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Research in actinide chemistry. Progress report, March 1, 1980-February 28, 1981

Description: Visible spectroscopy, NMR (/sup 1/H/sub 1/, /sup 6/C/sub 13/, /sup 57/La/sub 139/) spectroscopy, potentiometry, and calorimetry were used in lanthanide studies which have allowed much more thorough interpretation of actinide tracer studies. In the last several years, the studies were expanded to include actinides in the IV, V and VI oxidation states. Part of the research during this time was directed to investigation of actinide interaction with naturally occurring polyelectrolytes such as humic and fulvic acids. Since redox reactions seemingly occur in some of these interactions, a study of plutonium and neptunium redox behavior in the presence of organic complexing agents was started. Preliminary data are given for reduction of Np(VI) by various organic acids.
Date: January 1, 1981
Creator: Choppin, G.R.
Partner: UNT Libraries Government Documents Department

Research in actinide chemistry

Description: This research studies the behavior of the actinide elements in aqueous solution. The high radioactivity of the transuranium actinides limits the concentrations which can be studied and, consequently, limits the experimental techniques. However, oxidation state analogs (trivalent lanthanides, tetravalent thorium, and hexavalent uranium) do not suffer from these limitations. Behavior of actinides in the environment are a major USDOE concern, whether in connection with long-term releases from a repository, releases from stored defense wastes or accidental releases in reprocessing, etc. Principal goal of our research was expand the thermodynamic data base on complexation of actinides by natural ligands (e.g., OH[sup [minus]], CO[sub 3][sup 2[minus]], PO[sub 4][sup 3[minus]], humates). The research undertakes fundamental studies of actinide complexes which can increase understanding of the environmental behavior of these elements.
Date: January 1, 1993
Creator: Choppin, G.R.
Partner: UNT Libraries Government Documents Department

Research in actinide chemistry. Progress report, 1990--1993

Description: This research studies the behavior of the actinide elements in aqueous solution. The high radioactivity of the transuranium actinides limits the concentrations which can be studied and, consequently, limits the experimental techniques. However, oxidation state analogs (trivalent lanthanides, tetravalent thorium, and hexavalent uranium) do not suffer from these limitations. Behavior of actinides in the environment are a major USDOE concern, whether in connection with long-term releases from a repository, releases from stored defense wastes or accidental releases in reprocessing, etc. Principal goal of our research was expand the thermodynamic data base on complexation of actinides by natural ligands (e.g., OH{sup {minus}}, CO{sub 3}{sup 2{minus}}, PO{sub 4}{sup 3{minus}}, humates). The research undertakes fundamental studies of actinide complexes which can increase understanding of the environmental behavior of these elements.
Date: April 1, 1993
Creator: Choppin, G. R.
Partner: UNT Libraries Government Documents Department

Research in actinide chemistry. Final report, March 1, 1993--February 28, 1996

Description: The present three-year grant period has been a fruitful one for the laboratory as research entered some new areas while continuing in others in which the group has been successful. As in past grant periods, the principal focus has been on complexation of actinide elements with inorganic and organic ligands. The ligands to study have been chosen for their value (known or potential) in actinide separations or for their potential role in environmental behavior of the actinides. Since the radioactivity of some actinides limits the variety of techniques which can be used in their study, we have used {open_quotes}oxidation state analogs{close_quotes}. These analogs have the same oxidation state and very similar chemical behavior but are stable or very long-lived. Also, the analogs are chosen for their redox stability to avoid uncertainties in interpretation of systems in which several oxidations may coexist (e.g., in the case of Pu). Examples of such analogs which we have used are: Nd(III), Eu(III) for Pu(III), Am(III), Cm(III); Th(IV) for U(IV), Pu(IV); NpO{sub 2}{sup +} for PuO{sub 2}{sup +}; UO{sub 2}{sup 2+} for NpO{sub 2}{sup 2+}, PuO{sub 2}{sup 2+}. These analogs have allowed use of techniques which can increase significantly our understanding of actinide complexation.
Date: January 1, 1997
Creator: Choppin, G.R.
Partner: UNT Libraries Government Documents Department

