Sulfides large-scale oxidations

A very important but rather complex application of surface chemistry is to the separation of various types of solid particles from each other by what is known as flotation. The general method is of enormous importance to the mining industry it permits large-scale and economic processing of crushed ores whereby the desired mineral is separated from the gangue or non-mineral-containing material. Originally applied only to certain sulfide and oxide ores. 

Arbiter Previously known as the Sherritt-Gordon ammonia process. A process for leaching copper from sulfide concentrates, using ammoniacal ammonium sulfate solution at 85°C and relying on air oxidation. Copper is produced from the leachate by solvent extraction and electrowinning. Sulfur is recovered as ammonium sulfate. Operated on a large scale by the Anaconda Copper Company in Montana from 1974 to 1979. See Sherritt-Gordan. 

The present procedure is a specific example of the method generalized by Leonard and Johnson.8 The method employs extremely mild reaction conditions and affords high yields of sulfoxides (Note 9) free of contamination by sulfides or sulfones. Sodium periodate is easily and safely handled however, the higher cost of this reagent in comparison to certain other oxidants, e.g., hydrogen peroxide, may prohibit its use in large-scale reactions. 

The flotation process is applied on a large scale in the concentration of a wide variety of the ores of copper, lead, zinc, cobalt, nickel, tin, molybdenum, antimony, etc., which can be in the form of oxides, silicates, sulfides, or carbonates. It is also used to concentrate the so-called non-metallic minerals that are required in the chemical industry, such as CaF2, BaS04, sulfur, Ca3(P03)2, coal, etc. Flotation relies upon the selective conversion of water-wetted (hydrophilic) solids to non-wetted (hydrophobic) ones. This enables the latter to be separated if they are allowed to contact air bubbles in a flotation froth. If the surface of the solids to be floated does not possess the requisite hydrophobic characteristic, it must be made to acquire the required hydrophobicity by the interaction with, and adsorption of, specific chemical compounds known as collectors. In separations from complex mineral mixtures, additions of various modifying agents may be required, such as depressants, which help to keep selected minerals hydrophilic, or activators, which are used to reinforce the action of the collector. Each of these functions will be discussed in relation to the coordination chemistry involved in the interactions between the mineral surface and the chemical compound. 

The biotransformations of sulfur compounds by microorganisms can have large-scale impacts on global chemistry. As an example, sulfate-reducing bacteria have, throughout histoiy, formed major deposits of elemental sulfur and iron sulfides on Earth, and these processes are continuing today (1). Contemporary sulfate-reduction coupled with the oxidation of reduced inorganic sulfur... 

The large-scale production of esomeprazole is now successfully achieved by asymmetric oxidation of the same sulfide intermediate as is used in the production of omeprazole (Scheme 2.5). Using the titanium-based catalyst originally developed by K. Barry Sharpless for allyl alcohol oxidation [56] and by H.B. Kagan for certain sulfide oxidations [57], a process was developed that could achieve initial enantiomeric excesses of about 94% [53]. During the production process, the optical purity is further enhanced by the preparation of esomeprazole magnesium salt, with subsequent re-crystallization. 

Mond nickel A process for extracting nickel from its ores by the intermediary of the volatile nickel tetracarbonyl. Sulfide ores are first roasted to convert sulfides to oxides, and then reduced by heating in hydrogen and carbon monoxide (water gas). The crude metal is caused to react with carbon monoxide at 50°C, producing Ni(CO)4, which is subsequently decomposed at 180 to 200°C. Invented by L. Mond and C. Langer in 1889, piloted at the works of Henry Wiggin Company in Smethwick, Scotland in 1892, and subsequently commercialized on a large scale in Swansea, South Wales, where it still operates (under the ownership of CVRD Inco). A new plant was built in Canada in 1986. 

Since, at the present time, there is no general large-scale accumulation of reduced sulfur in sediments and soils, the combined rates of biological and chemical oxidation of sulfide can be assumed to be in the same order as those of sulfate reduction. Unfortunately, the few recorded rates of sulfide oxidation in the environment are not directly comparable with those of sulfate reduction. Aside from difficulties posed by the experimental... 

Since sulfate instead of oxygen serves as an oxidant for organic compounds like CH2O in the above back reaction, the dissimilatory process may be regarded as a form of anaerobic respiration or sulfate respiration. In the early Earth s history this reaction would have played a cmcial role as it would have been responsible for large-scale transformations of sulfide to sulfate in biological mediation of the sulfur cycle. 

The principal source of As is FeAs8, and the element is extracted by heating (equation 14.2) and condensing the As sublimate. An additional method is air-oxidation of arsenic sulfide ores to give AS2O3 which is then reduced by C AS2O3 is also recovered on a large scale from flue dusts in Cu and Pb smelters. 

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