Abstract
The physic and chemical characterization of the bentonite clay from the Chiqui Gómez 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)(Al1.11Fe3+0.49Mg0.18Ti0.07)(Ca0.24Na0.15K0.01)O10(OH)2. The Cuban bentonite clay has a specific surface area of 80 m2g-1, a pore volume of about 0.0776 cm3g-1, 61% porosity and both N2 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 ºC and others less accentuated (80.8, 94.0, 119.8 ºC) characteristic of sodium montmorillonite, that corresponds to the loss of water, and can be extended up to 250 ºC. 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 (pHPZC) obtained has a value of 8.1, which allows montmorillonite to be classified as basic.
Highlights
Bentonite clays are widely distributed in the world (Grim and Güven, 1978)
The physic and chemical characterization of the bentonite clay from the Chiqui Gómez 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)(Al1.11Fe3+0.49Mg0.18Ti0.07)(Ca0.24Na0.15K0.01)O10(OH)2
Bentonite can be used as an adsorbent in its natural form, some researchers have proposed experimental designs and methodologies for the acid activation of these minerals in order to optimize the purification process (Didi et al, 2009; Palanisamy et al, 2011; Ajemba, 2012; Usman et al, 2013; Larouci et al, 2015); when applying this activation method it should be borne in mind that excessive activation can be explained in terms of a loss of porosity and acid strength (Makhoukhi et al, 2009)
Summary
Bentonite clays are widely distributed in the world (Grim and Güven, 1978) They are ores with montmorillonite as the main component and besides montmorillonite; bentonite contains other minerals, such as quartz, calcite, feldspar, muscovite and biotite (Pеtrоvić et al, 2014). This mineral has properties such as charge density, surface charges, surface area, the type of exchangeable cations, silanol groups of crystalline defects or broken surfaces, hydroxyl groups on the edges, and Lewis and Bronsted acidity (Djomgoue and Njopwouo, 2013) which make it have a great adsorption capacity, this is why this mineral has multiple uses in different industrial processes. Acid treatment of bentonites has been shown to create mesoporosity depending on the acid concentrations and time of treatment involving major structural changes and partial decomposition of montmorillonite (Zheng et al, 2017)
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