Liquation

Liquation is a metallurgical refining process in which an alloy containing components with markedly different melting points is heated to a temperature at which the lower-melting constituents melt and form a separate liquid phase. The liquid can be drained or siphoned away, leaving behind a solid mass enriched in the higher-melting component. The operation may be repeated to improve purification, and it often requires specific furnace conditions and fluxes to manage oxides and slags.

The technique relies on the existence of a distinct liquid phase within the alloy and a suitable difference in melting temperatures between the constituents. By removing the liquid fraction, impurities or unwanted elements with lower melting points can be reduced from the desired metal. Liquation has historically been used in metal refining and ore processing, particularly in cases where a metal can be separated from impurities by differential melting rather than by chemical reduction or volatilization.

Applications and scope have varied across cultures and eras. In antiquity and early metallurgy, liquation aided the purification of metals where a low-melting impurity could be separated from a higher-melting base metal. It is most effective when the alloy is not a complete solid solution and when a clear liquid phase can be generated and drained without excessive dissolution of the target metal.

Limitations include limited applicability to systems with small melting-point differences or with strong mutual solubility, potential loss of material in the liquid flux, and energy costs. With the development of more advanced refining methods, liquation has largely been supplanted for industrial use, though it remains a historical reference in metallurgical science.