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Journal articles on the topic 'Nontronita'

Author: Grafiati

Published: 4 June 2021

Last updated: 13 February 2022

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1

Petit, S., F. Baron, and A. Decarreau. "Synthesis of nontronite and other Fe-rich smectites: a critical review." Clay Minerals 52, no. 4 (December 2017): 469–83. http://dx.doi.org/10.1180/claymin.2017.052.4.05.

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AbstractThe synthesis of clay minerals has been studied for decades in an attempt to better understand their formation in natural environments and more recently to obtain clay minerals with controlled compositions and properties. Even though nontronite has been synthesized successfully since 1935, the process is not a straightforward and has been poorly documented. In the present review concerning the synthesis of nontronite and other Fe-rich smectites, the experiments attempted in the past are discussed critically in light of the most recent data. Most notably, the application of relationships established recently, thanks to synthetic smectitic series, have allowed us to refine the chemical compositions of some nontronites synthesized previously.

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2

Köster, H. M., U. Ehrlicher, H. A. Gilg, R. Jordan, E. Murad, and K. Onnich. "Mineralogical and chemical characteristics of five nontronites and Fe-rich smectites." Clay Minerals 34, no. 4 (December 1999): 579–99. http://dx.doi.org/10.1180/000985599546460.

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AbstractFive Fe–bearing dioctahedral smectites (three nontronites and two Fe-rich smectites) were purified using a variety of physical and chemical procedures. The structural formulae indicate one nontronite and one Fe-rich smectite to be montmorillonitic, whereas the other three smectites are beidellitic. Mössbauer spectra showed Fe to be exclusively trivalent and were fitted with three doublets, two of which had quadrupole splittings characteristic of Fe3+ in octahedral coordination, whereas the third had a distinctly lower quadrupole splitting. Although the position of the Si–O stretching band in the infrared spectra could reflect tetrahedral Fe3+, the lack of distinctive features prevented a definitive attribution of this component to tetrahedral Fe3+. The 18O/16O data suggest that fractionation of nontronite-water at ambient temperatures (1000 lnα = 23 ± 2‰) is lower than that of Fe-rich smectite (1000 lnα = 27 ± 2‰). The estimated formation temperatures of the samples are below 70°C.

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3

Gaudin, A., O. Grauby, Y. Noack, A. Decarreau, and S. Petit. "Accurate crystal chemistry of ferric smectites from the lateritic nickel ore of Murrin Murrin (Western Australia). I. XRD and multi-scale chemical approaches." Clay Minerals 39, no. 3 (September 2004): 301–15. http://dx.doi.org/10.1180/0009855043930136.

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AbstractLateritic weathering profiles developed on serpentinized peridotites of Murrin Murrin (Western Australia) exhibit thick smectite zones (10–15 m). The smectites from plasma and fissures were characterized by XRD, chemical analyses (ICP-AES, SEM-EDX and TEM-EDX) and Mo¨ssbauer spectroscopy. These Fe-rich smectites, previously described as nontronites, are in fact more complex. Their layer charges originate from both the tetrahedral and octahedral sheets. Plasma and notably fissure smectites exhibit, from the bulk sample scale to the particle scale, large and continuous Al for (Fe+Cr) substitutions, covering a chemical gap previously described for dioctahedral smectites ranging between nontronite and beidellite end-members. Lastly, they exhibit an octahedral occupancy slightly above 2, due to a low (Mg+Ni) trioctahedral contribution. Thus, the smectites occurring in weathering profiles of ultrabasic rocks can have actual chemistries intermediate between four dioctahedral end-members (beidellite, nontronite, montmorillonite and previously rarely described ferric-montmorillonite) and a trioctahedral one ((Mg+Ni)-saponite).

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4

Corrêa, M. M., J. C. Ker, E. S. Mendonça, H. A. Ruiz, and R. S. Bastos. "Atributos físicos, químicos e mineralógicos de solos da região das Várzeas de Sousa (PB)." Revista Brasileira de Ciência do Solo 27, no. 2 (April 2003): 311–24. http://dx.doi.org/10.1590/s0100-06832003000200011.

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O presente trabalho teve por objetivo caracterizar, física, química e mineralogicamente, os solos localizados nas várzeas de Sousa (Sertão da Paraíba), bem como verificar o efeito dos cátions alcalinos e alcalino-terrosos na estabilidade das substâncias húmicas. Procurou-se, ainda, identificar os critérios de distinção de ambientes utilizados pelos pequenos agricultores e as diferentes formas de uso dos solos da região estudada. Para isso, foram selecionados, amostrados e analisados perfis de solos das classes: Neossolo Flúvico, Luvissolo, Planossolo Nátrico e Vertissolo Cromado. Constatou-se que, além do sódio, o magnésio teve participação efetiva na dispersão de argila, principalmente nos Vertissolos. Os teores de Fe2O3 foram baixos em todos os perfis, com provável predomínio das formas menos cristalinas, identificadas pelas altas relações Feo/Fed. A mineralogia cálcio-sódica da fração silte é condizente com os teores, relativamente elevados, de cálcio, magnésio e sódio, sendo, provavelmente, o principal responsável por esses valores nos solos estudados. Na fração argila de todos os solos, foi observada a presença marcante da vermiculita/esmectita e ilita. Nos Vertissolos, o teor expressivo de ferro na fração argila revela, além da presença da hematita, a ocorrência de mineral 2:1 expansivo rico em ferro, sobretudo a nontronita. O pré-tratamento para eliminação de carbonatos (HCl 0,1 mol L-1), efetuado durante o fracionamento das substâncias húmicas, resultou em aumentos de 300 e 340 % para as frações ácidos húmicos e fúlvicos, respectivamente, e redução de 60 % na fração humina, evidenciando a participação de humatos e fulvatos de cálcio e de magnésio na estabilização da matéria orgânica.

