Research Article Effects of Different Raw Materials in the ...downloads.hindawi.com/journals/jchem/2016/5353490.pdf · metastable alumina phase. 1. Introduction Alumina polymorphs

Research ArticleEffects of Different Raw Materials in the Synthesis ofBoehmite and 120574- and 120572-Alumina

Isabel Padilla1 Sol Loacutepez-Andreacutes2 and Aurora Loacutepez-Delgado1

1National Centre for Metallurgical Research (CSIC) Avda Gregorio del Amo 8 28040 Madrid Spain2Department Crystallography and Mineralogy Faculty of Geology UCM CJose A Novais 28040 Madrid Spain

Correspondence should be addressed to Aurora Lopez-Delgado alopezdelgadocenimcsices

Received 4 September 2016 Revised 10 October 2016 Accepted 19 October 2016

Academic Editor Jean-Marie Nedelec

Copyright copy 2016 Isabel Padilla et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Two alumina polymorphs the metaestable 120574-Al2O3 and the stable 120572-Al2O3 were obtained from thermal treatment of the precursor120574-AlOOH (boehmite) This precursor was prepared by a precipitation method employing different raw materials in order to studytheir effect on the synthesis process and several characteristics of thematerials such as the crystallite size the thermal behavior andthe surface area Aluminum chloride (AlCl3sdot6H2O) and an aluminum waste were used as the source of aluminum A 1M NaOHsolution and a 1M n-butylamine solution were used as alkalizing agents due to their strong and weak alkaline characteristicsrespectivelyTheXRDprofiles of the boehmites obtained fromwaste show lower crystallinity than samples obtained fromaluminumchloride The content of water from TG studies was higher in the samples obtained from waste which fit well with the smallercrystallite sizeThe use of n-butylamine as alkalizing agent favors the formation of 120574-aluminawith higher surface area (1772 cm2 gminus1for aluminumwaste and 1594 cm2 gminus1 for aluminumpure reagent)The temperature of transformation from gamma to alpha fromDTA results is higher for samples obtained from the waste and accordingly the presence of impurities in the waste stabilizes themetastable alumina phase

1 Introduction

Alumina polymorphs are mainly prepared by thermaldecomposition of precursors which are generally producedby precipitation of aluminum oxyhydroxides from solutionof reagent grade aluminum salts Depending on the synthe-sis conditions different alumina polymorphs are obtainedwhich differ in chemical composition and crystal structure[1] Boehmite 120574-AlOOH is one of the most popular precur-sors of alumina and its transformation into 120572-Al2O3 involvesa complex sequence of transitional alumina polymorphswhich among others depends strongly on the chemical syn-thesis routes the degree of crystallinity of the precursor thepresence of impurities the alkalinity and so forth [2ndash8] Nat-ural boehmite occurs in the orthorhombic crystal structurewhile synthetic boehmite is amorphous or nanocrystallinedepending on the experimental conditions [9] Syntheticboehmite is frequently developed in order to produce pureelectronic grade Al2O3 ceramics and components Boehmite

transforms into stable 120572-Al2O3 via the sequence AlOOHrarr120574 rarr 120575 rarr 120579 rarr 120572-Al2O3 [5 9]

Recently nanostructured alumina polymorphs wereobtained by the present authors from an aluminum solidwaste [10 11]This fine powdered solid waste can be describedas a complex and heterogeneous blend of several compo-nents among others metallic aluminum aluminum nitridecorundum spinel quartz calcite and iron oxide along withother minor oxides and salts [12] The process consisted ofthe formation of the precursor 120574-AlOOH by a precipitationmethod in which NaOH solution was used as the alkalizingagent [13] The thermal treatment at different temperaturesof the so-obtained boehmite led to the formation of differentpolymorphs of Al2O3 by means of topotactic reactions

The present work describes the application of the aboveprocedure to the synthesis of two polymorphs of aluminathemetastable 120574-Al2O3 and the stable120572-Al2O3 fromdifferentraw materials Thus the aim was to evaluate their effect onthe physical and chemical characteristics of boehmite and 120574-

Hindawi Publishing CorporationJournal of ChemistryVolume 2016 Article ID 5353490 6 pageshttpdxdoiorg10115520165353490

2 Journal of Chemistry

and 120572-alumina Two raw materials were used as aluminumsource the pure reagent AlCl3sdot6H2O and the aluminumwaste previously mentioned Also two different alkalizingagents were tested NaOH and n-butylamine in order toevaluate the effect of using strong or weak alkaline solutions

