Synthesis Of Phosphorus-modified Poly(Styrene-co-divinylbenzene)-PAMAM Chelating Resin And Their Adsorption Mechanism Of Uranium

Nuclear energy is developing rapidly, the treatment of wastewater containing uranium have received much attention in recent years. Various removal methods of U(VI) from wastewater have been developed. However, these methods are not widely used because of their high cost, low feasibility and poor selectivity. In this work, combining the separation advantages of polymer resin and adsorbed advantage of polyamidoamine dendrimers, the new poly(styrene-co-divinylbenzene)-polyamidoamine-P,P-dichlorophenylphosphine oxide chelating resins were synthesized and characterized. Experimental parameters of static and dynamic adsorption were contained to study the adsorption desorption and regeneration properties, and relationship between the chelating resin structure and adsorption and desorption performance. Molecular modeling of the system was used for relationship between the macroscopic properties of the experimental results and the microscopic molecular simulation trajectories to explore the uranium chelation mechanism at the molecular level, and to optimize the design of the resin. Also, the resin was applied to the treatment of wastewater containing uranium to optimize adsorption separation processes. The present work which combin molecular modeling with experimental study, will be used in the preparation of dendrimer chelating resin to provide new technologies for the separation of uranium, and the theory for guiding synthetic resin. The research has important theoretical and practical application prospects. The main contents of this paper include:(1) Phosphorus-modified poly(styrene-co-divinylbenzene)-PAMAM chelating resin (PS-PAMAM-PPA) were prepared and used as adsorbents for the adsorption of uranium(Ⅵ) from aqueous solution. The synthesized resins were characterized by FTIR and XPS. The results demonstrated that the chelating resin was synthesized successfully by functionalizing ammoniated polystyrene beads with P, P-dichlorophenylphosphine oxide. However, due to cross-linking reaction, chelating molecules with increasing dendrimer generation, the degree of crosslinking is enhanced.(2) Comparing adsorption capacity for U(VI) of the PS-NH2, PS-PPA and different generation PS-nGPAMAM-PPA, it can be seen that, phosphorus-modified poly(styrene-co-divinylbenzene) chelating resin is better than amino resin bed, and due to the branched chain lengths, the steric and degree of crosslinking, PS-1.0G PAMAM-PPA had the largest adsorption capacity for U(VI) compared with other prepared adsorbents.(3) The effects of many physio-chemical properties on metal ion adsorption to adsorbent phase, such as solution pH, contact time, initial uranium concentration, temperature, were investigated using batch method. The results showed that the maximum adsorption rate were observed at the pH5.0; the temperature influence on the adsorption; U(VI) adsorption is favoured at high temperature; Adsorption equilibrium was achieved in approximately4h; ionic strength increases will reduce the adsorption of uranium decreased with the increase ionic strength, but the effect was weak. The maximum adsorption capacity (99.89mg/g) of PS-1.0G PAMAM-PPA was observed.(4) Adsorption kinetics study results show that the adsorption kinetics onto chelating resin followed the mechanism of the pesudo-second-order equation; The calculated thermodynamic parameters (△G,△H,△S) stated that the adsorption of U(VI) onto chelating resin were spontaneous, endothermic and feasible; The adsorption isotherms obeyed the Langmuir isotherm models.(5) The dynamic adsorption studies of U(VI) onto PS-PPA and PS-1.0G PAMAM-PPA showed that PS-1.0GPAMAM-PPA resin is better than PA-PPA resin, and the operation flow rate has a great influence on the dynamic adsorption, the best adsorption flow rate is3mL/min. Dynamic adsorption process meets Yoon-Nelson model. The dynamic desorption study of PS-PPA and PS-1.0G PAMAM-PPA chelating resin found that the resin can be desorbed effectively (about95%) by10%NaCl+1mol/L HC1. The chelating resin could be used repeatedly and adsorption and desorption percentage didn’t have any noticeable loss after26cycles in a fixed bed.(6) To further exploring the adsorption mechanism of Phenyl phosphoramides modified resin to UO2+, we use quantum chemical methods to design a simple model. The interaction theoretical research between Phenyl phosphoramides and UO22+has been carried out in simulating condition. Through quantum chemical calculations, we conclude the UO22+was likely forming a cis-complexe with two Phenyl phosphoramides at the end of dendrimer on resin. In this way, the UO22+can be adsorbed and separated from solution.