A new instrumented flotation column that is halfway between the pilot and the lab scale is presented. This installation works in continuous mode and allows both bubble size distribution and gas hold up measurement in the slurry. In the present study, it was used in the context of clay extraction. The final objective was to employ this flotation process for radioactive soil remediation. Data were interpreted using a two-zone model based on mass balance. A cationic surfactant (TTAB) is able to adsorb on the negatively charged clay particles surface and modifies the hydrophobicity to different extents depending on the employed TTAB quantity. We looked at the influence of TTAB/clay mass ratio on flotation performances, bubble size distribution and gas hold up. Consistent and reproducible data were obtained. The flotation rate constant increases with the TTAB/illite ratio whereas bubble size decreases. Gas hold up measurements underlined an accumulation of small bubbles at the highest TTAB/illite ratio tested due to their small buoyancy.