CATION EXCHANGE IN KAOLINITE- IRON OXIDE SYSTEMS*

Kaolinite, to which iron oxides had been added by heating with FoC13 solution, was studied with regard to its cation exchange capacity. It was observed that net cations held (cations less anions) varied directly with pH. Cations and anions are removed in equivalent amounts when the clays arc washed with water, l%cmoval of exchangeable cations proceeds as the last anions are removed. As a consequence, the negative sites may become saturated with non-exchangeable hydroxy-aluminum ions. To obtain the true CEC of a kaolinite-iron oxide system, it is necessary toestimate the amount of non-exchangeable hydroxy-aluminum by conductometric titration