Key Processes and Techniques in Copper Extraction
A copper-alloy is a composite of copper with one or more other metals. Alloys usually contain more than 10 percent and in some cases 20 percent, of other metals. Copper is so widely used because of its low price, good ductility, high resistance to oxidation, and ease of work.
The great strength of copper over other metals is due to its softness. Although there are more than 20,000 copper alloy grades, pure copper is used for the manufacture of only a few grades, including brass, cupro-nickel, bronze, and bronze alloys. Although copper alloys can be prepared from a cast ingot or from scrap, in general, these alloys are produced by the melting and casting of copper into a mold to produce a shaped product.
What is Metallurgy?
Metallurgy is viewed as a technique that is used in the extraction of metals in their raw and pure form. Metal compounds mixed with soil, limestone, sand, and rock are known as minerals. Metals for commercial purposes are extracted from minerals at a reasonable cost and with relatively little effort. These minerals are known as ores. A substance that is incorporated into the charge in the kiln to take away the gangue (impurities) is called flux. Metallurgy mainly deals with the process of the formation of alloys and the purification of metals.
What is Copper Mining?
The most common ore used in copper extraction is Chalcopyrite (CuFeS2), also recognized as Copper Pyrites and other such sulfides. The proportion of copper in the real ore is too limited for straightforward copper extraction to be feasible. The concentration of ore is required, and the Froth Flotation method is used for this process.
Concentration of Ore
The copper ore is crushed into a fine powder, and the suspension is produced in water. Added to this are Collectors and Froth Stabilizers. Collectors like pine oils, fatty acids, etc. increase the non-wettability of both parts of the metal of the ore and enable it to develop froth and Froth stabilizers like cresols, aniline, etc. in order to maintain the froth. The oil washes the metal, and the gangue is made wet by water. Paddles and air are continuously trying to stir up the suspension to make the froth. This frothy metal is skimmed off onto the edge and left to dry in order to regain the metal.
Smelting of Copper
Smelting is really a metallurgical technique for extracting base metals from their ores with both the support of heat as well as a chemical reducing agent. Copper Smelting indicates that only the concentrated ore is intensely warmed up by silicon dioxide (silica), calcium carbonate (CaCO3), and air within the kiln. The main steps involved in the copper extraction method are as follows:
Reduction of copper in chalcopyrite to copper sulfide
Addition of calcium carbonate as a flux just like in blast furnaces, in order to create the slag
Removal of iron from chalcopyrite as iron silicate slag
Most of the sulphur present in chalcopyrite converts to sulphur dioxide during this process
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The chemical reactions associated with the above-mentioned steps can be written as:
2SiO2 + 2CuFeS2 + 4O2 → 3SO2 + Cu2S + 2FeSiO3
The copper produced from that whole procedure is combined with the slag and is termed Matte Copper because of its colour, texture, and appearance. This consists primarily of Cu2S, which is lessened to pure metal by blasting Matte Copper with air.
Cu2S + O2 → SO2 + 2Cu
Sulphur dioxide leaks out of copper, causing bubbles to show up and burst as and when the SO2 escapes. The above tends to cause the end product to have a really blistery appearance and is therefore called Blister Copper, which is actually 98 – 99.5 percent pure.
Copper is an exceptional conductor of electricity and, integrated with its ductility, is the perfect metal suitable for electrical wiring in both household and commercial areas due to its properties. The age of electricity and technology might have been a fantasy without such great metal.
Example Questions
Question 1: Which metals occur in nature in their native state?
Answer: Metals that lie below hydrogen in the electrochemical series like Copper, Silver, Gold, Platinum, etc. are not readily reacted by oxygen and carbon-di-oxide present in the atmosphere, and hence these occur in nature in their native state.
Question 2: What is gangue? And what is the role of a stabilizer in the froth floatation process?
Answer: The earthy impurities encountered during metal extraction from ores are called gangue. Chemical compounds like cresols and aniline help in stabilizing the froth and hence are called froth stabilizers and are used in the froth floatation process.
Conclusion
This is all about copper, its extraction metallurgy that the industries follow to recover pure copper. Learn how the process is being conducted in a stepwise method and understand the basic concept of metal extraction metallurgy.