Separations chemistry for f elements: Recent developments and historical perspective

Description: With the end of the cold war, the principal mission in actinide separations has changed from production of plutonium to cleanup of the immense volume of moderately radioactive mixed wastes which resulted from fifty years of processing activities. In order to approach the cleanup task from a proper perspective, it is necessary to understand the nature of the problem and how the wastes were generated. In this report, the history of actinide separations, both the basic science and production aspects, is examined. Many of the separations techniques in use today were developed in the 40`s and 50`s for the identification and production of actinide elements. To respond to the modern world of actinide separations new techniques are being developed for separations ranging from analytical methods to detect ultra-trace concentrations (for bioassay and environmental monitoring) to large scale waste treatment procedures. Some of these new methods are ``improvements`` or adaptations of the historical techniques. Total actinide recovery, lanthanide/actinide separations, and selective partitioning of actinides from inert constituents are of primary concern. This report, offers a historical perspective, review the current status of f element separation processes, and suggest areas for continued research in both actinide separations and waste cleanup/environment remediation.
Date: December 31, 1995
Creator: Nash, K.L. & Choppin, G.R.
Partner: UNT Libraries Government Documents Department

Complexation of Am(III) by oxalate in NaClO{sub 4} media

Description: The complexation of Am(III) by oxalate has been investigated in solutions of NaClO{sub 4} up to 9.0 M ionic strength at 25{degrees}C. The dissociation constants of oxalic acid were determined by potentiometric titration, while the stability constants of the Am(III)-oxalate complexation were measured by the solvent extraction technique. A thermodynamic model was constructed to predict the apparent equilibrium constants at different ionic strengths by applying the Pitzer equation using parameters for the Na{sup +}-HOx{sup -}, Na{sup +}-Ox{sup -}, AmOx{sup +}-ClO{sub 4}{sup -}, and Na{sup +}-Am(Ox){sub 2}{sup -} interactions obtained by fitting the data.
Date: September 1, 1995
Creator: Choppin, G.R. & Chen, J.F.
Partner: UNT Libraries Government Documents Department

Radiochemistry of uranium, neptunium and plutonium: an updating

Description: This report presents some procedures used in the radiochemical isolation, purification and/or analysis of uranium, neptunium, and plutonium. In this update of the procedures, we have not attempted to discuss the developments in the chemistry of U, Np, and Pu but have restricted the report to the newer procedures, most of which have resulted from the increased emphasis in environmental concern which requires analysis of extremely small amounts of the actinide element in quite complex matrices. The final section of this report describes several schemes for isolation of actinides by oxidation state.
Date: February 1, 1986
Creator: Roberts, R. A.; Choppin, G. R. & Wild, J. F.
Partner: UNT Libraries Government Documents Department

Research Program to Determine Redox Reactions and Their Effects on Speciation and Mobility of Plutonium in DOE Wastes

Description: Plutonium in geologic matrices undergoes a variety of complex reactions which complicate its environmental behavior. These complexities in plutonium chemistry whereby a large variety of precipitation, dissolution, adsorption/desorption, and redox reactions control plutonium speciation and concentrations, result in the need for a rather large amount of reliable, fundamental data to predict Pu behavior in geologic media. These data are also needed for evaluation of remediation strategies that involve removing most of the contaminants by selective methods, followed by in situ immobilization of residual contaminants. Two areas were studied during this project: (1) thermodynamic data for Th(IV) and Pu(IV) complexes of EDTA and for Pu(V) interactions with chloride; (2) kinetic data for redox reactions of Pu in the presence of common redox agents (e.g., H{sub 2}O{sub 2}, MnO{sub 2}, and NaOCl) encountered under waste disposal conditions. These studies are relevant to understanding Pu behavior in wastes disposed of in diverse geologic conditions (e.g., at the WIPP and YUCCA Mountain repositories and in contaminated sediments at many different DOE sites) and also for developing effective remediation strategies (e.g., processing of high level waste tanks). These studies have yielded data to address redox reactions of plutonium in the presence of environmentally important agents (e.g. organic and inorganic oxidants/reductants).
Date: October 1, 2000
Creator: Choppin, G.R. & Rai, D.
Partner: UNT Libraries Government Documents Department

