Local Cuban bentonite clay: composition, structure and textural characterization

The physic and chemical characterization of the bentonite clay from the Chiqui Gomez deposit, central Cuba, (Cuban bentonite clay) shows that it is mainly constituted by sodium montmorillonite (>90%), with a structural formula for one-layer unit determined as (Na3.99Al0.01)(Al1.11Fe0.493+Mg0.18Ti0.07)(Ca0.24Na0.15K0.01)O-10(OH)(2). The Cuban bentonite clay has a specific surface area of 80 m(2)g(-1), a pore volume of about 0.0776 cm(3)g(-1), 61% porosity and both N-2 adsorption-desorption isotherms exhibit a hysteresis loop of IV type. The thermogravimetric analysis (TGA) of the studied mineral presents the first endothermic peak, characteristic of montmorillonite, in 48.1 degrees C and others less accentuated (80.8, 94.0, 119.8 degrees C) characteristic of sodium montmorillonite, that corresponds to the loss of water, and can be extended up to 250 degrees C. The FT-IR spectra show the existence of Si-OH, Al-Al-OH, Al-Fe-OH, Al-Mg-OH and Si-O-Si functional groups in all clay samples, bands between 1,120 and 461 cm(-1) correspond to phyllosilicate structures and OH stretching vibrations were observed. pH at the point of zero charge (pH(PZC)) obtained has a value of 8.1, which allows montmorillonite to be classified as basic.