The design of an extraction tank is driven by the need to maximize the interfacial area between two phases for efficient mass transfer while allowing for their eventual clean separation. For liquid-liquid systems, a common design is the mixer-settler. The tank is functionally divided: one section contains a high-speed agitator to disperse one liquid phase into the other as small droplets, creating a large surface area for the solute to transfer. This mixed zone then overflows into a calm settling chamber, where the droplets coalesce and the two immiscible liquids separate into distinct layers for individual withdrawal.

Material construction is critical. Tanks are typically fabricated from stainless steel (grades 304 or 316L) for chemical resistance, or from lined carbon steel for more aggressive solvents. Internal surfaces are often polished to facilitate cleaning and prevent contamination. Temperature control is achieved through external jacketing or internal coils, as solubility is highly temperature-dependent. The tank incorporates multiple ports—for feeding raw material and solvent, for sampling, for introducing inert gases, and for discharging the separate phases. Level sensors and interface detectors are used to automate the discharge of the light and heavy phases.

Scalability is a key consideration; laboratory-scale extraction principles must translate effectively to large production vessels. The operational reliability of an extraction tank depends on this careful engineering balance between promoting turbulent mixing for extraction and providing quiescent conditions for separation. This dual-purpose design makes the vessel a versatile and critical component in processes ranging from the decaffeination of coffee and tea to the recovery of precious metals in hydrometallurgy.