《高等选矿学》课程教学资源（文献资料）From amine molecules adsorption to amine precipitate transport by bubbles - A potash ore flotation mechanism

Minerals Engineering 45 (2013) 170-179Contents lists available at SciVerse ScienceDirectMINERALSENGINEERINGMinerals EngineeringELSEVITERjournalhomepage:www.elsevier.com/locate/minengFrom amine molecules adsorption to amine precipitate transport by bubbles:A potash ore flotation mechanism *Janusz S. Laskowski*Norman B.Keevil Institute of MiningEngineering.University of British Columbia,Vancouver,BC, CanadINFOARTICLEABSIRACTArticle history:Recent investigations summarized in this review have been conveniently grouped into (i)those dealingReceived 3 November 2012with the mechanism of action of the reagents applied in the flotation of potash ores, and (ii) those focusedAccepted 11 February 2013on the flotation properties of salt-type minerals and explanation of the remarkable selectivity betweenfloatable sylvite, and non-floatable halite.This paper is confined to thefirst group.It is argued that in dis-cussing the mode of action of long-chain primary amines in the flotation of potash ores account must beThe paper is dedicated to the late Professotaken of the way in which these amines are applied by industry. Because they are water insoluble theyJan Lejaare melted by heating up to 70-90 °C and then they are dispersed in acidified aqueous solution, Onceadded to the flotation pulp,the hot amine dispersion rapidly cools down to a temperature far belowKeywords:the Krafft point.The rapid conversion from a hot emulsion to a cold precipitate is a very severe transfor-SylvitePotash oremation. Since nothing is known about the kinetics of these changes and phase instability only the labFlotationtests in which the adopted reagent preparation procedures closely follow the industrial practice havePotash ore flotationbeen considered in this review.Amines2013 Elsevier Ltd.All rights reservedPrecipitationContents1701.Introduction2.171Early research3.172Krafftpoint4173Electrical charge5.173Use of amines in commercial potash ore flotation1746.Amine precipitate in sylvite flotation1757.Molecular films.1768.The mechanism..9.176Frothersinpotashflotation17810.Summary178Acknowledgements178References1. Introductionnot considered until after Jeanprost (1928) showed that theflota-tionmustbeconducted ina saturated solution of suchminerals.Applying flotation to treat ores containing water-solublesalts-The minerals sylvite (KCl) and halite (NaCl), two major compo-as pointed out by Gaudin in his monograph (Gaudin, 1957)- wasnentsofthemostimportantpotashore-thesylviniteore-canbe separated by flotation that is carried out in a NaCl-KCl saturatedbrine.At20°C,1.450kgof theKCl-NaClsaturated solutioncon-* Based on 2010 Gaudin lecture which was presented at the SME Annual Meeting.tains about 0.300kg of NaCl, 0.150kg of KCl and 1kg of waterDenver, February 28, 2011.(Gaska et al., 1965). Thus the NaCI-KCI saturated brine is approxi-* Fax: +1 604 822 5599.mately6mol/Lsolution of thesetwo salts.TheNaClconcentrationE-mail address: jsi@apsc.ubc.ca0892-6875/$ - see front matter 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.mineng.2013.02.010

From amine molecules adsorption to amine precipitate transport by bubbles: A potash ore flotation mechanism q Janusz S. Laskowski ⇑ Norman B. Keevil Institute of Mining Engineering, University of British Columbia, Vancouver, BC, Canada article info Article history: Received 3 November 2012 Accepted 11 February 2013 The paper is dedicated to the late Professor Jan Leja Keywords: Sylvite Potash ore Flotation Potash ore flotation Amines Precipitation abstract Recent investigations summarized in this review have been conveniently grouped into (i) those dealing with the mechanism of action of the reagents applied in the flotation of potash ores, and (ii) those focused on the flotation properties of salt-type minerals and explanation of the remarkable selectivity between floatable sylvite, and non-floatable halite. This paper is confined to the first group. It is argued that in dis￾cussing the mode of action of long-chain primary amines in the flotation of potash ores account must be taken of the way in which these amines are applied by industry. Because they are water insoluble they are melted by heating up to 70–90 C and then they are dispersed in acidified aqueous solution. Once added to the flotation pulp, the hot amine dispersion rapidly cools down to a temperature far below the Krafft point. The rapid conversion from a hot emulsion to a cold precipitate is a very severe transfor￾mation. Since nothing is known about the kinetics of these changes and phase instability only the lab tests in which the adopted reagent preparation procedures closely follow the industrial practice have been considered in this review. 2013 Elsevier Ltd. All rights reserved. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 2. Early research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 3. Krafft point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 4. Electrical charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 5. Use of amines in commercial potash ore flotation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 6. Amine precipitate in sylvite flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 7. Molecular films. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 8. The mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 9. Frothers in potash flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 10. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 1. Introduction Applying flotation to treat ores containing water-soluble salts – as pointed out by Gaudin in his monograph (Gaudin, 1957) – was not considered until after Jeanprost (1928) showed that the flota￾tion must be conducted in a saturated solution of such minerals. The minerals sylvite (KCl) and halite (NaCl), two major compo￾nents of the most important potash ore – the sylvinite ore – can be separated by flotation that is carried out in a NaCl–KCl saturated brine. At 20 C, 1.450 kg of the KCl–NaCl saturated solution con￾tains about 0.300 kg of NaCl, 0.150 kg of KCl and 1 kg of water (Gaska et al., 1965). Thus the NaCl–KCl saturated brine is approxi￾mately 6 mol/L solution of these two salts. The NaCl concentration 0892-6875/$ - see front matter 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mineng.2013.02.010 q Based on 2010 Gaudin lecture which was presented at the SME Annual Meeting, Denver, February 28, 2011. ⇑ Fax: +1 604 822 5599. E-mail address: jsl@apsc.ubc.ca Minerals Engineering 45 (2013) 170–179 Contents lists available at SciVerse ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng

171JS. Laskowski/Minerals Engineering 45 (2013) 170-179in seawater is about 0.6 M, there is thus a huge difference in theelectrolyte concentrations between potash ore flotation pulpsand pulps in other flotation operations. Only now is it becomingHaliteapparent that dissimilarity between the potash ore flotation andother flotation systems results mostly from differences in the ionicstrength.This paper reviews recent advances made in understanding thenature of phenomena taking place in the flotation carried out inNacI+ KCl saturated brine, that is in the potash ore flotation pro-cess. The purpose of this paper is to draw a common threadthrough seemingly disparate pieces of evidence, and to reconcilevariousexperimentalresultsandvarioustheoriesputforwardinthe area of potash ore flotation.For the sake of discussion, the papers dealing with various as-pects of potash ore flotation have been grouped into:(i) Those which discuss the mechanism of action of long-chainflotation collectors in saturated brine that leads to a goodSylviteflotation of KCl in such an environment.(ii) Those studying the differences between flotation propertiesof various water soluble salts which make some of themfloatable while the others are not.The latter group will not be considered in this review, the read-Nater is referred to several excellent publications on this topic. RogersandSchulman(1957)andRogers(1957)werethefirsttoconsiderhydration as the phenomenon responsible for the surface proper-Kties of alkali halides. They pointed out that ions like Na, K, andCl-,etc.,arestronglyhydrated andthat thepropertiesof thesur-faces of the minerals containing such ions in water are to a largeCIextent determined by these ions' hydration. This model was fur-ther developed by Miller et al. (Hancer et al., 2001; Cao et al..Dodecylammonium ion2010:Cao et al..2011:Ozdemir et al.,2011).who were able toshow that hydration phenomena at salt crystal surfaces provide aFig.1. Schematic representation of the mechanism of collection of sylvite and lackgood explanation for the flotation properties of floatable sylviteof collection of halite by dodecylammonium ions (D.W. Fuerstenau and M.C.and non-floatable halite (advancing contact angle on KCl was mea-Fuerstenau, 1956).sured to be 7.9 ±0.5° while such an angle measured on NaCl wasO).ThedifferencesinthehydrationbetweenKclandNaClsurfacesis believed to affect the adsorption of flotation collectors on theseTable 1salts.Some important contributions in the area of potash ore flotationYearContributors2. Early research1937JE. Kirby1956D.W.Fuerstenau, M.C. Fuerstenau1957J. Rogers, J.H. SchulmanIt was not until the 1950s that the first detailed papers on the1951-1988R. Bachman,A Singewald, H. Schubertadsorption of aliphatic amines on halides were published by Fuer-1968RJ. Roman, M.C. Fuerstenau, D.C. Seidelstenau and Fuerstenau (1956) - papers that represent the begin-19771982J Leja, V.A. Arsentievning of scientific researchonthe flotation fundamentalsof1985D.A. Cormode1988V.A. Arsentiev, T.V. Dendyuk, S.L Gorlovskipotash ores. In this flotation process, two isomorphous minerals1982 -presentS.N.Titkov- sylvite and halite - are separated by flotation. The best separa-1990 -presentJD. Miller and co-workerstion between these minerals, which differ only in the cation, are1986 - presentJ.S. Laskowski and co-workersobtainedwithcationiccollectors.The only interpretation that makes sense (Gaudin, 1957)is thatthe ammonium ion fits in the place of potassium at the sylvite sur-However,a comparison of some fundamentalface but does not fit in the place of sodium at the halite surface.tionprocesses.correlations found in froth flotation, for example the relationshipFig.1 shows schematically themechanism proposed byFuerstenaubetweencollectorconcentrationandrecovery.forthecommonflo-and Fuerstenau (1956).Some of the benchmarks in the development of the potash oretationsystemsandthepotashoreflotationsystemisstunning.Itisknown that the recovery curve,plotted versus collector concentra-flotation process are listed in Table 1. While the author has triedtion, drops to zero when collector concentration approaches theto tabulate all important developments in this area, only those thatcritical micelle concentration. This is shown in Fig. 2.are consistent with the view presented in this paper will be dis-As Fig. 2 demonstrates, whenever the collector concentrationcussed further. The list begins with Kirby's patent (US Patentapproaches the critical micelle concentration, micelles appear in2,088,325), which introduced straight-chain primary amines intothe solution and flotation drops to zero. This is not surprising sincethe technology of potash ore flotation as a universal collector.micelles are colloidal hydrophilic entities and their accumulationMany ideas - especially in the early period of the process' devel-on the mineral surface must render such a surface hydrophilic.opmentweremoreorlessdirectlytransplantedfromotherflota-

