International Journal of Mining Science and Technology 23 (2013) 249–253

Contents lists available at SciVerse ScienceDirect

International Journal of Mining Science and Technology

journal homepage: www.elsevier .com/locate / i jmst

Flotation and adsorption of quaternary ammonium salts collectors on kaoliniteof different particle size

Jiang Hao a,⇑, Liu Guorong a, Hu Yuehua a, Xu Longhua b, Yu Yawen a, Xie Zhen a, Chen Haochuan a

a School of Resources Processing and Bioengineering, Central South University, Changsha 410083, Chinab Key Laboratory of Solid Waste Treatment and Resource Recycle of Ministry of Education, Southwest University of Science and Technology, Mianyang 621010, China

a r t i c l e i n f o

Article history:Received 28 July 2012Received in revised form 15 August 2012Accepted 20 September 2012Available online 3 May 2013

Keywords:KaoliniteParticle sizeQuaternary ammonium saltsFlotationAdsorption

2095-2686/$ - see front matter � 2013 Published byhttp://dx.doi.org/10.1016/j.ijmst.2013.04.011

⇑ Corresponding author. Tel.: +86 731 88830204.E-mail address: jianghao-1@126.com (H. Jiang).

a b s t r a c t

The flotation behaviors of decyltrimethylammonium (103C), dodecyltrimethylammonium chloride(DTAC), tetradecyltrimethylammonium chloride (TTAC) and cetyltrimethylammonium chloride (CTAC)on kaolinite of different particle size fraction were studied. The adsorbed amount and adsorption iso-therms of collectors on kaolinite were determined for painstaking investigation into the adsorption ofquaternary amines at kaolinite–water interface by ultraviolet spectrophotometer methods. The flotationresults show that the flotation recovery of kaolinite of different particle fraction increases with anincrease in pH when 103C, DTAC, TTAC and CTAC are used as collectors. As the concentration of collectorsincreases, the flotation recovery increases. Particle size of kaolinite has a strong effect on flotation. Theflotation recovery of fine kaolinite decreases with the carbon chain of quaternary ammonium salts collec-tors increasing, while coarse kaolinite is on the contrary. The adsorbed amount tests and adsorption iso-therms show that adsorbed amount increases when the particle size of kaolinite increases or when thecarbon chain length of quaternary ammonium salts increases. Within the range of flotation collector con-centration, the longer the hydrocarbon chain, the more probable to be absolutely adsorbed by fine kao-linite particles and then the lower the collector concentration in the bulk, which leds to lower flotationrecovery.

� 2013 Published by Elsevier B.V. on behalf of China University of Mining & Technology.

1. Introduction

Most of the bauxite in China is of diasporic characteristics. A un-ique undesirable feature of Chinese diasporic ores is its low A12O3

to SiO2 mass ratio. Flotation to remove silica from diasporic bauxiteis commonly used method to raise A12O3 to SiO2 mass ratio.Reverse flotation, with the characteristics of low collector con-sumption, low concentration rate and easy to achieve selectivecoarse grinding-reverse flotation, is becoming a hot topic of desilic-onization of bauxite by flotation [1].

Kaolinite is layer silicate mineral and the dominant silica-bearingmineral of Chinese bauxite. Kaolinite is easily sliming in the processof flotation, leading slime coating, fine-particle entrainment, andincrease in activity centers on mineral surface and the concentrateof inevitable ions in solution, which can seriously affect the functionof flotation [2,3]. Wang Yuhua reported that, in reverse flotation ofbauxite, if increasing the content of middle particle size by differentgrinding method, the ratio of Al2O3 to SiO2 and the recoveryincreased by 0.3–0.4% and 2–6%, respectively [4]. If the granularityof flotation was too small, no satisfactory results would be obtained

Elsevier B.V. on behalf of China Un

in flotation separation of diaspore and kaolinite when use sodiumoleate and dodecyl amine as collectors [5,6]. Piao reported that, insodium oleate and CPC flotation system, the separation of0–0.045 mm size of kaolinite and diaspore is more difficult than thatof coarse particles [7]. The particle size composition of millingmaterial has a strong effect on flotation of bauxite. Therefore, studyon kaolinite flotation as a function of particle size is significant toreverse-flotation separation of aluminum-silicate minerals frombauxite.

