chemical bleaching of brazilian kaolin_química nova_2011

8/13/2019 Chemical bleaching of Brazilian kaolin_Qumica Nova_2011

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Qumica Nova

Print versionISSN 0100-4042

Qum. Nova vol.34 no.2, p. 262-267, 2011

http://dx.doi.org/10.1590/S0100-40422011000200017

ARTIGO

Chemical bleaching of Brazilian kaolin: effect ofelectrochemical potential of the pulp and the pHadjustment

Chemical bleaching of the Brazilian kaolin: the effect of thepulp eletrochemical potential and pH adjustment

Fernanda Arruda Nogueira da Silva Gomes I, *, Francisco Manoel dosSantos Garrido I,Martha Medeiros Eloisa I.Joo Alves Sampaio II;WelcomeAdam of Light II, IIILivia da Silva Mello; Flvio Teixeira da Silva III

I

Department of Inorganic Chemistry, Institute of Chemistry, Federal University ofRio de Janeiro, Av Athos da Silveira Ramos, 149, CT, Bl A, City Island University,21941-909 Rio de Janeiro - RJ, BrazilIICentre for Mineral Technology, Av Pedro Calmon, 900 City Island University,21941-909 Rio de Janeiro - RJ, BrazilIIIDepartment of Metallurgical and Materials Engineering, Coordination of GraduateStudies and Research in Engineering, Federal University of Rio de Janeiro, AvHoracio de Macedo, 2030 CT, Bl F, Island of the City University, 21941-909 Rio deJaneiro - RJ, Brazil

ABSTRACT

Samples of Kaolin from different regions in Brazil were Characterized by XRD, SEMand chemical analysis.The chemical bleaching study with pH adjustment wasaccomplished with the fractions below 37m, after classification by screening.Themain objective was to Evaluate the conditions of chemical bleaching most queIncrease the brightness of these kaolin's samples.Increases between 2.63 and2.98% in the brightness (ISO) were Observed after the bleaching chemical.Couldwe say que the reduction of Fe 3 +to Fe 2 +During The chemical bleaching promotedan Increase in the brightness, based on the Pourbaix Diagrams.

Keywords:kaolin, chemical bleaching; brightness.


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INTRODUCTION

The term kaolin is used to describe the rock containing the mineral kaolinite (Al 2Si

2O 5(OH) 4),as the product of its processing.It is a rock made of clay material withlow iron content and white or nearly white and fine grained. 3.1Kaolin is consideredan industrial rock, and is used as a raw material in various types of industries suchas paper, ceramics, paint, plastic, concrete, glass, rubber, cosmetics,pharmaceuticals, catalysts, fertilizers, among others. 2.11However, the mostimportant use is the kaolin in paper, may be used as filler or covering, with aconsumption of approximately 45% kaolin produced around the world, so the 37million tons of kaolin in the world, about 16 million are used in the paper industry.Brazil accounts for about 7% of world production of kaolin and holds around 28% ofworld reserves. 2-5

Kaolins are the result of changes aluminum silicates, particularly feldspars and canoccur in two types of deposits: The primary or residual (eluvial) and secondary.Primary deposits are the result of changes of rocks in situ,while the secondary arefrom deposition of material transported by streams of fresh water. 1,2,5-7Braziliankaolin deposits have been studied by many researchers focusing mainly aspectsmineralogical, chemical, geological, and technological and environmental issuesrelated to its mining, processing and application. 1,2,5-15