in seawater is about 0.6 M, there is thus a huge difference in the electrolyte concentrations between potash ore flotation pulps and pulps in other flotation operations. Only now is it becoming apparent that dissimilarity between the potash ore flotation and other flotation systems results mostly from differences in the ionic strength. This paper reviews recent advances made in understanding the nature of phenomena taking place in the flotation carried out in NaCl + KCl saturated brine, that is in the potash ore flotation pro￾cess. The purpose of this paper is to draw a common thread through seemingly disparate pieces of evidence, and to reconcile various experimental results and various theories put forward in the area of potash ore flotation. For the sake of discussion, the papers dealing with various as￾pects of potash ore flotation have been grouped into: (i) Those which discuss the mechanism of action of long-chain flotation collectors in saturated brine that leads to a good flotation of KCl in such an environment. (ii) Those studying the differences between flotation properties of various water soluble salts which make some of them floatable while the others are not. The latter group will not be considered in this review, the read￾er is referred to several excellent publications on this topic. Rogers and Schulman (1957) and Rogers (1957) were the first to consider hydration as the phenomenon responsible for the surface proper￾ties of alkali halides. They pointed out that ions like Na+ , K+ , and Cl, etc., are strongly hydrated and that the properties of the sur￾faces of the minerals containing such ions in water are to a large extent determined by these ions’ hydration. This model was fur￾ther developed by Miller et al. (Hancer et al., 2001; Cao et al., 2010; Cao et al., 2011; Ozdemir et al., 2011), who were able to show that hydration phenomena at salt crystal surfaces provide a good explanation for the flotation properties of floatable sylvite and non-floatable halite (advancing contact angle on KCl was mea￾sured to be 7.9 ± 0.5 while such an angle measured on NaCl was 0). The differences in the hydration between KCl and NaCl surfaces is believed to affect the adsorption of flotation collectors on these salts. 2. Early research It was not until the 1950s that the first detailed papers on the adsorption of aliphatic amines on halides were published by Fuer￾stenau and Fuerstenau (1956) – papers that represent the begin￾ning of scientific research on the flotation fundamentals of potash ores. In this flotation process, two isomorphous minerals – sylvite and halite – are separated by flotation. The best separa￾tion between these minerals, which differ only in the cation, are obtained with cationic collectors. The only interpretation that makes sense (Gaudin, 1957) is that the ammonium ion fits in the place of potassium at the sylvite sur￾face but does not fit in the place of sodium at the halite surface. Fig. 1 shows schematically the mechanism proposed by Fuerstenau and Fuerstenau (1956). Some of the benchmarks in the development of the potash ore flotation process are listed in Table 1. While the author has tried to tabulate all important developments in this area, only those that are consistent with the view presented in this paper will be dis￾cussed further. The list begins with Kirby’s patent (US Patent 2,088,325), which introduced straight-chain primary amines into the technology of potash ore flotation as a universal collector. Many ideas – especially in the early period of the process’ devel￾opment were more or less directly transplanted from other flota￾tion processes. However, a comparison of some fundamental correlations found in froth flotation, for example the relationship between collector concentration and recovery, for the common flo￾tation systems and the potash ore flotation system is stunning. It is known that the recovery curve, plotted versus collector concentra￾tion, drops to zero when collector concentration approaches the critical micelle concentration. This is shown in Fig. 2. As Fig. 2 demonstrates, whenever the collector concentration approaches the critical micelle concentration, micelles appear in the solution and flotation drops to zero. This is not surprising since micelles are colloidal hydrophilic entities and their accumulation on the mineral surface must render such a surface hydrophilic. Fig. 1. Schematic representation of the mechanism of collection of sylvite and lack of collection of halite by dodecylammonium ions (D.W. Fuerstenau and M.C. Fuerstenau, 1956). Table 1 Some important contributions in the area of potash ore flotation. Year Contributors 1937 J.E. Kirby 1956 D.W. Fuerstenau, M.C. Fuerstenau 1957 J. Rogers, J.H. Schulman 1951–1988 R. Bachman, A. Singewald, H. Schubert 1968 R.J. Roman, M.C. Fuerstenau, D.C. Seidel 1977–1982 J. Leja, V.A. Arsentiev 1985 D.A. Cormode 1988 V.A. Arsentiev, T.V. Dendyuk, S.I. Gorlovski 1982 – present S.N. Titkov 1990 – present J.D. Miller and co-workers 1986 – present J.S. Laskowski and co-workers J.S. Laskowski / Minerals Engineering 45 (2013) 170–179 171

172J.S.Laskowski/MineralsEngineering45(2013)170-179CMC10-1100Distilledowater:Oe(%) 10250j6%Brine:4%BrineC142%Brine:8%BrineC12C10/10-P口-?2-6'5-4U-1Concentration (log C)Fig. 2. Effect of concentration of sodium alkyl-sulfonates on flotation of barite:empty circles, sodium tetradecyl sulfonate (C14): filled circles, sodium dodecylI1--10sulfonate (C12): empty squares, sodium decyl sulfonate (C10) Vertical arrows020406080100indicate the critical micelle concentrations for the three studied alkyl-sulfonates at40 -C.(Dobias, 1986),Right-hand side insert shows a micelleon solid surface.Temperature(C)Fig.5.Effectofelectrolyteconcentration on theKraftpointofdodecylammoniumchloride (Laskowskietal.,2007).100What is surprising is that this relationship - as shown by Romanet al. (1968) - is quite different in the potash flotation (Fig. 3).80Fig.3showsthattheflotationofsylvitecommenceswhentheainosianosoTetradecylsolubility limit of amineis exceeded. Together,Figs.2and 3oo:Dodecylindicate that critical micelle concentration (c.m.c.) should not be60confusedwiththesaturationconcentrationofthehydrated crystals(Cases andVillieras,1992).b40O3. Krafft point20Forionicsurfactants.thesolubilitycurveplottedasafunctionoftemperature reveals two large domains (Fig. 4). At temperaturesOdVbelow the Kraft point (Tk),the solubility curve describes the satu-010610610410-310-ration concentration of a hydrated crystal in equilibrium withmonomers (single surfactant molecules)in solution.At TTk.when the surfactant concentra-tion is increased, the monomers associate to form micellar aggre-gates; the concentration at which micelles first occur is referredto as a critical micelle concentration (cmc). In the three distinctSolubilityzones inFig.4distinctspeciesappear:inZoneIonlysinglesurfac-curvelamellarphasetant molecules (monomers): in Zone Il hydrated crystals in equilib-eLyotropicphasesrium with monomers; and in Zone Ill micelles in equilibrium withexagonalphasemonomers. At temperatures lower than the Krafft point, the solu-bility is too low for micellization. The Krafft point is also definednmasthetemperatureatwhich thesolubility curvereachesthe criti-cal micelle concentration;further increases in temperaturesharplyasymmetricmicellesenhancethesolubilityof thesurfactantduetotheformationofHydrated crystalsMicellarsolutionsphericalmicellesmicelles.ZAs this discussion reveals, the hydrated crystals which appear atAtemperature TTk.Fig.2demonstrates that flotation drops to zero whenSimplemolecules1thecollectorconcentrationapproachescmc,whileFig.3showsVthatsylviteflotationcommenceswhentheamine(collector)con-TkTemperature (deg C) The term "amine" stands in this publication for alkylamine with the number ofFig. 4. Schematic representation of the solubility of ionic surfactants versustemperature.carbonatomshigherthan12

