Kinetics of bubble-particle adhesion in flotation
Hernandez, Jorge L. Yordan
MetadataShow full item record
In order to study the role of electrical charge existing on air bubbles in the kinetics of the particle-bubble adhesion process in froth flotation, the zeta potential of microbubbles in the 40 -to 80-micron size range have been determined by means of a simple microelectrophoresis technique. In general, the bubble charge is determined by the charge of the polar head of the surfactants when ionic surfactants are used to produce bubbles. However, the magnitude of the zeta-potential is reduced when the surfactants are hydrolyzed. When using nonionic surfactants, the bubbles exhibit isoelectric points (i.e.p) in acidic and neutral pH ranges. It appears that the location of an i.e.p. is determined by the acid-base property of the surfactant molecule used. The negative charges observed with air bubbles and oil droplets in the absence of surfactants can be explained by the differences in the hydration energies of H⁺ and OH⁻ ions. An increase in the concentration of ionic surfactants results in an increase in bubble charge. However, the increase is minimal or non-existant when nonionic surfactants are used. The flotation chemistry of the quartz-amine system has been studied using an induction time apparatus constructed in the present work which has a sensitivity limit of 100-150 micro-seconds. The basic unit is similar to the one used by Eigeles and Volova (1960) and Trahar (1983), but it operates with a micro-computer and has a greater sensitivity. It has been found that at a given dodecyl ammonium hydrochloride concentration, the induction time is at a minimum at approximately pH 10.5. At this pH, the collector hydrolizes to form neutral amine and the flotation recovery reaches a maximum, suggesting that iono-molecular species are the surface-active species responsible for flotation. This finding confirms the earlier conclusions obtained using the surface tension (Somasundaran, 1976; Finch and Smith, 1973) and the contact angle (Smith, 1963) techniques. The induction time measurements have also been conducted as a function of particle size, collector concentration, indifferent electrolyte concentration and temperature. The results are compared with flotation data, bubble charge, particle charge and film thickness. Results of the induction time and microflctation experiments conducted using bubbles and particles of known electrical properties indicate that if the potential on the air/water interface is increase to a high value with the same sign as that of the s/l interface (e.g. by adding a suitable surfactant) the flotation kinetic is retarded; conversely, surfactant of the opposite sign can enhance the adhesion process.
- Masters Theses