Metal sulfide oxidation

The oxidation of organic matter via reactions similar to eq 2 is associated with metal sulfide oxidation and the release of metals (21). 

Minerals, electrochemistry of — Many minerals, esp. the ore minerals (e.g., metal sulfides, oxides, selenides, arsenides) are either metallic conductors or semiconductors. Because of this they are prone to undergo electrochemical reactions at solid solution interfaces, and many industrially important processes, e.g., mineral leaching and flotation involve electrochemical steps [i-ii]. Electrochemical techniques can be also used in quantitative mineral analysis and phase identification [iii]. Generally, the surface of minerals (and also of glasses) when in contact with solutions can be charged due to ion-transfer processes. Thus mineral surfaces also have a specific point of zero charge depending on their sur-... 

Animal studies have shown cadmium to be a teratogen and a reproductive toxin however, the results of mutagenesis experiments are equivocal. Cadmium produced local sarcomas in a number of rodent species when the metal, sulfide, oxide, or salts were administered subcutaneously. Intramuscular injection of cadmium powder and cadmium sulfate also produced local sarcomas. Injection of cadmium chloride into the ventral prostate resulted in a low incidence of prostatic carcinoma. Exposure via inhalation of cadmium chloride produced a dose-dependent increase in lung carcinomas in rats. 

The standard free energy, G, of various dissolved metallic, sulfide, oxide and other species in aqueous solution are listed in the Appendix. 

Schippers, A., 2004. Biogeochemistry of metal sulfide oxidation in mining environments, sediments, and soils. In Amend, J.P., Edwards, K.J., and Lyons, T.W. (eds), Sulfur biogeochemistry - Past and Present. Geological Society of America Special Paper 379, Boulder, Colorado, pp. 49-62... 

As mentioned, sulfuric acid is produced concomitantly with the metal sulfide oxidation. Sulfuric acid may react with metallic iron, Fe , to give ferrous sulfate and hydrogen. Both compounds may be oxidized biologically. Furthermore, ferric iron may react with metallic iron to form ferrous iron, Fe + 2Fe SFe ", which... 

In the case of pure metal sulfidation (oxidation), this mechanism starts to operate in later stages of the reaction, because the metal consumption zone may to some extent be compensated by the plastic flow of homogeneous... 

Roasting ofSulRdes. Most nonferrous metals occur in nature mainly as sulfides. These cannot be easily reduced directly to the metal. Burning metallic sulfides in air transforms them into oxides or sulfates which are more easily reduced. The sulfur is released as sulfur dioxide, as shown by the foHowing typical reaction for a divalent metal, M ... 

With hot metals, sulfur dioxide usually forms both metal sulfides as well as metal oxides. In aqueous solution, sulfur dioxide is reduced by certain metals or by borohydrides to dithionites. 

SoHd lubricants ate added to help control high friction characteristics in high speed or heavy-duty appHcations where high temperatures are generated. Molybdenum disulfide [1317-33-5] M0S2, may be used alone or in a complex compound formed by grinding with fine natural graphite, and zinc sulfide [1314-98-3] ZnS. Other compounds include calcium fluoride, cryoHte [15096-52-3] Na AlF, rare-earth oxides, and metal sulfides, eg, iron, antimony, or zinc (see LUBRICATION AND LUBRICANTS). 

Some friction materials may contain other potentially harmfiil materials. Lead has been found in some secondary linings. Class B and C organic disk pads, and other friction materials as lead metallic particles, oxides, and sulfides. Several original equipment and aftermarket suppHers are known to have a pohcy against incorporation of lead or other potentially harmfiil materials in thek products. 

Extensive research has been conducted on catalysts that promote the methane—sulfur reaction to carbon disulfide. Data are pubhshed for sihca gel (49), alurnina-based materials (50—59), magnesia (60,61), charcoal (62), various metal compounds (63,64), and metal salts, oxides, or sulfides (65—71). Eor a sihca gel catalyst the rate constant for temperatures of 500—700°C and various space velocities is (72)... 

CatalyticaHy Active Species. The most common catalyticaHy active materials are metals, metal oxides, and metal sulfides. OccasionaHy, these are used in pure form examples are Raney nickel, used for fat hydrogenation, and y-Al O, used for ethanol dehydration. More often the catalyticaHy active component is highly dispersed on the surface of a support and may constitute no more than about 1% of the total catalyst. The main reason for dispersing the catalytic species is the expense. The expensive material must be accessible to reactants, and this requires that most of the catalytic material be present at a surface. This is possible only if the material is dispersed as minute particles, as smaH as 1 nm in diameter and even less. It is not practical to use minute... 

L oss of Catalyst by Vapor Transport. The direct volatilisation of catalytic metals is generally not a factor in catalytic processes, but catalytic metal can be lost through formation of metal carbonyl oxides, sulfides, and hahdes in environments containing CO, NO, O2 and H2S, and halogens (24). 

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