Removal of dissolved metals by zero-valent iron (ZVI): kinetics, equilibria, processes and implications for stormwater runoff treatment.
Infiltration of stormwater runoff contaminated with metals is often questionable in several cases due to its long-term potential to cause deterioration of groundwater quality. To ensure the quality of filtrate, a pre-treatment of contaminated runoff is required. This study investigates the processes of copper and zinc ion removal from stormwater runoff using zero-valent iron (ZVI, Fe0). Kinetic and equilibrium tests were performed with laboratory-prepared and in situ stormwater runoff samples collected from roof, street and highway catchments. Based on the results, a substantial portion of Cu2+ is reduced and transformed to insoluble forms of Cu0 and Cu2O. Unlike copper, the adsorption and co-precipitation associated with freshly precipitated iron oxides play important roles for the removal of Zn2+. Investigations under various water quality conditions demonstrated a relatively minor impact on Cu2+ uptake rates. However, the different conditions apparently altered the removal stoichiometry and phases of the copper deposits. The removal rates of Zn2+ increase with higher dissolved oxygen (DO), ionic strength (IS), temperature (T) and pH. Dissolved organic carbon (DOC) in runoff samples forms complexes with metals and Fe2+, thereby kinetically decreasing the metal uptake rates. Furthermore, depending on its composition, a larger molecular weight organic fraction was found to preferentially compete for the adsorption sites. The study demonstrates that ZVI is a promising medium for achieving comparable capacity to a commercial adsorbent like granular ferric hydroxide (GFH). Long-term performance of ZVI, however, may be limited and governed by the formation of non-conductive layers of iron and cuprous oxides.
Rangsivek
R
R
Department of Water Quality Control, Technical University of Berlin, Sekr. KF4, Strasse des 17. Juni 135, 10623, Germany. ropru@rangsivek.com
Jekel
M R
MR
D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D008670:Metals / Q000302:isolation & purification*; D008855:Microscopy, Electron, Scanning; D009994:Osmolar Concentration; D013696:Temperature; D014874:Water Pollutants, Chemical
D008670:Metals; D014874:Water Pollutants, Chemical; D007501:Iron