Chapter 15
Reillex-HPQ Anion Exchange Column Chromatography: Removal of Pertechnetate Ion from DSSF-5 Simulant 1
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Norman C. Schroeder , Susan D. Radzinski , Jason R. Ball , Kenneth R. Ashley , and Glenn D. Whitener Downloaded by TUFTS UNIV on June 5, 2018 | https://pubs.acs.org Publication Date: February 11, 1999 | doi: 10.1021/bk-1999-0716.ch015
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Chemical Science Technology (CST-11), Los Alamos National Laboratory, Los Alamos, NM 87545 Department of Chemistry, Texas A&M University at Commerce, Commerce, TX 75429 Department of Chemistry, Macalester College, St. Paul, MN 55105 2
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The repetitive loading of pertechnetate anion (TcO -) from the Hanford tank waste simulant, DSSF-5, onto a 2.54 x 50 cm Reillex-HPQ anion exchange column has established the viability of this resin for pertechnetate anion removal. The column was loaded at a linear flow rate of 3.00 cm/min (15 mL/min) until at least 1% breakthrough occurred, and then up-flow eluted at the same flow rate with 0.005 M Sn /1.0 M ethylenediamine/1.0 M NaOH. A total of 11 cycles were run which kept the column in service and in contact with DSSF-5 simulant or caustic solution for 94 days. Recovery of technetium over this period of service was nearly quantitative (>98%). 4
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An early attempt to separate pertechnetate anion (Tc0 ) from neutralized Hanford waste was performed by Wheelwright's group during the early I960's (1). They used Dowex-1 anion exchange resin to recover pertechnetate anion from freshly generated waste. This work clearly demonstrated anion exchange as the baseline technology for this separation. An additional thirty years of anion exchange resin development has produced resins with improved performance compared to Dowex-1. These new resins may be able to exceed the decontamination factor of five obtained by Wheelwright's group. F. Marsh at Los Alamos National Laboratory (LANL), in collaboration with Reilly Industries, has developed a new resin, Reillex-HPQ, to separate plutonium nitrate (i.e., Pu(N0 ) ") from 7-8 M nitric acid solutions (2). This resin is a copolymer of divinylbenzene and 4-vinylpyridine that has been subsequently methylated at the pyridine nitrogen to give pyridinium [-C H N(CH ) ] strong base anion exchange sites. The pyridinium functionality of Reillex-HPQ is unique; most other strong base anion resins like Dowex-1 are alkyl quaternary amine resins. Reillex-HPQ, compared to other resins, has superior stability to radiolysis and nitric acid (3, 4). At LANL's plutonium facility, the lifetime of the resin is at least four times that of conventional resins under 7-8 M nitric acid processing conditions. More specifically for pertechnetate anion, this resin was included in a thesis project that evaluated 22 anion exchange resins for their ability to separate pertechnetate anion from acidic, neutral, and high salt solutions (5). Reillex-HPQ was the highest ranked resin in this study. On the basis of these data, we chose to examine the qualities of Reillex-HPQ to partition pertechnetate anion from caustic Hanford 4
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©1999 American Chemical Society
Bond et al.; Metal-Ion Separation and Preconcentration ACS Symposium Series; American Chemical Society: Washington, DC, 1999.
