Nano zero-valent iron/montmorillonite composite for the removal of Cr(VI) from aqueous solutions: Characterization, performance, and mechanistic insights

Infiltration of hexavalent chromium (Cr(VI)) into the human body poses significant health risks, including the risk of developing cancer and increased mortality rates. The discharge of chromium-contaminated wastewater from industrial processes exacerbates environmental pollution, highlighting the necessity for efficient, cost-effective, and environmentally friendly treatment methods. In recent years, there has been a growing emphasis on the application of nanoscale zero-valent iron particles (NZVI) for mitigating Cr(VI) water pollution. In the present study, NZVI was synthesized using a liquid-phase reduction method employing sodium borohydride (NaBH4), and natural montmorillonite (Mt) was incorporated as a carrier, resulting in the creation of NZVI/Mt., a composite material. Characterization of this composite was performed using scanning electron microscopy (SEM), Transmission Electron Microscope (TEM), Specific surface area and pore size (BET), X-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) techniques. The investigation encompassed an exploration of the influence of initial pollutant pH levels, adsorbent dosages, and initial pollutant concentrations on the adsorption process. The research findings indicate that, at an initial pH of 4.0, NZVI/Mt. achieves a removal efficiency of 92.41% for a Cr(VI) solution with an initial concentration of 40 mg/L. The NZVI/Mt. composite adheres to both a pseudo-second-order kinetic model and the Langmuir isotherm model, showcasing a significant maximum adsorption capacity of 67.75 mg/g for Cr(VI). Furthermore, thermodynamic analysis revealed an exothermic nature of the adsorption process. This experimental approach effectively resolved issues related to NZVI particle agglomeration, offering a simplified, cost-effective, and environmentally friendly preparation method. Consequently, the NZVI/Mt. composite material demonstrates effective treatment of Cr(VI) mildly contaminated wastewater.