Metal sulfides common

Hydrogen Sulfide. Hydrogen sulfide is a foul-smelling gas that is released into the atmosphere from volcanoes as well as in the course of decay of animal tissues. As an air pollutant, it reacts with almost all metals, with the exception of gold, forming a dark-colored corrosive layer of metal sulfide, commonly known as tarnish, which discolors the exposed surface of most metals. 

This reaction is strongly exothermic and proceeds spontaneously from left to right for most common metallic sulfides under normal roasting conditions, ie, in air, because P q + Pq = - 20 kPa (0.2 atm) at temperatures ranging from 650 to 1000°C. The physical chemistry of the roasting process is more complex than indicated by equation 3 alone. Sulfur trioxide is also formed,... 

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... 

Where fluids discharge from hot springs and mix with seawater, they cool quickly and precipitate clouds of fine-grained minerals. The clouds are commonly black with metal sulfides, giving rise to the term black smokers. Some vents give off clouds of white anhydrite these are known as white smokers. Structures composed of chemical precipitates tend to form at the vents, where the hot fluids discharge into the ocean. The structures can extend upward into the ocean for several meters or more, and are composed largely of anhydrite and, in some cases, sulfide minerals. 

Metal sulfides Hydrogenous sulfides, such as FeS2 and CUS2. Metal sulfides are common components of metalliferous sediments most of the constituents are hydrothermal in origin. 

Because there are so many metal sulfides, chemists usually use the letter M in the formula to indicate that sulfur can combine with just about any metal (e.g., MHS, M S, M2S3, and so on). Sulfate ions (SO ) also combine with many different metal atoms to form common compounds, such as copper sulfate (CuSO ) and magnesium sulfate, calcium sulfate, lead sulfate, zinc sulfate, and barium sulfate. 

The occurrence of indium-minerals is very rare in general, and indium substitutes in base metal sulfide minerals for elements with similar ionic radii. The most common In-bearing minerals are sphalerite where In is substituting for Zn and Fe, stannite, kesterite and cassiterite where In Is replacing Sn and Fe (Shwarz-Schampera Herzig 2002). 

The main classes of materials employed as catalysts are metals (generally transition and noble metals), oxides (including transition-metal oxides), transition-metal sulfides and zeolites. In the following sections, we discuss some of the more common structures and chemistry exhibited by catalytic systems. 

A comparatively large selection of thioureas can be formed from the reaction of amines with isothiocyanates, hence they are attractive starting materials for formation of guanidines. A common solution-phase approach to this reaction involves abstraction of the sulfur via a thiophillic metal salt, like mercuric chloride.10 For solid-phase syntheses, however, formation of insoluble heavy-metal sulfides can have undesirable effects on resin properties and on biological assays that may be performed on the product. A more relevant strategy, with respect to this chapter, is S-alkylation of thioureas and then reaction of the methyl carbamimidothioates formed (e.g., 5, Scheme 6) with amines. This type of process has been used extensively in solution-phase syntheses.1 Ul4 Two examples are shown in Scheme 6 11 the second is an intramolecular variant, which involves concomitant detrity-lation.15... 

Liquid wastes containing hexavalent chromium require reduction of chromium to the trivalent state prior to metal removal. Commonly used reducing agents are sodium metabisulfite, sulfur dioxide, ferrous sulfide, and other ferrous ions (ferrous sulfate, ferrous chloride, or electrochemically generated ferrous ion). All of these reagents create some form of chromium sludge, which must be separated and dewatered before disposal. 

OTHER METALS ARE MOST COMMONLY OBTAINED FROM METAL SULFIDES... 

Reducing agents commonly employed are iron, tin, or SnCI2 in hydrochloric acid and ammonium or alkali-metal sulfides catalytic hydrogenation and electrolytic reduction also are employed (see Section 23-12B). 

The common ancestor of life was probably a chemoautotrophic hyperthermophilic anaerobe. This metabolism first theory assumes that life started with catalytic metal sulfide surface/compartments in a hydro thermal-vent setting in the Hadean... 

Following consumption of dissolved O2, the thermodynamically favored electron acceptor is nitrate (N03-). Nitrate reduction can be coupled to anaerobic oxidation of metal sulfides (Appelo and Postma, 1999), which may include arsenic-rich phases. The release of sorbed arsenic may also be coupled to the reduction of Mn(IV) (oxy)(hydr)oxides, such as birnessite CS-MnCb) (Scott and Morgan, 1995). The electrostatic bond between the sorbed arsenic and the host mineral is dramatically weakened by an overall decrease of net positive charge so that surface-complexed arsenic could dissolve. However, arsenic liberated by these redox reactions may reprecipitate as a mixed As(III)-Mn(II) solid phase (Toumassat et al., 2002) or resorb as surface complexes by iron (oxy)(hydr)oxides (McArthur et al., 2004). The most widespread arsenic occurrence in natural waters probably results from reduction of iron (oxy)(hydr)oxides under anoxic conditions, which are commonly associated with rapid sediment accumulation and burial (Smedley and Kinniburgh, 2002). In anoxic alluvial aquifers, iron is commonly the dominant redox-sensitive solute with concentrations as high as 30 mg L-1 (Smedley and Kinniburgh, 2002). However, the reduction of As(V) to As(III) may lag behind Fe(III) reduction (Islam et al., 2004). 

Many of the catalysts for the hydrodesulfurization process are produced by combining (Table 5-5) a transition metal (or its salt) with a solid support. The metal constituent is the active catalyst. The most commonly used materials for supports are alumina, silica, silica-alumina, kieselguhr, magnesia (and other metal oxides), as well as the zeolites. The support can be manufactured in a variety of shapes or may even be crushed to particles of the desired size. The metal constituent can then be added by contact of the support with an aqueous solution of the metal salt. The whole is then subjected to further treatment that will dictate the final form of the metal on the support (i.e., the metal oxide, the metal sulfide, or even the metal itself). 

Many chondrules contain minor amounts of metals, sulfides, and oxides. These phases also occur as distinct grains and assemblages embedded in the chondrite matrix. The metallic mineral kamacite is a common chondrule component that contains significant amounts of minor elements such as cobalt, chromium, and phosphorus. Taenite is another alloy of iron and nickel. Sulfide minerals such as troilite, pyrrhotite, and pentlandite are also abundant in many chondrules. 

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