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Chemical Or Extractive Metallurgy

Metalliferous ores that are taken directly from the mine are seldom suitable for metal smelting. These ores must first undergo removal or separation of waste matter to increase the concentration of the desired mineral. These processes include sorting, crushing and grinding, sizing, and separation by magnetics, electrical conductivity, specific gravity, etc.

Flotation is a widely used separation technique that takes advantage of the fact that some mineral components attract water (hydrophilicity) and others repel it

Date Technology developed
Prior to 4000 B.C. Gold, copper, and meteoritic iron used occasionally without melting. Hammered into shape. Copper first annealed about 4000 B.C.
4000 to 3000 B.C. Reduction of oxidized ores of copper and lead. Bronzes produced by intentionally mixing copper and tin ores (about 3500 B.C.). Permanent molding of stone and metal. Soldering with copper-gold and lead-tin alloys.
3000 to 2000 B.C. Most jewelry techniques known before 2500 B.C.
2000 to 1000 B.C. Bellows used in furnaces by 1800 B.C. Wrought iron important by 1600 B.C. Steel produced by carburization in hearth.
1000 to 1 B.C. Cast iron known in China. Iron and steel welded into composite tools and weapons. Stamping of coins by 700 B.C.
1 to 1000 A.D. Zinc smelted in China and India.
1380 Blast furnaces used to carburize and melt iron.
&NA; 1440 Type metals for printing. The earliest type metals were tin-based. These were later displaced by lead-antimony in the 1600s.
1509 First cast iron cannon produced.
1627 Brass known to have been produced from copper and metallic zinc.
1718 Tables of metal affinities published.
1783 Phlogistron theory of metals disproved by Lavoisier. Phlogistron was a hypothetical substance thought to be a volatile constituent of all combustible substances released as flame in combustion.
1841 Objects shaped by powder metallurgy.
1875 Bessemer process for making steel developed.
1882 Manganese steel developed.
1886 Electrolytic aluminum produced.
1892 Carbonyl nickel process developed.
1898 Heat treatment of high speed steels, i.e., alloy steels that remain hard and tough at red heat.

(hydrophobicity). Finely divided air is introduced into a mixture of solid minerals and water. Air bubbles adhere to the hydrophobic particles, causing them to rise to the surface. These components are skimmed off. The hydrophilic components remain behind in the pulp. The sulfides of heavy metals are readily floatable, so flotation is an important method for concentrating copper, lead, and zinc ores.

Other methods of treating impure metals include magnetic separation and electrolytic refining. In magnetic separation, the magnetic components of an ore are separated from the nonmagnetic residual material. In electrolytic refining, the metal is cast into plates that serve as electrodes in electrolytic tanks. The electric current causes the metal to dissolve, and the pure metal is deposited at the electrode of opposite polarity to the plates.

The ores or concentrates of heavy metals such as copper, lead, zinc, and nickel (but not iron and tin) consist for the most part as sulfides of those metals. Removal of the sulfur is accomplished by a process called roasting. Roasting is a heat treatment carried out in an oxidizing atmosphere that produces a metal oxide and sulfur dioxide gas, which is usually processed to sulfuric acid. Arsenic and antimony are also removed by roasting. Roasting produces a powder, which may be agglomerated by sintering.

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Science EncyclopediaScience & Philosophy: Mathematics to Methanal trimerMetallurgy - Chemical Or Extractive Metallurgy, Mechanical Working - Physical metallurgy, Metallic coatings