EFFECT OF CAPILLARY PRESSURE IN NANOBUBBLES ON THEIR ADHERENCE TO PARTICLES DURING FROTH FLOATATION. PART 6. INFORMATIVITY OF BUBBLE SPREADING CURVES

Spreading curves (SCs) are calculated for bubble diameters (de) 1 mm and 1 μm on substrates with different wettability: from maximumhydrophobicity (Г) to maximum-hydrophilicity (Ф) as well as incompletely wettable (Нх) ones, where x = 0,8; 0,6; 0,4 and 0,2 is the fraction of an ionized collector monolayer under the bubble. The calculations were based on the results of a numerical solution of the Laplace equation in the form of 12-figure tables such as Bashforth and Adams tables. They demonstrate firstly that the SCs obtained are identical to those calculated for bubbles with de = 20 and 10 nm, and thus SC shapes are unchanged in the 105 range, i.e. virtually for all flotation bubbles, and secondly that SC shapes and their mutual arrangement depend on substrate wettability. Spreading curves clearly illustrate the advantages of substrate Г adhesion to the bubble in comparison with substrate Ф, and for Нх an advantage of the substrate with a larger fraction of x. It is quantitatively shown that even with small spreading of nanobubbles adhered to the particle, their adherence force increases billion times so that large bubbles can fix on their increased perimeters and lead the particle to flotation. If, however, the adhesion of large bubbles to nanobubbles occurs before spreading of the latter, they will come off together, and the particle will not float. This mechanism was used for particle flotation in the processes of the Bessel brothers, Potter-Delpra and two processes of F. Elmor in the late 19th and early 20th centuries. The prospect of increasing the productivity and cost-efficiency of modern froth flotation by activating particle flotation not only with nanobubbles but also with larger bubbles is considered.