Thermodynamics applied to potassium exchange in aluminosilicate minerals and soils.

The enthalpies of Ca-»K exchange in 2:1 layer silicate minerals and in soils identify six types of cation exchange site, with up to four in any one soil or clay, which control ion exchange and the extent to which clays swell on adsorption of glycol. It is suggested that these sites are on the planar surfaces of mica, illite, vermiculite and montmorillonite, with a particular type of strongly K selective site at steps, cracks and expansion boundaries (wedge zones) of micaceous clays. Such thermodynamic measurements permit the quantitative determination of very small amounts of 2:1 layer silicate minerals and their K contents in clays and soils with mainly 1:1 or amorphous minerals, and thus a more precise determination of K exchange behaviour, especially selectivity and fixation.

RESP-09886