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Abstract-Prompted by Foster's observation that free swelling is related to octahedral substitution, the authors determined the free swelling of six Na-montmorillonites with different amounts of octahedral and tetrahedral substitution. They found that the montmorillonites exhibited marked differences in free swelling. These differences were not related to differences in cation exchange capacity. Nor were they related to differences in ~ potential, which is a criterion of cation dissociation. Further, calculations indicated that they could not be accounted for by differences in double-layer repulsion or van der Waals attraction. Therefore, to see if dimensional changes produced by isomorphous substitution were responsible, free swelling was plotted against the b-dimension of the clay structure, which was calculated from its mineralogical composition. The result was a straight line with a negative slope. A similar result was obtained with Foster's data. In addition, free swelling was plotted against the degree of tetrahedral rotation in the clay structure, which was also calculated from its mineralogical composition. The result was a family of nearly parallel straight lines that were distinguished from each other by the amount of tetrahedral AI 3+ in the clays identified with them. These results led to the proposal that the clay surface acts as a template for the structure of the adjacent water and that, as the configuration of the surface changes, the water structure changes accordingly. This causes a change in the free energy of the water and, hence, in the swelling of the clay.

Key Words:Chromatography GC, HPLC, HFTLC stationary phase supporthystem open-pore foams fmm silica: two methods developed temperature stability at least up to 1000° porosity up to 0.9 pore size can vary from approximately 20 micrometer to 5 mm pore size distribution remarkably narrowThe resurgence of interest in capillary column gas chromatography [l, 2.31 has highlighted, once again, their tremendous potential for producing highly efficient separation systems. Unfortunately their inability to handle reasonable sample sizes is becoming increasingly apparent. Attempts to improve the latter aspect without at the same time detracting from the former must be viewed as being palliative rather than curative [4,5,6,7,8,9]. A similar impasse would appear to exist in the field of high performance liquid chromatography where high efficiency is attained at the cost of using very high pressures at the column inlet [lo, 111. Clearly a new type of support is needed which combines the "openess" of capillary columns with the large surface area of packed columns and also possesses such features as high-temperature stability and chemical inertness.Open-pore foams offer an attractive solution to this problem and have indeed been used for both gas and liquid chromatography [12,13]. Unfortunately these foams were made from organic polymers and had insufficient temperature stability; they also acted as solvents for many solutes and this caused excessive band-spreading.We therefore setout of make silicaopen-porefoams.Thechoiceof silica suggests itself, because the wealth of chromatographic experience with siliceous surfaces has shown that silica can be effectively deactivated and treated to produce stable stationary phase films [14,15,16]. Since the high melting point of silica makes conventional foam-forming techniques inapplicable, we turned our attention to solutions or suspensions containing high percentages of silica as the starting material. Examples of such mateials are sodium silicate and Ludox (E. I. du Pont de Nemours Co., Wilmington Delaware, USA) which can contain as much as 40% by weight of silica in suspension.Two methods of forming open-pore silica foams were developed. In the first of these the starting material is emulsified with a suitable oil (e.g. n-decane) and an emulsifying agent so as to produce an oil-in-water emulsion. The volume ratio of the oil and water phases should be 74 : 26, i.e. the oil droplets should approximate as nearly as possible to close-packed spheres; this is important when the cells are opened later. The emulsion is then carefully cooled until the water phase freezes (If so desired, the emulsion can first be poured or pumped into a column), During the freezing step, ice is formed, which excludes the silica, thereby increasing the silica content of the unfrozen water phase. Ultimately the silica gels and the emulsion is freeze-dried. During this step the lamella of the foam burst, the water is removed and the oil phase is pumped out. At this stage the foam is essentially open, but the residual ...

Hypothetical mechanisms for charge blocking on the surfaces of kaolinitic minerals are presented to account for the anomalous behaviour of ferrallitic soils on deferrification. On iron oxide removal, the following situations can arise where positive and negative charges (i) both increase, or (ii) both decrease, or (iii) increase and decrease concomitantly. These variations in charge after deferrification can adequately be explained on the basis of blocking which affects both the basal planes and edges of the clay minerals.

Dithiocarbonates (xanthates) have been the most widely used collectors in sulphide mineral flotation. More recently, research has resulted in the use of trithiocarbonate (TTC) collectors. The present study focuses on the effect of mixtures of C 12 trithiocarbonate (C 12 TTC) and sodium iso-butyl xanthate (SIBX) in the flotation of auriferous pyrite and the associated gold and uranium from cyanidation tailings.Improved gold and uranium flotation responses were observed with collector mixtures than with SIBX alone. Sulphur recoveries were not affected. Mineralogical analysis of flotation concentrates showed that gold and uranium were also hosted by kerogen. It was therefore proposed that the improved recoveries could have been mostly due to higher kerogen recovery rather than synergism in pyrite flotation. This mechanism opens possibilities into maximising uranium recoveries in auriferous flotation circuits where low recoveries are common.