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Ind. Eng. Chem. Res. 1999, 38, 1676-1682
Design, Synthesis, and Uptake Performance of ABEC Resins for the Removal of Pertechnetate from Alkaline Radioactive Wastes Andrew H. Bond,*,†,‡ Frank W. K. Chang,† Anil H. Thakkar,† Joel M. Williamson,† Michael J. Gula,† James T. Harvey,† Scott T. Griffin,§ Robin D. Rogers,*,§ and E. Philip Horwitz*,| Eichrom Industries, Inc., 8205 S. Cass Avenue, Ste. 107, Darien, Illinois 60561, Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama 35487, and Chemistry Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, Illinois 60439
Removal of technetium-99 and iodine-129 from alkaline radioactive wastes remaining from weapons processing is necessary as these radionuclides are long-lived and environmentally mobile in their most stable chemical forms (TcO4- and I-). Technetium-99 and iodine-129 are ill-suited to thermal processing because of the volatility of their high-temperature species. Resins based on Aqueous Biphasic Extraction Chromatography, ABEC, selectively extract TcO4- and I- from alkaline radioactive wastes and offer the advantage that stripping is accomplished by eluting with water. To date, most studies of ABEC resins have been performed using materials designed for analytical separations that are not suitable for process-scale applications. The development of ABEC resins compatible with a large-scale chromatographic apparatus is reported. ABEC resins of 50-100 mesh size showing 30 free column volumes) of 4 M NaOH over the bed. (Some individual resin beads were observed to float under static conditions, but the bed remained settled under gravity flow.) The 4 M NaOH was drained to the top of the resin bed and the bed height marked. The resin was then removed from the column which was thoroughly rinsed with H2O. The column was filled with H2O and drained to the mark representing the bed height in H2O, and this mass was recorded. The H2O was then drained to the bed height in 4 M NaOH and to the lower bed support, and the respective masses were recorded. The bed densities, with units of grams of dry resin per milliliter of bed in H2O or 4 M NaOH, were calculated using the mass of the wet resin, the percent solids, the density of H2O, and the mass of H2O occupied by the resin in each solution. Each bed density determination was performed in duplicate. Swelling Percentages. The extent of swelling that the resin undergoes upon crossover from a load solution of 4 M NaOH to a H2O strip was calculated using the bed density data. Because of the fixed geometric parameters of a chromatographic column, only the bed height changes when the resin swells or contracts. It is then possible to calculate the change in bed height, reported as percent swelling, using the following equation:
% swelling )
(
)
Fbed in 4 M NaOH - Fbed in H2O × 100 Fbed in 4 M NaOH
where Fbed represents the bed density in the respective solution. This equation represents a conservative estimate for calculating swelling characteristics. After contracting, most resins do not swell to 100% of their previous volume, and this behavior has been observed for these ABEC resins. Given the potential complications arising from resin swelling in large chromatographic columns, the most conservative approach was adopted. All swelling percentage experiments are relative to the bed density (height) in 4 M NaOH. Uptake Measurements. All dry weight distribution ratios were determined radiometrically by batch contacts of the resins with the desired solutions at 25 (2) °C. The dry weight distribution ratio is defined as
Dw )
(
)(
)
A0 - Af V Af mR(% solids/100)
where A0 ) count rate in solution prior to contact with the resin, Af ) count rate in solution after contact with the resin, V ) volume (mL) of solution in contact with the resin, mR ) mass (g) of wet resin, and the % solids allows conversion to the dry mass of resin. The batch uptake experiments were performed by adding microliter quantities of 99TcO4- in HNO3 or NaOH solution to 1.2 mL of the solution of interest, gently mixing, and removing a 100 µL aliquot for liquid scintillation counting (A0). A total of 1 mL of the remaining solution (V) was added to a known mass of wet resin (mR) and centrifuged for 1 min. The mixture was then stirred gently (so that the resin was just
