Adsorption of surface-active substances on air bubbles and the influence of their sizes relationship on the performance of bubble-film extraction

Bubble-film extraction as an improved form of bubbling flotation allows to reduce the concentration of surface-active impurities in water to the level of tenths of a milligram per liter. The use of a polydisperse stream of air bubbles during bubble-film extraction significantly accelerates the process of water purification, when the proportion of large and small air bubbles reaches a certain ratio in their mixed stream. The best case is when air bubbles of different sizes form an integrated structure inside the collecting funnel of the discharge channel of the bubble-film extractor. In the built-in structure, capillary waves accompanying the rupture of large bubbles in the upper part of the critical gas-filling zone inside the funnel of the bubble film extractor transmit their pulses to small-sized bubbles. These pulses overcome the electrostatic repulsion in the boundary menisci of the contacting bubbles and thereby initiate their fusion with the release of more adsorbed surface-active substances into that part of the discharge channel in the bubble-film extractor where a stream of flat liquid films of flotation concentrate appears. As a result, a significant increase in the rate of water purification from its surface-active pollution occurs. The features of bubble-film extraction (enhanced bubble flotation) for water purification are considered from the standpoint of the equilibrium and dynamics of adsorption of surface-active admixtures of water (surfactants) on air bubbles with various sizes. It is shown, that within a certain ratio of dimensions and quantity of air bubbles in their stream transferring surfactants from the water bulk into the bubble-film extractor, the productivity of bubble-film extraction process increases many times. The reason consists in the collective fusion of big and small air bubbles in their embedded structure inside of the bubble-films extractor under the action of capillary waves appearing at the bursting of large bubbles

water; purification; adsorption; bubble-film extraction