Facile encapsulation of nano zero-valent iron with calcium carbonate: synthesis, characterization and application for iron remediation

In this study, CaCO₃ was used as a modifier for nano zero-valent iron (nZVI) surface to prevent rapid aggregation and effectively utilized for iron remediation from aqueous solution. Surface chemistry and morphology of CaCO₃ encapsulated nZVI (CaCO₃–nZVI) before and after treatment of contaminant iron solution were characterized by scanning electron microscopy–energy dispersive X-ray (SEM–EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The mechanisms of surface modification as well as iron remediation were well depicted with the help of these characterisation tools. Iron removal efficacy of 96.4% was achieved with 0.25 g/L adsorbent dose for an influent iron of 0.5 mg/L at pH 10 after a 3 h treatment process. When the influent concentration was increased to 10 mg/L, the removal capacity decreased to 92.1%. The study demonstrates that CaCO₃ and nZVI in the encapsulated nanoparticle have a significant synergistic effect. The pseudo-second- order reaction kinetics and Freundlich isotherm model correctly portrayed the experimental data for iron removal by CaCO₃–nZVI. The CaCO₃–nZVI is a viable option for iron removal from various aqueous media due to its facile preparation, high iron removal capability, and reusability.