Journal of Radioanalytical and Nuclear Chemistry, Vol. 235, Nos 1 2 (1998) 213 219

G a m m a radiolysis of E D T A in a simulated, mixed nuclear waste A. P. Toste* Department of Chemistry, Southwest Missouri State University, Springfield, Missouri 65804, USA (Received February 5, 1998)

The effects of 7-irradiation on EDTA degradation have been studied. A simulant of Hanford's complex concentrate was prepared by adding EDTA to an inorganic matrix which was formulated based on past analyses of the actual Hanford complex concentrate waste. For the radiolysis study, aliquots of the simulated waste were then 7-irradiated. Each waste sample was analyzed to monitor the appearance of degradation products. Based on the results of this study, an assessment of the impact of EDTA degradation on the management of mixed wastes is offered.

Introduction* Enormous stockpiles of mixed nuclear wastes at the Department of Energy's Hanford Site, the original U.S. plutonium production facility, await permanent disposal. 1 Their management poses a major challenge to the scientists and engineers charged with daunting task of managing them. 2 The effort, already underway, is expected to last for another 75 years or so, and consume $50-plus billion dollars. 1 Considerable effort and resources are already being spent in characterizing the wastes, certainly a prerequisite for their optimal management. Considerable research already indicates that mixed wastes, particularly defense-related wastes, often contain complex mixtures of organics, including both hazardous and nonhazardous compounds. 3 9 One waste in particular, a complex concentrate waste derived from reprocessing spent fuel at the Hanford site 20-plus years ago, was found to contain numerous nuclear-related organics. 3~ Compounds identified include chelating agents like EDTA, NTA, and HEDTA and complexing agents like citric acid, which have been used extensively in the nuclear industry as decontamination agents, etclO 12 Other mixed wastes analyzed also contain chelating and complexing agents. 3,5,7 9 Considerable research indicates that such compounds may complicate the management of nuclear wastes by destabilizing waste forms, e.g., cementitious grouts, or by enhancing the subsurface migration of radionuclides in the environment 13 16 Analyses of mixed wastes also reveal the presence of myriad, structurally related chelator and complexor fragments, occasionally at relatively high concentrations, presumably derived from the degradation of the chelating and complexing agents. 3,5,8,9 For example, Hanford's complex concentrate waste contained 38 different chelator and complexor fragments 3 Chelator

fragments have also been detected in heated and irradiated aqueous solutions of chelating and complexing agents. 17 19 Their presence in actual mixed wastes indicates that the organic content of nuclear wastes is dynamic, not static. This situation may greatly complicate waste management efforts. For example, the chelator and complexor fragments may, in some cases, destabilize waste forms or enhance the environmental mobility of radionuclides even more than the parent compounds themselves. My laboratory is studying the chemodynamics of organics in mixed wastes by characterizing the degradation of chelating and complexing agents in simulants of the complex concentrate waste. Recent studies confirm that both radiolysis and waste chemistry do indeed mediate the degradation of mixtures of ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA) and N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA) into chelator and complexor fragments like those identified in the actual mixed waste. 2~ However, in both of these studies, the use of organic mixtures in the simulants precluded elucidating the specific degradation of each parent organic. In this report, I have studied the effects of 7-irradiation on EDTA degradation. A simulant of Hanford's complex concentrate was prepared by adding EDTA to an inorganic matrix (without any radioactivity), which was formulated based on past analyses of the actual Hanford complex concentrate waste. 3,9 For the radiolysis study, aliquots of the simulated waste were then 7-irradiated for 0-100 hr, up to a dose of 7.5x106_+10% R. Each waste sample was subsequently analyzed to monitor the disappearance of the EDTA and, most important, the appearance of degradation products. Based on the results of this study, an assessment of the impact of EDTA degradation on the management of mixed wastes is offered.

