Thermodynamics of Neptunium(V) in Concentrated Salt Solutions: II. Ion Interaction (Pitzer) Parameters for Np(V) Hydrolysis Species and Carbonate Complexes

A comprehensive set of ion interaction parameters of the Pitzer model, including the relevant thermodynamic constants and standard chemical potentials, is evaluated for the hydrolysis reactions and carbonate complexation of Np(V) in NaC104 and NaCl solutions. Based on the hitherto available solubility products, hydrolysis constants and carbonate complexation constants, the binary Pitzer parameters β'"' and β" ' for the interaction of the Np(V) complex species with Na are evaluated. The affinity of the NpOJ ion and its complexed species for the CI" ion is treated as a strong ion-ion interaction by taking into account mixing parameters <9,,. With these parameters, equilibrium constants for the hydrolysis reactions and carbonate complexation of Np(V) are calculated in a wide range of ionic strength, up to 6.5 m NaC104 and 5.6 m NaCl. Solubilities of various Np(V) solid phases are calculated for different NaC104 and NaCl concentrations in both carbonate-free solutions and systems with a constant C02 partial pressure, and the results are compared with experimental values.

[1]  K. Pitzer,et al.  The thermodynamics of aqueous carbonate solutions II. Mixtures of potassium carbonate, bicarbonate, and chloride , 1982 .

[2]  N. Møller,et al.  The prediction of mineral solubilities in natural waters: The Na-K-Mg-Ca-H-Cl-SO4-OH-HCO3-CO3-CO2-H2O system to high ionic strengths at 25°C , 1984 .

[3]  M. Yamawaki,et al.  Effect of Ionic Strength on the Solubility of Neptunium(V) Hydroxide , 1992 .

[4]  L Ciavatta,et al.  THE SPECIFIC INTERACTION THEORY IN EVALUATING IONIC EQUILIBRIA , 1980 .

[5]  A. Moskvin.  HYDROLYTIC BEHAVIOR OF NEPTUNIUM(IV, V, VI). , 1971 .

[6]  Ricardo M. Pytkowicz,et al.  Activity coefficients in electrolyte solutions , 1979 .

[7]  D. D. Wagman,et al.  The NBS tables of chemical thermodynamic properties : selected values for inorganic and C1 and C2 organic substances in SI units , 1982 .

[8]  G. Meinrath.  Np(V) carbonates in solid state and aqueous solution , 1994 .

[9]  Y. Inoue,et al.  Studies of the Formation of Complexes of Np(V) with Inorganic Ligands by Means of Solvent Extraction with 2-Thenoyltrifluoroacetone and 1,10-Phenanthroline. II. Fluoro, Sulfato, and Phosphato Complexes , 1985 .

[10]  G. Bidoglio,et al.  Studies on Neptunium (V) Carbonate Complexes under Geologic Repository Conditions , 1985 .

[11]  Chantal Riglet.  Chimie du neptunium et autres actinides en milieu carbonate , 1989 .

[12]  K. Pitzer,et al.  Thermodynamics of electrolytes. II. Activity and osmotic coefficients for strong electrolytes with one or both ions univalent , 1973 .

[13]  L. Maya.  Hydrolysis and carbonate complexation of dioxoneptunium(V) in 1. 0 M NaClO/sub 4/ at 25/sup 0/C , 1983 .

[14]  I. Grenthe,et al.  Chemical equilibria in actinide carbonate systems , 1986 .

[15]  S. Nagasaki,et al.  Speciation and solubility of neptunium in underground environments by paper electrophoresis , 1988 .

[16]  J. I. Kim,et al.  Solubility and Hydrolysis Behaviour of Neptunium(V) , 1992 .

[17]  K. Pitzer,et al.  THERMODYNAMICS OF ELECTROLYTES PART 4, ACTIVITY AND OSMOTIC COEFFICIENTS FOR MIXED ELECTROLYTES , 1974 .

[18]  W. Runde,et al.  Solid-liquid equilibria of neptunium(V) in carbonate solutions of different ionic strengths: II. Stability of the solid phases , 1995 .

[19]  J. I. Kim,et al.  Thermodynamics of Neptunium(Y) in Concentrated Salt Solutions: Chloride Complexation and Ion Interaction (Pitzer) Parameters for the NpO+2 Ion , 1995 .

[20]  J. I. Kim,et al.  Hydrolysis Reactions of Neptunium (V) , 1985 .

[21]  Kenneth S. Pitzer,et al.  Thermodynamics of electrolytes. IV. Activity and osmotic coefficients for mixed electrolytes , 1974 .

[22]  Gregory R. Choppin,et al.  The Chemical Thermodynamics of Actinide Elements and Compounds , 1979 .

[23]  S. Nakayama,et al.  Column Experiments on Migration Behaviour of Neptunium (V) , 1988 .