Novel Copper Ion-exchange Resin To Deal With Ammonia-nitrogen Wastewater

Ammonia-nitrogen is one of the main reasons that cause deterioration of water quality and water eutrophication. Because of the extensive source and difficulty of its treatment, there is no economic and effective method for NH₃-N wastewater treatment at present. Ion-exchange has been widely investigated in treating NH₃-N wastewater, however, zeolite- the representative of inorganic ion exchanger, still has some problems, such as small adsorption capacity, the instability of adsorption effects, treatment of concentrated NH₃-N solution desorbed and so on. It is not be extensively applied in industry.In this article, a new type of ion exchange resin- copper loaded Iminodiacetic Acid chelating ion exchange resin(copper loaded resin), which has high selectivity for ammonia and is easy to regenerate, has been found. The adsorption properties of the copper loaded resin for ammonia were investigated and the main tasks in this article can be summarized as follows:Copper loaded resin was prepared using iminodiacetic acid chelating cation exchange resin as the original resin, divalent copper ions as loading metal ion. The adsorption properties of copper loaded resin for NH₃-N in dilute ammonia water were studied and it is obtained that the saturation adsorption capacity of the resin for NH₃-N is 44mg/L(dry copper loaded resin) , and the molar ratio of copper ion to ammonia is 1:1.535.The stability of copper loaded resin in solution was also investigated, the results show that copper loaded resin can exist stably in the aqueous solution of pH=3.5-10.5.Through the static equilibrium experiments, the effect of the solution equilibrium pH on the adsorption properties of copper loaded resin to ammonia was emphatically analyzed in pure ammonia solution and the ammonia solutions containing competitive cations (Na⁺, Ca²⁺). When the competitive cations (Na⁺, Ca²⁺) exist, the concentration of NH₃-N in the solution after the adsorption equilibrium declined firstly with the increase of pH and then had an upward trend, the minimum equilibrium concentration of NH₃-N is attained at pH=9.5-10.0. NH₃-N adsorption isotherms were measured to investigate the impact of competitive cations on the adsorption capacity of copper loaded resin for NH₃-N. When the concentration of Na⁺ was 1000mg/L and 2000mg/L, the saturation adsorption capacity respectively achieves 28.8 and 25.08 mg/g(dry copper loaded resin). The Simultaneous existence of Na⁺ and Ca²⁺ will lead to the decline of NH₃-N adsorption properties of resin, and the equilibrium concentration of NH₃-N over 160mg/L will result in the loss of Cu²⁺.The dynamic exchange experiments of ion exchange column containing 63.5mL copper loaded resin was carried out to investigate the influence of the equilibrium pH of pretreatment copper loaded resin, influent pH, the types and concentration of competitive cations, the influent velocity and other factors on the treatment effect of the simulated NH₃-N wastewater. The results show that pH of the reaction system is the most important factor for treatment of NH₃-N wastewater with copper loaded resin. For the treatment of the simulated NH₃-N wastewater with the initial NH₃-N concentration 810mg/L,Na⁺ concentration 1000mg/L, the optimal effects are achieved when pH value of pretreated copper loaded resin pretreatment is 9 and the molar ratio [OH^-]:[NH₄⁺] is 1:1, where the NH₃-N breakthrough capacity is 19.6mg/g(dry copper loaded resin), the effluent residual of NH₃-N is below 1mg/L which is far lower than≤15 mg/L (primary standard of NH₃-N in the integrated national emission standard of wastewater). The copper loaded resin can effectively deal with the simulated NH₃-N wastewater containing Ca²⁺ below 400mg/L or Na⁺ below 3000mg/L, NH₃-N concentration of the effluent is both down to less than 1mg/L from initial 810mg/L of the influent solution NH₃-N concentration 810mg/L when copper loaded resin is pretreated at pH 9.0 or 9.5 respectively. With simulated NH₃-N wastewater of the initial NH₃-N 840mg/L,Na⁺ 1000mg/L, the adsorption behavior of NH₃-N were compared at three flow rates: 3.39mL/min, 5.1mL/min, and 8.33mL/min, the NH₃-N breakthrough capacity is 20.7, 19.6 and 16.52mg/g(dry copper loaded resin) respectively.The desorption experiment of NH₃-N loaded resin was also carried out. NH₃-N can be completely desorbed at pH=4 with dilute hydrochloric acid as desorbed solution and the desorption rate is still higher than 80% at pH=4 with concentrated ammonium chloride and hydrochloric acid as desorbed solution.It can be concluded that the copper loaded iminodiacetic acid chelating ion exchange resin is an effective for treatment of ammonia-nitrogen wastewater.