* E-mail: [email protected]

0236 5731/98/USD 17.00 9 1998 Akad6miai Kiad& Budapest All rights reserved

Elsevier Science B. K, Amsterdam Akad6miai Kiad& Budapest

A. P. TOSTE: GAMMA RADIOLYSIS OF E D T A IN A SIMULATED, MIXED NUCLEAR WASTE

Experimental Experimental design The EDTA simulants of the organic complexant waste from Hanford were prepared by combining an inorganic waste matrix and EDTA. Inorganic waste matrix preparation: The inorganic matrix of the simulated waste was prepared according to the following composition, based on past inorganic analyses of an actual complex concentrate waste: 3,9 HNO3, 2.60M; Al(NO3)3.9H20, 210 mM; Fe(NO3)3.9H20, 38 mM; Ca(NO3)2.4H20, 25 mM; Cr(NO3)3.9H20, 4.5 mM; KNO3, 46 mM; La(NO3)3.6H20, 0.28 mM; Nd(NO3)3.5H20, 0.98 mM; Mg(NO3)2.6H20, 11 mM; Mn(NO3)2, 7.2 mM; Ni(NO3)2.6H20, 8 mM; Zn(NO3)2.6H20, 7.4 mM; N%HPO4, 22 mM; NaC1, 41 mM; N%B407, 21 mM; Cu(NO3)2.3H20, 0.42 mM; Pb(NO3)2, 1.8 mM; (NH4)6Mo7024"4H20 , 0.45 mM; Cd(NO3)2.4H20, 0.55 mM; NaOH, 6.75M; NaNO3, 2.04M; Na2CO3, 1.22M; NaNO2, 800 mM; and Na2SO4, 7.2 mM. Concentrated nitric acid was added to half the final volume of deionized water followed by sequential addition of the above inorganics. Most of the salts were added to an acidic solution, in the order specified above, to maximize their initial solubility. The solution was then neutralized with sodium hydroxide. Sodium carbonate and sodium nitrite were added to a basic solution because they decompose in an acidic environment, releasing volatile species. The waste matrix was very alkaline (pH 13.5), biphasic (~31% solids), and amber in color. EDTA simulants: EDTA was added at a concentration of l l . 8 m M to 15-ml aliquots of the inorganic waste matrix in glass scintillation vials for each time point. This concentration was selected to match that determined in the earlier analyses of the actual complex concentrate waste 3,9 and earlier simulation studies. 20,21 Radiolysis study: The EDTA simulants were exposed to ,/-radiation in a 6~ for 5, 10, 50, and 100 hr to study the effect(s) of radiation on EDTA degradation. The 6~ generated a dose rate of 75,000+10% R/hr and a temperature of 90-95 ~ due to heat-producing radiodecay. An aliquot of each waste sample was immediately prepared for organic analysis.

N 2 at 50 ~ Given the high solids content of the simulated waste, samples had to be vortexed and quickly pipetted to insure uniform sampling. The resulting dried residue of each sample was methylated in the sealed vial with 1 ml BF3/methanol (14% w/v) at 100 ~ for 20 min. After cooling, 1 ml of chloroform was added to the methylation mixture in the reaction vial. The mixture was vortexed and transferred to a test tube containing 3 ml of 1M KH2PO 4 buffer solution (pH 7), with a 0.2ml chloroform rinse. The mixture was vortexed and then centrifuged on a low-speed, tabletop centrifuge to separate the two phases. Part of the chloroform layer (0.6 ml), which contained the methylated hydrophilic organics, was transferred to a reaction vial and frozen prior to gas chromatography (GC) and combined GC/mass spectrometry (GC/MS) analysis. GC analysis: Capillary GC analyses were performed on a Hewlett-Packard (HP) 5890 Gas Chromatograph equipped with a flame ionization detector (FID). The instrument was was also equipped with a splitless injection system attached to a 30 m• mm inside diameter (I.D.) fused silica capillary column coated with a 0.25-~tm film of DB-5. From an initial value of 40 ~ the column temperature was programmed at 5 ~ per minute to 300 ~ and finally maintained isothermally at 300 ~ for 10 minutes. GC/MS analysis: GC/MS analyses were performed on Hewlett Packard 5989A instrument in the electronimpact (EI, 70 eV) mode. The gas chromatographic separation was carried out as described previously. A mass range of 50-400 amu was scanned by the GC/MS instrument's computer. Quantitation: Hydrophilic organics identified in the simulants' methylated hydrophilic extracts were quantitated using external standards as described in earlier studies. 8,2~ A response factor, expressed as nanograms of analyte per Total Ion Chromatogram (TIC) area counts, was computed for each methyl ester of the commercially available standards (EDTA, HEIDA, IDA, oxalate and malonate) under analytical conditions identical to those of the sample analyses. Estimated response factors were assigned to the other chelator fragments, which are not commercially available, from the values obtained for the commercially available standards.

