Removal of ammonia-nitrogen in wastewater using a novel poly ligand exchanger-Zn(II)-loaded chelating resin

Abstract

In this study, a novel poly ligand exchanger-Zn(II)-loaded resin was designed to effectively remove ammonia-nitrogen (NH3-N) from wastewater. The surface morphology and structure of the Zn-loaded resin were characterized using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and Fourier transform infrared spectroscopy (FTIR), respectively. SEM shows the surfaces of the Zn(II)-loaded resin were rough and nonporous and EDS demonstrated that Zn2+ was loaded onto the resin successfully. In addition, the combination form of Zn(II) with NH3-N adsorption reagent was revealed by FTIR spectra; the complex could be R-N-R-O-Zn-O-R-N-R and R-N-R-(O-Zn)2. The kinetics and equilibrium of the NH3-N adsorption onto the Zn(II)-loaded resin has been investigated. The effects of pH, reaction time, and temperature on NH3-N removal from wastewater by Zn(II)-loaded resin were investigated, and the results showed that the maximum adsorption capacity reached 38.55 mg/g at pH 9.54 at 298 K in 240 min. The adsorption ability of the modified resin decreased with an increase in temperature. Moreover, the NH3-N adsorption followed a pseudo-second-order kinetic process. The kinetic data demonstrated that the adsorption process might be limited by a variety of mechanisms. The study can provide the scientific foundation for the extensive application of a novel poly ligand exchanger-Zn(II)-loaded resin to remove NH3-N from wastewater.

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

“…In addition, FTIR data from this study and previous work suggest that carboxylate groups on both resins bind to metal with bidentate coordination. However, the additional nitrogen in iminodiacetate may also bond with the metal, enhancing stability and decreasing metal elution compared to WACG at high TAN and potassium concentrations (Figure c) . Furthermore, enhanced metal–resin bond stability may explain why potassium percent adsorption was lower at all concentrations compared to WACG.…”

“…We hypothesize that selectivity is achieved because transition metals bind too strongly for competing cations to ion exchange with them. In a pH range of 9–10 where a high percentage of TAN is ammonia and the majority of loaded transition metal is not precipitated by hydroxides, ammonia bypasses ion exchange competition and binds to the metal through ligand exchange with metal‐aqua ligands . Selective recovery through metal‐nitrogen bonding in metal‐cation‐loaded resins has been successful in applications other than TAN recovery from wastewater.…”

“…For example, nickel‐nitrilotriacetate and cobalt‐carboxymethyl aspartate resin columns are commonly used for selective protein recovery through metal‐histidine nitrogen bonding . Previous studies on selective TAN adsorption have used copper‐ and zinc‐loaded polymeric resins with iminodiacetate and carboxylate functional groups . Due to high metal affinity for the lone pair of ammonia nitrogen, these removal‐focused studies demonstrated the use of ligand exchange to achieve some of the highest ammonia adsorption capacities reported, depending on concentration and pH (Iminodiacetate: 2.75–3.05 mequiv N g −1 , Carboxylate: 6.75–48.00 mequiv N g −1 , Table S2).…”

“…Previous studies on selective TAN adsorption have used copper‐ and zinc‐loaded polymeric resins with iminodiacetate and carboxylate functional groups . Due to high metal affinity for the lone pair of ammonia nitrogen, these removal‐focused studies demonstrated the use of ligand exchange to achieve some of the highest ammonia adsorption capacities reported, depending on concentration and pH (Iminodiacetate: 2.75–3.05 mequiv N g −1 , Carboxylate: 6.75–48.00 mequiv N g −1 , Table S2). These studies identified the optimal capacity pH range of 9–10 for selective ammonia adsorption over sodium, which we validated and continued to use in this study .…”

“…Due to high metal affinity for the lone pair of ammonia nitrogen, these removal‐focused studies demonstrated the use of ligand exchange to achieve some of the highest ammonia adsorption capacities reported, depending on concentration and pH (Iminodiacetate: 2.75–3.05 mequiv N g −1 , Carboxylate: 6.75–48.00 mequiv N g −1 , Table S2). These studies identified the optimal capacity pH range of 9–10 for selective ammonia adsorption over sodium, which we validated and continued to use in this study . To transition from removal to recovery, this study characterized resin regeneration in terms of the extent of TAN recovery (product purity).…”