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5

Marchel, C., and H. Stanjek. "Cation ordering incis-andtrans-vacant dioctahedral smectites and its implications for growth mechanisms." Clay Minerals 47, no. 1 (March 2012): 105–15. http://dx.doi.org/10.1180/claymin.2012.047.1.105.

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AbstractDifferent types of dioctahedral smectites (nontronite, beidellite, montmorillonite) were investigated by X-ray fluorescence analysis (XRF) and Fourier transmission infrared spectroscopy (FTIR). Starting with the chemical composition of the octahedral sheet, the occupancies within the octahedral sheet were adjusted by computer simulations to fit the occupancies derived from FTIR. For bothcis-andtrans-vacant smectites the AlAl and FeFe pairs are mainly randomly distributed but seem to be aligned along OH-bonded directions. Relative to the chemical composition, AlFe pairs are enriched incis-vacant smectites and depleted in nontronites. This behaviour can be explained by the necessity to dehydrate and hydrolyse cations when they become incorporated into the structure during crystal growth. The first and second hydrolysis steps are necessary for incorporating cations intrans-vacant smectites, whereas only the first hydrolysis step is necessary forcis-vacant smectites. The corresponding difference in energy may explain why mostlycis-vacant smectites occur in low-temperature environments.

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6

WANG, M. C., and P. M. HUANG. "CATALYTIC POLYMERIZATION OF HYDROQUINONE BY NONTRONITE." Canadian Journal of Soil Science 67, no. 4 (November 1, 1987): 867–75. http://dx.doi.org/10.4141/cjss87-083.

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The catalytic power of Ca-nontronite (0.2-2 μm) in the polymerization of hydroquinone was studied. The polymerization reaction proceeded abiotically, since there was no evidence of microbial growth in the system studied. The polymerization of hydroquinone in the presence of Ca-nontronite was substantially higher in air than in an N2 atmosphere, indicating the synergistic effect of Ca-nontronite and O2 in enhancing the reaction. After a sodium metaphosphate treatment to block the edges of Ca-nontronite, both absorbances at 472 and 664 nm of the supernatant and yield of humic macro-molecules in the Ca-nontronite-hydroquinone system were significantly decreased. However, the treatment did not eliminate the catalytic effect of Ca-nontronite. The results indicate that both Fe(III) on the edges and other Lewis acid sites of Ca-nontronite contributed to promoting the polymerization of hydroquinone. IR and ESR spectra of FA (MW > 1000) and HA (MW > 1000) formed in the supernatants of the Ca-nontronite-hydroquinone system were similar to those of natural humic substances. Key words: Catalysis, nontronite, iron(III), Lewis acid, oxygen, formation of humic macromolecules

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7

Wang, Xiaodong, Jian Li, Robert D. Hart, Arie van Riessen, and Robbie McDonald. "Quantitative X-ray diffraction phase analysis of poorly ordered nontronite clay in nickel laterites." Journal of Applied Crystallography 44, no. 5 (August 18, 2011): 902–10. http://dx.doi.org/10.1107/s0021889811027786.

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Studies of the extraction of nickel from low-grade laterite ores require a much better quantitative understanding of the poorly ordered mineral phases present, including turbostratically disordered nontronite. Whole pattern refinements with nontronite X-ray diffraction data from a Western Australian nickel deposit (Bulong) using a nontronite lattice model (Pawley phase) with two space groups (P3 andC2/m) and a peaks phase group model were performed to improve the accuracy of quantitative X-ray diffraction of nickel laterite ore samples. Modifications were applied when building the new models to accommodate asymmetric peak shape and anisotropic peak broadening due to the turbostratic disorder. Spherical harmonics were used as convolution factors to represent anisotropic crystal size and strain and asymmetric peak shape when using the lattice model. A peaks phase group model was also developed to fit the anisotropic peak broadening in the nontronite pattern. The quantitative results of the new Pawley phase and peaks phase group models were compared and verified with synthetic mixtures of nontronite, quartz and goethite simulating various West Australian laterite ore compositions. The models developed in this paper demonstrate adequate accuracy for quantification of nontronite in the synthesized reference materials and should be generally applicable to quantitative phase analysis of nontronite in nickel laterite ore samples.

