What is the name of the process that converts sulphide ores into oxides by heating strongly in the presence of excess air ?
Roasting
Understanding Ore Processing: Roasting Sulphide Ores
The question asks about a specific process used in metallurgy to convert sulphide ores into a more usable form, specifically oxides. This conversion happens by heating the ore strongly in the presence of excess air.
Identifying the Key Process: Roasting
Let's look at the options provided and compare them to the description given in the question:
- Calcination: This process involves heating carbonate or hydrated ores strongly in the absence or a limited supply of air. The purpose is usually to remove volatile substances like carbon dioxide (\(CO_2\)) from carbonates or water (\(H_2O\)) from hydrated ores. This doesn't match the description of heating sulphide ores in excess air.
- Roasting: This process involves heating sulphide ores strongly in the presence of excess air. The sulphide ore is converted into its corresponding metal oxide and sulphur dioxide gas is released. This exactly matches the description in the question. A general reaction can be represented as:
For example, roasting of zinc sulphide (\(ZnS\)):
Another example, roasting of lead sulphide (\(PbS\)):
- Smelting: This is a process of applying heat to ore in order to extract a base metal. It often involves a reducing agent, such as carbon, to chemically reduce the metal oxide to the metal. While it involves heating ores, it's typically done after processes like roasting or calcination and involves reduction, not the initial conversion of a sulphide to an oxide by oxidation in air.
- Incineration: This is a waste treatment process that involves the combustion of organic substances contained in waste materials. It's not related to the processing of metal ores.
Comparing Roasting and Calcination
Roasting and Calcination are both thermal decomposition processes applied to concentrated ores, but they differ significantly in the type of ore treated and the atmospheric conditions:
| Feature | Roasting | Calcination |
|---|---|---|
| Ore Type | Sulphide ores | Carbonate ores, Hydrated ores |
| Atmosphere | Presence of excess air (Oxidizing atmosphere) | Absence or limited supply of air |
| Main Reaction | Sulphide to Oxide (Oxidation) | Removal of \(CO_2\) or \(H_2O\) (Thermal decomposition) |
| Purpose | Convert sulphides to oxides for subsequent reduction; Remove sulphur impurities as \(SO_2\). | Convert carbonates/hydrates to oxides; Remove volatile impurities. |
Based on the definitions and the comparison, the process that converts sulphide ores into oxides by heating strongly in the presence of excess air is definitively called Roasting.
Revision Table: Key Terms in Ore Processing
| Term | Description | Typical Ore Type |
|---|---|---|
| Roasting | Heating strongly in excess air to convert sulphides to oxides. | Sulphide ores |
| Calcination | Heating strongly in absence/limited air to remove volatile matter. | Carbonate ores, Hydrated ores |
| Smelting | Heating ore with a reducing agent to extract metal. | Oxides (often after roasting/calcination) |
| Concentration/Beneficiation | Removal of gangue (impurities) from the ore. | Various ore types |
Additional Information: Why Convert Sulphide Ores to Oxides?
Sulphide ores are not directly reduced to metals as easily as oxides are. Oxides can be reduced relatively simply using common reducing agents like carbon or carbon monoxide in processes like smelting. Sulphides require more complex reduction methods. Therefore, converting sulphide ores into oxides through roasting is a crucial step in the extraction of metals from sulphide minerals. The sulphur dioxide gas produced during roasting is often captured and used for manufacturing sulphuric acid, which helps in pollution control and resource utilization.
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