The annular centrifugal contactor is a vertical, liquid-liquid, direct drive, centrifuge capable of both mixing and separating. Efficient mixing is achieved in the annulus between the spinning rotor and the stationary lower housing. Separation occurs in the rotor due to the enhanced density difference of two liquids at increased gravitational force. In this design, mixing and disengaging times of three and ten to thirty seconds, respectively, are typical. System equilibrium is reached in minutes, even for multiple stage processes, due to the low operating volume of these devices. Annular centrifugal contactors, capable of nearly one theoretical stage per unit, are readily employed in complex processes. They can be directly coupled to one another because the rotor pumps the liquids from the annular mixing zone to a height sufficient to feed the next unit. New designs have recently become available which offer such enhancements as interchangeable heavy phase weirs, a low mix option, and a clean in place rotor. This commercially available technology is now being utilized for polymer, organic peroxide, pharmaceutical, and metals recovery processes to improve throughput and efficiency, lower process inventory, and reduce waste. The ability to process during complete phase ratio changes, intermittent flows, and changes in flow rate without loss of performance make these contactors an attractive extraction tool.