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220 Double Shell Slurry (DSS) and Double Shell Slurry Feed (DSSF) tank waste simulants (6-9). The Tank Waste Remediation Program requested that we study these simulants because they represented wastes being considered for pretreatment at the time of these studies. We have previously reported the results of a flow study which measured the breakthrough volumes for DSS simulant using 1.00 χ 5.67 cm Reillex-HPQ columns (10). These preliminary results were encouraging with respect to using Reillex-HPQ resin for pertechnetate anion partitioning. We extended these studies to a 1.00 χ 20.0 cm column which was down-flow loaded with DSS simulant containing 5.0 χ ΙΟ" M pertechnetate anion (8). The column was down-flow eluted with a reducing/complexing eluent containing 0.005 M Sn , 1.0 M NH C H NH (en), and 1.0 M NaOH. The column was loaded and eluted for 11 cycles over a 52 day period. The 1% breakthrough volume decreased from an initial 57.7 bed volumes (BV) to 39.8 BV at the eighth loading to 24.0 BV at the eleventh loading. A 1% breakthrough volume is defined as the volume of effluent, measured in geometrical resin bed volumes (BV), that has a technetium activity equal to 1% of the column feed activity. The column elutions removed an average of 97% of the loaded activity. Column bleed was a problem during loadings 2-11; an average of 0.42% of the activity being loaded bled during the runs. Overall, these results were taken as positive and encouraging. This report describes research using 2.54 χ 50.0 cm columns with DSSF type simulants. The 1% breakthrough volumes are reported for 11 loading and eluting cycles for DSSF-5 simulant. Between cycles the resin column was slowly washed with a 6.0 M NaNO /2.0 M NaOH solution; thus the column was in contact with a caustic solution for 94 days. This work continues our prior studies to test the viability of using Reillex-HPQ to separate technetium, as pertechnetate anion, from Hanford waste streams by applying the baseline technology of anion exchange. It assumes that an efficient organic destruction process will precede technetium partitioning and that all the technetium has been brought to the pertechnetate anion state prior to processing. These problems are not trivial and are addressed in our other works (9, 11). (Schroeder, N. C ; Ashley, K. R.; Radzinski, S. D.; Truong, A. P.; Szczepaniak, P. Α.; Whitener, G. D. Science and Technology for Disposal of Radioactive Tank Waste, submitted.) Lastly, this report attempts to explain the decreasing column performance and column bleed problems observed in this work and our earlier studies. 5
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Downloaded by TUFTS UNIV on June 5, 2018 | https://pubs.acs.org Publication Date: February 11, 1999 | doi: 10.1021/bk-1999-0716.ch015
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Experimental Reagents. All water used was 18-ΜΩ water (Millipore, Bedford, MA). Reillex-HPQ resin, chloride form, 30-60 mesh, was obtained from Reilly Industries (Indianapolis, IN). Standard solutions of HN0 were prepared from concentrated HN0 (J. T. Baker) and standardized against P. S. sodium carbonate (J. T. Baker). Sodium hydroxide solutions were standardized against 0.1600 or 8.000 Ν H S0 solutions (Hach Chemical, Ames, IA). All other reagents were analytical grade, except where noted, and obtained from either Aldrich Chemical Co., J. T. Baker, EM Science (Merck), or Mallinckrodt. 3
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Pertechnetate Anion Preparation and Assay Techniques. Lithium pertechnetate (Li"Tc0 ) was added to simulants to produce a macro concentration of ~ 5 χ 10" M. The Li"Tc0 stock solution (0.12 M) was metathesized from NH "Tc0 (Oak Ridge National Laboratory) by a published procedure (10, 12). The lithium salt was initially prepared for accelerator transmutation of technetium studies; we deemed it unnecessary to convert it to the sodium salt for this work. A tracer technetium isotope, Tc (t =61 days), was also added to the simulants to give a Na Tc0 concentration of < 10' M. This gamma emitting isotope was readily obtained from 5
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Bond et al.; Metal-Ion Separation and Preconcentration ACS Symposium Series; American Chemical Society: Washington, DC, 1999.
