[en] The reduction of NpO²⁺ and PuO₂²⁺ by oxalate. citrate, and ethylenediaminetetraacetic acid (EDTA) was investigated in low ionic strength media and brines. This was done to help establish the stability of the An(VI) oxidation state in the presence of organic complexants. The stability of the An(VI) oxidation state depended on the pH and relative strength of the various oxidation state-specific complexes. At low ionic strength and pH 6, NpO₂O²⁺ was rapidly reduced to form NpO₂⁺ organic complexes. At longer times, Np(IV) organic complexes were observed in the presence of citrate. PuO₂²⁺ was predominantly reduced to Pu⁴⁺, resulting in the formation of organic complexes or polymeric/hydrolytic precipitates. The relative rates of reduction to the An(V) complex were EDTA > citrate > oxalate. Subsequent reduction to An(IV) complexes, however, occurred in the following order: citrate > EDTA > oxalate because of the stability of the An(V)-EDTA complex. The presence of organic complexants led to the rapid reduction of NpO₂²⁺ and PuO₂P²⁺ in G-seep brine at pHs 5 and 7. At pHs 8 and 10 in ERDA-6 brine, carbonate and hydrolytic complexes predominated and slowed down or prevented the reduction of An(VI) by the organics present

[en] This document reports on the work done by the Separations Science and Technology Programs of the Chemical Technology Division, Argonne National Laboratory (ANL), in the period October 1993-March 1994. This effort is mainly concerned with developing the TRUEX process for removing and concentrating actinides from acidic waste streams contaminated with transuranic (TRU) elements. The objectives of TRUEX processing are to recover valuable TRU elements and to lower disposal costs for the nonTRU waste product of the process. Other projects are underway with the objective of developing (1) evaporation technology for concentrating radioactive waste and product streams such as those generated by the TRUEX process, (2) treatment schemes for liquid wastes stored are being generated at ANL, (3) a process based on sorbing modified TRUEX solvent on magnetic beads to be used for separation of contaminants from radioactive and hazardous waste streams, and (4) a process that uses low-enriched uranium targets for production of ⁹⁹Mo for nuclear medicine uses

[en] Polymer-coated ferromagnetic particles with an absorbed layer of octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) diluted by tributyl phosphate (TBP) are being evaluated for application in the separation and the recovery of low concentrations of americium and plutonium from nuclear waste solutions. Due to their chemical nature, these extractants selectively complex americium and plutonium contaminants onto the particles, which can be recovered from the waste solution using a magnet. Chemical characterization of the extractant-absorbed particles from simulated solutions and various nitric acid solutions was performed by gamma and liquid scintillation counting of plutonium and americium. The concentration range is 0.01M HNO₃ to 6M HNO₃. The actinide partition constant (K_d) at 2M HNO₃ was determined to be between 3000 and 30,000, which is larger than those projected for actinides recovered by additional liquid/liquid extraction. Results from transmission electron microscopy (TEM) indicated a large dependence of K_d on relative magnetite location within the polymer and the polymer surface area. Monitoring the simulated waste solutions by inductively coupled plasma (ICP) analysis demonstrated that magnetite dissolution was 4% after 2 weeks in 5M HNO₃. Energy disperse spectroscopy (EDS) demonstrated homogeneous metal complexation on the polymer surface with no metal clustering. The radiolytic stability of the particles was studied using ⁶⁰Co gamma irradiation under various conditions. The results showed that K_d more strongly depends on the nitric acid dissolution rate of the magnetite than the gamma irradiation dose. Results of actinide separation from simulated high level waste representative of that at various DOE sites are discussed

[en] A caustic-side solvent extraction (CSSX) process to remove cesium from Savannah River Site (SRS) high-level waste was tested in a minicontactor (2-cm centrifugal contactor). In the first phase of this effort, the minicontactor stage efficiency was improved from 60% to greater than 80% to meet the SRS process requirements using a 32-stage CSSX flowsheet. Then, the CSSX flowsheet was demonstrated in a 32-stage unit, first without solvent recycle, then with it. In both cases, the key process goals were achieved: (1) the cesium was removed from the waste with decontamination factors greater than 40,000 and (2) the recovered cesium was concentrated by a factor of 15 in dilute nitric acid. Oak Ridge National Laboratory (ORNL) analysis of the recycled solvent showed no evidence of impurity buildup

[en] Conversion from high-enriched uranium (HEU) to low-enriched uranium (LEU) targets for the Mo-99 production requires certain modifications of the target design, the digestion and the purification processes. ANL is assisting the Argentine Comision Nacional de Energia Atomica (CNEA) to overcome all the concerns caused by the conversion to LEU foil targets. A new digester with stirring system has been successfully applied for the digestion of the low burn-up U foil targets in KMnO4 alkaline media. In this paper, we report the progress on the development of the digestion procedure with stirring focusing on the minimization of the liquid radioactive waste.

