ADSORPT ION OF ALCOHOLS BY SMECTITES: I. D IST INCT ION BETWEEN INTERNAL AND EXTERNAL SURFACES

ABSTRACT: The desorption of methanol and isopropanol by a series of charge-deficient Ca-montmorillonites (prepared by a partial Li-saturation and subsequent heat treatment of Camp-Berteau rriaterial) has been monitored gravimetrically and by XRD. The results indicate that about half the total adsorbed molecules do not occur within the interlamellar space of the montmorillonite but are occluded inmicropores between particles. In this paper we investigate, using gravimetry and XRD, the desorption of methanol and isopropanol by a series of charge-deficient montmorillonites. Use of such a series enables the number of organic molecules within the interlamellar porous volume to be modified relative to those in the pores between the particles ince amounts of the former depend on the net lattice charge. In addition, the use of two alcohols A and B of molecular weight MA and MB, should permit application of the Gurvitch rule (Gurvitch, 1915) which states that the number of molecules occluded in a specified porous volume V must be related to the density dA and dB by the following equation: nA MA nB MB _ _ -- I7 dA dB and thus may be used to double check the value calculated for V. By demonstrating that the relatively large amount of alcohol adsorbed on the external surfaces is occluded in micropores between clay particles, we show that the role played by the external surface in Ca-montmorillonite is important and larger than is generally assumed. MATERIALS Bi-ionic montmorillonite suspensions were prepared by mixing different volumes of Na-and Li-saturated Camp-Berteau montmorillonite and shaking for 48 h. After centrifuga-tion and drying at room temperature the clays were heated at 240 ~ for 24 h, this treatment causing most of the Li + (r=0.68A) to migrate into the octahedral sheet and neutralize part of the lattice charge. The clays were then redispersed and the remaining Na + exchanged by Ca 2 § using 1N CaC12. By choosing various Li/Na ratios, a series of Ca-montmorillonites was prepared, eac