The main impurities associated with commercial kaolins are quartz, feldspar,muscovite, biotite, titanium oxides and iron oxides or hydroxides, such as goethite,hematite and magnetite.These impurities significantly affect the whiteness ofkaolin, the main physical property related to its application in the paper industry, asthey contribute to light absorption and thus become less kaolin target, reducing itsvalue.To be used in the paper industry brightness of the kaolin must be between80-90% ISO. 2.3Therefore, the removal of impurities containing iron kaolin isextremely important for the paper industry, since in this segment, purity andwhiteness are the limiting factors for its use as filler or cover.When the iron isassociated with the kaolinite in the form of goethite, magnetite and / or pyriteremoval is possible by physical methods such as wet magnetic separation of highintensity. 2,5,6However, removal is not complete and no need for an additional stepof processing, that is, bleaching chemical that removes residual iron minerals,including hematite not removed by magnetic separation.The iron can also be foundas substitutional impurities in the kaolinite structure, where Fe 3 +replaces Al3 +inthe octahedral sites, and in this case, there is no possibility of removal by physicalprocessing or physicochemical. Two 0.5 to 7

The literature reports several alternatives to chemical bleaching kaolin. 2,15,16Intargeting a share of a reducing reagent, numerous redox reactions can occur, and

the reduction of Fe 3 +to Fe 2 +,the most important for achieving a high level ofwhiteness.The oxide and ferric hydroxide (Fe 2O 3and Fe (OH) 3)have very limitedsolubility, so that these impurities to be eliminated is necessary reduction reactionof Fe 3 +which occurs in acidic medium, the reducing agent plus has been usedsodium dithionite. 2.16

The reactions dithionite ion in aqueous solution are quite complex and itsdecomposition shows the oscillatory behavior, and the formation of radical speciesSO 2

-has been considered, and kinetic studies of the mechanism, responsible forthe great reducing power of the dithionite ion. 17thHowever, the reaction betweenferric oxide and sodium dithionite (Na 2S 2O 4)in acidic medium, may in principlebe expressed in a simplified manner by Equations 1 and 2: 2,6,7,15 - 17


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The redox potential of reactions 1 and 2 increases as pH decreases, since it favors

the reduction of Fe3 +

to Fe2 +. 2.7

However, the stability of reducing reagent (Na 2S2O 4)decreases at very low pH, occurring successive reactions that may lead to theformation of H 2S, Equation 3, and the precipitation of elemental sulfur (S),Equations 4 and 5, compromising thus the whiteness of kaolin. 2,6,7,16As aconsequence, the bleaching reaction is generally carried out at a pH valuecomprised between 3.0 and 4.5. 7

In this work, a study of the chemical bleaching three kaolin samples from differentregions of Brazil, through the reduction of Fe 3 +to Fe 2 +with sodium dithionite atdifferent pH values and the monitoring of the potential Electrochemical (Eh) of thepulp, since the main goal was to identify conditions that favor better performance inbleaching chemical, so as to obtain a value of the whiteness index that iscompatible with the application of kaolin in the paper industry.

EXPERIMENTAL

Samples of kaolin

In this work we used three kaolin samples from different regions of Brazil and twodeposit types, primary and secondary.The Table 1illustrates the kaolin used in thedevelopment of this study, as well as its origin and type of deposit.

Sample preparation

The first stage of the work, in the laboratory, consisted of sample preparation,using the standard procedure established by CETEM. 18Initially, we proceeded tothe quarters of the sample cell homogenization, samples were collected of which 20kg.In the next step, the sample mixed with 20 kg, was made a new stack ofhomogenization for collecting rates of 1.0 kg each.

The wet sieving was carried out with a pulp with 30% solids using a vibratorysieving.The fraction with a particle size of less than 37m was dried anddisaggregated quarteada in samples of 200 g were used in the tests of chemical

bleaching.


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Chemical and mineralogical characterization

Chemical analysis was done by atomic absorption Varian AA6 the equipment with awavelength of 248.3 nm, slit of 0.5 mm with the use of the air / acetylene.The X-ray diffraction of the samples with particle size less than 37m, were obtained bythe powder method, the Bruker-AXS D5005, Co Kradiation (35 kV and 40 mA);goniometer speed of 0.02 2by step, with counting time of 1 s per step andcollected 5-80 in 2 .The grain morphology of kaolinite was observed in ascanning electron microscope Leica, model F440 in high vacuum mode.The pre-dispersed particles were coated with silver to make them conductive.