suspended in the solution) for 30 min, followed by 1 min of centrifugation and another 30 min of stirring. After 1 min of centrifugation to settle the resin, the solution was pipeted away and filtered through a 0.45 µm poly(tetrafluoroethylene) filter to remove any suspended resin particles. A 100 µL aliquot (Af) was then taken for counting. All dry weight distribution ratio experiments were performed in duplicate and are accurate to two significant digits. The volume distribution ratio, Dv, has units of milliliters of solution per milliliter of bed and more accurately predicts column chromatographic performance than does the dry weight distribution ratio. The volume distribution ratio is defined as
Dv ) DwFbed and was calculated using the Dw values and bed densities in 4 M NaOH. Results and Discussion Chromatographic separations performed on the process scale can have many features in common with their bench-scale predecessors but often introduce new and complicated features. The chromatographic material must obviously exhibit the desired selectivity, but the resin also must be compatible with plant feed streams and should possess favorable physical properties so that process engineering considerations are minimized. These chemical and engineering factors collectively influence the process economics, which is a principal factor governing implementation of new process-scale separations. When these considerations are accounted for, four areas are key to developing an ABEC resin that is suitable for use in process-scale separations: (1) uptake properties, (2) capacity, (3) large particle size resins, and (4) changes in bed volume during loading and stripping. Points 1 and 2 relate to uptake performance and include high distribution ratios, favorable loading and stripping rates, and good selectivity, whereas points 3 and 4 are engineering considerations. Large particle size resins are needed so that useful flow rates can be achieved, and point 4 is discussed below. Because of the nature of ABEC separations, loading is performed from molar concentrations of salt (e.g., OH-, SO42-, CO32-, PO43-, etc.) and stripping is accomplished by eluting with water. Such drastic changes in eluent composition are often accompanied by changes in the bed density (or bed height in a chromatographic column) due to the changing hydration environment of the resin. Accounting for large changes in bed height in a chromatographic apparatus is nontrivial from an engineering perspective and would adversely affect the process economics. Thus, ABEC resins with favorable uptake properties and improved physical characteristics are needed to make process-scale separations more feasible. Synthesis Results. Table 1 lists the monomer compositions, mesh sizes, and percent solids for 20 resins prepared as part of this study. Two copolymer substrates were prepared: gel-type and Xero gel-type. The former is more common and has somewhat smaller pores of relatively uniform dimensions. Xero gel resins are prepared with the aid of a porogen (toluene in these studies) that serves to enlarge the pores, potentially offering enhanced access to subsequent reactants and to solutes during loading.
Ind. Eng. Chem. Res., Vol. 38, No. 4, 1999 1679 Table 2. Comparison of Physical Properties and Pertechnetate Uptake Performance of Different ABEC Resin Formulations sample name ABEC-5000 G1 G2 G3 XG1 XG2 XG3 XG4 XG5 XG6 XG7 XG8 XG9 XG10 XG11 XG12 XG13 XG14 XG15 XG16 XG17 a
% DVB
bed density in H2O (g/mL)
bed density in 4 M NaOH (g/mL)
Dw in 4 M NaOH (mL/g)
Dv in 4 M NaOH (mL/mL)
% swellinga
1 1 2 5 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2
0.058 0.0941 0.296 0.637 0.139 0.106 0.0948 0.153 0.119 0.098 0.153 0.118 0.115 0.205 0.140 0.116 0.240 0.376 0.384 0.366 0.226
0.110 0.192 0.328 0.637 0.234 0.187 0.211 0.227 0.194 0.189 0.216 0.205 0.212 0.292 0.193 0.186 0.260 0.426 0.384 0.366 0.226
1100 900 500 18 640 440 410 630 670 690 550 790 840 590 710 710 250 120 370 340 560
120 170 160 11 150 82 87 140 130 130 120 160 180 170 140 130 65 51 140 120 130
47.3 51.0 9.76 0.00 40.6 43.0 55.1 32.6 38.7 48.2 29.2 42.3 45.8 29.7 27.8 36.8 7.52 11.7 0.00 0.00 0.00
Percent swelling relative to the bed density in 4 M NaOH.