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8

Santos, Jean Cheyson Barros dos, Valdomiro Severino de Souza Júnior, Marcelo Metri Corrêa, Mateus Rosas Ribeiro, Maria da Conceição de Almeida, and Lucila Ester Prado Borges. "Caracterização de neossolos regolíticos da região semiárida do Estado de Pernambuco." Revista Brasileira de Ciência do Solo 36, no. 3 (June 2012): 683–96. http://dx.doi.org/10.1590/s0100-06832012000300001.

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Estudos de caracterização de solos em regiões ainda pouco exploradas, além de disponibilizarem e ampliarem a base de informações sobre as mais distintas ordens de solos do território nacional, também permitem sistematizar informações sobre suas propriedades, que poderão servir de subsídio para o desenvolvimento de práticas de manejo e uso sustentável das terras. Entre os principais solos recorrentes na região semiárida pernambucana, destacam-se os Neossolos Regolíticos, os quais perfazem aproximadamente 27 % da superfície do Estado e recobrem importantes áreas voltadas à produção agrícola, especialmente à agricultura familiar. Considerando a possibilidade de ocorrência de Neossolos Regolíticos com distintas propriedades físicas, químicas ou mineralógicas, em razão da existência de distintos contextos geológicos e climáticos ao longo do Estado de Pernambuco, o presente trabalho teve como objetivo caracterizar física, química e mineralogicamente Neossolos Regolíticos ao longo da região semiárida do Estado de Pernambuco, bem como relacionar os solos com sua litologia. Para isso, foram selecionados cinco perfis de Neossolos Regolíticos em diversos municípios do Estado de Pernambuco (P1=São Caetano, P2=Lagoa do Ouro, P3=Caetés, P4=São João e P5=Parnamirim). Os perfis foram descritos morfologicamente, coletando-se amostras de todos os horizontes do solo e da rocha do embasamento. Foram realizadas análises físicas e químicas para fins de classificação de solos, análises mineralógicas das frações grossas (cascalho e areia) por microscopia óptica e das frações silte e argila por difração de raios X, além de análises petrográficas das amostras de rochas. De acordo com os resultados, observou-se a ocorrência de solos semelhantes e com pequeno grau de desenvolvimento pedogenético, variando de medianamente a muito profundos, com sequência de horizontes A-AC-C e Cr e textura arenosa a média. Dois perfis apresentaram caráter solódico em profundidade. Todos os solos apresentaram baixos teores de matéria orgânica e P disponível. Apesar dos baixos teores de cátions trocáveis, todos os perfis são eutróficos. A assembleia mineralógica das frações cascalho, areia e silte é constituída essencialmente por quartzo, seguido de feldspatos e mica, corroborando a constituição petrográfica analisada. A caulinita é o principal argilomineral da fração argila em todos os perfis e horizontes estudados, indicando um importante processo de monossialitização em solos autóctones, em clima caracteristicamente semiárido. No perfil P2, devido à posição mais baixa do solo na paisagem, ocorreram minerais esmectíticos com misturas de fases entre montmorilonita, beidelita ou nontronita, identificados pela análise de DRX, empregando o teste de Greene-Kelly.

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9

Wang, Xiaodong, Robert D. Hart, Jian Li, Robbie G. McDonald, and Arie van Riessen. "Quantitative analysis of turbostratically disordered nontronite with a supercell model calibrated by the PONKCS method." Journal of Applied Crystallography 45, no. 6 (November 15, 2012): 1295–302. http://dx.doi.org/10.1107/s0021889812040484.

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Two calibration-based quantitative X-ray diffraction (XRD) models for turbostratically disordered Bulong nontronite, the PONKCS (partial or no known crystal structure) approach and the supercell structural model, were compared in terms of the accuracy and refinement error from Rietveld quantitative phase analysis. The PONKCS approach achieved improved nontronite quantitative results with synchrotron diffraction patterns compared with those achieved with laboratory XRD data as a result of better data quality and the use of Debye–Scherrer geometry with significantly reduced preferred orientation effects. The introduction of a peak shape modifier (spherical harmonics) to correct the quantification result is mainly useful for laboratory XRD patterns containing nontronite collected from Bragg–Brentano geometry with appreciable preferred orientation effects. A novel calibration approach for the nontronite supercell model was developed, based on the Rietveld quantitative formula in theTOPASsymbolic computation system. The calibrated supercell model achieved better accuracy (deviation within 1 wt%) and lower refinement error than the PONKCS approach because the physically based description of turbostratic disorder requires fewer refinable parameters than the PONKCS approach. The drawbacks and limitations of the supercell approach are also discussed.

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10

Grauby, Olivier, Sabine Petit, Alain Decarreau, and Alain Baronnet. "The nontronite-saponite series: An experimental approach." European Journal of Mineralogy 6, no. 1 (February 4, 1994): 99–112. http://dx.doi.org/10.1127/ejm/6/1/0099.

