Keywords: residence time distribution, RTD, radioactive tracers, froth flotation, flotation machines, modelling, industrial flotation cells, hydrodynamics
Residence time distribution in large industrial flotation cells
The radioactive tracer technique was used to measure the Residence Time Distribution (RTD) of the liquid and solid in a rougher flotation bank consisting of seven cells of a volume of 130 m³. Thus, a pneumatic system of high reliability was used in order to introduce a small amount of radioactive tracer (around 100 mL of liquid or pulp) at the feed pulp entrance. Then, the time response of the radioactive tracer was measured online along the flotation bank using noninvasive sensors located in the discharge pipe of each cell. Activity (cps) was measured by Saphymo Srat scintillating crystal sensors of NaI(Tl) of 1″ × 1.5″, thus allowing the simultaneous data acquisition of up to 12 control points with a minimum period of 50 ms. A solution of Br-82 was used as a liquid tracer, while mineral gangue was used as a solid nonfloatable tracer. The solid tracer was also tested at three size classes. An advantage of using the radioactive tracer technique is the direct testing of the actual solid particles (similar physical and chemical properties, shape, etc.). From a hydrodynamic point of view, the experimental data confirmed that single mechanical flotation cells of large size can deviate significantly from perfect mixing.