Leaching Process is used in the extraction of substances from solids. This is achieved by dissolving the given substance in a liquid. This can be done via an industrial process or even through a natural process.
What is Leaching Process?
Leaching Process describes the release of organic and inorganic contaminants or radionuclides from a solid phase into a water phase, when influenced by processes such as desorption, complexation, and mineral dissolution.
The Leaching Process is a universal process – Water will leach the components of any material it comes in contact with, from its surface or the interior of the material (based on the porous nature of the material).
Using this process, the ore of a metal can be concentrated by causing a chemical reaction with a reagent which would lead to the ore being dissolved but the impurities remaining undissolved.
Leaching Process Examples
An example of the leaching process would be the leaching of Al2O3.2H2O (or bauxite) with a heated and concentrated solution of sodium hydroxide. In this example, the concentrated NaOH dissolves the aluminium present in the bauxite whereas the impurities such as Fe2O3 , TiO2 , and SiO2, are not dissolved by the reagent. The chemical reaction for this example can be written as:
Al2O3.2H2O + 2NaOH → 2NaAlO2 + 3H2O
Another example of this process would be the leaching of noble metals such as gold and silver with the help of dilute aqueous solutions of sodium cyanide or potassium cyanide, with air present. The chemical reaction for the leaching of silver can be given by:
Ag2S + 4NaCN → 2Na[Ag(CN)2] + Na2S
Leaching is also responsible for the loss of nutrients present in soil due to heavy rains.
Advantages and Disadvantages of Leaching Process
Advantages of Leaching include:
- The process is easy to execute.
- It is not very harmful when compared to pyrometallurgical methods
- This process does not generate any gaseous pollutants.
Disadvantages of Leaching include:
- The residual liquid waste produced from this process are highly acidic.
- The effluent from this process can also be toxic.
- The efficiency of this process is dependent on temperature.
Types of Leaching Processes in Metallurgy
A few types of leaching processes used industrially for metallurgic purposes include:
- Heap leaching, a process used to extract copper, uranium, and some precious metals from their ores.
- Another process in which copper and uranium are recovered is via a process called In-Situ Leaching.
- Tank Leaching and Vat Leaching are processes wherein the ores are placed in large tanks (or vats) which contain leaching solutions. They can be used to extract metals from their ores.
Thus, the leaching process offers a wide range of variations which can be used to extract specific metals from their ores.