Performance Of Macroporous Polyacrylic Anion Exchange Resins For Removal Of Nitrate Ion In Aqueous Solutions

With the improvement of the standards for urban sewage plant treatments, the discharge of total nitrogen in sewage plant began to be strictly controlled. By the restriction of traditional biological nitrogen removal efficiency, many sewage plants were difficult to reach the total nitrogen emission standards, which high nitrate concentration was the main reason. Nitrate was carcinogenic, teratogenic and genetic variability, and excess nitrate in aquatic environment could cause eutrophication. Ion-exchange has become one of effective methods which was applied to remove nitrate in water because of its features of simple, stable and can be recycled to use. Compare to commonly used polystyrene anion exchange resin, polyacrylic anion exchange had a better resistance to organic pollution. To improve the adsorption capacity, selectivity, desorption performance and resistance to organic fouling of ion exchange resin, two new kinds of macroporous polyacrylic strong anion exchange resins D311-C2 and D311-C3 were synthesized by alkylation of a basic polyacrylic weakly anion exchange resin D311,and the polyacrylic strong anion exchange resin D213 and nitrate special resin Purolite A 520E were selected for comparison to research the adsorption-desorption performance of resins toward NO3-, the main contents are as follows:(1) Synthesis of resins:Two new kinds of macroporous polyacrylic anion exchange resins D311-C2 and D311-C3 were synthetized successfully by alkylation of ethyl bromide or n-propyl bromide with weakly anion exchange resin D311. Their exchange capacities were measured, indicating that their strong exchange capacities had improved significantly to more than 3.4mmol/g.(2) Adsorption performance of resins:In static experiments, the main results were as follows: The adsorption isotherm data of the four resins (D311, D311-C2, D311-C3 and D213) for NO3-could be well matched with Langmuir isotherm model. The maximum adsorption capacity (Qm) of the four resins(D311, D311-C2, D311-C3 and D213) for NO3- were 17.24,40.82,40.32, 41.15mg/g at 25℃.The kinetic data of the four resins could be well fitted by Pseudo-second-order equation. The adsorption thermodynamics analysis showed that the adsorption of four resins was a spontaneous and exothermic process. The impact of pH on the adsorption capacity of the three strong resins (D213, D311-C2 and D311-C3) were negligible. At the same concentration of chlorine or sulfate ions presented in the solution, D311-C3 had a better selectivity for nitrate.0.8M sodium chloride solution was the best regeneration for resin, desorption rate was more than 95%.(3) Resistance to organic fouling performance of resin:The experiment of four resins (D213, Purolite A 520E, D311-C2 and D311-C3) showed that the three kinds of polyacrylic resin had a higher efficiency of regeneration exchange, and they had a better resistance to organic fouling than polystyrene exchange resins.Application of resin showed that both D311-C2 and D311-C3 resin could be good for the depth removal of nitrate from secondary effluent in sewage treatment plants, so that they had good application prospects.