Abstract Thermochemical characterization of the partitioning of cesium and strontium from nitric acid solutions into mixtures of the acid form of chlorinated cobalt dicarbollide (H+CCD−) and polyethylene glycol (PEG-400) in FS-13 diluent has been completed using isothermal titration microcalorimetry and radiotracer distribution methods. The phase transfer reaction for Cs+ is a straightforward (H+ for Cs+) cation exchange reaction. In contrast, the extraction of Sr2+ does not proceed in the absence of the co-solvent molecule PEG-400. This molecule is believed to facilitate the dehydration of the Sr2+ aquo cation to overcome its resistance to partitioning. The phase transfer reactions for both Cs+ and Sr2+ are enthalpy driven (exothermic), but partially compensated by an unfavorable entropy. The results of the calorimetry studies suggest that the PEG-400 functions as a stoichiometric phase transfer reagent rather than acting simply as a phase transfer catalyst or phase modifier. The calorimetry results also demonstrate that the extraction of Sr2+ is complex, including evidence for both the partitioning of Sr(NO3)+ and endothermic ion pairing interactions in the organic phase that contribute to the net enthalpic effect. The thermodynamics of the liquid-liquid distribution equilibria are discussed mainly considering the basic features of the ion solvation thermochemistry.

A cloud point extraction method followed by inductively coupled plasma-mass spectrometry (ICP-MS) has been developed for the detection of trivalent lanthanides (Ln(III)) in aqueous samples. Ammonium pyrrolodinedithiocarbamate (APDC) was used as the chelating ligand with 2 wt% Triton X-114 as the surfactant. Various experimental parameters were investigated and the extraction efficiency, distribution ratios and concentration factors for the extraction of lanthanum (La), neodymium (Nd), europium (Eu) and thulium (Tm) were determined.

Abstract The properties of the chloro-protected cobalt bis(dicarbollide) anion in the acidic form (HCCD), and in the presence of polyethylene glycol (PEG-400), are well known for the recovery of Cs and Sr from acidic radioactive streams. In the early development of HCCD/PEG extraction processes, questions were raised regarding the ability to control the concentration of PEG-400 in the organic phase due to its high solubility in the aqueous process solutions relative to HCCD or the diluent. The purpose of this study was to quantify the partitioning behavior of PEG-400 under a wide variety of relevant process conditions. PEG distribution ratios (D PEG ) were measured by equilibrium batch contacts between the organic and aqueous phases over a wide range of conditions using radiometric techniques with 14C labeled PEG-400 to monitor the behavior of the bulk material. The results vary dramatically from 0.1 < DPEG < 50, indicate that the PEG phase transfer kinetics are rapid, and that the aqueous phase nitric acid concentration has minimal impact on PEG solubility. The molar concentration ratio of [HCCD]:[PEG] in the organic phase has the greatest impact on PEG solubility. This ratio should be maintained at [HCCD]:[PEG] greater than or equal to approximately 6 to minimize PEG losses from the organic phase.

The solvent formulation known as FPEX (Fission Product Extraction) contains calix[4]arene-bis-(tert-octylbenzo-crown-6) (BOBCalixC6) for Cs extraction; 4,4 ',(5 ')-di-(t-butyidicyclohexano)-18-crown-6 (DtBuCH18C6) for Sr extraction; 1-(2,2,3,3,-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) modifier and trioctylamine (TOA) to aid in Cs stripping, all in an Isopar L diluent. This formulation has favorable extraction efficiency for Cs and Sr from acidic solution, and was investigated here for gamma-radiation stability. When FPEX was irradiated in contact with aqueous nitric acid, the extraction efficiency decreased only slightly when irradiated to absorbed doses as high as 200 kGy. The color of the organic phase changed to a deep yellow-orange, and several new peaks related to radiolysis of the Cs-7SB modifier were detected by GC-ECD analysis. This had little effect on the solvent extraction distribution ratios. Possible reasons for this unexpected robustness under conditions of high radiation and acidity are discussed.

