Pyrometallurgy of Oxides

It is therefore possible to reduce magnesium oxide to the metal with coke above about 1600 °C (Fig. 17.8), even though there would be no intersection of the Ellingham lines for the oxidations of solid Mg and coke in an accessible temperature range. The practicability of producing magnesium in this way depends on rapid quenching of the Mg vapor below temperatures at which the reverse reaction 

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When common oxides, such as for instance of lead, are reduced, they form molten metal. Zinc oxide does not exactly follow the other oxides, because zinc has such a high vapor pressure at the temperature needed that it disappears as a vapor, from which the metal has to be condensed. In view of these facts, it is not strange that the pyrometallurgy of zinc was delayed and so also was knowledge about zinc in its metallic form. 

In the broadest sense, coordination chemistry is involved in the majority of steps prior to the isolation of a pure metal because the physical properties and relative stabilities of metal compounds relate to the nature and disposition of ligands in the metal coordination spheres. This applies both to pyrometallurgy, which produces metals or intermediate products directly from the ore by use of high-temperature oxidative or reductive processes and to hydrometallurgy, which involves the processing of an ore by the dissolution, separation, purification, and precipitation of the dissolved metal by the use of aqueous solutions. 4... 

In pyrometallurgy (high temperature dry smelting), however, hydrogen is much less effective as a reductant, but carbon becomes important. For reasons we discuss in Section 17.8, the concentrate to be reduced is usually in the form of a metal oxide, so the reductant has to be something that has a greater affinity for the available oxygen atoms than has the... 

Metals are important resources and have a wide range of applications. Metals are often extracted from ores. Once the ore is mined, the metals must be extracted, usually by chemical or electrolytic reduction. Pyrometallurgy uses high temperatures to convert ore into raw metals, while hydrometalluigy employs aqueous chemistry for the same purpose. The methods used depend on the metal and their contaminants. Most metals are obtained by hydrometallurgical processes such as aqueous acids or alkalis are predominantly used to dissolve the metal oxides, sulfides, or silicates. Electrowinning and solvent extraction are frequently used to recover and concentrate the metals. A limited number of high-temperature molten salts have also been used for the recovery of refractory metals, such as titanium and aluminum, from their ores... 

The processing of bauxite aluminium ore (hydrated alumina oxides) exemplifies these processes. In the Bayer process hot concentrated sodium hydroxide dissolves alumina which is subsequently separated and crystallized as aluminium hydroxide (hydrometallurgy). This is calcined to anhydrous alumina (pyrometallurgy) before being reduced in the Hall process (electrometallurgy) wherein alumina serves as the electrode from which elemental aluminium is deposited on the cathode. 

Relatively close to the term "geochemical engineering" is the technique of bacterial leaching. The technique is known for a long time from the treatment of metal-poor ores, where hydro- or pyrometallurgy is no more economically feasible. During these processes - mediated by specialized bacteria - oxidation of sulphur and sulphides produces sulphuric acid, and metals are mobilized such as copper. 

PyrometaUirrgy. Pyrometallurgy is a method of converting metallic compounds to different forms for easier processing and refining by using oxidation and reduction reactions. 

The most common minerals of high metric tonnage (iron, aluminum, copper, titanium, nickel, chromium, magnesium, zinc, etc.) are found in nature as oxides and sulfides and as a combination of both. Ores are sometimes a mixture of rich metal composition and poorer compositions called gangue. The gangue can be acidic or alkaline, and determines the type of flux used for pyrometallurgy. Since ores come in all levels of complexity, various methods of processing have been developed over the years. 

The pyrometallurgy process for refractory gold ores mainly refers to oxidative roasting. Since As and S are volatilized in the form of AS2O3 and SO2 during the roasting, not only a porous roasted... 

Bismuth concentrates are almost always obtained as by-products from metallic ores containing bismuthinite, bismite, and native bismuth in their gravity concentration, magnetic separation and floatation. Or from the further collection of bismuth-containing materials produced on the metal smelting process, they mainly exist with the phases of sulfide and oxide. The traditional extraction processes on the bismuth concentrates are classified as pyrometallurgy and hydrometallurgy smelt. It will be reviewed as follows. 

Pyrometallurgical Processes The metallurgical method based on roasting an ore, followed by reduction of the oxide to the metal, is called pyrometallurgy, the prefix pyro- suggesting that high temperatures are involved. Some of the characteristics of pyrometallurgy are as follows ... 

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