2 Experimental

21 Reagent and Synthesis The boehmite produced in thisstudy was based on the process described by Gonzalo-Delgado et al (2011) [14] Two aluminum raw materials wereused namely an aluminum waste from the scrap millingprocess in the tertiary aluminum industry [12] and a reagentgrade AlCl3sdot6H2O (Panreac)The waste consisted principallyof 312Almetal 200Al2O3 (corundum) 150MgAl2O4(spinel) 84AlN 80 SiO2 (quartz) 82CaCO3 (calcite)18 Fe2O3 (hematite) 15TiO2 15 chloride (NaK) 07Al2S3 and other minor metal oxides The starting solution ofAl3+ from the aluminum waste was prepared by dissolvingthe soluble aluminum phases contained in the waste (200 g)in a aqueous solution of HCl (10 vv) for two hours at 80∘Cunder continuous and vigorous stirring Then after coolingthe Al3+ solution was separated from the solid residue byfiltration in a pressure system (Millipore YT30 142 HW) at6 bar The resulting solution was adjusted to 1085 g Lminus1 ofAl3+ by adding distilled water A solution of similar concen-tration was prepared by dissolving AlCl3sdot6H2O in distilledwaterThe initial pH values of the aluminum solutions rangedbetween 389 and 398 Aliquots of 400mL of the correspond-ing Al3+ solutions were subjected to an alkalinizing processby dropwise addition of two different alkalinizing agents upto pH 8 a 1M solution of NaOH (Panreac reagent grade) ora 1M solution of n-butylamine (Aldrich C4H11N gt99) Inall the cases a colloidal suspension started to appear at lowpH values The massive precipitation took place at differentvalues of pH (57ndash63) depending on both the starting Al3+solution and the alkalinizing agentThus when n-butylaminewas used the precipitation occurred to a lower pH valuethan for NaOH At these values of pH the instantaneousprecipitation of the aluminum hydroxide occurs accordingto the following general equation

Al3+ + 3OHminus 997888rarr Al (OH)3 (1)

As the pH value increases the evolution of interintraparticleaggregates of the aluminum hydroxide takes place and alu-minum oxyhydroxide is formed

Al (OH)3 +OHminus 997888rarr AlOOH + 2H2O (2)

Figure 1 shows the pH curves for the four samples themassive precipitation is marked as a grey zone Images of theformation stage of the colloidal suspension and the massiveprecipitation stage are also included Alkalinization wasstopped to pH8 because this is the value inwhich boehmite isformed Values higher than 8 favor the formation of bayerite120572-Al(OH)3 and nordstrandite Al(OH)3 [15 16] As observedin this figure the amount of alkalizing agent used in theprecipitation process is higher when the aluminum source is

AlB

AlNa

AWNa

AWB

50 100 150 200 250 300 3500V (mL)

3

4

5

6

7

8

pH

Figure 1 Curves of pH for the formation of boehmite fromAlCl3sdot6H2O (AlNa with NaOH and AlB with n-butylamine)and aluminum waste (AWNa with NaOH and AWB with n-butylamine)

Figure 2 Macroscopic appearance of the boehmite gel obtainedafter filtration

the waste due to the presence of other elements such as ironThe suspensionswere kept stirring for 24 h for agingThen thesolid was filtered (Figure 2) washed three times with distilledwater and once with ethanol dried at 60∘C for 48 h andcrushed in a mortar to get a fine powder From hereinafterAlNa and AlB correspond to alumina precursors obtainedusing AlCl3sdot6H2O as the source of aluminum andNaOH andn-butylamine as the alkalizing agent respectively and AWNaand AWB correspond to alumina precursors obtained usingthe aluminum waste as the source of aluminum and NaOHand n-butylamine as the alkalizing agent respectively

The so-obtained alumina precursors were subjected tocalcinations under air atmosphere to 600∘C and 1400∘C intoa muffle furnace (Thermoconcept HT0417) for 7 h and aheating rate of 10∘Cminminus1 in order to get 120574- and120572-Al2O3Theproducts obtained at 600∘C are named as 120574-AlNa 120574-AlB 120574-AWNa and 120574-AWB and those obtained at 1400∘C as 120572-AlNa120572-AlB 120572-AWNa and 120572-AWB in relation to the nomenclatureused for the corresponding precursor

22 Techniques Samples were characterised as followsPowder X-ray diffraction (XRD) was carried out using a

Journal of Chemistry 3

051031120AlNa

AlB

AWBInte

nsity

(au

)

AWNa

020

20 30 40 50 60102120579 (∘)

0

100

200

300

400

500

Figure 3 XRD patterns of boehmite obtained from AlCl3sdot6H2O(AlNa with NaOH and AlB with n-butylamine) and aluminumwaste (AWNa with NaOH and AWB with n-butylamine)

