Rehydration Driven Na-Activation of Bentonite-Evolution of the Clay Structure and Composition

A new method of Na-activation of raw bentonite, rich in Ca-montmorillonite, consisting of combined thermal treatment at 200 degrees C, followed by immediate impregnation with aqueous solution of Na2CO3 of concentration corresponding to 0.5, 1.0, 1.5, or 2.0 cation exchange capacity (CEC) of clay, was investigated. Structural and compositional evolution of the activated solids after 1, 2, 3, and 4 weeks of storage was monitored by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). XRD analysis indicated that within the investigated period of ageing transformation to Na-rich montmorillonite required Na2CO3 concentration of at least 1.0 CEC. FTIR spectra showed that, depending on the Na2CO3 concentration and ageing time, formation of Na-rich montmorillonite was accompanied by precipitation of poorly crystalline calcite, amorphous calcium carbonate, gaylussite (a double calcium-sodium carbonate), and portlandite (Ca(OH)(2)).

Automated summary

The study revealed that a Na2CO3 concentration of at least 1.0 CEC is necessary for the transformation to Na-rich montmorillonite, and the process is accompanied by the precipitation of other compounds such as poorly crystalline calcite and gaylussite. XRD and FTIR analysis were used to monitor the structural and compositional changes of the activated solids during storage.