Separation of Organic Dyes from Water by Colloidal Gas Aphrons

TSINGHUA SCIENCE AND TECHNOLOGYISSN1007-0214olume 7, Number 1, February 2002Separation of Organic dves from Water by colloidalGas aphronsHUANG Yingyi(黄颖怡), WANG Yundong(王运东), DAI Youyuan(戴猷元)tate Key Laboratory of Solvent Extraction, Department of Chemical EngineeringTsinghua University, Beijing 100084, ChinaAbstract: Colloidal gas aphrons (CGAs are micron-sized gas bubbles produced by stirring surfactantsolutions at high speed. A single CGa dispersed in water is composed of a gaseous inner core, surrounded bya double water-soapy layer. CGAs have large interfacial area per unit volume and exhibit relatively hightable in flotatof organic dyes from water using CGAs. The experimental results show that the flotation process may followfour mechanisms, i. e., ion coupling of the oppositely charged species of the surfactant forming the CGA andthe organic dye, reactions between CGA and the organic dye, ion-dye complex adsorbed on the surface ofCGAs,and hydrophilic or hydrophobic characteristics of the organic dyes.Key words: colloidal gas aphrons (CGAs ) flotation: organic dye: surfactantIntroductionsuspensions for the removal of heavy metals fromthe aqueous phase has been reported 33. Hashim etColloidal gas aphrons (CGAs) are dispersions of[4.5 removed yeast cells and fine cellulose fibersvery small microbubbles (usually of diameters in Roy et al. J removed organic dyes, Jauregi andmedium.Sebba [1 first reported colloidal gas protein recovery. Sebba l fley[s applied CGAs tothe range of 25-125 um)distributed in an aqueohas described numerousaphrons in 1971. Colloidal gas aphrons are gasother applications of CG As. In this paper, Cgasbubbles encapsulated in a soapy film, but are quite have been used to separate organic dyes,i.edifferent from conventional air bubbles and soap methyl blue, sunset yellow, methyl orangebubbles. These bubbles show colloidal features. methylene blue, and reactive brilliant blue fromThe dispersions contain up to 50%-65% volume water. Separation mechanisms have beenof gas phase, but the viscosity of the suspension proposednd its flOwaracteristicse to waterwhich enables them to be pumped from one1 Experimentallocation to anotherDue to the special properties of CGAs, they have1.1 Materials and methodsbeen used in many areas of separation processes. CGA suspensions were generated using a cationicSubramaniam 2 reported the application of CGA in surfacthexadecvltrimethyl ammoniumclarification of suspensions. The use of Cga br中国煤化工 nic surfactant( sodiumdoCNMHG SDBS ), andReceived: 2001-03-15d:2001-08-16Supported by" 985"Project of Environment Science methyl blue, sunset yellow, methyl orange,methylene blue, and reactive brilliant blue wereUniversity and the National Natural Science used as solutes. The structures of these five dyess+shina (Nos. 29676021 and 29836130) are as follows兴并 To whependence should be addressedHUANG Yingyi(黄颖怡)etal: Separation of Organic Dyes from Water47(1)Methyl bluedetermine the ultraviolet (UV) absorbency. Thepassage of CGa suspension increased the overallSO,Nadilution in the case of CGa flotation was properlytaken into account in determining the concentrationof the dye in the sample and the percentage(2) Sunset vellowremoval of the original dye solution.column(3)Methyl orange一N(CH3)2Surfactant(4)Methylene blueCACHabaN(5) Reactive brilliant blueig. I Flotation experimental set-upSO3Na1. 4 AnalysiO3CH2CH2OSO3NaThe UV absorbency of these dye samples wason a diode array UV-VisibleSpectrophotometer(HP 8452). Size distributionsof the CGa suspension created by the generator1.2 CGA preparationwere determined using a Laser Particle SizeAnalyzer Malvern 2601). To analyze theSebba first reported a method for CGAinteraction between CGa and dyes, infraredgeneration. Most investigators now adopt thespectral analyzer (FTIR 8200) was used. Differentimproved apparatus, which was also suggested byfunctional groups have diffeSebballo] in 1985. The CGA generator used in thispeang of peaks or producing ostudy is a 1-L stirred vessel with four baffles and aon the spectra may indicate whether there are somefour-blade Rushton turbine. Stirrer speed is up toreactions7000 r/min. With this kind of arrangement, I Lsurfactant solution can be converted to CGAs 2 Results and discussionontaining over 60% gas volume in a few seconds2. 