Aqueous extracts from 31 samples, representative of deposits of kaolinite (weathered and hydrothermal), flint clay, halloysite, dickite, high-alumina minerals, illite, smectite, and Paleozoic shales and underclays, were prepared in the laboratory to simulate the seep and run-off waters from those rocks into the natural environment. The centrifuged extracts were analyzed by inductively-coupled-plasma spectrography and ion chromatography for 36 elements and radicals. Despite the traditionally known low solubility of clay in water, even low-mobility A1 was found in 13 of the extracts, e.g., in amounts up to 18.5 ug/mL from the illitic Fithian Shale.
The concentration of a “dissolved element” in an extract depends not only on the amount present in the sample but also on its aqueous solubility, the pH and Eh of the system, its possible combination with other ions present, the effect of organic matter as a combinant and complexer, the ion-exchange effect, and dispersibility of colloidal clay particles too small to settle out. The data on comparative amounts extracted are discussed from the viewpoint of individual elements and radicals, in terms of the clay mineral or rock deposits furnishing the extracts, and the relation of the extracted material to the genesis and geologic environment of the sample.