Showing papers on "Nontronite published in 1991"

Effects of iron oxidation state on the texture and structural order of Na-nontronite gels

Abstract: Aqueous gels of unaltered (oxidized) and chemically reduced ferruginous smectite (SWa-1 from the Source Clays Repository of The Clay Minerals Society) were characterized by transmission electron microscopy, electron diffraction, and energy-dispersive X-ray fluorescence to establish details regarding their texture, inter-layer and inter-particle arrangements, and chemical composition. Micrographs revealed that the reduction of structural Fe(III) to Fe(II) caused a consolidation of smectite particles from an extensive network of small crystals (1–6 layers thick) to distinct particles of limited size in the a-b direction and about 20–40 layers thick. The interlayer distances in the reduced sample appeared to be more uniform than in the oxidized sample, but both exhibited spacings of about 12.6 A. Chemical analysis showed no qualitative differences as a result of oxidation state. Electron diffraction patterns displayed marked differences. The pattern of the oxidized sample consisted of homogeneous rings, indicating that the stacking order in the a-b plane was turbostratic or disordered, whereas the reduced pattern exhibited much more order as evidenced by distinct spots amid low-intensity rings, suggesting that inter-layer attractive forces were stronger if Fe(II) was present in the clay crystal.

Extraction of iron oxides from sediments using reductive dissolution by titanium (III)

Abstract: A new iron oxide dissolution method designed to measure the abundance of “free” Fe oxide phases and associated elements in soils and sediments has been tested. The method employs a ternary complex of Ti(III), citrate, and ethylenediaminetetraacetate (EDTA) as a reductant and bicarbonate as a proton acceptor. The Ti(III)-citrate-EDTA-HCO3 method dissolved more synthetic amorphous ferric oxide and goethite, but less synthetic hematite, than the dithionite-citrate-HCO3 method of Mehra and Jackson. The production of acidity by the dissolution indicated that Ti(IV) is hydrolyzed to TiO2 during the extractions. The heated dithionite method dissolved 3–6 times more Al from kaolinite and nontronite standard clays than room temperature dithionite, and 4–6 times more Al than the Ti(III)-citrate-EDTA-HCO3 method. Furthermore, the release of Fe from the clay mineral samples consistently and rapidly reached a plateau during multiple extractions by the Ti(III)-citrate-EDTA-HCO3 method, indicating that a well-defined Fe oxide fraction was removed. Fe released by the dithionite method continued to increase with each extraction, suggesting that some release of structural Fe occurred. Tests on two natural sediments and one heavy mineral fraction from the Miocene Cohansey Sand in the New Jersey Coastal Plain suggested that the Ti(III)-citrate-EDTA-HCO3 method removed Fe oxides more effectively and more selectively than the dithionite method. The selectivity of the Ti(III)-citrate-EDTA-HCO3 method is enhanced by rapid extractions at room temperature and low free ligand concentrations.

A kaolin-smectite interstratification sequence from a red and black complex

Abstract: (Received 3 September 1990; revised 18 December 1990) ABSTRACT: The sequential development of kaolin by progressive alteration of smectite, involving kaolin-smectite interstratifications as a genetic link is described from a red and black complex. Mineral compositions were studied using XRD, DTA and XRF techniques. The basalt- derived soils are situated along a 600 m transect and grade in colour from dark grey (10 YR 3/1 ) to red (5 YR 3/3). The kaolin proportions in the interstratification increase almost linearly with increasing reddening up to ~80%. Whole-soil chemical analyses exhibit no significant variations in the major element composition, but dithionite extractable Fe increases along the transect from 1% to 4-16%. Hematite and goethite are the only secondary iron phases. Topographic differences are slight but sub-surface bedrock contours plus appreciable variations in sand content between red and black soils could be genetically significant. The interrelationship between dark black and red soils in the so-called "red and black complex" has intrigued soil scientists from many parts of the world. The sequences are specifically associated with basic igneous or volcanic rocks and their development is governed by topography-related differences in the degree of leaching (Ferguson, 1954; Kantor & Schwertmann, 1974; Herbillon et al., 1981; Norrish & Pickering, 1983). The conspicuous change in topsoil colour is associated with a change in clay mineral composition, with smectite dominating the black, low-lying, poorly-drained soils, and kaolinite the reddish, well-drained uplands (see above authors). The smectite species is of the nontronite or Fe-rich beidellite variety in accordance with the mafic composition of the parent rock (Paquet, 1970; Fitzpatrick & Le Roux, 1977; Herbillon et al., 1981). Progressive leaching of alkalis and alkaline earths, under oxidizing conditions, transforms smectite into kaolin with concomitant precipitation of structural Fe as secondary Fe

Detection of Tetrahedral Fe3+ Sites in Nontronite and Vermiculite by Mössbauer Spectroscopy

Abstract: Mossbauer spectra were obtained for five Ca-exchanged nontronites and one Ca-exchanged vermiculite as the 2-layer hydrates following dehydration at 200°C. Exchange of the samples with Ca2+ and subsequent dehydration resulted in the appearance of a shoulder at about −0.50 mm/s in the Mossbauer spectra of some of the samples. The appearance of these shoulders necessitated the inclusion of doublets with Mossbauer parameters corresponding to tetrahedrally-coordinated Fe3+ (IVFe3+) in the model used to fit the Mossbauer spectra. That the IVFe3+ sites detected in these samples were those in the nontronite structure was confirmed using samples whose IVFe3+ contents have been previously determined from chemical analysis. It appears that this sample preparation method allowed IVFe3+ contents to be determined to within 40%. On this basis, the IVFe3+ content appeared to be unrelated to the total Fe content for the samples studied.

Photostabilization of tetrahydro-2-(nitromethylene)-2H-1,3-thiazine adsorbed on clays

Abstract: The photochemical degradation of the insecticide tetrahydro-2-(nitromethylene)-2H-1,3-thiazine (NMH) adsorbed on montmorillonite, nontronite and hectorite was studied. In all cases, a considerable photostabilization was observed in comparison with samples of the pesticide in its free form (.)

57Fe Mössbauer Spectroscopic Study of Structural Changes During Dehydration of Nontronite: Effect of Different Exchangeable Cations

Abstract: Dehydration-induced migration of different exchangeable cations toward the layers of nontronite has been studied by Mossbauer spectroscopy. As interlayer water is removed exchangeable cations migrate toward Fe3+ sites in the tetrahedral sheets of the nontronite (IvFe3+) causing them to distort. The amount of distortion is linearly related to the ionic potential (IP) of the exchangeable cations and is greatest for cations with highest IP. Octahedral Fe3+ sites (VIFe3+) are also affected by migration of cations into the pseudohexagonal cavities. As exchangeable cations move into the pseudohexagonal cavities, interaction with VIFe3+ sites increases. The intensity of the outer VIFe3+ Mossbauer doublet increases with respect to the inner VIFe3+ doublet as the IP of the exchangeable cation increases. It appears that the exchangeable cations play a significant role in determining the thermal stability of nontronite.

Improvements in the method to differentiate montmorillonite from other smectites

Abstract: The purpose of the work was to obtain an improvement in the method, proposed by Greene-Kelly, to differentiate montmorillonite from other smectites using LiBr (substituting to LiCl) and plates of glass, Teflon or steel. For the test, montmorillonite Clay Spur and nontronite 33-a-Garfield Washington were used