What is surprising is that this relationship – as shown by Roman et al. (1968) – is quite different in the potash flotation (Fig. 3). Fig. 3 shows that the flotation of sylvite commences when the solubility limit of amine1 is exceeded. Together, Figs. 2 and 3 indicate that critical micelle concentration (c.m.c.) should not be confused with the saturation concentration of the hydrated crystals (Cases and Villieras, 1992). 3. Krafft point For ionic surfactants, the solubility curve plotted as a function of temperature reveals two large domains (Fig. 4). At temperatures below the Krafft point (TK), the solubility curve describes the satu￾ration concentration of a hydrated crystal in equilibrium with monomers (single surfactant molecules) in solution. At T TK, when the surfactant concentra￾tion is increased, the monomers associate to form micellar aggre￾gates; the concentration at which micelles first occur is referred to as a critical micelle concentration (cmc). In the three distinct zones in Fig. 4 distinct species appear: in Zone I only single surfac￾tant molecules (monomers); in Zone II hydrated crystals in equilib￾rium with monomers; and in Zone III micelles in equilibrium with monomers. At temperatures lower than the Krafft point, the solu￾bility is too low for micellization. The Krafft point is also defined as the temperature at which the solubility curve reaches the criti￾cal micelle concentration; further increases in temperature sharply enhance the solubility of the surfactant due to the formation of micelles. As this discussion reveals, the hydrated crystals which appear at temperature T TK. Fig. 2 demonstrates that flotation drops to zero when the collector concentration approaches cmc, while Fig. 3 shows that sylvite flotation commences when the amine (collector) con￾Fig. 5. Effect of electrolyte concentration on the Krafft point of dodecylammonium chloride (Laskowski et al., 2007). -6 -5 -4 -3 -2 -1 Concentration (log C) 0 50 100 Recovery (%) C14 C12 C10 CMC Fig. 2. Effect of concentration of sodium alkyl-sulfonates on flotation of barite: empty circles, sodium tetradecyl sulfonate (C14); filled circles, sodium dodecyl sulfonate (C12); empty squares, sodium decyl sulfonate (C10). Vertical arrows indicate the critical micelle concentrations for the three studied alkyl-sulfonates at 40 C. (Dobias, 1986). Right-hand side insert shows a micelle on solid surface. Fig. 3. Relationship between KCl recovery and amine addition (Roman et al., 1968). Fig. 4. Schematic representation of the solubility of ionic surfactants versus temperature. 1 The term ‘‘amine’’ stands in this publication for alkylamine with the number of carbon atoms higher than 12. 172 J.S. Laskowski / Minerals Engineering 45 (2013) 170–179

173JS.Laskowski/Minerals Engineering 45 (2013) 170-179centrationexceedsthesolubilitylimit.The difference between Figs. 2 and 3 suggest the obvious: thecolloidal species which appear in these two systems must havevery different properties, and a further discussion of these phe-nomena requires some knowledge of the Krafft point of long-chainamines.Additionally.theeffectofelectrolyteconcentrationontheamineKrafftpointmustalsobecharacterizedTheavailableinformationontheKrafftpointofaminesisratherlimited. The Krafft point values for dodecyl (C12) and octadecyl(C18)ammoniumchlorideswerereportedtobe26Cand56Crespectively (Brandrup and Immergut, 1975).For dodecyl ammo-nium chloride Dai and Laskowski (1991) provided a value of17 °C. Theoretic estimations (Laskowski, 1994) indicate that theKrafft point for amines should dramatically increase with brineconcentration (the term brine used in this text stands for theNaCl-KCl saturated brine at room temperature). Fig. 5 shows theeffectofbrineconcentrationontheKrafftpointofdodecylamineIt is 80C at 16% brine concentration (approximately1MsolutionFig. 6. NaCl (average size 280 μm) and KCI (average size 35 μm) particles inofNaCl-KCl).IfinconcentratedelectrolytesolutionsC12andC18saturated NaCl-KCI brine (Roman et al., 1968)aminesobservethesamerelationshipbetweenKrafftpointandchain length,then it can be expected that in a 1M solution ofNaCI-KCI the Krafft point for C18 amine exceeds 100C.This leadsto the conclusion that all commercial potash ore flotation plants,aswell as all lab flotation experiments, are carried out at tempera-tures much lower than the Krafft temperature of long-chain pri-5x10~MDDA·HCImary amines. Micelles do not exist in such systems. What will5appear in the pulp when amines precipitate are solid particles, hy-drated crystals.1x10-3M35x10M4.Electrical charge3.5x10-MAnother important contribution brought about in Roman et al.'s(1968) paper was evidence that the particles of sylvite and halitecarry an electrical charge. Postulation of the electrical charge onthe particles suspended in brine was considered a blasphemy at1x104M-1the time, but evidence for it was quite convincing. Roman et al.showed that while the suspensions of fine sylvite particles sus-Total ionic strength=2x10-3Mpended in their own brine were very stable,and the suspensions3of fine halite in their own brine were stable too, they both imme-981071112diately coagulated when mixed together (Fig. 6). The obviouspHexplanation was that these particles carried different electricalcharge.Somewhatlater,Milleretal.(1992)usedDopplerelectro-Fig, 7. Effect of pH and concentrationthe electrophoretic mobility of themphoresis and proved that while sylvite particles in brine carry neg-colloidal precipitate in aqueous solutions of dodecylamine (Laskowski et al., 1988)ative electrical charge, halite particles are charged positively.At that time it was already known (Castro et al. 1986: Laskow-Na'strongly interact with interfacial water molecules and stabilizeski et al., 1988) that the particles of the precipitating amine are alsothe interfacial water layer at the structure-maker Nacl surface.electrically charged. As Fig.7 demonstrates, colloidal amine parti-Consequently,octa-decyl amine (ODA)adsorption by the replace-clesare characterized by the clear iso-electricpoint which is situ-ment of interfacial of water molecules cannot take place. In theated at a pH ofapproximately11.Thus,theamineparticlesarecase of KCl with the larger cation, K',it is found that ODA adsorp-positivelycharged below pH 11 and negatively charged whention is possible by attachment of the positively charged polar headpH>11.group at the structure breaker KCl surface defects (Cao et al., 2010).These parallel but independent observations of electrical chargeHowever,whilethisexplainsthedifferencebetweengoodflotationof both sylvite and the precipitating amine,made it possible to ex-of KCI and poor flotation of NaCl it does not explain the correlationplain (Laskowski, 1994)the sylvite flotation curves published bybetween flotation response and surface charge of colloidal amineSchubert (1967, 1988) (Fig. 8). The analysis reveals that whileparticles shown in Fig. 8.KClfloatswithaminesatpH16 amines, solubility in brine converges to levelssalts is dictated bythe ability of respected cations and anionstobelow10-"mole/L.Thepoor solubilityof primary amines was alsoorganizethestructureof interfacial water.Small cationssuchas