[en] Polymeric-coated ferromagnetic particles with an absorbed layer of octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) diluted by tributyl phosphate (TBP) are being evaluated for application in the separation and the recovery of low concentrations of americium and plutonium from nuclear waste solutions. Due to their chemical nature, these extractants selectively complex americium and plutonium contaminants onto the particles, which can be recovered from the waste solution using a magnet. The effectiveness of the extractant-absorbed particles at removing transuranics (TRU) from simulated solutions and various nitric acid solutions was measured by gamma and liquid scintillation counting of plutonium and americium. The HNO₃ concentration range was 0.01 M to 6M. The partition coefficients (K_d) for various actinides at 2M HNO₃ were determined to be between 3,000 and 30,000. These values are larger than those projected for TRU recovery by traditional liquid/liquid extraction. Results from transmission electron microscopy indicated a large dependence of K_d on relative magnetite location within the polymer and the polymer surface area. Energy disperse spectroscopy demonstrated homogeneous metal complexation on the polymer surface with no metal clustering. The radiolytic stability of the particles was determined by using ⁶⁰Co gamma irradiation under various conditions. The results showed that K_d more strongly depends on the nitric acid dissolution rate of the magnetite than the gamma irradiation dose. Results of actinide separation from simulated high-level waste representative of that at various DOE sites are also discussed

[en] The reduction of NpO₂²⁺ and PuO₂²⁺ by oxalate, citrate, and ethylenediaminetetraacetic acid (EDTA) was investigated in low ionic strength media and brines. This was done to help establish the stability of the An(VI) oxidation state in the presence of organic complexants. The stability of the An(VI) oxidation state depended on the pH and relative strength of the various oxidation state-specific complexes. At low ionic strength and pH 6, NpO₂²⁺ was rapidly reduced to form NpO₂⁺ organic complexes. At longer times, Np(IV) organic complexes were observed in the presence of citrate, PuO₂²⁺ was predominantly reduced to Pu⁴⁺, resulting in the formation of organic complexes or polymeric/hydrolytic precipitates. The relative rates of reduction to the An(V) complex were EDTA > citrate > oxalate. Subsequent reduction to An(IV) complexes, however, occurred in the following order: citrate > EDTA > oxalate because of the stability of the An(V)-EDTA complex. The presence of organic complexants led to the rapid reduction of NpO₂²⁺ and PuO₂²⁺ in G-Seep brine at pHs 5 and 7. At pHs 8 and 10 in ERDA-6 brine, carbonate and hydrolytic complexes predominated and slowed down or prevented the reduction of An(VI) by the organics present. (orig.)

[en] The reduction of NpO₂²⁺ and PuO₂²⁺ by oxalate, citrate, and ethylenediaminetetraacetic acid (EDTA) was investigated in low ionic strength media and brines. This was done to help establish the stability of the An(VI) oxidation state depended on the pH nd relative strength of the various oxidation state-specific complexes. At low ionic strength and pH 6, NpO₂²⁺ was rapidly reduced to form NpO₂⁺ organic complexes. At longer times, Np(IV) organic complexes were observed in the presence of citrate. PuO₂²⁺ was predominantly reduced to Pu⁴⁺, resulting in the formation of organic complexes or polymeric/hydrolytic precipitates. The relative rates of reduction to the An(V) complex were EDTA > citrate > oxalate. Subsequent reduction to An(IV) complexes, however, occurred in the following order: citrate > EDTA > oxalate because of the stability of the An(VI)-EDTA complex. The presence of organic complexants led to the rapid reduction of NpO₂²⁺ and PuO₂²⁺ in G-Seep brine at pHs 5 and 7. At pHs 8 and 10 in ERDA-6 brine, carbonate and hydrolytic complexes predominated and slowed down or prevented the reduction of An(VI) by the organics present

[en] An alkaline-side solvent extraction process was developed for cesium removal from Savannah River Site (SRS) tank waste. The process was invented at Oak Ridge National Laboratory and developed and tested at Argonne National Laboratory using singlestage and multistage tests in a laboratory-scale centrifugal contactor. The dispersion number, hydraulic performance, stage efficiency, and general operability of the process flowsheet were determined. Based on these tests, further solvent development work was done. The final solvent formulation appears to be an excellent candidate for removing cesium from SRS tank waste.

[en] Our experimental investigations are focused on the use of XANES/EXAFS to identify actinide phases and oxidation state in environmentally-relevant samples. Oxidation state trends with XANES edge position were first established for plutonium and neptunium reference solids. The results for a series of plutonium solids that differ in oxidation state are shown. We have also examined a series of Pu(III) solids where we have shown that even though significant differences in the geometry exist, the edge positions do not change (to an uncertainty of ± 0.3 eV). Similar experiments were done with neptunium standards but the oxidation state trends are less clear. On the basis of the results with plutonium standards, XANES was used to establish oxidation state in actinide precipitates in WIPP brine, actinide waste forms, and biologically-induced actinide precipitation reactions. These experimental efforts are integrated with theoretical efforts to calculate XANES/EXAFS spectra to help interpret the experimental results. Calculations of the Pu L_III XANES of small cluster models of the local Pu environment in PuO₂ have been carried out to compare with the experimental results obtained at the APS. The resulting spectra give relative peak energies and intensities in good agreement with experiment. (authors)