On the influence of carbonate on mineral dissolution: III. The solubility of microcrystalline ThO[sub 2] in CO[sub 2]-H[sub 2]O media

Journal Article · Sat Jan 01 04:00:00 EST 1994 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(94)90492-8· OSTI ID:5241776

Oesthols, E; Grenthe, I ^[1]; Bruno, J ^[2]

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1. Royal Institute of Technology, Stockholm (Sweden)
2. MBT Technologia Ambiental, Cerdanyola (Spain)

The solubility of microcrystalline ThO[sub 2] as a function of pH has been studied under different partial pressures of CO[sub 2] in aqueous media, in order to obtain qualitative and quantitative information on the complexation of Th[sup 4+] with carbonate. Based on the results of the study, the existence of a mixed thorium-hydroxo-carbonate complex, Th(OH)[sub 3]CO[sup [minus]][sub 3], as well as a thorium carbonate complex Th(CO[sub 3])[sup 6[minus]][sub 5] is proposed, and their stability constants and the solubility product of microcrystalline thorium dioxide (ThO[sub 2](act)) are determined. The following equilibrium constants were determined in 0.5 M NaClO[sub 4] at 25[degrees]C 1 atm: ThO[sub 2](act) + 4H [r equilibrium] Th[sup 4+] + 2H[sub 2]O log K[sub s] = 9.37 [+-] 0.13; ThO[sub 2](act) + H[sup +] + H[sub 2]O + CO[sup 2[minus]][sub 3] [r equilibrium] Th(OH)[sub 3]CO[sup [minus]][sub 3] log [beta][sub 1, 3, 1 ] = 6.11 [+-] 0.19; ThO[sub 2](act) + 4H[sup +] rH[sup +] + 5CO[sup 2[minus]][sub 3] [r equilibrium] Th(CO[sub 3])[sup 6[minus]][sub 5] log[beta][sub 1, 0, 5] = 42.12 [+-] 0.32. The errors are given as three standard deviations in the fitted constants. By extrapolation, the following constants are obtained for the infinite dilution standard state: ThO[sub 2](act) + 4H[sup +] + 2H[sub 2]O log K[sub 5] = 7.31 [+-] 0.3; ThO[sub 2](act) + H[sup +] + H[sub 2]O + CO[sup 2[minus]][sub 3] [r equilibrium] Th(OH)[sub 3]CO[sup [minus]][sub 3] log[beta][sub 1, 3, 1] = 6.78 [+-] 0.3; ThO[sub 2](act) + 4H[sup +] + 5CO[sup 2[minus]][sub 3] [r equilibrium] log[beta][sub 1, 0, 5] = 39.64 [+-] 0.4.

• OSTI ID: 5241776
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 58:2; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540330* -- Environment
Aquatic-- Radioactive Materials Monitoring & Transport-- (1990-)
ACTINIDE COMPLEXES
ACTINIDES
AQUATIC ECOSYSTEMS
CARBON COMPOUNDS
CARBONATES
CHEMICAL REACTION KINETICS
COMPLEXES
ECOSYSTEMS
ELEMENTS
ENVIRONMENTAL TRANSPORT
KINETICS
MASS TRANSFER
METALS
OXYGEN COMPOUNDS
REACTION KINETICS
SOLUBILITY
SYNTHESIS
THORIUM
THORIUM COMPLEXES