Since the early 1980s flotation columns have been progressively incorporated in milling operations all over the world. Improvements in final concentrate grade, using single cleaning stages, have been in most cases the reason for using this new technology. However, the main disadvantage with respect to conventional mechanical cells is the large spread of results, mainly in terms of recovery, which is normally compensated by a high circulating load and high capacities (overdesign). Besides normal changes in Seed grade and flowrate, and the need for periodic maintenance for gas spargers, the following common troubles in plant practice are discussed: improper calibration and maintenance of instrumentation to measure froth depth and gas rate bias definition and estimation uneven wash water distribution uneven froth depth in baffled columns lack of robustness of control strategies Proper boundaries for superficial wash water rate (0.1-0.2 cm/s), froth depth (0.5-1.0 m) and superficial gas rate (1-2 cm/s), based on fundamental knowledge and experience in large size columns, are suggested for stable operation. Unfortunately, the lack of coordination between these variables is an important limitation for metallurgical improvements. The effect of altitude on gas rate and gas holdup in flotation columns operating at 1500-4500 m over the sea level is analysed.