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Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. [1] It is a form of extractive metallurgy that is used to obtain many metals such as iron , copper , silver , tin , lead and zinc .
The process, which uses mercury amalgamation to recover silver from ore, was first used at scale by Bartolomé de Medina in Pachuca, Mexico, in 1554. [2] It replaced smelting as the primary method of extracting silver from ore at Spanish colonies in the Americas.
Zinc smelting has historically been more difficult than the smelting of other metals, e.g. iron, because in contrast, zinc has a low boiling point. At temperatures typically used for smelting metals, zinc is a gas that will escape from a furnace with the flue gas and be lost, unless specific measures are taken to prevent it.
In pyrometallurgy, the metal ore is first oxidized through roasting or smelting. The target metal is further refined at high temperatures and reduced to its pure form. In hydrometallurgy, the object metal is first dissociated from other materials using a chemical reaction, which is then extracted in pure form using electrolysis or precipitation.
16th century cupellation furnaces (per Agricola). Cupellation is a refining process in metallurgy in which ores or alloyed metals are treated under very high temperatures and subjected to 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.
For sulfide ores, a different process is taken for beneficiation. The ore needs to have the sulfur removed before smelting can begin. Roasting is the primary method of separating, where wood was placed on heaps of ore and set on fire to help with oxidation. [6] [7] 2 Cu 2 S + 3 O 2 → 2 Cu 2 O + 2 SO 2
The blast furnace, used to produce pig iron from iron ore. These can be subdivided into: Cold blast furnaces; Hot blast furnaces; The bloomery, a precursor to the blast furnace that produces sponge iron from ore; The blowing house, a traditional furnace for smelting tin; The smeltmill, a traditional furnace for smelting lead
Smelting involves thermal reactions in which at least one product is a molten phase. Metal oxides can then be smelted by heating with coke or charcoal (forms of carbon ), a reducing agent that liberates the oxygen as carbon dioxide leaving a refined mineral.