The main collectors of bauxite ores reverse flotation are fattyprimary amine, aliphatic tertiary amine, quaternary ammonium,acylamide, ether amine, polyamine, amidoamine, imines ureaand its salts, etc. [8]. Among them, quaternary ammonium saltscollectors are character stability, low toxicity, light irritation andlow corrosive, etc. At the same time, the collecting properties ofquaternary ammonium salts are stronger than fatty primary amineand aliphatic tertiary amine. Quaternary ammonium salts collec-tors are less influenced by pH and existing in the form of ions ina wide range of pH. With all these advantages, quaternary ammo-nium salts collectors draw more and more attention in the field ofmineral processing.

In this work, the flotation behaviors of kaolinite of different par-ticle fraction with cationic surfactants 103C, DTAC, TTAC and CTAC

iversity of Mining & Technology.

250 H. Jiang et al. / International Journal of Mining Science and Technology 23 (2013) 249–253

were studied. Adsorption mechanisms of quaternary ammoniumcationic collectors on kaolinite of different particle size were inves-tigated by absorbed amount measurement and adsorption iso-therm study. The structural anisotropic characteristics ofkaolinite were also discussed for a further illustration of flotationbehaviors.

2. Experimental

2.1. Materials and chemicals

Kaolinite was obtained from Xiaoyi in Shanxi province, China.The samples were hand-picked, crushed and ground in a laboratoryporcelain mill and screened to three different size fractions (0.075–0.1 mm, 0.045–0.075 mm, and 0–0.045 mm). Chemical composi-tion analysis and X-ray diffractometry (XRD) were used to studythe characteristics of chemical and mineral compositions. The re-sults showed that the purity of kaolinite was about 90%. The sur-face areas for kaolinite of different size fractions were 10.013,11.632 and 14.246 m2/g, respectively.

103C, DTAC, TTAC and CTAC of chemical pure from Nanjing Ro-biot Co., Ltd were used as collectors. Bromothymol blue (BTB) ofchemical pure was used as indicator in absorption tests. HCl,NaOH, phosphate and emulsifier op-10 were in analytical purityin this experiment. The water for all experiments was de-ionizedwater.

2.2. Flotation

Mineral particles (2 g) were placed in a flotation cell (40 mL)with 35 mL distilled water. Then pH regulators were added to ad-just the desired pH. After adding desired amount of reagents, thesuspension was agitated for 3 min. The flotation was conductedfor 4 min. The froth products and tails were weighed separatelyafter filtration and drying, and the recovery was calculated basedon the mass of the products.

2.3. Adsorption measurements

Ultraviolet spectrophotometer method was used to measurethe absorption of quaternary ammonium salts collectors [9]. A cer-tain amount of a collector was added in a 50 mL volumetric flask.Thereafter, added with 2.0 mL aqueous solution with 0.5% of emul-sifier op-10, 10.0 mL 2.5 � 10�4 mol/L BTB solution, and 5.0 mLphosphate buffer solution of pH 7.7, respectively. At last, bring tovolume by de-ionized water. The absorbance of solution with dif-ferent concentration of cationic collectors was obtained by usinga UV-2012 spectrophotometer with a wave length of 618 nm.The adsorbed amount of cationic collectors was calculated basedon the absorbance.

3. Results and discussion

3.1. Flotation

Flotation tests were conducted to determine the collectingproperties of 103C, DTAC, TTAC and CTAC to kaolinite of differentparticle fraction (0.075–0.1 mm, 0.045–0.075 mm, 0–0.045 mm).

The recovery–pH curves (Fig. 1) tested with 4.0 � 10�4 mol/Lcollectors show that with pH increasing there is a decrease inrecovery for all of the three particle fractions of kaolinite.