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11

Kułacz, Karol, and Kazimierz Orzechowski. "Nontronite and intercalated nontronite as effective and cheap absorbers of electromagnetic radiation." Dalton Transactions 48, no. 12 (2019): 3874–82. http://dx.doi.org/10.1039/c9dt00132h.

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12

Murad, E., J. D. Cashion, and L. J. Brown. "Magnetic ordering in Garfield nontronite under applied magnetic fields." Clay Minerals 25, no. 3 (September 1990): 261–69. http://dx.doi.org/10.1180/claymin.1990.025.3.02.

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AbstractMössbauer spectra of Garfield nontronite H33a were taken at temperatures between 2·5 and 37 K under longitudinally applied magnetic fields up to 9 T. While no magnetic order was apparent in the absence of an applied field above 7 K, the application of external magnetic fields led to the induction of magnetic hyperfine splitting up to at least 19 K. Variation of the applied fields allowed determination of hyperfine fields of bulk nontronite, and indicated the bulk sample to have a Néel temperature of about 20 K. The non-ideal behaviour of this nontronite, leading to the lack of magnetic order in the absence of applied magnetic fields, is in line with the frustration of antiferromagnetic order in the octahedral sheets due to the presence of about 6% of the iron content in tetrahedral sites, although some influence of magnetic dilution cannot be excluded.

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13

Baron, Fabien, Sabine Petit, Martin Pentrák, Alain Decarreau, and Joseph W. Stucki. "Revisiting the nontronite Mössbauer spectra." American Mineralogist 102, no. 7 (July 2017): 1501–15. http://dx.doi.org/10.2138/am-2017-1501x.

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14

Miller, Matthew A., Andrew S. Madden, Megan Elwood Madden, and R. Douglas Elmore. "Laboratory-Simulated Diagenesis of Nontronite." Clays and Clay Minerals 60, no. 6 (December 1, 2012): 616–32. http://dx.doi.org/10.1346/ccmn.2012.0600607.

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15

MacGregor-Ramiasa, Melanie, Christoffer Abrahamsson, Magnus Röding, and Magnus Nydén. "Magnetic alignment of nontronite dispersions." Applied Clay Science 116-117 (November 2015): 167–74. http://dx.doi.org/10.1016/j.clay.2015.08.014.

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16

Melo, Vander de Freitas, Julian Martins S. M. Mattos, and Valmiqui Costa Lima. "Métodos de concentração de minerais 2:1 secundários na fração argila visando sua identificação por difratometria de raios x." Revista Brasileira de Ciência do Solo 33, no. 3 (June 2009): 527–39. http://dx.doi.org/10.1590/s0100-06832009000300006.

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Além dos baixos teores normalmente encontrados na fração argila dos solos sob clima tropical e subtropical, o tamanho reduzido e a baixa cristalinidade dos minerais 2:1 secundários dificultam sua identificação por difratometria de raios X (DRX). Este estudo objetivou avaliar métodos químicos e físico de concentração de minerais 2:1 secundários na fração argila para facilitar a identificação por DRX, incluindo a natureza dos minerais quanto ao local de formação de cargas permanentes (lâmina tetraedral ou octaedral). Coletaram-se amostras de dois Cambissolos originados de argilito da Formação Guabirotuba na Bacia Sedimentar de Curitiba (PR): horizontes A, Bi, C1 (1,2 a 1,5 m), C2 (2,2 a 2,5 m), C3 (3,2 a 3,5 m) e C4 (4,2 a 4,5 m). Após remoção da matéria orgânica e dispersão da terra fina seca ao ar, a fração argila foi submetida a tratamentos sequenciais com ditionito-citratobicarbonato (DCB) (amostra desferrificada - remoção de óxidos de Fe pedogenéticos) e com soluções de NaOH a quente, em diferentes concentrações (0,5; 1,0; 1,5; 2,5; 3,5; 4,0; 4,5 e 5,0 mol L-1), para extração de gibbsita e caulinita, em diferentes graus. A fração argila desferrificada também foi submetida à separação física (centrifugação) em argila grossa (0,2 a 2 m) e fina (< 0,2 m). Foram realizados tratamentos auxiliares para identificar as espécies minerais 2:1 na fração argila: saturação com Mg e solvatação com etilenoglicol; saturação com K e secagem ao ar e aquecimento a 550 ºC; e saturação com Li (teste de Greene-Kelly). Os resultados mostraram que o método clássico de extração da caulinita, com solução de NaOH 5,0 mol L-1 a quente, não deve ser aplicado para concentração de minerais 2:1 secundários, pois também removeu grande parte desses minerais. O tratamento com DCB e com solução de NaOH 3,5 mol L-1 possibilitou, com maior eficiência, a concentração e identificação de minerais 2:1 secundários por DRX nas amostras dos horizontes A, Bi e C1. Nas amostras tomadas em maiores profundidades (horizontes C2, C3 e C4), devido aos maiores teores desses minerais e ao menor tamanho dos cristais (argila fina), a solução menos concentrada de NaOH (1,5 mol L-1) foi mais eficiente para esse propósito. No horizonte A, os minerais 2:1 concentraram-se na fração argila grossa, compatível com o maior grau de intemperismo desse horizonte. Identificou-se esmectita com hidroxi-Al entrecamadas nos horizontes mais superficiais (A e Bi) e esmectita nas amostras do horizonte C. A saturação com Li permitiu a identificação das esmectitas dioctaedrais montmorilonita e beidelita/nontronita. As adaptações ao métodopadrão (NaOH 5 mol L-1) favoreceram a concentração de minerais 2:1 secundários na fração argila dos solos; a concentração da solução de NaOH deve ser maior para horizontes com menor teor do mineral.

