An investigation of the effect of physical and chemical variables on bubble generation and coalescence in laboratory scale flotation cells

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dc.contributor Aalto-yliopisto fi
dc.contributor Aalto University en Grau, Rodrigo A. 2012-02-17T07:29:29Z 2012-02-17T07:29:29Z 2006-01-09
dc.identifier.isbn 951-22-7988-6
dc.identifier.issn 1795-0074
dc.description.abstract A new technique for measuring bubble size in laboratory scale flotation cells was developed. A method of sampling and photographing bubbles from a flotation cell was combined with modern methods of image processing and analysis. The technique is capable of sizing accurately a large number of bubbles by exposing a stream of bubbles to a progressive scan camera. The technique was used to study the effect of several physical and chemical variables on bubbles size in laboratory scale flotation cells. Three mechanically agitated Outokumpu flotation cells were used in the tests, the size of the cells being 50 dm3, 70 dm3 and 265 dm3, respectively. The last mentioned was especially designed and constructed for this study. The cells were operated under batch conditions. The hydrodynamic conditions prevailing in the cells were modified mainly by altering the impeller speed and aeration conditions, as well as the frother concentration. An extensive study of the effect of frother concentration on the bubbles generated in flotation cells was carried out. A series of common flotation frothers, DF-200, DF-250 and DF-1012, was chosen to test the effect of frothers on bubble coalescence and the bubble break-up process. The experimental tests revealed that bubble size strongly depends on frother concentration. With increasing frother concentration, the degree of bubble coalescence decreases, while at a particular frother concentration, known as the Critical Coalescence Concentration (CCC), bubble coalescence is totally hindered. The experimental results also indicate that frothers appear to affect the break-up process or bubble generation. While the DF-200 frother, characterized by much larger CCC values than DF-1012 and DF-250, has the ability to produce finer bubbles at concentrations exceeding the CCC value, the bubbles generated in the DF-1012 solutions at concentrations exceeding CCC are much larger. The aeration rate has a profound impact on bubble generation; bubble size increases with an increase of the air flow rate entering the flotation cell. The aeration rate seems to determine to a large extent the size, shape and behaviour of the aerated cavities formed behind the blades of the rotor of the cell. These gassed cavities appear to control the mechanism of bubble generation in a flotation cell. The formation and behaviour of aerated cavities behind the Outokumpu rotor was examined using a high-speed camera. While the maximum stable bubble diameter seems to characterize the bubble break-up process adequately, the Sauter mean bubble diameter and the number bubble mean diameter turned out not to be very sensitive to the changes in impeller speed. These two diameters are not always able to reveal adequately differences between bubble-size distributions. Since bubble coalescence can be entirely prevented in the cell at frother concentrations exceeding the CCC values, it was possible to assess the impact of two commercial rotor/stator mechanisms on bubble generation. With the aid of a new sensor developed for measuring continuously local gas velocity, a series of tests was conducted to study how efficiently the incoming air is dispersed throughout the volume of the cell by the rotor/stator mechanism. en
dc.format.extent 78, [app]
dc.format.mimetype application/pdf
dc.language.iso en en
dc.publisher Helsinki University of Technology en
dc.publisher Teknillinen korkeakoulu fi
dc.relation.ispartofseries Helsinki University of Technology doctoral theses in materials and earth sciences en
dc.relation.ispartofseries 4 en
dc.relation.haspart Grau, R. A., Heiskanen, K., 2002. Visual technique for measuring bubble size in flotation machines. Minerals Engineering 15 (7), 507-513.
dc.relation.haspart Grau, R. A., Heiskanen, K., 2003. Gas dispersion measurements in a flotation cell. Minerals Engineering 16 (11), 1081-1089.
dc.relation.haspart Grau, R. A., Laskowski, J. S., Heiskanen, K., 2005. Effect of frothers on bubble size. International Journal of Mineral Processing 76 (4), 225-233.
dc.relation.haspart Grau, R. A., Heiskanen, K., 2005. Bubble size distribution in laboratory scale flotation cells. Minerals Engineering 18 (12), 1164-1172.
dc.relation.haspart Rudolphy, L., Grau, R. A., Heiskanen, K., 2005. On-line sensor for measuring superficial gas velocity in laboratory scale flotation machines. In: Jameson G. (Ed.), Proceedings of the Centenary of Flotation Symposium. Australasian Institute of Mining and Metallurgy, Melbourne, pp. 573-580.
dc.relation.haspart Grau, R. A., Laskowski, J. S., 2005. Role of frothers in bubble generation and coalescence in a mechanical flotation cell. Canadian Journal of Chemical Engineering, accepted for publication.
dc.subject.other Materials science en
dc.subject.other Geoinformatics en
dc.title An investigation of the effect of physical and chemical variables on bubble generation and coalescence in laboratory scale flotation cells en
dc.type G5 Artikkeliväitöskirja fi
dc.description.version reviewed en
dc.contributor.department Department of Materials Science and Engineering en
dc.contributor.department Materiaalitekniikan osasto fi
dc.subject.keyword flotation en
dc.subject.keyword bubble size en
dc.subject.keyword gas dispersion en
dc.subject.keyword flotation frothers en
dc.subject.keyword critical coalescence concentration en
dc.identifier.urn urn:nbn:fi:tkk-006475
dc.type.dcmitype text en
dc.type.ontasot Väitöskirja (artikkeli) fi
dc.type.ontasot Doctoral dissertation (article-based) en
dc.contributor.lab Laboratory of Mechanical Process Technology and Recycling en
dc.contributor.lab Mekaaninen prosessi- ja kierrätystekniikka fi

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