Synthesis, structural characterization, and performance evaluation of resorcinol-formaldehyde (R-F) ion-exchange resin
DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. Summary The 177 underground storage tanks at the U.S. Department of Energy's Hanford Site contain an estimated 180 million tons of high-level radioactive wastes consistmg of a mixture of sludge, salt cake, and alkaline supernatant liquids. The insoluble sludge, composed of metal oxides and hydroxides, contains the bulk of most of the radionuclides
... le the salt cake is composed primarily of sodium salts. The alkaline supernates are concentrated solutions consistug primarily of sodium nitrate and nitrite in which water soluble radionuclides, such as I3%s, are found. Economically, it is desirable to remove and concentrate the highly radioactive fraction of the tank wastes for vitrification, with the bulk of the waste being disposed of in a relatively low-cost method. Ion-exchange technology is being evaluated for removal of cesium from waste tanks of both the W o r d and Savannah River Sites. This report summarizes studies into the synthesis and characterization of resorcinol-formaldehyde (R-F) resin, an organic ion-exchange resin with high selectivity and capacity for the cesium ion, which is a candidate ion-exchange material for use in remediation of tank wastes. The report includes idormation on the structure/fbnction analysis of R-F resin and the synthetic factors that affect performance of the resin. Some comparison with CS-100, a commercially available phenol-formaldehyde (P-F) resin, and currently the baseline ion-exchanger for removal of cesium ion at Hanford, is made with the R-F resin. The primary structural unit of the R-F resin was determined to consist of a 1,2,3,4-tetrasubs&uted resorcinol ring unit while the CS-100, a P-F resin, was composed mainly of a 1,2,4-trisubstiMed ring. The CS-100 resin shows the presence of phenoxy-ether groups. This factor may account for the much lower decontamination factor or performance of CS-100 for cesium ion compared to the R-F resin. Curing temperatures for the R-F resin were found to be optimal in the range of 105-130 "C. At lower temperatures, insuflicient curing, hence crossldung, of the polymer resin occurs and the selectivity for cesium drops. Curing at elevated temperatures, even under inert atmosphere, leads to chemical degradation ofthe polymer resin with drastic reduction in performance. The 0ptuna.l particle size for R-F resin is in the range of 20-50 mesh-sized particles. Larger particles have lower performance for cesium, due to of particle diffusion limitations. Smaller particles, which have higher surface areas and greater access to ion-exchange sites, probably have lower performance because a large number of the sites are chemically degraded, and are thus not available for ion-exchange. R-F resin undergoes chemical degradation or oxidation, which destroys ion-exchange sites as correlated with lower cesium k ' s . The ion-exchange sites (hydroxyl groups) are converted to quinones and ketones. CS-100, though it has much lower performance for cesium ion-exchange, is significantly more chemically stable than R-F resin. Exposure to gamma radiation also shows that CS-100 is more radiolytically stable than R-F resin. ... 111 thermogravimetric analysis/mfrared dab; Ronald K. Stephens for the Brunauer, Emmett, Teller analysis; David E. McCready for the x-ray diffraction analysis; Shelley J. Carlson for providing the scanning electron microscopy; and Betty E. Tanaka, Robert J. Elovich, and Jaquetta R. Deschane for performing the Kd analyses.