Materials

Analytical procedure

Simulated waste components and analytical standards: The parent organic EDTA, the commercially

Preparation of analytical samples: Triplicate 0.5-ml aliquots of each time point were carefully transferred to 5-ml reaction vials and dried on a heating block under

available chelator fragments, HEIDA and IDA, and the carboxylic acids, oxalate and malonate, all used as GC standards, were purchased from Aldrich Chemical

214

A. P. TOSTE: GAMMA RADIOLYSIS OF E D T A IN A SIMULATED, MIXED NUCLEAR WASTE

Table 1. Organicsidentifiedin an irradiated, simulatedmixedwaste Compoundb Parent organic Ethylenediaminetetraaceticacid (EDTA) Chelator fragments N-hydroxymethyl-N-methyliminoaceticacid (HMMIA) N-(ethyl)ethylenediamine-N',N'-carboxyaceticacid (EtEDCA)c N-(methylamine)iminodiaceticacid (MAIDA) N-(ethyl)-N,N'-(dimethylamine)propylenediamineN'-acetic acid (EtDMAPD'A) Ethylenediaminetriaceticacid (ED3A)c N-(methylamine)-N'(methyl)ethylenediamineN,N'-diacetic acid (MeMAEDD'A) N-(methylamine)ethylenediaminetriacetic acid (MAED3A)

0

100

11.45

6.14

2.71

1.51

1.29

0.08

2.16

1.94

1.66

1.31

0.10

2.53

2.00

0.95

trace 0.32

trace trace

0.33 0.26

0.22 0.57

0.30 0.35

0.27 0.16

0.14

0.21

0.19

0.20

0.09

0.66

0.30

0.14

0.04 0.05 0.15

0.03 0.05 0.16

0.02 0.04 0.13

0.02 0.03 0.11

70.4

46.8

28.3

34.7

trace

Dicarboxylicacids Ethanedioicacid Propanedioicacid Heptanedioicacid TOC Recovery,d %

Concentration(raM)a after n hours 5 10 50

98.7

aNo entry indicatedcompoundis below detectionlevel. bMethylated(BF;/methanol),acids identifiedas methyl esters. cIdentifiedas lactamby GC/MS and past GC/FTIRanalyses.l'2 dPercent total organiccarbon(TOC) computedas the ratio of the concentration(p.g C/l) of organics identifiedvs. nominalconcentrationsof source-termorganicsadded to the simulatedwaste.

Company (Milwaukee, Wisconsin). The chemicals used to prepare the inorganic waste matrix were purchased from a variety of sources. Chromatographic columns: The DB-5 fused silica capillary columns used in the GC and GC/MS analyses were purchased from J & W Scientific (Folsom, California). Reagents, solvents, and glassware: The BF3/methanol (14%w/v) used in the methylation reaction was purchased from PIERCE (Rockford, Illinois). All of the solvents used in the analytical procedure, described previously, were redistilled-inglass solvents purchased from Fisher Scientific (Fair Lawn, New Jersey). Deionized water, pre-purified for laboratory use, was further purified on a SYBRON/Barnstead NANOpure | system (Barnstead) containing two ion-exchange resins and one charcoal filter. All glassware was cleaned in an RBS 35 |

detergent/deionized water solution ( 2 0 m l RBS 35 concentrate/1 water, v/v) followed by NANOpure | water rinses.

