Effects of selected ligands on U (VI) immobilization by zerovalent iron

The effects of Cl-, CO3 2-, EDTA, NO2 -, NO3 -, PO4 3-, SO4 2-, and humic substances (HS) on U(VI) co-precipitation from aqueous solutions by zerovalent iron (ZVI) in the neutral pH range was investigated. Not shaken batch experiments were conducted for 14 days mostly with 15 g/L of five different ZVI materials and 10 mM of selected ligands and 20 mg/l (0.084 mM) of an U(VI) solution. Apart from Cl- all tested ligands induced a decrease of U(VI) coprecipitation. This decrease is attributed to surface adsorption and complexation of the ligands to reactive sites on the surface of ZVI and their corrosion products. The extent of U(VI) removal decrease was not uniform for the five materials. Generally, groundwater with elevated EDTA concentration should not be remediated with the ZVI barrier technology. A rational selection of material can enable the selection of appropriated materials for any specific site with other tested ligands. The response of the system on pre-treating two ZVI materials with 250 mM HCl indicated that in situ generated corrosion products favor irreversible U(VI) uptake. Thus for the long term performance of ZVI barrier, iron dissolution should continue such that fresh iron oxide is always available for U(VI) co-precipitation.