centration exceeds the solubility limit. The difference between Figs. 2 and 3 suggest the obvious: the colloidal species which appear in these two systems must have very different properties, and a further discussion of these phe￾nomena requires some knowledge of the Krafft point of long-chain amines. Additionally, the effect of electrolyte concentration on the amine Krafft point must also be characterized. The available information on the Krafft point of amines is rather limited. The Krafft point values for dodecyl (C12) and octadecyl (C18) ammonium chlorides were reported to be 26 C and 56 C, respectively (Brandrup and Immergut, 1975). For dodecyl ammo￾nium chloride Dai and Laskowski (1991) provided a value of 17 C. Theoretic estimations (Laskowski, 1994) indicate that the Krafft point for amines should dramatically increase with brine concentration (the term brine used in this text stands for the NaCl–KCl saturated brine at room temperature). Fig. 5 shows the effect of brine concentration on the Krafft point of dodecylamine. It is 80 C at 16% brine concentration (approximately 1 M solution of NaCl–KCl). If in concentrated electrolyte solutions C12 and C18 amines observe the same relationship between Krafft point and chain length, then it can be expected that in a 1 M solution of NaCl–KCl the Krafft point for C18 amine exceeds 100 C. This leads to the conclusion that all commercial potash ore flotation plants, as well as all lab flotation experiments, are carried out at tempera￾tures much lower than the Krafft temperature of long-chain pri￾mary amines. Micelles do not exist in such systems. What will appear in the pulp when amines precipitate are solid particles, hy￾drated crystals. 4. Electrical charge Another important contribution brought about in Roman et al.’s (1968) paper was evidence that the particles of sylvite and halite carry an electrical charge. Postulation of the electrical charge on the particles suspended in brine was considered a blasphemy at the time, but evidence for it was quite convincing. Roman et al. showed that while the suspensions of fine sylvite particles sus￾pended in their own brine were very stable, and the suspensions of fine halite in their own brine were stable too, they both imme￾diately coagulated when mixed together (Fig. 6). The obvious explanation was that these particles carried different electrical charge. Somewhat later, Miller et al. (1992) used Doppler electro￾phoresis and proved that while sylvite particles in brine carry neg￾ative electrical charge, halite particles are charged positively. At that time it was already known (Castro et al., 1986; Laskow￾ski et al., 1988) that the particles of the precipitating amine are also electrically charged. As Fig. 7 demonstrates, colloidal amine parti￾cles are characterized by the clear iso-electric point which is situ￾ated at a pH of approximately 11. Thus, the amine particles are positively charged below pH 11 and negatively charged when pH > 11. These parallel but independent observations of electrical charge of both sylvite and the precipitating amine, made it possible to ex￾plain (Laskowski, 1994) the sylvite flotation curves published by Schubert (1967, 1988) (Fig. 8). The analysis reveals that while KCl floats with amines at pH 16 amines, solubility in brine converges to levels below 108 mole/L. The poor solubility of primary amines was also Fig. 6. NaCl (average size 280 lm) and KCl (average size 35 lm) particles in saturated NaCl–KCl brine (Roman et al., 1968). Fig. 7. Effect of pH and concentration on the electrophoretic mobility of the colloidal precipitate in aqueous solutions of dodecylamine (Laskowski et al., 1988). J.S. Laskowski / Minerals Engineering 45 (2013) 170–179 173

174J.S. Laskowski/Minerals Engineering 45 (2013) 170-179100treatmentwiththecationiccollector.Inaddition-intheflotationof coarse fractions - an extender oil is also utilized. A frother (e.g.0MIBC) is added just prior to the flotation cells (Strathdee et al.,KCI2007).6C126. Amine precipitate in sylvite flotation40Ci6!As demonstrated by Leja (1983)."in quiescent environment no20contact angle or pick-up of sylvite particleswasobserved even100afterdepositionofamine-alcoholpasteonthesurfaceoftheun-104stirred brine. However, after thorough stirring for a few minutes,80KCl particles were picked up and contact angle was developed onNaciKCl discs." The bubble/sylvite attachment was clearly possibleSwhen the collector was manually placed directly on the surfaceof the bubble. When a wire coated with the collector-alcohol pasteCi6 i40was placed in brine on the other hand, there was no bubble/sylvite"particle pick-up,even after hours of immersion. But as soon as theC1220probe was touched first to the captive bubble, and the latter wascontactedwithaKCldisc,contactangleimmediatelydevelopedI0These findings point toward adequate agitation as an important24681012step,withoutwhichthesurfactantsutilizedinpotashoreflotationpHare not ableto perform theirfunction.Since long-chain amines are insoluble in brine, this led to theFig. 8. The effect of pH on flotation of sylvite and halite with C12 and C16 primaryamines (Schubert, 1967).conclusion that the mechanism responsible for flotation in thisparticular case must be different from conventional flotation inwhich collector adsorption renders the treated mineral hydropho-evidenced by Rogers (1957).He observed that the surface tensionbic.Itwaspostulatedthatthecollectorinthepotashoreflotationmeasurements with saturated NaCl-KCI brine to which dodecy-pulpistransportedbybubbles.lammoniumchloridecrystals were added(equivalent ofTheeffectsdescribedbyLejawerequantifiedbyBurdukovaand2.26 × 10-4 mole/L) did not froth even after a week and surfaceLaskowski (2009). Their tests were designed to clarify how the pre-tension dropped only by a few mJ/m2cipitating amine particles function in a potash ore flotation system.The dosage of amines in industrial plants in Saskatchewan is inThe amine dispersion was placed either onto the surface of a bub-the range from 60 to 95 g/t (Strathdee et al., 1982) which corre-ble,whichwasthencontactedwithaKClplateandmeasurementsponds to approximately 10-mole/L, thus exceeding by far theofcontactanglefollowed,or the amine dispersion was placed ontoamine solubility limit. Before use the amines are melted by heatingthe surface of aKCl plate,which was then contacted witha bubblethem up to 70-90 C, and are then neutralized with hydrochloric orto measure the contact angle (Fig. 9). Special procedures had to beaceticacids.Thehot emulsion/dispersion isintroduced into theflo-developed for these tests since, in the former case, any previoustation pulp,which is at room temperature.Since this temperaturecontactof theKClplatewiththesolution/airinterfacewasto beismuchbelowtheKrafftpointoftheutilizedamines.precipitationtotallyprevented.Inthelattercasethebubblewasnottobecon-ensues.Accordingtoallreportedobservations,awhiteprecipitatetaminatedbypossiblesurfactantadsorption(SchreithoferandLas-appears immediately when the hot emulsion of amine is added tokowski,2006;Burdukova and Laskowski,2009:Laskowski,2010).thepotashflotationpulp,andthat it accumulatesonthesurfaceofIn 1995, Wang et al. reported (Wang et al., 1995) that frother.bubbles.depending on the way it is introduced into the pulp, may have aIn commercial plants, after crushing and mechanical deslimingstrong effect on potash oreflotation (this effect wasalso confirmedthe potash ore still requires the subsequent application of "blind-by other researchers, see for example Monte and Oliveira, 2004).ers" to depress residual slimes and conserve valuable collectorThe effect of thepresence of MiBC was also studied in the tests dis-(Arsentiev et al.,1988).Depressants (blinders) include: carboxy-cussed in this paper. Dodecyl amine was heated (70 C) and thenmethyl cellulose, guar gum, and starch, etc. This is followed bydispersed in a hot (70 °C) diluted HCl solution. In separate testsBAFig. 9. (A) DDA colloidal particles on the surface of the KCl, and (B) DDA colloidal particles on the surface of the bubble (Burdukova and Laskowski, 2009)

evidenced by Rogers (1957). He observed that the surface tension measurements with saturated NaCl–KCl brine to which dodecy￾lammonium chloride crystals were added (equivalent of 2.26 104 mole/L) did not froth even after a week and surface tension dropped only by a few mJ/m2 . The dosage of amines in industrial plants in Saskatchewan is in the range from 60 to 95 g/t (Strathdee et al., 1982) which corre￾sponds to approximately 104 mole/L, thus exceeding by far the amine solubility limit. Before use the amines are melted by heating them up to 70–90 C, and are then neutralized with hydrochloric or acetic acids. The hot emulsion/dispersion is introduced into the flo￾tation pulp, which is at room temperature. Since this temperature is much below the Krafft point of the utilized amines, precipitation ensues. According to all reported observations, a white precipitate appears immediately when the hot emulsion of amine is added to the potash flotation pulp, and that it accumulates on the surface of bubbles. In commercial plants, after crushing and mechanical desliming the potash ore still requires the subsequent application of ‘‘blind￾ers’’ to depress residual slimes and conserve valuable collector (Arsentiev et al., 1988). Depressants (blinders) include: carboxy￾methyl cellulose, guar gum, and starch, etc. This is followed by treatment with the cationic collector. In addition – in the flotation of coarse fractions – an extender oil is also utilized. A frother (e.g. MIBC) is added just prior to the flotation cells (Strathdee et al., 2007). 6. Amine precipitate in sylvite flotation As demonstrated by Leja (1983), ‘‘in quiescent environment no contact angle or pick-up of sylvite particles was observed even after deposition of amine-alcohol paste on the surface of the un￾stirred brine. However, after thorough stirring for a few minutes, KCl particles were picked up and contact angle was developed on KCl discs.’’ The bubble/sylvite attachment was clearly possible when the collector was manually placed directly on the surface of the bubble. When a wire coated with the collector-alcohol paste was placed in brine on the other hand, there was no bubble/sylvite particle pick-up, even after hours of immersion. But as soon as the probe was touched first to the captive bubble, and the latter was contacted with a KCl disc, contact angle immediately developed. These findings point toward adequate agitation as an important step, without which the surfactants utilized in potash ore flotation are not able to perform their function. Since long-chain amines are insoluble in brine, this led to the conclusion that the mechanism responsible for flotation in this particular case must be different from conventional flotation in which collector adsorption renders the treated mineral hydropho￾bic. It was postulated that the collector in the potash ore flotation pulp is transported by bubbles. The effects described by Leja were quantified by Burdukova and Laskowski (2009). Their tests were designed to clarify how the pre￾cipitating amine particles function in a potash ore flotation system. The amine dispersion was placed either onto the surface of a bub￾ble, which was then contacted with a KCl plate and measurement of contact angle followed, or the amine dispersion was placed onto the surface of a KCl plate, which was then contacted with a bubble to measure the contact angle (Fig. 9). Special procedures had to be developed for these tests since, in the former case, any previous contact of the KCl plate with the solution/air interface was to be totally prevented. In the latter case the bubble was not to be con￾taminated by possible surfactant adsorption (Schreithofer and Las￾kowski, 2006; Burdukova and Laskowski, 2009; Laskowski, 2010). In 1995, Wang et al. reported (Wang et al., 1995) that frother, depending on the way it is introduced into the pulp, may have a strong effect on potash ore flotation (this effect was also confirmed by other researchers, see for example Monte and Oliveira, 2004). The effect of the presence of MIBC was also studied in the tests dis￾cussed in this paper. Dodecyl amine was heated (70 C) and then dispersed in a hot (70 C) diluted HCl solution. In separate tests Fig. 8. The effect of pH on flotation of sylvite and halite with C12 and C16 primary amines (Schubert, 1967). Fig. 9. (A) DDA colloidal particles on the surface of the KCl, and (B) DDA colloidal particles on the surface of the bubble (Burdukova and Laskowski, 2009). 174 J.S. Laskowski / Minerals Engineering 45 (2013) 170–179

