| Popis: |
A study was made of a Red-Yellow Podzolic soil with particular regard to the properties of dioctahedral vermiculite, one of its major clay minerals. The soil, Nason silt loam, which is derived from a muscovite schist residuum, was found to be nearly devoid of exchangeable calcium and low in other bases. Although the cation exchange capacity of the B₃ horizon was 25 me. per 100 gm. soil, this horizon contained only 0.08 me. Ca per 100 gm. Clay minerals present were kaolinite, dioctahedral vermiculite, and regularly and randomly interstratified illite-vermiculite. The 14.7A basal spacing of vermiculite from the C₁ horizon moved to 10.5A when the clay was K saturated, but the effectiveness of K saturation decreased from the C₁ horizon through the A horizon where there was only slight collapse. Boiling the clay from the B₁ horizon for 102 hours in 1N KCl caused a change of the 14.7A basal spacing to only 14.2A. However, treatment of the clay in 1N KCl plus 0.1N HCl or treatment with 1N NH₄F altered this spacing to near 10A. The difficultly collapsed mineral had a high internal surface, high base exchange capacity, and low divalent cation content. Easily collapsed dioctahedral vermiculite was made difficultly collapsed by repeated Al saturation and drying. Heat treatment at 800°C. collapsed the 14.7A spacing of the mineral in all horizons to 10.3A. Glycerol solvation caused no increase of the 14.7A spacing. These results together with D.T.A. data support the theory that non-exchangeable Al in the interlayer position in vermiculite restricts collapse of the mineral on K saturation. |
