Rehydration Driven Acid Impregnation of Thermally Pretreated Ca-Bentonite—Evolution of the Clay Structure

Materials

Adam Gaweł¹  Agnieszka Klimek¹  Krzysztof Bahranowski¹  Zbigniew Olejniczak²  Ewa M. Serwicka³ 

[1] Faculty of Geology, Geophysics and Environmental Protection, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Krakow, Poland;Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, 31-342 Krakow, Poland;Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Krakow, Poland;

关键词: bentonite;    thermal activation;    acid-activation;    dry impregnation;   

DOI  :  10.3390/ma15062067

来源: DOAJ

【 摘 要 】

A new approach to acid activation of raw Ca-bentonite was explored. The method consisted in dehydration of clay by thermal pretreatment at 200 °C, followed by immediate impregnation with H₂SO₄ solution. The acid concentration was 1.5 × or 2.0 × cation exchange capacity (CEC) of clay. The volume of the liquid was adjusted so as to leave the material in the apparently dry state. Structural evolution of the activated solids after 1, 2, 3, and 4 weeks of storage was monitored with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR), and chemical analysis. In the macroscopically dry solids, the rehydrated interlayer Ca²⁺ underwent rapid exchange with H₃O⁺ and formed extra-framework gypsum. Acid attack on montmorillonite structure resulted in continuous removal of layer forming Mg, Al, and Fe cations, with Mg²⁺ being eliminated most efficiently. No significant damage to the montmorillonite lattice was observed. Al was extracted both from the tetrahedral and the octahedral sheets. Under less acidic conditions, the monohydrated H-montmorillonite changed upon storage to bi-hydrated form, as a result of clay auto-transformation. Higher concentrations of acid in the pore network of clay stabilized the H-form of montmorillonite. The data indicate that compositional transformation of acid impregnated bentonite extended beyond the one month of aging investigated in the present work.

【 授权许可】

Unknown