Results and discussion

EDTA degradation EDTA degradation began immediately and continued with increasing radiation (Table 1 and Fig. 1a). The degradation rate was exponential, with the most pronounced decline occurring in the first 10 hr of irradiation (Fig. la). After 100 hr of radiolysis, 89.1% of the EDTA had degraded (Table 1). These observations compare well with the results of a past radiolysis study of a mixture of chelating agents and citrate. 21 In that study, 77.5% of the EDTA disappeared after 100 hr of y-irradiation (y-dose of 7.5• 106+10% R).

| NANOpure is a registered trademark of The Barnstead Company, Boston, Massachusetts. | RBS 35 is a registeredtrademark of PIERCE, Rockford, Illinois. 215

A. P. TOSTE: GAMMA RADIOLYSIS

OF EDTA IN A SIMULATED, MIXED NUCLEAR WASTE

operating temperature of the 6~ 90-95 ~ must also be considered, although solution studies in the literature indicate that thermal degradation of EDTA is most pronounced above 200 ~

100 a) :_~

~<

80

60

8

Formation of degradation products' 40

i

i

i

i

20

40

60

80

100

Radiolysis time, hr

25

b)

20

5 O

0 20

40

60

80

100

Radiolysis time, hr

Fig. 1. Degradationof EDTAin a simulatedmixedwaste subjected to 7-irradiationin a 6~ as a function of irradiation time (0, 5, 10, 50 and 100 hr): (a) Total degradationplots depictthe degradation of the parent organic, EDTA(~), and the collective formationof its degradationproducts (I~), chelatorfragmentsplus carboxylicacids. (b) Individualplots depict the formationof each degradation productin the simulant: MAIDA(~), HMMIA( 7 , ED3A (~), MAED3A(I~), EtMAPD'A(x), MeMAEDDA(4), heptanedioic acid (~), propanedioicacid (@) and ethanedioic acid (O ). The ordinate values for both figures were computedas the percent ratio of the followingspeciesvs. total EDTA(raM) originallyaddedto the simulant: EDTAremaining(raM) (a); total degradationproducts detected (raM) (a); or individual degradationproducts detected (raM) (b)

The rapid EDTA degradation in this irradiation study is clearly due to 7-radiolysis. However, a number of other factors likely contributed to the degradation as well. The harsh chemical environment of the waste matrix, e.g., its caustic pH and high metal ion content, undoubtedly contributed to EDTA degradation. A past chemo-degradation study of a simulant containing a mixture of chelating agents and citrate, which was stored at ambient temperature in the dark, revealed that the harsh, complex chemical environment of a mixed waste causes considerable organic degradation. 21 The

