Abstract: In the froth flotation of ore in a column, the froth/pulp interface level and the efficiency of the froth washing operation are controlled by determining a profile of temperatures measured in the froth layer and slurry below the interface. Temperatures are measured with temperature sensing elements immersed in the froth layer and extending to below the interface level. The measured profile is compared with a target profile and deviations are corrected by changing the tailings flowrate or the washwater flowrate to return a measured profile to the target profile. An inflection point in the profile occurs at the interface level. The inflection point in a measured profile is compared with a level set point, and a deviation from set point value is corrected by increasing or decreasing the flow of tailings whereby the interface level returns to its set point.