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17

Butler, Elizabeth C., Lixia Chen, Colleen M. Hansel, Lee R. Krumholz, Andrew S. Elwood Madden, and Ying Lan. "Biological versus mineralogical chromium reduction: potential for reoxidation by manganese oxide." Environmental Science: Processes & Impacts 17, no. 11 (2015): 1930–40. http://dx.doi.org/10.1039/c5em00286a.

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18

Moura, C. P. de, M. V. S. Fernandes, L. R. D. da Silva, L. C. G. Vasconcellos, R. F. do Nascimento, and A. Valentini. "N-octane catalytic isomerization with aluminium and aluminiumlanthanum pillared nontronite." Cerâmica 61, no. 360 (December 2015): 420–27. http://dx.doi.org/10.1590/0366-69132015613601901.

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Abstract Nontronite samples pillared with aluminium (Pt/Al-PilM) and aluminium-lanthanum (Pt/AlLa-PilM) were prepared from natural nontronite, characterized and tested as catalyst in n-octane hydroisomerization reaction. The results were compared with those obtained from the same reaction using commercial Y-zeolite impregnated with platinum (Pt-Y). Experiments with commercial zeolite show that platinum is essential to maintain the reactional selectivity of the products. The conversion capacities of (Pt/Al- PilM) and (Pt/AlLa-PilM) were 70% and 40%, respectively, surpassing the Pt-Y performance of 30%, but with the same selectivity. X-ray diffraction data show that organic matter oxidation followed by cationic homogenization is of paramount importance for pillared clay preparation.

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19

Delvaux, B., M. M. Mestdagh, L. Vielvoye, and A. J. Herbillon. "XRD, IR and ESR study of experimental alteration of Al-nontronite into mixed-layer kaolinite/smectite." Clay Minerals 24, no. 4 (December 1989): 617–30. http://dx.doi.org/10.1180/claymin.1989.024.4.05.

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AbstractThe formation of kaolinite from Al hydroxy interlayered Garfield nontronite has been carried out at 225°C in hydrothermal conditions. The kaolinitization process, which proceeds through mixed-layer kaolinite/smectite intermediates, was followed by XRD, IR and ESR spectroscopy, chemical analysis and charge properties. The smectite content of the clay products decreases regularly with the duration of the hydrothermal treatment. The CEC and the structural Fe content of the deferrated products show a similar trend. IR features specific to nontronite disappear and are barely detectable as the smectite content of the mixed-layer clay falls below 30%. In contrast, the ESR spectrum of nontronite is characterized by a broad g2 signal that remains even after prolonged hydrothermal treatment. The calibration of the g2 ESR signal, due to Fe-smectite, shows that the synthetic kaolinites have low Fe contents (∼ 1% Fe2O3) indicating that the kaolinitization process involves destruction of the 2:1 layers and the subsequent neoformation of kaolinite and Fe oxides. As illustrated by the study of deferrated soil clay samples, representing a weathering sequence Fe-smectite → kaolinite + Fe oxides, ESR spectroscopy proved to be a powerful Fe probe for detecting Fe-rich smectite in kaolinite/Fe-smectite mixed-layer clays.

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20

Ding, Z., and R. L. Frost. "Controlled rate thermal analysis of nontronite." Thermochimica Acta 389, no. 1-2 (July 2002): 185–93. http://dx.doi.org/10.1016/s0040-6031(02)00059-x.

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21

Jaisi, Deb P., Chongxuan Liu, Hailiang Dong, Ruth E. Blake, and Jeremy B. Fein. "Fe2+ sorption onto nontronite (NAu-2)." Geochimica et Cosmochimica Acta 72, no. 22 (November 2008): 5361–71. http://dx.doi.org/10.1016/j.gca.2008.08.022.

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22

Abrahamsson, Christoffer, Lars Nordstierna, Johan Bergenholtz, Annika Altskär, and Magnus Nydén. "Magnetically induced structural anisotropy in binary colloidal gels and its effect on diffusion and pressure driven permeability." Soft Matter 10, no. 24 (2014): 4403–12. http://dx.doi.org/10.1039/c4sm00315b.

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23

Dainyak, Lidia G., Bella B. Zviagina, Viacheslav S. Rusakov, and Victor A. Drits. "Interpretation of the nontronite-dehydroxylate Mossbauer spectrum using EFG calculations." European Journal of Mineralogy 18, no. 6 (December 20, 2006): 753–64. http://dx.doi.org/10.1127/0935-1221/2006/0018-0753.

