1、翻译原文 Flotation behaviour of ne particles with respect to contact angleD. Chipfunhua, M. Zanina, S. Granoba Ian Wark Research Institute, ARC Special Research Centre for Particle and Material Interfaces, University of South Australia,Mawson Lakes, SA 5095, Australiab Institute for Mineral and Energy R
2、esources, University of Adelaide, Santos Petroleum Building, Level 3, Adelaide, SA 5005, AustraliaAbstract The flotation behaviour of methylated quartz particles of different size, but within the size range from 0.2 to 50 _m,and varying contact angle, was probed in a mechanical flotation cell. Resul
3、ts suggest that particles of a given sizeneed to possess a minimum critical contact angle (_crit) for flotation to occur. This behaviour is shown not to be solelydependent on fine particles having lower collision efficiency with bubbles, but rather due to a combination of lowcollision efficiency and
4、 particles not having enough kinetic energy at collision with bubbles to form the three phaseline of contact and initiate the attachment process. In the particle size range investigated, the critical contact angleincreases with a decrease in particle size.Keywords: Flotation; Critical contact angle;
5、 Fine particles1. IntroductionIt has long been established that fine particles (particle diameter10 _m) exhibit low flotation rate and recovery (Traharand Warren, 1976), with the best flotation rate and recoveryoccurring in the 10100 _m particle size range (Sutherlandand Wark, 1955). The low recover
6、y of fine particles is oftenattributed to their low mass and inertia that leads to low probabilityof particle colliding with bubbles (Schulze et al., 1989;Weber and Paddock, 1983) as fine particles follow bubble fluidstreamlines instead of colliding with the bubble. The other, but less explored and
7、discussed reason for thelow floatability of fine particles is that they possess insufficientkinetic energy (due to low mass) to displace the thin water filmbetween the colliding particle and bubble and form the threephase line of contact. This school of thought assumes that forbubble and particle to
8、 attach, the particle must possess minimumkinetic energy to be able to cause the thinning of theliquid film to critical rupture thickness and subsequent formationand expansion of the three phase line of contact (TPLC)(Hewitt et al., 1993). The foregoing suggests that the problemsof fine particles fl
9、otation are both kinetic and thermodynamicin nature. Scheludko et al. (1976) derived the only theoretical modelfor attachment of fine particles to bubbles. In deriving thismodel, Scheludko et al. (1976) assumed that after collision, kinetic energy is equal to, or more than, the energy requiredto thi
10、n, form and expand the three phase line of contact. Atequilibrium, the kinetic energy balances the forces that resistthe thinning and formation of the three phase line of contact.By balancing these forces, a minimum particle diameter forflotation was calculated as a function of particle contact angl
11、e.The lower the contact angle, the higher is the minimum particlesize for attachment to occur (Scheludko et al., 1976), whichalso implies that the flotation of particles of a given size can only occur if the particles attain a certain minimum criticalcontact angl Validation of the Scheludko model wi
12、th experimental data has been hampered by lack of flotation data for fine particles(Drelich and Miller, 1992). The model is strictly validfor particles 12 _m in size, and is premised on the accuracyand validity of the magnitude of the line tension value (Crawford and Ralston, 1988; Drelich and Mille
13、r, 1992). Thevalue of the line tension is largely debatable and difficultto determine, hence the introduction of pseudo line ten- sion (Drelich and Miller, 1992), which takes into consideration particle inhomogeneity, surface roughness and general nonideality of conditions in real flotation systems.
14、 In a previous publication (Chipfunhu et al., 2011) poor agreement was found between experimental results and theoretical predictions when employing the values of the line tension given in Scheludko et al. (1976). However, when validated using the pseudo line tension as suggested by Drelich and Mill
15、er (1992), good agreement was found between the experimental data and the theoretical predictions over a broader particle size range (Chipfunhu et al., 2011).Other experimental work published to date also supports the existence of a critical contact angle below which flotation does not occur (Crawfo
16、rd and Ralston, 1988; Gontijo et al., 2007; Miettinen, 2007). After floating fine methylated quartz particles of size 3 _m (d50) in both a mechanically agitated Rushton cell and a quiescent Hallimond tube, Miettinen (2007) found that a contact angle of about 60 needed to be attained before flotation could commence.In this paper, evidence that points to the poor floatability of fine particles as being mainly due to the fact that t