The benchmark resin, ABEC-5000, was synthesized using Me-PEG-5000, whereas the other materials prepared in this study used Me-PEG-2000. The lower molecular weight Me-PEG-2000 was selected as previous studies showed that the weight distribution ratios were only slightly higher for ABEC-5000 than for ABEC-2000;25,26,29,30 the latter typically had higher percent solids, indicating a potentially higher bed density and volume distribution ratio, and the cost of Me-PEG-2000 is approximately half that of Me-PEG5000 on a mole basis. Three 50-100 mesh gel-type resins with increasing DVB cross-linking percentages were prepared to determine the influence of copolymer substrate rigidity on the distribution ratios, bed densities, and swelling properties of ABEC resins. As the degree of cross-linking increases, resins become more mechanically rigid and show lower swelling percentages. Accompanying an increase in rigidity (in the absence of diluent), the resin pores become smaller and less accessible to reactants in subsequent synthetic steps and to solutes during loading. Thus, the potential increase in the number of stagnant pores within the resin and the concomitant decrease in uptake performance must be balanced with improvements in the physical properties of a resin, in this case, the rigidity and resistance to swelling. For ABEC resins in particular, a decrease in pore size could greatly diminish Me-PEG grafting yields as molecules of this size may be excluded from the pores, resulting in lower distribution ratios. Approximate information relating to the amount of Me-PEG on an ABEC resin can be derived from the percent solids data. The copolymer substrates are typically nonwettable in aqueous media, and it is grafting of the Me-PEGs that imparts hydrophilicity to ABEC materials. Table 1 shows that the percent solids for the three gel-type resins increases with increasing DVB content, in accordance with decreasing Me-PEG content. The Xero gel resins were prepared using 1 and 2% (w/w) DVB cross-linking and variable VBC contents and diluent percentages. The VBC content influences the extent of Me-PEG grafting and, therefore, was thought to be an important variable for the Xero gel resins where
the large pores offer greater accessibility to the Me-PEG during synthesis. (VBC is the alkyl halide group with which the Me-PEG alkoxide reacts during the grafting reaction.) As the data in Table 1 show, the percent solids for these resins generally decrease with increasing VBC content, implying higher Me-PEG contents. The ratios of toluene diluent were varied to gain some understanding of the role of porosity on the Me-PEG grafting yields and the uptake properties of the Xero gel resins. Higher diluent percentages effect larger cavities within the copolymer substrate, which should aid diffusion into the pores and anchoring of the Me-PEG. For the 1 and 2% DVB-containing Xero gel resins, the percent solids generally increases with decreasing diluent percentages, indicating slightly lower Me-PEG grafting as the pore size decreases. The major differences between the 1 and 2% DVB cross-linked Xero gel resins are the smaller mesh sizes and higher percent solids for the latter materials. Both of these observations are in agreement with the increased rigidity and smaller pore size of the substrate. Physical Characteristics and Uptake Properties. Table 2 shows a comparison of the bed densities, weight and volume distribution ratios, and percent swelling for the various ABEC resin formulations. In early studies, ABEC-5000 showed the highest Dw values for TcO4- from various media25,26,29,30 and was chosen as a benchmark to which the uptake and physical performance characteristics of new resin formulations would be measured. ABEC resins are quite hydrophilic, with ABEC-5000 deriving up to 88.85% of its mass from water (Table 1). Such a high water content and, hence, high Me-PEG content yield low bed densities in both water and 4 M NaOH (Table 2). The difference in bed densities corresponds to a swelling percentage of 47.3% upon crossover from a 4 M NaOH load solution to a water strip. ABEC-5000 shows the highest Dw for TcO4- in 4 M NaOH (chosen to approximate the loading conditions for an alkaline radioactive waste simulant) of all resins listed in Table 2, and the highest overall Dw up to 5 M NaOH, as shown in Figure 1. A steady increase to a maximum Dw of 2000 in 5 M NaOH is exhibited by
1680 Ind. Eng. Chem. Res., Vol. 38, No. 4, 1999
Figure 1. Plot of Dw for TcO4- vs [NaOH] for different gel-type ABEC resins at 25 °C.