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24

Ribeiro, Fabiana R., José D. Fabris, Joel E. Kostka, Peter Komadel, and Joseph W. Stucki. "Comparisons of structural iron reduction in smectites by bacteria and dithionite: II. A variable-temperature Mössbauer spectroscopic study of Garfield nontronite." Pure and Applied Chemistry 81, no. 8 (July 24, 2009): 1499–509. http://dx.doi.org/10.1351/pac-con-08-11-16.

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The reduction of structural Fe in smectite may be mediated either abiotically by reaction with chemical reducing agents or biotically by reaction with various bacterial species. The effects of abiotic reduction on clay surface chemistry are much better known than the effects of biotic reduction, and differences between them are still in need of investigation. The purpose of the present study was to compare the effects of dithionite (abiotic) and bacteria (biotic) reduction of structural Fe in nontronite on the clay structure as observed by variable-temperature Mössbauer spectroscopy. Biotic reduction was accomplished by incubating Na-saturated Garfield nontronite (sample API 33a) with Shewanella oneidensis strain MR-1 (FeII/total Fe achieved was ~17 %). Partial abiotic reduction (FeII/total Fe ~23 %) was achieved using pH-buffered sodium dithionite. The nontronite was also reduced abiotically to FeII/total Fe ~96 %. Parallel samples were reoxidized by bubbling O2 gas through the reduced suspensions at room temperature prior to Mössbauer analysis at 77 and 4 K. At 77 K, the reduction treatments all gave spectra composed of doublets for structural FeII and FeIII in the nontronite. The spectra for reoxidized samples were largely restored to that of the unaltered sample, except for the sample reduced to 96 %. At 4 K, the spectrum for the 96 % reduced sample was highly complex and clearly reflected magnetic order in the sample. When partially reduced, the spectrum also exhibited magnetic order, but the features were completely different depending on whether reduced biotically or abiotically. The biotically reduced sample appeared to contain distinctly separate domains of FeII and FeIII within the structure, whereas partial abiotic reduction produced a spectrum representative of FeII–FeIII pairs as the dominant domain type. The 4 K spectra of the partially reduced, fully reoxidized samples were virtually the same as at 77 K, whereas reoxidation of the 96 % reduced sample produced a spectrum consisting of a magnetically ordered sextet with a minor contribution from a FeII doublet, indicating significant structural alterations compared to the unaltered sample.

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25

Baker, Leslie L., and Daniel G. Strawn. "Temperature Effects on the Crystallinity of Synthetic Nontronite and Implications for Nontronite Formation in Columbia River Basalts." Clays and Clay Minerals 62, no. 2 (April 1, 2014): 89–101. http://dx.doi.org/10.1346/ccmn.2014.0620202.

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26

Frost, Ray L., and J. Theo Kloprogge. "Raman Spectroscopy of Nontronites." Applied Spectroscopy 54, no. 3 (March 2000): 402–5. http://dx.doi.org/10.1366/0003702001949483.

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Smectites including the iron-bearing smectites have proved difficult to measure using the techniques of Raman spectroscopy. The use of Fourier transform (FT)-Raman spectrometers using indium-gallium-arsenide detectors has enabled the spectra of a selection of high iron-bearing smectites and nontronites to be measured. Low-intensity hydroxyl stretching Raman bands were found at 3436 and 3355 cm−1 and are attributed to the Fe–FeOH unit. Low-frequency bands were observed at around 201, 163, 128, and 90 cm−1. The 90 cm−1 band is ascribed to the stretching vibration of the hydrated cation. Bands observed at around 780 and 880 cm−1 are ascribed to the hydroxyl deformation modes of the Fe–FeOH and Fe–AlOH.

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27

Gangas, N. H. J., J. van Wonterghem, S. Morup, and C. J. W. Koch. "Magnetic bridging in nontronite by intercalated iron." Journal of Physics C: Solid State Physics 18, no. 31 (November 10, 1985): L1011—L1016. http://dx.doi.org/10.1088/0022-3719/18/31/007.

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28

Ogorodova, L. P., I. A. Kiseleva, L. V. Melchakova, M. F. Vigasina, V. V. Krupskaya, and Yu Yu Bugel’skii. "Thermodynamic properties of Fe-rich smectite-nontronite." Geochemistry International 52, no. 5 (May 2014): 421–27. http://dx.doi.org/10.1134/s0016702914030057.

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29

Tang, Jessica, and Marjorie Valix. "Leaching kinetics of limonite and nontronite ores." International Journal of Environment and Waste Management 3, no. 3/4 (2009): 244. http://dx.doi.org/10.1504/ijewm.2009.026341.

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30

Frost, Ray L., and J. Theo Kloprogge. "Vibrational spectroscopy of ferruginous smectite and nontronite." Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 56, no. 11 (October 2000): 2177–89. http://dx.doi.org/10.1016/s1386-1425(00)00279-1.

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31

Köhler, Birgit. "Biogenic Nontronite from Marine White Smoker Chimneys." Clays and Clay Minerals 42, no. 6 (1994): 689–701. http://dx.doi.org/10.1346/ccmn.1994.0420605.

