Question

Explain the process of roasting and smelting in the extraction of copper from copper pyrites

Short answer

Question: Explain the process of roasting and smelting in the extraction of copper from copper pyrites. Answer: Roasting and smelting are the two key steps employed in the extraction of copper from copper pyrites. In roasting, the ore is heated in the presence of air to remove impurities and convert the sulfides into oxides, resulting in the formation of sulfur dioxide gas and iron(III) oxide. Smelting then involves heating the roasted ore to a high temperature in the presence of a reducing agent and a flux to remove further impurities, especially the remaining iron. Carbon monoxide gas reduces iron(III) oxide impurities to metallic iron, while limestone decomposes into calcium oxide and forms calcium silicate (slag) to remove any remaining impurities, leaving behind the refined copper metal.

Step-by-step solution

Understanding the Composition of Copper Pyrites

Copper pyrites is a mineral with the chemical formula CuFeS2. This means it is composed of copper (Cu), iron (Fe) and sulfur (S). Roasting and smelting are the two key steps employed in the extraction of copper from copper pyrites.

Roasting of Copper Pyrites

Roasting is a process where the ore is heated in the presence of air (oxygen) to remove impurities and convert the sulfides into oxides. During the roasting process, the following reactions occur: 1. The sulfur in the ore reacts with oxygen to form sulfur dioxide gas: 2S(s) + 3O2(g) -> 2SO2(g) 2. The iron sulfide (FeS) in the ore reacts with oxygen to form iron(III) oxide (Fe2O3) and sulfur dioxide gas: 4FeS(s) + 7O2(g) -> 2Fe2O3(s) + 4SO2(g) As a result of roasting, most of the sulfur and iron impurities get removed from the ore, obtaining a partially purified form of copper pyrites.

Smelting the Roasted Copper Pyrites

Smelting is the process of heating the roasted ore to a high temperature in the presence of a reducing agent (like coke) and a flux (like limestone) to remove further impurities, especially the remaining iron and to refine the copper. During smelting, the following reactions take place: 1. The coke (carbon) reacts with the oxygen present in the air to form carbon monoxide gas: C(s) + O2(g) -> CO(g) 2. The carbon monoxide gas produced reduces any remaining iron(III) oxide (Fe2O3) impurities to form metallic iron and carbon dioxide gas: 3CO(g) + Fe2O3(s) -> 2Fe(s) + 3CO2(g) 3. The limestone (CaCO3) decomposes into calcium oxide (CaO) and carbon dioxide gas which are used to form slag and to remove any remaining impurities: CaCO3(s) -> CaO(s) + CO2(g) 4. The calcium oxide (CaO) further reacts with silicon dioxide (SiO2) impurities to form calcium silicate (CaSiO3) slag, which can be easily separated from the molten copper: CaO(s) + SiO2(s) -> CaSiO3(l) At the end of the smelting process, the refined copper metal is obtained. The copper obtained through this process may still contain some impurities, which will be removed in the subsequent refining processes.