Speciation aqueous

The most widely studied interactions between biologically active ligands and organotin(lV) cations relate to the amino acids and their derivatives (N- or S-protected amino acids and peptides), though new data on several of the most commonly occurring amino acids are still being published. This is specially true for aqueous speciation studies. Nice and very detailed reviews were published in this area by Molloy and Nath. ... 

DOE. 1995c. Solubility-limited concentrations and aqueous speciation of U, Pu, Np, Am and Tc Comparison between results of Bruno and Sellin (1992) and calculations using GEMBOCHS (version R16). Washington, DC U.S. Department of Energy. NTIS/DE95015124. 

Wolery, T. J., 1983, Eq3nr, a computer program for geochemical aqueous speciat-ion-solubility calculations user s guide and documentation. Lawrence Livermore National Laboratory Report UCRL-53414. 

KEYWORDS Kinetic Testing, AMD, Tailings, Aqueous Speciation, PHREEQC, Nickel Mining. 

Speciation is a dynamic process that depends not only on the ligand-metal concentration but on the properties of the aqueous solution in chemical equilibrium with the surrounding solid phase. As a consequence, the estimation of aqueous speciation of contaminant metals should take into account the ion association, pH, redox status, formation-dissolution of the solid phase, adsorption, and ion-exchange reactions. From the environmental point of view, a complexed metal in the subsurface behaves differently than the original compound, in terms of its solubility, retention, persistence, and transport. In general, a complexed metal is more soluble in a water solution, less retained on the solid phase, and more easily transported through the porous medium. 

Wolery T. I (1983). EQ3NR. A Computer Program for Geochemical Aqueous Speciation-Solubility Calculations User s Guide and Documentation Lawrence Livermore Laboratory, Livermore, Cal., UCRL-53414. 

The U(Vl) aqueous speciation will depend on the actual chemical composition of the contacting fluid. According to what we have discussed in the previous section, the U(VI) speciation will be mainly controlled by hydroxo or carbonato complexes. Hence the dissolution reaction will be described by the following set of reactions. 

Neck, V., Muller, R., Bouby, M., Altmaier, M., Rothe, J., Denecke. M. Kim, J. I. 2002. Solubility of amorphous Th(lV) hydroxide - application of L1BD to determine the solubility product and EXAFS for aqueous speciation. Radiochimica Acta, 90, 485 -494. 

Two considerations (1) kinetic limitations in aqueous sulfate/ sulfide species equilibration and (2) observed lateral and vertical differences in Grande Ronde groundwater chemistry, were evaluated for their effect on calculated solubilities and associated aqueous speciation. 

For these reasons, it is useful to evaluate the effects of forming or not forming aqueous sulfide complexing agents and sulfide precipitates on radionuclide solubilities and aqueous speciation. Therefore, calculations were performed for key radionuclides for two cases (1) reduction of sulfate to sulfide and bisulfide was allowed to occur as Eh was lowered and (2) sulfate reduction as a function of Eh was prohibited so that sulfate was the only sulfur complexing agent available at all Eh values. 

A number of studies have been reported in the literature in which theoretical aqueous speciation of key radionuclides has been determined from available thermodynamic data (4.9.21-25). In general, where comparisons are possible, one finds reasonably close agreement in the calculated dominant dissolved species, the solids controlling solubility, and computed total solubilities for this study and those listed above. 

All three Group 5 elements are expected to have +V oxidation states in seawater and are very strongly hydrolysed. The aqueous speciation of Vv in seawater... 

In Chapter 1 the broad statement is made that the rates of metal complexation reactions are generally high. A more refined conclusion can be drawn from Table 2.3, which lists the time scales over which a number of complex formation and dissociation reactions occur that are important in soil solutions and other natural waters.7 Perusal of these data makes clear the point that although they are usually very rapid, complexation reactions do span a time scale ranging over at least 10 orders of magnitude. Thus the kinetics of these reactions can be very important to understanding the aqueous speciation of metals and ligands in detail. 

Wilkins, R. G., Kinetics and Mechanism of Reactions of Transition Metal Complexes, VCH Publishers, New York, 1991. This classic textbook, by one of the key figures in the study of complexation reactions, offers a wealth of detail on the experimental aspects of aqueous speciation. 

Wolery TJ (1992b) EQBNR, A computer program for geochemical aqueous speciation-solubility calculations Theoretical manual, user s guide, and related documentation (Ver.7.0).-UCRL - MA - 110662 Pt I Lawrence Livermore Natl. Lab... 

More immediate goals differ from one scientific discipline to another. One goal of which I am most aware is the prediction of the role of aqueous speciation on the bioavailability and toxicity of trace elements to plankton and estuarine detritusfeeding invertebrates. In the longer range, these studies would be extended to include the various aquatic organisms higher in the... 

Does the above imply that all attempts to compute speciation in such natural systems are fruitless While calculation of the ocfrwpZete aqueous speciation in these natural systems is not presently feasible, there is an alternative approach where one is primarily interested in distinguishing between the free and total complexed metal in solution. As a compromise measure and pragmatic approach to studying metal complexation in complicated data-deficient systems, we have developed an alternative model. 

Much has been published concerning toxicity of metals to aquatic life although only during the past decade have there been interpretations of the toxicity data in terms of ]jie rela ive toxicity of particular speciation forms, e.g., Cu, CuOH, CuCO The specific objective of this paper is to illustrate the use of Factor Analysis in discriminating between toxic and nontoxic species. The procedure to be followed is determination of equilibrium aqueous speciation, calculation of appropriate factory correlation of toxicity with these factors, and interpretation of the correlation analysis in terms of particular species activities. 

The protection of ecosystems, upon which our health and lives depend (J ), requires that we understand natural processes and develop the capability to predict the effect of changes, such as the addition of pollutants, on these ecosystems. The prediction of trace-element behavior in ecosystems requires a multicomponent model by which one can 1) calculate aqueous speciation of the trace elements among both natural organic and inorganic ligands ... 

Models are applied to a system, or a portion of the observable universe separated by well-defined boundaries for the purpose of investigation. A chemical model is a theoretical construct that permits the calculation of chemical properties and processes, such as the thermodynamic, kinetic, or quantum mechanical properties of a system. A geochemical model is a chemical model developed for geologic systems. Geochemical models often incorporate chemical models such as ion association and aqueous speciation together with mineralogical data and assumptions about mass transfer to study water-rock interactions. 

Aqueous speciation. The distribution of dissolved components among free ions, ion pairs, and complexes. For example, dissolved iron in acid mine drainage (AMD) can be present as Fe( q) (free ferrous iron), FeS04(aq> (ion pair), Fef q) (free ferric iron), Fe(OH)(j q), and FeS04(aq) species. These species are present in a single phase, aqueous solution. Aqueous speciation is not uniquely defined but depends on the theoretical formulation of mass action equilibria and activity coefficients, i.e. it is model dependent. Some aqueous speciation can be determined analytically but operational definitions and assumptions are still unavoidable. 

The USGS has developed several codes that are useful for the interpretation of water chemistry data and for simulating water-rock interactions. Two similar aqueous speciation codes were developed in parallel, WATEQ (Truesdell and Jones, 1974) and SOLMNEQ (Kharaka and Barnes, 1973). The primary aim of these programs was to aid in the interpretation of water quality data. SOLMNEQ, however, had a different subroutine for calculating temperature and pressure dependence and could calculate reaction equihbria above 100 °C. WATEQ was intended for temperatures of 0-100 °C. Both of these programs have been updated. WATEQ4F v. 2 (Ball and Nordstrom, 1991, with database updates to 2002) uses the lA method with an expanded... 

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