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

• Main Authors: Huei-Fen Chen, Yi-Jun Lin, Bo-Hong Chen, Iizuka Yoshiyuki, Sofia Ya-Hsuan Liou, Rong-Tan Huang
• Format: Article
• Language: English
• Published: MDPI AG 2018-11-01
• Series: Minerals
• Subjects: zeolite; ion exchange; adsorption; ammonium; Si/Al; temperature
• Online Access: https://www.mdpi.com/2075-163X/8/11/499

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—natural mordenite, chabazite, erionite, clinoptilolite, and synthetic merlinoite—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 (0.398⁻0.468 meq/g), whereas those under lower ammonium concentrations (20 mg/kg) possess greater ion exchange properties (64⁻99%). 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 (5⁻50 °C), we found that the zeolites exhibited the highest ammonium removal ability at 30 °C and the potassium release was enhanced at 30⁻40 °C.