Compositional and structural features of the octahedral sheet in mixed-layer illite/smectite from bentonites

Analysis of Fe segregation in the octahedral sheet of bentonitic illite-smectite by means of FTIR, 27 Al MAS NMR and reverse Monte Carlo simulations

“…For a detailed description of the samples, their origin, and their preparation for the study, see Cuadros and Altaner (1998). Briefly, they are the Ͻ1 or Ͻ0.5 µm size fraction.…”

“…The amount of Fe ranges from low (0.08 per O 20 (OH) 4 ) to fairly high (0.95). Based on the good match of the structural formulae, all Fe is considered to be Fe(III) (Cuadros and Altaner, 1998).…”

“…Briefly, they are the Ͻ1 or Ͻ0.5 µm size fraction. Some of them contain minor amounts of mineral impurities (table 1) detected by XRD analysis (Cuadros and Altaner, 1998). The chemical analyses of the samples were corrected for these impurities.…”

“…The samples studied showed a tendency for Fe segregation from Al and Mg in a previous study (Cuadros and Altaner, 1998). Here, we quantify the extent of this segregation and present a visualization of it.…”

“…The different results obtained by the different authors show that octahedral cation ordering is a complex problem that seems to be influenced by many variables and needs to be further investigated. Other studies have shown another kind of structural variation in the I/S octahedral sheet, namely the change from a cis-vacant to a trans-vacant sheet with increasing illitization (Drits, Salyn, and Š ucha, 1996;Cuadros and Altaner, 1998).…”