Leaching: Aluminium :

Leaching is often used if the ore is soluble in some suitable solvent like acids, bases and suitable chemical reagents. For example Al, Ag, and Au ore and low grade copper ore.

Leaching of alumina from bauxite:

The principal ore of aluminium, bauxite, usually contains SiO₂, iron oxide and titanium oxide (TiO₂) as impurities. Concentration is carried out by digesting the powdered ore with a concentrated solution of NaOH at 473-523 K and 35-36 bar pressure. This way, Al₂O₃ is leached out as sodium aluminate (and also SiO₂ as sodium silicate) leaving behind the impurities, iron oxide and titanium oxide.

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MacArthur-Forrest Process:

(A) Extraction of Gold: In the Mac Arthur process, solid gold reacts with sodium cyanide to form a soluble gold complex. The impurities are filtered out of the solution and the gold is reduced back to elemental gold with a reactive metal such as zinc. (B) Extraction of Silver: Metallic Ag is dissolved from its ore in dilute NaCN solution, and the solute so obtained is treated with scrap Zn when Ag is precipitated. Air is blown into the solution oxidize Na 2 S. Leaching the metals like silver, gold with CN - is an oxidation reaction Here Zn act as reducing agent Leaching has been practiced for many years and often results in the contamination of streams and rivers with cyanide. New alternatives, using the thiosulfate ion (S 2 O 3 - ) , are being investigated to replace it. (C) Extraction of Copper: Different acid, base, and salt solutions are sometimes used to selectively separate out metal-bearing minerals. For example, sulfuric acid is used to separate the copper

Cupellation-Metallurgy:

Cupellation is a refining process in metallurgy, where ores or alloyed metals are treated under very high temperatures and have controlled operations to separate noble metals, like gold and silver, from base metals like lead, copper, zinc, arsenic, antimony or bismuth, present in the ore. The process is based on the principle that precious metals do not oxidise or react chemically, unlike the base metals; so when they are heated at high temperatures, the precious metals remain apart and the others react forming slags or other compounds. Since the Early Bronze Age, the process was used to obtain silver from smelted lead ores. By the Middle Ages and the Renaissance, cupellation was one of the most common processes for refining precious metals . By then, fire assays were used for assaying minerals, that is, testing fresh metals such as lead and recycled metals to know their purity for jewellery and coin making. Cupellation is still in use today.

Bessemerisation-Metallurgy:

The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is removal of impurities from the iron by oxidation with air being blown through the molten iron. The oxidation also raises the temperature of the iron mass and keeps it molten. Related decarburizing with air processes had been used outside Europe for hundreds of years, but not on an industrial scale.One such process has existed since the 11th century in East Asia, where the scholar Shen Kuo of that era described its use in the Chinese iron and steel industry. In the 17th century, accounts by European travelers detailed its possible use by the Japanese.

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