1 Flotation of methyl blue1.3 Experimental procedure of flotation usingCGAsFlotation experiments were performed on thenegatively charged methyl blue dye in the columnThe entire experimental setup used for CG\ Expe riments can be divided into two partsflotation of the synthetic dyes is shown in Fig. 1Figure 2 shows the flotation of methyl blueThe surfactant reservoir for Cga was filled withusing CGa generated by SDBS and HTAB atHTAB. SDBS or Tween 20 at differentdifThe initial concentrationconcentrations. The flotation column was filled中国煤化工0.0625mmol/1th the dye solution to be treated. The CGasuspension was injected into the column using aCN MHGoduced from HTAB ofperistaltic pump at the designed flow rate. Thedifferent concentrations and sDbs of differentely The Cga floCGA suspension was allowed to rise in the column fed to the column was maintained at 30 mL/minfor 15 min. The total volume of the solution wasolume fed to themeasuredFAsxenus samples were collected from column is 900 mL. The results presented in fig. 2the columner each run and were analyzed toshow that the percentage removal of CGa fromTsinghua Science and Technology, February 2002,7(1): 46-51HTAB is better than the percentage removal of film, and screen some HTA. So the flotationcga from SDbs, and atefficiency decreases.concentration (CMC), 90% of methyl blue wasremoved by CGa from HTAB as 80% of methylblue was removed by CGa from SDBS. At firstseparation efficiency increased with increasingconcentration of surfactants, when thereached CMC. theefficiency was the highest Then it decreased withthe concentration of surfactants. CMC is a criticalvalue. When the concentration of surfactantreached that value, the hydrophobic tails of thesurfactant will cluster together inside the structureth the hydrophilic heads exposedform entities called micelles. As micelles areFig2 Flotation of methyl blue upon treatment withHTAB CGAs and SDBS CGAs: F=30 mL/formed. the electronic characteristic of CGAmin: V=0.9 L; Co=0. 0625 mmol. Lchanges greatly. Electronic potential gradientsdecrease because of micelles, and the separationefficiency also decreases. It was found that whenGa from HTAB passed through, insolubleproducts with the color of initial solution formed a- G SDBS-OHTABthe top of the liquid column and the flocculationproduced in the column rose up. But in theflotation using CGA from SDBS, no flocculationwas found. The formation of a thick blue coloredproduct at the top of the surface of the liquid witha clear liquid beneath, indicated the efficiency ofion flotation. Production of the flocculationFig3 Flotation of methyl blue at different initialindicated that there were reactions between CGaconcentration upon treatment with HTABfrom hTAB and methyl blue.CGAs and SDBS CGAs: F=30 mL/min: V=Figure 3 shows the flotation of methyl blue at0.9 L: C(HTAB)=0mol·Lt;Cdifferent original methyl blue concentrations using(SDBS)=1.43mmol·LCGa generated by HTAB and sdbs at Cmc2.2 Flotation of methylene blueEfficiency of methyl blue removal with CGAsgenerated from HTAB was better than that with Methylene blue is a positively charged dye.CGAs generated from SDBS. The flotation reached Figure 4 shows the flotation experiments on 0.13a peak at the initial methyl blue concentration of mmol/ L methylene blue with CGas generated0. 0625 mmol/L with CGAs generated from SDBS. from HTAB and SDBS, respectively, at differentAs is well known, surfactant has hydrophobic surfactant concentrations. The result shows thatheads as well as hydrophilic heads. Methyl blue is about 40% of methylene blue was removed aftera kind of organic dye that has complex organic passing 0. 9 L of CGa generated from SDBS. Instructure. At very low concentration, a little this case, flotation with CG as generated fromincrease of the dye concentration means that more surfactant of opposite electric charge surfactantorganic structure can enter the hydrophobic heads. SDBS has better separation performanceortant factor that influences Flciency is highest at the critical micellflotation is electronic characteristic. As the dye corconcentration increases, there will be moreTHE中国煤化工 B and sdbs. CaballeroCNMHGe concentration of thenegatively charged ions in the water. Flotationed tor the production of CGAs canefficiency using CGAs generated from an anionic influence the process of flotation. It can influencesurfactant SDBS will decrease. These ions could not only the quantity of surfactant added to thealso influence CGAs generated from a cationic column but also the stability of