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32

Felix, N. S., and B. S. Girgis. "Isothermal and nonisothermal gravimetry of nontronite dehydroxylation." Journal of Thermal Analysis 35, no. 3 (May 1989): 743–50. http://dx.doi.org/10.1007/bf02057229.

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33

Gainey, S. R., E. M. Hausrath, J. A. Hurowitz, and R. E. Milliken. "Nontronite dissolution rates and implications for Mars." Geochimica et Cosmochimica Acta 126 (February 2014): 192–211. http://dx.doi.org/10.1016/j.gca.2013.10.055.

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34

Cardile, CM, CW Childs, and JS Whitton. "The effect of citrate bicarbonate dithionite treatment on standard and soil smectites as evidenced by 57Fe Mössbauer spectroscopy." Soil Research 25, no. 2 (1987): 145. http://dx.doi.org/10.1071/sr9870145.

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The 57Fe Mossbauer spectra of a selection of smectitic clay fractions of CBD-treated soil samples were measured and computer-fitted with appropriate Fe3+ and Fe2 + resonances. The shape of the Fe3+ spectral envelopes suggested that all the clays were dominated by montmorillonite, contradicting the indications of the Greene-Kelly test. Experiments with untreated and CBD-treated nontronite and montmorillonite showed, however, that the apparent contradiction was probably the result of significant disruption of the smectites by the CBD treatment. The occurrence of this disruption also casts doubt on the validity of using the Greene-Kelly test on CBD-treated samples. The computer-fitted Mossbauer spectra of nontronite with different particle sizes (specifically aggregate size) demonstrated a relationship between particle size and the line-width of the Fe3+ tetrahedral site resonance. This relationship probably reflects an increasing degree of variability in the tetrahedral site with increasing particle size.

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35

Bishop, J., J. Madejová, P. Komadel, and H. Fröschl. "The influence of structural Fe, Al and Mg on the infrared OH bands in spectra of dioctahedral smectites." Clay Minerals 37, no. 4 (December 2002): 607–16. http://dx.doi.org/10.1180/0009855023740063.

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AbstractVisible to near-infrared (NIR) reflectance spectra and mid-IR transmittance spectra are presented here for a collection of dioctahedral smectites. Analysis of the structural OH vibrations is performed by comparing the NIR combination and overtone bands with fundamental stretching and bending absorption features in the mid-IR region. Second derivatives are used to determine the actual band centres, which are often shifted slightly by a spectral continuum in the reflectance or transmittance spectra. New bands have been identified near 4170 and 4000 cm–1 in the NIR spectra of nontronite with tetrahedral substitution. A related band is observed near 4100 cm–1 for montmorillonites with substantial tetrahedral and/or octahedral substitution. These bands are correlated with the mid-IR bands near 680 cm–1 for nontronite and near 630 cm–1 for montmorillonite. Comparison of the OH overtone and combination bands with the fundamental stretching and bending vibrations gives consistent results.

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36

Komadel, P., J. Madejová, D. A. Laird, Y. Xia, and J. W. Stucki. "Reduction of Fe(III) in griffithite." Clay Minerals 35, no. 4 (September 2000): 625–34. http://dx.doi.org/10.1180/000985500547089.

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AbstractGriffithite is a trioctahedral smectite with dioctahedral domains, found in the <2 μm fraction of weathered basic rock from Griffith Park, California, USA. Crystalline admixtures (albite, calcite, quartz and maghemite) are concentrated in the 0.2 – 2 μm fraction, while the <0.06 μm fraction contains only trace amounts of other minerals. Griffithite is primarily an Fe–rich saponite with negative charge located in the tetrahedral sheets. The octahedral occupancy is ∼91%, and ∼26% of the octahedra contain trivalent atoms imparting a net positive charge to the octahedral sheet. Medium levels of Fe(III) reduction in griffithite, up to 60% of total Fe, can be achieved by adding solid sodium dithionite to clay dispersions in a citrate–bicarbonate buffer. By contrast >90% reduction of Fe(III) to Fe(II) is achieved in nontronites using the same method. The lower reducibility of Fe(III) in griffithite relative to nontronites may be due to structural differences between griffithite and nontronites, such as a more negative tetrahedral charge and a positive octahedral charge.

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37

Wu, Jun, Charles B. Roth, and Philip F. Low. "Biological Reduction of Structural Iron in Sodium-Nontronite." Soil Science Society of America Journal 52, no. 1 (January 1988): 295–96. http://dx.doi.org/10.2136/sssaj1988.03615995005200010054x.

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38

Knöchel, C., J. Thieme, S. Gleber, G. Schneider, W. Bates, and G. Schmahl. "Tomographic studies of nontronite particles in aqueous media." Journal de Physique IV (Proceedings) 104 (March 2003): 425–28. http://dx.doi.org/10.1051/jp4:20030114.

