Removal of contaminants from aqueous solution by reaction with iron surfaces

Irrigation drainage and industrial wastewaters often contain elevated level s of toxic oxyanions and oxycations such as selenate, chromate, and uranyl. A potential remediation method is to react contaminated water with zero-va lent iron, which transforms the mobile contaminants into immobile forms. In this work, iron foil was exposed to aqueous solutions containing the relev ant ions, and the reacted surfaces were characterized by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM images co llected in situ show that the protrusions on the foil surface associated wi th iron oxides are smoothed out by the reaction. XPS indicates that partial ly reduced Se(IV) and Cr(III) are adsorbed on the surface, while uranium is deposited as U(VI), i.e., without reduction. More Se and Cr are deposited when the atmospheric gases are removed from solution because of the elimina tion of a competing process in which dissolved O-2 increases the thickness of the iron oxide overlayer to the point where the reduction reaction is qu enched. The amount of U deposited is greatly increased when the atmospheric gases are removed because of the elimination of dissolved CO2, which can f orm carbonate complexes with uranium.