Modification of different grades of Korean natural zeolites for increasing cation exchange capacity

Three different grades of Korean natural zeolites which contained clinoptilolite or both clinoptilolite and mordenite were treated with 2 M NaOH solution at 103 degrees C during different times ranging from 1 to 16 h. The reacted products were all identified as zeolite Na-P by X-ray diffraction and scanning electron microscopy. Zeolite Na-P was formed from both clinoptilolite and mordenite but not from coexisting primary minerals such as feldspars and quartz. During the reaction, a large amount of Si was dissolved into solution. The cation exchange capacities of the products after 8 or 16 h reaction were higher by more than 2 times than those of the corresponding raw materials. The purity in zeolite Na-P of the products depended on the purity of the raw materials.