Arsenic Adsorption on Iron-Modified Montmorillonite: Kinetic Equilibrium and Surface Complexes

As(V) adsorption mechanisms on an iron-modified montmorillonite (Fe-Mt) were studied by analysis from kinetic and equilibrium perspectives, and applicability of Fe-Mt for As(V) removal from groundwater was evaluated. Iron-modified montmorillonite was characterized by Small Angle X-Ray Scattering (SAXS), Wide Angle X-Ray Scattering (WAXS) and scanning electron microscopy technique and an excellent performance for As(V) removal, even at neutral and basic pH values and high conductivity conditions, was determined. Moreover, As(V) adsorption was higher with the increasing of ionic strength of the solution. Both Langmuir and Freundlich models provided a suitable fit to the experimental data, and the maxima adsorption capacity was 6.3 g/kg. Kinetic studies indicated that about 99% of As(V) was removed in the first 30 min of time from a starting concentration of 3 mg/L following a pseudo-second order kinetic. Formation of inner-sphere complexes of As(V) at the surface of Fe-Mt was stated by evaluation of As(V) adsorption in the presence of Cl−, NO3−, and PO43− ions and of the zeta potential versus pH curves.