Selenate ions, reactions

The only protonation reaction of the selenate ion that needs to be considered is SeO + HSeO . (V.23)... 

Reactions of selenate ions To study these reactions use a 0.1m solution of potassium selenate, K2Se04, or sodium selenate, Na2Se04 - IOH2O. 

The stripped extractant is now free to diffuse back to the exterior oil-water interface to extract another selenium anion and the extracted selenite or selenate ion is now trapped in the interior aqueous phase. The net result of this simultaneous extraction and stripping process is an aqueous internal phase with significantly higher selenium concentrations than the original process stream. Thus, one has significantly reduced the volume of the waste stream. The overall reactions are ... 

Positively polarized selenation reagents for oxyselenation reactions can be substituted by an indirect electrochemical procedure in which the bromide ion acts as the redox catalyst. The active bromine species generates the phenylselenyl cation from the added diphenyl diselenide (Eq. (48) Table 4, No. 21-26)... 

Redox reactions in soils are affected by a number of parameters, including temperature, pH (see Chapter 7), and microbes. Microbes catalyze many redox reactions in soils and use a variety of compounds as electron acceptors or electron donors. For example, aerobic heterotrophic soil bacteria may metabolize readily available organic carbon using NO3, NOj, N20, Mn-oxides, Fe-oxides and compounds such as arsenate (As04 ) and selenate (Se04 ) as electron acceptors. Similarly, microbes may use reduced compounds or ions as electron donors, for example, NH4, Mn2+, Fe2+, arsenite (AsCXj), and selenite (SeO ). 

Adsorption of Anions. The general nature of the adsorption model and computational method allow one to describe the uptake of anions also ( ). Similar to the approach for metal ions, we included a term in the mass-law expression to correct for the effect of potential on surface equilibria. Although adsorption of some anions (e.g. chloride, nitrate, syringic acid, thiosulfate) can be simulated by one surface reaction (24), formation of two surface complexes is probable for other anions, e.g. chromate, selenate (J ). Model calculations were more consistent with experimental adsorption data when the following surface reactions were considered, i.e. 

Wu. Ch.H. et al.. Modeling competitive adsorption of molybdate, sulfate, and selenate on y-ALO, hy the triple-layer model, J. Colloid Interf. Sci., 233, 259, 2001. Hachiya. K. et al.. Static and kinetic studies of adsorption-desorption of metal ions on y-ALO, siuface. 1. Static study of adsorption-desoiption, J. Pltys. Chem., 88, 23, 1984. Tamiu a, H.. Katayama. N., and Furuichi, R.. Modeling of ion-exchange reactions on metal oxides with the Frumkin isotherm. 1. Acid-base and charge characteristics of MnO,. TiO,. Fe,O4. and ALO, surfaces and adsorption affinity of alkali metal ions. Environ. Sci. Technol.. 30. 1198. 1996. 

The standard Gibbs energy of formation of lead selenate is calculated from the Gibbs energy of Reaction (V.61) and the selected values of AfG° for the ions to be ... 

Parker, Tice, and Thomason [97PAR/T1C] measured the Ca activity in solutions containing total Ca concentrations in the range 20 x 10 to 200 x 10 M and the selenate concentration 0.004, 0.01, or 0.03 M with a carefully calibrated ion-selective Ca electrode. Activity coefficient corrections were made by Davies equation. The equilibrium constant of the reaction ... 

Wells and Salam have made extensive studies of the kinetics of the reaction between Fe and hydrogen peroxide in the presence of various anions. It was observed that the oxidation rate was unaffected by perchlorate and nitrate ions, whereas a large number of other anions including selenate changed the rate. These anions were all potential ligands and the following reaction scheme, somewhat simplified here, was proposed to account for the findings. It is written for SeO " but the same scheme applies to other anions as well ... 

---