Scientists at the Idaho National Laboratory (INL) and Khlopin Radium Institute (KRI) collaboratively developed and validated the concept of a Universal Extraction (UNEX) process for simultaneously removing the major radionuclides (Cs, Sr, actinides, and lanthanides) from acidic radioactive waste in a single solvent extraction process. The process chemistry is unique and complicated, since the extractants, chlorinated cobalt dicarbollide (CCD), polyethylene glycol (PEG), and diphenyl-N,N-di-n-butylcarbamoylmethylphosphine oxide (Ph2CMPO), operate synergistically to extract the major radionuclides. A combination of classical chemistry techniques, infrared (IR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy were utilized to identify and explain the structures formed in the organic phase with protons or metal ions. Model systems, CCD-PEG and CCD-bidentate organophosphorus compounds were studied and possible structures of complexes, existing in the organic phase, are proposed and properties of the UNEX extractant are discussed.

It is well known that cesium extraction from acidic media by HCCD proceeds through a liquid-liquid ion exchange extraction mechanism. Four data sets with 25 experimental measurements of Cs distribution ratios, DCs = [Cs]org/[Cs]aq, at a variety of initial conditions (various concentrations of [HCCD] and [HNO3]) have been modeled using the SXLSQI computer program developed at ORNL. The SXLSQI program was used in this analysis to help elucidate the general chemical equilibria operative in the extraction of Cs+ into an organic phase comprised of HCCD in FS-13. The experimental data sets are best modeled with four chemical equilibria (T = 25°C). The equilibrium constant for the primary exchange reaction of log Keq = 3.07 is in excellent agreement with values reported in the literature of log Keq = 3.00 for the HCCD/nitrobenzene system. In general, the equilibria representing the mechanism of Cs extraction by HCCD are consistent with earlier literature reports, albeit derived by different experimental and modeling schemes.

A regenerable methylamine carbonate (MAC)/diethylenetriamine pentaacetic acid (DTPA) strip solution has been developed, as a collaborative effort between the Khlopin Radium Institute (KRI) and the Idaho National Engineering and Environmental Laboratory (INEEL), for the stripping of actinides, lanthanides, Cs, and Sr from cobalt dicarbollide-based solvent extraction processes. Methodology and experimental results of developing this strip reagent and a distillation method for regeneration of the resulting strip solution are presented. Additionally, countercurrent flowsheet testing of the Universal Solvent Extraction (UNEX) process, using 26 stages of 3.3 cm diameter centrifugal contactors, has been performed at the INEEL using dissolved pilot plant calcine and this regenerable strip solution. Results of stripping Cs, Sr, actinides, and lanthanides from the UNEX solvent with a MAC + DTPA strip solution that was freshly prepared and that has been regenerated are presented. Overall results of the flowsheet test are also presented.

Extraction of Am and Eu using mixtures of diphosphine dioxides (DPDO, e.g., (R-1)(2)P(O)(CH2)(n)P(O)(R-2)(2) where R-1, R-2 = Ph, Bu; n = 1,2), with and without chlorinated cobalt dicarbollide (CCD) in the polar diluents 1,2-dichloroethane (DCE), meta-nitrobenzotrifluoride (F-3), bis-tetrafluoropropyl ether of diethylene glycol (F-8) and phenyltrifluoromethyl sulfone (FS-13) from HNO3, HClO4, LiNO3 and LiClO4 solutions has been investigated. The anomalous aryl strengthening (AAS) effect, i.e. the anomalous increase of extraction ability of methylene bridged diphosphine dioxides due to substitution of aromatic (i.e., phenyl) for alkyl (e.g., butyl or octyl) moieties (D-Am increases by three to four orders of magnitude), is only observed during the extraction of Am and Eu from acidic media. In salt media the AAS effect is weakly observed, and is practically absent in such diluents as F-3 and FS-13. The extraction isotherm in the case of DPDO with an observed AAS effect indicates the distribution coefficients of Eu decrease by a factor of two to three, even at the concentration ratio of DPDO:Eu = 50:1; however, these values decrease only by 10% for the DPDO that do not indicate an observed AAS effect. It is proposed that the presence of water in the diluent is necessary for manifestation of the AAS effect. The synergistic effects of adding chlorinated cobalt dicarbollide (CCD) with the DPDO that has been reported for other systems was also found to prevail in several of the systems investigated in this study. Oil addition of CCD with the DPDO, a considerable synergistic effect is observed (D-Am increases by three to four orders of magnitude) during Am and Eu extraction from nitrate media. In perchlorate media the synergistic effect is absent. The most probable reason for synergism in the presence of CCD is the higher hydrophobicity of the CCD anion as compared to the nitrate anion. The results of this work will be of utility in understanding existing and developing new extraction systems designed for the simultaneous removal of multiple radionuclides from acidic streams.

