The Geobiochemical Cycle of Iron

Murad, E.

doi:10.1007/978-94-009-4007-9_1

Cited by 40 publications

(34 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…These values are consistent with those expected for weakly ferromagnetic hematite with the sublattice magnetization directions in the basal plane. 36 This shows that there is no Morin transition at temperatures as low as 5 K. At this temperature, the absorption lines have a nearly Lorentzian line shape with the width 0.42 mm s Ϫ1 of lines 1 and 6. This width is slightly larger than the corresponding 0.29 mms Ϫ1 obtained for the bulk polycrystalline hematite.…”

Section: Resultsmentioning

confidence: 86%

Magnetic properties of hematite nanoparticles

et al. 2000

View full text Add to dashboard Cite

The magnetic properties of hematite (␣-Fe 2 O 3 ) particles with sizes of about 16 nm have been studied by use of Mössbauer spectroscopy, magnetization measurements, and neutron diffraction. The nanoparticles are weakly ferromagnetic at temperatures at least down to 5 K with a spontaneous magnetization that is only slightly higher than that of weakly ferromagnetic bulk hematite. At Tտ100 K the Mössbauer spectra contain a doublet, which is asymmetric due to magnetic relaxation in the presence of an electric field gradient in accordance with the Blume-Tjon model. Simultaneous fitting of series of Mössbauer spectra obtained at temperatures from 5 K to well above the superparamagnetic blocking temperature allowed the estimation of the pre-exponential factor in Néel's expression for the superparamagnetic relaxation time, 0 ϭ(6Ϯ4)ϫ10 Ϫ11 s and the magnetic anisotropy energy barrier, E bm /kϭ590 Ϫ120 ϩ150 K. A lower value of the pre-exponential factor, 0 ϭ1.8 Ϫ1.3 ϩ3.2 ϫ10 Ϫ11 s, and a significantly lower anisotropy energy barrier E bm magn /kϭ305Ϯ20 K was derived from simultaneous fitting to ac and dc magnetization curves. The difference in the observed energy barriers can be explained by the presence of two different modes of superparamagnetic relaxation which are characteristic of the weakly ferromagnetic phase. One mode involves a rotation of the sublattice magnetization directions in the basal ͑111͒ plane, which gives rise to superparamagnetic behavior in both Mössbauer spectroscopy and magnetization measurements. The other mode involves a fluctuation of the net magnetization direction out of the basal plane, which mainly affects the magnetization measurements.

show abstract

Section: Resultsmentioning

confidence: 86%

Magnetic properties of hematite nanoparticles

et al. 2000

View full text Add to dashboard Cite

show abstract

“…In addition to enhancing the potential for water-logging in soils, clay minerals such as smectites are known to be amongst those secondary minerals which can serve as sources of Fe in soils (Murad and Fischer, 1988).…”

Section: Clay Mineral Abundancementioning

confidence: 99%

Iron occurrence in soils and sediments of a coastal catchment

et al. 2010

View full text Add to dashboard Cite

“…Iron is the most abundant element in the Earth as a whole and the fourth most abundant element in the Earth's crust. In sedimentary environments the average total iron content is approximately 3.9 wt%, and the average Fe(III)/Fe(II) ratio is 1.35 (Murad & Fischer, 1988). Therefore, Fe(III) is the most abundant potential electron acceptor for microbial respiration in many sedimentary environments.…”

Section: Introductionmentioning

confidence: 99%

Importance of clay size minerals for Fe(III) respiration in a petroleum‐contaminated aquifer

et al. 2004

View full text Add to dashboard Cite

The availability of Fe(III)‐bearing minerals for dissimilatory Fe(III) reduction was evaluated in sediments from a petroleum‐contaminated sandy aquifer near Bemidji, Minnesota (USA). First, the sediments from a contaminated area of the aquifer, in which Fe(III) reduction was the predominant terminal electron accepting process, were compared with sediments from a nearby, uncontaminated site. Data from 0.5 m HCl extraction of different size fractions of the sediments revealed that the clay size fraction contributed a significant portion of the ‘bio‐available’ Fe(III) in the background sediment and was the most depleted in ‘bio‐available’ Fe(III) in the iron‐reducing sediment. Analytical transmission electron microscopy (TEM) revealed the disappearance of thermodynamically unstable Fe(III) and Mn(IV) hydroxides (ferrihydrite and Fe vernadite), as well as a decrease in the abundance of goethite and lepidocrocite in the clay size fraction from the contaminated sediment. TEM observations and X‐ray diffraction examination did not provide strong evidence of Fe(III)‐reduction‐related changes within another potential source of ‘bio‐available’ Fe(III) in the clay size fraction – ferruginous phyllosilicates. However, further testing in the laboratory with sediments from the methanogenic portion of the aquifer that were depleted in microbially reducible Fe(III) revealed the potential for microbial reduction of Fe(III) associated with phyllosilicates. Addition of a clay size fraction from the uncontaminated sediment, as well as Fe(III)‐coated kaolin and ferruginous nontronite SWa‐1, as sources of poorly crystalline Fe(III) hydroxides and structural iron of phyllosilicates respectively, lowered steady‐state hydrogen concentrations consistent with a stimulation of Fe(III) reduction in laboratory incubations of methanogenic sediments. There was no change in hydrogen concentration when non‐ferruginous clays or no minerals were added. This demonstrated that Fe(III)‐bearing clay size minerals were essential for microbial Fe(III) reduction and suggested that both potential sources of ‘bio‐available’ Fe(III) in the clay size fraction, poorly crystalline Fe(III) hydroxides and structural Fe(III) of phyllosilicates, were important sources of electron acceptor for indigenous iron‐reducing microorganisms in this aquifer.

show abstract

The Geobiochemical Cycle of Iron

Cited by 40 publications

References 32 publications

Magnetic properties of hematite nanoparticles

Magnetic properties of hematite nanoparticles

Iron occurrence in soils and sediments of a coastal catchment

Importance of clay size minerals for Fe(III) respiration in a petroleum‐contaminated aquifer

Contact Info

Product

Resources

About