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Title: Thermodynamic Model for the Solubility of NdF 3(cr) in the Na +-NH 4 + – Nd 3+–F -–H 2O System at 25 °C

The objectives of this study were to develop a reliable thermodynamic model for the Nd-F system based on critical review and experimental studies. The SIT model was used to convert concentration constants reported in the literature to constants at zero ionic strengths for cross comparison and selection of reliable values. The critically evaluated thermodynamic constants for the formation of NdF 2+ and NdF 2+ were then used to interpret the extensive NdF3(cr) solubility data in NaF and NH 4F solutions, ranging in concentrations from extremely low values to as high as 1.0 mol.kg-1, equilibrated for different periods ranging up to as long as 72 days. These efforts have resulted in log β n 0 for the reaction [Nd 3+ + nF - = NdF n3-n] of (3.81 ± 0.10), (5.89 ± 0.77), and <12.48 for n of 1 through 3, respectively. The log10 K sp 0 for the solubility of NdF 3(cr) (NdF3(cr) = Nd 3+ + 3F -) was determined to be -(20.49 ± 0.37). Because 1) Nd is an excellent analog for trivalent actinides -- An(III) (e.i., Pu(III), Am(III), and Cm(III)) -- and 2) the available data for the An(III)-F system, especially the solubility products of AnF 3(cr),more » are of extremely poor quality, the critical literature review in combination with the experimental Nd-F system data have been used to assign thermodynamic constants for the An(III)-F reactions until good quality specific data for them becomes available.« less
Authors:
 [1] ;  [2] ;  [2] ;  [2] ;  [3]
  1. Rai Enviro-Chem, LLC., Yachats, OR (United States)
  2. Japan Atomic Energy Agency (JAEA), Tokai (Japan)
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
OSTI Identifier:
1094934
Report Number(s):
PNNL-SA-91840
Journal ID: ISSN 0095-9782; KP1702030
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solution Chemistry; Journal Volume: 42; Journal Issue: 7
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; solubility; neodymium; fluoride complexes of Nd; solubility product; thermodynamic data; NdF2+; NdF39cr); Nd(OH)3(aq)