Abstract: Rates of exchange of K with Ca for fine (0·2–2μm) and coarse (54–75μm) and for thin and thick (37–45μm) phlogopite particles were determined using a repeated batch technique, which gave a measure of K selectivity.
Potassium selectivity of the fine fraction was higher than that of the coarse one throughout the exchange process in which 93 per cent of the total K was exchanged from the fine fraction and 100 per cent from the coarse one. Potassium selectivity of the thin 37–45μm particles was higher initially than that of the thick 37–45μm particles but the difference disappeared subsequently and practically 100 per cent of the total K was exchanged from both the thin and thick particles.
The results are interpreted as tentatively confirming the hypothesis that bending and deformation of elementary layers during K exchange increase with particle thickness, which in turn increase K exchange and decrease K selectivity.
The K exchange curves for the fine and coarse phlogopite fractions suggest that in natural conditions, as in soils, where K is not continuously removed from solution, vermiculization of coarse mica particles may be not only more complete but also more rapid than vermiculization of fine mica particles.