As is shown in Fig. 1, there is a huge difference in flotationbehaviors of kaolinite of different particle fraction. As carbon chainof quaternary ammonium salts increases, the recovery of kaolinitein 0.075–0.1 mm size and 0.045–0.075 mm size increases, the col-

lecting ability of collectors is 103C < DTAC < TTAC < CTAC. But incase of 0–0.045 mm size, the flotation recovery decreases as hydro-carbon chain of quaternary ammonium salts increase, the collect-ing ability of collectors is 103C > DTAC > TTAC > CTAC. At thesame time, the coarser particle size of kaolinite is, the better it isfloated, e.g. when CTAC is used as collector, the flotation recoveryof kaolinite in 0.075–0.1 mm size is above 90% in pH 2–9, whilein 0.045–0.075 mm size, a narrower pH fraction, pH 2–4, can therecovery reach 90%. In case of 0–0.045 mm size, the recovery main-tains fewer than 10%.

Recovery-collector dosage curves of kaolinite of different parti-cle fraction obtained at pH = 7 (Fig. 2) indicate that with collectordosage increasing there is an increase in recovery for all of thethree particle fractions of kaolinite. But the uptrend in recoveryof different particle fraction is different. In 0.075–0.1 mm sizeand 0.045–0.075 mm size, there is a sharp increase in recovery ofkaolinite in the collector concentration range between 0.2 and0.6 mmol/L. When the concentration is between 0.6 and0.9 mmol/L, further increase in recovery becomes slow. As the con-centration is above 0.8 mmol/L, a flat horizontal is presented andthe recovery reaches the maximum value. In case of kaolinite in0–0.045 mm size, the increase rate of recovery is lower than thatof coarser fraction when collector concentration is between0.2 mmol/L and 0.6 mmol/L. But recovery increases with almost aconstant speed when collector dosage is above 0.8 mmol/L. Atthe same time, Fig. 2 shows that influence of the length of collec-tor’s carbon chain on kaolinite of different particle fraction is con-sistent with Fig. 1.

As is shown in Fig. 2, compared with the fine particle size, thecoarse particle size of kaolinite is more susceptible to collectorconcentration. It could be attributed to the specific surface areaof kaolinite. The finer kaolinite particles are consistent with largerspecific surface and lower adsorption density of collector. There-fore, the concentration of collector has relatively small influenceon fine kaolinite. The different flotation behaviors of coarse andfine kaolinite could be attributed to the collector’s absorption ruleon kaolinite and the crystal structure of kaolinite.

3.2. Adsorbed amount and adsorption isotherms

The adsorbed amount of this test is the adsorption per specificsurface area. The adsorbed amount of collectors as a function ofpulp pH tested with 4.0 � 10�4 mol/L collectors shown in Fig. 3.With pH increasing there is a slight increase in adsorption for allof the three particle fractions of kaolinite. But the adsorption startsto decline due to the interaction between OH� and quaternaryammonium salt cations when pulp pH is above 10. According toFig. 3, the absorption increases with carbon chain of collectorsincreasing. The coarser particle size of kaolinite, the larger increaserate of adsorbed amount is.

The absorption of collectors increases while the flotation recov-ery of kaolinite decreases with pH increasing. This discrepancycould be attributed to the structural anisotropic characteristics ofkaolinite [10–12]. Kaolinite is layer silicate mineral. The finer par-ticle size of kaolinite is; the greater relative surface area of edgeplanes is. The edge planes have a poor adsorption capacity to cat-ionic collectors [13]. At the same time, the finer kaolinite particle isconsistent with larger specific surface and lower adsorption den-sity of collector. All these influence factors contribute to higher flo-tation recovery of coarse kaolinite.

In case of 0–0.045 mm kaolinite, its absorption increases whilethe flotation recovery decreases when the carbon chain of collectorincreases. This discrepancy could be attributed to the absoluteadsorption of surfactant on fine kaolinite surface. The low concen-tration of collector resulted to an undesired flotation result, such as

2 4 6 8 10 120

102030405060708090

100

pH2 4 6 8 10 12

0102030405060708090

100

pH2 4 6 8 10 12

0102030405060708090

100R

ecov

ery

(%)

pH

103CDTACTTACCTAC

(a) Kaolinite in 0.075-0.1 mm size (b) Kaolinite in 0.045-0.075 mm size

Rec

over

y(%

)

(c) Kaolinite in 0-0.045 mm size

Reco

very

(%)

Fig. 1. Flotation recovery of kaolinite of different particle size as a function of pH.

