Leaching is a chemical process in mining for extracting valuable minerals from ore. Leaching also takes place in nature, where the rocks are dissolved by water. Post leaching, the rocks are left with a smaller proportion of minerals than they originally contained. The leaching process in mining is carried out either as heap leaching or insitu leaching.
Precious metals such as gold are extracted from their ores by a cyanide or ozone leaching process. Radioactive metals, such as uranium are extracted by the process of acid leaching. Choosing the appropriate leaching method for metal extraction is done based on economic and environmental viability.
Types of Leaching
The two main types of leaching are heap and insitu leaching.
Heap leaching is also known as acid leaching. This method is most effective for the extraction of metals from difficult ores, and is one of the most tried and tested methods. The pre-processing of ore before leaching involves the grinding and roasting of the ore. Roasting is done to remove the carbonaceous elements trapped inside the ore. After pre-processing, the ore is leached with acid of alkali solutions to extract the metal. Heap leaching is carried out in the extraction of copper, nickel, uranium and precious metals.
Insitu leaching is also known as insitu recovery, or solution mining. This is especially used to extract copper and uranium. In this process, holes are drilled into the ore deposit by explosive or hydraulic fracturing methods. The leaching solution is then pumped through these channels. The solution that dissolves the ore is then pumped out and processed.
Disadvantages of Leaching
Leaching is a chemical process, hence it is ridden by certain disadvantages as listed below.
- Highly acidic process, resulting in production of toxic effluents
- Lower efficiency at low temperatures