Chemical speciation of strontium, americium, and curium in high-level waste: Predictive modeling of phase partitioning during tank processing. 1997 annual progress report

Description: 'In this research program, Pacific Northwest National Laboratory (PNNL) and Florida State University (FSU) are investigating the speciation of Sr and Am/Cm in the presence of selected organic chelating agents (ethylenediaminetetraacetic acid (EDTA), N-(2-hydroxyethyl) ethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA), and iminodiacetic acid (IDA)) over ranges of hydroxide, carbonate, and ionic strength conditions present in high-level waste tanks. This fundamental understanding of chemical speciation reactions is essential to develop methodologies for removal of Sr and Am/Cm from the chelates, via competition, displacement or other reactions, without the need for the development of costly and potentially hazardous organic destruction technologies. These studies specifically focus on the effects of hydrolysis, carbonate concentration, ionic strength, and selected cation competition on the removal of Sr and Am/Cm from the organic chelates.'
Date: June 1, 1997
Creator: Felmy, A.R. & Choppin, G.R.
Partner: UNT Libraries Government Documents Department

Research program to determine redox properties and their effects on speciation and mobility of Pu in DOE wastes. 1998 annual progress report

Description: 'The goal of the authors research is to develop data to allow successful modeling of the effects of redox chemicals present in Hanford waste tanks on the oxidation state and chemical speciation of plutonium in the wastes. As of May 1998, scoping experiments on PuO{sup 2+} in a solution of 1.0 M NaCl and pH 8 in the dark showed no reduction of PuO{sup 2+} concentration over a week nor was reduction observed when this experiment was repeated with 10{sup -5} M H{sub 2}O{sub 2}. Reduction was observed over hours/days as the H{sub 2}O{sub 2} concentration was raised above 10{sup -3} M. The rate of reduction in the dark was measured at pcH = 8, 1.0 M (NaCl) for [H{sub 2}O{sub 2}] = 10{sup -2} to 4 x 10{sup -2} and [PuO{sup 2+}] = 1.2 x 10{sup -10} to 3.5 x 10{sup -10} M and first order kinetics observed. From the rate constants, they calculate for [H{sub 2}O{sub 2}] = 10{sup -2} M and [PuO{sub 2+}] = 10{sup -6} M, a half life of reduction in the dark of 0.06 min and for [H{sub 2}O{sub 2}] = 10{sup -6} M, [PuO{sup 2+}] = 10{sup -6} M, of 10 hr. These data indicate that radiolytic production of H{sub 2}O{sub 2} in the wet tank wastes would serve to reduce PuO{sup 2+} (and PuO{sub 2}{sup 2+}) to Pu(IV), thereby reducing the concentration of dissolved Pu due to the strong hydrolytic tendency of the Pu(IV). The oxidation of Pu(IV) by NaOCl is also being investigated. As of May, 1998, the methodology to measure the oxidation state speciation at tracer Pu(IV) concentrations has been developed and scoping experiments conducted. At pcH 4.7, I = 1.0 M (NaCl), [Pu(IV)] = 10{sup -10} M and [NaOCl] = 10{sup -5} to 10{sup -3} M, no oxidation (i.e., ...
Date: June 1, 1998
Creator: Choppin, G.R. & Rai, D.
Partner: UNT Libraries Government Documents Department

Variation of stability constants of thorium citrate complexes and of thorium hydrolysis constants with ionic strength

Description: Citrate is among the organic anions that are expected to be present in the wastes planned for deposition in the Waste Isolation Pilot Plant repository. In this study, a solvent extraction method has been used to measure the stability constants of Thorium(IV)[Th(IV)] with citrate anions in aqueous solutions with (a) NaClO{sub 4} and (b) NaCl as the background electrolytes. The ionic strengths were varied up to 5 m (NaCl) and 14 m (NaClO{sub 4}). The data from the NaClO{sub 4} solutions at varying pH values were used to calculate the hydrolysis constants for formation of Th(OH){sup 3+} at the different ionic strengths.
Date: September 1, 1995
Creator: Choppin, G.R.; Erten, H.N. & Xia, Y.X.
Partner: UNT Libraries Government Documents Department

