Aqueous complexation

The pregnant organic solvent is stripped by agitation with a strong carbonate solution which removes uranium as the stable U02(C02) 3 aqueous complex. 

A critical assessment of the chemical thermodynamic properties of the actinides and their compounds is presently being prepared by an international team of scientists under the auspices of the International Atomic Energy Agency (Vienna). As a result of this effort, four publications (1, 2, 3, 5) have already become available and a further ten 6-T4), including the halides (8) and aqueous complexes with Tnorganic ligands (12),... 

Langmuir, D., Techniques of estimating thermodynamic properties for some aqueous complexes of geochemical interest, in Chemical Modeling in Aqueous Systems Speciation, Sorption, Solubility and Kinetics, Jenne, E.A., Ed., ACS Symposium, American Chemical Society, Washington, DC, 1979, pp. 353-387. 

Similar logic gives the mass balance equations for the species components. The mass of the i th component is distributed among the single basis species A, and the secondary species in the system. By Equation 3.22, there are v, j moles of component i in each mole of secondary species Aj. There is one mole of Na+ component, for example, per mole of the basis species Na+, one per mole of the ion pair NaCl, two per mole of the aqueous complex Na2SC>4, and so on. Mass balance for species component i, then, is expressed... 

This review will introduce basic techniques for calculating equilibrium and kinetic stable isotope fractionations in molecules, aqueous complexes, and solid phases, with a particular focus on the thermodynamic approach that has been most commonly applied to studies of equilibrium fractionations of well-studied elements (H, C, N, O, and S) (Urey 1947). Less direct methods for calculating equilibrium fractionations will be discussed briefly, including techniques based on Mossbauer spectroscopy (Polyakov 1997 Polyakov and Mineev 2000). 

The chromate anion is a highly soluble, toxic tetrahedral complex (point group Tj) that occurs in oxidized, neutral-basic solutions. It is also one of a small number of aqueous complexes that have been thoroughly characterized by spectroscopic measurements on numerous isotopic compositions (Muller and Kbniger 1974), so it will be possible to check the vibrational model against real data. Here the MUBFF is applied under the assumption that aqueous chromate can be approximately modeled as a gas-phase molecule. 

Solvent extraction is used in nnmerons chemical industries to produce pure chemical compounds ranging from pharmaceuticals and biomedicals to heavy organics and metals, in analytical chemistry and in environmental waste purification. The scientific explanation of the distribution ratios observed is based on the fundamental physical chemistry of solute-solvent interaction, activity factors of the solutes in the pure phases, aqueous complexation, and complex-adduct interactions. Most university training provides only elementary knowledge about these fields, which is unsatisfactory from a fundamental chemical standpoint, as well as for industrial development and for protection of environmental systems. Solvent extraction uses are important in organic, inorganic, and physical chemistry, and in chemical engineering, theoretical as well as practical in this book we try to cover most of these important fields. 

Here the conditions have been chosen so that the aqueous complexes of TTA can be neglected as has been described earlier, and thus Eq. (4.71) is valid, and the relation Dm = [HA] ,g [H] so that... 

Table 8.17 Main predominance limits of aqueous complexes and saturation limits between solutes and condensed phases in iron-bearing aqueous solutions (see figure 8.22). Standard state Gibbs free energies of formation of species are listed in table 8.18. (c) = crystalline ... 

Although the predominant species forming in the C-H-O system (besides H2O) are methane CH4, carbon dioxide CO2 and its aqueous complexes HCO3 and... 

Let us consider again an isotopic exchange reaction of the type shown in equation 11.53, such as, for instance, the already treated equilibrium between stannous chloride and an aqueous complex... 

The large isotopic fractionations observed between oxidized and reduced forms of sulfur compounds and aqueous complexes require accurate appraisal of the effective cogeneticity of sulfur minerals utilized as geothermometric couples, and of their equilibrium condition, to avoid erroneous deductions. In fact, besides temperature, the isotopic composition of sulfur minerals is also affected by the bulk isotopic composition of the sulfur in the system (which is controlled... 

