The objective of this program has been to develop faster, more accurate methods for the concentration and determination of actinides at their maximum permissible concentration (MPC) levels in a controlled zone. These analyses are needed to characterize various forms of Hanford high rad waste and to support characterization of products and effluents from new waste management processes. The most acceptable methods developed for the determination of /sup 239/Pu, /sup 238/Pu, /sup 237/Np, /sup 241/Am, and /sup 243/Cm employ solvent extraction with the addition of tracer isotopes. Plutonium and neptunium are extracted from acidified waste solutions into Aliquat-336. Americium and curium are then extracted from the waste solution at the same acidity into dihexyl-N,N-diethylcarbamylmethylenephosphonate (DHDECMP). After back extraction into an aqueous matrix, these actinides are electrodeposited on steel disks for alpha energy analysis. Total uranium and total thorium are also isolated by solvent extraction and determined spectrophotometrically

Johnson, S.J.

Winters, W.I.

Johnson, S. J.

Winters, W. I.

UNT Digital Library

ACTINIDE ANALYTICAL PROGRAM FOR CHARACTERIZATION OF HANFORD WASTE S. J. Johnson W. I. Winters Chemical Sciences Group Research Department Research and Engineering Division MASTER Rockwell Hanford Operations R i c h l a n d , Washington To be published 1n the proceedings of the 1977 G a t H n b u r g Conference G a t H n b u r g , Tennessee October 4-6, 1977 •PollOfdbyihiUMttZu.Tn^. HMm< " Work I praera d u e l e d ' """"""ii W r a l u i , producti» LafeS-MBr , , , , , * - E2ru Operated for the Energy Research and Development Administration by Rockwell Hanford Operations under Contract EY-77-C-06-1030 DlSTfitBUXlObl OF THIS DOCUMENT IS 'JNIW? 1 • : ACTINIDE ANALYTICAL PROGRAM FOR CHARACTERIZATION OF HANFORD WASTE S. J. Johnson U. I. Winters Rockwell Harifdrd Operations Richland, Washington, U.S.A. ABSTRACT The objective of this program has been to develop faster, more accurate methods for the concentration and determination of actlnldes at their maximum permissible concentration (MPC) levels 1n a controlled zone. These analyses are needed to characterize various forms of Han-ford high rad wasta and to support characterization of products and effluents from new waste management processes. The most acceptable methods developed for the deter-mination of 2 3 9 P u , 2 3 8 P u . 2 3 7 N p , 2 , . 1 A m , and 2 4 3 C m employ solvent extraction with the addition of tracer Isotopes, Plutonium and neptunium are extracted fran acidified waste solutions Into AHquat-336, Amerldum and curium are then extracted from the waste solution at the same acidity Into d1hexyl-N,N-d1ethylcarbamylmethylenephosphonate (DHDECMP), After back extraction Into an aqueous matrix, these acti-nldes are electrodeposlted on steel disks for alpha energy analysis, Total uranium and total thorium are also Iso-lated by solvent extraction and determined spectrophoto-metHcally. INTRODUCTION The concentration of actlnldes in defense-generated wastes at the Hanford site is an Important criteria 1n the development of long-term waste management programs because of their very long half-lives and toxic characteristics. The origins of the actinides contained 1n the large quan-tities of Hanford waste were the effluents from the bismuth phosphate, Redox, Purex and plutonium reclamation chemical separation plants. Since these effluents were neutralized with NaOH, the majority of the actlnldes can be expected to be found with other Insoluble metals as solids at the bottom of the tanks. However, soluble actinide species 2 could result from the various organic and Inorganic com-plexonts frequently