Nanoscale zero-valent iron modified with carboxymethyl cellulose in an impinging stream-rotating packed bed for the removal of lead(II)

Abstract

A novel impinging stream-rotating packed bed (IS-RPB) was proposed to continuous, macro and industrialized prepare nanoscale zero-valent iron (nZVI) with simultaneously modified with carboxymethyl cellulose (CMC) for the removal of Pb2+. The obtained CMC-nZVI particles were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The components on the surface of CMC-nZVI after react with Pb2+ were also analyzed by X-ray photoelectron spectroscopy (XPS). The IS-RPB makes it possible for the continuous, macro and industrialized preparing of CMC-nZVI particles, and CMC can significantly improve the dispersion and reduce aggregation of nZVI particles. The effects of solution pH, initial Pb2+ concentration and reaction time on the removal efficiency of Pb2+ by nZVI and CMC-nZVI particles were also investigated. The results show that CMC-nZVI particles outperform nZVI particles in removing Pb2+, and the removal efficacy reaches a maximum of 838.84 mg·g−1 for nZVI particles and 1237.32 mg·g−1 for CMC-nZVI particles at pH = 6.0. The adsorption of Pb2+ by nZVI and CMC-nZVI particles can be described by the Langmuir isotherm adsorption model with a R2 of 0.999, and the calculated maximum adsorption capacity is 900.90 and 1376.07 mg·g−1 for nZVI and CMC-nZVI particles. The adsorption of Pb2+ follows the pseudo second-order kinetics with a linear correlation coefficient R2 of 0.999. In addition, the effect of co-existing cations such as Na+, Cu2+, Ni2+ and Cd2+ on Pb2+ removal efficiency was also investigated. The results showed that Na+ had no effect on Pb2+ removal efficiency and Cu2+ and Ni2+ had inhibited Pb2+ removal efficiency. Cd2+ had an inhibitory effect on Pb2+ removal efficiency when the concentration was 50 mg·L−1 and 100 mg·L−1, Cd2+ enhanced Pb2+ removal efficiency while the concentration of Cd2+ was 200 mg·L−1.