ANS:B - leaching

Leaching is a process used to extract soluble materials from a solid by dissolving them in a liquid solvent. It is a common technique used in various industries such as metallurgy, mining, agriculture, and food processing to separate desired compounds from raw materials or waste streams. Here's how leaching typically works:

1. Selection of Solvent: A suitable solvent is chosen based on its ability to selectively dissolve the desired compound(s) from the solid material while leaving undesirable components behind. The choice of solvent depends on factors such as solubility, selectivity, cost, and environmental considerations.
2. Contact between Solvent and Solid: The solid material containing the target compound(s) is placed in contact with the solvent. This can be done in various ways, such as immersing the solid in the solvent, spraying the solvent onto the solid, or passing the solvent through a bed of solid material.
3. Mass Transfer: As the solvent comes into contact with the solid material, it dissolves the soluble compounds present in the solid. The soluble components diffuse from the solid phase into the liquid phase, where they form a solution.
4. Separation: Once the leaching process is complete, the solution containing the dissolved compounds is separated from the solid residue. This separation can be achieved through methods such as filtration, settling, centrifugation, or decantation.
5. Recovery of Solutes: The desired compounds are then recovered from the leach solution by further processing, such as precipitation, crystallization, solvent extraction, or other separation techniques. The remaining solid residue, known as the leach residue or leachate, may undergo further treatment or disposal.

Leaching can be performed using various types of solvents, including water (hydrometallurgical leaching), organic solvents, acids, bases, and complexing agents, depending on the nature of the solid material and the compounds to be extracted. The process parameters such as temperature, pressure, agitation, and contact time are also adjusted to optimize the leaching efficiency. Overall, leaching is a versatile and widely used method for extracting valuable compounds from solid materials, enabling the recovery of metals, minerals, nutrients, flavors, and other substances for various industrial and commercial applications.