Adsorption Behaviors Of Nitrate Ion On Ion-Exchange Fiber

In recent years,nitrate pollution in groundwater and surface water has attracted worldwide attention.Nitrate is very soluble in water,and too high nitrate concentration poses a serious threat to human health.At present,the national 1A-level discharge standard proposed by the country makes the comprehensive improvement of the sewage treatment plant in China more urgent.The excessive concentration of NO₃^--N has become an important factor restricting the TN compliance.The ion exchange method is one of the main methods for the removal of NO₃^--N in water.In this paper,the ion exchange fiber with fast adsorption and desorption rate and good anti-organic pollution performance is applied to the deep treatment of the secondary effluent of the actual sewage plant.In our study,Polyacrylonitrile fiber（PAN）was used as a carrier to graft polyethyleneimine（PEI）and PEI polymer was N-treated by bromoalkane（bromopropane,bromopentane,bromooctane and bromosane）.Four kinds of anion exchange fibers with different functional groups（PAN-PEI-B,PAN-PEI-W,PAN-PEI-X,PAN-PEI-S）were optimized by alkylation modification.The physicochemical structure of the prepared fiber adsorbent was characterized,and the surface morphology,chemical structure and composition of the fiber adsorbent were analyzed.The effects of temperature,initial concentration of NO₃^--N,time,solution pH and coexisting inorganic anions and organics on the removal performance of NO₃^--N were investigated.Results show that under the single system,the adsorption process is almost unaffected by the pH and temperature of the solution,and the adsorption and desorption rate is very fast,which can be completed within 10²0min.The whole adsorption process conforms to the pseudo second-order kinetic model and the adsorption isotherm data of the four kinds of fibers can be accurately fitted by the Langmuir model.Adsorption thermodynamic studies show that the adsorption process of NO₃^--N is exothermic and can occur spontaneously.For the desorption process,when the concentration of NaCl solution is 0.3mol/L,the rapid and efficient desorption of the new ion exchange fiber can be achieved,and the desorption performance is good.After six cycles of adsorption and desorption,the NO₃^--N still has good adsorption performance.Under the coexistence of inorganic salts and nitrate nitrogen,the presence of sodium sulfate and sodium chloride will affect the adsorption performance of the fiber.The degree of interference is:sodium sulfate>sodium chloride.Under the condition of anion coexistence,order of the maximum adsorption of four fibers predicted by Langmuir model is:PAN-PEI-S>PAN-PEI-X>PAN-PEI-W>PAN-PEI-B,indicating that the selectivity of nitrate ions is better as the chain length of the alkylated fiber increases.After the comprehensive consideration of material synthesis conditions,adsorption capacity and selectivity,the PAN-PEI-W fiber with best comprehensive performance is optimized,and its anti-organic pollution performance is also compared with Purolite A520E resin.Results show that the PAN-PEI-W ion exchange fiber can be efficiently regenerated,and its anti-organic pollution ability is stronger than that of A520E.At the same time,in the dynamic experiment of treating NO₃^--N in the secondary effluent of the actual sewage plant,PAN-PEI-W fiber has fast adsorption-desorption rate and stable performance.Besides,it can be reused,which has certain application prospects.