1、Effect of mechanical and chemical clay removals by hydrocycloneand dispersants on coal flotationWilliam J.Oats,Orhan Ozdemir,Anh V.Nguyen*School of Chemical Engineering,The University of Queensland Brisbane,Queensland 4072,Australiaa r t i c l ei n f oArticle history:Received 26 July 2009Accepted 9
2、December 2009Available online 13 January 2010Keywords:Coal flotationSlimeClayDispersantsHydrocycloneColloid stabilityDLVO forcesa b s t r a c tFine minerals,mostly clays,are known to have a detrimental effect on coal flotation.This paper focuseson the effect of mechanical and chemical removals of fi
3、ne minerals by hydrocyclone and dispersants oncoal flotation.The experimental results showed that the flotation recovery slightly increased from med-ium acidic to medium alkaline ranges.The flotation experiments carried out with dispersants at differentdosages showed that the dispersants did not enh
4、ance the flotation recovery significantly.However,theremoval of the fine fraction from the feed using a hydrocyclone significantly increased the flotationrecovery.The bubbleparticle attachment tests also indicated that the attachment time between an airbubble and the coal particles increased in the
5、presence of clay particles.These attachment time resultsclearly showed that the clay particles adversely affected the flotation of coal particles by covering the coalsurfaces which reduced the efficiency of bubblecoal attachment.An analysis based on the colloid stabil-ity theory showed that the clay
6、 coating was governed by the van der Waals attraction and that the dou-ble-layer interaction played a secondary role.It was also concluded that the best way to increase theflotation recovery in the presence of clays was to remove these fine minerals by mechanical means suchas hydrocylones.?2009 Else
7、vier Ltd.All rights reserved.1.IntroductionFine particles less than 10lm coat the surface of many valuableminerals,making the particles hydrophilic and preventing theadsorption of flotation collectors onto the mineral surfaces,whichhinders mineral separation.These fine particles also consume flo-tat
8、ion reagents and increase the operational costs.There have been many studies conducted to investigate thenegative effects caused by fine particles(Arnold and Aplan,1986a;Burdon et al.,1976;Celik et al.,1998,2002;Jowett et al.,1956;Mishra,1978;Quast et al.,2008;Xu et al.,2003).These stud-ies showed t
9、hat the slime coating of the mineral surface occurs dueto electrostatic attraction between opposite charged coarse andfine particles.For example,while there was no attraction betweenthe same charged fine and coarse galena particles,there was a sig-nificant loss on flotation recovery when oppositely
10、charged fineswere present in the system(Gaudin et al.,1960).It is explainedthat the fine clay particles are electrostatically attracted to the sur-face of coal particles and the attachment is heavily dependent onthe magnitude and sign of the zeta potentials of the coal particlesand the fines(Arnold
11、and Aplan,1986a;Xu et al.,2003).The effectof clay minerals on boron flotation was also specifically studied(Celik et al.,2002).The studies showed that while boron minerals(colemanite,ulexite,etc.)floated with both anionic and cationicsurfactants in the absence of clay,even as little as 1%of clay add
12、i-tion reduced the boron flotation recovery considerably(Celik et al.,2002).The effect of fine clay particles on several coal samples frommore hydrophobic to moderate hydrophobic was also the subjectof many studies(Jowett et al.,1956;Burdon et al.,1976;Mishra,1978;Arnold and Aplan,1986a,b;Quast et a
13、l.,2008).The resultsconfirmed that the presence of fine particles decreased the recov-ery and rate of coal flotation.Dispersants are widely used to modify the colloidal interactionsbetween particles by creating electrostatic and/or steric repulsionwhich counterbalances the contribution of the van de
14、r Waalsattraction to the total net force.These dispersants are mostly anio-nic polymers and adsorb on mineral surfaces,making them morenegative(Huynh et al.,2000).Classification methods such as cy-clones are more economical and efficient for separating fine parti-cles from the coarse minerals(Salter
15、 and Childs,1984;Greet andSmart,1997).Removing fine particles from coal samples by sievingor desliming with a hyrocyclone improved the coal flotation per-formance(Quast et al.,2008).The ultrasonic treatment to dispersethe clay particles from boron minerals also increased the flotationrecovery of the
16、 minerals and reduced the required collector dosage(Celik et al.,1998).In addition,some studies showed that tablingshould also be used for removing the fine particles(Burdon et al.,1976).0892-6875/$-see front matter?2009 Elsevier Ltd.All rights reserved.doi:10.1016/j.mineng.2009.12.002*Corresponding author.E-mail address:Anh.Nguyeneng.uq.edu.au(A.V.Nguyen).Minerals Engineering 23(2010)413419Contents lists available at ScienceDirectMinerals Engineeringjournal homepage: the coal industry,clay part
