Structural nontronite

Nontoxic chlorofluorocarbons, 24 188 Nontronite (iron smectite), 6 664, 696 structure and composition, 6 669 Nonuniqueness, 24 446 Nonvessel operating common carriers (NVOCC), 25 328 Nonvolatile compounds, as taste substances, 11 566 Nonvolatile food components,... 

Fig. 1.5 The crystal structure of smectite, illustrating beidelite, montmorillonite and nontronite (Borchard 1989 after Brindley and MacEwan 1953)...

Manceau, A., Chateigner, D., and Gates, W. P. (1998). Polarised EXAFS distance least squares valence modelling (DVLS) and quantitative texture analysis approaches to the structural refinement of Garfield nontronite. Phys. Chem. Miner. 25, 347-65. 

Figure 17. Proposed phase relations where K is a mobile component and Al, Fe are immobile components at about 20°C and several atmosphere water pressure for aluminous and ferric-ferrous mica-smectite minerals. Symbols are as follows I illite G = non-expanding glauconite Ox = iron oxide Kaol = kaolinlte Mo montmorillonite smectite N nontronitic smectite MLAL aluminous illite-smectite interlayered minerals Mlpe = iron-rich glauconite mica-smectite interlayered mineral. Dashed lines 1, 2, and 3 indicate the path three different starting materials might take during the process of glauconitization. The process involves increase of potassium content and the attainment of an iron-rich octahedral layer in a mica structure.

Source Reprinted with permission from Wang, M. C., and Huang, P. M. (1994). Structural role of polyphenols in influencing the ring cleavage and related chemical reactions as catalyzed by nontronite. In Humic Substances in the Global Environment and Implications on Human Health, Senesi, N., and Miano, T. M., eds., Elsevier, Amsterdam, The Netherlands, 173-180. 

Wang, M. C, and Huang, P. M. (1994). Structural role of polyphenols in influencing the ring cleavage and related chemical reactions as catalyzed by nontronite. In Humic Substances... 

Chemical analyses and structural formulas of some iron-bearing dioctahedral montmorillonites and nontronites... 

There is considerable overlap between minerals named montmorillonite and nontronite. Many of the montmorillonite samples that overlap the nontronite field are relatively high in iron but so are a number of samples that lie in the restricted montmorillonite zone. The structural formulas indicate that there is a complete gradation between montmorillonite-beidellite and nontronite so that any boundary is arbitrary. 

Electronic Structure of Fe3 in Tetrahedral Coordination. As mentioned earlier, some Fe3 in clays may substitute for Si in the tetrahedral sheet. In the case of nontronite, the fraction of tetrahedrally coordinated iron is only a few percent. Other phyl-losilicates (such as cronstedite) can have a considerable fraction of iron in tetrahedral coordination. 

The precise location of Fe in the crystal structure of nontronite is a subject of much current interest As much as 1-15% of Fe3 may exist in the tetrahedral sheets (2-7) with the remainder in the octahedral sheets, but the precise quantitative distribution among tetrahedral, cte-octahedral, and trana-octahedral sites is unknown ... 

The IT transition in reduced SWa-1 nontronite is observed as a broad band centered near 730 nm (13,700 cm 1), which increases in intensity as the Fe2 content approaches 40% of the total Fe (Figure 9) Lear and Stucki (33) used computer simulations to relate this behavior to the number of Fe2 -0-Fe3 linkages present in the structure as a function of the Fe2 content At very high levels of reduction, the intensity of the IT transition decreases and finally almost disappears due to the formation of Fe2 -0-Fe2 linkages at the expense of the Fe2 -0-Fe3 linkages, which produce the IT transition (Figure 10). 

Figure 7 Experimental XRD spectra for odinite and calculated diagrams for hypothetical minerals using the NEWMOD program (Reynolds, 1985) are shown. The berthierine spectrum was simulated using a ferrous-aluminous 7 A clay structure with 3-6 coherent diffracting domain structure. The mixed layer 7 A/smectite mineral berthierine/nontronite was modeled using 60% berthierine layers and 3-6 layer coherent diffracting domains in a disordered (R = 0) structure (after Odin, 1988, p. 162).

Berthierine, as shown by Brindley (1982) is essentially a trioctahedral mineral, following the line of trioctahedral chlorites in Figure 7. In our simulations of the XRD spectra of odinite, we use a ferrous serpentine and a ferric dioctahedral smectite component. Translated into constituent ions of a mineral structure, this mineral combination will give a bulk average composition between nontronite (ferric, dioctahedral smectite) and berthierine (trioctahedral chlorite). 

Figure 11.1 X Ray diffraction pattern (Co Ka) for a sample of 3 1 nontronite (N) corundum (C). The poor crystallinity of the nontronite is evident from the peak broadening in the diffraction peaks. The lack of an adequate crystal structure for nontronite precluded the use of a conventional Rietveld analysis technique.

Figure 11.2 Comparison of weighed and measured values for the series of synthetic mixtures of nontronite and corundum. The analyses were derived using a modified Rietveld approach in which nontronite is defined using a file of refiection Afcfs and intensities rather than the full crystal structure. The line represents a 1 1 relationship.

It has been found surprisingly, that adsorbent clays such as bentonite, nontronite, bleaching earth, and Fuller s earth have an unusually high adsorption capacity at the natural pH value of the culture suspension not only for the ergometrin, but for all the investigated ergot alkaloids of the most diverse structures. 

Roth, C.B. and Tullock, R.J., 1972. Deprotonation of nontronite resulting from chemical reduction of structural ferric iron. Proceedings of the International Clay Conference, Madrid, 89-98. 

Manceau A, Lanson B, Drits VA, Chateigner D, Gates WP, Wu J, Huo DF, Stucki JW (2000a) Oxidation-reduction mechanism of iron in dioctahedral smectites. 1. Structural chemistry of oxidized nontronite... 

According to Savin and Lee (1988) tetrahedral aluminium and iron in the smectite structure should influence isotopic fractionation. An Fe and A1 " free smectite compared to nontronite should provide a difference in 6 0 of nearly 5 °/m- The chemical variability of the Ishirini smectites is very small. Therefore, the chemical variability of smectites on isotope fractionation is assumed to be negligible. The... 

Ueshima and Tazaki [104] describe mineral formation in the acidic polysaccharides associated with microbial cell surfaces. They find that polysaccharides, associated with extracellular polymeric substances (EPS), direct the preferential formation of nontronite, a sodium-iron (111) phyllosi-licate in simulation studies. It is suggested that the chain structure of the polysaccharides affect layer silicate orientation. They observed only Si-bearing amorphous iron hydroxides forming outside of the EPS. 

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