A theoretical treatment is prcsented which attempts to quantify the benefits obtained by using smaller bubbles or larger particles in dispersed air flotation. The limited experimental data obtained so far suggest that the theory is sound, particularly in its prediction of the effect of bubble size.any liquid effluents contain particles which are M too small to be removed economically in sedimentation tanks or by conventional filters. The diameters of such particles are normally less than 20 microns. Dispersed air flotation removes them by adsorbing them on small rising air bubbles, typically of diameters up to 0.1 mm. The bubbles may be generated either by electrolysis, or by forcing air through a porous plate or through spargers. As they rise through the liquid they contact particles either by collision or by Brownian diffusion, depending on particle size. An example of an industrial application is Saint Gobain's Electro-flotation process"', designed initially for removing oil-covered iron dust particles from rolling mill effluents.In dissolved-air flotation, a technique long established in industry, the bubbles are formed by nucleation on the particles'e', For this to happen a substantial portion of the clarified effluent must be recycled, compressed to 4 to 6 atmospheres and saturated with air. Dispersed air flotation has the advantage of eliminating the need for recycling and compression. However, bubble-particle contacting is necessarily less efficient and contacting efficiency becomes an important design parameter. This paper explores the effect of bubble size and particle size on contacting efficiency.
Previous workThe removal of suspended solids from effluents by dispersed air flotation is obviously similar in many ways to the froth flotation process used in mineral dressing. The mineral flotation literature records little or no quantitative work on the effect of bubble size, although it is known qualitatively that smaller bubbles tend to increase the flotation rate and a subsidiary function of frothers (long-chain alcohols) is t o reduce bubble size"). Many empirical studies have been made on the effect of particle size in mineral flotation without any clear-cut relation emerging. If the first order flotation rate constant is k, and the particle diameter is d, then Morris") found k, a In dp; Bushell"' found ?c, independent of d, ; Tomlinson and
On prksente un traitcment thhriqne par lequel on cherche A dkterniiner quantitativement les avantages qu'on obtient en employant des bulles plus petites ou des particules plus grosses flottant disperdxs dam l'air. Les rksultats maigres qu'on a obtenus expkrimentaleriient jusqn'ici tendent 8 indiquer que la thCorie est bien fondke, surtout en ce qui a trait i sa prkdiction de I'effet des dimensions des bulles.Fleming'" found kl a d,? for easily floated minerals and kl a d, for poorly floated minerals; Gaudin et a P found k1 to be independent of d, for d, = 1 to 4 microns and kl a d , for d , = 4 to 20 microns. Only Tomlinson and Fleming reported the bubble size us...
Flotation rates of glass beads and of latex particles have been measured as a function of particle size using very small bubbles. With glass beads the observed rate versus size relationship agreed quite well with the prediction of a simple hydrodynamic collision model, but that found with latex particles did not. It is suggested that electrical forces may have to be taken into account when the particles have a significant zeta potential. With both types of particle, the relationship between flotation rates measured at two different bubble sizes is consistent with the model's predictions.
A modified group solution model for liquid mixtures is presented. The model differs from previous models in that the Bronsted‐Koefoed congruence principle is used to describe the effect of molecular size. The model has been tested for mixtures involving paraffin hydrocarbons, alcohols and water at low pressures. Such systems involve binary mixtures of the groups methylene and hydroxyl, and are reasonably represented by the model.
Data presented enable the approximate equilibrium properties of such solutions at low pressures to be predicted at 40°C and 90°C. Interpolation and reasonable extrapolation from these temperatures should be satisfactory.
The Gillespie-type still used by Lu was modified to provide a better approach to equilibbrium. It was tested by comparing experimental and literature data for binary mixtures of ethanol-benzene and methanol-water. Isothermal vapor-liquid equilibrium data were then determined for acetone-n-heplane mixtures at 65°C. Redlich-Kister constants were evaluated by a weighted least-squares fit and are presented.
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