ABEC-5000, followed by tailing to 6 M NaOH. ABEC5000 also exemplifies the deleterious effects that a low bed density can have on the volume distribution ratio. The low bed density of ABEC-5000, stemming from high Me-PEG and water contents, transforms a Dw of 1100 to a far lower Dv of 120. For the gel-type resins designated G1, G2, and G3, the bed densities in water increase from 0.0941, to 0.296, to 0.637 g of dry resin/mL of bed as the DVB content increases from 1, to 2, to 5%, respectively. In 4 M NaOH, the bed densities increase from 0.192, to 0.328, to 0.637 as the DVB content increases. The bed densities are greater in 4 M NaOH for the 1 and 2% cross-linked resins as anticipated but are equal for the 5% DVB-containing resin. More importantly, the difference in bed densities in 4 M NaOH and water, from which swelling percentages are derived, decreases with increasing DVB content. The swelling percentages are shown in the last column of Table 2. A 41.2% decrease in swelling from 51.0 to 9.76% is observed on changing from 1 to 2% DVB for G1 and G2, respectively. There is no change in bed density and consequently no observable swelling at 5% DVB cross-linking. The weight distribution ratios for TcO4- vs [NaOH] for these gel resins are shown in Figure 1, where the maximum in Dw is observed in the 5-6 M NaOH region. The Dw values in 4 M NaOH (Table 2) decrease as the DVB content of the ABEC resin increases, and this effect is likely related to a decreasing Me-PEG content in the more highly cross-linked resins. By contrast to the decrease in Dw for TcO4- with increasing cross-linking, the volume distribution ratios in 4 M NaOH remain nearly equivalent at 170 and 160 for the 1 and 2% DVB-containing resins, respectively. A sharp decrease to Dv ) 11 for the 5% DVB resin is observed and is due to the low Dw discussed above. The remaining 17 resins in Table 2 possess Xero gel substrates with 1 or 2% DVB cross-linking and more complicated synthesis parameters (Table 1). In general, the resins with the highest VBC content and porosity (i.e., high diluent percentages) show the lowest bed densities and largest swelling percentages. The differences in bed densities in 4 M NaOH and water for the 1% DVB Xero gel resins result in large swelling percentages that range from 27.8 to 55.1%. The 2% DVB cross-linked resins show more rigidity, as expected, ranging from negligible to 11.7% swelling. The resin prepared with 15% VBC and 20% diluent (XG16) has
Figure 2. Plot of Dw for TcO4- vs [NaOH] for 1% DVB crosslinked Xero gel resins (20-50 mesh) at 25 °C. Only one data point at 4 M NaOH is reported for XG12.
Figure 3. Plot of Dw for TcO4- vs [NaOH] for 2% DVB crosslinked Xero gel resins (50-100 mesh) at 25 °C. Only one data point at 4 M NaOH is reported for XG15, XG16, and XG17.