Shock E. L. and Koretsky C. M. (1995). Metal-organic complexes in geochemical processes Estimation of standard partial molal thermodynamic properties of aqueous complexes between metal cations and monovalent organic acid ligands at high pressures and temperatures. Geochim. Cosmochim. Acta, 59 1497-1532. 

Jeveral aspects of the photolytic behavior of aqueous complex ions have been studied in this laboratory over the past few years. One continually interesting question has been the extent to which the photochemistry of a complex depends on the absorption band irradiated. In the case of Co(III) acidopentamines, such as Co(NH3)5Br+2, we found that irradiation of Ajg —> g) bands showing appreciable charge transfer led to redox and aquation reactions which were competitive. It was reasonable to suppose that the common precursor was the species formed by a prompt heterolytic bond fission (7). The ( Aig —> Tig) band was far less photoactive, and in model cases, irradiation led only to aquation. Each excited state or excited state manifold thus tended to show a distinct photochemistry, which meant that conversion from one excited state to another was not important. 

The values of equilibrium constants of aqueous complexes and solids are expected to reveal systematic patterns when different groups of metals... 

Metal ion Freshwater Significant aqueous complexes Seawaterb Ref... 

Horwitz, E.P., Diamond, H., Gatrone, R.C., Nash, K.L. 1990. TUCS A new class of aqueous complexing agents for use in solvent extraction processes. ISEC 90, Kyoto, Japan, July 16-21. ANL/CP-71262. 

Nash, K. 1999. Aqueous complexes in separation of f-elements Options and strategies for future development. Separation Science and Technology 34(6 7) 911-929. 

In the presence of nitric acid, the degradation was more important due to the hydrolysis of H2 MEHP in the aqueous phase, and the resulting H3P04 degradation product led to competitive aqueous complexing of Am(III) and Ln(III) (160). 

The reactions with the surface hydroxyls are considered analogous to the formation of soluble aqueous complexes. 

This is not to say that no progress has been made in surface speciation kinetics related to soils (Sparks and Suarez, 1991). Adaptation of elementary reaction mechanisms established for aqueous complexes, for example, has proved to be an effective means of classifying kinetic surface species and establishing rate laws for... 

Chloride complexation studies of the actinide ions An3+, An4+, An02, and AnO + (An = U, Np, Pu) were reported in several comprehensive reviews [293-295], More recent investigations on aqua and chloro complexes of U02+, NpOz+, Np4+, Pu3+, etc., by x-ray absorption fine structure spectroscopy (XAFS) were reported [296,297]. In particular, it was established for U(IV) and Th(IV) aqua ions and fluoride complexes that both M(IV) aqua ions are 10-coordinate with M — O bond distances for U(IV) and Th(IV) of 2.42 0.01 A and 2.45 0.01 A, respectively [297], Physical and chemical studies of uranium aqueous complexes are reported [298,299a], A series of articles is dedicated to specific sequestering agents for the actinides [299b-e],... 

A new thermodynamic model for the Cu(I,II)-HC1-H20 system was developed on the basis of the representative data on GuGl(s) solubility in aqueous solutions of HC1 in a concentration interval from 1 to 6 mol kg1 HG1 (Akinfiev, 2009). The model takes into account a number of aqueous Cu(I) species [Cu+, CuOH°, Cu(OH)2, CuC1°, CuClj, HCuCL ], aqueous Cu(II) species [Cu2 CuOH+, CuO°, HCuO , CuOJ- CuCl+, CuCL , GuGlg, CuClJ)] and a mixed Cu(I)/Cu(II) chloride aqueous complex, Cu2Cl . The thermodynamic approach used a modelling approach based on i) the standard thermodynamic properties of the listed above species ii) a model for the activity coefficients iii) use of HCh software (Shvarov, 1999). 

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