Effect of acid treatment on cation exchange capacity of clays

The effects on cation exchange capacity (CEC) of four clay minerals (smectite, illite, poorly crystallized kaolinite, well crystallized kaolinite) treated with four different acids (citric, acetic, nitric, hydrochloric), each at 3 different concentrations have been evaluated. Concurrent pH monitoring and quantitative determination of aluminum ions released from the clay minerals into the acid media were also performance. Most significant, 0.1 molar citric acid (a weak organic acid, pKal 3.14) increased the CEC of smectite and illite 17% and 30% respectively. It is believed that the observed increases in CEC are related to the removal of fixed cations, thereby freeing up surface functional groups for exchangeable cations.