Removal characteristics of ammonium nitrogen from wastewater by modified Ca-bentonites

• A modified inorganic bentonite (Na/Al) based on purified Ca-bentonite was prepared.
• Batch experiments were performed for the adsorption of ammonium nitrogen.
• The ammonium nitrogen adsorption capacity of MB (46.904 mg/g) was improved compared to raw bentonite.
• The described process provides a potential pathway for the removal of ammonium nitrogen at low concentrations.

A modified inorganic bentonite (Na/Al) based on purified Ca-bentonite was prepared through exchanging Al and Na ions in the interlayer space of Ca-bentonite. The structural properties of purified and modified bentonites were characterized by XRD and SEM analysis. Batch experiments were performed for the adsorption of ammonium nitrogen and different experimental conditions were studied in order to investigate the optimum adsorption conditions. Comparative experiments were also carried out for natural Ca-bentonite (RB), unmodified purified bentonite (PB) and modified purified bentonite (MB). Through the thermodynamic analysis, the ammonium nitrogen adsorption process can be spontaneous, the standard heat was − 41.46 kJ mol− 1, and the adsorption process based on ion exchange adsorption. The ammonium nitrogen adsorption capacity of MB (46.904 mg/g) was improved compared to raw bentonite (RB) (26.631 mg/g), which was among the highest values of ammonium nitrogen adsorption compared with other adsorbents according to the literatures. The described process provides a potential pathway for the removal of ammonium nitrogen at low concentrations encountered in most natural waters.