PROTON GENERATION BY DISSOLUTION OF INTRINSIC OR AUGMENTED ALUMINOSILICATE MINERALS FOR IN-SITU CONTAMINANT REMEDIATION BY ZERO VALENCE STATE IRON

Metallic, or zero-valence-state, iron is being incorporated into perme able reactive subsurface barriers for remediating a variety of contami nant plume types. The remediation occurs via reductive processes that are associated with surface corrosion of the iron metal. Reaction rate s for these processes vary widely with both the form of iron and the c ontaminant but have previously been shown to increase when certain aqu ifer materials are present in the mix. Knowledge of such geochemical e ffects is important for planning an in situ remediation, as well as un derstanding the transport and fate of the contaminant within the barri er. The increase in reaction rate has been hypothesized to be due to t he presence of aluminosilicate minerals in some aquifer materials that can dissolve and participate in the reaction sequences. Current resul ts show that a variety of aluminosilicate minerals, including kaolinit e, montmorillonite, and a range of feldspars, can undergo dissolution in these disequilibrium systems and provide protons as electron accept ers at a rate sufficient to maintain and/or enhance the reactions. The proposed reactions are illustrated for aluminosilicate dissolution an d chromate reduction. A potential benefit for TCE dechlorination is al so depicted. These aluminosilicates may occur naturally in the aquifer geology and become mixed with the iron during emplacement, or they ca n be added to the iron as amendments prior to emplacement. Both scenar ios provide greater confidence that contaminant reactions will be comp lete before the reactants exit the barrier and may allow the engineeri ng of thinner barriers in situations constrained by cost or the presen ce of physical structures.