Abstract
Nanoscale zerovalent iron (nZVI) is efficient for removing Pb2+ and nitrate from water. However, the influence of nitrate, a common groundwater anion, on Pb2+ removal by nZVI is not well understood. In this study, we showed that under excess Fe0 conditions (molar ratio of Fe0/nitrate>4), Pb2+ ions were immobilized more quickly (<5min) than in nitrate-free systems (∼15min) due to increasing pH. With nitrate in excess (molar ratio of Fe0/nitrate<4), nitrate stimulated the formation of crystal PbxFe3−xO4 (ferrite), which provided additional Pb2+ removal. However, ∼7% of immobilized Pb2+ ions were released into aqueous phase within 2h due to ferrite deformation. Oxidation–reduction potential (ORP) values below −600mV correlated with excess Fe0 conditions (complete Pb2+ immobilization), while ORP values ≥−475mV characterized excess nitrate conditions (ferrite process and Pb2+ release occurrence). This study indicates that ORP monitoring is important for proper management of nZVI-based remediation in the subsurface to avoid lead remobilization in the presence of nitrate.
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