ADSORPTION AND PHYSICOCHEMICAL PROPERTIES OF NATURAL MONTMORILLONITES AND THEIR MODIFIED FORMS

Abstract

The data, earlier published and obtained by us, concerning an influence of various factors on physicochemical properties and structural parameters for montmorillonites of different origin are summarized. Some regularities of water vapor ad/desorption by bentonites depending on their origin and activation method as well as the nature of metal cations have been revealed. The data concerning the influence of a hydration degree of bentonites on a value of basal spacing, d(001), in montmorillonite are presented and analyzed. Ad/desorption properties towards water vapor in the case of natural bentonites from three Ukrainian deposits, i.e. Gorbskoe (Bent(G)), Dashukovskoe (Bent(G)), and Kirovogradskoe (Bent(K)), as well as for their modified forms, i.e. H2O-Bent (obtained by bentonite boiling in distilled water for 1 h), 300-Bent (obtained by bentonite calcination at 300 °C for 1 h), and 1H-Bent-1 (obtained by bentonite boiling in 1 M HNO3 for 1 h), have been systematically investigated. It has been found that values of a monolayer capacity, аm, for natural bentonites decrease in the order NBent(D) > N-Bent(G) > N-Bent(K). It is interesting to note that аm slightly increases after the acid modification of bentonites and significantly decreases in the case of supporting Pd(II) and Cu(II) complexes on them. Values of a specific surface area for natural bentonites and their modified forms determined as a result of both water vapor adsorption-desorption and thermal argon desorption are presented and they are significantly varied depending on the bentonite origin. Values of an activity of water adsorbed on natural bentonite, аH2O = P/Ps , determined from the water vapor isotherms at the same adsorption value increases in the order N-Bent(D)< N-Bent(G) < N-Bent(K). The same orders are observed for the bentonite samples after both their acid treatment and anchoring Pd(II) and Cu(II) ions on their surfaces.