Occurrence and Extraction of Soil Clays
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Clay mineral particles provide the inorganic source of the electrical charge and the predominant area of surfaces for reactions with other entities in soils, including organic constituents, both living and dead, and also other clay mineral particles. There are strong implications for the extraction of clays arising from the observations of close associations between minerals and organic matter. The effect of the hexametaphosphate, commercially known as ‘Calgon’ is to increase the negative charge of the edges of clay particles, which increases their mutual repulsion. The observation that different agents led to maximum production of clay in different soils illustrated that the forces and agents responsible for aggregating and cementing fine material in soils may differ with each type of soil. A more general recommendation has been made that adequate dispersion of soils with variable charge needs to occur in a solution with a pH well above or else below the zero point of charge.