Spherical Resorcinol-Formaldehyde Resin Research Articles

Cesium removal from AP-105 Hanford tank waste using spherical resorcinol formaldehyde resin

ABSTRACTSpherical resorcinol formaldehyde (SRF) resin is planned for use in removing cesium (137Cs) from Hanford tank waste supernates in preparation for waste vitrification at the Waste Treatment and Immobilization Plant. The results of six complete load/elute cycles using 12 L of Hanford tank waste supernatant collected from Tank AP-105 are provided. Testing exposed SRF to the combined sources of chemical degradation, physical stresses, and radiolytic exposure. Decreased flowrates and increased elution volumes improved performance. Increased cycling decreased performance; increased flowrate increased mass transfer zones; Cs leakage into ensuing cycle increased with decreased eluate volume, and analyte mass fractionation were examined.

Small- to large-scale comparisons of cesium ion exchange performance with spherical resorcinol formaldehyde resin

ABSTRACTIon exchange performance using spherical resorcinol formaldehyde resin was compared at three process scales (10 mL, 34 gal, and 297 gal). The small-scale test demonstrated earlier cesium breakthrough, but higher cesium capacity, relative to the large-scale tests. The low superficial flow velocity at the small scale impacted the cesium load profile resulting in a longer transition zone. Based on these results, small-scale column test results with actual tank waste will likely be worst case bounding with respect to initial cesium breakthrough and transition zone length, but could overpredict cesium capacity when extrapolated to large-scale column operations.

Removal of cesium by spherical resorcinol–formaldehyde resin beads: Sorption and kinetic studies

Batch equilibrium studies were conducted at 20 ± 0.5 °C with indigenously synthesized spherical resorcinol–formaldehyde resin beads, using radioanalytical technique, to determine their capacity for sorption of cesium ions from alkaline medium. Equilibrium isotherm studies were carried out, by varying the initial concentrations of cesium from 0.1 to 50 mM. The liquid-to-solid phase ratio of ~100 ml:1 g was maintained for all the sorption experiments. The equilibrium data were fitted to Langmuir and Freundlich isotherm models. It was observed that Freundlich isotherm explains sorption process nicely. The effect of resin size on percentage cesium ion uptake was also investigated, and 20–40 mesh size was found to be the optimum particle size. The cesium sorption capacity of the beads was determined to be ~238 mg/g. The kinetics of the sorption was studied at different initial cesium ion concentrations, and the kinetics data were fitted into various kinetics models. The kinetics of the cesium ion sorption was found to be pseudo second-order. The mechanistic steps involved were found to be complex, consisting of both film diffusion and intraparticle diffusion with film diffusion as the rate limiting step.

Preparation and evaluation of alginate-assisted spherical resorcinol–formaldehyde resin beads for removal of cesium from alkaline waste

A novel method of synthesis of spherical resorcinol–formaldehyde resin was developed, using calcium alginate beads as template. Batch sorption experiments were carried out, to remove cesium ions from aqueous alkaline solutions, using the synthesized resin beads. The effect of operating variables, such as the initial cesium ion concentration, sodium ion concentration, and contact time, on the sorption of cesium ions was studied. Equilibrium data were found to fit better to Langmuir isotherm equation, with a monolayer sorption capacity of 490.2mg/g, and the complete elution of the sorbed cesium ions was also possible. Sorption data were also analyzed in terms of both Lagergren first-order and pseudo second-order kinetic models, and were found to follow pseudo second-order kinetics at lower initial cesium ion concentration. The kinetic parameters were determined at different initial concentrations. The process mechanism was found to be complex, consisting of both film diffusion and intraparticle diffusion. Sorption data were also analyzed, using a Boyd plot, which confirmed that the rate-limiting step is the film diffusion.