Before measurements are performed in brightness samples, after drying in an ovenfor approximately 30 min, were dissociated in analytical mill brand Tekmar modelA-10 Analytical Mill for 1 min.The insert was prepared using a pressure of about457 Pa. The brightness values were determined in the photometer Color Touch 2ISO model, manufactured by Technidyne.

Chemical bleaching

The tests were carried out with chemical bleaching pulp with 30% solids withcontrolled stirring (90 rpm) for a period of up to 2 h.The reagent used was sodiumdithionite (Na 2S 2O 4)at a concentration of 3 kg / tonne of kaolin.The pH was oneof the process variables, so the tests were performed with pH values equal to 3.0,3.5, 4.0 and 4.5.The pH of the pulp was measured continuously, and, whennecessary, adjustment of pH was carried out with the addition of sodium hydroxidesolution (NaOH) or sulfuric acid (H 2SO 4)0.1 mol / L.The Eh of the pulp wasmeasured at 15 min intervals.During the tests, aliquots of 100 mL were collectedevery 30 min, filtered and dried at about 100 C.After drying the whiteness wasdetermined from specimens using the procedure described above.Importantly,during rehearsals pulp Kaolin is stirring.However, it should be slow agitation(approximately 90 rpm), so that no oxidation of Na 2S 2O 4in an accelerated byoxygen from the air, reducing the efficiency of the process.

The pH measurements were performed in the pulp pH meter Digimed brand, modelDM-200.The equipment was calibrated with the use of buffer solutions with pH 4and 7.The electrode used was a glass combination with the reference electrode ofAg / AgCl.

The electrochemical potential of the reactions was measured using a platinumelectrode Analion brand, model ROX 673, with the reference electrode of Hg / Hg 2Cl 2(calomel), previously calibrated with the standard solution Zobelat 550 5mV.

RESULTS AND DISCUSSION

The X-ray diffraction (XRD) is the main technique used to identify mineralogicalkaolin.The XRD patterns of the samples of crude kaolin are shown in Figure 1.Theresults indicate that in principle these are kaolin kaolin, since they have no peaksrelating to the mineral illite and exhibit peaks associated with lamellar mineralkaolinite with basal interplanar distance of 715 pm, a value typical of materials withlamellar structure. 5 , 19,20However, kaolin RN and AM are associated with themineral quartz and muscovite, and one can not completely rule out the presence ofhalloysite (interplanar basal distance of about 1000 pm for hydrated halloysite.) 19

notes It is also the diffraction pattern of the AM kaolin has a higher intensity peaksof quartz.


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The kaolin samples were subjected to chemical analysis by atomic absorption as acomplementary technique to XRD.The results in Table 2indicate that the AP ismainly kaolinitic kaolin, since the percentage of SiO 2and Al 2O 3approach thetheoretical values established for the kaolinite (46.5 and 39.5%, respectively).

However, the analysis of the RN and BF showed kaolin content of SiO 2and Al 2O 3different from the expected kaolin to kaolin.21Wilson researched and compared thechemical composition of different kaolin, Kaolin Kaolinite (China), haloistico(England) and kaolinitic / haloistico (New Zealand), and proved that the kaolinhaloistico has a higher content of SiO 2(50%) and lower content of Al 2O 3(35%)compared with the kaolinitic kaolin.Once the kaolin RN and AM exhibited a differentchemical and mineralogical composition of kaolin PA, a study was made ofcharacterization by scanning electron microscopy (SEM) in order to identify themorphology of kaolin studied.


