Metallurgy

Submitted by admin on Tue, 01/18/2011 - 02:13

Most metals are chiefly useful in elemental form, but they usually occur in compounds on the earth’s surface. An oreNaturally occurring minerals from which metals and other substances can be extracted commercially. is a naturally occurring material from which one or more useful elements or compounds may be obtained at a cost that is economically feasible. As can be seen from the table, most metal ores are oxides, carbonates, or sulfides. A few of the least electropositive metals occur as the element.


Occurrence of Metals.

Type of Ore
Examples
Native Metals Cu, Ag, Au, As, Sb, Bi, Pd, Pt
Oxides Al2O3, Fe2O3, Fe3O4, SnO2, MnO2, TiO2, FeO•Cr2O3, FeO•WO3, Cu2O, ZnO
Carbonates CaCO3, CaC03•MgCO3,MgCO3, FeCO3, PbCO3, BaCO3, SrCO3, ZnCO3, MnCO3,

CuCO3•Cu(OH) 2

Sulfides Ag2S, Cu2S, CuS, PbS, ZnS, HgS, FeS•CuS, FeS2, Sb2S3, Bi2S, MoS2, NiS, CdS
Halides NaCl, KCl, AgCl, KCl•MgCl2•6H2O, NaCl and MgCl2 in seawater
Sulfates BaSO4, SrSO4, PbSO4, CaSO4•2H2O, CuSO4•2Cu(OH)2
Silicates Be3Al2Si6O18, ZrSiO4, Sc2Si2O7
Phosphates LaPO4, LiF•AlPO4


Whether a mineral can usefully be regarded as an ore or not depends on such factors as how concentratedIncreased the concentration of a mixture or solution (verb). Having a large concentration (adjective). it is, its exact location, and whether there is a suitable process for extracting the metal. As the more accessible higher-grade ores become exhausted, less accessible and lower-grade ores are becoming increasingly utilized with a consequent shift in the meaning of the word ore. It is conceivable that many silicates could become sources of metals, notably aluminum. Currently, though, silicates are expensive decompose chemically, and silicates form ores only for relatively expensive metals like zirconium and beryllium.

The processing of ores may be divided into three steps. Often concentrationA measure of the ratio of the quantity of a substance to the quantity of solvent, solution, or ore. Also, the process of making something more concentrated. or other beneficiation is required to remove worthless material (gangue) or to convert the mineral into an appropriate form for subsequent processing. The second and most-important step is reduction of the metal from a positive oxidation stateA formally defined charge that an atom in a compound or ion would have if the compound or ion consisted entirely of monatomic ions. Based on a Lewis diagram, the charge that an atom would have if all electrons in bonds were assigned to the more electronegative atom or divided equally between atoms of the same electronegativity.. This may involve elevated temperatures, chemical reducing agents, electrolysisA process in which a reaction that would otherwise be non-spontaneous (reactant-favored) is forced to occur by passage of electric current., or some combination of these treatments. Usually a third step, refining, is required to achieve the purity (or precise mixed composition in the case of an alloyA solid that has metallic properties and is made up of two or more elements.) desired in the final productA substance produced by a chemical reaction..