Removal of ammonium nitrogen (NH4+-N) by Cu-loaded amino-functionalized adsorbents

Cu-loaded amino-functionalized SiO2 and weak-base-anion-exchange resin were prepared as advanced adsorbents for NH4+ removal and their adsorption ability and mechanisms were insightfully studied. Ammonium adsorption went through endothermic deprotonation followed by exothermic complexation (Delta H = -68.03 kJ/mol) to the Cu2+ ions. Such chemisorption followed a second-order kinetics and the Langmuir isotherm. The adsorption quickly reached an equilibrium within 1.0-60 min with an extraordinarily high rate constant of 0.01-2.86 g/mg-min. Besides, a high adsorption capacity of 9.30-21.37 mg/g was obtained. The adsorption ability effectively increased with increasing initial pH values, and the final pH was maintained at 5.3-5.8 due to the buffering effect in the -NH/CuCl2/NH3 system. Coexistence of 1.0-5.0 mM chloride-based salts (NaCl, KCl, CaCl2, MgCl2) promoted the NH4+ adsorption by 1.5-1.9 times. However, over amounts of salts inhibited the adsorption. The used adsorbent was successfully recovered by soaking with 0.15 M NaCl solution and 94.37-99.97% adsorption ability was preserved within four recovery cycles.

Automated summary

The Cu-loaded amino-functionalized SiO2 and weak-base-anion-exchange resin demonstrated advanced adsorption capability for NH4+ removal, with the adsorption process involving endothermic deprotonation and exothermic complexation. The adsorption ability increased with higher initial pH values, and coexistence of certain chloride-based salts promoted NH4+ adsorption. The adsorbent could be successfully recovered with 0.15 M NaCl solution, preserving high adsorption ability over multiple recovery cycles.