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The kaolinite has significant variations in morphology and grain size, and thesevariations may be associated with the origin of the deposit and the degree ofcrystallinity of the mineral.The images obtained by scanning electron microscopy(SEM), Figures 1Sa, band c, supplementary material, illustrating the morphologyof the kaolinite in three different samples of kaolin, with a diameter less than 37m.As observed in three samples of kaolinite particles have a morphology formcrystals with lamellar, hexagonal-like jagged edges, that is, pseudo-hexagonalplates.The particles are agglomerated, non-delaminated in the form of booklets.Bymeans of the SEM can be observed that the kaolin RN and AM Figures 1Saand c,additional material, containing no halloysite, once the crystals have not observedformat "jelly roll" morphology of the characteristics of this mineral.Theseobservations complement the results obtained by XRD and chemical analysis,confirming that all three samples are of the type kaolinitic kaolin and that the largeramount of SiO 2on kaolin RN and BF can be exclusively attributed to quartz.

21st

Tests of chemical bleaching were intended to remove iron impurities cancompromise the whiteness of kaolin.These tests consisted in the acid leaching offerric oxide (Fe 2O 3)under reducing conditions to yield a reduction of Fe 3 +to Fe 2+and, consequently, increase the level of brightness of kaolin studied.During thedevelopment of the bleaching tests similar behavior was observed betweendifferent pH values for the three kaolin studied.It is observed that as the pHincreases, the initial Eh value tends to be negative, this behavior can be seen inFigures 2, 3and 4for the RN kaolin, PA and PM, respectively.


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Another important observation is that the electrochemical potential of the pulptends to increase with time bleaching, heading towards the stability region ofelemental sulfur in the graph of pH versus Eh for the S / H 2O (Pourbaix diagram) ,

Figure 5.Importantly, at pH higher than 7.0 and very positive values of Eh, Fe 2 +ion is not stable, so the ferric ion (Fe 3 +)will not be released from its oxide and itsreduction will not occur to Fe 2 +as shown in Figure 6, the graph Eh vs pH for thesystem Fe / H 2O (Pourbaix diagram).However, with appropriate adjustment of pHand Eh value control, one can in principle maintain the pulp of kaolin within thestability field of Fe 2 +(aq).These two limiting factors are essential to the reduction ofFe 3 +ions and hence the bleaching kaolin.


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In Table 3are presented the Eh values and whiteness index (% ISO) versus timefor targeting to the pH at which each of the kaolin has achieved its best value ofwhiteness, i.e. at pH 4 5, 4.5, and 3.0, respectively, for the kaolin RN, PA and AM.In Table 1S, supplementary material presents the full results of the bleaching,measured at different times and pH of the pulp.


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The Figures 7, 2Sand 3S, additional material for the RN kaolin, PA and PMrespectively show the variation of the brightness index value (% ISO) versus timefor bleaching and for the study shown in Table 3.

The evaluation results for the case of kaolin RN Figure 7and Table 3, show thatthe best value of the whiteness index was achieved after 60 min of bleach, and theHS is negative and corresponds to point A in Figures 5and 6.Therefore, underthese conditions iron is solubilized as Fe 2 +(aq) and there is no possibility ofprecipitation of elemental sulfur.However, if the bleaching continue for longer

observed a decrease in whiteness index value, this result can be explainedconsidering that there is a progressive increase in the Eh value, moving the system


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towards the region of stability sulfur elementary.This sulfur, by having a yellowishtinge, contributes to the decrease in whiteness index of kaolin.

In the case of kaolin PA the same type of behavior is observed, and the point B inFigures 5and 6corresponds to the best condition for the bleaching of kaolin.Amore detailed analysis can be seen by Table 3and Figure 2S, supplementary

material.

Finally, for the case of kaolin AM observed in Table 3and Figure 3S, additionalmaterial, which has a smaller variation in brightness index values, and the point Cin Figures 5and 6, represents the best condition bleach.However, to this point weobserve that, in spite of having a Eh within the region of stability of Fe 2 +(aq), thisvalue corresponds to the stability region of elemental sulfur, consequently, shouldthis occur the precipitation, affecting the efficiency the bleaching process.All theresults obtained here suggests a possible alternative to improve the bleaching ofkaolin AM, would be to reduce the Eh of the pulp, for example, by increasing theconcentration of sodium dithionite, which according to the diagram of Pourbaix ,Figure 5, to prevent precipitation of sulfur.

