The effect of microwave treatment of clinoptilolite on its ion-exchange kinetic properties
Abstract
Ion-exchange properties of clinoptilolite (KLT) samples in the original natural (Na, Ca) and ammonium
forms, untreated and exposed to microwave treatment of different duration, were studied in the kinetic
experiments of batch mode. Continuous microwave (2.45 GHz) treatment of KLT for 25 minutes at 500W of
radiation power significantly reduces the capacity of the sorbent in a natural form toward ammonium due to
the effect of dehydration («drying») of ion exchange materials. The effect of short microwave treatment (up
to 5 minutes) on the kinetics of exchange in systems: NH4
+ → (Na+, Ca2+) and K+ → NH4
+ was insignificant.
Analysis of the results obtained from ion exchange experiments, together with the results of the study of the
microstructure of different samples of KLT indicates that the observed kinetic properties are determined by
the bi-disperse structure of sorption material. By the analogy with the diffusion Helfferich criterion for mixed
diffusion at nonlinear isotherms, the expression is suggested for the criterion in the case, where the kinetics is
defined by mass-transfer processes within the sorbent phase with a complex structure characterized by two
kinetic coefficients. At the studied conditions, there takes place a mixed diffusion kinetic mechanism, determined
primarily by the properties of microcrystals, rather than the transporting pores into which the microwave
treatment may be affected.
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