A liquid-liquid contactor column 10 has a solvent input 16 and an aqueous phase input 22. Lighter phase liquid is discharged at 31 and heavier phase is moved by an air lift 26 to a receiver. The air supply line 28 to the air lift 26 includes valve 32 and a pressure sensing transducer 34 senses pressure in line 28 and sends electric signals to signal processing unit 52 which may for example close down operation of the column, or effect other changes to maintain operating characteristics of the column. The column could be pulsed by means which also send signals to unit 52, and could deliver to an external settler.