In Table 4one can observe the specific conditions of chemical bleaching, where thebest whiteness indices were obtained for each sample studied kaolin.

CONCLUSIONS

Kaolin studied were classified as essentially kaolinitic, with pseudo-hexagonalmorphology and form of booklets.The iron content is converted into Fe 2O 3isbetween 1.1 and 0.26%, which impairs the whiteness index, however, it is possibleto carry out bleaching chemical reactions with the purpose of reducing the Fe 3 +ions Fe 2 +.

After the tests of chemical bleaching, the results were considered satisfactorybecause the kaolin had their whiteness index values increased between 2.63 and2.98%.Importantly, an increase of approximately 0.50% in the whiteness index ofkaolin can increase, significantly, their aggregate value.

With regard to the application of these kaolin in paper industry can be said thatafter the bleaching kaolin PA samples exhibited RN and whiteness suitable for useas filler or as cover.While the process of bleaching kaolin AM needs to be optimizedso that you can improve your whiteness, its high quartz content should make itabrasive, which compromises their application.

The control of the pH monitor the Eh during the bleaching chemical has proven

essential to ensure removal of impurities containing iron and inhibit theprecipitation of elemental sulfur, which can compromise the brightness of the


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kaolin.Note that the monitoring values of Eh, performed in this work, allowed toobtain best results bleaching than those reported in a recent article, in the case ofkaolin RN. 6

SUPPLEMENTARY MATERIAL

It is available in http://quimicanova.sbq.org.brpdf file, with free access, thefollowing material: Figures 3S 1Sand Table 1S.

THANKS

To CAPES and CNPq for financial support.

REFERENCES

1.Coelho, ACV, Santos, PS; Santos, HS; Quim.New2007,30,146, [ Links]Wilson, IR, Santos, HS, Santos, PS; Ceramics1998,44,118, [ Links]Light, AB;Damasceno, EC series In Mineral Technology;Fernandes, FRC, ed.; CETEM / MCT:Rio de Janeiro, 1994, vol.65, ch.1.[ Links]

2.Light, AB, Campos, AR, Carvalho, EA; Bertolino, LC; Scorzelli, RB IndustrialRocks and Minerals;Light, AB; Lins, FAF, eds.; CETEM / MCT: Rio de Janeiro, 2nded., 2009 , ch.12; [ Links]Light, AB, Chaves, AP In Industrial Minerals and Rocks;Light, AB, Albuquerque, GASC, eds.; CETEM / MCT: Rio de Janeiro, 2000, vol.1, ch.1; [ Links]Santos, PS; Science and Technology Clays,ed.Edgard Blcher: SoPaulo, 1989, vol.I.[ Links]

3.Conceio, S., Santos, NC, Old, J., Ferreira, JMF,Appl.Clay Sci,2005,30, 165, [Links]

Murray, HH; Kogel, JE, Appl.

Clay Sci,2005,28,199, [ Links]

Murray, HH;

Appl.Clay Sci2000,17,207.[ Links]

4.Nkoumbou, C.; Njoya, A.; Njoya, D.; Grosbois, C.; Njopwouo, D., Yvon, J.,Martin, F.,Appl.Clay Sci,2009,43,118, [ Links]Jimenez, AF; Palomo, A.,Vazquez, T.; Vallepu, R.; Terai, T., Ikeda, K.,J.Am Ceram.Soc,2008,91,1231; [Links]Siddiqui, MA, Ahmed, Z.; Saleemi, AA;Appl.Clay Sci2005,29,55.[ Links]

5.Scorzelli, RB; Bertolino, LC, Light, AB; Duttine, M., Silva, FANG; munayco, P.;Clay Miner.,2008,43,129, [ Links]Silva, FANG, Silva, FT; Light, AB; Sampaio, JAIn Industrial Minerals and Rocks;France, SCA; Bertolino, LC, eds.; CETEM / MCT:Rio de Janeiro, 2008, vol.14, ch.1.[ Links]

