GB847528A - Improvements relating to the treatment of clay - Google Patents

Abstract

The replacement of exchangeable cations in a clay of the expanding lattice type, for example a bentonite or hectorite, is effected by first replacing the exchangeable cations by treatment with a cation exchange resin charged with intermediate cations, which are then eliminated as a gas by contacting the treated clay with a solution containing the final cations. The final cations are usually those of an organic base, and are preferably derived from an amine of high molecular weight and boiling point, for example diethylene triamine, triethanolamine, pentamethylene hexamine, para-diisobutyl phenoxy ethoxy ethyl dimethyl benzyl ammonium chloride, or dimethyl octadecylamine; they are advantageously polymerizable, such as the reaction product of a polyamine and a polycarboxylic acid, for example diethylene triamine and phthalic anhydride; or they may be metallic cations, for example lead, larger than the original cations, such as may be derived from lead acrylate, in which case the product will contain some polymerizable material. The final cations are preferably larger than the initial cations, which are normally sodium or calcium. The intermediate cations are preferably ammonium ions, but may also be substituted ammonium ions derived from compounds of low molecular weight, for example methylamine and dimethylamine. This treatment reduces the swelling properties of the clay in water, and is suitable for use as a dielectric film, having improved dielectric properties. The cation exchange resin may be a sulphonated phenol-formaldehyde resin or a sulphonated cross-linked polystyrene resin. The intermediate cation may either be eliminated as a gas by ensuring that it is a weaker base than the final cation, or by carrying out the final replacement at above the temperature at which the cation is evolved as a gas from the clay. Low molecular weight silicates, sulphates, and chlorides may be removed from the p initial clay suspension by treating with a strongly basic anion-exchange resin, either before or after the introduction of the intermediate cations, or by employing a mixed bed of the resins, simultaneously. In one example, an aqueous hectorite suspension was treated with a cation exchange resin in the ammonium form, and was then spread out as a film on glass plates and dried. This film was then treated with a solution of diethylene triamine and phthalic anhydride in water, dried, and the organic cation polymerized by heating.