D.A. Deglon

Review of hydrodynamics and gas dispersion in flotation cells on South African Platinum concentrators

Hydrodynamic and gas dispersion parameters, obtained from industrial flotation cells on South African Platinum concentrators, are reviewed in this paper. Hydrodynamic results show that power intensities are slightly higher than those typically observed in industrial flotation cells while impeller tip speeds and Froude numbers are within the range found in industrial cells. Gas dispersion results show that air flow rates, air flow numbers and air flow velocities vary significantly from cell to cell but are within the range typically found in industrial flotation cells. Gas dispersion results also show reasonably broad variations in bubble size, gas holdup and superficial gas velocity, although bubble surface area fluxes are shown to lie within a fairly narrow range of 50-70 /s

A model to relate the flotation rate constant and the bubble surface area flux in mechanical flotation cells

Abstract Two recent flotation models developed by the authors are discussed, viz. the bubble population balance model and the attachment-detachment model. The bubble population balance model describes the history of a bubble population in a flotation cell in terms of the sub-processes of bubble breakage and coalescence. The attachment-detachment model allows for the presence of a gas phase in the flotation cell, both in terms of a gas residence time and the attachment and detachment of mineral particles to/from bubbles. When combined the two models predict a near-linear region about a point of inflexion on the (simulated) response between the flotation rate constant (k) and the flux of bubble surface area through the flotation cell (S b ). It is proposed by the authors that this region corresponds to the linear k−S b relationship observed in a recent research project on flotation kinetics in mechanical flotation cells by Gorain et al. (1997).

An evaluation of a direct method of bubble size distribution measurement in a laboratory batch flotation cell

Abstract In this paper a novel bubble sampler is described which allows the measurement of bubble size distributions in flotation cells containing slurries of high solids concentration. The device separates bubbles fromo a slurry into a water solution where they may be measured using a bubble size analyser. An experimental programme of measuring bubble sizes in two and three-phases is reported in which the bubble sampler was evaluated and the effect of different frothers on the bubble size distribution in two and three-phases was investigated. In two-phase operation (liquid/gas), the bubble sampler was proved to supply accurate and reproducible measurements when compared with measurements made by the bubble size analyser without the sampler fitted. The frother type was found to have the greatest influence on bubble size. With the addition of solids (gold plant tailings) to form a three phase (solid/liquid/gas) system, the mean bubble size was found to increase, and only the further addition of frother could reduce it to its former value. Different frothers were found to have very different effects on the size of bubbles produced in slurries compared with those produced in two-phase systems. Of the frothers tested MIBC was found to be the best all around performer in terms of bubble size reduction with increasing solids concentration.

An on-site evaluation of different flotation technologies for fine coal beneficiation

Abstract This paper presents the results of an investigation of the performance of a number of different flotation cell technologies for the beneficiation of fine coal. The work was conducted on-site at the Grootegeluk Colliery in the northern Transvaal province of South Africa, using a pilot-scale conventional column cell, a pilot-scale Jameson-type cell, and an air-sparged hydrocyclone (ASH). In addition, characterisation and conventional batch flotation tests were conducted in the laboratory in the Department of Chemical Engineering at the University of Cape Town. All three units tested on-site demonstrated improved selectivity compared to conventional subaeration flotation. In the column cell, optimum performance could only be achieved at very low throughputs. Substantial losses of coal occured in the coarser size fractions. The Jameson-type cell was able to operate effectively at about double the throughput of the column cell at similar recoveries. Coal recovery in the coarser size fractions was still poor, but better than that of the column cell. The ASH was characterised by a very high throughput, more than 150 times that of the column cell on the basis of solids capacity per unit cross-sectional area. However, the ASH required more than three times the reagent dosage of the other two units to achieve this. The ASH performed particularly well in the recovery of the coarser size fractions, but was less effective than the other cells on the finer size fractions. Overall, the best performance for this application was that of the Jameson cell, owing to its higher capacity in comparison to the column cell. The high reagent requirement of the ASH makes this technology uneconomic in this application.