The role of iron in the weathering of a climosequence of soils derived from schist

Soil Research ◽  
1991 ◽  
Vol 29 (3) ◽  
pp. 387 ◽  
Author(s):  
LP Aldridge ◽  
GJ Churchman
Keyword(s):  
New Zealand ◽  
Mössbauer Spectra ◽  
Ferric Ions ◽  
Ferrous Ions ◽  
Rock Samples ◽  
Mossbauer Spectra ◽  
Muscovite Mica ◽  
Primary Minerals ◽  
Close Parallel

Mossbauer spectra were obtained of the whole soil and clay fractions and some of the sand fractions, as well as some rock samples that were taken from eight soils forming a climosequence on schist in South Island, New Zealand. They show that the main changes in iron across the sequence involve the oxidation of ferrous ions in muscovite mica and its initial weathering products to ferric ions in these minerals and also in oxyhydroxides. The extremes of weathering in the sequence led to the mobilization of iron from primary minerals in soils at the surface of profiles into oxyhydroxides that were deposited lower down in these profiles. While these changes in iron have occurred alongside the loss of K+ from the interlayers of the micas to form expanded phases, there is not a close parallel between the changes on oxidation and those from the initial loss of interlayer potassium.

Magnetische und Mößbauer-spektroskopische Untersuchungen von zeolithischen Eisenkontakten/ Magnetic and Mössbauer Spectroscopic Studies of Iron-Clusters in Zeolites

1975 ◽  
Vol 30 (12) ◽  
pp. 1627-1632 ◽  
Author(s):  
F. Schmidt ◽  
W. Gunsser ◽  
A. Knappwost
Keyword(s):  
Magnetic Susceptibility ◽  
Temperature Dependence ◽  
Mössbauer Spectra ◽  
Bulk Material ◽  
Spectroscopic Studies ◽  
Ferrous Ions ◽  
Iron Clusters ◽  
Mossbauer Spectra

Abstract Iron clusters have been prepared within zeolite holes by reduction of zeolites containing ferrous ions. The diameter of these particles must therefore be smaller than 13 Å. They are super-paramagnetic and their Mössbauer spectra show no HFS, even at 4 K.The temperature dependence of the magnetic susceptibility of the unreduced zeolites obeys a Curie-Weiss law with peff = 4,54 μB and Θ = 105 K. The Weiss curves of the reduced samples lie distinctly below those of the bulk material.

Leaching of Zinc Sulfide by Thiobacillus ferrooxidans: Experiments with a Controlled Redox Potential Indicate No Direct Bacterial Mechanism

1998 ◽  
Vol 64 (10) ◽  
pp. 3570-3575 ◽  
Author(s):  
T. A. Fowler ◽  
F. K. Crundwell
Keyword(s):  
Redox Potential ◽  
Zinc Sulfide ◽  
Thiobacillus Ferrooxidans ◽  
Experimental Period ◽  
Electrolytic Cell ◽  
Ferric Ions ◽  
Ferrous Ions ◽  
Bacterial Leaching ◽  
Dissolved Iron

ABSTRACT The role of Thiobacillus ferrooxidans in bacterial leaching of mineral sulfides is controversial. Much of the controversy is due to the fact that the solution conditions, especially the concentrations of ferric and ferrous ions, change during experiments. The role of the bacteria would be more easily discernible if the concentrations of ferric and ferrous ions were maintained at set values throughout the experimental period. In this paper we report results obtained by using the constant redox potential apparatus described previously (P. I. Harvey and F. K. Crundwell, Appl. Environ. Microbiol. 63:2586–2592, 1997). This apparatus is designed to control the redox potential in the leaching compartment of an electrolytic cell by reduction or oxidation of dissolved iron. By controlling the redox potential the apparatus maintains the concentrations of ferrous and ferric ions at their initial values. Experiments were conducted in the presence of T. ferrooxidans and under sterile conditions. Analysis of the conversion of zinc sulfide in the absence of the bacteria and analysis of the conversion of zinc sulfate in the presence of the bacteria produced the same results. This indicates that the only role of the bacteria under the conditions used is regeneration of ferric ions in solution. In this work we found no evidence that there is a direct mechanism for bacterial leaching.

Mössbauer effect in the system Ca2Fe2O5-Ca2FeAlO5

1967 ◽  
Vol 20 (5) ◽  
pp. 859 ◽  
Author(s):  
HJ Whitfield
Keyword(s):  
Magnetic Structure ◽  
Octahedral Site ◽  
Mössbauer Spectra ◽  
Mossbauer Spectrum ◽  
Ferric Ions ◽  
Mossbauer Effect ◽  
Mossbauer Spectra ◽  
Tetrahedral Sites ◽  
Hyperfine Splittings ◽  
Calcium Ferrites

Mossbauer spectra were measured on Ca2Fe2O5, Ca2Fe1.5Al0.5O5, Ca2FeAlO5, and Ca2Fe0.67Al1.33O5 at temperatures from 95�K to above the Neel points. The Mossbauer spectrum of Ca2Fe2O5 below its Neel point shows lines which were assigned to tetrahedral and octahedral site ferric ions on the basis of the observed isomer shifts and hyperfine splittings. The Mossbauer spectra of the aluminium-substituted calcium ferrites give unequivocal evidence that the aluminium goes preferentially into tetrahedral sites. A four-sublattice magnetic structure is suggested for Ca2Fe2O5.

Mossbauer spectra of proto-ferrihydrite at 77 K and 295 K, and a reappraisal of the possible presence of akaganeite in New Zealand soils

Soil Research ◽  
1980 ◽  
Vol 18 (2) ◽  
pp. 245 ◽  
Author(s):  
CW Childs ◽  
JH Johnston
Keyword(s):  
New Zealand ◽  
Mössbauer Spectra ◽  
Mossbauer Spectra

The Mossbauer spectra of a synthetic proto-ferrihydrite and a synthetic aluminous proto-ferrihydrite are similar broad paramagnetic doublets at both 77 K and 295 K, with � ~ 0.75 mm s-1 and � ~ 0.33 mm s-1 (295 K), ~ 0.43 mm s-1 (77 K). Each spectrum can be fitted by two Lorentzian doublets, having � ~ 0.60mm s-1, 0.95 mm s-1, but the iron nuclei probably exist in a range of very similar sites, related to the poorly ordered nature of the material, rather than in two specific sites. An earlier assignment of akagankite as one of the iron-containing minerals in some soil and soil concretion samples, from Mossbauer evidence, is now considered to be an error. Those peaks attributed previously to akagankite can equally well be accounted for in terms of ferrihydrite phases, and this is supported by evidence from other techniques.

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