Solid metal sulfides

Precipitation and Dissolution. A special case of ionization is the dissolution of a neutral solid phase into soluble species. For example, the binary solid metal sulfide, CuS, dissolves in water according to... 

An informative paper by Di Toro et al. (1991), on predicting the acute toxicity of Cd and Ni in sediments by assessing the acid volatile suflide (AVS), illustrates that the sediment properties that determine the concentration (activity) of the sediment in the interstitial water determine the fraction of the metal that is bioavailable and potentially toxic. The study of Di Toro et al. is based on measurements of acute toxicity to benthic organisms (amphipodes, oligo-chaetes, and snails). It is shown that this toxicity is essentially related to the free metal ions in solubility equilibrium with the solid metal sulfides present. 

Charles et al. (1985) observed that in oilfield waterflood systems, some attempts to use metallic salts and oxides as scavengers have resulted in the formation of undesirable solid, metallic sulfides. But both formaldehyde and acrolein are aldehydes and are the most frequently nsed chemical scavengers in oilfield waterflood operations. However, they noted that the best performance of these sulfide scavengers can be seen in surface cleaning operations such as the treatment of oilfield water-flood systems (Charles et al. 1985). 

All solid metal sulfides, natural or synthetic, and also the sulfo salts (e.g., HgCl2 2HgS and similar addition compounds of sulfides) react immediately with sodium azide solutions with evolution of nitrogen. They may thus be detected in the presence of sulfates, sulfites, free sulfur, sele-nides, etc. 

The solubility of a solid can be increased by removing one of its ions from solution acid can be used to dissolve a hydroxide, sulfide, sulfite, or carbonate precipitate and nitric acid can be used to oxidize metal sulfides to sulfur and a soluble salt. 

The preparation of some polychalcogenide solids can be achieved at 200-450 °C by molten salt (flux) methods. The reaction of tin with alkali metal sulfides in the presence of Ss at 200-450 °C gives a variety of alkali metal tin sulfides depending on the ratio of the starting materials, the reaction temperature, and the alkah metals (Scheme 30) [90]. These alkali metal tin sul-... 

We have already referred to the Mo/Ru/S Chevrel phases and related catalysts which have long been under investigation for their oxygen reduction properties. Reeve et al. [19] evaluated the methanol tolerance, along with oxygen reduction activity, of a range of transition metal sulfide electrocatalysts, in a liquid-feed solid-polymer-electrolyte DMFC. The catalysts were prepared in high surface area by direct synthesis onto various surface-functionalized carbon blacks. The intrinsic... 

Recently was estimated an expected impact on the global chemistry of the atmosphere of the indirect heterogeneous photocatalytic reactions under the much more abundant near ultraviolet, visible and near infrared solar light [2]. As photocatalysts may serve atmospheric aerosols, i.e. ultrasmall solid particles that sometimes are embedded into liquid droplets. Aerosols are known to contain Ti02, Fc203, ZnO and other natural oxides, as well as metal sulfides of volcanic or antropogenic origin, that may serve as semiconductor photocatalysts (see Fig.5). Aerosols are known to be concentrated mainly in the air layers near the surface of the Earth, i.e. in the troposphere, rather than stratosphere. 

This work is a contribution to the understanding of the effect of spillover hydrogen in a type of catalyst of considerable industrial importance, namely that composed of transition metal sulfides and amorphous acidic solids. This is typically the case of sulfided CoMo supported on silica-alumina used for mild hydrocracking. 

The typical solid catalyst used in technology consists of small catalytically active species, such as particles of metal, metal oxide, or metal sulfide, dispersed on a low-cost, high-area, nearly inert porous support such as a metal oxide or zeolite. The catalytic species are typically difficult to characterize in-... 

The electrochemical process differs from the chemical process by the fact the solid to be dissolved has to be electrically conducting (as for example, a metal), or a semiconductor (as for example, certain oxides and metal sulfides). As some specific examples of dissolution occurring electrochemically, mention may be made of (i) metals in oxygenated water,... 

Chemical precipitation/coagulation methods transfer the target substances (mainly metals) in solution into a solid phase. Many heavy metal hydroxides and sulfides have very low solubility (within a certain pH range) and are therefore insoluble. The metal sulfides have significantly lower solubility than their hydroxide counterparts over a broad range of pH.26 Precipitation/coagulation is also applicable for removing certain anionic species such as phosphate, sulfate, and fluoride. 

Besides the multiplicity of defects that can be envisaged, there is a wide range of host solid phases within which such defects can reside. The differences between an alloy, a metallic sulfide, a crystalline fluoride, or a silicate glass are significant from... 

Bedard, R.L, Wilson, S.T., Vail, L.D., Bennett, J.M., and Flanigen, E.M. (1989) The next generation synthesis, characterization, and structure of metal sulfide-based microporous solids, in Zeolites Facts, Figures, Future (eds... 

---