Bruker D8 Advance diffractometer with CuK120572 radiationfrom 5 to 60∘ 2120579 at a scan rate of 0025∘ 2120579 1 s per step 40 kVand 30mADTATG studywas performed up to 1300∘C in airatmosphere (flow rate 100mLminminus1) at a ramp of20∘Cminminus1 on a SDTQ600 by TA Instruments In this tech-nique alumina crucibles were filled with 20mg of thesample In order to obtain 120574-Al2O3 and 120572-Al2O3 theprecursors were calcined in a muffle furnace up to 600 and1300∘C respectively for 7 h in static air atmosphere Thespecific surface areawas determined by theBETmethod fromnitrogen adsorptiondesorption isotherms at 77K on samplespreviously outgassed overnight at 50∘C on a ASAP2020Micromeritics Instrument

3 Results and Discussion

The XRD patterns of the alumina precursors obtained fromalkalinization of Al3+ solutions are shown in Figure 3 All ofthem exhibit the characteristic XRD profile of boehmite 120574-AlOOH according to the reference file JCPDS 01-088-2112(2120579 value for the hkl index 120 = 2813∘) Nevertheless severaldifferences are observed The samples obtained from wasteexhibit lower crystallinity than those obtained from purereagent The four hkl indexes 020 120 031 and 051 are welldefined for samples AlNa and AlB but the first one is scarcelyobserved in samples AWNa and AWB The absence of 020reflection is generally observed for boehmites with very lowcrystallite size such as those obtained by ldquosol-gelrdquo methods[17] The hkl index 120 of boehmite appears centered at ahigher 2120579 value for samples obtained from waste (sim288∘)than for samples obtained from pure aluminum chloride(273ndash275∘)This reflectionwas used to determine the crystal-lite size by the Scherrer equation [18]The results are shown inTable 1 All samples present crystallite size smaller than 3 nmthis indicates that all the boehmites are nanocrystallineSimilar crystallite sizes are reported by Bokhimi et al [17]for boehmites obtained at low temperature fromAlCl3sdot6H2O

Table 1 Diffraction angle reticular space and crystallite size ofboehmites

hkl 120 2120579 (∘) 119889 (A) Cryst size (nm)AlNa 2754 32362 240AlB 2733 32601 234AWNa 2881 30967 182AWB 2886 30911 267

and NH4OH as the alkalizing agent Thus it might beassumed that for the formation of boehmite in our exper-imental conditions the source of Al3+ produces a higherinfluence on the position of XRD reflections the reticularspace and the crystallinity than the alkalizing agent

The TGDTA curves of samples are shown in Figure 4The profile of TG curves is quiet similar for all cases It canbe observed that the total dehydrationdehydroxylation takesplace in consecutive stages with bad defined inflexions Thetotal mass loss (from room temperature to 1300∘C) variedaccording to the starting Al3+ solution and the alkalizingagent Thus for samples obtained from AlCl3 the mass loss(321 forAlNa and 358 forAlB) is smaller than for samplesobtained from waste (391 for AWNa and 409 for AWB)indicating that the boehmite (AlOOHsdot119899H2O) obtained fromwaste retains higher amount of water The value of 119899 cal-culated from total mass loss was 084 108 132 and 146for AlNa AlB AWNa and AWB respectively For the samealuminum starting solution the water content is higher whenn-butylamine is used as alkalizing agentThewater content inboehmite is strongly dependent on the experimental synthe-sis conditions [2] From 600 to 1300∘C the metastablealumina polymorphs evolve towards the stable polymorphand mass losses should not be observed Nevertheless masslosses ranging between 1 and 2 are observed in TG curves Itis attributable to certain amount of remnant hydroxyl groupsaccording to Tsukada et al [19] which is favored by boththe waste and n-butylamine Thus this mass loss is higherfor samples from waste and also higher from samples fromn-butylamine (AlNa 105 AlB 147 AWNa 151 andAWB 186)

The results of the thermal analyses are collected inTable 2From the profile of the DTA curves it can be observed thatnot only the dehydrationdehydroxylation processes but alsothe transformation of the metastable alumina phase into thestable polymorph is highly affected by the alumina precursorThus this last process is attained at very much highertemperature for samples obtained from the waste (1280 and1293∘C) than for samples obtained from the reagent gradeAl3+ solution (1024 and 1103∘C) and it can be attributable tothe presence of impurities in the waste which stabilize themetastable alumina phase [10]

