Environmental Chemistry

Leaching – Definition, Process, and Questions

Whenever we brew a cup of tea or make an instant coffee, leaching in action is visible. Leaching is basically a process of extracting any substance from a solid material that has to come in contact with a liquid element. However, leaching the liquid is much important. The liquid facilitates the ability to remove or extract any given substance from a solid matrix i.e. material.


Definition of Leaching

Leaching is a primary process in hydrometallurgy, in this, the metal values of a solid metal bearing elements are transferable into an aqueous solution by the action of a lixiviant. Within the industry of the chemicals, the process of leaching is usually referred to as the extraction process. When we make a hot cup of green tea we need a green tea bag and some hot water for making it.

Moreover, we proceed with boiling it and then add it to a cup. As we steep our green tea bag inside the hot water, what we notice? Notably, the water here not only just changes in color but it also extracts the green tea from the tea bag into the water. After steeping it for a couple of minutes, we sip it and not just taste the hot water but also the taste of the green tea leaves through it.

Although preparing tea is a very common process. This process of making tea is also an ideal example of working of the leaching. We take a solid matrix like a tea bag then we introduce it to a liquid. During this process, the hot water extracts the components from the tea bag and the water gets a flavor. Now that we know what actually leaching is, let’s look at this process in more detail.

Download Leaching Cheat Sheet PDF

Process of Leaching

Firstly, the solvent comes in contact with the solid matrix. A solvent is usually a liquid substance that functions for dissolving a substance or the solute. A solute is an element that a solvent dissolves. Thus, the solvent will become the liquid and the solute would be the substance we would extract from the solid matrix. Moreover, referring to our example of the tea, the solute would be our green tea extracted whereas the hot water would be the solvent.

Above all, the solvent moves through the solid matrix, separating the substance, or solute, from this matrix so that we can collect it. This step of the process is usually known as percolation. Percolation is just a fancy word we generally use for filtering. We essentially filter out, or separate, the solute that we desire from the solid matrix, with the use of a solvent.

Shrinking-Core Model

As we know, while leaching a solid with a liquid the solid goes to the liquid phase while the earlier one remains. The removal of the solid as liquid dissolves into a particle that leads to a diameter of a non-leached core that shrinks with the time.

Eco-Friendly Leaching

We are able to see if organic acids are eligible for the use of leaching of lithium and cobalt from the batteries with a little success. Experiments that we perform with varying temperatures and the concentrations of metal acid shows that the optimal situations are 2.0 m/L of the organic acid at a temperature of near about 90 °C. The reaction has overall efficiency exceeding 90% with no other harmful byproducts.

4 LiCoO2(solid) + 12 C4H6O5(liquid) → 4 LiC4H5O5(liquid) + 4 Co(C4H6O5)2(liquid) + 6 H2O(liquid) + O2(gas)

Questions on Leaching

Ques. The boiling point of any solvent is:

(A). Boiling solvent.
(B). Decoction.
(C). Leaching.
(D). None of the mentioned.

Ans. (B). Decoction.

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