Leaching (chemical science)

Leaching is the process of extracting substances from a solid by dissolving them in a liquid, either in nature or through an industrial process. In the chemical processing industry, leaching has a variety of commercial applications, including separation of metal from ore using acid, and sugar from beets using hot water.

Another term for this is lixiviation, or the extraction of a soluble particle from its constituent parts.

In a typical leaching operation, the solid mixture to be separated consists of particles, inert insoluble carrier A and solute B. The solvent, C, is added to the mixture to selectively dissolve B. The overflow from the stage is free of solids and consists of only solvent C and dissolved B. The underflow consists of slurry of liquid of similar composition in the liquid overflow and solid carrier A. In an ideal leaching stage, all the solute is dissolved by the solvent; none of the carrier is dissolved. The mass ratio of the solid to liquid in the underflow is dependent on the type of equipment used and properties of the two phases.

Leaching is the process by which inorganic, organic contaminants or radionuclides are released from the solid phase into the water phase under the influence of mineral dissolution, desorption, complexation processes as affected by pH, redox, dissolved organic matter and (micro)biological activity. The process itself is universal, as any material exposed to contact with water will leach components from its surface or its interior depending on the porosity of the material considered.

One such reaction is:

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