Cesium Ion Exchange Loading Kinetics Testing with SRF Resin

Ion exchange using the Spherical Resorcinol-Formaldehyde (SRF) resin has been selected by the U.S. Department of Energy's Office of River Protection for use in the Pretreatment Facility of the Hanford Tank Waste Treatment and Immobilization Plant (WTP) and for potential application in an at-tank deployment for removing 137Cs. Recent proposed changes to the WTP ion exchange process baseline indicate that loading may include a broader range of sodium molarities (2 to 8 M) due to caustic leaching and higher temperatures (50°C) to alleviate post-filtration precipitation issues prior to reaching the ion exchange columns. Therefore, it is important to understand the behavior of SRF resin performance under the conditions expected with the new equipment and process changes. This research examined the impact of linear load velocity (4, 6, 8 cm/min), initial sodium concentration (2, 5, 8 M), initial sodium-to-cesium ratio (1.4E + 05, 2.1E + 05, 2.8E + 05 mol/mol), initial sodium-to-hydroxide ratio (2.0, 3.0, 4.0 mol/mol), and resin degradation during extended solution flow using elevated temperature (45°, 50°, 55°, 60°, 65°, 75°C). Testing was performed using a ∼2 mL column packed with SRF resin with feed flowing through it in an up-flow pattern. Samples were taken at set intervals and the data analyzed to help understand the impact of these conditions on the SRF resin performance. It was found that the loading kinetics were not significantly impacted by the sodium concentration over the range tested. However, the loading kinetics were impacted by the linear load velocity. These results indicated that at the test temperature, the adsorption of cesium is strongly dependent on mass transfer through the film and not significantly impacted by interparticle diffusion. Testing for extended times at elevated temperatures showed that the resin does degrade and loading capacity is reduced at and above 45°C. Above 60°C the resin appears to not load at all.

Evaluation of Potential Eluants for Non-Acid Elution of Cesium from Spherical Resorcinol-Formaldehyde Resin

Ion exchange column loading and elution of cesium from spherical resorcinol-formaldehyde resin have been conducted for two potential non-acid eluants – (NH4)2CO3 and CH3COONH4. The results revealed encouraging cesium elution performance. Virtually complete cesium elution was achieved with 28 or less bed volumes. Elution performance was fairly high at ∼8 bed volumes for some of the eluants and also practically comparable to the benchmark acid eluant (HNO3). Elution is generally enhanced by increasing the concentration and pH of the eluants, and combining the eluants.

Characterization of Spherical Resorcinol-Formaldehyde Resin Cesium Adsorption with Batch Contact Tests

Batch contact tests provided data that will be useful in cesium isotherm modeling of spherical resorcinol-formaldehyde ion exchange resin. This resin is the baseline for cesium removal from alkaline high sodium nuclear waste at the Hanford River Protection Project Waste Treatment Plant and is being considered for other applications. Batch contact work at 25°C found that increasing potassium concentration in alkaline solution simulating waste unexpectedly improves cesium adsorption when cesium concentration exceeds about 0.001 M. At lower cesium levels potassium competes with cesium for adsorption on the resin as expected. Additional batch work found that dimethylamine cation competes strongly with sodium adsorption with no significant reduction in cesium adsorption.

Spherical Resorcinol‐Formaldehyde Resin Testing for Cesium Removal from Hanford Tank Waste Simulant

A new spherical form of resorcinol‐formaldehyde (RF) resin was tested for efficacy of cesium removal from Hanford tank waste. Two spherical RF formulations, prepared by varying curing temperature, were tested. Both resins had a tight particle size distribution and a high degree of sphericity. Small‐scale column testing (on ∼20‐mL resin beds) was conducted evaluating the cesium load profile with AZ‐102 simulated tank waste and the cesium elution profile using 0.5 M HNO3 eluant. The load and elution profiles were compared in side‐by‐side testing with ground‐gel RF resin and SuperLig® 644, the Waste Treatment Plant baseline ion exchanger. Although breakthrough capacity was not as high as the other resins tested, the spherical RF resin met plant cesium loading requirements with the AZ‐102 simulant matrix. Excellent reproducibility of cesium load and elution was demonstrated over three process cycles with no evidence of degraded performance. Residual cesium on the resin beds after elution was nearly a factor of 10 lower than that of the ground‐gel RF and SuperLig® 644.