We obtain copper and iron through distinct extraction methods, each suited to the specific properties and ores of the metal.
Copper Extraction
Copper is often extracted from sulfide ores, and the method varies based on the ore's grade (copper concentration). A common method involves a process of concentration, roasting, smelting, and refining. In some cases, a "self-reduction" method is employed, especially with copper sulfide ores. This process leverages the inherent chemistry of copper sulfide to facilitate the metal's release.
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Concentration: The ore is crushed and then concentrated, often through froth flotation, to increase the copper sulfide content.
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Roasting: The concentrated ore is heated in air. This converts some of the copper sulfide to copper oxide. Sulfur is driven off as sulfur dioxide, a crucial step for minimizing pollution and potentially recovering sulfur as sulfuric acid.
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Smelting: The roasted ore is mixed with silica and limestone and heated in a furnace. The copper oxide reacts with remaining copper sulfide to form molten copper metal and sulfur dioxide. The silica and limestone act as a flux, removing impurities as slag.
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Refining: The copper obtained from smelting, known as blister copper, is not pure enough for most applications. It is refined either by electrolytic refining or by fire refining. Electrolytic refining, commonly used, involves using impure copper as an anode and pure copper as a cathode in an electrolytic solution. Copper ions migrate from the anode to the cathode, resulting in a deposit of high-purity copper.
Iron Extraction
Iron is primarily extracted from iron oxides, mainly hematite (Fe₂O₃) and magnetite (Fe₃O₄), using the blast furnace. The blast furnace process relies on carbon reduction.
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Ore Preparation: The iron ore is typically crushed and beneficiated (enriched) to increase the iron content. It is also mixed with coke (a form of carbon) and limestone.
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Blast Furnace Process: The mixture of iron ore, coke, and limestone is fed into the top of the blast furnace. Hot air is blasted into the bottom of the furnace.
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Reduction: Inside the blast furnace, coke burns in the hot air to produce carbon monoxide. The carbon monoxide acts as a reducing agent, reacting with the iron oxide to produce molten iron and carbon dioxide:
Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g) -
Slag Formation: The limestone decomposes to calcium oxide, which reacts with silica and other impurities in the ore to form slag (calcium silicate).
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Tapping: The molten iron and slag are tapped from the bottom of the furnace at regular intervals. The molten iron is then further processed to make different grades of steel.
Summary
| Metal | Primary Ore Types | Extraction Method | Reducing Agent | Key Reactions |
|---|---|---|---|---|
| Copper | Sulfide ores | Self-reduction, Roasting, Smelting, Refining | Copper Sulfide | Cu₂S + O₂ → 2Cu + SO₂ (Simplified) |
| Iron | Oxide ores | Blast Furnace | Carbon Monoxide (CO) | Fe₂O₃ + 3CO → 2Fe + 3CO₂ |