used 1n the chemical separation plants or from carbonates formed from COj absorbtlon 1n the NaOH matrix. The purpose of the actlnlde analytical program has been to test and evaluate potential analytical procedures and, at the same time, provide development groups with actlnlde concentration data for their programs. The arm* lytical procedures developed in these studies w11l be utilized 1n the characterization of waste tank supernates, salt cake, waste sludge, terminal liquors from the vacuum evaporators, volume reduction effluents, and solids from soils and equipment. These analyses are also needed to support characterization of products and effluents from new processes such as silicate melt, aqueous silicate, and radionuclide removal. From this data, the hazard poten-tials of actlnldes can be more accurately evaluated. Future separation and Immobilization processes can then be devel-oped to reduce and contain any of these potential hazards. The basis for the actlnlde analytical procedures 1s the separation of the actlnldes by solvent extraction fol-lowed by alpha counting and alpha energy analyses for plu-ton1um-239, -238, amer1dum-24l, and neptunium-237; Because of the complex and varying matrices found 1n Hanford waste, 2 3 6 P u and 2l.3Aiii are used as tracers to determine chemical yields through the procedure. Neptunlum-239 which is present In equilibrium with the 2 U 3 A m tracer and separated from 1t by solvent extraction provides a con-venient and usable neptunium tracer. Neptun1um-239 recov-eries are determined within eight hours of separation from 2 J* 3Am by gamma energy analyses. Because of salts and residual organics carried through the solvent extraction procedures, electrodeposited mounts are necessary for high resolution alpha energy analyses. Thorium and uranium are also analyzed by using solvent extraction to separate them from the waste solutions. After Isolation, their concentrations are determined spec-trophotometHcally. 3 EXPERIMENTAL Reagents and Standards Sample Preparation Plutoniuro-236 and americlum-243 (lO'MO 1' d/m/ml).— Stock solutions of each are obtained from Oak Ridge National Laboratory. Thorium (Th-O.l g/i).—Prepare an 0.1M Th stock solu-tion by dissolving 4.8 g of analytical grale thorium nitrate 1n 100 ml of 1M HCl. AHquat-336 Extraction AHguat-336 in xylene (30 v/v%).—Dissolve 300 ml of AHquat-336 IC1) LGeneral Mills, Inc., Kankakee, Illinois] In 700 ml of reagent grade xylene In a 2 liter separatory funnel. Shake for five minutes with two successive 500 ml portions of 4M HN0 3. Wash the organic three successive times with 50(1 ml deionized H 20. Allow the phases to thoroughly separate and collect the organic 1n a dark liter bottle. DHDECMP Extraction D1hexyl-N,N-d1ethylcar^ in trichlorobenzene (pHDECMP/TC8-30%).--Dilute 150 ml of DHDECMP LWateree Chemical Company, Lugoff, South Carolinaj with 350 ml of reagent grade TCB in a 1500 ml beaker. Add 500 ml ethylene glycol. Emulsify for 30 minutes. If a good emulsion cannot be attained, stir for one hour. Separate the phases In a separatory funnel and discard the glycol. Run the 30% DHDECMP through an 1on exchange column packed with Amberllst-A 26. 1 Emulsify the DHDECMP twice with 500 ml 4M HN0 3 for 15 minutes. Allow the phases to separate in a separatory funnel. Discard the acid. The residual aqueous can be removed by passing the organic through Whatman phase separating paper. Store 1n a dark glass bottle. Electrodeposition Electrolyte.—Dissolve 132 g of ammonium sulfate in one liter of deionized H 20. Adjust pH to 3.5 with 15M NH„0H and 18M H2S0... 4 Thorium - Arsenazo H I Determination Arsenazo III (0.05%).