Facile synthesis of copper-substituted Prussian blue analog immobilized ion exchange resins for high-performance ammonium recovery from wastewater: Adsorption kinetics, isotherms, and regeneration

Ammonium is one of the major pollutants in aquatic environments, resulting in eutrophication, ammonia gas emission, and soil acidification. In this study, a facile synthesis procedure was developed for preparing high-performance ammonium adsorbent via in-situ immobilization of Prussian blue analog, viz. copper hexacyanoferrate (CuHCF) on a weakly acidic cation exchange resin (WAC) without any pretreatment. From the analysis of physicochemical properties of the synthesized CuHCF-based adsorbents using powder X-ray diffractometry, Fourier-transform infrared attenuated total-reflectance spectroscopy, scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy, it was found that CuHCF appears to be located on the surface of WAC, allowing access to NH₄⁺ for adsorption. The pseudo-second-order kinetics model fits best suggesting that the adsorption of ammonium occurring was chemisorption. The isotherm model that fit best was the Langmuir isotherm, which showed that the maximum equilibrium adsorption capacity was 47.07 mg NH₄⁺ per g of WAC-CuHCF at pH 6.5. The adsorption efficiency of NH₄⁺ changed slightly in the presence of Na⁺ and decreased by only ∼ 10 % in the presence of K⁺. The ability of WAC-CuHCF to regenerate was also assessed in the column test, and the regenerated adsorbent was found to adsorb and desorb NH₄⁺ to essentially the same extent. Thus, WAC-CuHCF developed in this study, which could be prepared in a facile synthesis method, is promising as a regenerative adsorbent material for the selective adsorption of NH₄⁺ ions over a wide pH range and can be applied for wastewater treatment and environmental remediation.