Hydrothermal synthesis and characterization of dioctahedral smectites: A montmorillonites series

Abstract

International audienceThe aim of this study is to synthesize and finely characterize montmorillonite samples, dioctahedral smectites without tetrahedral charges (structural formulae Nax(Al(2 − x)Mgx)Si4O10(OH)2), to allow their use as reference samples in clay science. The montmorillonites synthesis under hydrothermal conditions at different pressures and with various layer charge deficit has been attempted. The temperature was fixed at 320 °C, the pressure parameter values were 20 MPa, 80 MPa, 120 MPa and 200 MPa. The Mg content varied from 0.25 to 0.60 per half unit cell. The reaction products have been characterized with multi-technique analyses (ICP-AES, EMP, CEC, XRD, FTIR, NMR and TGA). Montmorillonite phase was only produced at 120 and 200 MPa. At 20 and 80 MPa, the results suggest that a 0.33 and 0.16-tetrahedral charge deficit exist in the formed samples. Moreover, the octahedral occupancies are higher than two (2.15 and 2.07 at 20 and 80 MPa respectively). In these experimental conditions, the synthetic smectites are mixtures between montmorillonite, beidellite and saponite. At 120 MPa and for a Mg content of 0.25 or higher than 0.33, the synthetic products were also mixtures of smectites. Tetrahedral charge deficits of 0.11, 0.11 and 0.15 were found for Mg contents of 0.25, 0.50 and 0.60 respectively. The octahedral occupancy was also higher than 2.00. A montmorillonite phase with only octahedral charges and an octahedral occupancy near 2.00 was synthesized for a Mg content of 0.33 and at pressures equal to or higher than 120 MPa. This low charge reference smectite shows a very low amount of accessory minerals and an octahedral charge deficit only created by the presence of magnesium in the structure. This montmorillonite can be compared structurally to the most studied natural one: the montmorillonite SWy-2 from Wyoming

Preparation and characterization of novel clay/PLA nanocomposites

“…The most-studied natural montmorillonite is SWy-2 (Lantenois et al, 2008), and so research regarding nanocomposite preparation and characterization using this Wyoming montmorillonite is extensive, to say the least (for example, Kong and Park, 2003;Mansa and Detellier, 2013;Praus et al, 2013;Valandro et al, 2013). In this study, however, a cost-centric approach is employed to the preparation of polylactide nanocomposites by the characterization and use of the clay fraction of the Bragança formation, which is located in the north-eastern part of Portugal.…”

Hydrothermal synthesis of beidellites: Characterization and study of the cis- and trans-vacant character

“…All of these studies were summarized in a critical review by Kloprogge et al (1999). Using these stability fields as guidelines, it is possible to synthesize beidellites (Kloprogge et al, 1990(Kloprogge et al, , 1993Grauby et al, 1993), saponites (Suquet et al, 1977(Suquet et al, , 1982Grauby et al, 1993), hectorites (Torii et al, 1983;Torii, 1985;Torii andIwasaki, 1986, 1987), nontronites (Decarreau et al, 1987), and montmorillonites Yamada et al, 1991Yamada et al, , 1994Lantenois et al, 2007a). These last studies highlighted the difficulties involved in the synthesis of high-purity smectite with the desired chemical composition.…”

“…Saponites with various layercharge deficits were synthesized and characterized by Suquet et al (1977). However, synthesis of montmorillonites with variable layer-charge deficits is difficult (Lantenois et al, 2007a).…”

Na-Montmorillonite Edge Structure and Surface Complexes: An Atomistic Perspective

“…The random assignment of substitutions and the first constraint that prohibits the presence of Mg-(OH) 2 -Mg pairs in the octahedral sheet are based on 1 H magic angle spinning nuclear magnetic resonance (MAS NMR) and FT-IR spectra from MMTs that show no contributions from Mg-(OH) 2 -Mg moieties and QM simulations that demonstrated that Mg 2+ substitutions are randomly distributed within the octahedral layer [35][36][37]. The second constraint, informed by the properties of synthetic MMTs [38][39][40][41], limits the substitution ratio of the edge PBC (i.e., Mg edge substitutions: total number of octahedral edge sites in the PBC) to less than 0.20, which is the maximum substitution ratio for a synthetic MMT with only octahedral substitutions. The structural characterization of synthetic MMTs with divalent cation substitution ratios greater than 0.20 revealed octahedral sheet occupancies greater than 2.00, which is indicative of an MMT structure with some trioctahedral character, and isomorphic substitutions in the tetrahedral sheet.…”