Removal of cadmium from aqueous solution using montmorillonite-supported nanoscale zero-valent iron

Cadmium (Cd) contamination in water poses a critical global challenge. A novel nanocomposite, montmorillonite (Mt)-supported nanoscale zero-valent iron (Mt-nZVI), synthesized by liquid phase reduction, offers a promising method for effectively removing Cd. The material underwent characterization through various techniques, including X-ray diffraction (XRD) and Scanning Electron Microscope(SEM). The effects of initial pH, Cd concentration, solid-to-liquid ratio, temperature, solid dosage, and reaction time on the performance of Mt-nZVI in removing Cd were investigated. Remarkably, a notable 93.12% removal rate was achieved for Cd concentration of 10 mg·L^-1 under a 2-h reaction time, pH 7, and 0.5 g·L^-1 Mt-nZVI dosage. The adsorption process exhibited an excellent fit with both the pseudo-second-order kinetic model and the intra-particle diffusion model, suggesting that the adsorption mechanisms involve both the chemical adsorption and intra-particle diffusion. Dynamic adsorption experiments were conducted using Mt-nZVI. Under optimized conditions (adsorbent-to-quartz sand mass ratio of 1:250 and flow rate of 2 mL·min^-1), Mt-nZVI achieved optimal Cd removal efficiency, demonstrating its potential for continuous wastewater treatment applications. The removal mechanism of Cd, as inferred from a series of characterization analyses, likely involves processes including rapid adsorption facilitated by electrostatic interactions, hydrolysis of Fe leading to the formation of precipitates with Cd, and surface corrosion of nZVI resulting in the formation of surface complexes with Cd. Overall, these findings highlight the excellent potential of Mt-nZVI for treating Cd-containing wastewater.