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39

Merola, Rose B., Eric D. Fournier, and Molly M. McGuire. "Spectroscopic Investigations of Fe2+Complexation on Nontronite Clay." Langmuir 23, no. 3 (January 2007): 1223–26. http://dx.doi.org/10.1021/la062467e.

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40

Ueshima, Masato. "Possible Role of Microbial Polysaccharides in Nontronite Formation." Clays and Clay Minerals 49, no. 4 (2001): 292–99. http://dx.doi.org/10.1346/ccmn.2001.0490403.

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41

Wano, M. C. "Catalysis of Nontronite in Phenols and Glycine Transformations." Clays and Clay Minerals 39, no. 2 (1991): 202–10. http://dx.doi.org/10.1346/ccmn.1991.0390212.

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42

Komadel, Peter. "Reduction and Reoxidation of Nontronite: Questions of Reversibility." Clays and Clay Minerals 43, no. 1 (1995): 105–10. http://dx.doi.org/10.1346/ccmn.1995.0430112.

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43

Heller-Kallai, L. "Reduction and Reoxidation of Nontronite: The Data Reassessed." Clays and Clay Minerals 45, no. 3 (1997): 476–79. http://dx.doi.org/10.1346/ccmn.1997.0450316.

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44

Karakassides, Michalis A. "Mössbauer and Infrared Study of Heat-Treated Nontronite." Clays and Clay Minerals 48, no. 1 (2000): 68–74. http://dx.doi.org/10.1346/ccmn.2000.0480109.

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45

Ilgen, A. G., R. K. Kukkadapu, D. R. Dunphy, K. Artyushkova, J. M. Cerrato, J. N. Kruichak, M. T. Janish, C. J. Sun, J. M. Argo, and R. E. Washington. "Synthesis and characterization of redox-active ferric nontronite." Chemical Geology 470 (October 2017): 1–12. http://dx.doi.org/10.1016/j.chemgeo.2017.07.010.

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46

Singh, Rajesh, Hailiang Dong, Qiang Zeng, Li Zhang, and Karthikeyan Rengasamy. "Hexavalent chromium removal by chitosan modified-bioreduced nontronite." Geochimica et Cosmochimica Acta 210 (August 2017): 25–41. http://dx.doi.org/10.1016/j.gca.2017.04.030.

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47

Farmer, V. C. "hk-Ordering in Aluminous Nontronite and Saponite Synthesized Near 90°C: Effects of Synthesis Conditions on Nontronite Composition and Ordering." Clays and Clay Minerals 42, no. 2 (1994): 180–86. http://dx.doi.org/10.1346/ccmn.1994.0420208.

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48

Lee, Yongmoon, Pyosang Kim, Hyeonsu Kim, and Donghoon Seoung. "Comparative Compressibility of Smectite Group under Anhydrous and Hydrous Environments." Materials 13, no. 17 (August 27, 2020): 3784. http://dx.doi.org/10.3390/ma13173784.

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High-pressure synchrotron X-ray powder diffraction studies of smectite group minerals (beidellite, montmorillonite, and nontronite) reveal comparative volumetric changes in the presence of different fluids, as pressure transmitting media (PTM) of silicone oil and distilled water for anhydrous and hydrous environments at room temperature. Using silicone oil PTM, all minerals show gradual contraction of unit-cell volumes and atomistic interplane distances. They, however, show abrupt collapse near 1.0 GPa under distilled water conditions due to hydrostatic to quasi-hydrostatic environmental changes of water PTM around samples concomitant with the transition from liquid to ICE-VI and ICE-VII. The degrees of volume contractions of beidellite, montmorillonite, and nontronite up to ca. 3 GPa are ca. 6.6%, 8.9%, and 7.5% with bulk moduli of ca. 38(1) GPa, 31(2) GPa, and 26(1) GPa under silicone oil pressure, whereas 13(1) GPa, 13(2) GPa, and 17(2) GPa, and 17(1) GPa, 20(1) GPa, and 21(1) GPa under hydrostatic and quasi-hydrostatic environments before and after 1.50 GPa, respectively.

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49

Suquet, H., C. Malard, and H. Pezerat. "Structure et proprietes d'hydratation des nontronites." Clay Minerals 22, no. 2 (June 1987): 157–67. http://dx.doi.org/10.1180/claymin.1987.022.2.04.

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RésuméLes nontronites ne présentent pas les propriétés caractéristiques des phyllosilicates 2:1 magnésiens ou alumineux à substitutions tétraédriques: domaines d'hydratation homogène, isotherme de désorption d'eau avec paliers, organisation structurale ordonnée ou semi-ordonnée. Or les analyses structurales montrent que ce sont des beidellites ferriffères et l'étude de l'effet Hofmann–Klemen confirme le taux très faible de lacunes et de substitutions octaédriques. Diverses hypothèses justifiant ces propriétés sont présentées et discutées.

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50

Gates, W. P., P. G. Slade, A. Manceau, and B. Lanson. "Site Occupancies by Iron in Nontronites." Clays and Clay Minerals 50, no. 2 (April 1, 2002): 223–39. http://dx.doi.org/10.1346/000986002760832829.

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