6.Silva, FANG; Light, AB; Sampaio, JA; Bertolino, LC; Scorzelli, RB; Duttine, M.,Silva, FT,Appl.Clay Sci.,2009,44,189.[ Links]

7.Light, AB, PhD Thesis,University of So Paulo, Brazil, 1998.[ Links]

8.Varela, ML, Ant, FL, Dutra, RPS; Birth, RM; Paskocimas, CA; Ceramics,2009,55,209, [ Links]Milk, JYP, Veras, MM, Santos, EP, Lima RFS; Paulo, JBA, Pinheiro,M.; Minerals Engineering2007,20,959, [ Links]Menezes, RR, Almeida, RR;Santana, LNL; Ferreira, HS, Neves, GA, Ferreira, HC; Magazine Matter2007,12,226, [ Links]Menezes, RR; Oliveira, MF; Santana, LNL; Neves, GA, Ferreira, HC;Ceramics2007,53,388, [ Links]Vieira, CMF; Terrones, LA, Snchez, R.,

Monteiro, SM; Ceramics2007,53,249, [ Links]Fields, TW, Santos, HS; Ceramics1986,32,355.[ Links]


13/17

9.Rock, AKA; Menezes, RR; Neves, GA, Ferreira, HC, Melo, WA; REM: R.EscapeMinas2008,61,505, [ Links]Rezende, MLS; Menezes, RR; Neves, GA; Birth,JWB; Leal, AF; REM: Rev. Esc Mines2008,61,285, [ Links]Menezes, RR,Almeida, RR; Santana, LNL; Neves, GA, Lira, HL, Ferreira, HC; Ceramics2007,53,192, [ Links]Gerotto, MV; Cable, SS; Innocentini, MDM; Pandolfelli, VC; Ceramics2000,46,200.[ Links]

10.Rigo, RT; Pergher, SBC; Petkowicz, DI; Santos, JHZ; Quim.Newin 2009,32,21; [ Links]Maia, AAB; Anglica, RS, Neves, RF; Ceramics2008,54,345, [ Links]Maia, AAB; Saldanha, E.; Anglica, RS, Souza, CAG; Neves, RF; Ceramics2007,53,319, [ Links]Pereira, MC, Tavares, CM, Fabris, JD, Lake, RM, Murad, E.;Criscuolo, PS, Clay Miner.,2007,42,299, [ Links]Mignoni, ML; Detoni, C.;Pergher, BC; Quim.New2007,30,45; [ Links]Nakagaki, S., Machado, GS;Halma, M.; Marangon, AAS; Castro, KADF; Mattoso, N.; Wypych, F.,J.Catal.,2006,242,110, [ Links]Nakagaki, S.; Flavio Luiz Benedito, FB; Wypych, F.,J.MolCatal.A: Chem.2004, 217, 121,[ Links]Araujo, CS, Silva, LRD, Quim.New2003,26,161.[ Links]

11.Ribeiro, FR; Egreja Son, FB; Fabris, JD; Mussel, WN; Novais, R.F, RBras.CiSolo2007,31,939.[ Links]

12.Faria, EH; Lima, OJ; Ciuffi, KJ; Nassar, EJ; Vicente, MA; Trujillano, R.; Calefi,PS,J.Colloid Interface Sci, 2009,335,210, [ Links]Budziak Fukamachi, CR;Wypych, F.; Mangrich, AS,J.Colloid Interface Sci, 2007,313,537, [ Links]Coelho, AC V, Santos, PS; Santos, HS; Quim.New2007,30,1282; [ Links]Oliveira, MTG; Furtado, SMA; Formoso, MLL, Eggleton, RA, Dani, N.;Anopheles

