Metalurgia

Int. J. Miner. Process. 59 Ž2000. 25–43 www.elsevier.nlrlocaterijminpro

A parametric study of froth stability and its effect on column flotation of fine particles
D. Tao ) , G.H. Luttrell, R.-H. Yoon
Center for Coal and Minerals Processing, Virginia Polytechnic Institute and State UniÕersity, Blacksburg, VA 24061-0258, USA Received 12 March 1999; received in revised form 7 July 1999;accepted 7 July 1999

Abstract Laboratory flotation tests have been conducted to examine the effect of froth stability on the column flotation of finely pulverized coal. It has been demonstrated that the upgrading of coal in a flotation column can be significantly improved when froth stability is properly controlled through the manipulation of appropriate variables such as gas flow rate Ž Vg ., washwater flow rate Ž Vw ., froth height, wash water addition point, and feed solid concentration. Increases in wash water flow rate and gas flow rate promoted froth stability, resulting in higher combustible recovery, but possibly higher ash recovery as well. The optimum rates were determined to be 2 and 0.3 cmrs for Vg and Vw , respectively. The specific influence of wash water flow rate on waterrecovery was found to be closely related to how the frother dosage was maintained. Coal particles could stabilize or destabilize the froth, depending on their size and concentration in the cell. Those in y100 mesh fraction destabilized froth at lower concentrations and stabilized it at higher concentrations while micronized particles always showed froth-breaking power. The froth profiles of solidcontent and ash content were established at varying wash water flow rates and wash water addition points, from which it was concluded that froth cleaning occurred primarily at the pulp–froth interface and drainage above the wash water addition point. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: coal; column flotation; entrainment; froth properties; surfactants

) Correspondingauthor. Present address: Department of Mining Engineering, 234E MMRB, University of Kentucky, Lexington, KY 40506-0107, USA. Tel.: q 1-606-257-2953; Fax: q 1-606-323-1962; E-mail: dtao@engr.uky.edu

0301-7516r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 1 - 7 5 1 6 Ž 9 9 . 0 0 0 3 3 - 2

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D. Tao et al.r Int. J. Miner. Process. 59 (2000) 25–43

1.Introduction It has long been realized that the behavior of the froth phase is important in determining flotation performance. Tomlinson and Fleming Ž1965. and Feteris et al. Ž1987. showed that the flotation rate constant is directly proportional to the probability that a particle survives the cleaning action of the froth zone and reports to the froth product. Yianatos et al. Ž1988. reported that theseparation efficiency of column flotation depends on froth depth. Bisshop and White Ž1976. found the strong dependence on the froth residence time of the amount of drainage of hydrophilic particles from the froth. It is generally accepted that a froth of proper stability is essential for the achievement of good grade and high recovery. From the study of two-phase column froths, Finch et al.Ž1989. concluded that wash water can stabilize the froth providing bias rate J b ) 0.1 cmrs. Work with several minerals ŽKlassen and Mokrousov, 1963; Moys, 1989. has shown that an increase in gas rate would result in more stable froth and higher water recovery. Engelbrecht and Woodburn Ž1975. and Feteris et al. Ž1987. have demonstrated that froth stability is dependent on the height Ždepth. of the frothzone. Froth would eventually collapse with increasing height due to liquid film thinning by drainage. Mineral particles have been reported to show pronounced effects on froth stability. Szatkowski and Freyburger Ž1985. observed that fine quartz particles rendered bubbles to be more resistant to coalescence and promoted the production of the stable froth. Livshits and Dudenkov Ž1965. believed...