Thermodynamic modeling of neptunium(V)-acetate complexation in concentrated NaCl media

Description: The complexation of neptunium(V), Np(V), with the acetate anion, Ac{sup -}, was measured in sodium chloride media to high concentration using an extraction technique. The data were interpreted using the thermodynamic formalism of Pitzer, which is valid to high electrolyte concentrations. A consistent model for the deprotonation constants of acetic acid in NaCl and NaClO{sub 4} media was developed. For the concentrations of acetate expected in a waste repository, only the neutral complex NpO{sub 2}Ac(aq) was important in describing the interactions between the neptunyl ion and acetate. The thermodynamic stability constant log {beta}{sup 0}{sub 101} for the reaction NpO{sub 2}{sup +} + Ac{sup -} {leftrightarrow} NpO{sub 2}Ac was calculated to be 1.46{plus_minus}0.11. This weak complexing behavior between the neptunyl ion and acetate indicates that acetate will not significantly enhance dissolved Np(V) concentrations in ground waters associated with nuclear waste repositories that may contain acetate.
Date: September 1, 1995
Creator: Novak, C.F.; Borkowski, M. & Choppin, G.R.
Partner: UNT Libraries Government Documents Department

Complexation study of NpO{sub 2}{sup +} and UO{sub 2}{sup 2+} ions with several organic ligands in aqueous solutions of high ionic strength

Description: The acid dissociation constants, pK{sub a}, and the stability constants for NpO{sub 2}{sup +} and UO{sub 2}{sup 2+} have been measured for certain organic ligands [acetate, {alpha}-hydroxyisobutyrate, lactate, ascorbate, oxalate, citrate, EDTA, 8-hydroxyquinoline, 1, 10-phenanthroline, and thenoyltrifluoroacetone] in 5 m (NaCl) ionic strength solution. The pK{sub a} values were determined by potentiometry or spectrometry. These methods, as well as solvent extraction with {sup 233}U and {sup 237}Np radiotracers, were used to measure the stability constants of the 1:1 and 1:2 complexes of dioxo cations. These constants were used to estimate the concentrations required to result in 10 % competition with hydrolysis in the 5 m NaCl solution. Such estimates are of value in assessing the solubility from radioactive waste of AnO{sub 2}{sup +} and AnO{sub 2}{sup 2+} in brine solutions in contact with nuclear waste in a salt-bed repository.
Date: September 1, 1995
Creator: Borkowski, M.; Lis, S. & Choppin, G.R.
Partner: UNT Libraries Government Documents Department

Conformational changes in polyelectrolytes and the effect on metal binding

Description: There has been considerable interest in the complexation of metals and other cations by natural humic and fulvic acids, as well as synthetic polyelectrolytes. In order to explain the binding observed for metals, and other species by organic polyelectrolytes, steric effects have been proposed. In this work, the effects of pH changes in aqueous solution on two synthetic polyelectrolytes, polymaleic acid (PMA) and polyacrylic acid (PAA), have been examined by laser Raman spectroscopy and turbidity measurements. These results are compared to Fourier-transform infrared (FTIR) and (/sup 13/C) nuclear magnetic resonance (NMR) spectra for solid samples of PMA, PAA, and fulvic and humic acids. Two types of carboxylic acid groups were detected for PMA in aqueous solution. Crystallization of PMA in a narrow pH range was observed. These data are consistent with strong intramolecular hydrogen bonding occurring in PMA at a pH of approximately 4. This implication of these results on the use of these compounds as models for fulvic and humic acids is discussed. 27 refs., 3 figs., 1 tab.
Date: September 1, 1988
Creator: Marley, N.A.; Gaffney, J.S.; Minai, Y. & Choppin, G.R.
Partner: UNT Libraries Government Documents Department

