Metal sulphides oxidation

The released energy is used to heat the sulphide particles and the gas phase, and it is lost in part through the reaction shaft sidewalls. Equation (2) differs from Equation (3) only in the factor of Qi. Thus, the metal sulphide oxidation processes and heat release from the feed particles during autogenous smelting are unambiguously interrelated. 

Gases which are high in FIjS are subject to a de-sulphurisation process in which H2S is converted into elemental sulphur or a metal sulphide. There are a number of processes based on absorption in contactors, adsorption (to a surface) in molecular sieves or chemical reaction (e.g. with zinc oxide). 

Heating with the following solids, their fusions, or vapours (a) oxides, peroxides, hydroxides, nitrates, nitrites, sulphides, cyanides, hexacyano-ferrate(III), and hexacyanoferrate(II) of the alkali and alkaline-earth metals (except oxides and hydroxides of calcium and strontium) (b) molten lead, silver, copper, zinc, bismuth, tin, or gold, or mixtures which form these metals upon reduction (c) phosphorus, arsenic, antimony, or silicon, or mixtures which form these elements upon reduction, particularly phosphates, arsenates,... 

Crucibles fitted with permanent porous plates are cleaned by shaking out as much of the solid as possible, and then dissolving out the remainder of the solid with a suitable solvent. A hot 0.1 M solution of the tetrasodium salt of the ethylenediaminetetra-acetic acid is an excellent solvent for many of the precipitates [except metallic sulphides and hexacyanoferrates(III)] encountered in analysis. These include barium sulphate, calcium oxalate, calcium phosphate, calcium oxide, lead carbonate, lead iodate, lead oxalate, and ammonium magnesium phosphate. The crucible may either be completely immersed in the hot reagent or the latter may be drawn by suction through the crucible. 

Although not strictly included within the scope of the present review, decompositions have been considered in the context of related rate processes including sulphide oxidations, sulphidation of oxides and/or metals and diffusion in sulphide phases [689],... 

In contrast to the asymmetric procedures discussed above, the metal-catalyzed oxidation of alkyl aryl sulphides by t-butylhydroperoxide carried out in a chiral alcohol gives rise to chiral sulphoxides of low optical purity290 (e.e. 0.6 9.8%). Similarly, a very low asymmetric induction was noted when prochiral sulphides were oxidized by sodium metaperiodate in chiral alcohols as solvents291. 

There are many transition metal ion oxidants used in organic chemistry for the interconversion of functional groups. Those which have been used for the preparation of sulphones from sulphoxides will be discussed below. It is very interesting to note that this type of oxidant often reacts more rapidly with sulphoxides than with sulphides and so sulphoxides may be selectively oxidized with transition metal ion oxidants in the presence of sulphides. This is in direct contrast to the oxidation of sulphides and sulphoxides with peracids and periodate, for example, where the rate of reaction of the sulphide is more than 100 times that for the corresponding sulphoxide. 

The application of ly transition metal carbides as effective substitutes for the more expensive noble metals in a variety of reactions has hem demonstrated in several studies [ 1 -2]. Conventional pr aration route via high temperature (>1200K) oxide carburization using methane is, however, poorly understood. This study deals with the synthesis of supported tungsten carbide nanoparticles via the relatively low-tempoatine propane carburization of the precursor metal sulphide, hi order to optimize the carbide catalyst propertira at the molecular level, we have undertaken a detailed examination of hotii solid-state carburization conditions and gas phase kinetics so as to understand the connectivity between plmse kinetic parametera and catalytically-important intrinsic attributes of the nanoparticle catalyst system. 

Sulphur, hydrogen sulphide and metal sulphides also led either to the ignition of the sulphurous substance (S and H2S) or the incandescence of the mixture. Note that sulphides and cyanides are amongst the most dangerous salts in the presence of oxidants, a fact not to be ignored. 

Occurrence. Important commercial ores of Ni are sulphides (such as pentlandite (Ni,Fe)9Sg) generally associated with Cu, Co and precious metals and oxide/silicate ores (as (Ni,Mg)6Si40io(OH)8 and (Fe,Ni)0(0H)nH20). It is also found in combination with As and Sb (as NiAs or in deposits consisting ofNiSb, NiAs2, etc.). It is also present as Fe alloys in several meteorites and probably in the core of the earth. 

Eor a long time, CD was then essentially limited to PbS and PbSe. It was not until 1961 that deposition of CdS, now the most widely studied material in CD, was explicitly reported [11] (although CdS deposited from a thiosulphate solution which sticks obstinately to the glass was already noted in 1912 [11a]). The range of materials deposited by CD was gradually extended, particularly in the 1980s, to include sulphides and seleiudes of many metals, some oxides, and also many ternary compounds (Tables 2.1 and 2.3 in this chapter list films deposited by CD). 

A large range of other metal sulphides and selenides have been deposited by CD. Since these will be individually described in Chapter 6, it will be sufficient here to list all binary sulphides and selenides (along with oxides) in Table 2.1, along with up to three references to each compound. 

There is increasing experimental evidence for the superlattice ordering of vacant sites or interstitial atoms as a result of interactions between them. Superlattice ordering of point defects has been found in metal halides, oxides, sulphides, carbides and other systems, and the relation between such ordering and nonstoichiometry has been reviewed extensively (Anderson, 1974, 1984 Anderson Tilley, 1974). Superlattice ordering of point defects is also found in alloys and in some intermetallic compounds (Gleiter, 1983). We shall examine the features of some typical systems to illustrate this phenomenon, which has minimized the relevance of isolated point defects in many of the chemically interesting solids. 

Relations between the structure and properties have been investigated in a variety of solids such as metal oxides, chalcogenides, pnictides and halides. In addition to studying model systems for testing theoretical predictions, solid state chemists have been preparing new classes of solids as well as novel members of known types of solids. In this section, we have chosen three classes of solids, viz. metal oxides, metal sulphides and metal fluorides, to discuss structure-property relations we shall concentrate especially on their electrical and magnetic properties. 

Correlations between catalytic activity and a variety of bulk properties of semiconductors have been reported (i) the average band gap of III-V and II-VI semiconductors and activity towards hydrogenation of isopropanol (ii) enthalpy of oxides and their activity towards oxidation of propylene and (iii) number of d-electrons (and crystal field stabilization energy) or 3rf-metal oxides and their activity towards N2O decomposition. The last correlation, due to Dowden (1972), is important since it provides a connection between heterogeneous catalysis and coordination chemistry of transition-metal compounds. A correlation between the catalytic activity of transition-metal sulphides towards hydrodesulphurization of aromatic compounds and the position of the transition metal in the periodic table has been made by Whittingham ... 

---