216

Chelator fragments': The emergence of the degradation products mirrors the degradation of EDTA (Fig. l a). Seven chelator fragments, all bearing structural resemblance to EDTA, were formed via radiolysis of EDTA. In comparison, radiolysis of the mixture of EDTA, NTA, HEDTA and citrate yielded 27 degradation products. 2~ The chelator fragments ranged from the relatively small N-hydroxymethyl-Nmethyliminoacetic acid (HMMIA, MW 105) to MAED3A (MW 263, see Table 1 for complete nomenclature). The shape of the chelator fragment curve in Fig. la reveals that their collective formation peaks at 5-10 hr of irradiation, corresponding to a 7-dose of 3.757.50.105+10R, followed by a steady disappearance. Examination of Fig. lb illustrates that the formation of HMMIA and MAIDA, first and second in abundance, respectively, accounts for most of the EDTA degradation. As Table 1 illustrates, the concentration of HMMIA (1.31 mM) eclipsed that of EDTA (1.29 mM) by 100 hr of irradiation. Formation of the other chelator fragments lags behind. Genesis of the dicarboxylic acids is even slower, with the possible exception of heptanedioic acid. One of the chelator fragments, ED3A, can be envisioned as simply a fragment of EDTA degradation, arising from the loss of an acetate moiety. In contrast, the structures of all the other fragments suggest degradation, such as decarboxylation, etc., followed by reattachment of carboxyl or amino groups, presumably formed via radiolysis. The structural diversity of the fragments clearly indicates that the radiolytic degradation of EDTA is both varied and complex. Dicarboxylic acids': Radiolysis of EDTA in the simulant also yielded three dicarboxylic acids: ethanedioic acid, or oxalic acid; propanedioic, or malonic acid; and heptanedioic acid. In past radiolysis and chemo-degradation studies of the mixture of chelating and complexing agents, several mono- and dicarboxylic acids were identified. 2~ Also, in a study on citrate degradation in a simulant, ethanedioic and propanedioic acids were the major products. 22 We speculated that carboxylic acids in mixed wastes might be derived from the degradation of citrate or other acids. The citrate degradation study supports this conclusion, but it is now clear that EDTA radiolysis also generates carboxylic acids.

A. P. TOSTE: GAMMA RADIOLYSIS OF E D T A IN A SIMULATED, MIXED NUCLEAR WASTE

Organic recoveries and EDTA degradation The mass balance for the organic content of each time point was computed as the percent total organic carbon (TOC) recovery, relative to the concentration of the parent organic EDTA (11.8 mM) originally added to the simulated waste. The TOC content of the original EDTA and each time point was, in turn, computed by quantitating each organic species as g C/1. The TOC recovery declined from 98.7% to a low of 34.7% with increasing radiation dose (Table 1). In other words, 65.3% of the organic content disappeared after 100 hr of irradiation, corresponding to a 7-dose of 7.5.106+10% R. Based on past analyses and methods validation studies, 5,s,9 not to mention the high TOC recovery of the zero radiation time point, the loss does not appear to be due to inherent deficiencies in the analytical procedure, or to artifactual EDTA loss, e.g., precipitation. The explanation for the TOC loss is undoubtedly dispersive degradation, the formation of degradation products, e.g., gases, which lie outside the "scope" of the analytical procedure used in this study. The methylation reaction, combined with GC and GC/MS analysis, has worked very well, even quantitatively, for analyzing source-term organics like EDTA, as well as chelator and complexor fragments. 3,5,8,9,20,21 However, no single analytical procedure is capable of isolating and characterizing the complex mixtures of organics often present in mixed wastes. Based on solution studies in the literature, gases like CO2, volatile organics, and polar compounds like amines are among the likely candidates for the missing organics. 17 19

Literature comparisons Insights on EDTA degradation via radiolysis can be gleaned from the literature. A number of solution studies on the degradation of chelating and complexing agents have been published. However, most of the information available on the radiolytic stability of chelating and complexing agents deals with synthetic, singlecomponent solutions. The complex composition, e.g., 18 different cations, of the simulated waste used in this study precludes any facile comparisons. The radiolytic stability of EDTA has been studied in both alkaline and acidic solutions. 17 EDTA undergoes attack by the free radicals H" and OH" (radiolysis products) with the production of many organic species, some with complexing ability. Two studies examined the combined thermal and radiolytic decomposition of EDTA. MARGULOVA reported extensive decomposition of Fe-EDTA, with no product analysis given, 23 but postulated formation of soluble iron complexes. Decontamination, or "decon", studies conducted in Germany also examined the

