Synthesis and characterization of montmorillonite-type phyllosilicates in a fluoride medium

Abstract

The fluorine route is thoroughly investigated for the hydrothermal synthesis of montmorillonite in the Na2O-MgO-Al2O3-SiO2-H2O system. Using the optimal conditions suggested by Reinholdt et al. (2001) for the crystallization of pure montmorillonites with the formula Na2x(Al2(1-x)Mg2x☐)Si4O10(OH)2, several parameters (x, Mg content, duration of crystallization, F/Si atomic ratio, pH, nature of counterbalance cation) are varied independently from their ideal values. The products are analysed by various techniques (X-ray diffraction, thermogravimetric analysis-differential thermal analysis, 29Si, 27Al and 19F magic angle spinning-nuclear magnetic resonance). It appears that a pure montmorillonite can only be obtained within a narrow x range (0.10 ≤ x ≤ 0.20). The presence of F in the starting hydrogel and the crystallization time also have significant effects on the purity of the final products. It is shown that a small amount of fluorine is needed for the crystallization of pure montmorillonite phyllosilicates.

Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study

“…Radiotracers were obtained from CERCA (French Nuclear Fuel Research Centre). Two model phases were used: a synthetic montmorillonite (SM) (Reinholdt et al, 2005) and illite from Le Puy in France (ILL) (Gabis, 1958). The latter was purified to remove calcite (11% by weight) by adjusting the pH of a clay suspension to 3 with HCl.…”

Hydration and hydrolysys of Sm3+ and Eu3+ in a clay interlayer: a neutron diffraction study with isotopic substitution

“…A synthetic montmorillonite used for sample preparation was made at LMPC, Mulhouse, France [8]. The isotopes 152 Sm, 154 Sm, 151 Eu and 153 Eu were obtained as oxides from CHEMGAS, France (www.chemgas.fr).…”

Synthesis and characterization of montmorillonite clay intercalated with molecular magnetic compounds

“…In this case, fluoride can substitute structural hydroxyl groups, since they have similar charge and size. Such replacement creates defects in the structure, thus increasing the thermal stability of smectite [21,22].…”