mixersettlers

A mixer-settler is a type of continuous liquid-liquid contacting device used to mix two immiscible liquids and then separate them by gravity. It consists of a mixer chamber equipped with an agitator or jet mixer to achieve intimate contact, followed by a settler or quiescent chamber where the phases disengage and separate by density difference. The unit is typically integrated with feeds and product outlets for the two phases, and may include pumps, valves, and flow controls to direct streams between stages.

Operation and design rely on creating a high interfacial area in the mixer to promote solute transfer between phases, after which the mixture flows into the settler where turbulence is minimized so that the two liquid layers can separate. The equipment is commonly arranged in banks to provide multiple contact stages, often with counter-current flow of the phases to optimize extraction efficiency. Settler design may incorporate baffles, weirs, demisters, and weep holes to improve phase separation and minimize back-mixing.

Applications for mixer-settlers are widespread in solvent extraction processes. They are used in hydrometallurgy for copper, uranium, and rare-earth separations, in nuclear reprocessing, and in pharmaceutical and chemical processing for purification and recovery steps. They are preferred where simplicity, robustness, and ease of operation are required, and where flow rates are moderate to high.

Advantages include straightforward operation, good robustness, and compatibility with viscous or slurried feeds. Limitations include a large footprint for high-throughput systems, potential emulsion formation, and the need for careful control to avoid back-mixing and poor phase disengagement.