title: Formation of ferrihydrite and associated iron corrosion products in permeable reactive barriers of zero-valent iron.
abstract: Ferrihydrite, which is known to form in the presence of oxygen and to be stabilized by the adsorption of Si, PO4 and SO4, is ubiquitous in the fine-grained fractions of permeable reactive barrier (PRB) samples from the U.S. Coast Guard Support Center (Elizabeth City, NC) and the Denver Federal Center (Lakewood, CO) studied by high-resolution transmission electron microscopy and selected area electron diffraction. The concurrent energy-dispersive X-ray data indicate a strong association between ferrihydrite and metals such as Si, Ca, and Cr. Magnetite, green rust 1, aragonite, calcite, mackinawite, greigite and lepidocrocite were also present, indicative of a geochemical environment that is temporally and spatially heterogeneous. Whereas magnetite, which is known to form due to anaerobic Fe0 corrosion, passivates the Fe0 surface, ferrihydrite precipitation occurs away from the immediate Fe0 surface, forming small (<0.1 microm) discrete clusters. Consequently, Fe0-PRBs may remain effective for a longer period of time in slightly oxidized groundwater systems where ferrihydrite formation occurs compared to oxygen-depleted systems where magnetite passivation occurs. The ubiquitous presence of ferrihydrite suggests that the use of Fe0-PRBs may be extended to applications that require contaminant adsorption rather than, or in addition to, redox-promoted contaminant degradation.
authors.affiliation: Naval Research Laboratory, Seafloor Sciences Branch, Code 7431, Stennis Space Center, Mississippi 39529, USA. yoko.furukawa@nrlssc.navy.mil
authors.forename: Yoko
authors.initials: Y
authors.lastname: Furukawa
authors.forename: Jin-Wook
authors.initials: JW
authors.lastname: Kim
authors.forename: Janet
authors.initials: J
authors.lastname: Watkins
authors.forename: Richard T
authors.initials: RT
authors.lastname: Wilkin
mesh_terms: D000327:Adsorption; D000693:Anaerobiosis; D002118:Calcium / Q000737:chemistry; D002119:Calcium Carbonate / Q000138:chemical synthesis; D002857:Chromium / Q000737:chemistry; D003343:Corrosion; D005290:Ferric Compounds; D005293:Ferritins / Q000138:chemical synthesis*; D052203:Ferrosoferric Oxide; D007501:Iron / Q000737:chemistry*; D058085:Iron Compounds / Q000138:chemical synthesis*; D008670:Metals / Q000737:chemistry*; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010087:Oxides / Q000138:chemical synthesis; D010539:Permeability; D012822:Silicon Dioxide / Q000737:chemistry; D013440:Sulfides / Q000138:chemical synthesis; D014874:Water Pollutants, Chemical / Q000032:analysis; D014877:Water Pollution, Chemical / Q000517:prevention & control
chemical_list: D005290:Ferric Compounds; D058085:Iron Compounds; D008670:Metals; D010087:Oxides; D013440:Sulfides; D014874:Water Pollutants, Chemical; C111959:greigite; D002857:Chromium; D012822:Silicon Dioxide; C092844:ferric oxyhydroxide; D005293:Ferritins; D007501:Iron; D002119:Calcium Carbonate; D002118:Calcium; D052203:Ferrosoferric Oxide