Leaching is the process by which constituents of a solid material are released into a contacting water phase. Although some species may be more of an environmental concern than others, the leaching process is indiscriminant such that all constituents (e.g., major or minor matrix components as well as inorganic, organic and radionuclide contaminants) are released under a common set of chemical phenomena which may include mineral dissolution, desorption and complexation, and mass transport processes. In turn, these phenomena are affected by certain factors that can alter the rate or extent of leaching. Among these factors are:
external stresses from the surrounding environment
physical degradation of the solid matrix due to erosion or cracking, and
loss of matrix constituents due to the leaching process itself.
The process of leaching includes the partitioning of contaminants between a solid and liquid phase (e.g., assuming local equilibrium) coupled with the mass transport of aqueous or dissolved constituents. Mass transport is the summation of diffusion, hindered diffusion, tortuosity effects, and effective surface area effects through the pore structure of the material to the environment. Important chemical factors, those that influence the liquid-solid partitioning (LSP) of a constituent, include solution pH, redox, the presence of dissolved organic matter, and biological activity. Physical factors, such as relative hydraulic conductivity, porosity and fill geometry, play an important role in determining the rate at which constituents transport through a solid into a passing liquid phase.
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.
Leaching is a process of extracting a substance from a solid material that is dissolved in a liquid. This process is commonly referred to as extraction, particularly in the chemical industry. Three basic steps are involved in the leaching process: contact, separation, and extraction.
Leaching is the loss or extraction of certain materials from a carrier into a liquid (usually, but not always a solvent), and may refer to: Leaching (agriculture), the loss of water-soluble plant nutrients from the soil; or applying a small amount of excess irrigation to avoid soil salinity.
The 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.
Leaching occurs as excess water removes water-soluble nutrients out of the soil, by runoff or drainage. Leaching is an environmental problem for agricultural professionals whether chemical-heavy fertilisers or chemicals are swept out and find their way into water bodies.
is the movement of contaminants, such as water-soluble pesticides or fertilizers, carried by water downward through permeable soils. Generally speaking, most pesticides adsorb to soil particles (especially clay), become immobile, and do not leach.
Hint:In order to the question, the leaching or extracting of alumina from bauxite ore is done by the Bayer's Process. First step is to digest the powdered ore with a solution of $NaOH$ and then filtered the impurities, and finally heat the hydrated alumina unless we get the pure alumina.
Leaching is defined as the 'treatment of complex substances, such as an ore, with a specific solvent to separate its soluble parts from the insoluble ones' (CED, 2021).
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