continuous fixed-bed column experiments further validated the material's practical feasibility, achieving prolonged breakthrough times (up to 32 days for U6+ and 28 days for Cd2+ at 10 cm bed height). Continuous fixed-bed column tests showed increased adsorption with bed height, highlighting the potential of LDH/g-C3N4 foam as an eco-friendly U6+ and Cd2+ removal adsorbent for industrial use. Moreover, the adsorbent maintained high removal efficiency in real groundwater spiked with contaminants, despite the presence of competing ions. These findings affirm the LDH/g-CC3N3 foam as a scalable, recyclable, and eco-friendly adsorbent for sustainable remediation of metal-contaminated waters.