CHARACTERIZATION OF ARSENATE ADSORPTION ON HYDROUS IRON-OXIDE USING CHEMICAL AND PHYSICAL METHODS

The adsorption of arsenate by hydrous iron oxide was investigated by both chemical and physical energy dispersive analysis of X-rays (EDAX) and Fourier transform infrared (FTIR) methods. The chemical methods for characterizing arsenate adsorption sites on hydrous iron oxide surfaces in this work were investigations of the effect of ionic strength and zeta potential measurements of iron oxide systems containing various arsenate concentrations over the pH range 4-10. An inner-sphere complexation at the aqueous arsenate/iron oxide interface was identified from the results of the ionic strength effect and the shift in isoelectric point of the system. Evidence for direct coordination of arsenate to the surface of iron oxide was obtained by EDAX and FTIR techniques. Results from these physical methods showed that arsenate was chemisorbed on the iron oxide surface. Specific adsorption could therefore be deduced, on the basis of both chemical and physical methods, to occur at the aqueous arsenate and solid iron oxide interfaces.