Tactoid formation in montmorillionite: effect on ion exchange kinetics.
Exchange between calcium from montmorillonite and hydrogen from resin is much slower than exchange between sodium from montmorillonite and hydrogen from resin. Film kinetics are prevailing in both cases, but the location of the rate-determining step is shifted from the Nernst films of the resin particles in the sodium-hydrogen exchange to the Nernst films of the clay particles in the calcium-hydrogen exchange. The increased particle size of the montmorillonite in the calcium state, caused by tactoid formation, appears to be the main reason for the shift.
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