Oxidation-Reduction Mechanism of Octahedral Iron in Mica Type Structures

Ismail, F

doi:10.1097/00010694-197009000-00004

Cited by 15 publications

(12 citation statements)

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“…Contrary to the above findings, a change in LC when structural Fe changes its valency, in accord with the Gruner (1934) hypothesis, was inferred by Ismail (1969Ismail ( , 1970 and Barshad and Kishk (1970). Ismail (1969) states that after Fe(II) oxidation, "The change in surface charge was measured by the amount of Na and K that diffused to the oxidizing solution".…”

Section: Discussionmentioning

confidence: 61%

“…One hypothesis (Gruner, 1934) suggests that a balancing loss of interlayer cations occurs when structural Fe(II) is oxidized. This hypothesis was supported by Ismail (1969Ismail ( , 1970 and by Barshad and Kishk (1970), who reported a significant change in layer charge when octahedral Fe changed its valency. On the other hand, data published by Newman and Brown (1966), Raman and Jackson (1966), Newman (1967), Roth et al (1968Roth et al ( , 1969, Leonard andWeed (1970), Farmer et al (1971), Robert (1971) showed that the decrease in layer charge (in mequiv) of K-depleted trioctahedral micas was always unequal to the amount of Fe(II) oxidized (in mmole).…”

Section: Introductionmentioning

confidence: 75%

“…." according to Ismail (1970). This would involve evolution of H2; however, H 2 is well known to be a stronger reductant than Fe(lI) and, therefore, the proposed oxidation reaction with H 2 evolution from water is physicochemically unlikely.…”

Section: Discussionmentioning

confidence: 99%

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Iron Oxidation and Reduction Effects on Structural Hydroxyl and Layer Charge in Aqueous Suspensions of Micaceous Vermiculites

Veith

1974

Clays and Clay Minerals

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Abstract--Four Na2S20,-reduced Na-vermiculites, each with some trioctahedral mica interstratified, were oxidized with H20 2 at pH 6.5 and again reduced with Na2S20 * in suspensions at pH 7.5-8.0. The layer charge (CEC + K +), measured at pH 6.50, did not change significantly when octahedral Fe was oxidized (7-92 mmole I00 g-1) or reduced (6-71 mmole 100 g-1). Electroneutrality was maintained within the octahedral sheet when Fe was oxidized or reduced. When Fe(II) was oxidized, electroneutrality was maintained by deprotonation of octahedral OH-groups,and by ejection of (dissolution of structural) octabedral metallic cations, The weathering increment was small since, of the total amount of Fe + Mg, less than 1"3 per cent was ejected from any of the four vermiculitic materials. When biotite was K-depleted, about 20 m-equiv of layer charge per 100g (300~ basis) was lost, while 51 mmole of Fe(II) per 100g was oxidized in the presence of Na2SzO 4 and 82 mmoles in its absence in the aqueous suspensions. Since sequential reduction-oxidation-reduction treatments of K-depleted biotite and mica-containing vermiculites did not cause signifcant changes in layer charge (r 2 = 0"04), the layer charge changes were concluded to be entirely independent of the oxidation or reduction of Fe in these minerals.

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Section: Discussionmentioning

confidence: 61%

Section: Introductionmentioning

confidence: 75%

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Iron Oxidation and Reduction Effects on Structural Hydroxyl and Layer Charge in Aqueous Suspensions of Micaceous Vermiculites

Veith

1974

Clays and Clay Minerals

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“…The literature is replete with examples of how the crystal components of montmorillonite can participate in electron transfer reactions causing either oxidation or reduction of sorbed species under non-extreme conditions (Barshad and Kishk, 1970;Ismail, 1970;Raman and Jackson, 1966;Solomon, 1968;Theng, 1971;Theng and Walker, 1970). In addition, Meisal et al (1971) reported that Fe 3 § in mordenite can be reduced to Fe 2 § by electron transfer from perturbed water molecules on the surface or by reaction with edge AIO4 groups.…”

Section: Oxidation Reactionsmentioning

confidence: 99%

Fe2+-Fe3+ Transformations in Clay and Resin Ion-Exchange Systems

Gerstl

Banin

1980

Clays and Clay Minerals

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Abstract----The pH, Eh, electrical conductivity (EC), and the amounts and valency of replaceable iron were measored periodically on Fe ~+-and Fe3+-saturated montmorillonite and cation-exchange resin at three temperatures. Differences in the pattern of change of pH, Eh, and EC with time appear to be related more to the histories and modes of preparation of the systems than to intrinsic differences in the hydrolysis of the iron in them. Electron transfer reactions involving crystal components of the clay can cause oxidation of adsorbed Fe 2 § ions; the activation energy (Ea) for oxidation on the clay's surface was 6 kcal/mole, less than a third of the activation energy reported for Fe z+ oxidation in solution. In the Fe2+-resin, where Ea = 10.7 kcal/mole, perturbed surface-water molecules may act as electron acceptors enhancing Fe 2+ oxidation.Polymerization and precipitation of the adsorbed iron is affected by the necessity to maintain electroneutrality, the ability of the iron-hydroxy ions and small polymers to move about in the voids of the ion exchanger, and the steric hindrance posed by the matrix of the ion exchanger to the formation of large polymers. In resin, little or no iron precipitates, probably due both to steric hindrance and the inability of the resin to release ionic components to maintain electroneutrality. In clays, steric hindrance is small, and AI and Mg are released from the crystal to maintain electroneutrality, thus the precipitation of iron is abundant and is controlled by the rate of release of AI and Mg from the crystal.

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“…One hypothesis (Gruner, 1934) suggests that a balancing loss of interlayer cations occurs when structural Fe(II) is oxidized. This hypothesis was supported by Ismail (1969Ismail ( , 1970 and bv -3 * Barshad and Kishk (1970), who reported a significant change in layer charge when octahedral Fe changed its valency. On the other hand, data published by Newman and Brown (1966), Raman and Jackson (1966), Newman (1967), Roth et al (1968Roth et al ( , 1969, Leonard and Weed (1970), Farmer et al (1971),and Robert (1971) showed that the decrease in layer charge (in meq) of K-depleted trioctahedral micas was always smaller than the amount of Fe(II) oxidized (in mmole).…”

Section: Introductionmentioning

confidence: 77%

Iron oxidation and reduction effects on structural hydroxyl and layer charge in aqueous suspensions of biotitic vermiculites

Veith¹,

Jackson²

1972

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Oxidation-Reduction Mechanism of Octahedral Iron in Mica Type Structures

Cited by 15 publications

References 0 publications

Iron Oxidation and Reduction Effects on Structural Hydroxyl and Layer Charge in Aqueous Suspensions of Micaceous Vermiculites

Iron Oxidation and Reduction Effects on Structural Hydroxyl and Layer Charge in Aqueous Suspensions of Micaceous Vermiculites

Fe2+-Fe3+ Transformations in Clay and Resin Ion-Exchange Systems

Iron oxidation and reduction effects on structural hydroxyl and layer charge in aqueous suspensions of biotitic vermiculites

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