Roasting of metal sulfides

Sulfur for commercial purposes is derived mainly from native elemental sulfur mined by the Frasch process. Large quantities of sulfur are also recovered from the roasting of metal sulfides and the refining of crude oil, i.e., from the sulfur by-products of purified sour natural gas and petroleum (the designation sour is generally associated with high-sulfur petroleum products). Reserves of elemental sulfur in evaporite and volcanic deposits and of sulfur associated with natural gas,... 

Snlfur dioxide, and to a lesser extent nitrogen oxides, generated mainly from the bnming of fossil fuels and from the roasting of metal sulfides, causes acid rain. 

We see that acid rain is largely caused by human activities such as the burning of fossil fuels and roasting of metal sulfides. We discuss ways to minimize sulfur dioxide and nitrogen oxides productions. (17.6)... 

Examples of eq. (6.14) include the roasting of metal sulfides the absorption of sulfur dioxide by calcium oxide that is formed by simultaneous calcination of limestone the formation of silicon nitride from silica, carbon and nitrogen. Examples of eq. (6.15) the baking of clay the burning of limestone the pyrolysis of coal, lignite, wood, peat, or other organic materials the calcination of sodium bicarbonate and similar salts. 

Processes in which one solid is converted into another that has a smaller volume, so that a product with a higher porosity is obtained (such as the roasting of metal sulfides). 

The roasting of metal sulfides is of considerable technological and commercial interest because the ores of the majority of heavy metals such as copper, nickel, lead, and zinc are in a sulfide form. One important step in the recovery of these metals from their ores involves roasting, that is, their oxidation to metal oxide. 

H. H. Kellogg, Equilibrium considerations in the roasting of metallic sulfides. Trans. Amer. Inst. Min. Eng. 206, 1105-1111 (1956). 

The main commercial methods of producing S02(g) are the direct combustion of sulfur, reaction (22.19), and the roasting of metal sulfides, reaction (22.20) ... 

Among the methods for extracting metals from their ores are (i) roasting a metal sulfide, (ii) chemical reduc-tion of a metal oxide, and (iii) electrolysis. The preferred method depends on the E° value for the reduction half-reaction Mn+(aq) + ne —> M(s). 

In addition to rotary and vertical kilns, hearth furnaces or fluidized-bed reactors may be used. These high-temperature reactors convert minerals for easier separation from gangue or for easier recovery of metal. Fluidized beds are used for the combustion of solid fuels, and some 30 installations are listed in Encyclopedia of Chemical Technology (vol. 10, Wiley, 1980, p. 550). The roasting of iron sulfide in fluidized beds at 650 to 1100°C (1202 to 2012°F) is analogous. The pellets have 10-mm (0.39-in) diameter. There are numerous plants, but they are threatened with obsolescence because cheaper sources of sulfur are available for making sulfuric acid. 

The International Nickel Company developed a method to refine impure nickel sulfide anodes directly to metal, using mixed sulfate-chloride electrolyte [45]. Nickel sulfide (cz-Nf ) anodes can be cast directly from low-copper converter matte or from melted nickel sulfide concentrate produced by the matte separation process. Controlled cooling is necessary to produce anodes with the required mechanical properties. The cooling of anodes can take up to 36 hours. Using nickel sulfide anodes eliminates the intermediate roasting of the sulfide... 

One of the most tantalizing chemical transformations known to ancient practitioners of inorganic chemistry involved roasting of mercuric sulfide ores such as cinnabar to form hydrargyrum or quicksilver (60). As the toxic properties of mercury became more widely appreciated in the middle ages, formulations of the metal and its salts were used in medical applications. 

In the gases from the roasting of molybdenum sulfide the ore s content of the metal rhenium is present as rhenium oxide. This is an important source of this interesting metal, see Chapter 29 Rhenium. 

Pure nickel metal is used for battery electrodes and as a catalyst. After roasting of the sulfide ore and reduction of the oxide to nickel, the metal may be purified for further use by the Mond process. The Mond process is a chemical procedure for the... 

C. L. McCabe and J. A. Morgan, Mechanism of sulfate formation during the roasting of cuprous sulfide, J. Metals 8, 800A (1959). 

Examples of similar processes are the decomposition of precipitated aluminum trHiydroxide to alumina, which is the feed for the electrolytic production of aluminum metal, and the drying of wet sulfide concentrates in preparation for flash roasting (see Aluminumand aluminum alloys). 

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,... 

The matte can be treated in different ways, depending on the copper content and on the desired product. In some cases, the copper content of the Bessemer matte is low enough to allow the material to be cast directly into sulfide anodes for electrolytic refining. Usually it is necessary first to separate the nickel and copper sulfides. The copper—nickel matte is cooled slowly for ca 4 d to faciUtate grain growth of mineral crystals of copper sulfide, nickel—sulfide, and a nickel—copper alloy. This matte is pulverized, the nickel and copper sulfides isolated by flotation, and the alloy extracted magnetically and refined electrolyticaHy. The nickel sulfide is cast into anodes for electrolysis or, more commonly, is roasted to nickel oxide and further reduced to metal for refining by electrolysis or by the carbonyl method. Alternatively, the nickel sulfide may be roasted to provide a nickel oxide sinter that is suitable for direct use by the steel industry. 

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