title: Influence of Coprecipitated Organic Matter on Fe2+(aq)-Catalyzed Transformation of Ferrihydrite: Implications for Carbon Dynamics.
abstract: Aqueous Fe(II) is known to catalyze the abiotic transformation of ferrihydrite to more stable Fe minerals. However, little is known about the impacts of coprecipitated OM on Fe(II)-catalyzed ferrihydrite transformation and its consequences for C dynamics. Accordingly, we investigated the extent and pathway of Fe(II)-induced transformation of OM-ferrihydrite coprecipitates as a function of C/Fe ratios and aqueous Fe(II) concentrations, and its implications for subsequent C dynamics. The coprecipitated OM resulted in a linear decrease in ferrihydrite transformation with increasing C/Fe ratios. The secondary mineral profiles upon Fe(II) reaction with OM-ferrihydrite coprecipitates depend on Fe(II) concentrations At 0.2 mM Fe(II), OM completely inhibited goethite formation and stimulated lepidocrocite formation. At 2 mM Fe(II), whereas goethite was formed in the presence of OM, OM reduced the amount of goethite and magnetite formation and increased the formation of lepidocrocite. The solid-phase C content remained unchanged after reaction, suggesting that OM remains associated with Fe minerals following ferrihydrite transformation to more stable Fe minerals. However, C desorbability by H2PO4(-) from the resulting Fe minerals following reaction was enhanced. The study indicates a "lepidocrocite favoring effect" by OM and suggests that Fe(II)-catalyzed transformation of ferrihydrite may decrease OM stability in natural environments under moderately reducing conditions.
authors.affiliation: Department of Plant and Soil Sciences, Delaware Environmental Institute, University of Delaware , Newark, Delaware 19711, United States.
authors.forename: Chunmei
authors.initials: C
authors.lastname: Chen
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: Ravi
authors.initials: R
authors.lastname: Kukkadapu
authors.affiliation: Department of Plant and Soil Sciences, Delaware Environmental Institute, University of Delaware , Newark, Delaware 19711, United States.
authors.forename: Donald L
authors.initials: DL
authors.lastname: Sparks
mesh_terms: D002244:Carbon / Q000737:chemistry*; D002384:Catalysis; D011232:Chemical Precipitation; D005290:Ferric Compounds / Q000737:chemistry*; D005453:Fluorescence; D007501:Iron / Q000737:chemistry*; D008903:Minerals / Q000737:chemistry; D009930:Organic Chemicals / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors; D056928:X-Ray Absorption Spectroscopy
chemical_list: D005290:Ferric Compounds; D008903:Minerals; D009930:Organic Chemicals; D002244:Carbon; C092844:ferric oxyhydroxide; D007501:Iron