GGR205H1 Lecture Notes - Lecture 4: Cation-Exchange Capacity, Soil Acidification, Aluminium Oxide
13 Dec 2016
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Document Summary
General properties and types of soil colloids . The clay and humus particles in soils are referred to collectively as the colloidal fraction because of their extremely small size and colloid-like behavior. Because of their small size, all soil colloids expose a large external surface area per unit mass, more than 1000 times the surface area of the same mass of sand particles. Some silicate clays also possess extensive internal surface area between the layers of their platelike crystal units. Of particular significance is the attraction of positively charged ions (cations) to the surfaces of negatively charged soil colloids. In addition to adsorbing cations and anions, soil colloids attract and hold a large number of water molecules. Generally, the greater the external surface area of the soil colloids, the greater the amount of water held when the soil is air-dry. The most important silicate clays are known as phyllosilicates (greek phyllon, leaf ) because of their leaflike or planar structure.
