Effect of common ions on nitrate removal by zero-valent iron from alkaline soil

Zero-valent iron (Fe(0))-based permeable reactive barrier (PRB) technology has been proved to be effective for soil and groundwater nitrate remediation under acidic or near neutral conditions. But few studies have been reported about it and the effects of coexistent ions under alkaline conditions. In this study, nitrate reduction by Fe(0) was evaluated via batch tests in the presence of alkaline soil and common cation (Fe(2+), Fe(3+) and Cu(2+)) and anion (citrate, oxalate, acetate, SO(4)(2-), PO(4)(3-), Cl(-) and HCO(3)(-)). The results showed that cation significantly enhanced nitrate reduction with an order of Fe(3+)>Fe(2+)>Cu(2+) due to providing Fe(2+) directly or indirectly. Most anions enhanced nitrate reduction, but PO(4)(3-) behaved inhibition. The promotion decreased in the order of citrate>acetate>SO(4)(2-)>Cl(-)≈HCO(3)(-)≈oxalate≫PO(4)(3-). Ammonium was the major final product from nitrate reduction by Fe(0), while a little nitrite accumulated in the beginning of reaction. The nitrogen recovery in liquid and gas phase was only 56-78% after reaction due to ammonium adsorption onto soil. The solution pH and electric conductivity (EC) varied depending on the specific ion added. The results implied that PRB based Fe(0) is a potential approach for in situ remediation of soil and groundwater nitrate contamination in the alkaline conditions.