short-term (5 hr) thermal and radiolytic stability of EDTA in "decon" solutions, l~ A number of issues remain unclear: the radiation dose rates involved; or whether the authors identified the degradation products. Below 160 ~ the amount of EDTA decomposition is less than 50%. However, it should be noted that this was a 5-hr test, as opposed to a real "decon" procedure, which may last for 1-3 days. ANSTINE 24 examined the radiation and thermal stabilities of metal-free and complexed acids. Solutions of metal-free chelates (oxalic acid, EDTA, NTA, citric acid, and ascorbic acid) at concentrations of 0.01M were irradiated, and the gases produced were analyzed by gas chromatography. The residual acid concentrations were measured by standard techniques. Large quantities of H 2 gas were produced as well as CO and CO 2. In the case of EDTA, ammonia was also produced. Other gaseous species (CH4, C2H6, etc.) were present as well as "nonvolatile species," degradation products of EDTA, NTA, citric acid, and ascorbic acid. The relative rates of radiolytic decomposition observed were: EDTA > oxalic acid > NTA. For both NTA and EDTA, it was concluded that they decompose to "nonvolatiles". Thermal degradation at 90 ~ resulted in very little decomposition of EDTA or NTA. Unfortunately, a complete analysis was not undertaken and the decomposition products were not characterized. The radiation stabilities of complexed organic ligands have also been investigated by ANSTINE. 24 The results, as the authors note, are not directly comparable to the uncomplexed studies because the concentration of organic acids was not the same. They felt, however, that Fe 3+ may, in fact, act as a stabilizer. Increasing the [Fe] from ~2.10 4 to 9.10 4 M appeared to decrease the rate of radiolytic decomposition, but above 9.10 4M the decomposition appears to be independent of the [Fe]. Despite the possible stabilizing effect of Fe on organic ligands like EDTA, decomposition can still be significant. After a total dose of 4.106 R, a solution of 0.01M EDTA and ascorbic acid with Fe exhibited 30% decomposition. This represented decreased decomposition, which was attributed to the presence of ascorbic acid, which had also probably undergone decomposition, resulting, perhaps, in competition for free radicals generated by radiolysis. Interestingly, whereas Fe-EDTA appears to be more resistant to radiolysis, thermal degradation of Fe-EDTA may be auto-catalytic.ll

Potential impact of EDTA degradation on mixed waste management Understanding the degradation behavior of EDTA and the products formed should assist engineers in managing mixed wastes which contain EDTA. The results of this simulation study not only agree well with

217

A. P. TOSTE: GAMMA RADIOLYSISOF EDTA IN A SIMULATED,MIXEDNUCLEARWASTE

but also amplify information obtained from past analyses of the actual mixed waste. 3,9 For example, EDTA degradation accounts for 10 of the 27 chelator fragments formed in the radiolysis of the simulant containing the mixture of chelating and complexing agents. 3 To be completely rigorous, specific assessments will require reconfirmation studies on actual wastes. One approach might be to spike actual mixed waste samples with 14C-labelled EDTA and follow the labeling pattern in the degradation compounds. Nevertheless, a few tentative assessments can be offered on the basis of this simulation study. The loss of T o e may well result in the formation of gases like CO2, CO, and H 2. Such gases may destabilize wastes by causing volume expansion, slurry growth, increasing the risk of explosion, etc. Detailed laboratory studies of gas evolution in mixed wastes certainly need to be carried out and are being initiated. 25 Another source of concern is the chelating capacity of the simulant. Many degradation products of chelating agents may have considerable or even higher affinities for metals and radionuclides than the parent compounds. 18 As noted earlier, a high chelating/complexing capacity may destabilize a waste form and increase the environmental mobility of toxic metals and radionuclides in groundwater leachates of buried wastes. To resolve this issue, the chelating capacities of the simulant will have to be measured.

