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Ferric Hydroxide (ferric + hydroxide)

Distribution by Scientific Domains

Earth and Environmental Science	40%

Selected Abstracts

The potential significance of microbial Fe(III) reduction during deposition of Precambrian banded iron formations

GEOBIOLOGY, Issue 3 2005
K. O. KONHAUSER
ABSTRACT During deposition of late Archean,early Palaeoproterozoic Precambrian banded iron formations (BIFs) the downward flux of ferric hydroxide (Fe(OH)3) and phytoplankton biomass should have facilitated microbial Fe(III) reduction. However, quantifying the significance of such a metabolic pathway in the Precambrian is extremely difficult, considering the post-depositional alteration of the rocks and the lack of ideal modern analogues. Consequently, we have very few constraints on the Fe cycle at that time, namely (i) the concentration of dissolved Fe(II) in the ocean waters; (ii) by what mechanisms Fe(II) was oxidized (chemical, photochemical or biological, the latter using either O2 or light); (iii) where the ferric hydroxide was precipitated (over the shelf vs. open ocean); (iv) the amount of phytoplankton biomass, which relates to the nutrient status of the surface waters; (v) the relative importance of Fe(III) reduction vs. the other types of metabolic pathways utilized by sea floor microbial communities; and (vi) the proportion of primary vs. diagenetic Fe(II) in BIF. Furthermore, although estimates can be made regarding the quantity of reducing equivalents necessary to account for the diagenetic Fe(II) component in Fe-rich BIF layers, those same estimates do not offer any insights into the magnitude of Fe(III) actually generated within the water column, and hence, the efficiency of Fe and C recycling prior to burial. Accordingly, in this study, we have attempted to model the ancient Fe cycle, based simply on conservative experimental rates of photosynthetic Fe(II) oxidation in the euphotic zone. We estimate here that under ideal growth conditions, as much as 70% of the biologically formed Fe(III) could have been recycled back into the water column via fermentation and organic carbon oxidation coupled to microbial Fe(III) reduction. By comparing the potential amount of biomass generated phototrophically with the reducing equivalents required for Fe(III) reduction and magnetite formation, we also hypothesize that another anaerobic metabolic pathway might have been utilized in the surface sediment to oxidize the fermentation by-products. Based on the premise that the deep ocean waters were anoxic, this role could have been fulfilled by methanogens, and maybe even methanotrophs that employed Fe(III) reduction. [source]

Enhancing effect of chemically reduced gold on surface Raman scattering for organic sulfides chemisorbed on iron

JOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2001
Yun Lu
Chemically reduced gold particles on an organic sulfide-covered plate can effectively enhance surface Raman scattering signals. This method was used to investigate the adsorption states of 4-aminophenyl disulfide and benzyl disulfide attached to the iron surface by Fourier transform surface-enhanced Raman scattering. The results indicate that these sulfide molecules can be chemisorbed perpendicularly and form a self-assembled film dotted with ferric hydroxide on the iron surface. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Role of iron chemistry in controlling the release of pollutants from resuspended sediments

REMEDIATION, Issue 1 2005
Anne Jones-Lee
Aquatic sediments often contain a large number of chemical contaminants that are potential pollutants. It is often presumed that such contaminants are released to the water column during sediment resuspension and, in there, adversely impact aquatic life and other beneficial uses of the water. However, extensive laboratory and field studies of about 100 contaminated sediments from across the United States that specifically addressed this type of release showed that of about 30 common heavy metals, organic compounds, and other potential pollutants, only manganese II and ammonia were released to then remain in the water column after sediment resuspension. These results indicated that the chemistry of aqueous iron controls the availability of many contaminants in resuspended sediment. The formation of ferric hydroxide during sediment suspension into the water column, as a result of the reaction between ferrous iron in the sediments and dissolved oxygen in the water column, leads to rapid scavenging of many contaminants in the Fe(OH)3 precipitate. The scavenged contaminants are redeposited in the sediments. This article reviews the role of the aqueous chemistry of iron as it relates to controlling the release of potential pollutants from resuspended sediments. © 2005 Wiley Periodicals, Inc. [source]

Biologically mediated mobilization of arsenic from granular ferric hydroxide in anaerobic columns fed landfill leachate

BIOTECHNOLOGY & BIOENGINEERING, Issue 6 2008
Irail Cortinas
Abstract To gain insight on the fate of arsenic (As) from drinking water treatment residuals in landfills, the mobilization of arsenate adsorbed onto granular ferric hydroxide (GFH) was studied in continuous anaerobic columns fed with a synthetic landfill leachate. The release of As was compared in biologically active and abiotic columns. More than 150 days of incubation were required before noteworthy As release occurred. After 400 days of operation, 19% of the As was mobilized as identified species in the biologically active column, which was 25.5-fold greater than that of the abiotic column. Fine colloids accounted for up to 81% of the As released. Arsenite was the predominant species identified in filtered (0.45 µm) effluent samples. Dimethylarsinic acid and monomethylarsonic acid were also observed as metabolites. During column operation, approximately 30% of the iron (hydr)oxide mass was lost and most of the mass loss was attributed to changes in iron mineralogy that could be demonstrated in a batch bioassay. The results indicate that As-laden GFH residuals from drinking water treatment are subject to mobilization in municipal landfills and that biologically mediated changes in the iron mineralogy may play an important role in the mobilization mechanism. Biotechnol. Bioeng. 2008;101: 1205,1213. © 2008 Wiley Periodicals, Inc. [source]