Abstract-The mechanism of boron uptake by clays, especially illitic clays, and the factors which control such uptake have long been debated issues. In an attempt to answer some of the questions of the controversy, three illites were treated in solutions containing boron. In the study, boron concentration, salinity, temperature, and time were varied independently over rather wide ranges.For the illites studied, irreversible uptake of boron was increased by increasing boron concentration, salt concentration, temperature, and time of treatment. The amount of boron which was fixed also varied with the type of illite treated. The amount of fixation was controlled primarily by the specific surface area of the clay and also by the crystallinity, K content, and/or amount of mixed-layer material ("frayed-edge" development?), and apparently was independent of the original boron content of the clay.A two-step mechanism is proposed for boron fixation by illite, consisting of rapid chemical adsorption of the tetrahedral B(OH)+ anion at the "frayed-edge" of the illite flake followed by much slower diffusion of boron into the tetrahedral part of the structure.

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38SHORT NOTES spectrum (below) of the product obtained after 16 days of ageing. That the reaction is still not complete is indicated by the broad band around 22 ~ 20 on the X-ray trace, (CuK~ radiation). This appears to be the first time that the crystallization of kaolinite is realized at such a low temperature from an amorphous material and in an almost neutral solution. It is thought that the transformation occurs through an undetectable "zeolitic" phase, which readily forms at high pH and facilitates the subsequent crystallization into kaolinite under neutral conditions. The direct transformation from the gel into a clay mineral using an acid solution or water is not feasible as it has been shown (De Kimpe, 1967) that under these conditions, the final products are pseudo-boehmite and an amorphous alumino-silicate with a different composition.Further experiments are in progress to investigate in more detail this reaction, and a complete report will be given later.