Manganese aqueous system

Oscarson DW, Huang PM, Liaw WK, Hammer UT (1983) Kinetics of oxidation of arsenite by various manganese dioxides. Soil Sci Soc Am J 47 644-648 Pang LP, Close M, Flintoft M (2005) Degradation and sorption of atrazine, hexazinone and pro-cymidone in coastal sand aquifer media. Pest Man Sci 61 133-143 Paris DF, Lewis DL (1976) Accumulation of metoxychlor by microorganisms isolated from aqueous systems. BuU Environ Contam Toxicol 13 443-450 Parr JF, Smith S (1976) Degradation of toxaphene in selected anaerobic soil environments. Soil Science 121 52-57... 

The rhodium complex [CpRh(bipy)Cl2] is reported (162) to act as one-half of a redox couple that, in concert with a manganese porphyrin system, catalyzes the epoxidation of olefins by dioxygen. In this two-phase system, the aqueous phase contains sodium formate, and the organic phase is a trichloroethane solution of [Mnm(tpp)]1+ and the rhodium complex (tpp = meso-tetraphenylporphyrin). Apparently, the rhodium complex catalyzes the reduction of [Mnin(tpp)]1+ by formate, and the manganese(II) species thus formed binds dioxygen and reacts with the substrate olefin to form the epoxide. However, the intermedi-... 

Literally hundreds of complex equilibria like this can be combined to model what happens to metals in aqueous systems. Numerous speciation models exist for this application that include all of the necessary equilibrium constants. Several of these models include surface complexation reactions that take place at the particle-water interface. Unlike the partitioning of hydrophobic organic contaminants into organic carbon, metals actually form ionic and covalent bonds with surface ligands such as sulfhydryl groups on metal sulfides and oxide groups on the hydrous oxides of manganese and iron. Metals also can be biotransformed to more toxic species (e.g., conversion of elemental mercury to methyl-mercury by anaerobic bacteria), less toxic species (oxidation of tributyl tin to elemental tin), or temporarily immobilized (e.g., via microbial reduction of sulfate to sulfide, which then precipitates as an insoluble metal sulfide mineral). 

Hem J. D. (1981) Rates of manganese oxidation in aqueous systems. Geochim. Cosmochim. Acta 45, 1369-1374. 

Hem J. D. (1972) Chemical factors that influence the availability of iron and manganese in aqueous systems. Geol Soc. Am. Spec. Pap. 140, 17—24. 

A comparison of the behaviour of manganese species with that of iron species is essential in any consideration of Eh-pH relationships in aqueous systems. The formation of insoluble, higher valency forms of iron in mixed iron-manganese systems, for instance, results in the disappearance of Mn(ll) from solution under Eh-pH conditions where this normally would not be predicted. 

Chromium (III) and Pu (III/IV) cations are sorbed to soil constituents and, thus, immobile in most aqueous and soil environments. On the other hand, Cr(VI) and Pu(VI) are quite mobile in soils and aqueous systems, because they are not sorbed by soil components to any extent. Therefore, in the hexavalent form, these elements are readily bioavailable (Amacher and Baker, 1982) and are of concern in food chain contamination. Chromium(III) and Pu(in/IV) can be oxidized to Cr(VI) and Pu(VI) by Mn(III/IV) oxides (Cleveland, 1970 Amacher and Baker, 1982). Manganese oxides can, thus, enhance the mobility and toxicity of Cr and Pu in soil and associated environments. 

An extensive survey of the thermodynamic and kinetic properties of manganese in natural aqueous systems has been presented by Morgan (3). From a thermodynamic standpoint, Mn(II) is unstable with respect to oxidation in natural waters. The kinetics of the oxidation reactions are sufficiently slow so that Mn(II) can exist as a metastable species in natural waters. The solubility of Mn(II) in most natural systems probably is limited by the solubility of MnC03. Soluble complexes such as MnHCCV make varying contributions to the total soluble Mn(II) species in natural waters. Some of the equilibria which are relevant to this study are listed in Table I. 

The same reaction (R = H) was run to 80% conversion in 50 h with palladium(II) chloride and a manganese phos-phomolybdovanadate on silica.288 Palladium(II) sulfate was used with a phosphomolybdovanadic acid to convert 1-butene (R = C2H5) to 2-butanone with more than 95% selectivity at 98% conversion.289 Cyclohexene was converted to cyclohexanone with 97% selectivity using Pd(N03) 2 /CuS04 /H3PM012O40/O2 in 1 h at 80°C.290 Pal ladium(II) sulfate and copper(II) sulfate have been used with a phosphomolybdovanadic acid and a per(2,6-di-0-methyl) /3-cyclodextrin in an aqueous system to convert 1-... 

The precipitation of manganese oxides from aerated aqueous systems may be viewed as a two-step process involving oxidation of Mn to the Mn state, and disproportionation of Mn to form Mn. Thermodynamic data show that the reaction aflBnities for both processes will be positive when the fluxes of dissolved oxygen and Mn toward the reaction site are at levels commonly attained in river water and some other natural systems. 

Macdonald, D. D., The Thermodynamics and Theoretical Corrosion Behavior of Manganese in Aqueous Systems at Elevated Temperatures, Corrosion Science, 16 482 (1976). 

Macdonald, D.D. (1976) The thermodynamics and theoretical corrosion behaviour of manganese in aqueous systems at elevated temperatures. Corros. Sci., 16, 461—482. 

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