Influence of Crosslinking and Porosity on the Uranium Adsorption of Macroreticular Chelating Resin Containing Amidoxime Groups

Macroreticular chelating resins (RNH) containing amidoxime groups with various degrees of crosslinking were synthesized by using various amounts of divinylbenzene (DVB) or/and poly(ethylene glycol) dimeth-acrylate [ethylene glycol dimethacrylate (IG), diethylene glycol dimethacrylate (2G), triethylene glycol dimethacrylate (3G), tetraethylene glycol dimethacrylate (4G), and nanoethylene glycol dimethacrylate (9G)] as crosslinking reagent. The effects of crosslinking reagents on the pore structure, ion-exchange capacity, swelling ratio, and adsorption ability for uranium of RNH were investigated. The adsorption ability of RNH for uranium was tested by use of natural seawater or U-spiked seawater. RNH-1G samples prepared by using 1G were shown to have macroreticular structures by measuring the specific surface area. RNH-1G had high adsorption ability and good physical stability. Though RNH-4G samples obtained by using 4G had little macroreticular structure (macropore), these resins showed high adsorption ability for uranium on treatment with 0. 1 M NaOH at 30°C for 15 h. RNH-4G was found to have low physical and chemical stability. For the preparation of RNH with effective pore structure for the recovery of uranium, as well as chemical and physical stability, the simultaneous use of DVB and 1G or 4G as crosslinking reagent was examined (abbreviated as RNH-DVB-1G and RNH-DVB-4G). The RNH-DVB-1G showed high adsorption ability for uranium. Repeated use did not cause deterioration of either RNH-DVB-1G or RNH-DVB-4G. RNH-DVB-1G samples with various degrees of crosslinking were prepared, and the uranium recovery of the resins was also investigated by a column method. Although the RNH-DVB-1G samples with the same degree of crosslinking had almost the same content of amidoxime groups, the uranium recovery of each RNH-DVB-1G sample was considerably different and increased by treatment with alkali solution. These results indicate that the adsorption ability of RNH-DVB-1G for uranium in seawater was not only affected by the macropores but also by the micropores formed by swelling of the resins.