The solubility of (UO[sub 2])[sub 3](PO[sub 4])[sub 2][center dot]4H[sub 2]O(s) and the formation of U(VI) phosphate complexes: Their influence in uranium speciation in natural waters

Journal Article · Tue Dec 01 04:00:00 EST 1992 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(92)90256-I· OSTI ID:7030941

Sandino, A; Bruno, J ^[1]

---

1. Royal Institute of Technology, Stockholm (Sweden)

Uranium is commonly associated in natural waters with O-containing ligands both in the aqueous and the solid phases. Phosphate is present in most of these systems; however, the thermodynamics of the U(VI)-H[sub 3]PO[sub 4] system are poorly known, particularly in the pH range of interest 6 to 9. Hence, the effect of phosphate on the migration of uranium in natural waters is not well understood. We have investigated the solubility of a well-characterized U(VI)-phoshpate phase in the pH range 3 to 9: (UO[sub 2])[sub 3](PO[sub 4])[sub 2][center dot]4H[sub 2]O(s). Analysis of these data indicates the formation of the predominant species UO[sub 2]HPO[sub 4](aq) and UO[sub 2]PO[sub 4] in the pH range 4-9. Their formation constants as well as the solubility constant of (UO[sub 2])[sub 3](PO[sub 4])[sub 2][center dot]4H[sub 2]O(s) have been determined. From the same experiments we have established the equilibrium constant of the hydroxide complex UO[sub 2](OH)[sub 3][sup [minus]]. A discussion of the hydrolysis of U(VI) is also reported. The effect of phosphate on the mobility of U in natural waters is assessed in the light of these new data. They indicate that in the pH range of most natural waters, 6 to 9, U(VI) will be associated to aqueous phosphate complexes when the total concentration ratio [PO[sup 3[minus]][sub 4]]T/CO[sup 2[minus]][sub 3]T is greater than 10[sup [minus]1].

• OSTI ID: 7030941
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 56:12; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360606 -- Other Materials-- Physical Properties-- (1992-)
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
54 ENVIRONMENTAL SCIENCES
540220 -- Environment
Terrestrial-- Chemicals Monitoring & Transport-- (1990-)
ACTINIDE COMPOUNDS
CHEMICAL REACTIONS
COMPLEXES
DECOMPOSITION
ENVIRONMENTAL TRANSPORT
EQUILIBRIUM
GROUND WATER
HYDROGEN COMPOUNDS
HYDROLYSIS
HYDROXIDES
LYSIS
MASS TRANSFER
OXYGEN COMPOUNDS
PH VALUE
PHOSPHATES
PHOSPHORUS COMPOUNDS
SOLUBILITY
SOLVOLYSIS
URANIUM COMPOUNDS
URANIUM HYDROXIDES
URANIUM PHOSPHATES
URANYL COMPOUNDS
URANYL PHOSPHATES
WATER