bed densities intermediate between those prepared with 15% VBC and 30 and 10% diluent (XG13 and XG14, respectively), implying trends similar to those observed for the 1% DVB Xero gel resins. The swelling properties for these resins have not yet been fully explained but may indicate a complicated relationship between the copolymer substrate structure and the resulting physical properties of ABEC resins. The dry weight distribution ratios for pertechnetate in 4 M NaOH show significant discontinuity but typically increase with increasing VBC and diluent percentages, with the 1% DVB cross-linked resins showing the highest Dw values of the Xero gel materials. The Dw profiles as a function of [NaOH] are presented in Figures 2 and 3 for the 1 and 2% cross-linked Xero gel resins, respectively. As with the gel-type resins, a maximum in Dw for TcO4- is typically observed in the 5-6 M NaOH range, but the Xero gel resins show far less systematic variations in Dw as a function of [NaOH] than the gel resins (hence, the absence of curve fits in Figures 2 and 3). The low bed densities of the 1% DVB Xero gel resins yield volume distribution ratios ranging from a low of 82 (XG2) to a maximum of 180 (XG9). The 2% DVB resins show slightly lower uptake and range from Dv ) 51 (XG14) to 140 (XG15). Analysis of the data in Tables 1 and 2 and Figures 1-3 provides insight as to which resins are most
Ind. Eng. Chem. Res., Vol. 38, No. 4, 1999 1681
suitable for scale-up application. Most telling are the last two columns of Table 2, where the volume distribution ratios and swelling percentages are reported. These two values are part of the four developmental areas important to the success of process-scale applications of ABEC resins. The maximum Dv for pertechnetate in 4 M NaOH of 170 and 180 are obtained with resins showing 29.7-51.0% swelling of the bed during stripping with water. When a small decrease in Dv to the range 140-160 is accepted, two resins with less than 10% swelling are apparent. The 50-100 mesh gel-type resin labeled G2 has Dv ) 160 for TcO4- in 4 M NaOH and 9.76% swelling. The second, designated XG15, is a 50-100 mesh Xero gel resin affording Dv ) 140 and no change in bed height during stripping. These two resins represent a balance between the uptake and physical properties required for engineering large-scale chromatographic separations using ABEC resins. Conclusions The principal hurdles to process-scale application of ABEC separations have been overcome by the development of new materials. The gel-type resin G2 and the Xero gel XG15 are both 50-100 mesh materials allowing flow rates and pressure drops acceptable for use in a large-scale chromatographic apparatus. These two resins also show volume distribution ratios for TcO4-, bed densities, and swelling percentages that surpass those of the previous benchmark ABEC-5000. Future research will focus on reproducing the synthetic procedures for the 2% cross-linked gel resin G2, measuring its capacity for TcO4- from 4 M NaOH and from alkaline radioactive waste simulants, and optimizing its synthetic scale-up parameters. The high selectivity and uptake for TcO4- and the ability to strip using only water make ABEC resins well-suited for alkaline radioactive waste treatment applications. The next paper in this issue describes potential uses of ABEC resins in the remediation of radioactive wastes and in the treatment of alkaline scrubber solutions used to control technetium-99 and iodine-129 off-gases from thermal processing. Acknowledgment This work was funded by the U.S. Department of Energy Morgantown Energy Technology Center under Contract No. DE-AC21-97MC33137. Assistance from Cara M. Tomasek and Jon Duffey is acknowledged. Literature Cited (1) Kolarik, Z. Separation of Actinides and Long-Lived Fission Products from High-Level Radioactive Wastes (A Review); KfK 4945; Institu¨t fu¨r Heiβe Chemie: Karlsruhe, Germany, 1991. (2) Kupfer, M. J. Disposal of Hanford Site Tank Waste; WHCSA-1576-FP; Westinghouse Hanford Co.: Hanford, WA, 1993. (3) Bell, J. T.; Bell, L. H. Separations Technology: The Key to Radioactive Waste Minimization. In Chemical Pretreatment of Nuclear Waste for Disposal; Schulz, W. W., Horwitz, E. P., Eds.; Plenum: New York, 1994. (4) Kupfer, M. J. Disposal of Hanford Site Tank Wastes. In Chemical Pretreatment of Nuclear Waste for Disposal; Schulz, W. W., Horwitz, E. P., Eds.; Plenum: New York, 1994. (5) Swanson, J. L. CLEAN Option: An Alternative Strategy for Hanford Tank Waste Remediation: Detailed Description of First Example Flowsheet. In Chemical Pretreatment of Nuclear Waste for Disposal; Schulz, W. W., Horwitz, E. P., Eds.; Plenum: New York, 1994.