A synergistic extraction solvent for the simultaneous removal of cesium and strontium from acidic solutions has been investigated. The extraction solvent consists of, 4,4',(5')-di-(t-butyldicyclo-hexano)-18-crown-6 ( DtBuCH18C6), calix[ 4]arene-bis(tert-octylbenzo-crown-6) (BOBCalixC6), and 1-(2,2,3,3- tetrafluoropropoxy)-3-(4sec- butylphenoxy)-2-propanol (Cs-7SB modifier) in a branched aliphatic kerosene (Isopar (R) L). Extraction synergy for strontium was observed when DtBuCH18C6 was combined with the BOBCalixC6 cesium extractant solvent and Cs-7SB modifier or if the Cs-7SB modifier was substituted into the SREX ( Strontium Extraction) solvent in place of TBP. The novel process extracted both cesium and strontium simultaneously from 1M nitric acid solutions with distribution ratios of 8.8 and 7.7 for strontium and cesium, respectively, at ambient temperature. Distribution coefficients for cesium and strontium as a function of nitric acid concentration and temperature were also obtained with 0.5M < [HNO3] < 2.5M giving favorable distribution ratios. This new process utilizing the combined solvent has been named the Fission Product Extraction Process ( FPEX).

This report describes an initial set of small scale lab tests conducted on surrogate waste materials to investigate mass release behavior of volatile organics (VOC’s) from a solidified liquid organic sludge matrix under vacuumaided, low-temperature thermal desorption conditions. Low temperature thermal desorption is being considered as a potential processing technology alternative to incineration, to remove gas generation limitations affecting the transportation of transuranic (TRU) contaminated organic sludge wastes to a designated off-site repository (i.e., the Waste Isolation Pilot Plant). The lab-scale tests provide initial exploratory level information on temperature profiles and rates of volatile organic desorption for a range of initial VOC/oil liquid mixture concentrations in a calcium silicate matrix, under low temperature heating and vacuum boundary conditions that are representative of potentially desirable “in-drum desorption” conditions. The results of these tests indicate that reduced operating pressures have a potential for significantly enhancing the rate of thermal desorption experienced from a liquid organic/oil solidified “sludge” waste. Furthermore, the results indicate that in-drum thermal desorption can be performed on organic sludge wastes, at reduced pressures, while maintaining an operating temperature sufficiently low to prevent destruction of the waste drum packaging materials (confinement) surrounding the waste. The results also indicate that VOC release behavior/rates in the vacuum thermal desorption process cannot be represented by a simple liquid-liquid mass-diffusion model, since overall mass release rates observed are generally two orders of magnitude greater than predicted by simple liquid-liquid mass diffusion. This is partially attributed to the effects of the transient temperature profiles within the sludge during heat up; however, the primary cause is thought to be micro boiling of the volatile organics within the simulated sludge. Micro boiling of VOC’s would be expected to occur in localized volumes within the organic sludge where temperatures exceed the volatile organic saturation temperature sufficiently to form vapor bubbles. Further model based evaluations reflecting the transient temperatures, local boiling, and subsequent vapor in liquid/sludge transport conditions are needed, with supporting controlled testing of the vacuum-aided thermal desorption process at small and full-scale conditions in order to fully develop this process.

