Experimental Pros and Cons to the Theories of Bubble-Particle Interactions: Progress in the Past Two Decades

"Bubble-mineral complexes could be formatted by an attaching of hydrophobic particles to the surface of air bubbles or by an evolution of bubbles from solution onto hydrophobic surfaces. Measurements of contact angles, detachment forces (DF), induction times (IT), evolution pressures (EP) and flotation recoveries (FR) for the studying of minerals wettability at various pH and electrochemical potentials were used. An analysis of the obtained IT results show that a process of bubble attachment to a mineral surface is a rather slow one and it will scarcely be enough for bubble-mineral complex formation under the conditions of real flotation.The ranges of adhesion potentials obtained by DF measurements, Figure 1, correlate with the data of floatability-potential for pyrite. The ranges of adhesion potentials obtained by DF measurements for galena (-1 ÷0.2V) and chalcocite (-0.5÷1.2V) correlate with the potential ranges of floatability for galena (<0.2V) and chalcocite (>-0.4V). An increase of the DF and the cathodic limit of the adhesion potential with increasing length of the hydrocarbon chain were observed. EP-pH curves for sulfides are a mirror-like to the DF-pH curves, Figure 2. Structure of solid-liquid and liquid-gas borders has a determinative importance for formation of bubble-mineral complexes and subsequently flotation results. Under vacuum on the mineral surface there are produced micro bubbles and preferably they will be appeared on the hydrophobic sites. Water structure breaks near a hydrophobic surface facilitate water mass destruction and formation of gaseous phase embryos under decompression in the impeller zone. It simultaneously reduces a probability of produced micro bubbles dissolution as a result of pressure increasing owing to constant fluctuation of liquid densities into impeller zone. Comparison of Taggart’s evaluation of the suction behind blades of the impeller of an agitation-froth machine and ABEP data on galena, Figure, shows that gas evolution will be observed in the range of 1300-2700 revolutions of impeller per minute for hydrophobic and hydrophilic surfaces successively."