the colloidal gassurfactantHH*tE These negatively charged ions aphrons. So we can get highest floating rate usingcould press the soap film of CGAs, enter into that CGa from CMC surfactants. Compared toHUANG Yingyi(黄颖怡)etal: Separation of Organic Dyes from Waterflotation experiments of methyl blue, there was no with hydrophilic characteristics. According to theTheompercentage removal is much lower than that of HTAB would have better flotation efficiency thanthat the experimental results fit the gure 6 showse ion couplingtr SDBO HTABsunset yello, well. The initial concentration of0.117mmol/Flocculation and insoluble product were producedbrilliant blue with CGAs generated from H1A8'cas in the flotation of methyl blue and reactivO- SDBSFig4 Removal of methylene blue using HTAB CGAsand SDBS CGAs: F=30 mL/min: V=0.9LC=0.132. 3 Flotation of reactive brilliant blueReactive brilliant blue has much lower solubility inFig 6 Flotation of sunset yellow using HTAB CGAswater than all the other dyes used in this study. Itnd SDBS CGAs: Ca=0. 117 mmol.L F=is more hydrophobic. But this kind of dye, like30 mL/min: V=0.9Lmethyl blue, has functional group of--SO3 Na2. 5 Flotation of methyl orangeCGAs generated from cationic, anionic, and nonionic surfactants were investigated. The During the flotation with CGAs generated fromlocculation was produced during the flotation HTAB, insoluble product and flocculation wereprocess using CGA generated from HTAB. Figure produced. Figure 7 shows that 92% of the methyl5 shows that flotation with CGAs generated from orange dye was removed with CGAs generatedHTAB has much higher separation efficiency than from HTAB while there was almost no removal ofany other two surfactants. Tween 20 is a non-ionic methyl orange with CGAs generated from HTABrfactant. Reactive brilliant blue is hydrophobicSo the flotation with CGAs generated from Tween20 has slightly higher percentage of removal. Thetr hTABflotation mechanism thus depends on the reaction-aH SDBSwith CGAs and the hydrophilic or hydrophobiccharacteristics of organic dyC(mmol L)A HTAB-O- SDBSFig 7 Flotation of methyl orange using HTAB CGAsnd SDBS CGAs: Ca=0. 15 mmol .L F=30C/mg·LymL/ min: V=0.9L2IV凵中国煤化工 flotatFig5 Removal of reactive brilliant blue using HTAB MCNMHGunge, and sunset yellowCGAs, Tween 20 CGAs and SDBS CGAs: Care all hydrophilic organic dyes with sulfonic acid082 mmolL F-30 mL/ming: V=0.9L groups. When these three dyes were treated with2.4 Flotation of sunset yellowCGAs generated from HTAB, the separation布京数据efficiency increased with the total volume of CGasSunset yea negatively charged organic dye introduced to the flotation column, as shown inTsinghua Science and Technology, February 2002,7(1): 46-51Fig. 8. It does not mean that the larger volume the analyzed using infrared spectral analyzer (FTIRhigher separation efficiency. The volume of CGa 8200). Infrared spectra showed that there werecan not be increased infinitely. At the first stage, shifts of peaks. From Figs. 9-11, we can findwith the larger volume of CGA, the greater area those peaks attributed to sulfonic acid groups incan be used to flotation. As the volume of CGa flocculation's spectra, moving to some lower waveincreases, water entrained to column by CGa also numbers. Shifts of these peaks were not veryincreases. Concentration of ion will decreasesignificant. This shows that hydrogen bond existsFloating electric potential of CGA will decreasebetIt means thateparation efficiency will no longer increase with during flotation of dyes with sulfonic acid groupsthe Cgas volume. To get the highest separation using CGAs generated from HTAB, althoughefficiency, we must find a proper volume of CgA. there is no salt produced, there is ion-surfactantcomplex formed bet ween the ammonium ion of the-o- Sunset yellosurfactant and the sulfonic acid group in the dye.亠 Meth] blueFrom the ion-surfactant complex it can beconcluded that flotation process is related to thesurface adsorption and electric characteristic ofCGA and solution. Zhu Dezhi et al. 12 reportedthat the ability of adsorption of CGa and thefloating electric potential decreases when theconcentration of solution increases, Fig 12Fig 8 Effect of total CGA volume used in flotationCa(methyl orange)=0. 150 mmol.L ICa(sunset yellow )=0. 