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Limitations of the ferrozine method for quantitative assay of mineral systems for ferrous and total iron 总被引：1，自引：0，他引：1
Alexandre S. Anastácio Hae-In Yoo Joseph W. Stucki 《Geochimica et cosmochimica acta》2008,72(20):5001-5008
The quantitative assay of clay minerals, soils, and sediments for Fe(II) and total Fe is fundamental to understanding biogeochemical cycles occurring therein. The commonly used ferrozine method was originally designed to assay extracted forms of Fe(II) from non-silicate aqueous systems. It is becoming, however, increasingly the method of choice to report the total reduced state of Fe in soils and sediments. Because Fe in soils and sediments commonly exists in the structural framework of silicates, extraction by HCl, as used in the ferrozine method, fails to dissolve all of the Fe. The phenanthroline (phen) method, on the other hand, was designed to assay silicate minerals for Fe(II) and total Fe and has been proven to be highly reliable. In the present study potential sources of error in the ferrozine method were evaluated by comparing its results to those obtained by the phen method. Both methods were used to analyze clay mineral and soil samples for Fe(II) and total Fe. Results revealed that the conventional ferrozine method under reports total Fe in samples containing Fe in silicates and gives erratic results for Fe(II). The sources of error in the ferrozine method are: (1) HCl fails to dissolve silicates and (2) if the analyte solution contains Fe3+, the analysis for Fe2+ will be photosensitive, and reported Fe(II) values will likely be greater than the actual amount in solution. Another difficulty with the ferrozine method is that it is tedious and much more labor intensive than the phen method. For these reasons, the phen method is preferred and recommended. Its procedure is simpler, takes less time, and avoids the errors found in the ferrozine method. 相似文献
2.
Reduction of octahedral Fe in the crystalline structure of smectites influences, possibly controls, surface-sensitive physical and chemical properties. The purpose of this study was to investigate if reduction of structural Fe by Na-dithionite or bacteria affects the chemical environment of constituent cations in montmorillonite, employing solid state multinuclear (29Si and 27Al) magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Reduction of structural Fe resulted in a positive (down field) chemical shift of the main Si Q3 (Q3(0Al)) site which was strongly correlated with Fe(II) content and inferred that distortions in Si-OT (T=Si, Al) bond angles and Si-O bond lengths occur with increasing layer charge. The line width (W) of the 29Si Q3 signal also increased with increasing levels of reduction. No change occurred in the position of the peak maximum for the octahedral Al (27AlVI) signal; however, an increased W was observed for this peak with increasing Fe(II) content. These results are attributed to decreases in Si-O-T bond angles and Si-O bond distances, corresponding to a better fit between the tetrahedral and octahedral sheets brought about by the presence of Fe(II) in the clay structure. The increased 27AlVI signal width (W) may also be due to a lessening of the paramagnetic influence of Fe(III) nuclei and enhancement of 27AlVI signals with different quadrupole coupling constants (QCC). Multinuclear MAS NMR analyses of dithioniteand microbially-reduced montmorillonite indicate that reduction of structural Fe caused reversible changes in the smectite structure, at least as far as this method could discern. 相似文献
3.
The morphology of the Alpine and adjacent landscapes is directly related to glacial erosion and associated sediment transport.
Here we report the effects of glacio-hydrologic erosion on bedrock topography in the Swiss Plateau. Specifically, we identify
the presence of subsurface valleys beneath the city of Bern and discuss their genesis. Stratigraphic investigations of more
than 4,000 borehole data within a 430 km2-large area reveal the presence of a network of >200 m-deep and 1,000 m-wide valleys. They are flat floored with steep sided
walls and are filled by Quaternary glacial deposits. The central valley beneath Bern is straight and oriented towards the
NNW, with valley flanks more than 20° steep. The valley bottom has an irregular undulating profile along the thalweg, with
differences between sills and hollows higher than 50–100 m over a reach of 4 km length. Approximately 500 m high bedrock highlands
flank the valley network. The highlands are dissected by up to 80 m-deep and 500 m-broad hanging valleys that currently drain
away from the axis of the main valley. We interpret the valleys beneath the city of Bern to be a tunnel valley network which
originated from subglacial erosion by melt water. The highland valleys served as proglacial meltwater paths and are hanging
with respect to the trunk system, indicating that these incipient highland systems as well as the main gorge beneath Bern
formed by glacial melt water under pressure. 相似文献
4.
Lake Ägeri hosts three crayfish species: Austropotamobius torrentium, Astacus astacus and Astacus leptodactylus. To study the interspecific competition and a possible scenario of displacement, we monitored the distribution and relative densities of the different species during the years 1996-1999 by SCUBA diving. We examined the association of the species with different types of substrate and investigated the frequency of limb loss and the life history characteristics of the three species.¶A. leptodactylus was found at more sites than A. astacus and A. torrentium. It was also present in much higher densities than the other two species. A. torrentium preferred areas with hard substrate, whereas A. astacus was more often found at sites with soft substrate and reed vegetation. A. leptodactylus was observed on soft and hard substrate. The frequency of limb loss was highest in A. astacus and more frequent at sites with a high density of A. leptodactylus. Limb loss in A. leptodactylus and A. torrentium was more frequent at sites with high self-densities. Females of the two Astacus species carried more eggs than A. torrentium females. The eggs of A. astacus were larger than the eggs of the other two species. Juveniles of A. leptodactylus grew significantly faster in their first year than juveniles of A. astacus and A. torrentium. During the four years of the study A. leptodactylus expanded its range along the southeastern shore of Lake Ägeri. At the northwestern border of its distribution the portion of A. leptodactylus had slightly increased by the end of the study period. In two areas of the lake the population of A. astacus and A. leptodactylus declined between 1997 and 1999. 相似文献
5.
