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 mil ls, specially as a final cleaning stage. However, they differ in many aspects from conventional flotation cells. Different physical dimensio ns of collection and froth zones, different ways of generating and dis tributing the air bubbles in the system and the new use of wash water on the top of the froth, pose different control problems and opportuni ties. New operational variables, with different variability and relati onships among them, demand new efforts in better process variable meas urements, models development and control strategies of flotation colum ns. Most of the actual installations still use conventional instrument ation and conventional distributed PI control. Improvements in operati on and control of flotation columns can be achieved by a better knowle dge of its dynamics. In the literature some phenomenological model dev elopments have been reported, but a rather large number of model param eters have to be estimated from experimental data. In this work an exp erimental study of the dynamic behaviour of two flotation columns at d ifferent 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 pilo t scale column were used to obtain dynamic relationships for the air-w ater system. Field instrumentation was installed and calibrated, and d ata signals communicated to a PC computer through a serial A/D/A inter face. Changes in gas, wash water and feed flowrates, and tailing valve opening were specially designed and carried out to obtain experimenta l 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.