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Isotopic Exchange of Potassium in an Illite under Equilibrium Conditions¹

ABSTRACT

The kinetics of K exchange in an illite were studied using K⁴². The influence of various pretreatments was investigated, and a comparison was made between exchange with K⁴² under equilibrium conditions during 1 week and repeated extraction with 0.5 N NH₄NO₃ and 0.5 N NaNO₃. Except for the samples containing 0.5 N CaCl₂ the K⁴² exchange appeared to be very fast and no further increase could be observed during shaking from 6 hours up to 1 week.

Prolonged pretreatment with 0.5 N CaCl₂ apparently caused an opening up of the clay lattice. The 0.5 N NH₄-extraction following this treatment always removed considerably more K than was exchangeable against K⁴² under equilibrium conditions.

On the other hand, extraction with 0.5 N NaNO₃ removed even less than was exchangeable against K⁴², indicating that part of the exchangeable K was still in interlattice positions.

¹ Contribution from the Laboratory of Soils and Fertilizers, State Agricultural University, Wageningen, Netherlands.

² Senior Lecturer in Soil Science, University of Natal, Pietermaritzburg, South Africa, and Reader in Soil Science, Agricultural State University, Wageningen, Netherlands, respectively.

Received for publication February 8, 1962. Accepted for publication March 1, 1962.