(6) Darab, J. G.; Smith, P. A. Chemistry of Technetium and Rhenium Species During Low-Level Radioactive Waste Vitrification. Chem. Mater. 1996, 8, 1004. (7) Table of Isotopes, 7th ed.; Lederer, C. M., Shirley, V. S., Eds.; John Wiley and Sons: New York, 1978. (8) Blanchard, D. L., Jr.; Kurath, D. E.; Golcar, G. R.; Conradson, S. D. Technetium Removal Column Flow Testing with Alkaline, High Salt, Radioactive Tank Waste; Pacific Northwest National Laboratory: Richland, WA, 1996. (9) Blanchard, D. L., Jr.; Brown, G. N.; Conradson, S. D.; Fadeff, S. K.; Golcar, G. R.; Hess, N. J.; Klinger, G. S.; Kurath, D. E. Technetium in Alkaline, High-Salt Radioactive Tank Waste Supernate: Preliminary Characterization and Removal; PNNL11386; Pacific Northwest National Laboratory: Richland, WA, 1997. (10) Yoshihara, K. Technetium in the Environment. In Technetium and Rhenium: Their Chemistry and Its Applications; Yoshihara, K., Omori, T., Eds.; Springer-Verlag: Berlin, 1996; Vol. 176. (11) Sasahira, A.; Hoshikawa, T.; Kamoshida, M.; Kawamura, F. Application of Hydration Model to Evaluate Gas-Phase Transfer of Ruthenium and Technetium from Reprocessing Solutions. J. Nucl. Sci. Technol. 1994, 31, 1222. (12) Hoshikawa, T.; Sasahira, A.; Fukasawa, T.; Kawamura, F.; Sugimoto, Y. Volatilization of Technetium from Simulated Reprocessing Solutions. J. Nucl. Sci. Technol. 1996, 33, 728. (13) Schulz, W. W.; Bray, L. A. Solvent Extraction Recovery of Byproduct 137Cs and 90Sr from HNO3sA Technology Review and Assessment. Sep. Sci. Technol. 1987, 22, 191. (14) Horwitz, E. P.; Dietz, M. L.; Fisher, D. E. Extraction of Strontium from Nitric Acid Solutions Using Dicyclohexano-18crown-6 and its Derivatives. Solvent Extr. Ion Exch. 1990, 8, 557. (15) Horwitz, E. P.; Dietz, M. L.; Diamond, H.; Rogers, R. D.; Leonard, R. A. Combined TRU-Sr Extraction/Recovery Process. In Solvent Extraction in the Process Industries, Proceedings of ISEC’93; Logsdail, D. H., Slater, M. J., Eds.; Elsevier Applied Science: London, 1993; Vol. 3. (16) Hobbs, D. T.; Walker, D. D. Chemical Pretreatment of Savannah River Site Nuclear Waste for Disposal. In Chemical Pretreatment of Nuclear Waste for Disposal; Schulz, W. W., Horwitz, E. P., Eds.; Plenum: New York, 1994. (17) Horwitz, E. P.; Kalina, D. G.; Kaplan, L.; Mason, G. W.; Diamond, H. Selected Alkyl(phenyl)-N,N-dialkylcarbamoylmethylphosphine Oxides as Extractants for Am(III) from Nitric Acid Media. Sep. Sci. Technol. 