Solubility of uranium(IV) hydrous oxide in high pH solution under reducing condition

Abstract

The solubility of uranium(IV) hydrous oxide was measured at 25 • C in NaClO 4 solution containing Na 2 S 2 O 4 as a reducing agent in the pH range from 12 to 14. The experiment was carried out from oversaturation at I = 0.5, 1.0 and 2.0 mol/dm 3 (M). The solubility data were analyzed to obtain the hydrolysis constants (β m ) of U(OH) m (4−m) . By taking the specific ion interaction theory (SIT) for ionic strength corrections and by using the solubility product log K • sp = −53.93 ± 0.20, the hydrolysis constants at I = 0, log β • 5 < 48.10 and log β • 6 = 48.95 ± 1.01, were determined together with the ion interaction coefficients of U(OH) 5 − and U(OH) 6 2− .

Solubility of Zr(IV), Th(IV) and Pu(IV) hydrous oxides in CaCl2solutions and the formation of ternary Ca-M(IV)-OH complexes

“…Besides the mononuclear species Zr(OH) n 4−n with n = 0, 1, 2, 4 and 6 the model included two trimers, Zr 3 (OH) 4 8+ and Zr 3 (OH) 9 3+ , and the tetramers Zr 4 (OH) 8 8+ , Zr 4 (OH) 15 + , and Zr 4 (OH) 16 (aq). However, the exact stoichiometries of the oligomeric species dominant in acidic solutions are not well ascertained, e.g.…”

“…Numerous solubility studies with An(IV) hydrous oxides (An = Th, U, Np, Pu) in alkali hydroxide solutions up to pH 14 show no indication for the formation of anionic hydroxide complexes An(OH) n 4−n with n > 4 (cf ., discussion in [1,2,4]). The solubility increase observed in a few studies with U(IV), Np(IV) and Pu(IV) in highly basic solutions [9][10][11] may be caused by the interference of carbonate or by species at higher oxidation states; the proposed data for An(OH) 5 − or An(OH) 6 2− complexes are therefore not accepted in the database of the OECD/Nuclear Energy Agency (NEA-TDB). Solely the formation of Zr(OH) 6 2− at high hydroxide concentrations (e.g.…”

Determination of Apparent Formation Constants of Eu(III) with Humic Substances by Ion Selective Liquid Membrane Electrode

“…As shown in Scheme 1, the inner solution of ISE was 1 × 10 -3 M Eu 3+ at pH 2, and the identical supporting electrolyte, 0.1 M LiCl, was adopted in the inner solution for the silver-silver chloride electrode (SSE1) and reference electrode (SSE2). The pH combination electrode was calibrated to measure the hydrogen ion concentration ([H + ] = 10 -pHc ), based on the reference method [23,24]. A combination glass electrode (Kyoto Electronics, 98-100-C171) was used to measure the pH, and the reference electrode was filled with 3.6 M NaCl + 0.4 M NaClO 4 .…”

Systematics of Hydrolysis Constants of Tetravalent Actinide Ions

“…16) In order to exclude such sources of error, in the present study, the 1;1 , 1;2 and 1;3 values of Th(IV) 17) and U(IV) 18) are selected, which have been obtained by solvent extraction method with considerably low solute concentrations. Although the 1;5 and 1;6 values of U(IV) 19) have been obtained by the solubility measurement with relatively low solute concentration up to 10 À5 M, these values are not selected by considering possible colloid formation. Then the 1;5 value of <10 47 , which has been suggested by Neck and Kim 10) to be consistent with the experimental data in neutral and alkaline solutions, is selected.…”

“…Figure 3 shows a comparison of the predicted solubility curve with the experimental results of U(IV). 18,19,[25][26][27][28] In…”