Local Cuban bentonite clay: composition, structure and textural characterization

The Cuban bentonite clays have a specific surface area of 79.9098 m2.g-1, a pore volume of about 0.077612 cm3.g-1 and both isotherms exhibited a hysteresis loop of IV type. X-ray diffractogram of raw bentonite shows that the main mineralogical component is montmorillonite (> 90%). The mineral object study presents the first endothermic peak, characteristic of montmorillonite, in 48.11 ºC and others less accentuated (80.81, 94.01, 119.81 ºC) characteristic of calcium montmorillonite, that corresponds to the loss of water, and can be extended up to 250 ºC. The FTIR spectra showed the existence of Si-OH, Al-Al-OH, Al-Fe-OH, Al-Mg-OH and Si-O-Si functional groups in all clay samples, confirmed the presence of hydrated aluminosilicate in the clay, bands between 1120 and 461 cm-1 correspond to phyllosilicate structures and OH stretching vibrations were observed. The pH at the point of zero charge (pHPZC) obtained has a value of 8.1, which allows montmorillonite to be classified as basic. The structural formula for one-layer unit of montmorillonite was determined as (Na3.99Al0.01)(Al1.11Fe3+0.49Mg0.18Ti0.07)(Ca0.24Na0.15K0.01)O10(OH)2, indicate the location of the different cations in metal oxide octahedrons or tetrahedrons, respectively. From the results obtained by different methods and the analysis of the calculated structural formula, it can be concluded that the bentonite under study is a calcium montmorillonite, with a low specific surface area and little porosity.