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Effect of impeller rotational speed on the size dependent flotation rate of galena in full scale plant cells

Ian Wark Research Institute, The ARC Special Research Centre for Particle and Material Interfaces, University of South Australia, Mawson Lakes, SA 5095, Australia
Minerals Engineering (Impact Factor: 1.71). 11/2006; 19(13):1307-1318. DOI: 10.1016/j.mineng.2005.11.008

ABSTRACT The first three rougher cells in the lead circuit of the Elura concentrator (formerly Pasminco Australia Limited) were selected as the plant cells for investigation. Metallurgical surveys were performed and various hydrodynamic measurements taken, allowing the galena flotation rate constant and the bubble surface area flux (Sb) in these cells to be calculated over a wide range of gas flow rates, and at two impeller rotational speeds. It was determined that altering the impeller rotational speed did not significantly change the rate constant dependency on Sb when flotation was considered on an unsized basis.The analysis was further extended to examine the same cells parameters on a size-by-size basis. The results obtained have been used to identify differences in the flotation behaviour of the various particle size fractions, independently of surface hydrophobicity. It is shown that the physical conditions for effective flotation of fine (<9 μm) and coarse (>53 μm) particle size fractions differ substantially, suggesting that a specific hydrodynamic environment will favour a high flotation rate for fine galena, which may be detrimental to the recovery of coarse galena, and vice versa. These observations are in accord with metallurgical practice that suggest that it is difficult to improve fine particle flotation without also compromising coarse particle stability efficiency simply by modifying the cell hydrodynamics alone. A fundamental flotation model was applied to quantify differences in the flotation rate of the various particle size fractions with impeller rotational speed.

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    • "Schulze (1977) demonstrated that the levels of turbulence within the cell maybe the primary deterministic factor for the successful recovery of a particle to the concentrate launder. As such, operational factors such as impeller speed must be altered to meet the specific requirements of coarser particles, with some authors stating that a slower speed (or lower power input to the slurry) is recommended for coarse particle flotation (whilst still exceeding the minimum level of agitation for suspension of solids) (Grano, 2006; Schubert, 2008; Deglon, 2005; Kallioinen and Heiskanen, 1993; Ahmed and Jameson, 1985) and others recommending a faster impeller speed be employed to target coarse particles and avoid sedimentation, this is depicted in Fig. 9 (Johnson, 2006; Trahar and Warren, 1976). As pointed out by Kallioinen and Heiskanen (1993) even the design of the rotor-stator system can significantly impact on the size range that can be effectively recovered. "
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    • "High concentrations of sodium oleate reduce the floc strength and the presence of modifiers like sodium carbonate and sodium silicate decreases the flocculation rate. The studies by GRANO[13] showed that the physical conditions for effective flotation of fine (<9 μm) and coarse (>53 μm) particles differ substantially, suggesting that a specific hydrodynamic environment will favor a high flotation rate for fine galena, which may be detrimental to the recovery of coarse galena, and vice versa. A fundamental flotation model was applied to quantifying differences in the flotation rate of the various size particles with impeller rotational speed. "
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