Structural Fe(III) reduction in smectites

Iron reduction in nontronite-type clay minerals: Modelling a complex system

“…The state of oxidation versus reduction in phyllosilicate clays determines many of the chemical and physical properties of clays, such as: specific surface area, cation exchange capacity, magnetic exchange interactions (Komadel et al, 2006), mineral availability, the degree of swelling in water, reactivity with organic chemicals and pesticides and the potential for mineral dissolution and transformation (Stucki and Kostka, 2006). This direct effect on the smectite layers has consequences for the local environment of the clay, as clay is one of the key ingredients of soil.…”

Utilization of rarasaponin natural surfactant for organo-bentonite preparation: Application for methylene blue removal from aqueous effluent

“…The excess of H + ions in solution will penetrate into raw bentonite surface and then attack the hydroxyl groups in silanol, causing an imbalance positive charge on its surface. The successive of protonation in silicate layer of bentonite can be readily followed by the changes in characteristics of absorption spectra corresponded to vibration of OH groups and octahedral exchangeable cations, leading to the formation of Si-rich phase in bentonite structure [16][17][18]. The protonation of silanol group in raw bentonite produce water molecules (H 2 O) with imbalance positive charge on its surface as indicated in step 2 in Fig.…”

Changes in clay minerals and potassium fixation capacity as a result of release and fixation of potassium in long-term field experiments

“…Other processes that may affect release and fixation of interlayer K are redox processes and the formation of hydroxy interlayers. Redox processes may change layer charge, and hence the readiness by which K fixation occurs; e.g., a reduction of structural Fe 3+ to Fe 2+ promotes fixation of interlayer cations (Chen et al, 1987;Stucki et al, 2002;Komadel et al, 2006). Fixation of K is inhibited if hydroxyaluminium interlayers are formed in the mineral (Saha and Inoue, 1998;Aide et al, 1999).…”