Difference Between Leaching and Extraction

Main Difference – Leaching vs Extraction

Leaching and extraction are two methods of extracting substances. Leaching is the process of extracting a substance from a solid by dissolving in a liquid. This can be either a natural process or an industrial process. Extraction is also a type of extraction that can be used to extract something from a liquid or a solid. There are mainly three types of extraction techniques used in analytical chemistry: liquid-liquid extraction, soli-liquid extraction and high pressure extraction. The main difference between leaching and extraction is that leaching is done to extract something from a solid using a liquid whereas extraction can be used to extract something either from a solid or a liquid.

Key Areas Covered

1. What is Leaching
     – Definition, Process, Metal Extraction
2. What is Extraction
     – Definition, Process, Different Types
3. What is the Difference Between Leaching and Extraction
     – Comparison of Key Differences

Key Terms: Acid, Distribution, Distribution Coefficient, Extraction, Leaching, Metal Extraction, Separatory Funnel 

What is Leaching

Leaching is the process of extracting something from a solid by dissolving it in a liquid. This can occur either naturally or can be done industrially. In order for leaching to occur, the substance to be extracted should be soluble in the liquid used for the extraction while other components should do not dissolve. Therefore, the sample solid consists of an insoluble carrier along with soluble solute particles. Some examples include separating a metal from its ore (the liquid used here is a suitable acid), extracting sugar from beet (using hot water), etc.

Figure 1: An Iron Leaching Area

In metal ores, there are many unwanted components present along with the useful metal. Therefore, in the leaching process, the metal is extracted in the form of a metal salt using an acid. Most commonly, sulfuric acid is used to make soluble metal sulfates. However, this process is harmful to the environment because of the production of harmful byproducts.

What is Extraction

Extraction is the action of extracting something, especially using effort or force. Extraction can be done for liquid-liquid separations and solid phase separations. The theory used in this extraction is the distribution of a substance in two different phases.

Let us consider a general apparatus of liquid-liquid extraction. This is done using a separatory funnel. An aqueous solvent and an organic solvent are used as the two phases. The solvents can be chosen depending on the distribution coefficient of the chemical components that are going to be separated.

Figure 2: A Liquid- Liquid Extraction

First, the aqueous liquid mixture that is going to be separated is added. Then the separatory funnel is filled with an aqueous phase and an organic phase. Since they are immiscible, the two layers are separated. The funnel is shaken several times carefully and allowed to stand for few minutes with the lid of the funnel opened. Then the two layers are collected in two different containers. The separation should be done several times in order to get accurate results. At the end, the required substance is in the organic phase. We can simply evaporate or use any other suitable technique to obtain pure substance from the organic phase.

Difference Between Leaching and Extraction

Definition

Leaching:  Leaching is the process of extracting something from a solid by dissolving it in a liquid.

Extraction: Extraction is the action of extracting something, especially using effort or force.

Phase of Matter

Leaching:  Leaching is done for solid phase substances.

Extraction: Extraction can be done with either solids or liquids.

Principle

Leaching:  Leaching involves the dissolution of the desired substance in a suitable liquid.

Extraction: Extraction involves the distribution of the desired substance between two phases of matter.

Conclusion

Leaching and extraction are two techniques used to extract a substance from a mixture. Leaching involves the extraction of a substance using a solvent that can dissolve the desired substance. Extraction includes the extraction of a substance using the distribution of the substance between two liquids. The main difference between leaching and extraction is that leaching is done to extract something from a solid using a liquid whereas extraction can be used to extract something either from a solid or a liquid.

Reference:

1. “Leaching (Chemistry).” Wikipedia, Wikimedia Foundation, 7 Jan. 2018, Available here.
2. “Extraction .” Chem 211 – Techniques, Available here.

Image Courtesy:

1. “IRON LEACHING (SEPARATING) AREA OF INSPIRATION CONSOLIDATED COPPER COMPANY’S SMELTER – NARA – 544044” By Keyes, Cornelius M. (Cornelius Michael), 1944-, Photographer (NARA record: 8463989) – U.S. National Archives and Records Administration (Public Domain) via Commons Wikimedia
2. “Liquid liquid extraction” By Sjantoni – Own work (CC BY-SA 3.0) via Commons Wikimedia