A mixer-settler pairs a mixing compartment with a settling compartment. In the mixer, an impeller disperses the aqueous and organic phases so the target metal transfers across the droplet interface. In the settler, the dispersion separates by gravity into a light organic layer and a heavy aqueous layer. Pumping between stages makes the circuit counter-current, and each stage is a physical box that can be sampled and adjusted independently.
Why it matters in practice
Stage efficiency of 90%+ per stage is measurable, and the phase boundary is visible, so performance is diagnosable rather than inferred. That predictability is why mixer-settlers remain the default for lab and pilot campaigns even where a column would use less floor space.
How it is measured or specified
The mixer is specified by residence time of one to three minutes and power input of 2 to 5 kW per cubic metre; the settler by specific flow of 2 to 5 mm/s across its plan area. Stage efficiency is measured by assaying all four streams around a stage and comparing the actual concentration change with the equilibrium change, with 90 to 95 per cent being normal for a well-built unit. Interface position, organic-to-aqueous ratio in the mixer and impeller condition are the three things checked on every inspection.
Calculators that use this
Equipment referenced in this entry
Related terms
Where this appears on this site
Reference entry GL-MIXER-SETTLER. Source slug mixer-settler · segment liquid-liquid-separation. Definitions on this page describe engineering practice in hydrometallurgical process design; they are not a substitute for test work on your own material.
Working with Mixer-Settler? Send the feed material, the throughput and the medium — an engineer replies with a preliminary configuration and the sizing reasoning attached.