Selective Recovery of Ammonia Nitrogen from Wastewaters with Transition Metal‐Loaded Polymeric Cation Exchange Adsorbents
Brandon Clark, William A. Tarpeh
Abstract
Abstract 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 + , Ca 2+ ) 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.