Leaching
Introduction
leaching (from the Latin lixivia, -ae, "lye"[1]) or solid-liquid extraction is a unit operation that consists of the separation of one or several substances (solutes) contained in a solid matrix (carrier phase), usually pulverized, through the use of liquid solvents. The raw material formed by the solid carrier phase together with the solute or mixture of solutes is called extraction material.[2] If the substance of interest is one that dissolves in the solvent, the process is called extraction; If what is intended to be dissolved are the impurities and the substance of interest is the solid, the process is called washing.
Chemical principles
Leaching is a process by which one or more solutes are extracted from a solid, using a liquid solvent.
Both phases come into intimate contact and the solute or solutes can diffuse from the solid into the liquid phase, resulting in a separation of the original components of the solid.
Leaching is based on the solubility of the solute in the solvent that will be used to extract it. For leaching to be effective, the solute must be more similar to the liquid phase than to the solid phase in which it was originally found.[3] Being an equilibrium between phases, leaching, like liquid-liquid extraction, can be quantitative (>99.9%) but never total (100%); This means that the solid phase will always contain a portion of the solute.
The process consists of four stages:[4].
Some examples are:
Leaching has great importance in the field of metallurgy, since it is frequently used in the extraction of some minerals such as gold, silver and copper. It is also used in pharmaceutical technology.
Factors affecting extraction
There are four determining factors in the speed of extraction:[4].
History
Leaching has been known since Antiquity. It was used in metallurgy in ancient Rome and in pre-Hispanic culture to extract copper and gold with water and natural acid solutions. In the Middle Ages, alchemists used it to separate metals. With the Industrial Revolution, cyanide leaching (at the end of the century) made it possible to recover gold and silver more efficiently. In the 19th century, methods were developed with acids and bacteria to extract metals from low-grade ores, which meant a revolution in mining and metallurgy.[5].