Influence of the capillary pressure in nanobubbles on their adherence to particles during froth flotation: Part 5. Spreading curves of nanobubbles on the surface with different wettability

Abstract

To increase the accuracy of results, two methods for investigating wetting and spreading processes on a solid substrate are studied. In the first method, liquid drops are used; in the second method, bubbles are used. The shapes of drops and bubbles vary upon spreading, and this fact can be evaluated quantitatively only by means of the Laplace equation, but the equation is applied only in the case of bubbles (the second method). In the case of the first method, this circumstance excludes the purity control of the spreading drop surface. The influence of microcontaminations on the results is considered based on precision calculations performed for both methods. Spreading curves of nanobubbles with initial diameters of 20 and 10 nm on the substrates with various wettabilities are calculated, and wettability is evaluated not by the numerical value of the wetting angle but by the corresponding easily implemented examples of such substrate Γ, Φ, and H_x, where x is the surface fraction under a bubble coated by ionogenic collector molecules: 0.8, 0.6, 0.4, and 0.2. Spreading curves clearly illustrate the range of possible nanobubble spreading from the limiting one on the Γ substrate to the almost zero one on the Φ substrate, as well as the sources of energy provision of spreading and their depletion causes. The informativity of spreading curves is caused by the fact that more than ten bubble and substrate parameters are applied in their calculation. When using the reagents, the flotation activation can spread to larger bubbles.