--Dissolve 0.05 g of Arsenazo III In 100 ml of deionized H2O. Use glassware that Is free of any residual H N 0 3 t as 1t will destroy the purple arsenazo color. Since this reagent dissolves slowly, allow at least one hour of stirring for the dissolution. The solution Is stable and will not deteriorate with time 1f kept 1n a closed bottle, Uranium Determination Tr1-n-octylphosph1ne Oxide (0.1M TOPO).—Dissolve 2.868 g of TOPO 1n 100 ml of cyclohexane, Complexlng Solution.—Add 25.0 g of (1,2-cyclohexylene-dlnltrllo) tetraacetlc a d d (CDTA), 5.0 g of sodium fluoride (NaF), and 65 g of sulfosallcylic a d d to 500 ml of de-ionized H 20. Neutralize to a pH of 8.5 with NaOH and dilute to 1.0 liter with deionized HoO. Dilute 500 ml of this reagent with 500 ml of delonlzeci H z0 and store 1n a dark bottle for use 1n the procedure. Final pH is 8.35. Trlethanolarolne Buffer (TEA).—Add 149 g (132.5 ml) of TEA to 800 ml of deionized H 20. Neutralize to a pH of 8.5 with HC1 and dilute to 1.0 liter with deionized H 20. Store 1n a dark bottle. Bromo-PADAP [G. Frederick Smith Chemical Company No. 587].—Dissolve 0.05 g of bromo-PADAP in 100 ml of ethanol and store 1n a dark bottle. Aliquat-336 [General Mills, Inc.,-15%],-Dissolve 75 ml of Aliquat-336 (chloride form) Into 4Z5 ml of xylene. Wash the organic twice in a separatory funnel with an equal volume of 2.5M NaOH, twice with 3M HC1, and twice with deionized water. Uranium Standard (1.0089 g/& U).—Prepare by dissolving NBS U 3 0 8 1n HN0 3. Final HN0 3 concentration is 1.8M. Equipment and Apparatus Electrodeposition Electrodeposition cell constructed according to Idaho Nuclear Corp. (Idaho Falls, Idaho) drawing nj. 340594.?-5 Glass, 0-r1ng Joint chimney - 15 mm 1.d. x 15 cm height. Teflon 0-r1ngs constructed to fit glass chimney. Polished 22 mm diameter, 24 mils thickness, steel disks. Clean disks by rinsing completely with acetone, heating 1n cone HNO3 for 30 minutes and rinsing completely with H 20, Store cleaned disks 1n deionized H 20 until ready to use. Rotating platinum electrode - 45 mesh cylinder of pure platinum supported by wire and stem of 95 percent platinum, 5 percent rhodium [Englehard Industries, Carteret, New Jersey], Dimensions - Cylinder diameter - 1.27 cm Cylinder height - 5.08 cm Overall height - 19.05 cm Stem diameter - 0.15 cm Overhead stirrer with removable chuck capable of oper-ating at 50 rpm. DC - Power supply capable of operating In constant current or constant voltage mode having a single output, 0-10 volts DC, 5 amps. Constant temperature water circulator to cool the cell bass. Spectrophotometry Methods Spectrophotometer capable of scanning from 750 nm to 500 nm using an absorbance range of 1. Procedures Sample Preparation For the Analysis of Pu, Np. Am, Cm, and Th Method.—If solids are present 1n the sample, it is heated, diluted with a known amount of deionized water, and filtered through an 0.25 \im Solvinert [Mi H i pore Corporation] filter. The filtered insolubles are dissolved and analyzed separately. A sample aliquot ranging from 2 ml to 5 ml is spiked with an appropriate concentration of 2 3 6 P u and zk3/\m. If also analyzing for total thorium, samples are run in duplicate with one being spiked with additional Th of a 6 known amount, The sample and spikes are allowed to equili-brate for about 24 hours. They are then acidified with cone. HNO3 to 4M H*, Any HNO2 or N0 X present 1s destroyed w U h heat and urea. Plutonium and neptunium are reduced using hydroxylamlnehydrochlorlde and ferrous sulfamate. After cooling, Pu(III) 1s oxidized to Pu(IV) with sodium nitrite. AHquat-336 Extraction of Pu. Np, and Th This procedure 1s patterned after a procedure developed by C. W. S111 3 at the ERDA Idaho Falls site for actlnlde analyses of soils. Method.