2 4 6 8 100

102030405060708090

100

(b) Kaolinite in 0.045-0.075 mm size

2 4 6 8 100

102030405060708090

100

(c) Kaolinite in 0-0.045 mm size

2 4 6 8 100

102030405060708090

100

Concentration of cation surfactant (10-4 mmol/L)

103CDTACTTACCTAC

Rec

over

y(%

)

Concentration of cation surfactant (10-4 mmol/L)

Rec

over

y(%

)

(a) Kaolinite in 0.075-0.1 mm size

Concentration of cation surfactant (10-4 mmol/L)

Rec

over

y(%

)Fig. 2. Flotation recovery of kaolinite of different particle size as a function of collector dosage.

2 4 6 8 10 123035404550556065707580

Ads

orbe

dam

ount

(10-8

mol

/m2 )

pH

123114311631

(a) Kaolinite in 0.075-0.1 mm size

3035404550556065707580

3035404550556065707580

Concentration of cation surfactant (4×10-4 mmol/L)

Ads

orbe

dam

ount

(10-8

mol

/m2 )

Ads

orbe

dam

ount

(10-8

mol

/m2 )

2 4 6 8 10 12pH

Concentration of cation surfactant (4×10-4 mmol/L)

2 4 6 8 10 12pH

Concentration of cation surfactant (4×10-4 mmol/L)

(b) Kaolinite in 0.045-0.075 mm size (c) Kaolinite in 0-0.045 mm size

Fig. 3. Adsorbed amount of collectors of kaolinite in different size as a function of pH.

H. Jiang et al. / International Journal of Mining Science and Technology 23 (2013) 249–253 251

unstable flotation froth. Afterwards, adsorption isotherms werestudied for a further explanation standpoint.

The measured adsorption isotherms of DTAC and CTAC on kao-linite in particle fractions of 0.075–0.1 mm and 0–0.045 mm aredepicted in Fig. 4, with adsorbed amount as a function of equilib-rium concentration. As is shown in Fig. 4, within the range of col-lector concentration, adsorbed amount of collector on coarsekaolinite (0.075–0.1 mm) is larger than that of on fine kaolinite(0–0.045 mm), and The adsorbed amount of CTAC is larger thanDTAC. When the adsorbed amount of collector on fine kaolinite in-creased to 10�6 mol/m2, up from 0, the equilibrium concentrationof CTAC remained unchanged at 0, while the equilibrium concen-tration of DTAC increased to 10�3 mol/L. As a consequence, CTACis absolutely adsorbed by fine kaolinite particles within the range

of flotation collector concentration, which leads to the relativelylow flotation recovery when CTAC is used as collector.

It is suggested in Fig. 4 that adsorption mechanism of cationiccollectors on kaolinite can be divided into four stages. In the firststage, there are ion exchange and electrostatic interactions be-tween quaternary ammonium salts and kaolinite [14]. These twokinds of strong forth lead the adsorbed amount increasing greatlywith the increasing of cationic surfactants concentration. In thesecond stage, the charge of ion exchange has been neutralized,and the adsorbed amount under the function of electrostatic inter-actions shows a linear ascending with the concentration of collec-tors. Quaternary ammonium salts are still adsorbed as monomersin this stage. The adsorbed amount increases slowly in the thirdstage. In this stage, the solution surfactant concentration is

0 2 4 6 8 10 12 14 160

10

20

30

40

50

60

70

pH=7Kaolinite in 0.075-0.1 mm size

Equilibrium concentration (10-3 mol/L)

12311631

0 2 4 6 8 10 12 14 16 180

10

20

30

40

50

60

70

pH=7Kaolinite in 0-0.045 mm size

Equilibrium concentration (10-4 mol/L)

Ads

orbe

dam

ount

(10-8

mol

/m2 )

Ads

orbe

dam

ount

(10-8

mol

/m2 )

Fig. 4. Adsorption isotherms of DTAC and CTAC on kaolinite in particle fractions.

252 H. Jiang et al. / International Journal of Mining Science and Technology 23 (2013) 249–253

sufficient to lead to hydrophobic interactions between monomers.Semi micelle adsorption occurs on kaolinite surface and concentra-tion of cationic surfactants reaches to CMC [15]. The fourth stageoccurs above the CMC, the formation of agglomerations fully formsand the saturation levels of surface coverage reach.

