Solubility of B-Nb2O5 and the Hydrolysis of Niobium(V) in Aqueous Solution as a Function of Temperature and Ionic Strength
- Nancy Universite, Vandoeuvre, France
- ORNL
- SPCTS, Limoges Cedex, France
- ANDRA, Chatenay-Malabry Cedex, France
B-Nb{sub 2}O{sub 5} was recrystallized from commercially available oxide, and XRD analyses indicated that it is stable in contact with solutions over the pH range 0 to 9, whereas solid polyniobates such as Na{sub 8}Nb{sub 6}O{sub 19} 13H{sub 2}O(s) appear to predominate at pH > 9. Solubilities of the crystalline B-Nb{sub 2}O{sub 5} were determined in five NaClO{sub 4} solutions (0.1 {le} Im/mol {center_dot} kg{sup -1} {le} 1.0) over a wide pH range at (25.0 {+-} 0.1) C and at 0.1 MPa. A limited number of measurements were also made at Im = 6.0 mol {center_dot} kg{sup -1}, whereas at Im = 1.0 mol {center_dot} kg{sup -1} the full range of pH was also covered at (10, 50 and 70) C. The pH of these solutions was fixed using either HClO{sub 4} (pH {le} 4) or NaOH (pH {ge} 10) and determined by mass balance, whereas the pH on the molality scale was measured in buffer mixtures of acetic acid + acetate (4 {le} pH {le} 6), Bis-Tris (pH {approx} 7), Tris (pH {approx} 8) and boric acid + borate (pH {approx} 9). Treatment of the solubility results indicated the presence of four species, Nb(OH){sub n}{sup 5-n} (where n = 4-7), so that the molal solubility quotients were determined according to: 0.5Nb{sub 2}O{sub 5}(cr) + 0.5(2n-5)H{sub 2}O(l){sup {center_dot}-} Nb(OH){sub n}{sup 5-n} + (n-5)H{sup +} (n = 4-7) and were fitted empirically as a function of ionic strength and temperature, including the appropriate Debye-Hueckel term. A Specific Interaction Theory (SIT) approach was also attempted. The former approach yielded the following values of log 10 K{sub sn} (infinite dilution) at 25 C: -(7.4 {+-} 0.2) for n = 4; -(9.1 {+-} 0.1) for n = 5; -(14.1 {+-} 0.3) for n = 6; and -(23.9 {+-} 0.6) for n = 7. Given the experimental uncertainties (2{sigma}), it is interesting to note that the effect of ionic strength only exceeded the combined uncertainties significantly in the case of log 10 K{sub s6} to I{sub m} = 1.0 mol {center_dot} kg{sup -1}, such that these values may be of use by defining their magnitudes in other media. Values of {Delta}{sub f} g{sup o}, {Delta}{sub f} H{sup o}, 5{sup o} and C{sub p}{sup o} (298.15 K, 0.1 MPa) for each hydrolysis product were calculated and tabulated.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 1037167
- Journal Information:
- Journal of Solution Chemistry, Vol. 39, Issue 2; ISSN 0095-9782
- Country of Publication:
- United States
- Language:
- English
Similar Records
Thermal and light-induced reduction of Ru(bpy)/sub 3//sup 3 +/ in aqueous solution
Association quotients of aluminum sulphate complexes in NaCl media from 50 to 125 C: Results of a potentiometric and solubility study