175J.S.Laskowski/Minerals Engineering 45 (2013) 170-17918%14 Amine on bubbles Amine + MIBC on bubbles16%aaaaeuoooas12Amine on Particles+Amine+MIBCon partilces14%NoAmineA81012%oananA.8010%88%6S6%44%242%0%005101520253035404550556065707580Amine onAmine + MIBCAmine +MIBCAmine onbubblesAdvancing Contact Angle (deg)particlesonparticleson bubblesFig.11.Standard deviation of advancing contact angle as a function of the locationFig. 10. Advancing contact angle measurements on KCI plates in NaCl-KCIof amine and the presence/absence of MIBC (Burdukova and Laskowski, 2009)saturated brine. The 1% amine dispersion was placed directly onto the surface ofthe capillary used to generate the bubble, or onto the surface of KCl plate(Burdukovaand Laskowski,2009).precipitate prepared with MIBC resembles ratherfine amorphousparticles, the precipitate without MIBC seems to be more crystal-MIBC was added to the hot HCI solution before the amine was dis-line. A more detailed study on the crystalline nature of such parti-persed in it.cles is, however, missing. Several experiments showed that whileThe results of these contact angle measurements are shown insuch amine particles easily attach to KCl plates, they do not attachFig.1o in theform of Gaussian distributions.It is worth noting thatto Nacl plates.the contact angle values exhibit a very high degree of scatter andthis necessitated up to 30 repeat measurements per condition toobtainarepresentativecontactangledistribution.Theresultsob-7.Molecularfilmstained with the use of amine fall more or less distinctly into twogroups. In one group,represented byfilled markers,the KCl surfaceAmphipathiccompounds,insolubleinwater,canformmolecu-was not very hydrophobic when the amine dispersion was placedlar films at the water/gas interface (Gaines, 1966), The stability ofon the KCl surface (mean contact angle was approximately 40°)monolayers depends on solubility;fatty acids form stablemono-and the surface was very heterogeneous.The other group,depictedlayers on waterinacidic solutions when theyare not ionized,whilewith unflled markers, showed the largest contact angle valueslong-chain amines form stable monolayers on water over alkaline(50-60°); in these tests the amine was placed onto the bubble be-pH range (Gaines,1982)Itwasreported thatwithlong-chainforecontactingitwithKClplate.Thepresenceof MIBCintheamineamines(e.g.C22amine)condensedmonolayersareformedunderclearlyincreased thehydrophobicityoftheKClplate,especiallyina wide range of conditions.Spreadingon concentrated salt solutionthose tests in which amine was deposited onto bubbles. As the left-is enhanced.mostcurveindicates,theKClplateinsaturatedbrineistosomeex-Arsentiev and Leja (1976) studied the monolayers of primarytenthydrophobic,afactfirstreportedbyHancer et al.(2001)amines(fromC12toC18)spreadandcompressedon saturatedsaltThis was further confirmed by Ozdemir et al. (2011).who weresolutions. The spreading of surfactants as films was carried outable to show that sylvite in its saturated brine is slightly hydropho-usingsolutionsofthesesurfactantsinhexane.Severalfindingsdis-bic(advancing contact angleon KCl was measured tobe7.9±0.5°).cussed in their paper deserve to be highlighted. The adhesion be-The mean contact angle values are not the only information thattween planar discs of KCl brought up from underneath and thecan be derived from the measured contact angle distributions. Asaminemolecular film were very strongthe adhesion betweenFig. 10 reveals and Fig. 11 summarizes, there is a significant differ-the Nacl discs and the film was about three times weakerence in the degree of spread of the results.The lowest standard(Fig. 13). The ability of a surfactant to adhere to a KCl disc de-deviations are obtained when the amine collector is present onpended to a great extent on the degree to which the surfactantthesurfaceofbubbles.Inthiscasetheresultingcollectorcoveragemolecules form a condensed film. With progressive compressionis apparently more even and uniform than when the collector isof the film (achieved using Langmuir balance), the adhesion forcesdeposited directly on the KCI surface. In the absence of MIBC,increasedtoamaximum.Inflotationsystems,thestructureoftheaminecolloidalparticlesprovidepatchyandunevensurfacecover-collectorfilmattheliquid/gasinterfaceisdeterminedbythestrucage.As rheologic tests demonstrate (Laskowski et al.,2008).theture of the surfactant molecule and the length of the hydrocarbonprecipitatingamineis better dispersed when MiBC is present inchain. Arsentiev and Leja reported no adhesion between the filmthe system.This was confirmed by direct measurements of the par-spread using the amines containing branch chains and the solidticle size distribution of the amine precipitate in brine, and by tur-KCl crystal. This provides strong corroborative evidence for Bach-bidity measurements of such disperse systems (Burdukova et al.,mann's postulate (Bachmann, 1951), that the flotation of KCl using2009). These later tests reveal that MIBC serves as a strong dispers-primary amines is due to a favorable correlation in the dimensionsing agent, affecting both the size and the morphology of the amineof theKcl crystallatticeandthequasicrystallinestructureoftheparticles,when it is added to the system at thesametime as thecondensed aminefilm.hot amine is dispersed in hot water.In 1983, 0'Brien et al. (1983) and Leja (1983) provided furtherFig.12 demonstrates that solid particles are presentin theexperimentalresultsregardingaminemolecularfilms.Sinceinflo-prepared amine dispersion. Furthermore, it reveals that while thetation particle-bubble collisions take place within milliseconds, the

