Preparation Of Nitrate Selective Anion Exchange Resin And Its Adsorption Performance

Nitrate pollution in drinking water resources has raised public concerns worldwide due to its potential risk of carcinogenic and teratogenetic effects to human.Among several feasible methods for nitrate removal,the ion exchange process seems to be the most suitable method for drinking water purification owing to its simplicity,effectiveness,renewability and chemical stability.Poly(styrene-co-divinylbenzene)(PS-DVB)particles is the ideal material for the preparation of nitrate selective anion exchange resin due to its insolubility,remarkable chemical stability and mechanical strength,the most of available nitrate selective anion exchange resins were prepared by employing it as matrix materials.However,the study of the effects of porosity,degree of cross-linking and functional groups on nitrate selectivity has not been published,especially the porosity and degree of cross-linking.In this study,an excellent nitrate selective anion exchange resin was also formulated via PS-DVB particles.Firstly,the optimum preparation conditions of PS-DVB anion exchange resin were investigated.Then,30 kinds of PS-DVB anion exchange resins of various porosities,degree of cross-linking and functional groups were synthesized under the optimized preparation conditions.According to the analysis of the nitrate adsorption isotherms,kinetics,thermodynamics and the nitrate selectivities of the 30 kinds of resins,and the effects of the polymer skeleton structure and functional groups on physicochemical property and adsorption selectivity of PS-DVB anion exchange resin.The polymer skeleton structure and functional group of the optimal nitrate selective anion exchange resin were confirmed.The experimental results indicated that the anion exchange resin with higher nitrate selectivity can be prepared by PS-DVB particles via chloromethylation and quaternarization using triethylamine,the porosity(porous agent was liquid paraffin)and the degree of cross-linking of the PS-DVB particles were respective 90%and 10 to18%.The anion exchange resin prepared by the above method with 90%of porosity and 14%of degree of cross-linking was considered as the optimal nitrate selective anion exchange resin and was named PBE-8 resin.In order to investigate the nitrate adsorption performance of PBE-8 resin,two strong nitrate selective anion exchange resins,Purolite A 520E(A 520E)and HZ-222 were chosen for comparative experiments and were respectively provided by Purolite Int.Ltd.,England,and Hebei Huazhong Chemical Co.,Ltd.,China.The experimental results are as follows:The maximum equilibrium nitrate uptake of PBE-8 was 26.19 mg-N/g,which was higher than that of Purolite A 520E(23.07 mg-N/g)but lower than that of HZ-222(33.57 mg-N/g).The regeneration ability of PBE-8 was close to A 520 E and better than HZ-222.The nitrate selective adsorption ability of PBE-8 resin was the best,and PBE-8 resin was more suitable for the treatment of low nitrate-polluted water than A 520 E and HZ-222.The nitrate adsorption by the PBE-8 and A 520 E resin showed a better fit to the Langmuir isotherm and pseudo-second-order kinetic model,The nitrate adsorption behaviors by the HZ-222 resin could be better expressed by Freundlich isotherm and pseudo-second-order kinetic model.The process of nitrate adsorption by A 520 E and PBE-8 resin were limitted by intraparticle diffusion.However,the process of nitrate adsorption by HZ-222 may be controlled by film diffusion and intraparticle diffusion together.The Gibbs free energy change(-12.15 to-1.15 kJ/mol),enthalpy change(0.35 to 7.73 kJ/mol)and entropy change(0.005 to 0.066 kJ/mol·K)indicated that the adsorption of aqueous nitrate by PBE-8 was feasible,endothermic and spontaneous.The results of column study for nitrate adsorption showed that: the breakthrough curves of nitrate could be better predicted by the Thomas and Yoon-Nelson models than the Adams-Bohart model.The elution curves of nitrate indicates that the amount of eluted nitrate and the regeneration liquid were positive correlated to the nitrate adsorption quantity in PBE-8 column.The optimal regeneration option should need to be balanced against the power and regeneration liquid consumption in practical application.Consequently,the PBE-8 resin with selective adsorption ability toward nitrate could potentially be applied in the purification of practical polluted drinking water resources.