Selective Recovery of Ammonia Nitrogen from Wastewaters with Transition Metal‐Loaded Polymeric Cation Exchange Adsorbents

Extracting valuable products from wastewaters with nitrogen-selective adsorbents can offset energy-intensive ammonia production, rebalance the nitrogen cycle, and incentivize environmental remediation. Separating nitrogen (N) as ammonium from other wastewater cations (e.g., K⁺ , Ca²⁺ ) presents a major challenge to N removal from wastewater and N recovery as high-purity products. High selectivity and capacity were achieved through ligand exchange of ammonia with ammine-complexing transition metals loaded onto polymeric cation exchange resins. Compared to commercial resins, metal-ligand exchange adsorbents exhibited higher ammonia removal capacity (8 mequiv g^-1 ) and selectivity (N/K⁺ equilibrium selectivity of 10.1) in binary equimolar solutions. Considering optimal ammonia concentrations (200-300 mequiv L^-1 ) and pH (9-10) for metal-ligand exchange, hydrolyzed urine was identified as a promising candidate for selective TAN recovery. However, divalent cation exchange increased transition metal elution and reduced ammonia adsorption. Ultimately, metal-ligand exchange adsorbents can advance nitrogen-selective separations from wastewaters.