A Further Investigation of NH4+ Removal Mechanisms by Using Natural and Synthetic Zeolites in Different Concentrations and Temperatures

We investigated the ammonium removal abilities of natural and synthetic zeolites with distinct Si/Al ratios and various surface areas to study how adsorption and ion exchange processes in zeolites perform under different ammonium concentrations and different temperatures. Five zeolites&mdash
natural mordenite, chabazite, erionite, clinoptilolite, and synthetic merlinoite&mdash
were immersed in 20, 50, and 100 mg/kg ammonium solutions. The results demonstrate that zeolites under high ammonium concentrations (100 mg/kg) possess higher physical adsorption capacity (0.398&ndash
0.468 meq/g), whereas those under lower ammonium concentrations (20 mg/kg) possess greater ion exchange properties (64&ndash
99%). The ion exchange ability of zeolites is extremely dependent on the cation content of the zeolites, and the cation content is affected by the Si/Al ratio. The surface area of zeolites also has a partial influence on its physical adsorption ability. When the surface area is less than 100 m2/g, the adsorption ability of zeolite increases obviously with surface area
however, adsorption ability is saturated as the surface area becomes larger than this critical value of 100 m2/g. When we placed the zeolites in 50 mg/kg ammonium concentration at different temperatures (5&ndash
50 &deg
C), we found that the zeolites exhibited the highest ammonium removal ability at 30 &deg
C and the potassium release was enhanced at 30&ndash
40 &deg
C.