Effects of seawater carbonate ion concentration and temperature on shell U, Mg, and Sr in cultured planktonic foraminifera

http://www3.nd.edu/~fein/Publications/Gorman-Lewis%20JThermo%20(40)335.pdf

Review of uranyl mineral solubility measurements

The speciation of uranium (U) in relation to its bioavailability is reviewed for surface waters (fresh- and seawater) and their sediments. A summary of available analytical and modeling techniques for determining U speciation is also presented. U(VI) is the major form of U in oxic surface waters, while U(IV) is the major form in anoxic waters. The bioavailability of U (i.e., its ability to bind to or traverse the cell surface of an organism) is dependent on its speciation, or physicochemical form. U occurs in surface waters in a variety of physicochemical forms, including the free metal ion (U4+ or UO2(2+)) and complexes with inorganic ligands (e.g., uranyl carbonate or uranyl phosphate), and humic substances (HS) (e.g., uranyl fulvate) in dissolved, colloidal, and/or particulate forms. Although the relationship between U speciation and bioavailability is complex, there is reasonable evidence to indicate that UO2(2+) and UO2OH+ are the major forms of U(VI) available to organisms, rather than U in strong complexes (e.g., uranyl fulvate) or adsorbed to colloidal and/or particulate matter. U(VI) complexes with inorganic ligands (e.g., carbonate or phosphate) and HS apparently reduce the bioavailability of U by reducing the activity of UO2(2+) and UO2OH+. The majority of studies have used the results from thermodynamic speciation modeling to support these conclusions. Time-resolved laser-induced fluorescence spectroscopy is the only analytical technique able to directly determine specific U species, but is limited in use to freshwaters of low pH and ionic strength. Nearly all of the available information relating the speciation of U to its bioavailability has been derived using simple, chemically defined experimental freshwaters, rather than natural waters. No data are available for estuarine or seawater. Furthermore, there are no available data on the relationship between U speciation and bioavailability in sediments. An understanding of this relationship has been hindered due to the lack of direct quantitative U speciation techniques for particulate phases. More robust analytical techniques for determining the speciation of U in natural surface waters are needed before the relationship between U speciation and bioavailability can be clarified.

/pdf/uranium-speciation-and-bioavailability-in-aquatic-systems-an-2fscpfkhtb.pdf

Uranium speciation and bioavailability in aquatic systems: an overview.

Radioactivity in the marine environment

Re-evaluating the 238U-salinity relationship in seawater: Implications for the 238U–234Th disequilibrium method

The physicochemical characterization of uranium(VI) in seawater is described on the basis of species distribution calculations and experiments using polarography and spectrophotometry in artificial seawater at elevated uranium concentrations. Various dissolved uranium(VI) species are identified under different conditions of pH and carbonate concentration. Below pH 4, the hydrated uranyl ion is present in the free state (forming labile complexes). Above pH 4, a stepwise coordination of uranyl by the carbonate ion occurs. The monocarbonate complex is formed in the pH range 4-5, the bicarbonate uranyl complex between 5 and 6. Above pH 8, uranium is present predominately as the tricarbonate and to a smaller extent as a trihydroxide complex. There is satisfactory agreement between our experiments and the theoretically computed distribution of uranium(VI) in seawater based on published stability constants. The experiments done at higher concentrations are justified by theoretical distributions showing that there is no great difference in species distribution between the uranium at concentrations of 10/sup -4/ and /sup -8/ mol dm/sup -3/.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1986.31.5.1122

Characterization of uranium(VI) in seawater

Precipitation diagrams were constructed using the data obtained in experiments with direct mixing of uranyl ion ([UO 2 ] 2 + ) and hydrogen peroxide. Three days after mixing the system, equilibrium was established in the [H 2 O 2 ] t o t >[UO 2 ] t o t concentration region, resulting in stability of the concentration boundary. From this boundary condition, the solubility product (K s p = [UO 2 2 + ] x [O 2 2 - ]) was defined. The mean value of the solubility product was (1.32 ′ 0.02) x 10 - 3 6 mol dm - 3 . From the solubility border, where equilibrium was established, i.e., at [UO 2 2 + ] = 1.4 x 10 - 4 mol dm - 3 , the heterogeneous distribution diagrams of uranyl species, including the solid phase, were calculated.

/pdf/precipitation-of-uranium-vi-peroxide-uo4-in-sodium-1fn2zb5gdg.pdf

Precipitation of Uranium(VI) Peroxide (UO4) in Sodium Perchlorate Solution

Square-wave cathodic stripping voltammetry of hydrolyzed uranyl species

The effect of the adsorption of uranyl species on the static mercury drop electrode is used for the electrochemical determination of dissolved uranium concentration in untreated and estuarine sea-water. The measurements were performed by square-wave cathodic stripping voltammetry. The standard additions method is successfully applied for measurements of natural uranyl concentrations in water samples which were found to be in the range between 4.3 and 15 nmol l–1 depending on the sampling location with detection limits of 2.4 and 10 nmol l–1, respectively.

Renata Djogić

Papers

Characterization of uranium(VI) in seawater

Precipitation of Uranium(VI) Peroxide (UO4) in Sodium Perchlorate Solution

Square-wave cathodic stripping voltammetry of hydrolyzed uranyl species

Direct determination of dissolved uranyl(VI) in sea-water by cathodic stripping voltammetry

Dissolved uranyl complexed species in artificial seawater