Removal of low-concentration ammonia in water by ion-exchange using Na-mordenite

Removal of low-concentration ammonia (2–10 ppm) in water by ion exchange with Na-form zeolites was investigated using a flow system at 278–333 K. Results indicated that Na-mordenite was the most efficient cation-exchanger (compared with Na-ferrierite, Na-ZSM-5, Na-β, and Na-Y, as well as the K- and H-form mordenite) for the removal of low-concentration ammonia. The ammonia uptake and the ion-exchange level achieved using mordenite with NH4+ for removal of 10 ppm ammonia at 333 K were 1.21 mmol g−1 and 79.1%, respectively. The high efficiency of Na-mordenite for removal of low-concentration ammonia in water is due to the strong acidity of the corresponding H-form mordenite as demonstrated by ammonia temperature-programmed desorption. Ammonia uptake on the Na-mordenite was minimally influenced by operating temperature in the range of 278–333 K. The coexistent K+ and Na+ in water had little influence on ammonia uptake of the Na-mordenite. In contrast, coexistent Ca2+ and Mg2+ significantly lowered the efficiency of the Na-mordenite for ammonia removal.