Flotation Particle Size Research Articles

An experimental study of the recovery of hydrophilic silica fines in column flotation

This paper presents results of tests performed to investigate the effect of gas rate (1.2–2.5 cm/s), hydrophilic fines content (5–20% w/w silica) and froth depth (10–30 cm) on fines recovery in a laboratory-scale flotation column operating without wash-water addition and absence of floatable particles. A model was developed based on the entrainment coefficients presented by [Trahar, W.J., 1981. A rational interpretation of the role of particle size in flotation. International Journal of Mineral Processing 8, 289–327], which describes the mass contribution of the different size classes to the solids recovered in the concentrate. The entrainment model of [Zheng, X., Johnson, N.W., Franzidis, J.P., 2006. Modelling of entrainment in industrial flotation cells: water recovery and degree of entrainment. Minerals Engineering 19, 1191–1203] was also tested. The results show both models described well the dependence of the mass flow rate of hydrophilic solids in the concentrate.

Capillary-rheological effects at liquid-gas interfaces containing oil films, and their relation to the flotation process

1. The surface activity of mineral oils, which can be rated according to the magnirude of dσ/dh, depends on the quantity of substance in the film, its chemical composition, and the properties of the water. 2. The dynamic characteristics Δσ and tp depend on the chemical composition and specific mass of substance of the film, reaching their highest values at thickness hc ≲ 2hp, where hp is the average film thickness at the Pockels point; the dynamic characteristics also depend on the water composition. 3. The relaxation process has several components, and theσt curves in the region of asymptotic stability are described by the equation\(\sigma _t = \sigma _p + \sum\limits_{i = 1}^N {\Delta \sigma _{0i} e^{ - b_i ^1 } } \). Transition of the surface to a stable state is due to a change of form of the film under the influence of capillary forces and related convective surface diffusion and molecular volume diffusion of surfactants, as well as a change in orientation of the surface-active molecules at the oil-water interface. 4. With thickness h ≫ hp, the film changes over to a different state, and this is accompanied by the formation of structures in the form of oil accumulations without any contact angle (continuous thick films) or with a finite contact angle (lenses). In the latter case, the relaxation process is governed by the establishment of the equilibrium contact angle of the structures that are formed. 5. Correlation of the quantities Δσ, tp, m/S (or h), andɛ shows that at the liquid-gas boundary, reagents are the most effective when used in amounts such that continuous films are created on the bubble surfaces, with film thicknesses twice the minimum thickness that is reached when the oil is completely extended. With increasing m/S, the flotation activity (from the standpoint of the capillary mechanism) of a liquid-gas interface containing an oil film will drop off and approach a state in which Δσ ≤ 0 and there is no strengthening of the contact between the bubble and particles; this has an adverse effect on the degree of extraction and on the particle size in flotation — a relationship that is in qualitative agreement with experimental data and practical experience in flotation.

A rational interpretation of the role of particle size in flotation

From the examination of data from detailed plant surveys and associated laboratory batch testing, the principal effects of particle size in flotation have been identified. The current state of knowledge concerning the role of this variable is discussed in terms of the evidence presented. It is concluded that the minimum degree of hydrophobicity necessary for the flotation of a particle depends upon its size and as a result, recovery-size curves are a valuable diagnostic aid to the assessment of flotation performance. Entrainment is shown to be an important contributory mechanism to the recovery of fine particles which, when coupled with a low rate of genuine flotation, can account for much of the observed behaviour of such fines. The significance of particle size and its consequences in flotation research, in plant operations and in control schemes has been under-rated. The separate conditioning or flotation or both of separate size fractions seems inevitable as ores become increasingly difficult to concentrate.