Four smectites with different total Fe contents (two nontronites, one ferruginous smectite, and one montmorillonite) were
reduced to obtain a range of Fe(II)/Fe(III) ratios and their magnetic properties measured with a SQUID (superconducting quantum
interference device) as a function of applied magnetic field strength at 5 K and as a function of temperature in a field of
0.1 T. The unaltered nontronite and ferruginous smectite specimens showed antiferromagnetic coupling, whereas the coupling
in the reduced samples was ferromagnetic; the paramagnetic Curie temperature increased with increasing Fe(II) content. Data
collected after cooling samples in both the presence and absence of an external magnetic field of 0.1 T showed that at low
temperatures the reduced (ferromagnetic) nontronite and ferruginous smectite samples exhibit a memory effect of previous magnetic
field exposure consistent with superparamagnetic or spin glass behavior. The superparamagnetic/ferromagnetic transition temperature,
T
f
, increased linearly with increasing Fe(II) content for each of the nontronites, but the relationship between T
f
and Fe(II) content differed for different clays, thus demonstrating that T
f
is sensitive to isomorphous substitutions in the clay structure. The montmorillonite was paramagnetic in both oxidized and
reduced forms.
Received: 23 March 1999 / Revised, accepted: 27 August 1999 相似文献
6.
The in situ alteration of Fe redox states in subsurface soils by bacteria, otherwise known as bioreduction, may play a key role in the immobilization of hazardous redox active metals such as U, Tc, and Cr. The objective of this study was to characterize changes in Fe mineralogy occurring in a subsurface soil as a result of biostimulation in order to evaluate the bioremediation potential of this approach. Biostimulation was achieved by injecting glucose into the soil through a small well next to a sampling well. Cores taken from the sampling well were analyzed by variable-temperature 57Fe Mössbauer spectroscopy. Results revealed that biostimulation resulted in an overall loss of Fe from the system and major changes in the distribution of its oxide and oxyhydroxide mineral forms. Compared to the non-biostimulated soil, the spectral components assigned to goethite were greatly diminished in intensity in the samples that had been biostimulated, whereas the hematite component was appreciably increased. The Fe(II):Fe(III) ratio in the non-oxide phase (aluminosilicate clay minerals) also increased, indicating that the bioreduction processes in the soil also affected the redox state of Fe in the constituent clay minerals. 相似文献
7.
Joseph W. Stucki 《Comptes Rendus Geoscience》2011,343(2-3):199-209
The oxidation state of Fe in soils is one of the few properties that can be altered in situ and is known to have a large effect on chemical and physical properties. Understanding this phenomenon enables the possible manipulation or management of the soil in such a way as to maximize the benefit of such changes in properties. The effects of redox cycles, however, are less understood because most studies have focused only on a single reduction event. The purpose of this report is to review the current state of knowledge of the effects of redox cycles on clay and soil behavior, with the hope that this background will encourage further investigations of these processes. Evidence clearly indicates that the means by which reduction of Fe in clay minerals occurs significantly influences the potential reversibility of the process. 相似文献
8.
K. Stucki S.K. Solanki I. Rüedi J.O. Stenflo A. Brković U. Schühle K. Wilhelm M.C.E. Huber 《Astrophysics and Space Science》1998,264(1-4):53-61
We present a preliminary analysis of spectral lines obtained with the SUMER instrument (Solar Ultraviolet Measurements of
Emitted Radiation) onboard the Solar and Heliospheric Observatory (SOHO), as observed during three observing campaigns. From
the 70 observed spectral lines, we selected 12, representing 9 ions or atoms, in order to analyse line intensities, shifts
and widths in polar coronal holes as well as in the normal quiet Sun.
We find that coronal lines show a distinct blueshift in coronal holes relative to the quiet Sun at equal heliospheric angle,
while there is no evidence for such a shift for lines formed at temperatures below 105K. The widths of lines formed at temperatures above 3 – 104K are slightly increased inside the coronal hole, but unaffected for lower temperatures. Intensity measurements clearly show
the center-to-limb variation, as well as an intensity diminution inside the coronal hole for lines formed above approximately
105K.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Brázdil Rudolf Stucki Peter Szabó Péter Dobrovolný Petr Řezníčková Ladislava Kotyza Oldřich Valášek Hubert Dolák Lukáš Zahradníček Pavel Suchánková Silvie 《Theoretical and Applied Climatology》2018,132(3-4):1201-1216
Theoretical and Applied Climatology - One of the most disastrous windstorms to take place over the Czech Lands occurred on the night of 26/27 October 1870. It is here analysed through the use of... 相似文献
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