Thermodynamic Model for the Solubility of NdF₃(cr) in the Na⁺-NH₄⁺ – Nd³⁺–F^-–H₂O System at 25 °C

Journal Article · Fri Aug 02 00:00:00 EDT 2013 · Journal of Solution Chemistry

DOI:https://doi.org/10.1007/s10953-013-0049-z· OSTI ID:1094934

Rai, Dhanpat ^[1]; Yui, Mikazu ^[2]; Kitamura, Akira ^[2]; Yoshikawa, Hideki ^[2]; Felmy, A. R. ^[3]

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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)

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 NdF²⁺ and NdF²⁺ were then used to interpret the extensive NdF3(cr) solubility data in NaF and NH₄F 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_n⁰ for the reaction [Nd³⁺ + nF^- = NdF_{n^3-n] of (3.81 ± 0.10), (5.89 ± 0.77), and <12.48 for n of 1 through 3, respectively. The log10} K^sp0 for the solubility of NdF₃(cr) (NdF3(cr) = Nd³⁺ + 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 AnF₃(cr), 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.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1094934
• Report Number(s): PNNL-SA-91840; KP1702030
• Journal Information: Journal of Solution Chemistry, Vol. 42, Issue 7; ISSN 0095-9782
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
solubility
neodymium
fluoride complexes of Nd
solubility product
thermodynamic data
NdF2+
NdF39cr)
Nd(OH)3(aq)