Concluding remarks Based on this study, combined with past analyses of actual and simulated wastes, it is clear that EDTA undergoes extensive degradation in mixed wastes. Gamma irradiation resulted in very rapid degradation (89.1%) by 100 hr, at a 7-dose of 7.5"106_+10% R. The results of this simulation study certainly bear on the chemistry of the actual complex concentrate waste, which has been stored at Hartford for over two decades. The high radiation field, ~1 Ci/1, of the actual waste is certainly more than enough to produce such organic degradation. 3,9 However, it is also likely that the actual waste's harsh chemical environment and thermal energy, heat produced by J3-emitting radionuclides, which typically ranges from 100-150 ~ all contribute to the organic degradation. 3,9 Compared to such energies, combined with the age of the actual waste, the chemical and radiolytic energies used in this simulation study, along with the thermal contribution from the 6~ source, are modest indeed. It is hoped that the findings of such laboratory studies on simulated wastes are beneficial to engineers charged with the daunting task of managing actual mixed wastes. A priori assumptions based on paper studies may not always match actual observations.

218

The use of simulants to study actual mixed nuclear wastes appears to be very promising. Recent studies in our laboratory indicate that well-designed simulants mimic actual wastes very well. 20,21 The results of this simulation study indicate that the source of a number, but not all, of the chelator fragments detected in the actual mixed waste is clearly EDTA degradation. The other chelating agents, NTA and HEDTA, detected in the actual waste still need to be studied. Moreover, the use of nonradioactive simulants permits the systematic study of the chemodynamics of organics in mixed wastes in a controlled laboratory setting, without the hazards of radiation exposure, particularly to students.

The Hewlett-Packard 5989A GC/MS (MS Engine) instrument was purchased with the generous support of the National Science Foundation's Instrumentation and Laboratory Improvement (ILI) Program (Grant USE-9051582) and Syntex Corporation, combined with university matching funds.

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A. P. TOSTE: GAMMA RADIOLYSISOF EDTA IN A SIMULATED,MIXED NUCLEARWASTE

16. A. P. TOSTE, L. J. KIRBY, W. H. RICKARD, D. E. ROBERTSON, Rad. Wst. Mgt., IAEA, Vienna, Austria, IAEA-CN-43/470, 5 (1984) 213. 17. S. N. BHATTACHARYYA, K. P. KURDU, Intern. Radiat. Phys. Chem., 4 (1972) 31. 18. A. E. MARTELL, U. J. MOTEKARTES,A. U. FRIED, J. S. WILSON, D. T. MACMILLAN,Can. J. Chem., 53 (1975) 3471. 19. C. H. DELEGARD, Identity of the HEDTA Decomposition Product in Synthetic Hanford High-level Wastes, Rockwell Hanford Operations, Hanford, WA, RHO-RE-TI-062, 1983. 20. A. P. TOSTE, J. Radioanal. Nucl. Chem., 161 (1992) 549. 21. A. P. TOSTE, T. J. LECHNER-FISH, Waste Mgt., 13 (1993) No. 3,237.

22. A. P. TOSTE, K. J. POLACH, T. W. WHITE, Waste Mgt., 14 (1994) No. 1, 27. 23. T. KH. MARGULOVA, S. A. TEVLIN, Y. E. LEBEDEV, A. I. MELAEV, Thermal Eng., 19 (1972) No. 3, 15. 24. L. D. ANSTINE, The Dilute Chemical Decontamination Program, Quarterly Progress Reports, General Electric Company, Pleasanton, CA, NEDC-12705-2-7, 1978 80. 25. T. H. DUNNING, JR., E. P. HOROWITZ, D. M. STRACHAN, E. H. ASHBY, E. J. HART, D. A. REYNOLDS, W. W. SCHULTZ, D. D. SIEMER, W. J. THOMSON, D. S. TRENT, R. M. WALLACE, Chemical and Physical Processes in Tank 241-SY-101 : A Preliminary Report, Pacific Northwest Laboratory, Richland, WA, PNL-7595, 1991.

219