XRD patterns of the phases obtained at 600∘C for 7 h areshown in Figure 5 All the patterns are quiet similar and con-sist of diffuse profiles with very significant background andonly a very broad peak which can be indexed as the hkl index400 of the 120574-alumina according to the reference file JCPDS00-029-0063 (2120579 diffraction angle for the hkl index 400 =4583∘)Thediffraction angles reticular spaces and crystallite


AWNa166

151

5519

AWB128

34

167

79

AlB119

129

7238

AlNa183

111

27

50

60

70

80

90

100

Wei

ght (

)

230∘C

885∘C1280∘C

1113∘C1024∘C

200 400 600 800 1000 12000Temperature (∘C)

200 400 600 800 1000 12000Temperature (∘C)

200 400 600 800 1000 12000Temperature (∘C)

200 400 600 800 1000 12000Temperature (∘C)

50

60

70

80

90

100

Wei

ght (

)

50

60

70

80

90

100

Wei

ght (

)

50

60

70

80

90

100

Wei

ght (

)

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

125∘C

441∘C872∘C

811∘C

201∘C133∘C

128∘C

377∘C118∘C

193∘C

402∘C

Figure 4 TG and DTA curves of the boehmites obtained AlCl3sdot6H2O (AlNa with NaOH and AlB with n-butylamine) and aluminumwaste(AWNa with NaOH and AWB with n-butylamine)

Table 2 Thermal analyses results

Sample TG DTA119879 (∘C) Δ119898119901 (wt ) Δ119898119905 (wt ) 119879peak (

∘C) 119864(120583vsdotminmg)

AlNa25ndash283 183

321128 Endo 79

283ndash475 111 377 Endo 09475ndash1300 27 1024 Exo 06

AlB25ndash349 119

358

118 Endo 128129 193 Endo


AWB

25ndash168 128

409

125 Endo 208168ndash343 168 230 Endo343ndash523 79 441 Endo 11

523ndash1300 34 883 Exo 041293 Exo nd

AWNa

25ndash348 166

391

133 Endo 158151 201

348ndash556 55 mdash mdash

556ndash1300 19811 Exo 088731280 Exo nd

nd not determined


120574-AlNa

120574-AlB

120574-AWB

120574-AWNa

400

20 30 40 50 60102120579 (∘)

Inte

nsity

(au

)

0

100

200

300

400

500

Figure 5 XRD patterns of 120574-Al2O3 obtained from AlCl3sdot6H2O(AlNa with NaOH and AlB with n-butylamine) and aluminumwaste (AWNa with NaOH and AWB with n-butylamine)

Table 3 Diffraction angle reticular space and crystallite size of thehkl index 400




size are collected in Table 3 This peak is shifted to a lowerangle when NaOH solution was used as the alkalizing agentBecause the transformation of boehmite into 120574-Al2O3 ispseudomorphic at this temperature [10 17] these transi-tional alumina polymorphs will have a crystallite size highlydependent on the precursor crystal dimensions and thusnanocrystalline gamma alumina polymorphs were obtainedwith crystal size below 4 nm

XRD patterns of samples obtained at 1300∘C for 7 hare shown in Figure 6 All the patterns are quiet similarand consist of well-defined and very narrow peaks whichare characteristic of well-crystallized samples with largecrystallite size Patterns fit well with that of 120572-Al2O3 of thereference file JCPDS 01-075-1862 The position of the XRDreflections is quiet similar for the four samples but the effectof butylamine in peaks intensity is noticeable In this waythe samples obtained using this alkalizing agent are morecrystalline than those using NaOH The diffraction anglesreticular spaces and crystallite size are collected in Table 4

611

420

311

011

210

401

120572-AlNa

120572-AlB

120572-AWB

120572-AWNa

Inte

nsity

(au

)

0

100

200

300

400

500

600

700

800

900

1000

20 30 40 50 60102120579 (∘)


Table 5 Specific area (BET) of boehmites and 120574-aluminas

Samples Surface area (m2sdotgminus1)AlNa 669 plusmn 06 1449 plusmn 17

AlB 668 plusmn 04 1594 plusmn 13

AWNa 1195 plusmn 08 1405 plusmn 07

AWB 1166 plusmn 11 1772 plusmn 10

The 120574-Al2O3 is generally described as a defect spinelstructure with aluminum cations distributed over octahedraland tetrahedral sites while 120572-Al2O3 has a trigonal structurein which every aluminum atom is coordinated octahedrallyDuring the transformation of gamma to alpha alumina thealuminum and oxygen atoms arrange and the gaps betweenthe chains and the crystal defects are reduced and accordinglythe crystal dimension enlarges

