Anions selenite

A new structure type is found for Ag2Hg(Se03)2. Both Ag+ and Hg2+ ions are in octahedral coordination in this compound.137 The polyhedra are linked by the pyramidal shaped selenite anions.138 In the crystal structure of the red tellurate Ag2Hg2(Te04)3, the tellurium atoms are in octahedral coordination of oxygen atoms, and the octahedra are linked to infinite chains running along the u-axis. 

The structure of Np(Np02)2(Se03)3 is extraordinarily complex as it contains three crystallographically unique Np centers with three different coordination environments in two different oxidation states. Two of the Np centers are +V and one is +IV. The Np(V) centers are found as both NpOy pentagonal bipyramids and NpOs hexagonal bipyramids. The Np(IV) center is found as a distorted NpOs dodecahedron. Cation-cation interactions (CCTs), exist between both the neptunyl units, and these units also coordinate the Np(IV) center creating a two-dimensional substructure. There are three crystallographically unique selenite anions. 

Cheng, L., Lyman, P. E., Sturchio, N. C., and Bedzyk, M. J., 1997, X-ray standing wave investigation ofthe surface structure of selenite anions adsorbed on calcite Surface Science, v. 382, p. L690-L695. 

Kinetics and mechanism of the reaction of hydroxocobalt(III) and hydroxorhodium(lll) cations with monomeric and dimeric selenite anions, Inorg. Chem., 16, (1977), 1282-1286. Cited on page 140. 

This reaction is very favorable and for this reason, the major part of the selenium contained in the zinc sulfide concentrate is found in the scrubbing liquor as selenous acid, which in turn dissociates into the selenite anion, Se03. ... 

Of the studies reviewed here, only the work by Papelis et al. [10] directly examined the effects of pore size. Under similar experimental conditions, they reported that when adsorbents with micropores and mesopores were compared, diffusivity values for Cd and Se(IV) increased by factors of about 2 and 33, respectively. As noted by those authors, the fact that Se(IV) is more sensitive to changes in the pore size is likely due to the fact that the hydrated selenite anion is large relative to Cd (diameters of about 6.5 A and 4.5 A, respectively). The larger selenite anion may be significantly hindered while diffusing through smaller diameter pores. 

Hydrophilic Strong acids I, Cr, Br , N02, NOj- P04 , S03 , S04 , ClOz", ClOa Arsenate, selenate, selenite Anion exchange Anion exchange, ion exclusion Conductivity, UV Conductivity... 

Table Activation parameters for oxygen exchange between selenate or selenite anions and water...

Selenosulfate is an analogue of thiosulfate wherein one of the S atoms is replaced by a Se atom. Thiosulfate and selenosulfate anions are known to have tetrahedral structure as constituting the S and Se analogues, respectively, of the sulfate anion. The isomeric thioselenate anion SSeO " is not produced by the reaction of sulfur with selenite nor is the selenoselenate ion 86203 formed from selenium and selenite. Actually, SSeOj may be produced as a metal salt by boiling an aqueous solution of selenite with sulfur, but in aqueous solution thioselenates are not stable and isomerize to selenosulfates. 

Figure 3 Gradient separation of anions using suppressed conductivity detection. Column 0.4 x 15 cm AS5A, 5 p latex-coated resin (Dionex). Eluent 750 pM NaOH, 0-5 min., then to 85 mM NaOH in 30 min. Flow 1 ml/min. 1 fluoride, 2 a-hydrox-ybutyrate, 3 acetate, 4 glycolate, 5 butyrate, 6 gluconate, 7 a-hydroxyvalerate, 8 formate, 9 valerate, 10 pyruvate, 11 monochloroacetate, 12 bromate, 13 chloride, 14 galacturonate, 15 nitrite, 16 glucuronate, 17 dichloroacetate, 18 trifluoroacetate, 19 phosphite, 20 selenite, 21 bromide, 22 nitrate, 23 sulfate, 24 oxalate, 25 selenate, 26 a-ketoglutarate, 27 fumarate, 28 phthalate, 29 oxalacetate, 30 phosphate, 31 arsenate, 32 chromate, 33 citrate, 34 isocitrate, 35 ds-aconitate, 36 trans-aconitate. (Reproduced with permission of Elsevier Science from Rocklin, R. D., Pohl, C. A., and Schibler, J. A., /. Chromatogr., 411, 107, 1987.)...

Generally, oxo-selenates can be classified according to the oxidation state of the selenium atom as oxu-selenates(IV), and o.Yo-selenates(VI). The same applies for the respective tellurates. Besides this systematically correct naming, chemists usually use the terms selenites and tellurites instead of o. o-selenates(IV) and oxo-tellurates(IV), and selenates and tellurates instead of OAO-selenates(VI) and oxo-tellurates(VI). Therefore, both nomenclatures will be used in parallel throughout this chapter. Compared to the respective sulfur species, the oxo-selenate(IV) and oxo-tellurates(IV) ions are very stable so that numerous compounds with these anions have been prepared. 

The free selenite ion has a pyramidal shape (C3v symmetry) owing to the lone electron pair at the selenium atom. Thus, the Se032- ion can be treated as a pseudo-tetrahedral anion and the lone electron pair often acts as an invisible ligand within the crystal structures of selenites. This observation is called the stereochemical activity of the lone electron pair and it will turn out as one of the... 

Wells, J.M. and D.H.S. Richardson. 1985. Anion accumulation by the moss Hylocomium splendens uptake and competition studies involving arsenate, selenate, selenite, phosphate, sulphate and sulphite. New Phytol. 101 571-583. 

Selenium has a complex chemistry in the environment because of its multiple oxidation states and variable surface adsorption properties. Qualitatively it is analogous to sulfur occurring in the oxidation states +6 (selenate, Se04 ), +4 (selenite, SeOs "), 0 (elemental selenium) and —2 (Se, selenide) The Se anion closely resembles S (radii 0.20 and 0.185nm, respectively) and is often associated with sulfide minerals. Also, like S, Se is subject to volatilization through biological methylation. 

Phosphate must be applied as fertilizer to the soil. Ideally it is added in quantities sufficient to guarantee optimal yields, but not in excess in order to avoid P transportation into other compartments of the ecosystem. The amount added should be based on an accurate estimation of the plant-available fraction of P already present in a soil.This is an old and difficult task and a large number of extraction methods have been used since intensive land use was practised. Recently methods have been worked out in which a strip of filter paper impregnated with an Fe oxide (2-line ferri-hydrite) is dipped into a soil suspension and the amount of P adsorbed by the paper is taken as being plant-available (Sissingh,1988 Van der Zee et ah, 1987 Sharpley, 1993 Sharpley et ah,1994 Kuo and Jellum, 1994 Myers et ah 1997). Anion and cation resins extracted more P from four heavily fertilized soils than from goethite (Delgado Torrent, 2000). Other oxyanions adsorbed by soil Fe oxides are silicate, arsenate, chromate, selenite ( ) and sulphate. Adsorption of sulphate led to a release of OH ions and was substantially lowered once the Fe oxides were selectively removed (Fig.16.17). 

Adsorption of anions at mineral surfaces is important in soils because of the limit this process imposes on the availability of plant nutrients such as P, S, and Mo which occur naturally as anions and are added in anionic form in fertilizers. Anion adsorption is also relevant in geochemistry, ore processing, and other fields where minerals with high surface areas are brought into contact with aqueous solutions of anions. Selenite and goethite were chosen for this study because in Western Australia a selenium deficiency in pastures has been shown to be related to the incidence of white muscle disease in sheep (3), and according to workers quoted by Rosenfeld and Beath (9) selenium in soils of higher... 

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