Comparison of structural, textural and thermal characteristics of pure and acid treated bentonites from Aleksinac and Petrovac (Serbia)

Bentonite samples collected from vicinity of Petrovac and Aleksinac were treated with different sulfuric acid molarities. Acid attack dissolved the octahedral sheets by interlayer and edge attack. The effects of the H2SO4 acid caused an exchange of Al3+, Fe3+ and Mg2+ with H+ ions leading to a modification of the smectite crystalline structure. The Mg and Fe substitution in the octahedral sheets promoted the dispersion of corresponding layers and formation of amorphous silicon. The activated bentonites, after the treatment of sulfuric acid, exhibited a lower cation-exchange capacity (CEC) and significant increase of specific surface area from 6 to 387 m2 g−1 (bentonite from Petrovac) and from 11 to 306 m2 g−1 (bentonite from Aleksinac). The acid reaction caused a splitting of particles within the octahedral sheet which led to an increase in specific surface area and decrease in CEC in both bentonites.

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► Bentonites exhibit different behavior in treatment with H2SO4 depending on the adsorbed water and content of Mg, Fe and Al in the octahedral sheets.
► The sulfuric acid treatment provoked abundance of the octahedral cation positions in bentonites resulting by an increase of amorphous Si.
► The cation abundance enabled attachment of the remaining Al with oxygen confirmed by sudden increase of the intensity of d(0 0 1) peak.
► Reduction of the layer charge resulted in lowering the cation exchange capacity (CEC) and increase of the specific surface area.
► The bentonites treated with H2SO4 acid, due to their large surface area, can be used as good adsorbents and catalysts in many industries.