Concerning the BET specific surface area of boehmiteswhen the waste was used as aluminum source the value ishigher (1195m2 gminus1 for AWNa and 1166m2 gminus1 for AWB)than for samples obtained from reagent grade aluminumsolution (669m2 gminus1 for AlNa and 668m2 gminus1 for AlB)Nevertheless these values are in general low in comparison tothose reported in the literature for nanocrystalline boehmite[14 20] This can be attributable to the very low temperatureof outgassing (50∘C) used prior to adsorptionmeasurementswhich was not high enough to remove or absorb waterandor other species generated during the synthesis processGuzman-Castillo et al [7] reported that pseudoboehmitesexhibit higher values of specific area than boehmites In ourcase samples obtained fromwaste exhibit higher specific areaand according to the XRD profiles (Figure 3) they may beconsidered as pseudoboehmites

The values of specific surface area (BET) for boehmitesand 120574-alumina are collected in Table 5 The specific surfacearea of 120574-alumina is higher when n-butylamine is used as thealkalizing agent


4 Conclusions

The characteristics of boehmite are highly dependent on theAl source and the alkalizing agent used in the process of syn-thesis The samples with smaller crystallite size are obtainedusing the waste as aluminum sourceThus the source of Al3+produces a higher influence on the position of XRD reflec-tions the reticular space and the crystallinity than the alka-lizing agent The value of 119899 in the stoichiometry of boehmite120574-AlOOHsdot119899H2O is very dependent on both the aluminumsource and the alkalizing agent It is higher for samplesobtained from the aluminum waste and for the same alumi-num starting solution when n-butylamine is used as thealkalizing agent

The dehydrationdehydroxylation process of boehmite toform 120574-Al2O3 is highly affected by the raw materials and alsothe process of transformation of the metastable alumina intothe stable polymorph corundumThis last process is attainedat very much higher temperature for samples obtained fromthe waste than for samples obtained from reagent grade Al3+solution and it can be attributable to the presence of impuri-ties in the waste which stabilize the metastable alumina

Boehmites with highest specific surface area are obtainedfrom waste The use of n-butylamine as the alkalizing agentfavors the formation of 120574-Al2O3 with the highest 119878BET

In the case of 120572-Al2O3 the samples obtained using n-butylamine as the alkalizing agent are more crystalline thanthose using NaOH but any effects are not observed for thedifferent aluminum source

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

Authors thank CSIC for the financial support and CAI ofGeological Techniques de la UCM for the technical support

References

[1] P Alphonse andM Courty ldquoStructure and thermal behavior ofnanocrystalline boehmiterdquoThermochimica Acta vol 425 no 1-2 pp 75ndash89 2005

[2] Y Liu D Ma X Han et al ldquoHydrothermal synthesis ofmicroscale boehmite and gamma nanoleaves aluminardquo Mate-rials Letters vol 62 no 8-9 pp 1297ndash1301 2008

[3] J Sanchez-Valente X Bokhimi and J A Toledo ldquoSynthesisand catalytic properties of nanostructured aluminas obtainedby sol-gel methodrdquo Applied Catalysis A General vol 264 no 2pp 175ndash181 2004

[4] L K Hudson C Misra A J Perrotta K Wefers and FS Williams ldquoAluminum oxiderdquo in Ullmannrsquos Encyclopedia ofIndustrial Chemistry vol 2 pp 607ndash645 Wiley-VCH Wein-heum Germany 2012

[5] A Boumaza L Favaro J Ledion et al ldquoTransition aluminaphases induced by heat treatment of boehmite an X-raydiffraction and infrared spectroscopy studyrdquo Journal of SolidState Chemistry vol 182 no 5 pp 1171ndash1176 2009

[6] J Li X Wang L Wang et al ldquoPreparation of alumina mem-brane from aluminium chloriderdquo Journal of Membrane Sciencevol 275 no 1-2 pp 6ndash11 2006

[7] M L Guzman-Castillo X Bokhimi A Toledo-AntonioJ Salmones-Blasquez and F Hernandez-Beltran ldquoEffect ofBoehmite crystallite size and steaming on alumina propertiesrdquoJournal of Physical Chemistry B vol 105 no 11 pp 2099ndash21062001

[8] X Bokhimi J A Toledo-Antonio M L Guzman-Castillo BMar-Mar FHernandez-Beltran and J Navarrete ldquoDependenceof boehmite thermal evolution on its atom bond lengths andcrystallite sizerdquo Journal of Solid State Chemistry vol 161 no 2pp 319ndash326 2001

[9] S Ram ldquoInfrared spectral study of molecular vibrations inamorphous nanocrystalline and AlO(OH)sdot120572H2O bulk crys-talsrdquo Infrared Physics and Technology vol 42 no 6 pp 547ndash5602001