3.3. Influence of structural anisotropic and surface electrical behavioron kaolinite flotation

The mechanism of cationic collectors on flotation has beenstudied extensively. It is generally accepted that cationic collectorabsorbs readily due to electrostatic interactions on oppositelycharged surfaces. Zeta-potential measurements are the familiarmeans to investigate surface electrical behavior of minerals. How-ever, in case of kaolinite, the surface electrical behavior cannot beexplained from Zeta-potential measurements because of its struc-tural anisotropic characteristics [16].

Kaolinite is a two-layer alumino-silicate mineral {Al4Si4O10

(OH)8}. There are two basal planes, alumina octahedral faceð00 �1Þ and silica tetrahedral face (001), with different surfaceproperties, and the edge surfaces (010) and (110) are exposedwhen kaolinite is cleaved. The charging mechanism of the edgescan be described by schematic diagram (Fig. 4) [17].

Si

OH2+

O

Al

2H+ Si

Al OH

OH Si

Al

O-2OH-H2+

O-

Depending on solution pH, the edge is positively charged due toH+ ion adsorption in acidic solution or negatively charged byadsorption of OH� or by dissociation of H+ in alkaline solution.The iso-electric point of edges is at pH 7.2 [18]. The iso-electricpoint of the silica tetrahedral face (001) is at pH < 4, and that theiso-electric point of the alumina octahedral face lies between pH6 and 8 [19,20].

The cationic flotation recovery of kaolinite in alkaline media de-creases, although quaternary ammonium salts collectors adsorp-tion increases at higher pH values. This could be explained asfollow. In alkaline media, both edges and basal planes are nega-tively charged. The kaolin particles are dispersed. In the presenceof amine collectors, the (001) edge might adsorb amine to becomehydrophobic. However, the weak interaction of ð00 �1Þ planes withcollectors makes the ð00 �1Þ plane hydrophilic. Hydrophobic aggre-gation of kaolinite particles may take place between (001) faceswith adsorbed collectors by chain–chain interaction leaving thehydrophilic faces ð00 �1Þ exposed [21]. Thus results in a low flota-

tion recovery of kaolinite in alkaline media. In acid media, basalplane ð00 �1Þ and edges surfaces are positively charged, while thebasal plane (001) is negatively charged. Aggregation of kaoliniteparticles by electrostatic attraction may take place between posi-tively charged faces and negatively charged faces [22,23]. The(001) faces adsorb amine to become hydrophobic, and the edgesplanes and ð00 �1Þ faces cannot adsorb amine because of positivelycharged. Thus the flotation recovery of kaolinite is relatively highin acid media.

4. Conclusions

(1) The flotation recovery of kaolinite with different particlefraction increases with an increase in pH when 103C, DTAC,TTAC and CTAC are used as collectors. As the concentrationof collectors increases, the flotation recoveries of kaoliniteincrease. The coarser particle size of kaolinite is, the betterit is floated.

(2) Particle size of kaolinite has a strong effect on flotation. Ascarbon chain of quaternary ammonium salts increases, therecovery of kaolinite in 0.075–0.1 mm size and 0.045–0.075 mm size increases. But in case of 0–0.045 mm size,the flotation recovery decreases as the length of hydrocar-bon chain of quaternary ammonium salts increases.

(3) The adsorbed amount of collectors on kaolinite increase withcarbon chain of collectors increasing, and the adsorption oncoarse particles of kaolinite is larger than that of on fine par-ticles. Within the range of flotation collector concentration,collector with longer hydrocarbon chain is more probableabsolutely adsorbed by fine kaolinite particles, which resultsto an undesirable flotation result. Therefore, the flotationrecovery of fine kaolinite decreases with the carbon chainof quaternary ammonium salts collectors increasing.

Acknowledgments

The authors would like to thank the National Natural ScienceFoundation of China (No.50974134) and the National Basic Re-search Program of China (No.2005CB623701) for their support ofthis research.

References

[1] Huang CB, Wang YH, Chen XH, Ye L, Hu YM, Yu FS. Review of research ondesilication of bauxite ores by reverse flotation. J Metal Mine 2005;6:21–4.