Acad.Bras.Cinc2007,79,665, [ Links]Arajo, JC; Assisi, JT; Monine, VI;Bertolino, LC; Magazine Matter2006,11,361, [ Links]Pinheiro, PG; Fabris, JD;Mussel, WN; Murad, E.; Scorzelli, RB, Garg, VK,J.South Am Earth Sci,2005,20,267, [ Links]Gardolinski, JE; Martins Filho, HP, Wypych, F.; Quim.Nova,2003,

26,30; [ Links]Fonseca, MG; Airoldi, C.; Quim Nova2003,26,699, [ Links]Carneiro, BS; Anglica, RS; Scheller, T., Castro, EAS; Neves, RF; Ceramics2003,49,237, [ Links]Lombardi, KC; Guimares, JL; Mangrich, AS; Mattoso, N.;Abbate, M., Schreiner, WH; Wypych, F.,J.Braz.Chem.Soc,2002,13,270.[ Links]

13.Silva, FANG; Medeiros, ME, Sampaio, JA, Santos, RD, Carneiro, MC, Costa, LS;Garrido, FMS, Light Metals2009,139, [ Links]Silva, FANG; Santos, RD; Sampaio,JA, Garrido, FMS; Medeiros, ME, Light Metals 201069.[ Links]

14.Picarelli, S.; Koppe, JC, Costa, JFCL; Luft, CF; REM: Rev. Esc Mines2008,61,179, [ Links]Silva, AC, Vidal, M., Pereira, MG; REM: Rev. Esc Mines2001,54,

133.[ Links]

15.Mussel, WN; Murad, E.; Criscuolo, PSR; Pinheiro, PG; Fabris, JD, Clay Miner.,2008,43,381, [ Links]Gonzlez, JA, Ruiz, M.del C.,Appl.Clay Sci,2006,33,219, [ Links]Varela, JJ; Gliese, R.; Petter, CO; Peixoto, CA; REM: Rev. Esc Mines2005,58,201, [ Links]Schreiner, WH; Lombardi, KC; Oliveira, AJA; Mattoso, N.;Abbate, M., Wypych, F.; Mangrich, AS,J.Magn.Mater., 2002,241,422, [ Links]Milk, SQM; Colodete, CHA; Dieguez, LC; San Gil, RAS; Quim.New2000,23,297.[Links]

16.Conley, RF, Lloyd, MK; Ind.Chem Eng.Process Des.Develop.1970,9,595.[Links]


14/17

17.Gasana, E.; Westbroek, P., De Wael, K., Temmerman, E., De Clerck, K.;Kiekens, P.,J.Electroanal.Chem.,2003,553,35; [ Links]Westbroek, P., DeStrycker, J., van Uytfanghe, K., Temmerman, E.,J.Electroanal.Chem.,2001,516,83; [ Links]Camacho, F.; Pez, MP, Jimnez, MC, Fernndez, M., Chem.Eng Sci,1997,52,1387; [ Links]Stucki, JW, Bailey, GW, Gan, H.,Appl.Clay Sci,1996,10,417, [ Links]Rueda, EH; Ballesteros, MC, Grassi, RL; Blesa, MA, Clays Clay

Miner.199240,5 75.[ Links]

18.Oliveira, MLM; Aquino, JA In Mineral Processing: Laboratory Practice;Sampaio,JA; France, SCA; Braga, PFA, eds.; CETEM / MCT: Rio de Janeiro, 2007, ch.1.[Links]

19. http://rruff.geo.arizona.edu/AMS/amcsd.php, accessed November 2009.[Links]

20.Garrido, FMS, Alves, OL,J.Non-Cryst.Solids1990,121,98; [ Links]Medeiros,ME, Alves, OL,J.Mater.Chem. 1 992,2,1075.[ Links]

21.Wilson, IR, Clay Miner.2,004,391.[ Links]

Received on 3/16/10, accepted on 9/19/10; published on the web on 8/12/10

*e-mail: [email protected]


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chemical bleaching of brazilian kaolin_química nova_2011

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