[10] J A Jimenez I Padilla A Lopez-Delgado L Fillali andS Lopez-Andres ldquoCharacterization of the aluminas formedduring the thermal decomposition of boehmite by the rietveldrefinement methodrdquo International Journal of Applied CeramicTechnology vol 12 no 2 pp E178ndashE186 2015

[11] L Fillali S Lopez-Andres A Lopez-Delgado I Padilla and JA Jimenez ldquoStructural and morphological evolution of pow-ders nanostructured ceramics transitional aluminasrdquo Chem-istry and Materials Research vol 4 pp 45ndash49 2013

[12] R Galindo I Padilla O Rodrıguez R Sanchez-HernandezS Lopez-Andres and A Lopez-Delgado ldquoCharacterizationof solid wastes from aluminum tertiary sector the currentstate of spanish industryrdquo Journal of Minerals and MaterialsCharacterization and Engineering vol 3 no 2 pp 55ndash64 2015

[13] A Lopez-Delgado L Fillali J A Jimenez and S Lopez-AndresldquoSynthesis of 120572-alumina from a less common raw materialrdquoJournal of Sol-Gel Science and Technology vol 64 no 1 pp 162ndash169 2012

[14] L Gonzalo-Delgado A Lopez-Delgado F A Lopez F JAlguacil and S Lopez-Andres ldquoRecycling of hazardous wastefrom tertiary aluminium industry in a value-added materialrdquoWaste Management and Research vol 29 no 2 pp 127ndash1342011

[15] S Music D Dragcevic S Popovic and N Vdovic ldquoMicrostruc-tural properties of boehmite formed under hydrothermal con-ditionsrdquoMaterials Science and Engineering B vol 52 no 2-3 pp145ndash153 1998

[16] G C Bye and J G Robinson ldquoCrystallization processes inaluminium hydroxide gelsrdquo Colloid and Polymer Science vol198 no 1 pp 53ndash60 1964

[17] X Bokhimi J A Toledo-Antonio M L Guzman-Castillo andF Hernandez-Beltran ldquoRelationship between crystallite sizeand bond lengths in boehmiterdquo Journal of Solid State Chemistryvol 159 no 1 pp 32ndash40 2001

[18] S Music D Dragcevic and S Popovic ldquoHydrothermal crys-tallization of boehmite from freshly precipitated aluminumhydroxiderdquoMaterials Letters vol 40 no 6 pp 269ndash274 1999

[19] T Tsukada H Segawa A Yasumori and K Okada ldquoCrys-tallinity of boehmite and its effect on the phase transitiontemperature of aluminardquo Journal of Materials Chemistry vol 9no 2 pp 549ndash553 1999

[20] K Okada T Nagashima Y Kameshima A Yasumori and TTsukada ldquoRelationship between formation conditions proper-ties and crystallite size of boehmiterdquo Journal of Colloid andInterface Science vol 253 no 2 pp 308ndash314 2002

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and 120572-alumina Two raw materials were used as aluminumsource the pure reagent AlCl3sdot6H2O and the aluminumwaste previously mentioned Also two different alkalizingagents were tested NaOH and n-butylamine in order toevaluate the effect of using strong or weak alkaline solutions

2 Experimental

21 Reagent and Synthesis The boehmite produced in thisstudy was based on the process described by Gonzalo-Delgado et al (2011) [14] Two aluminum raw materials wereused namely an aluminum waste from the scrap millingprocess in the tertiary aluminum industry [12] and a reagentgrade AlCl3sdot6H2O (Panreac)The waste consisted principallyof 312Almetal 200Al2O3 (corundum) 150MgAl2O4(spinel) 84AlN 80 SiO2 (quartz) 82CaCO3 (calcite)18 Fe2O3 (hematite) 15TiO2 15 chloride (NaK) 07Al2S3 and other minor metal oxides The starting solution ofAl3+ from the aluminum waste was prepared by dissolvingthe soluble aluminum phases contained in the waste (200 g)in a aqueous solution of HCl (10 vv) for two hours at 80∘Cunder continuous and vigorous stirring Then after coolingthe Al3+ solution was separated from the solid residue byfiltration in a pressure system (Millipore YT30 142 HW) at6 bar The resulting solution was adjusted to 1085 g Lminus1 ofAl3+ by adding distilled water A solution of similar concen-tration was prepared by dissolving AlCl3sdot6H2O in distilledwaterThe initial pH values of the aluminum solutions rangedbetween 389 and 398 Aliquots of 400mL of the correspond-ing Al3+ solutions were subjected to an alkalinizing processby dropwise addition of two different alkalinizing agents upto pH 8 a 1M solution of NaOH (Panreac reagent grade) ora 1M solution of n-butylamine (Aldrich C4H11N gt99) Inall the cases a colloidal suspension started to appear at lowpH values The massive precipitation took place at differentvalues of pH (57ndash63) depending on both the starting Al3+solution and the alkalinizing agentThus when n-butylaminewas used the precipitation occurred to a lower pH valuethan for NaOH At these values of pH the instantaneousprecipitation of the aluminum hydroxide occurs accordingto the following general equation

