Taking soil colloid and hydrated silica (quartz sand) as the experimental material, thecomparative study has been made on the kinetics of ion diffusion and ion exchange in chargedcolloid and charged coarse disperse systems. The results showed that ion exchange kinetics in thetwo systems conform to the kinetic law of ion diffusion. Besides, through this comparative studyon the kinetics of ion exchange and ion diffusion, a method has been advanced theoretically toestimate the quantity of adsorbed ion that is located in the inner of the Helmholtz layer. As far ashydrated silica is concerned , there were about 33 per cent of the total adsorbed quantity of Mg2+that were located in the inner of the Helmholtz layer under the given experimental conditions, butfor soil colloid tlle pcrcentage was only 7.5.
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