Goethite Mossbauer

Fig. 8.31 Left) In the Mossbauer spectrum taken in the Columbia Hills at a rock called Clovis the mineral goethite (GT) (a-FeOOH) could be identified. GT is a clear mineralogical evidence for aqueous processes on Mars. Right) The rock Clovis is made out of rather soft material as indicated by the electric drill-current when drilling the - - I cm deep hole seen in the picture. Drill fines are of brownish color. The pattern to the right of the drill hole was made by bmshing the dust off the surface by using the RAT...

On the basis of a number of physico-chemical methods (Mossbauer spectroscopy, electron diffraction, EXAFS) the iron cores of naturally occurring haemosiderins isolated from various iron-loaded animals and man (horse, reindeer, birds and human old age) were consistently shown to have ferrihydrite-like iron cores similar to those of ferritin (Ward et ah, 1992, 2000). In marked contrast, in the tissues of patients with two pathogenic iron-loading syndromes, genetic haemochromatosis and thalassaemia, the haemosiderins isolated had predominantly amorphous ferric oxide and goethite cores, respectively (Dickson etah, 1988 Mann etah, 1988 ... 

Spectroscopic techniques may provide the least ambiguous methods for verification of actual sorption mechanisms. Zeltner et al. (Chapter 8) have applied FTIR (Fourier Transform Infrared) spectroscopy and microcalorimetric titrations in a study of the adsorption of salicylic acid by goethite these techniques provide new information on the structure of organic acid complexes formed at the goethite-water interface. Ambe et al. (Chapter 19) present the results of an emission Mossbauer spectroscopic study of sorbed Co(II) and Sb(V). Although Mossbauer spectroscopy can only be used for a few chemical elements, the technique provides detailed information about the molecular bonding of sorbed species and may be used to differentiate between adsorption and surface precipitation. 

Final justification for using terms such as inner- or outer-sphere awaits direct spectroscopic confirmation. Electron Spin Resonance, Mossbauer, and Fourier Transform Infrared-Cylindrical Internal Reflection Spectroscopic techniques are being used to establish the structure of surface complexes (see, e.g., McBride, Ambe et al., and Zeltner et al., this volume). The potential for using EXAFS (extended x-ray absorption fine structure) to establish the type of surface complex for Pb + adsorbing onto goethite is currently being undertaken in our laboratory. 

Fig. 7.5 Room temperature Mossbauer spectra and distributions of magnetic hyperfine fields for four goethites, decreasing in crystallinity from a to d (Murad, 1982a, with permission).

The laboratory derived model of hematite formation in soils via ferrihydrite has received general acceptance. So far, it is the only way to produce hematite at ambient temperatures and in the pH range of soils. Support from soil analysis, however, is meagre. Hematite is usually associated with other Fe oxides, mainly with goethite but not with ferrihydrite. There seems to be only one report of a ferrihydrite-hema-tite association (based on XRD and Mossbauer spectra) viz. in several andisols formed from basalt in the warm and moist climate of Hawaii (Parfitt et al., 1988). In this case, in addition to the low age of the soils, high release of Si may retard the transformation of ferrihydrite to hematite, whereas normally, the rate of transformation of ferrihydrite seems to be higher than that of ferrihydrite formation, so that this mineral does not persist. 

De Endredy, A.S. (1963) Estimation of free iron oxides in soils and clays by a photolytic method. Clay Min. Bull. 5 209-217 de Faria, D.L.A. Venancio Silva, S. de Oliveira, M.T. (1997) Raman Microspectroscopy of some iron oxides and oxyhydroxides. J. Raman Spectrosc. 28 873-878 De Grave, E. Vandenberghe, R.E. (1986) 57Fe Mossbauer effect study of well-crystallized goethite (a-FeOOH) Hyp. Interact. 28 643-646... 

De Grave, E. Vochten, R. Quenard, O. Van San, E. Desseyn, Ei. Rousset, A. (1999) Mossbauer characterisation of the products resulting from hydrothermal treatments of nanosized goethite. NanoStruct. Mater. 11 493-504... 

Galvez, N. Barr6n,V. Torrent,. J. (1999 a) Effect of phosphate on the crystallization of hematite, goethite, and lepidocrodte from ferrihydrite. Clays Clay Miner. 47 304-311 Gancedo, J.R. Grada, M. Marco, J.F. Pala-dos, J. (1988) Comparative Mossbauer and SEM study of the corrosion reaction of iron and weathering steel in SO2 polluted atmospheres. Hyperfine Interactions 41 637-640... 

Goodman, B.A. Cheshire, M.V. (1987) Characterization of iron-fulvic acid complexes using Mossbauer and FPR spectroscopy. Sci. Total Fnviron. 62 229-240 Goodman, B.A. Lewis, D.G. (1981) Mossbauer spectra of aluminous goethites (a-FeOOH). J. Soil Sci. 32 351-363 Goodman, B.A. (1988) An introduction to physical and chemical principles. In Studd, J.W. Goodman, B.A. Schwertmann, U. (eds.) Iron in soils and day minerals. D. Reidel Publ. Co., Dordrecht, Holland, NATO ASI Sen 217 19-36... 

J. Koch, C.J.W. (1983) A new interpretation of Mossbauer spectra of microcrystalline goethite super-ferromagnetic" or superspin-glass" behavior J. Magn. Mag. Mat. 40 163-174... 

E. Stiers,W. (1986) Fe Mossbauer effect study of Mn-substituted goethite and hematite. Hyperfme Interactions 29 1157-1160... 

There appear to be two possible explanations for these central peaks in the natural hematite. One is that some of the ferric material is actually not hematite but is bound to clay that might be present. Other workers (11) obained similar results when they prepared samples of iron compounds absorbed on kaolinite or bentonite. The second reason concerns the effect of small crystal size on Mossbauer spectra and perhaps is better illustrated for goethite. 

Figure 2 The Mars Exploration Rover Spirit s Mossbauer spectrometer. The hydroxyl containing mineral goethite (FeOOH) has been identified with this spectrometer in the Columbia Hills of Mars. This finding produced strong evidence for past water activity in the area that Spirit has been exploring. (Reproduced from web page with permission G Klingelhofer)...

Fe Mossbauer spectra of the mature teeth (Fig. 18) showed two components with different magnetic hyperfine field splitting values. Whereas the major component gave six-line magnetically split spectra characteristic of stoichiometric goethite (a-FeOOH) at all tempera-... 

The method produces ca. 5-6 g goethite of low crystallinity and a surface area of about 80 m /g. The crystals resemble goethites from various natural environments. An X-ray diffractogram is shown in Fig. 5-9, an EM photo in Fig. 5-10 and a Mossbauer spectrum in Fig. 5-11. An X-ray... 

Murad, E. and Sehwertmann, U. (1983) The influenee of aluminium substitution and crystallinity on the MOssbauer spectra of goethite. Clay Min. 18 301-312. 

Properties XRD pattern, Mossbauer spectrum available [1318]. PZC/IEP of hematite-goethite composite is presented in Table 3.468. 

In this work, the possibilities of using Fe Mossbauer spectrometry in corrosion research are reviewed in the case of three accelerated corrosion tests in chloride environments. Some suggestions for further research in this field are also proposed. Before introducing these examples, we will briefly discuss some models used to fit some of the iron phases in rust layers, such as goethite, akaganeite, and spinel phases. Additional information for other iron phases can be found elsewhere [I 1-13,19-22,26]. 

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