direct bubble size measurement in a mechanical flotation cell by image analysis and laser diffraction technique - a comparative study

in this study, a comparative measurement of bubble sizes in a two-phased medium (water and air) was performed in a mechanical flotation cell by image analysis (ia) and laser diffraction (ld) methods. the bubbles were generated in a mechanical cell with dimensions of 25*15*17 cm3. to determine the bubbles size by the ld method, the bubbles were transferred from the cell to the laser particle size analyzer (lpsa) device through a hole in the cell, and db(50) of bubbles were also calculated from their scattering pattern data. a bubble viewer, made of plexiglass with certain dimensions, including two main parts (sampling tube and viewing chamber) was employed for the ia method. comparative experiments were conducted in the different conditions affecting the bubble sizes, which are the impeller speed, solution temperature, ph value, and frother types. results indicated that the two measurement methods were in good agreement while bubbles sizes were in a range of +400-800 microns. the difference between ld and ia results was less than 7% in the range of +400-800. in the size range of -200 microns, ld and ia results difference increased to 36%. moreover, in all experiments with the same conditions, the size of the bubbles by the ld method was recorded smaller than that by the ia method. considering the fact that bubbles in the mechanical flotation cell are usually in the size range of +600 -2000 microns, and in this range, ld and ia results had a negligible disagreement, ld can be successfully employed for the bubble size measurement in mechanical flotation cells.