1982, 17, 1261. (18) Horwitz, E. P.; Kalina, D. G.; Diamond, H.; Vandegrift, G. F.; Schulz, W. W. The TRUEX ProcesssA Process for the Extraction of the Transuranic Elements from Nitric Acid Wastes Utilizing Modified PUREX Solvent. Solvent Extr. Ion Exch. 1985, 3, 75. (19) Kupfer, M. J. Preparation of Nonradioactive Substitutes for Radioactive Wastes; DOE/ET/41900-8(ESG-DOE-13352); Rockwell Hanford Operations: Hanford, WA, 1981. (20) Schulz, W. W.; Kupfer, M. J. Candidate Reagents and Procedures for the Dissolution of Hanford Site Single-Shell Tank Sludges; WHC-EP-0451; Westinghouse Hanford Co.: Hanford, WA, 1991. (21) Ashley, K. R.; Ball, J. R.; Pinkerton, A. B.; Abney, K. D.; Schroeder, N. C. Sorption Behavior of Pertechnetate on ReillexHPQ Anion Exchange Resin from Nitric Acid Solution. Solvent Extr. Ion Exch. 1994, 12, 239. (22) Ashley, K. R.; Ball, J. R.; Abney, K. D.; Turner, R.; Schroeder, N. C. Breakthrough Volumes of TcO4- on Reillex-HPQ Anion Exchange Resin in a Hanford Double Shell Tank Simulant. J. Radioanal. Nucl. Chem. 1995, 194, 71. (23) Ashley, K. R.; Cobb, S. L.; Radzinski, S. D.; Schroeder, N. C. Sorption Behavior of Perrhenate Ion on Reillex-HPQ Anion Exchange Resin from Nitric Acid and Sodium Nitrate/Hydroxide Solutions. Solvent Extr. Ion Exch. 1996, 14, 263. (24) Rogers, R. D.; Bond, A. H.; Bauer, C. B.; Zhang, J.; Rein, S. D.; Chomko, R. R.; Roden, D. M. Partitioning Behavior of 99Tc and 129I from Simulated Hanford Tank Wastes Using Polyethylene Glycol-Based Aqueous Biphasic Systems. Solvent Extr. Ion Exch. 1995, 13, 689. (25) Bond, A. H. Heavy Main Group Metal Ions: Structural Chemistry of Polyether Complexes and Aqueous Biphasic Separations. Ph.D. Dissertation, Northern Illinois University, DeKalb, IL, 1995.
1682 Ind. Eng. Chem. Res., Vol. 38, No. 4, 1999 (26) Rogers, R. D.; Bond, A. H.; Griffin, S. T.; Horwitz, E. P. New Technologies for Metal Ion Separations: Aqueous Biphasic Extraction Chromatography (ABEC). Part I. Uptake of Pertechnetate. Solvent Extr. Ion Exch. 1996, 14, 919. (27) Rogers, R. D.; Griffin, S. T.; Horwitz, E. P.; Diamond, H. Aqueous Biphasic Extraction Chromatography (ABEC): Uptake of Pertechnetate from Simulated Hanford Tank Wastes. Solvent Extr. Ion Exch. 1997, 15, 547. (28) Rogers, R. D.; Bond, A. H.; Zhang, J.; Horwitz, E. P. New Technetium-99m Generator Technologies Utilizing Polyethylene Glycol-Based Aqueous Biphasic Systems. Sep. Sci. Technol. 1997, 32, 867. (29) Rogers, R. D.; Horwitz, E. P.; Bond, A. H. Process for Recovering Pertechnetate Ions from an Aqueous Solution also Containing Molybdate Ions. U.S. Patent 5,603,834, 1997.
(30) Rogers, R. D.; Horwitz, E. P.; Bond, A. H. Process for Recovering Chaotropic Anions from an Aqueous Solution also Containing Other Ions. U.S. Patent issuing, 1997. (31) Rogers, R. D.; Horwitz, E. P.; Bond, A. H. Process for Separating and Recovering an Anionic Dye from an Aqueous Solution. U.S. Patent 5,707,525, 1998. (32) Rogers, R. D.; Zhang, J. In Ion Exchange and Solvent Extraction; Marinsky, J., Marcus, Y., Eds.; Marcel Dekker: New York, 1997; Vol. 13.
Received for review February 9, 1998 Revised manuscript received May 11, 1998 Accepted May 12, 1998 IE980072N