Al3+ + 3OHminus 997888rarr Al (OH)3 (1)

As the pH value increases the evolution of interintraparticleaggregates of the aluminum hydroxide takes place and alu-minum oxyhydroxide is formed

Al (OH)3 +OHminus 997888rarr AlOOH + 2H2O (2)

Figure 1 shows the pH curves for the four samples themassive precipitation is marked as a grey zone Images of theformation stage of the colloidal suspension and the massiveprecipitation stage are also included Alkalinization wasstopped to pH8 because this is the value inwhich boehmite isformed Values higher than 8 favor the formation of bayerite120572-Al(OH)3 and nordstrandite Al(OH)3 [15 16] As observedin this figure the amount of alkalizing agent used in theprecipitation process is higher when the aluminum source is

AlB

AlNa

AWNa

AWB

50 100 150 200 250 300 3500V (mL)

3

4

5

6

7

8

pH

Figure 1 Curves of pH for the formation of boehmite fromAlCl3sdot6H2O (AlNa with NaOH and AlB with n-butylamine)and aluminum waste (AWNa with NaOH and AWB with n-butylamine)

Figure 2 Macroscopic appearance of the boehmite gel obtainedafter filtration

the waste due to the presence of other elements such as ironThe suspensionswere kept stirring for 24 h for agingThen thesolid was filtered (Figure 2) washed three times with distilledwater and once with ethanol dried at 60∘C for 48 h andcrushed in a mortar to get a fine powder From hereinafterAlNa and AlB correspond to alumina precursors obtainedusing AlCl3sdot6H2O as the source of aluminum andNaOH andn-butylamine as the alkalizing agent respectively and AWNaand AWB correspond to alumina precursors obtained usingthe aluminum waste as the source of aluminum and NaOHand n-butylamine as the alkalizing agent respectively

The so-obtained alumina precursors were subjected tocalcinations under air atmosphere to 600∘C and 1400∘C intoa muffle furnace (Thermoconcept HT0417) for 7 h and aheating rate of 10∘Cminminus1 in order to get 120574- and120572-Al2O3Theproducts obtained at 600∘C are named as 120574-AlNa 120574-AlB 120574-AWNa and 120574-AWB and those obtained at 1400∘C as 120572-AlNa120572-AlB 120572-AWNa and 120572-AWB in relation to the nomenclatureused for the corresponding precursor

22 Techniques Samples were characterised as followsPowder X-ray diffraction (XRD) was carried out using a


051031120AlNa

AlB

AWBInte

nsity

(au

)

AWNa

020

20 30 40 50 60102120579 (∘)

0

100

200

300

400

500












AWNa166

151

5519

AWB128

34

167

79

AlB119

129

7238

AlNa183

111

27

50

60

70

80

90

100

Wei

ght (

)

230∘C

885∘C1280∘C

1113∘C1024∘C

200 400 600 800 1000 12000Temperature (∘C)

200 400 600 800 1000 12000Temperature (∘C)

200 400 600 800 1000 12000Temperature (∘C)

200 400 600 800 1000 12000Temperature (∘C)

50

60

70

80

90

100

Wei

ght (

)

50

60

70

80

90

100

Wei

ght (

)

50

60

70

80

90

100

Wei

ght (

)

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

125∘C

441∘C872∘C

811∘C

201∘C133∘C

128∘C

377∘C118∘C

193∘C

402∘C




∘C) 119864(120583vsdotminmg)

AlNa25ndash283 183

321128 Endo 79


AlB25ndash349 119

358

118 Endo 128129 193 Endo


AWB

25ndash168 128

409


523ndash1300 34 883 Exo 041293 Exo nd

AWNa

25ndash348 166

391

133 Endo 158151 201


556ndash1300 19811 Exo 088731280 Exo nd

nd not determined


120574-AlNa

120574-AlB

120574-AWB

120574-AWNa

400

20 30 40 50 60102120579 (∘)

Inte

nsity

(au

)

0

100

200

300

400

500








611

420

311

011

210

401

120572-AlNa

120572-AlB

120572-AWB

120572-AWNa

Inte

nsity

(au

)

