Reduction of ore

Fluoridation of UO2 peUets Catalyst regeneration Hydrogen reduction of ores Titanium dioxide... 

An alternative commercial form of a metallic mixed lanthanide-containing material is rare-earth siUcide [68476-89-1/, produced in a submerged electric-arc furnace by the direct reduction of ore concentrate, bastnasite, iron ore, and quart2. The resulting alloy is approximately 1/3 mischmetal, 1/3 sihcon, and 1/3 iron. In addition there are some ferro-alloys, such as magnesium—ferrosilicons, derived from cerium concentrate, that contain a few percent of cerium. The consumption of metallic cerium is overwhelmingly in the mixed lanthanide form in ferrous metallurgy. 

Redox reactions occur in the reduction of ores (metal oxides) into pure metals and the corrosion (oxidation) of pure metals in the presence of oxygen and water. Rusting iron, 4Fe + 30, + 611,0 —> 4Fe(OH), is a good example of metal oxidation. Strong oxidizing agents can be used as antiseptics (hydrogen peroxide, Fd,0,) or bleaches (sodium hypochlorite, NaOCl). 

Iron is produced in a blastfurnace by reduction of ores its properties are modified by blending with other metals. 

To guard against incomplete reduction of ore fines which would be elutriated prematurely during preheating, the midsection combustion was adjusted to produce a mildly reducing flame containing approximately 4%... 

Copper from the reduction of ores must be purified for use in making electrical wiring because impurities increase its electrical resistance. The method used is electrorefining (Figure 18.19), an electrolytic process in which copper is oxidized to Cu2+ at an impure copper anode, and Cu2+ from an aqueous copper sulfate solution is reduced to copper at a pure copper cathode. The process is described in Section 18.12. 

Tellurium 2.1 221 Nagyagite (mixed sulfide and telluride) Reduction of ore with S02... 

If the reaction is carried out in a closed vessel, the conversion is not complete, as the partial pressures of the gases formed would attain very large values if any considerable quantity of water vapour, the gases are removed as fast as they are formed, so that their partial pressure at the surface of the carbon is maintained at a small value. In this way only is the complete oonversion of the carbon into water gas possible. Currents of gases are employed in a similar manner in the decomposition of calcium carbonate (the burning of lime) and in the reduction of ores by carbon monoxide. This procedure is used extensively in technical processes. 

Manufacture Magnesium is manufactured either electrolytically from magnesium chloride (from seawater or salt lakes and salt deposits) or by thermal reduction of ores, such as dolomite, with ferrosilicon. 40% of the magnesium producers in the Western world u.se electrolysis processes. 

The crucial event in Lavoisier s career was his realization that air (which nearly everyone believed to be a simple substance defined by its physical, rather than by any chemical, properties) must play a part in chemical transformations - most dramatically those observed in ordinary combustion, the roasting (calcining) of metals, and the reduction of ores or cakes . ... 

So much for the heating of liquids. Frequently, however, it was necessary to heat substances to higher temperatures. For instance, in the calcination of metals— that is, the "burning" of them to form oxides—very strong heat is required. Similarly in the reverse process— the smelling, or "reduction" of ores to the metal— high temperatures are required. For these temperatures, a crucible was necessary. 

Decoking of catalyst pellets Ion exchange reactions Hydrogen storage in metal lattice Semiconductor doping Combustion of coal Reduction of ore Production of acetylene from CaC2 Semiconductor etching... 

Scoria, scoriae The refuse from the smeltlngof metals, reduction of ores, etc. dross slag, ate. 

The chemical stability domain of a compound represents the range of activity or gaseous partial pressure over which that compound is stable. For example, experience has shown that under sufficiently reducing conditions, all oxides are unstable and are reducible to their parent metal(s). Conversely, all metals, with the notable exception of the noble ones, are unstable in air — their oxides are more stable. From a practical point of view, it is important to be able to predict the stability or lack thereof of a ceramic in a given environment. A related question, whose answer is critical for the successful reduction of ores, is this at what oxygen partial pressure will an oxide no longer be stable ... 

Fluidized beds of fine solids are used for catalytic reactions in the petroleum and chemical industries, where the main advantages are nearly uniform temperature, good heat transfer to the wall or immersed surfaces, high effectiveness factors (because of the small particle size), and easy transfer of solids from one vessel to another. Fluidized beds are also used for combustion of coal, reduction of ores, and other solid-gas reactions, and these processes often use moderately large particles. 

Phases Gas plus reactant solid. Regeneration of adsorbents, catalysts, incineration of sludges, reduction of ores and roasting of some solids. Capacity about 0.01-10 kg/s solid particle diameter 0.2-20 mm. Temperatures for incineration in the range 790-980 °C. 

Mass transfer with chemical reaction in multiphase systems" covers, indeed, a large area. Table 1 shows a general classification of the systems encountered. From the possible two-phase systems, solid-solid reactions, liquid-solid (reactive or catalytic) and gas-solid (reactive or catalytic) reactions are not discussed here. The first one was reviewed by Tamhankar and Doraiswamy (2) and gas-solid (reactive) systems, such as, coal gasification, calcination of limestone, reduction of ores, etc. have been treated in some detail in recent reviews (3-5). The industrially important fluid-solid catalytic processes were the topic of a previous Advanced Study Institute (6) and have been also discussed authoritatively elsewhere (5,7). Concerning solid (reactive)-liquid two-phase systems, only some interesting examples are presented in Table 2 (1). 

Pores and macroscopic inclusions are three-dimensional crystal defects. From the standpoint of the reactivity of solids, pores can be very important. Consider, for instance, the formation of porous scales during oxidation (tarnishing) [11]. (For example, the decarburization of iron cannot occur if a non-porous oxide scale without grain boundaries is formed on its surface.) Or consider the direct reduction of ore [10] in which the reduction rate is greatly dependent upon the formation of porous metal surface layers. In many so-called solid state reactions, gaseous products are formed as well as solid reaction products as, for example, during the reaction of TiOa with BaCOs to produce BaTiOs with the formation of In such cases, just as in the case of ore reduction, the formation of a porous product surface layer is of decided importance for the progress of the reaction. 

Mineral Processing. This older application dating back to the 1950 s is used to decompose or purify ores through calcination or the roasting and pre-reduction of ores. Fluidized bed processing is also used in cement manufacture. 

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