117 mmol.LCo(methyl blue )=0.0625 mmol. L2.7 Effect of sulfonic acid group number onflotation efficiency3431.y3261.440003502000The sulfonic acid group number for sunset yellowmethyl orange, and methyl blue is one, two, andthree, respectively. When these three dyes weretreated with CGAFig.9 Infrared spectra of flocculation produced duringflotation of methyl blueflocculation and insoluble materials werea, HTAB; b, methyl blue; c, flocculation producedproduced. Table 1 lists the removed mole numberflotation of methyl blueof dyes for these three dyes. More sulfonic acidgroups lowered the flotation efficiencyTable 1 Effect of sulfonic acid group numberon flotation efficiencyNumber ofMole number4388⊥Ordyulforemove14196Methyl blSunset yellow0.1940X0Methyl orangeWave number(cmNote: C:=0.9 mmol/L; V-0.9 L: F=30 mL/min;H中国煤化工Co(sunset yellow )=0. 117 mmol/Liof flocculation produceCo(methyl orange)=0. 15 mmol/ICNMHGmethyl orangeCo(methyl blue)=0. 0625 mmol/L.a,HTAB; b, flocculation produced during flotationand surfactants, flocculation produced duringFrom the experiments and infrared spectrumflotation万数据 nts of methyl blue, methylanalysis, it can be seen that there exist fourorange, and sunset yellow were collected andmechanisms during the Cga flotation process ofHUANG Yingyi(黄颖怡)etal: Separation of Organic Dyes from Water1the Cga flotation process. During the flotationCGAs generated from HTAB. Infrared spectrumanalysis shows that this flocculation is an ion-surfactant complex between ammonium andsulfonic acidL00NWave number (cm)Co initial concentration of organic dye, mmol/C. surfactant concentration, mmol/LFig 11 Infrared spectra of flocculation producedF volume flow rate of CGAs. mL/ minduring flotation of sunset yellowV total volume of cgas added to the column, Ia, HTAB; b, flocculation produced during flotationE flotation efficiency defined as E=(C+-Ct)/Cowhere C, is the terminal concentration of dye, mmol/LReferences-o- Methyl blue-c- Sunset yellow-t Methyl orange[1 Sebba F. Microfoams--An unexploited colloidstem. Colloid. Surf. Sci., 1971,35(4):643[2 Subramaniam M B, Blakebrough N, Hashim M AClarification of suspensions by colloidal gas aphrons.Chem. Technol. Biotechnol., 1990, 48: 41-60[3 Cabezon L M, Caballero M, Perez-BustanmantA, Coflotation separation for the determination ofheavy metals in water using colloidal gas aphronsSci. Technot1491-1500.Fig. 12 Flotation of sulfonic dye at different initial[41 Hashim M A, Sengupta B, Suvramaniam M Bconcentration using HTAB CGAs: Cs=0. 9nvestigationsthe flotation of yeast cellmmol.L F=30 mL/min V=0.9Iby colloidal gas aphron (CGA) depersionsBiose paration, 1995, 5(3): 167-173organic dyes. First, if the surfactant used to formIpta B S. The application ofthe cga has an opposite electric charge with theolloidal gas aphrons in the recovery of fine celluloseorganic dye, there is an ion coupling between thefibres from paper mill wastewater. BiresourceCGA and the organic dye. Secondly, reactionsTechnology,1998,64:199-204between CGa and the organic dye willoccur aorganic dyes from wastewater by using collidal gaform a flocculation or ion-dye complex if theaphrons. Sepn. Sci. Technol.,1992, 27(5):573opposite charged surfactant is used to separat588organic dye. Thirdly, the formed ion-dye comple[7 Jauregi P, Varley J. Colloidal gas aphrons: A noveladsorbs on the surface of CGLastlyapproach to protein recovery. Biotechnol. Bioeng.1998,59(4):471-488hydrophilic or hydrophobic characteristics of the [81 Noble M J, Varley J. Colloidal gas aphrons as aorganic dyes is another factor for a sufficientential technique for protein recovery. Jubileeseparation process. The flotation process usingResearch Event, Nottingham, UK, 1997:873-876CGA may follow the above four mechanisms or at [9] Sebba F. Foams and Biliquid Foams. UK: Wileyleast one of thenChichester, 1987[10 Sebba F. An improved generator for micron-sized3 Conclusionsbubbles. Chemistry and Industry,1985: 91CGAs can be used to effectively separate organicdyes from water. Up to 92% of organic dyes withTHS中国煤化工 ez-BustamenteJ A. StudiesCNMHGSes: A comparison withsulfonic acid groups, e. g, methyl blue, methylonal technique. Sepn. Sci. Technol., 1989orange, and sunset yellow, can be removed from24(98.10):629-640aqueous solutions with CGAs generated from the [12] Zhu Dezhi, Wu Shusen, Tian Yongwang,et alInterfacial electricalproperties and interfacialcationic surfactant, HTAB. Experimental resultsadsorption properties of CGA. East Chihow tha万亦数掘 pling of the oppositely chargedUniversity of Science and Technology, 1995,21surfactants with organic dyes is the mechanism of06.(in Chinese