This device consists of a small mixing chamber followed by a larger gravity settling chamber
Each mixer-settler unit provides a single stage of extraction. The two phases enter the mixing
section where they are mixed using an impeller. The two-phase solution flows into the settling
section where they are allowed to separate by gravity due to their density differences. Typical
mixer settlers have mixing times on the order of a few minutes and settling times of several
minutes. The separate phases exit the settling section by flowing over a weir (organic solution)
or through an underflow then over a weir (aqueous phase). The separation interface is
controlled by the height of the weirs on the outlets of the settler section. Only minimal
instrumentation is required and mechanical maintenance is limited to occasional mixing motor
replacement. In a countercurrent process, multiple mixer settlers are installed with mixing and
settling chambers located at alternating ends for each stage (since the outlet of the settling
sections feed the inlets of the adjacent stage’s mixing sections). Mixer-settlers are used when a
process requires longer residence times and when the solutions are easily separated by gravity.
They require a large facility footprint, but do not require much headspace, and need limited
remote maintenance capability for occasional replacement of mixing motors.