MIBC was added to the hot HCl solution before the amine was dis￾persed in it. The results of these contact angle measurements are shown in Fig. 10 in the form of Gaussian distributions. It is worth noting that the contact angle values exhibit a very high degree of scatter and this necessitated up to 30 repeat measurements per condition to obtain a representative contact angle distribution. The results ob￾tained with the use of amine fall more or less distinctly into two groups. In one group, represented by filled markers, the KCl surface was not very hydrophobic when the amine dispersion was placed on the KCl surface (mean contact angle was approximately 40) and the surface was very heterogeneous. The other group, depicted with unfilled markers, showed the largest contact angle values (50–60); in these tests the amine was placed onto the bubble be￾fore contacting it with KCl plate. The presence of MIBC in the amine clearly increased the hydrophobicity of the KCl plate, especially in those tests in which amine was deposited onto bubbles. As the left￾most curve indicates, the KCl plate in saturated brine is to some ex￾tent hydrophobic, a fact first reported by Hancer et al. (2001). This was further confirmed by Ozdemir et al. (2011), who were able to show that sylvite in its saturated brine is slightly hydropho￾bic (advancing contact angle on KCl was measured to be 7.9 ± 0.5). The mean contact angle values are not the only information that can be derived from the measured contact angle distributions. As Fig. 10 reveals and Fig. 11 summarizes, there is a significant differ￾ence in the degree of spread of the results. The lowest standard deviations are obtained when the amine collector is present on the surface of bubbles. In this case the resulting collector coverage is apparently more even and uniform than when the collector is deposited directly on the KCl surface. In the absence of MIBC, amine colloidal particles provide patchy and uneven surface cover￾age. As rheologic tests demonstrate (Laskowski et al., 2008), the precipitating amine is better dispersed when MIBC is present in the system. This was confirmed by direct measurements of the par￾ticle size distribution of the amine precipitate in brine, and by tur￾bidity measurements of such disperse systems (Burdukova et al., 2009). These later tests reveal that MIBC serves as a strong dispers￾ing agent, affecting both the size and the morphology of the amine particles, when it is added to the system at the same time as the hot amine is dispersed in hot water. Fig. 12 demonstrates that solid particles are present in the prepared amine dispersion. Furthermore, it reveals that while the precipitate prepared with MIBC resembles rather fine amorphous particles, the precipitate without MIBC seems to be more crystal￾line. A more detailed study on the crystalline nature of such parti￾cles is, however, missing. Several experiments showed that while such amine particles easily attach to KCl plates, they do not attach to NaCl plates. 7. Molecular films Amphipathic compounds, insoluble in water, can form molecu￾lar films at the water/gas interface (Gaines, 1966). The stability of monolayers depends on solubility; fatty acids form stable mono￾layers on water in acidic solutions when they are not ionized, while long-chain amines form stable monolayers on water over alkaline pH range (Gaines, 1982). It was reported that with long-chain amines (e.g. C22 amine) condensed monolayers are formed under a wide range of conditions. Spreading on concentrated salt solution is enhanced. Arsentiev and Leja (1976) studied the monolayers of primary amines (from C12 to C18) spread and compressed on saturated salt solutions. The spreading of surfactants as films was carried out using solutions of these surfactants in hexane. Several findings dis￾cussed in their paper deserve to be highlighted. The adhesion be￾tween planar discs of KCl brought up from underneath and the amine molecular film were very strong; the adhesion between the NaCl discs and the film was about three times weaker (Fig. 13). The ability of a surfactant to adhere to a KCl disc de￾pended to a great extent on the degree to which the surfactant molecules form a condensed film. With progressive compression of the film (achieved using Langmuir balance), the adhesion forces increased to a maximum. In flotation systems, the structure of the collector film at the liquid/gas interface is determined by the struc￾ture of the surfactant molecule and the length of the hydrocarbon chain. Arsentiev and Leja reported no adhesion between the film spread using the amines containing branch chains and the solid KCl crystal. This provides strong corroborative evidence for Bach￾mann’s postulate (Bachmann, 1951), that the flotation of KCl using primary amines is due to a favorable correlation in the dimensions of the KCl crystal lattice and the quasicrystalline structure of the condensed amine film. In 1983, O’Brien et al. (1983) and Leja (1983) provided further experimental results regarding amine molecular films. Since in flo￾tation particle-bubble collisions take place within milliseconds, the Fig. 10. Advancing contact angle measurements on KCl plates in NaCl–KCl saturated brine. The 1% amine dispersion was placed directly onto the surface of the capillary used to generate the bubble, or onto the surface of KCl plate (Burdukova and Laskowski, 2009). Fig. 11. Standard deviation of advancing contact angle as a function of the location of amine and the presence/absence of MIBC (Burdukova and Laskowski, 2009). J.S. Laskowski / Minerals Engineering 45 (2013) 170–179 175

176J.S. Laskowski/Minerals Engineering 45 (2013) 170-179500micron500micronFig.12. Images of the DDA particlethe right: without MIBC (Burdukova et al.,2009)MNaCIKCFig. 13. Schematically adhesion of the amine film to either NaCl crystal or KCI crystal (Arsentiev and Leja, 1976)kinetics of the studied phenomena largely determine whetherfast and efficient in the presence of a co-surfactant (e.g. frother).these sub-processes are or are not important in the flotation. Init is not so in its absence (Arsentiev and Leja, 1976).The appear-spreadingratemeasurements,itwasshownthatwhilethespread-anceof anaminemolecularfilmonthebubblesconvertsthesebubbles into "active bubbles," which easily pick up KCI particles.ing rates on saturated salt solutions were negligible for pure long-chain amines, these rates increase dramatically when the aminesIn the proposed mode of the action of amines in potash ore flo-are mixed with alcohols (e.g. hexanol). The tested flotation fro-tation, the precipitating amine coats bubbles but also attaches tothers, such as MIBC and DF-250, behave similarly to hexanol. TheKCl particles (Burdukova and Laskowski, 2009).Theoutcome isvery different in these two cases. While the amine coating bubblesspreading rates for C16-C18 amines mixed with hexanol were intherangefrom300to400mm/s,which-whenthesizeofthebub-startsspreadingintomolecularfilmthatactivatesthebubbleswithbles in flotation systems is considered -should be quite sufficientregard to their ability to attach to KCl surfaces, such spreading isfor the spreading to play an important role in the potash flotationimpossibleinthecaseofamineparticlesattachedtoKClsurfacesAs Fig.10 demonstrates,the KCI particles attaching to the"active"system.bubbles (bubbles with amine molecular films) become very hydro-phobic,buttheKClparticlescoatedbytheprecipitatingamineare8.Themechanismnot.Theproposedmechanism stronglydependsontheabilityoftheprecipitatingamine to quickly spread at the liquid/gas inter-In this chapter the author has endeavored to reconcile variousface into a molecular film.This depends on the presence of a co-groups offacts, some established, accepted principles, others ten-surfactant, such as a flotation frother. If the frother is mixed withtative. The basis for the proposed reconciliation is the way thatthe amine at the stage when the amine is dispersed in a hot, acid-the amines are utilized in commercial potash ore flotation pants.ified aqueous solution, the spreading of amine into a molecularIn industrial practice, the long-chain amines, since they arefilm is dramatically enhanced. Therefore, incorporation of theinsoluble in water, are melted by heating up to 70-90°C. Theyfrother into the amine-frother combination increases the propor-are then neutralized with hydrochloric (or acetic) acid and such ation of the amine which acts as an active component in the potashhot emulsion/dispersion is introduced into the flotation pulporeflotationprocess.whichisatroomtemperature,thetemperaturemuchlowerthantheKrafftpoint of theutilized long-chainamine.Asaresult,a9. Frothers in potash flotationwhiteprecipitateimmediatelyappearsandthefineparticlesoftheprecipitatingaminecoatthesurfaceofbubbles.Theaminepar-ticles also attach to the KCl particles. The amine deposited at theOn a practical level, it is of interest to point out how the pro-liquid/gas interfacestarts spreadinginto amolecularfilm.Thisposed mechanism might beused to furtherimprovethepotashmechanism is schematically shown in Fig. 14. While spreading isoreflotationprocess

kinetics of the studied phenomena largely determine whether these sub-processes are or are not important in the flotation. In spreading rate measurements, it was shown that while the spread￾ing rates on saturated salt solutions were negligible for pure long￾chain amines, these rates increase dramatically when the amines are mixed with alcohols (e.g. hexanol). The tested flotation fro￾thers, such as MIBC and DF-250, behave similarly to hexanol. The spreading rates for C16–C18 amines mixed with hexanol were in the range from 300 to 400 mm/s, which – when the size of the bub￾bles in flotation systems is considered – should be quite sufficient for the spreading to play an important role in the potash flotation system. 8. The mechanism In this chapter the author has endeavored to reconcile various groups of facts, some established, accepted principles, others ten￾tative. The basis for the proposed reconciliation is the way that the amines are utilized in commercial potash ore flotation pants. In industrial practice, the long-chain amines, since they are insoluble in water, are melted by heating up to 70–90 C. They are then neutralized with hydrochloric (or acetic) acid and such a hot emulsion/dispersion is introduced into the flotation pulp which is at room temperature, the temperature much lower than the Krafft point of the utilized long-chain amine. As a result, a white precipitate immediately appears and the fine particles of the precipitating amine coat the surface of bubbles. The amine par￾ticles also attach to the KCl particles. The amine deposited at the liquid/gas interface starts spreading into a molecular film. This mechanism is schematically shown in Fig. 14. While spreading is fast and efficient in the presence of a co-surfactant (e.g. frother), it is not so in its absence (Arsentiev and Leja, 1976). The appear￾ance of an amine molecular film on the bubbles converts these bubbles into ‘‘active bubbles,’’ which easily pick up KCl particles. In the proposed mode of the action of amines in potash ore flo￾tation, the precipitating amine coats bubbles but also attaches to KCl particles (Burdukova and Laskowski, 2009). The outcome is very different in these two cases. While the amine coating bubbles starts spreading into molecular film that activates the bubbles with regard to their ability to attach to KCl surfaces, such spreading is impossible in the case of amine particles attached to KCl surfaces. As Fig. 10 demonstrates, the KCl particles attaching to the ‘‘active’’ bubbles (bubbles with amine molecular films) become very hydro￾phobic, but the KCl particles coated by the precipitating amine are not. The proposed mechanism strongly depends on the ability of the precipitating amine to quickly spread at the liquid/gas inter￾face into a molecular film. This depends on the presence of a co￾surfactant, such as a flotation frother. If the frother is mixed with the amine at the stage when the amine is dispersed in a hot, acid￾ified aqueous solution, the spreading of amine into a molecular film is dramatically enhanced. Therefore, incorporation of the frother into the amine-frother combination increases the propor￾tion of the amine which acts as an active component in the potash ore flotation process. 9. Frothers in potash flotation On a practical level, it is of interest to point out how the pro￾posed mechanism might be used to further improve the potash ore flotation process. Fig. 12. Images of the DDA particles precipitating in a rapidly cooled dispersion. On the left: with MIBC; on the right: without MIBC (Burdukova et al., 2009). Fig. 13. Schematically adhesion of the amine film to either NaCl crystal or KCl crystal (Arsentiev and Leja, 1976). 176 J.S. Laskowski / Minerals Engineering 45 (2013) 170–179