Direct laser excitation of aqueous Eu(III) bound to specific RNA fragments was used to probe the metal-binding sites of the anticodon loop of tRNA(Phe) from E. coli and of a tetraloop containing a GNRA consensus sequence. Binding of Mg(II) or Eu(III) to either RNA fragment resulted in a higher melting transition, but no global change in structure was observed. Aqueous Eu(III) exhibits a single weak excitation peak at 17273 cm(-1), the intensity of which increased upon addition of the tRNA loop fragment. Analysis of incremental increases in the luminescence intensity upon complexation with the tRNA loop indicated a stoichiometry of one high-affinity Eu(III)-binding site per loop fragment, with a Kd of 1.3 +/- 0.2 microM. Competition experiments between Eu(III) and Mg(II) were consistent with the two metal ions binding to a common site and with an approximately 30-fold lesser affinity of the tRNA loop for Mg(II) than for Eu(III). The rate of luminescence decay following excitation of Eu(III) bound to the tRNA loop corresponded to displacement of up to 4-5 (of a possible 9) waters of hydration on binding to the tRNA loop. By comparison, Eu(III) binds to the DNA analogue of the tRNA loop with an 8-fold lesser affinity and one fewer direct coordination site than to the RNA sequence, suggesting that a 2'OH of RNA is one of the direct ligands. In contrast with the absence of a shift in the excitation peak of aqueous Eu(III) upon formation of the tRNA loop complex, direct excitation of Eu(III) bound to a GNRA tetraloop fragment resulted in a substantially blue-shifted excitation peak (17290 cm(-1)). The tetraloop fragment also has a single Eu(III)-binding site, with a Kd of 12 +/- 3 microM. The bound Eu(III) was competed by Mg(II), although the relative affinity for Mg(II) was approximately 150-450-fold less than that for Eu(III). The Eu(III)-binding site of the tetraloop site is highly dehydrated, with approximately 7 water molecules displaced upon binding by RNA ligands, suggesting that the blue-shift of the excitation peak is the result of Eu(III) specifically bound in a nonpolar site within the GNRA loop structure.

Chemical separation technologies for the treatment of radioactive wastes, including highly radioactive liquid wastes and solid calcined wastes, mixed wastes, and contaminated groundwater have been under development at the Idaho National Engineering and Environmental Laboratory (INEEL) since 1992. The INEEL Environmental Management (EM) Chemical Separations Program has successfully developed and demonstrated numerous technologies on simulated and actual radioactive wastes to support the INEEL High Level Waste Program. These technologies have repeatedly shown that the tank waste and dissolved calcine at the INEEL can be decontaminated to levels below NRC Class A Low Level Waste Criteria. The technologies used to separate radionuclides from INEEL radioactive wastes include solvent extraction and ion exchange technologies. Solvent extraction technologies tested at the INEEL include the transuranium extraction (TRUEX) process for the removal of U, Pu, Am and Tc; the strontium extraction (SREX) process for the removal of Sr and Pb; the cobalt dicarbollide process for the removal of Cs and Sr; and the universal extraction (UNEX) process for the simultaneous removal of U, Pu, Am, Cs, and Sr from acidic waste solutions. Ion exchange processes using inorganic ion exchange sorbents such as hexacyanoferrates, silicotitanates and ammonium molybdophosphate to remove cesium have been demonstrated on actual waste solutions. Other ion exchange sorbents to remove contaminants from groundwater or drinking water have been developed and tested. Successful development and testing efforts by the INEEL EM Chemical Separations Program have included numerous national and international collaborations. These collaborations have led to numerous demonstrations of novel technologies as well as the generation of intellectual property.