FAQs on Extractive Metallurgy of Copper: Complete Guide for Students
1. What are the primary ores used in the extractive metallurgy of copper?
The principal ore used for the extraction of copper is chalcopyrite (CuFeS₂), also known as copper pyrites. Other important copper ores include:
Chalcocite (Cu₂S)
Cuprite (Cu₂O)
Malachite (CuCO₃·Cu(OH)₂)
Azurite (2CuCO₃·Cu(OH)₂)
However, sulphide ores like chalcopyrite are the most common commercial source for large-scale copper production.
2. How is copper ore concentrated using the froth flotation method?
The froth flotation method is ideal for concentrating sulphide ores of copper. The process involves grinding the ore into a fine powder and mixing it with water to form a slurry. Collectors (like pine oil) and froth stabilisers (like cresols) are added. When air is blown through the slurry, the oil-wetted metallic copper sulphide particles attach to the air bubbles and rise to the surface as a froth, while the heavier gangue (impurities like silica and dirt) gets wetted by water and settles down. The froth containing the concentrated ore is then skimmed off for the next stage.
3. What is the importance of roasting copper pyrites ore before smelting?
Roasting is a critical step where the concentrated copper pyrites ore (CuFeS₂) is heated strongly in a reverberatory furnace with a controlled supply of air. The primary objectives are:
To remove volatile impurities like arsenic (As), sulphur (S), and antimony (Sb) as their volatile oxides (e.g., SO₂).
To convert the copper pyrites into a mixture of cuprous sulphide (Cu₂S) and ferrous sulphide (FeS), which is then partially oxidised to ferrous oxide (FeO). This sets up the subsequent reactions in the smelting process.
Essentially, roasting prepares the ore for efficient smelting by removing unwanted elements and converting it into a more suitable chemical form.
4. What is the role of silica (sand) during the smelting of copper ore?
During the smelting of roasted copper ore in a blast furnace, silica (SiO₂) is added as a flux. Its primary role is to react with the ferrous oxide (FeO), an impurity present in the roasted ore. The acidic silica combines with the basic ferrous oxide to form ferrous silicate (FeSiO₃), a fusible compound known as slag. This slag is lighter than the molten copper matte (a mixture of Cu₂S and FeS) and floats on top, allowing for its easy removal. The reaction is: FeO + SiO₂ → FeSiO₃ (Slag).
5. What is "blister copper" and why is it named so?
Blister copper is the impure form of copper (about 98-99.5% pure) obtained after the Bessemerisation process. It is named for its characteristic blistered and rough surface. This appearance is caused by the escape of dissolved sulphur dioxide (SO₂) gas from the molten metal as it solidifies. The SO₂ is produced during the auto-reduction of the copper matte within the Bessemer converter. As the gas bubbles out of the cooling copper, it leaves behind pits and blisters, giving the final product its distinctive name.
6. Why is electrolytic refining the final and crucial step in producing high-purity copper?
While blister copper is about 99% pure, it still contains impurities like iron, nickel, zinc, gold, and silver. For applications requiring high electrical conductivity, such as wiring, even these small amounts of impurities are unacceptable. Electrolytic refining is crucial because it removes these impurities to produce copper with over 99.9% purity. In this process, the impure blister copper anode dissolves, and pure copper ions from the electrolyte solution deposit onto the pure copper cathode. The less reactive impurities like gold and silver settle at the bottom as anode mud, from which they can be recovered, adding economic value to the process.
7. What is the chemical principle behind the auto-reduction process for copper extraction?
The principle of auto-reduction is a key feature of copper extraction from its sulphide ore in a Bessemer converter. In this process, the copper compound itself acts as the reducing agent. After a portion of the copper sulphide (Cu₂S) is oxidised to copper oxide (Cu₂O) by a blast of hot air, the remaining copper sulphide reacts with the newly formed copper oxide to produce molten copper and sulphur dioxide gas. The reaction is: 2Cu₂O + Cu₂S → 6Cu + SO₂. No external reducing agent like carbon is needed, as the sulphide of the metal reduces its own oxide, hence the term 'auto-reduction'.
