Adsorption of arsenic on modified montmorillonite

Fe polycations and cetyltrimethylammonium bromide (CTMAB) were used to synthesize modified montmorillonite. Arsenic removal by modified montmorillonite was investigated through effects of reaction time, adsorbent dosage, solution pH, as well as the associated adsorption isotherms and kinetics. X-ray diffraction (XRD), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used to explore the characteristics of the raw and modified montmorillonite. It was found that CTMAB had entered the interlayer of the raw montmorillonite (Mont) while Fe polycations adsorbed on the outer surface and formed small flocculent particles. All adsorption processes reached equilibrium within 20 min. Pseudo-second-order kinetics and Langmuir adsorption model fit the experimental well. The adsorption capacity on C–Fe–M and Fe–M were 8.85 and 15.15 mg g− 1 for As(V), respectively, and 13.89 and 16.13 mg g− 1 for As(III). The adsorption of As(V)/As(III) on modified montmorillonite was significant in the pH range of 4–10. The removal rate exceeded 99% under the condition of pH range 2–10 for As(V). All results showed that modified montmorillonite has a good affinity towards As(V) and As(III). The sorption mechanisms were mainly surface adsorption and electrostatic adhesion.