Computer Science
Scientific paper
Jan 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989gecoa..53...69w&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 53, Issue 1, pp.69-77
Computer Science
13
Scientific paper
The aquatic chemistry of vanadium is dominated by V(IV) and V(V). Their species VO 2+ , VO(OH) + and H 2 VO - 4 , HVO 2- 4 , respectively, occur primarily in natural waters. VO 2+ , as a very hard Lewis acid, has a strong tendency to coordinate with oxygen donor atoms and is thus capable of both forming strong complexes with soluble organic chelates and becoming specifically adsorbed to particles, especially hydrous oxides. Vanadates (V), like phosphates, also have a tendency to form, by ligand exchange, surface complexes with hydrous oxides. The V(IV)-V(V) couple is an interesting redox sensor because the redox transition occurs at E H -values typically often encountered at the sediment water interface; organic chelate formation may extend the redox boundary to E H -values of about +0.4V (pH 7-8), but in the presence of dissolved oxygen vanadate(V) prevails. Experimental data on the adsorption of VO 2+ and of V(V) (HVO 2- 4 , VO + 2 ) on -Al 2 O 3 and TiO 2 (anatase) surfaces provide evidence for strong specific adsorption. The interaction of VO 2+ with oxide surfaces is interpreted in terms of inner-sphere bidentate surface complexes with the surface central metal ions of the oxide VO(OM<) 2 ; vanadate and VO 2 + form monodentate surface species. The rate of oxidation of VO 2+ by oxygen is significantly enhanced by hydrolysis or adsorption to hydrous oxide surfaces. The rate law, derived earlier ( and , 1988) shows a first order dependence on the concentration of VO(OH) + in homogeneous solution or on the concentration of the surface complex of VO(OM<) 2 in heterogeneous systems. A comparison with published data on Mn(II) and Fe(II) oxidation shows that coordinated OH-groups of solid surfaces are able, like soluble hydroxo complexes, to mediate the electron transfer from the metal ions to the O 2 -molecule.
Stumm Werner
Wehrli Bernhard
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