EXPERIMENTAL STUDIES ON FLOTATION COLUMN DYNAMICS

Flotation columns have been widely used in mineral processing all over the world. They have been systematically incorporated in a lot of mills, specially as a final cleaning stage. However, they differ in many aspects from conventional flotation cells. Different physical dimensions of collection and froth zones, different ways of generating and distributing the air bubbles in the system and the new use of wash water on the top of the froth, pose different control problems and opportunities. New operational variables, with different variability and relationships among them, demand new efforts in better process variable measurements, models development and control strategies of flotation columns. Most of the actual installations still use conventional instrumentation and conventional distributed PI control. Improvements in operation and control of flotation columns can be achieved by a better knowledge of its dynamics. In the literature some phenomenological model developments have been reported, but a rather large number of model parameters have to be estimated from experimental data. In this work an experimental study of the dynamic behaviour of two flotation columns at different scales is presented. A 5x10 cm rectangular section and 1.35 m high laboratory scale column and a 10 cm diameter and 8.5 m high pilot scale column were used to obtain dynamic relationships for the air-water system. Field instrumentation was installed and calibrated, and data signals communicated to a PC computer through a serial A/D/A interface. Changes in gas, wash water and feed flowrates, and tailing valve opening were specially designed and carried out to obtain experimental responses of pulp level, gas holdup and bias, at different operating conditions. Main nonlinearities and interactions were show to be very useful to explain common control problems.