Roasting of Low Reactive Metals: Concentration or Extraction?

Roasting is a process that involves heating a substance strongly in the presence of oxygen. In the context of low reactive metals, roasting is usually done to concentrate the metal rather than extract it. Let's discuss this in detail.

1. Concentration of Low Reactive Metals:
Roasting is commonly used as a method of concentrating low reactive metals such as zinc, lead, and copper. These metals are often found in their sulfide ores, which are compounds of the metal with sulfur. The purpose of roasting is to convert the metal sulfide ores into metal oxides, which can then be further processed to obtain the metal.

2. Conversion of Metal Sulfides to Metal Oxides:
During roasting, the metal sulfide ores are heated strongly in the presence of excess oxygen. This causes the sulfur in the sulfide ores to combine with oxygen, forming sulfur dioxide gas (SO2). The metal in the sulfide ores combines with oxygen to form metal oxides. The balanced chemical equation for the roasting of metal sulfides can be represented as follows:

Metal Sulfide (MS) + Oxygen (O2) → Metal Oxide (MO) + Sulfur Dioxide (SO2)

3. Removal of Impurities:
Roasting also helps in the removal of impurities present in the metal sulfide ores. Many impurities, such as arsenic and antimony, are converted to volatile oxides or gases during the roasting process. These impurities can be easily removed, leaving behind the desired metal oxide.

4. Further Processing:
Once the metal sulfide ores are converted to metal oxides, further processing techniques are employed to extract the metal from the oxides. The metal oxide is usually reduced using a suitable reducing agent, such as carbon or coke, in a process known as reduction. This reduction reaction converts the metal oxide back into the pure metal form.

Conclusion:
In conclusion, the roasting of low reactive metals is primarily done to concentrate the metal rather than extract it. Roasting converts metal sulfide ores into metal oxides, which can then undergo further processing to obtain the pure metal. Roasting also helps in the removal of impurities present in the metal sulfide ores, making the extraction process more efficient.