--After sample preparation Pu, Np, and Th are extracted Into 30% A11quat-336 1n xylene. At this point 2 3 9 N p Is separated from 2 <* 3Am and begins decaying without an equilibrium source. Due to the short half life of 2 3 9 N p , the final mounts and gamma energy analysis (GEA) are made within 8 hours of the separation time. Residual Am 1s removed from the AHquat-336 with an 8M HNO3 wash. Thorium 1s quantitatively stripped from the "~ organic Into 10M HC1 and saved for spectrophotometry analysis. Plutonium and neptunium are then stripped Into 0.25M sodium oxalate and prepared for electrodeposition. DHDECMP Extraction of Am and Cm Bldentate organophosphorus extractants were first found to b.e favorable extractants of trlvalent actinides by Slddall.1*-6 Schulz and Mclsaac 1 have done further work using some of these bidentates, such as dihexyl-N,N-diethyl-carbamylmethylene phosphonate, for the removal of actinides from the acidic wastes generated at the Hanford and Idaho Falls sites. Method.—After sample preparation and the removal of Pu and Np with Aliquat-336, Am and Cm are extracted into 30% DHDECMP in trichlorobenzene (TCB). Amerlcium and curium are then stripped from the organic into 0.1M HN0 3 and pre-pared for electrodeposition. Electrodeposition of Pu, Np, Am, and Cm Due to excessive salts and residual or dissolved or-ganlcs carried through the Aliquat-336 and DHDECMP proce-dures, mounts for radiochemical counting could not be made 7 by evaporation, To produce undegraded alpha energy spectra tt was npressary to set up an electrodeppsttion system. A system . n oMar to one described by Puphal 2 at the Idaho Falls site, w'th minor modifications, was found to be compatible with our laboratory. However, a deposition method modified from one used at the Mound Laboratories 7 produced higher recoveries and was less corrosive to our steel disks than the Idaho method. Method.—An aliquot of the aqueous strip is evaporated to near dryness with cone. HN0 3. It 1s then redlssolved 1n cone. HN0 3 and 5% sodium bisulfate in 9M H2SO4 and evaporated to dryness. This melt is dissolved 1n 5 ml of electrolyte and transferred to the deposition cell with an additional 10 ml of electrolyte, The pH 1s adjusted with 1.8M H2S0j, or 1.5M NH 20H to a thymol blue Indicator color of Talmon pink. The actlnldes are deposited for two hours with a constant current of 1.2 amps requiring about 8 volts. Deposition 1s terminated with the addition of 15M NHi^OH. After drying with ethanol and heat the mounts are sent for alpha total counting, alpha energy analyses and gamma energy analyses. All results are corrected for spike recovery. Spectrophotometry Determination of Thorium The analytical utilization of Arsenazo III, first exploited in 1959, has been extensively reviewed by Savoin 8» 9, who pointed out Its high sensitivity and selec-tivity for thorium, zirconium, and uranium. Method.--After sample preparation and extraction into AHquat-336, thorium is stripped into 10M HC1. An aliquot of HC1 is evaporated to near dryness and redissolved in fresh 10M HC1. Sulfamic acid is added to destroy any resid-ual nitrite which would interfere with the stability of the Arsenazo III color. Before diluting with water, 0.05% Arsenazo III in water is added to the HC1. This 1s scanned spectrophotometrically against a reagent blank from 750 nm tc 580 nm. The Arsenazo Ill-thorium complex has maximum absorbance at 660 nm. Concentrations are determined using a least squares calculation. Spectrophotometry Determination of Uranium The total uranium content of the samples is determined by a spectrophotometry method using Br-PADAP £2-(5-bromo-8 2-pyr1da1azo)-5-d1ethylam1nopbeno1]. This method has been used extensively for the determination of U 1n ores and natural waters.' 