Roe-Hoan Yoon

The Effect of Bubble Size on Fine Particle Flotation

Abstract Expressions for the probability of collision (Pc) and adhesion (Pa) have been derived for fine particle flotation by calculating the trajectory of particles as they flow past a bubble in streamline How. Three different flow regimes have been considered in the present work, i.e., Stokes, potential and intermediate. For the intermediate flow conditions in which most flotation operations are carried out, the particle trajectories have been determined using an empirical stream function derived in the present work. For the case of a very hydrophobic coal sample, the values of the probability of collection (P) determined experimentally have been found to be in close agreement with the theoretically predicted Pc values over a range of bubble and particle sizes The expression for Pa has been derived by determining the time it takes for a particle to slide along the surface of a bubble after collision. It has been assumed that the bubble-particte adhesion occurs when the sliding time is equal to or exceed...

The role of hydrodynamic and surface forces in bubble–particle interaction

Abstract In modeling flotation, the process of bubble–particle interaction is usually divided into three subprocesses, including collision, adhesion and detachment. Of these, the hydrodynamics of bubble–particle collision has been studied most extensively by many investigators, and the results are useful for the design and scale-up of flotation cells. The process of adhesion, on the other hand, is least understood because it is essentially controlled by the chemistry of the system, which is complex and difficult to model mathematically. However, it is possible to determine the probability of the bubble–particle adhesion from the induction times that can be measured experimentally under different chemical environments. Furthermore, the new information reported in the literature on the hydrophobic forces of both particles and bubbles allow prediction of adhesion probabilities using various surface chemistry parameters. Consideration of both the hydrodynamic and surface force parameters is essential in predicting flotation rates from first principles.

Zeta-potential measurements on microbubbles generated using various surfactants

The zeta-potentials of microbubbles in the 40- to 80-μm size range have been determined by means of a simple microelectrophoresis technique. In general, the sign of the bubble charge is determined by the polar head of the surfactant when an ionic surfactant is used to produce the bubbles. When using hydrolyzable ionic surfactants, however, the bubble charge is significantly affected by the hydrolysis products. In the presence of nonionic surfactants, bubbles can be charged either positively or negatively depending on the pH, and the isoelectric points appear to be related to the oxygen-to-carbon ratio of the surfactant molecule. With ionic surfactants, an increase in concentration results in an increase in bubble charge, while with nonionic surfactants the zeta-potentials change little in the concentration range studied. 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.

In-situ FTIR study of ethyl xanthate adsorption on sulfide minerals under conditions of controlled potential

Abstract A spectroelectrochemical ATR cell has been constructed for in-situ FTIR measurements of ethyl xanthate adsorption on chalcocite, chalcopyrite, pyrite and galena at pH 9.2. It allows potential control while conditioning the mineral bed electrode and subsequently recording the spectra. The results obtained with chalcocite identify three different potential regions of xanthate adsorption, including chemisorption, copper ethyl xanthate formation on the surface and multilayer formation. On chalcopyrite, xanthate initially forms dixanthogen, followed by copper ethyl xanthate at higher potentials. Dixanthogen is the only surface species identified on the surface of pyrite. Lead ethyl xanthate-like species are formed on the surface of galena at potentials where the voltammogram shows a pre-wave for chemisorption.

A parametric study of froth stability and its effect on column flotation of fine particles

Abstract Laboratory flotation tests have been conducted to examine the effect of froth stability on the column flotation of finely pulverized coal. It has been demonstrated that the upgrading of coal in a flotation column can be significantly improved when froth stability is properly controlled through the manipulation of appropriate variables such as gas flow rate (Vg), wash water flow rate (Vw), froth height, wash water addition point, and feed solid concentration. Increases in wash water flow rate and gas flow rate promoted froth stability, resulting in higher combustible recovery, but possibly higher ash recovery as well. The optimum rates were determined to be 2 and 0.3 cm/s for Vg and Vw, respectively. The specific influence of wash water flow rate on water recovery was found to be closely related to how the frother dosage was maintained. Coal particles could stabilize or destabilize the froth, depending on their size and concentration in the cell. Those in −100 mesh fraction destabilized froth at lower concentrations and stabilized it at higher concentrations while micronized particles always showed froth-breaking power. The froth profiles of solid content and ash content were established at varying wash water flow rates and wash water addition points, from which it was concluded that froth cleaning occurred primarily at the pulp–froth interface and drainage above the wash water addition point.

A study of hydrophobic coagulation

Abstract A series of coagulation experiments conducted on aqueous suspensions of methylated silica provides evidence that non-DLVO interaction energy controls the stability. This additional energy, which may be referred to as the hydrophobic interaction energy, can be estimated from the results of coagulation experiments. An expression has been derived to describe the hydrophobic interaction energy in terms of the nondispersion component of work of adhesion of water and the distance between two interacting particles.

Induction time measurements for the quartz—amine flotation system

Abstract An induction time apparatus which has a sensitivity limit of 100–150 μs has been constructed in the present work. The basic unit is similar to the one used by Eigeles and Volova and Trahar, but it operates with a microcomputer and has a greater sensitivity. Using this apparatus, the flotation chemistry of the quartz—amine system has been studied. It has been found that at a given dodecylaniminium 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 ionomolecular species are the surface-active species responsible for flotation. This finding confirms the earlier conclusions obtained using the surface tension and contact angle techniques. Induction time measurements have also been conducted as a function of particle size, collector concentration, indifferent electrolyte concentration, bubble change, and temperature. The results are compared with flotation data, and the activation energy for the bubble—particle adhesion has been calculated.

The role of hydrophobia interactions in coagulation

Abstract The coagulation behavior of coal and silica samples has been studied in view of the classical DLVO theory. It has been found, however, that this theory is applicable to weakly hydrophobic solids but not to strongly hydrophobic ones. To extend the theory, hydrophobic interaction energies, which are on the order of 2900 kT for very hydrophobic solids, have been considered. An expression describing the hydrophobic interaction energy in terms of the nondispersion interaction between water and solid has been derived.

Characterization of silica surfaces hydrophobized by octadecyltrichlorosilane

Abstract Adsorption of octadecyltrichlorosilane (OTS) on fused silica plates from cyclohexane solution has been studied at room temperature. By controlling solution conditions and reaction times, it is possible to produce surfaces of varying OTS coating, exhibiting a range of hydrophobicities. The amount of water in the system is the most critical factor in forming a stable, homogeneous OTS film. Based on contact angle data, atomic force micrographs, and FT-IR spectra of the OTS-covered silica surfaces, the kinetics of the silanation process have been studied, and a reaction mechanism is proposed.

Effect of media size in stirred ball mill grinding of coal

Abstract As a prerequisite to producing super-clean coal with any physical coal-cleaning process, such as microbubble flotation, the feed coal must be micronized to liberate finely disseminated mineral matter. The stirred ball mill is regarded as one of the most efficient devices for micronizing coal. Using a 13.4 cm batch mill, the optimum operating conditions have been determined in terms of media size, feed size and media type. The rate of breakage determined with monosized feeds are compared on the basis of specific energy consumption. It has been found that a 20:1 ball size/particle size ratio gives optimum grinding conditions.