177J.S.Laskowski/MineralsEngineering45 (2013)170-179LAMINEMELTING[70-90Centigrade)COOOOOODISPERSIONINHOTACIDICSOLUTIONPRECIPITATIONIN PULPATROOMTEMPERATUREFig. 14. Schematic dispersion of amine and its introduction to the flotation pulp, spreadingoftheamineintomolecularfilmonthesurfaceofbubblesfollowedbytheattachment of KCI particles to such active bubbles.The flotation process commonly requires various flotation re-2.5agents, not only collectors but also frothers and various modifiers.The frothers are used to make dispersion of air into fine bubblesaaeaeespossible, to stabilize the froth to some extent, and to facilitateDthe particle-to-bubble attachment,,as postulated by Lejaand2口Distilled waterSchulman in their penetration theory (Leja and Schulman, 1954).A50%saturated brineVarious reagents utilized in potash ore flotation are added to theO100%saturatedbrinepulp in the following order: depressants (blinders), amine collec-1.5tor, and frother (commonly MIBC) just prior to the flotation cells.In spite of the very important differencesbetween potash oreflo-tation and conventional flotation processes, flotation technologyas used in thepotash ore flotation was derived from its ore flota-tion sibling. The use of the frother is a typical example.But if it is used as in any other flotation operation, then the0.5question arises whether the frother is needed in brine to enhanceproductionoffinebubbles.As Fig. 15 demonstrates, the use of a frother (e.g. MIBC) is abso-10lutely necessary in distilled water (or, in general, in aqueous solu-2040600tions of a low ionic strength). The bubbles coalesce when theyConcentration (ppm)collide in the cell and MIBC is needed to stabilize them against coa-lescence. At concentrations exceeding the critical coalescence con-Fig 15.Effect of MIBC and electrolyte concentration on bubble size in an open-topcentration (c.c.c.), which is approximately 10 ppm for MIBC, theLeeds flotation cell (Laskowski et al., 2003).bubbles generated in a flotation cell do not coalesce. Under suchconditions, it is possible to produce fine bubbles that are essential(+0.8 mm) fraction is separately conditioned not only with aminein the flotation process. Fig. 15 also shows that in brine (and also inbut also with extender oil (ESSO904,a distilled refinery bottom-50% brine),the bubbles are quite stable and do not coalesce even indistillate, is commonly used by the Potash Corporation of Saskatch-the absence of frother. Evidently,a frother is not needed in potashoreflotation to enhance production of fine bubbles.There isquiteaewan). In the paper presented at the 24th International Minerallargenumber of papers inwhichprevention of bubblecoalescenceProcessingCongressinBeijing(Laskowskietal.,2oo8),thePcsLanigan potash ore crushed below1mm was used.The results ofwasstudiedinelectrolytesolutions;thistopicisoutsidethescopeof the present paper and will not be discussed further.theadditional labbench flotation tests,carried outtofurtherexamine the effect of the way of the collector and frother prepara-Since coarse concentrate from potash oreflotation can be soldtion and addition, are given in Tables 2 and 3. When the Armeento the fertilizer industry without compaction, it has a special value.HTD (from AKZO Nobel) aqueous dispersion is prepared in theThe ore is therefore not extensively comminuted, and the coarse

The flotation process commonly requires various flotation re￾agents, not only collectors but also frothers and various modifiers. The frothers are used to make dispersion of air into fine bubbles possible, to stabilize the froth to some extent, and to facilitate the particle-to-bubble attachment, as postulated by Leja and Schulman in their penetration theory (Leja and Schulman, 1954). Various reagents utilized in potash ore flotation are added to the pulp in the following order: depressants (blinders), amine collec￾tor, and frother (commonly MIBC) just prior to the flotation cells. In spite of the very important differences between potash ore flo￾tation and conventional flotation processes, flotation technology as used in the potash ore flotation was derived from its ore flota￾tion sibling. The use of the frother is a typical example. But if it is used as in any other flotation operation, then the question arises whether the frother is needed in brine to enhance production of fine bubbles. As Fig. 15 demonstrates, the use of a frother (e.g. MIBC) is abso￾lutely necessary in distilled water (or, in general, in aqueous solu￾tions of a low ionic strength). The bubbles coalesce when they collide in the cell and MIBC is needed to stabilize them against coa￾lescence. At concentrations exceeding the critical coalescence con￾centration (c.c.c.), which is approximately 10 ppm for MIBC, the bubbles generated in a flotation cell do not coalesce. Under such conditions, it is possible to produce fine bubbles that are essential in the flotation process. Fig. 15 also shows that in brine (and also in 50% brine), the bubbles are quite stable and do not coalesce even in the absence of frother. Evidently, a frother is not needed in potash ore flotation to enhance production of fine bubbles. There is quite a large number of papers in which prevention of bubble coalescence was studied in electrolyte solutions; this topic is outside the scope of the present paper and will not be discussed further. Since coarse concentrate from potash ore flotation can be sold to the fertilizer industry without compaction, it has a special value. The ore is therefore not extensively comminuted, and the coarse (+0.8 mm) fraction is separately conditioned not only with amine but also with extender oil (ESSO 904, a distilled refinery bottom￾distillate, is commonly used by the Potash Corporation of Saskatch￾ewan). In the paper presented at the 24th International Mineral Processing Congress in Beijing (Laskowski et al., 2008), the PCS Lanigan potash ore crushed below 1 mm was used. The results of the additional lab bench flotation tests, carried out to further examine the effect of the way of the collector and frother prepara￾tion and addition, are given in Tables 2 and 3. When the Armeen HTD (from AKZO Nobel) aqueous dispersion is prepared in the Fig. 14. Schematic dispersion of amine and its introduction to the flotation pulp, spreading of the amine into molecular film on the surface of bubbles followed by the attachment of KCl particles to such active bubbles. Fig. 15. Effect of MIBC and electrolyte concentration on bubble size in an open-top Leeds flotation cell (Laskowski et al., 2003). J.S. Laskowski / Minerals Engineering 45 (2013) 170–179 177