0

100

200

300

400

500

600

700

800

900

1000

20 30 40 50 60102120579 (∘)











4 Conclusions





Competing Interests


Acknowledgments


References






























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


051031120AlNa

AlB

AWBInte

nsity

(au

)

AWNa

020

20 30 40 50 60102120579 (∘)

0

100

200

300

400

500












AWNa166

151

5519

AWB128

34

167

79

AlB119

129

7238

AlNa183

111

27

50

60

70

80

90

100

Wei

ght (

)

230∘C

885∘C1280∘C

1113∘C1024∘C

200 400 600 800 1000 12000Temperature (∘C)

200 400 600 800 1000 12000Temperature (∘C)

200 400 600 800 1000 12000Temperature (∘C)

200 400 600 800 1000 12000Temperature (∘C)

50

60

70

80

90

100

Wei

ght (

)

50

60

70

80

90

100

Wei

ght (

)

50

60

70

80

90

100

Wei

ght (

)

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

125∘C

441∘C872∘C

811∘C

201∘C133∘C

128∘C

377∘C118∘C

193∘C

402∘C




∘C) 119864(120583vsdotminmg)

AlNa25ndash283 183

321128 Endo 79


AlB25ndash349 119

358

118 Endo 128129 193 Endo


AWB

25ndash168 128

409


523ndash1300 34 883 Exo 041293 Exo nd

AWNa

25ndash348 166

391

133 Endo 158151 201


556ndash1300 19811 Exo 088731280 Exo nd

nd not determined


120574-AlNa

120574-AlB

120574-AWB

120574-AWNa

400

20 30 40 50 60102120579 (∘)

Inte

nsity

(au

)

0

100

200

300

400

500








611

420

311

011

210

401

120572-AlNa

120572-AlB

120572-AWB

120572-AWNa

Inte

nsity

(au

)

0

100

200

300

400

500

600

700

800

900

1000

20 30 40 50 60102120579 (∘)











4 Conclusions





Competing Interests


Acknowledgments


References






























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


AWNa166

151

5519

AWB128

34

167

79

AlB119

129

7238

AlNa183

111

27

50

60

70

80

90

100

Wei

ght (

)

230∘C

885∘C1280∘C

1113∘C1024∘C

200 400 600 800 1000 12000Temperature (∘C)

200 400 600 800 1000 12000Temperature (∘C)

200 400 600 800 1000 12000Temperature (∘C)

200 400 600 800 1000 12000Temperature (∘C)

50

60

70

80

90

100

Wei

ght (

)

50

60

70

80

90

100

Wei

ght (

)

50

60

70

80

90

100

Wei

ght (

)

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

minus2

minus15

minus1

minus05

0

05

Tem

pera

ture

diff

eren

ce (120583

V m

minus1 )

125∘C

441∘C872∘C

811∘C

201∘C133∘C

128∘C

377∘C118∘C

193∘C

402∘C




∘C) 119864(120583vsdotminmg)

AlNa25ndash283 183

321128 Endo 79


AlB25ndash349 119

358

118 Endo 128129 193 Endo


AWB

25ndash168 128

409


523ndash1300 34 883 Exo 041293 Exo nd

AWNa

25ndash348 166

391

133 Endo 158151 201


556ndash1300 19811 Exo 088731280 Exo nd

nd not determined


120574-AlNa

120574-AlB

120574-AWB

120574-AWNa

400

20 30 40 50 60102120579 (∘)

Inte

nsity

(au

)

0

100

200

300

400

500








611

420

311

011

210

401

120572-AlNa

120572-AlB

120572-AWB

120572-AWNa

Inte

nsity

(au

)

0

100

200

300

400

500

600

700

800

900

1000

20 30 40 50 60102120579 (∘)











4 Conclusions





Competing Interests


Acknowledgments


References






























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


120574-AlNa

120574-AlB

120574-AWB

120574-AWNa

400

20 30 40 50 60102120579 (∘)

Inte

nsity

(au

)

0

100

200

300

400

500








611

420

311

011

210

401

120572-AlNa

120572-AlB

120572-AWB

120572-AWNa

Inte

nsity

(au

)

0

100

200

300

400

500

600

700

800

900

1000

20 30 40 50 60102120579 (∘)











4 Conclusions





Competing Interests


Acknowledgments


References






























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


4 Conclusions





Competing Interests


Acknowledgments


References






























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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Research Article Effects of Different Raw Materials in the ...downloads.hindawi.com/journals/jchem/2016/5353490.pdf · metastable alumina phase. 1. Introduction Alumina polymorphs