221 the Medical Radioisotopes Group at LANL. Both macro and tracer technetium were adjusted to the same chemical form (i.e., Tc0 ") before adding them to the simulants by taking each isotope solution to incipient dryness, three times, in HN0 under mild heating conditions; the surface of the hot plate never exceeded 200° C. Each technetium isotope, as T c 0 , was tested with a standard 60 minute batch contact experiment between DSS simulant and Reillex-HPQ resin; a batch K value of (330 ± 30) mL simulant/g dry resin qualified the isotope (8). Gamma counting of Tc was performed using a Packard Auto-Gamma Model 5530 instrument (Packard Instrument Company, Downers Grove, IL). The detector is a three inch diameter thallium activated sodium iodide (Nal(Tl)) crystal that has a through-hole design. Technetium-95m decays by isomeric transition (4%), positron emission (0.4%), and electron capture with gamma emission (>95%). Seventy percent of all decay events produce a gamma photon of energy 204.2 keV (13). These are the photons that are counted (the lower and upper limits of photon energies counted by the instrument were set as 165 and 245 keV, respectively). Counting efficiency for the 204.2 keV gamma peak of Tc is 45%. Samples were counted in 25 mL polyethylene scintillation vials. The number of counts per minute (cpm) for each sample and for several blanks (background, bkg) were recorded. Corrections for the decay of the Tc were automatically made by the instrument. The macro "Tc concentration does not interfere with the gamma counting of Tc since it decays 100% by B" emission without producing any gamma photons. The instrument is equipped with a OA program to correct for background change and position of the calibration peak ( Cs). An auto-calibration program adjusts the detector voltage to compensate for temperature and detector drift. 4
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Downloaded by TUFTS UNIV on June 5, 2018 | https://pubs.acs.org Publication Date: February 11, 1999 | doi: 10.1021/bk-1999-0716.ch015
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Simulants. DSSF-7 simulant (7.00 M Na ) was prepared; the composition is shown in Table I. Weights of the reagents in the table were added to water with complete dissolution of each reagent prior to the addition of the next reagent (8). The simulant after preparation was a clear, slightly yellow solution, which yielded a small amount of white precipitate upon cooling. DSSF-5 (5.00 M Na ) simulant was prepared from filtered (medium fritted disc glass funnel) DSSF-7 simulant by diluting 5.00 L of DSSF-7 simulant with 2.00 L of water to give a total volume of 7.00 L. Other dilutions of DSSF-7 were prepared similarly. There was less than 1% deviation from the volumes being additive. Simulants were characterized by some of the qualification methods (density, percentage water, and [OH] titer) described previously (8). The proper amount of Li Tc0 and Na Tc0 to give a macro concentration of 3.5 χ ΙΟ" M and « 6000 cpm/4 mL, respectively, were added to the simulants. The simulants were then mixed vigorously and stirred for 24 hours prior to the column chromatography experiments. +
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Batch Distribution Coefficients. Reillex-HPQ resin was converted to the nitrate form as previously described and was stored in water (9, 14). A weighed portion of 60 °C dried resin was placed into a polyethylene vial (caps with Teflon liners were used) with the desired amount of simulant solution; the solution-to-resin ratio was 10:1. The sample was then contacted for the desired length of time using a Burrell Wrist-Action Shaker or Lab-Line Constant Temperature Shaker Bath at 25 °C. At the end of the contact period, the resin/solution sample was poured into a Bio-Rad Econo-Column and the filtrate collected. Appropriate aliquots of the initial solution and filtrate were counted and the technetium batch distribution coefficient (K ) calculated as described previously (8). Equation 1 defines K with (Tc0 ") as the total mmols of pertechnetate anion in the solution before contact with the resin, [Tc0 "] as the concentration of pertechnetate anion in V mL of solution in contact with the mass of dry resin (g), cpm as the counts per minute of the uncontacted solution, and cpm as the total counts per minute of the contacted solution. d
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Bond et al.; Metal-Ion Separation and Preconcentration ACS Symposium Series; American Chemical Society: Washington, DC, 1999.
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222 Table I. Double-Shell Slurry Feed (DSSF-7) Tank Waste Simulant Formulation Molarity Material Material Molarity 3.885 NaOH 1.162 NaN0 Α1(Ν0 ) ·9Η 0 0.721 0.196 KN0 KOH 0.749 Na^O, 0.147 CsN0 7.00 χ ΙΟ NaCl 0.102 1.512 NaN0 0.008 Na^O, Ν32ΗΡ0 ·7Η 0 0.014 Li"Tc0 5 χ ΙΟ" Na Tc0