178J.S. Laskowski/Minerals Engineering 45 (2013) 170-179Table 2still satisfactory for the flotation of fine particles,these conditionsEffect of the way MIBC is utilized on the flotation of -1 mm potash ore fraction. Testare obviously not good enough for the flotation of the coarse par-conditions: Addition of 300 g/t CMC was followed by the introduction of 100 g/t ofticles. The flotation of the coarse fraction strongly depends onArmeen HTD and 50 g/t of MIBC either separately or as a combination (WI stands forthe proportion of amine which appears in the flotation system inwater insoluble minerals).its active form (on the surface of bubbles), These results imply thatMethodAssayTailingsConcentratethecoarsefractionsofpotashore,whichtodayarefloatedwiththeGrade (%)Recovery (%)Grade (%)Loss (%)addition of not only aminebut also of extender oil,could be floated8.996.986.313.7SeparateKCIusing the same amine and frother but prepared as a singleWI0.416.21.383.8combination.1_4.0CombinedKCI94.196.0WI0.624.975.110. SummaryWhile advances in experimental techniques for studying sur-Table 3face chemistryeffects and theuse of these techniques in examiningEffect of the way MIBC is utilized in rougher and scavenger flotation of potash ore.thephenomenaaccompanyingflotationof solublesaltsarewellTest conditions: Addition of 300 g/t CMC was followed by the separate introduction ofdocumentedthetopicofthepreparationofreagentsthatareused100 g/t of Armeen HTD and 50 g/t of MIBC in rougher flotation. In the scavengerintheseexperimentsisshamefullyavoided.Thesilentassumptionflotation 50 g/t of Armeen HTD and 35 g/t of MIBC were either added as a combinationseems to be that this topic is not different from similar studies inor separately (WI stands for water insoluble minerals).other areas and does not need any special attention. But thisTailingsFlows.AssayRougher conc.Scavenger conc.assumption is totally baseless and it is important to realize thatGradeRecoveryGradeRecovery GradeLossthere are some fundamental differences between the conditions(%) (%)(%)(%)(%)(%) of commercial potash flotation and the most lab bench flotationASeparate additionCombined additiontests reported in literature.KCI80.096.77.95.698.114.3Since long-chain amines used in potash ore flotation as collec-WI0.524.00.53.91.772.1tors are water-insoluble, in commercial practice, to improve its0handling. the amine is melted at 70-90 °C before dispersion inKCI98.716.598.080.92.619.4hot acidified water. Once added to the flotation pulp, the hot amineWI0.423.60.50.81.475.5dispersion rapidly cools down to a temperature far below the Kafftpoint.All reported observations reveal that a white precipitateimmediately appears wen the hot amine dispersion is added to100-the potash ore flotation pulp. The rapid conversion from a hotXOemulsiontoacoldprecipitateisaveryseveretransformationbutcombinenothing is known about the kinetics of these changes. As we80-% Osshowed it (Burdukova and Laskowski, 2009)the precipitatingamine coats bubbles, but can also attach to KCl particles. In the60 -presence of co-surfactants (e.g. frothers), the amine spreads intoa molecular film at the liquid/gas interface, activating bubbles.Such active bubbles easily pick up KCl particles.40-separateThe proportion between the active form of amine (the part thatspreads into a molecular film on bubbles)and the non-active form&20-(the part that attaches directly to KCl particles)depends ontheTway the amine and frother (co-surfactant) are utilized. Evidence0is presented that this proportion is particularly important for flota-tion of coarse sylvite particles.00.20.40.60.81.21Particle size, mmAcknowledgementsFig.16. Comparison of KCI size-by size recoveries in the flotation of the-1 mmThis work has been supported by grants from the Natural Sci-potash ore fraction (Laskowski et al., 2008).ences and Engineering Research Council of Canada,the Potash Cor-poration of Saskatchewan,AKzO Nobel, Agrium Potash Inc.,andstandard way at 70 C and used at room temperature, the KClIMC Kalium.recoveries in batch flotation tests are very different depending onThe research reported emanates from the papers and theses ofwhether the collector and frother are used separately or in combi-many graduate students and post-docs of the University of Britishnation(86.3%and96.0%,respectively).IftherougherflotationisColumbia: Ms. Elena A. Alonso, Dr. Elizaveta Burdukova-Forbes, Dr.followed by a scavenger flotation in which the collector and frotherMarek Pawlik, Mr. Carlos Perucca, Dr.X.M. Yuan and Dr. Qun Wang.are added separately,the overall recovery improves from 80.9% toExtensivediscussions with Dr.GraemeStrathdee are gratefully83.6%, thus only by 2.6%. When the rougher flotation is followed byacknowledged. Special thanks go to Ms. Sally Finora for her friendlythe scavenger flotation with the use of the amine-MIBC combina-help with figures, and to Dr. Kornel Laskowski for the final lan-tion, the overall KCl recovery increases by 14.3 % (Table 2)guage adjustment. The paper is dedicated to the late ProfessorAs Fig. 16 reveals, the difference in KCl recovery in the flotationJan Leja.experiments with either"combined" or"separate"use of ArmeenHTD and MIBC results from the much better flotation of coarse par-ticles in the tests with the Armeen HTD-MIBC combination. TheReferencesflotation of coarse particles is much more sensitive to the hydro-phobicity of the particles than in the flotation of relatively finepar-Arsentiev, V.A., Leja, J., 1976. Interaction of alkali halides with insoluble films ofticles (Trahar, 1981). While conditions far from the optimum arefatty amines and acids. In: Kerker, M. (Ed.), Colloid Interface Sci. 5, 251-270

standard way at 70 C and used at room temperature, the KCl recoveries in batch flotation tests are very different depending on whether the collector and frother are used separately or in combi￾nation (86.3% and 96.0%, respectively). If the rougher flotation is followed by a scavenger flotation in which the collector and frother are added separately, the overall recovery improves from 80.9% to 83.6%, thus only by 2.6%. When the rougher flotation is followed by the scavenger flotation with the use of the amine-MIBC combina￾tion, the overall KCl recovery increases by 14.3 % (Table 2). As Fig. 16 reveals, the difference in KCl recovery in the flotation experiments with either ‘‘combined’’ or ‘‘separate’’ use of Armeen HTD and MIBC results from the much better flotation of coarse par￾ticles in the tests with the Armeen HTD–MIBC combination. The flotation of coarse particles is much more sensitive to the hydro￾phobicity of the particles than in the flotation of relatively finepar￾ticles (Trahar, 1981). While conditions far from the optimum are still satisfactory for the flotation of fine particles, these conditions are obviously not good enough for the flotation of the coarse par￾ticles. The flotation of the coarse fraction strongly depends on the proportion of amine which appears in the flotation system in its active form (on the surface of bubbles). These results imply that the coarse fractions of potash ore, which today are floated with the addition of not only amine but also of extender oil, could be floated using the same amine and frother but prepared as a single combination. 10. Summary While advances in experimental techniques for studying sur￾face chemistry effects and the use of these techniques in examining the phenomena accompanying flotation of soluble salts are well documented the topic of the preparation of reagents that are used in these experiments is shamefully avoided. The silent assumption seems to be that this topic is not different from similar studies in other areas and does not need any special attention. But this assumption is totally baseless and it is important to realize that there are some fundamental differences between the conditions of commercial potash flotation and the most lab bench flotation tests reported in literature. Since long-chain amines used in potash ore flotation as collec￾tors are water-insoluble, in commercial practice, to improve its handling, the amine is melted at 70–90 C before dispersion in hot acidified water. Once added to the flotation pulp, the hot amine dispersion rapidly cools down to a temperature far below the Kafft point. All reported observations reveal that a white precipitate immediately appears wen the hot amine dispersion is added to the potash ore flotation pulp. The rapid conversion from a hot emulsion to a cold precipitate is a very severe transformation but nothing is known about the kinetics of these changes. As we showed it (Burdukova and Laskowski, 2009)the precipitating amine coats bubbles, but can also attach to KCl particles. In the presence of co-surfactants (e.g. frothers), the amine spreads into a molecular film at the liquid/gas interface, activating bubbles. Such active bubbles easily pick up KCl particles. The proportion between the active form of amine (the part that spreads into a molecular film on bubbles) and the non-active form (the part that attaches directly to KCl particles) depends on the way the amine and frother (co-surfactant) are utilized. Evidence is presented that this proportion is particularly important for flota￾tion of coarse sylvite particles. Acknowledgements This work has been supported by grants from the Natural Sci￾ences and Engineering Research Council of Canada, the Potash Cor￾poration of Saskatchewan, AKZO Nobel, Agrium Potash Inc., and IMC Kalium. The research reported emanates from the papers and theses of many graduate students and post-docs of the University of British Columbia: Ms. Elena A. Alonso, Dr. Elizaveta Burdukova-Forbes, Dr. Marek Pawlik, Mr. Carlos Perucca, Dr.X.M. Yuan and Dr. Qun Wang. Extensive discussions with Dr. Graeme Strathdee are gratefully acknowledged. Special thanks go to Ms. Sally Finora for her friendly help with figures, and to Dr. Kornel Laskowski for the final lan￾guage adjustment. The paper is dedicated to the late Professor Jan Leja. References Arsentiev, V.A., Leja, J., 1976. Interaction of alkali halides with insoluble films of fatty amines and acids. In: Kerker, M. (Ed.). Colloid Interface Sci. 5, 251–270. Table 2 Effect of the way MIBC is utilized on the flotation of 1 mm potash ore fraction. Test conditions: Addition of 300 g/t CMC was followed by the introduction of 100 g/t of Armeen HTD and 50 g/t of MIBC either separately or as a combination (WI stands for water insoluble minerals). Method Assay Concentrate Tailings Grade (%) Recovery (%) Grade (%) Loss (%) Separate KCl 96.9 86.3 8.9 13.7 WI 0.4 16.2 1.3 83.8 Combined KCl 94.1 96.0 3.3 4.0 WI 0.6 24.9 1.5 75.1 Table 3 Effect of the way MIBC is utilized in rougher and scavenger flotation of potash ore. Test conditions: Addition of 300 g/t CMC was followed by the separate introduction of 100 g/t of Armeen HTD and 50 g/t of MIBC in rougher flotation. In the scavenger flotation 50 g/t of Armeen HTD and 35 g/t of MIBC were either added as a combination or separately (WI stands for water insoluble minerals). Flows. Assay Rougher conc. Scavenger conc. Tailings Grade (%) Recovery (%) Grade (%) Recovery (%) Grade (%) Loss (%) A Separate addition Combined addition KCl 98.1 80.0 96.7 14.3 7.9 5.6 WI 0.5 24.0 0.5 3.9 1.7 72.1 B KCl 98.0 80.9 98.7 2.6 19.4 16.5 WI 0.4 23.6 0.5 0.8 1.4 75.5 0 0.2 0.4 0.6 0.8 1 1.2 Particle size, mm 0 20 40 60 80 100 Size recovery, % combine separate Fig. 16. Comparison of KCl size-by size recoveries in the flotation of the 1 mm potash ore fraction (Laskowski et al., 2008). 178 J.S. Laskowski / Minerals Engineering 45 (2013) 170–179

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