Solubility of Nd in brine

Description: The solubility of Nd(III) has been measured in a synthetic brine at pcH 6.4, 8.4, 10.4 and 12.4. The brine consisted predominantly of (Na+K)Cl and MgCl{sub 2}, with an ionic strength of 7.8M (9.4m). The experimental solubility is much less than that estimated from modeling of the species in solution in equilibrium with the Nd solid using S.I.T. The predominant solid compound of Nd (III) at each pcH was determined from X-ray diffraction patterns.
Date: December 31, 1993
Creator: Khalili, F.; Symeopoulos, V.; Chen, J. F. & Choppin, G. R.
Partner: UNT Libraries Government Documents Department

Variation of stability constants of thorium and uranium oxalate complexes with ionic strength

Description: Extraction of Th(IV) and UO{sub 2}{sup 2+} by a solution of TTA and HDEHP, respectively, in toluene was used to obtain stability constants of their oxalate complexes in 1, 3, 5, 7 and 9 M ionic strength (NaClO{sub 2}) solutions. The complexes formed were the MOx, MHOx, MOx{sub 2} and M(HOx){sub 2} (M = Th, UO{sub 2}) species. The values were analyzed by the Specific Interaction Theory and agreed to I {le} 3 M but required an additional term for fitting at I > 3 M.
Date: December 31, 1993
Creator: Erten, H. N; Mohammed, A. K. & Choppin, G. R.
Partner: UNT Libraries Government Documents Department

The New ELement Mendelevium, Atomic Number 101

Description: We have produced and chemically identified for the first time a few atoms of the element with atomic number 101. Very intense helium ion bombardments of tiny targets of 99{sup 253} have produced a few spontaneously fissionable atoms which elute in the eka-thulium position on a cation resin column.
Date: April 4, 1955
Creator: Ghiorso, A.; Harvey, B.G.; Choppin, G.R.; Thompson, S.G. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

Chemical Properties of Elements 99 and 100

Description: A description of some of the chemical properties and of the methods used in the separations of elements 99 and 100 is given. The new elements exhibit the properties expected for the tenth and eleventh actinide elements. Attempts to produce an oxidation state greater than 111 of element 99 have been successful. In normal aqueous media only the 111 state of element 100 appears to exist. The relative spacings of the elution peaks of the new elements in some separations with ion exchange resin columns are the same as the relative spacings of the homologous lanthanide elements. The results of experiments involving cation exchange resins with very concentrated hydrochloric acid eluant show that the new elements, like the earlier actinides, are more strongly complexed than the lanthanides. The new elements also exist partially as anions in concentrated hydrochloric acid, as do earlier actinide elements, and they may be partially separated from each other by means of ion exchange resins. With some eluants interesting reversals of elution positions are observed in the region Bk-Cf-99-100, indicating complex ion formation involving unusual factors.
Date: July 23, 1954
Creator: Thompson, S.G.; Harvey, B.G.; Choppin, G.R. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

Physical chemistry and the environment

Description: From the ozone hole and the greenhouse effect to plastics recycling and hazardous waste disposal, society faces a number of issues, the solutions to which require an unprecedented understanding of the properties of molecules. We are coming to realize that the environment is a coupled set of chemical systems, its dynamics determining the welfare of the biosphere and of humans in particular. These chemical systems are governed by fundamental molecular interactions, and they present chemists with an unparalleled challenge. The application of current concepts of molecular behavior and of up-to-date experimental and computational techniques can provide us with insights into the environment that are needed to mitigate past damage, to anticipate the impact of current human activity, and to avoid future insults to the environment. Environmental chemistry encompasses a number of separate, yet interlocking, areas of research. In all of these areas progress is limited by an inadequate understanding of the underlying chemical processes involved. Participation of all chemical approaches -- experimental, theoretical and computational -- and of all disciplines of chemistry -- organic, inorganic, physical, analytical and biochemistry -- will be required to provide the necessary fundamental understanding. The Symposium on ``Physical Chemistry and the Environment`` was designed to bring the many exciting and challenging physical chemistry problems involved in environmental chemistry to the attention of a larger segment of the physical chemistry community.
Date: August 1, 1994
Creator: Dunning, T. H. Jr.; Garrett, B. C.; Kolb, C. E. Jr.; Shaw, R. W.; Choppin, G. R. & Wagner, A. F.
Partner: UNT Libraries Government Documents Department