Preparation Of Novel Polystyrene Resin With High Total Ion Exchange Capacity For Nitrate Removal From Water

Water pollution due to excessive presence of nitrogen species is a serious problem worldwide in recent years.Several methods were used to remove nitrate from water including chemical denitrification,reverse osmosis,electrodialysis,biological de-nitrification,adsorption/ion exchange.Among these technologies,adsorption/ion exchange by ion exchange resins was more popular due to high adsorption capacity and simple operation.The chloromethyl content of chloromethylated cross-linked polystyrene limited more amine groups modified on the resin.Thus,new method to prepare anion exchange resin with high anion exchange capacity still remained to be developedIn the present work,we synthesized new polystyrene resin P-Q with higher total ion-exchange capacity by amination and quaternization.Compared with traditional anion exchange resin reported in previous literatures,P-Q had higher adsorption capacity for nitrate.The mechanism of nitrate adsorption by P-Q was investigated The effects of pH and co-existing anions on nitrate removal in natural water were tested.Furthermore,the dynamic column adsorption-desorption experiments were conducted in order to provide more practical application for nitrate removal.The main conclusions of this thesis are shown as follows:1)New polystyrene resin P-Q with high total ion-exchange capacity was prepared using a simple method.The FT-IR,BET and ion-exchange capacity were used to characterize the resin P-Q.The weak base ion-exchange capacity and the strong base ion-exchange capacity were 3.10 mmol/g and 2.60 mmol/g,respectively.Thus,the total ion-exchange capacity was 5.70 mmol/g.2)Nitrate was absorbed not only by ionic bonding but also by hydrogen bonding(NO3-…H2N-,NO3-…HO-)formed between nitrate and P-Q.The equilibrium adsorption isotherms of P-Q for nitrate were well fitted by Langmuir equation,and the maximum monolayer adsorption capacity for nitrate was 221.81 mg g-1.The enthalpy change(-12.32?-9.65 kJ/mol)and free energy change(-2.7?-0.76 kJ/mol)were indicative of an exothermic and spontaneous adsorption process.Both pseudo-first-order and pseudo-second-order equations could fit the adsorption kinetic curves of nitrate well,suggesting that both film diffusion and intra-particle diffusion as the rate limiting step of the adsorption in solution.3)Solution pH had no obvious effect on nitrate adsorption within the natural water pH range(6.5-8.5).The adverse influence of coexisting anions on nitrate removal followed the order of 'SO42->HCO3->Cl-'.However,even as the initial molar ratio was up to 4,P-Q could still remain 50%of equilibrium adsorption capacity for nitrate.4)It was found that as the flow rate and inlet concentration increased,the breakthrough point and saturated point were reached earlier.The adsorption capacity of P-Q increased,whereas the height of adsorbents showed an opposite trend.Thomas model,Yoon-Nelson model and Bohart-Adams model could predict the breakthrough curves well.Finally,the P-Q could be regenerated by eluting the adsorbed nitrate with 1 mol/L NaCl solution.There was no significant decrease in its sorption capacity when repeatedly used for at least five times.