0" 1 3 It was expanded further by extracting the colored uranium complex Into AHquat-336 and thereby Increasing sensitivity by a factor of 5 . 1 4 Method.—When applied to waste tank solutions the sam-ples are acidified to 3M HN0 3. Fluoride and ascorbic a d d are added to complex otFer extractable 1ons and to reduce Ce, V, and Fe. Hydroxylamine hydrochloride 1s also added to reduce Pu(IV) to Pu(III). The U 1s then extracted Into TOPO. An aliquot of the TOPO is placed In a mixed complex-1ng solution of tr1-ethanulam1ne buffer and Br-PADAP to develop a colored U complex. The uranium complex 1s then extracted Into 15% AHquat-336 and Its absorbance measured against a reagent blank. Maximum absorbtlon 1s at 578 nm. RESULTS AND DISCUSSION These methods of analyses have been applied to both synthetic wastes containing known concentrations of actl-nldes and to actual waste task sample. Satisfactory and usable data have been obtained 1n all cases. Since the lower permissible limits in a controlled zone for Pu, Am, and Np are about 10 3 disintegrations ;u£r minute per milliliter, our studies have concentrated on sample allquots containing from 10 3 to 101* d/m. In this concentration range, spike recoveries for Pu and Np have ranged from 90 to 100% and Am and Cm from 80 to 90%. Thorium being analyzed at the 1 to 10 pg level has produced recoveries of 90 to 100%, Uranium analyses are run on sam-ple allquots containing from 1 to 20 yg. Recoveries range from 117.7+19.4% at lower concentrations of U to 97.5±2.6% at the higher levels. These methods have four major advantages over other methods investigated: (1) larger sample sizes can be used if needed (up to 5 ml); (2) caustic, high salt waste sam-ples are analyzed at a higher, more easily controlled acidity (3-5M H + ) ; (3) high resolution alpha energy analy-sis are attained from electrodeposited mounts; and (4) the use of the 2 3 9 N p daughter present in equilibrium in the 2 I f 3 A m tracer makes a very convenient and usable neptunium tracer. 9 ACKNOWLEDGMENTS The authors wish to express appreciation to Larry L. Curfman and Donald £. Nelson for the enormous amount of laboratory work performed In this program. Secretarial and editorial assistance were efficiently carried out by Judy A. Foley. REFERENCES 1. W. W. Schulz and L. D. Mclsaac* Bidentate Orqanophos-phorus Extractants: Purification. Properties, and Applications to Removal of Actlnldes from Acidic Waste Solutions, USERDA Report ARH-SA-263, Atlantic Richfield Hanford Company, Richland, Washington, May 1977. 2. K. W. Puphal and D. R. Olsen, Anal. Chem., 44 (1972) 284. "~ 3. C. W. Sill, K. W. Puphal, and F. D. Hlndman, Anal. Chem., 46 (1974) 1725. 4. T. H. Siddall, III, J. Inorg. Nucl. Chem., 25 (1963) 883. ~~ 5. T. H. Siddall, III, J. Inorg. Nucl. Chem., 26 (1964) 1991. ~~ 6. T. H. Slddall, III, U, S. Patent 3,243,254, March 1966. 7. Interlaboratory exchange, Mound National Laboratories, 1977. 8. V. I. Kuznetsor and S. B. Savvln, Radiokh1m1ya, Vol. Ill (1961) 79. 9. S. B. Savvin, Talanta, Jl (1964) 1. 10. D. Pakalns, Anal. phim. Acta, 69 (1974) 211. 11. D. A. Johnson and T, M. Florence, Anal. Chim. Acta, 53 (1971) 73. 12. J, R. Prall, The Semi-Automatic Determination of Traces of Uranium, NLCO-1091, National Lead Company of Ohio, Cincinnati, Ohio, April 27, 1972. 10 13, f. M. Florence and Y. Farrar, Analy, Chem,. 42 (1970) 271, 14, W. 1. Winters, SpectrophotometHc Determlnat1on of Uranium In Nuclear Waste, ARH-SA-250, Atlantic Richfield Hanford Company, Richland, Washington, June 1976. 

Actinide analytical program for characterization of Hanford waste

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