Effects of Octahedral-Iron Reduction and Swelling Pressure on Interlayer Distances in Na-Nontronite

Wu, Jun; Low, Philip F.; Roth, Charles B.

doi:10.1346/ccmn.1989.0370303

Cited by 45 publications

(3 citation statements)

References 17 publications

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“…These observations are also consistent with the decrease in interlayer spacing found in dithionite-reduced smectites [47]. Such profound changes in surface area with redox cycling undoubtedly alter the chemical behavior of the minerals toward plant nutrients and environmental pollutants that enter the soil.…”

Section: Basal Spacing and Cation Fixationsupporting

confidence: 81%

Microbial reduction of iron in smectite

Stucki

Kostka

2006

Comptes Rendus. Géoscience

117

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Bacteria-mediated changes in the oxidation state of iron in soil clay minerals play an important role in determining the chemical and physical properties of soils and sediments. As structural Fe(III) in the octahedral sheet of smectites is reduced to Fe(II) by bacteria, specific surface area decreases, cation exchange capacity (CEC) increases, swelling in water decreases, reactivity with organic chemicals and pesticides increases, and the potential for mineral dissolution and transformation increases. Changes in clay mineral structure due to bacterial reduction is, however, small. Because of the large potential for the redox state of soil minerals to change with natural environmental conditions, the chemical properties of the soil must be regarded as constantly changing. The resulting dynamic nature of soil behavior must be taken into account in management strategies to maximize soil fertility and structural performance.

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Section: Basal Spacing and Cation Fixationsupporting

confidence: 81%

Microbial reduction of iron in smectite

Stucki

Kostka

2006

Comptes Rendus. Géoscience

117

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“…The remaining fourth corner of each tetrahedron forms a part connecting to an adjacent octahedral sheet. The octahedral sheet is usually composed of aluminium in six-fold coordination with oxygen from the tetrahedral sheet and with hydroxyl [7,8]. Located in the interlayer are the hydrated exchangeable cations Ca 2+ , Na + , Mg 2+ , and K + , respectively.…”

Section: Introductionmentioning

confidence: 99%

Thermal Behavior of Ceramic Bodies Based on Fly Ash and Smectites

Plevová,

Vaculíková

2024

Minerals

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Clay minerals have a great influence on the resulting properties of ceramic bodies. Fly ash as a waste material from burning black coal in power plants is a potentially valuable source of oxides (Al2O3, SiO2 or Fe2O3) for this production. Considering the process of ceramic firing, it is important to understand the thermal behavior of individual ingredients. The thermal behavior of natural smectite minerals (montmorillonite, beidellite, hectorite and nontronite) and their mixtures with added fly ash at different ratios (10%, 30% and 50%) was investigated. The phase analysis was obtained using X-ray diffraction and FT-IR spectroscopy. Under heating to 1200 °C, the structural changes of smectites were divided into four steps including dehydration, dehydroxylation, decomposition and crystallization of new phases. The addition of fly ash caused a shift in the reaction temperatures for all the mentioned phases. These changes were most noticeable for mixtures with hectorite; on the contrary, they were least noticeable for beidellite mixtures. Total mixture mass loss continually decreased with increasing fly ash amount. The obtained experimental thermal data can be applicable not only in the production of ceramic bodies or energy waste processing but also in construction and ensuring the safety of municipal waste landfills.

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“…The redox properties of iron can affect the properties of the bentonite barrier. For example, under reducing conditions, Fe(III) can be reduced into Fe(II), increasing the layer charge, which can result in a decrease in the swelling capacity [8]. Redox transitions can also affect the hydraulic conductivity and layer charge of the clay.…”

Section: Introductionmentioning

confidence: 99%

Effect of Iron Chloride (II) on Bentonites under Hydrothermal Gradients: A Comparative Study between Sodium Bentonite and Calcium Bentonite

Mota-Heredia,

Cuevas,

Fernández

2024

Minerals

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This study investigates the performance of two bentonite materials, specifically MX-80 (Na-bentonite) and FEBEX (Ca-Mg-Na-bentonite), employed as engineered barriers in deep geological disposal facilities for the isolation of high-level radioactive waste, contained in metallic canisters. Experiments conducted at the laboratory scale focused on the interaction of these bentonites with FeCl2 powder, used as a soluble iron source, to observe enhanced alteration of the bentonite. The experiments were carried out under a hydrothermal gradient. A dominant Na-Cl-SO4 saline solution was put in contact with the compacted bentonites from the top, while a constant temperature of 100 °C was maintained at the bottom using a heater in contact with the layer of FeCl2. The experimental cells were examined after six months of interaction. Various changes in the physical and chemical properties of the bentonites were observed. An increase in the water content, a reduction in the specific surface area and cation exchange capacity, changes in the distribution of aqueous species, and the formation of secondary minerals were observed. Reaction products formed at the bentonite interface with FeCl2, primarily comprising akaganeite, goethite, and hematite. The smectites showed evident structural modifications, with an enrichment in iron content, and a shift in the exchangeable ion distribution in the case of MX-80 bentonite. This work provides valuable insights into the complex interactions between bentonite barriers and materials that dissolve iron, serving as proxies for deep geological disposal environments and indicating the potential long-term behavior, taking into account higher concentrations of dissolved iron than those expected in a real repository.

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Effects of Octahedral-Iron Reduction and Swelling Pressure on Interlayer Distances in Na-Nontronite

Cited by 45 publications

References 17 publications

Microbial reduction of iron in smectite

Microbial reduction of iron in smectite

Thermal Behavior of Ceramic Bodies Based on Fly Ash and Smectites

Effect of Iron Chloride (II) on Bentonites under Hydrothermal Gradients: A Comparative Study between Sodium Bentonite and Calcium Bentonite

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