Remediation of arsenic(III) from aqueous solutions using improved nanoscale zero-valent iron on pumice

The removal of arsenic(III), one of the most poisonous wastewater pollutants, was investigated using nanoscale zero-valent iron supported onto pumice and modified by chitosan (CS-P-NZVI). Scanning electron microscopy (SEM) analysis revealed that NZVI was distributed dispersedly on CS-P-NZVI without being oxidized. As(III) could be removed by adsorption on CS-P-NZVI in a very short time (minute scale) with high removal rates (more than 99.5%) over a wide range of pH (2.01-12.54) and concentration (20-100 mg/L). The removal of As(III) by CS-P-NZVI agreed well with the pseudo-first-order reaction kinetics and pseudo-second-order reaction kinetics. Reaction rate constants (Kobs) ranged from 0.27 to 0.96 min−1 at varied NZVI dosage. Freundlich isotherm provided a good model of the sorption system, indicating that CS-P-NZVI was heterogeneous in the surface properties. The thermodynamic parameters suggested that As(III) adsorption by CS-P-NZVI was a spontaneous and exothermic process. X-ray photoelectron spectroscopy (XPS) and atomic fluorescence spectrophotometer (AFS) analyses indicated that As(III) was only physically adsorbed on the surface of CS-P-NZVI within 60 min. Our results indicated that CS-P-NZVI might be an effective material for both in situ and ex situ remediation.