[2] Wei XC, Han YX, Yin WZ, Zai YC, Tian YW, Chen BC. Study on the necessity ofselective grinding for bauxite. J Metal Mine 2001;10:29–31.

[3] Qiu GZ, Hu Y, Wang DZ. Interaction between particles and fine particlesflotation. Changsha: Central South University Press; 1993.

H. Jiang et al. / International Journal of Mining Science and Technology 23 (2013) 249–253 253

[4] Wang YH. The effect of the particle size composition of materials on thereverse flotation of bauxite. J Metal Mine 2002;8:29–30.

[5] Zhang Y, Wang YH, Li SL. Flotation separation of calcareous minerals usingdidodecyldimethylammonium chloride as a collector. Int J Mining Sci Technol2012;22(2):285–8.

[6] Liu CM, Feng AS, Guo ZX, Cao XF, Hu YH. Flotation behavior of four dodecyltertiary amines as collectors of diaspore and kaolinite. Mining Sci Technol2011;21(2):249–53.

[7] Piao ZJ. Studies on effect of CPC and sodium oleate on the floatability ofaluminum-silicon minerals of different particle size and itsmechanism. Changsha: Central South University; 2010.

[8] Yu XY, Zhong H, Liu GY, Su XM. A novel cationic organ silicon collector QAS222for reverse flotation of bauxite. J Cent S Univ 2011;42(7):1865–72.

[9] Li J, Yang HL. Study on adsorption property of CTAB on the mineral. JPetrochem Ind Appl 2010;5:25–6.

[10] Jiang H. Studies on solution chemistry of interactions between cationiccollectors and aliminosilicate aluminum minerals in bauxite flotationdesilica. Changsha: Central South University; 2004.

[11] Li HP, Hu YH, Wang DZ, Xu J. Mechanism of interaction between cationicsurfactant and kaolinite. J Cent S Univ 2004;35(2):228–33.

[12] Sun W, Chen C, Tang HH. Effects and action mechanism of CO2�3 on flotation

rate of calcite. J China Univ Mining Technol 2012;41(6):48–51.[13] Li HP. Structure-performance of modified polymer and the mechanism for

flotation of aluminum and silicate minerals. Changsha: Central SouthUniversity; 2002.

[14] Wang JB, Hab BX, Dai M, Yan HK, Li ZX, Thomas RK. Effects of chain length andstructure of cationic surfactants on the adsorption onto Na-kaolinite. J ColloidInterface Sci 1999;213:596–601.

[15] Gao YY, Du JZ, Gu TR. Hemimicelle formation of cationic surfactants at thesilica gel-water interface. J Chem Soc 1987;83(8):2671–9.

[16] Luckham PF, Rossi S. The colloidal and rheological properties of bentonitesuspensions. J Adv Colloid Interface Sci 1999;82(1–3):43–92.

[17] Zhao SM, Wang DZ, Hu YH, Xu J. The flotation behavior of N-(3-aminopropyl)-dodecanamide on three aluminosilicates. J Miner Eng 2003;16(12):1391–5.

[18] Williams DJA, Williams KP. Electrophoresis and zeta potential of kaolinite. JColloid Interface Sci 1978;65:79.

[19] Zhao HY, Subir Bhattacharjee, Ross Chow. Probing surface charge potentials ofclay basal planes and edges by direct force measurements. J Langmuir2008:12899–910.

[20] Gupta Vishal, Miller Jan D. Surface force measurements at the basal planes ofordered kaolinite particles. J Colloid Interface Sci 2010;334:362–71.

[21] Hu Y, Wei S, Hao J, Miller JD, FA KQ. The anomalous behavior of kaoliniteflotation with dodecyl amine collector as explained from crystal structureconsiderations. Int J Miner Process 2005;76(3):163–72.

[22] Gupta V, Hampton MA, Stokes JR. Particle interactions in kaolinite suspensionsand corresponding aggregate structures. J Colloid Interface Sci2011;359(1):95–103.

[23] Qin WQ, Wang PP, Ren LY. Effect of matching relationship between particlesand bubbles on the flotation of fine cassiterite. J China Univ Mining Technol2012;41(3):420–4.