Baes-Mesmer diagram

Figure 2. Eh-pH diagram of dissolved Mo speciation in the system M0-H2O-S. ZMo = 10 M ES = 10 M. Modified after Manheim and Landergren (1974), using molybdate protonation constants from Baes and Mesmer (1986). H2M0O4 is related to Mo(OH)g by addition of two water molecules (see text). MoO +, included in earlier Eh-pH diagrams, is omitted because this and other Mo(V) species are typically unstable except as dimers (e.g., Mo20/ ) at higher EMo than common in natiwe. Speciation at Eh below fiie SO/ - H2S ftansition is not well characterized and is commonly out of equilibrium. The boundary between MoS/ and MoO/ is based on Erickson and Helz (2000) intermediate oxythiomolybdates are metastable and hence not indicted.

The chemistries of Ru, Os, Rh, and Ir in seawater are poorly understood. Available evidence suggests that the probable oxidation state of Ru is + IV OSO4 has a large field of stability on oxidation potential vs pH diagrams and can thereby be considered as an important species in seawater. Rh and Ir are expected to exist in lower oxidation states than Ru and Os. Available evidence (Baes and Mesmer, 1976) indicates that the most important oxidation state for Rh and Ir is + III. Rhm and Irm form strong chloride complexes and should, as well, hydrolyse extensively in solution at pH 7.4-8.2. This speciation assessment is consistent with the relative enrichment of Os in seawater compared to Ir. OSO4 should be substantially less reactive towards particles than is the case for Ir(Cl) - and Ir(OH) - species. 

FIGURE 6 Phase diagram of aqueous vanadium (V) solution species, present in aqueous solutions at 25 °C, on the basis of data in Baes C.F., Jr., and Mesmer R.E.,... 

Figure 6.4. Hydrolysis of metal ions, (a) Predominant pH range for the occurrence of aquo, hydroxo, hydroxo-oxo, and 0x0 complexes for various oxidation states. The scheme attempts to show a useful generalization, but many elements cannot be properly placed in this simplified diagram because other factors, such as radius and those related to electron distribution, have to be considered in inteipreting the acidity of metal ions, (b) The linear dependence of the log,o of the first hydrolysis constant Ki = MOH H / M on the ratio of the charge to the M-O distance (z/d) for four groups of cations (25°C). (Note change of abcissa zero for different groups.) (From Baes and Mesmer, 1976.) (c) Hydrolysis constants of some important metal ions.

Figure 1 Diagram of potential (vs. SHE) vs. pH for vanadium species present in dilute solutions. The upper and lower dashed lines represent 1 atm 02 and 1 atm H2, respectively (reproduced with permission from Baes and Mesmer 3 1976,Wiley. This material is used by permission of Wiley).

Fig. 15 Speciation of soluble Cr(VI) as a function of pH and concentration. Many commercial CCC bath formulations have Cr(VI) concentrations that fall in the shaded box so that the film-forming species is dichromate (equilibrium constants used in diagram construction from Baes and Mesmer [113]).

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