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 (ΔH = −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.