The desired component diffuses into the solvent from its natural solid form. Examples of leaching include the removal of sugar from sugar beets with hot water and the removal of nickel salts or gold from their natural solid beds with sulfuric acid solutions. There are many different types of equipment used for leaching. Popular for extreme amounts of solids.
Temperature is adjusted to optimize solubility and mass transfer.
Solvent selection plays an important role in solubilities as well as the separation steps that follow leaching. Nearly all leaching equipment employs some type of agitation to aid in mass transfer and to ensure proper mixing. The most popular leaching equipment can be seen in Perry's Chemical Engineers' Handbook . A plot of N vs. X,Y is used to step off stages for leaching calculations. But, just as equilibrium data is necessary for a McCabe-Thiele diagram in distillation, leaching calculations require that you know something about how the solids and liquids interact.