Research Article Thermal Decomposition of Hydrocalumite over a...

Research ArticleThermal Decomposition of Hydrocalumite over a TemperatureRange of 400ndash1500∘C and Its Structure Reconstruction in Water

Jiao Tian and Qinghai Guo

State Key Laboratory of Biogeology and Environmental Geology and School of Environmental Studies China University of Geosciences388 Lumo Road Wuhan Hubei 430074 China

Correspondence should be addressed to Qinghai Guo qhguo2006gmailcom

Received 25 May 2014 Accepted 8 July 2014 Published 17 July 2014

Academic Editor M Fernanda Carvalho

Copyright copy 2014 J Tian and Q Guo 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

The thermal decomposition process and structure memory effect of hydrocalumite were investigated systematically for the firsttime over a wide temperature range of 400ndash1500∘C The calcined hydrocalumite samples and their rehydrated products werecharacterized by XRD FT-IR and SEM-EDX The results show that the calcination products at temperatures ranging from 500to 900∘C are basically mayenite and lime while one of the final products obtained by calcination at and above 1000∘C is probablytricalcium aluminate (Ca

3

Al2

O6

) For the hydrocalumite samples calcined at temperatures below 1000∘C their lamellar structurecan be completely recovered in deionized water at room temperature However the further increase of calcination temperaturecould impair the regeneration ability of hydrocalumite via contact with water Upon calcination of hydrocalumite at 1000ndash1500∘Cfollowed by reaction with water a stable compound tricalcium aluminate hexahydrate (Ca

3

Al2

O6

sdot6H2

O) was produced which isthe reason why less hydrocalumite could be regenerated

1 Introduction

Hydrocalumite also known as Friedelrsquos salt [1] or AFm phasein cement science [2] belongs to the family of layered doublehydroxides (LDHs) [3] It is commonly synthesized by usingcalcium and aluminum salts However hydrocalumite couldalso be formed as the major stable hydration product ofcement paste and concrete or as secondary precipitate duringthe hydration of fly ash spent oil shale and some other solidwaste materials [4] In the crystal structure of hydrocalumitethe divalent Ca2+ are located in the center of edge-sharingoctahedra and partially substituted by trivalent Al3+ whichresults in a net positive charge to the layers that has to becompensated by intercalation of gallery anions In view of itsunique structure and chemical characteristics hydrocalumitehas been applied in not only catalysis industry but also envi-ronmental remediation In recent years it was widely used forremoving undesirable anions from wastewaters or contami-nated natural waters including B(OH)

4

minus CrO4

2minus H2PO4

minusAsO2

minus MoO4

2minus SeO4

2minus [4 5] and even some organic anions(eg dodecyl benzene sulfate (DBSminus) and methyl orange

(MO)) [6 7] The involved anion uptake mechanisms com-prise surface adsorption anion exchange and dissolution-reprecipitation Our group has also made use of hydrocalu-mite to remove a wide range of concentrations of fluoride andarsenate from water successfully via anion exchange andprecipitation [8]

Since 1989 when the ldquostructure memory effectrdquo of layereddouble hydroxides was first reported [9 10] it has beenacknowledged that thermal treatment of LDHs is an effectiveway to enhance their anion uptake capacity [11ndash13] andtherefore a full understanding of thermal behavior of hydro-calumite is quite important for its efficient application as asorbent in reducing aqueous anionic contaminants It is gen-erally accepted that the thermal decomposition process ofhydrocalumite can be divided into three steps Lopez-Salinaset al [14] denoted that the layered structure of hydrocalumitecollapses when heated above 250∘C turns into amorphousphases at 300∘C and becomes a solid solution of calciumoxide (CaO) and mayenite (Ca

12Al14O33) at 600ndash700∘C

Vieille et al [15] indicated that the thermal decomposition ofhydrocalumite consists of dehydration dehydroxylation and

Hindawi Publishing CorporationJournal of ChemistryVolume 2014 Article ID 454098 8 pageshttpdxdoiorg1011552014454098

2 Journal of Chemistry

anion decomposition These processes may overlap witheach other in different extents [16] Upon cooling to roomtemperature in ambient atmosphere low-temperature cal-cined hydrocalumite (lt280∘C) can recover its initial layeredstructure spontaneously and the reaction rate depends on airhumidity and other experimental conditions [15] In compar-ison the amorphous compounds obtained via calcination at400∘C have an ability to reconstruct the original structure ofhydrocalumite when exposed to aqueous solution of KCl Inthe relevant literatures the conversion of calcined productsto layered hydrocalumite was referred to as different termssuch as regeneration reconstruction and rehydration whilethe whole process was reported as ldquocalcination-rehydrationprocessrdquo or ldquostructurememory effectrdquo [17] Although the ther-mal decomposition of hydrocalumite has been investigatedat comparatively low temperature there is so far a lack ofsystematic studies on the thermal behavior and structurememory effect of hydrocalumite at higher temperaturesThisstudy focuses on the structural and compositional changesof hydrocalumite upon calcination over a much wider tem-perature range (400ndash1500∘C) The rehydration process of thecalcination products obtained at different temperatures indeionized water was also evaluated

2 Experimental

21 Synthesis of Hydrocalumite Hydrocalumite was preparedby the coprecipitation method that has been describedelsewhere [18] Typically the synthesis was carried out at65∘C under vigorous magnetic stirring A mixed solutionof 066M CaCl

2sdot2H2O and 033M AlCl

3sdot6H2O was added

dropwise to a beaker filled with a mixture consisting of waterand ethanol in a 2 3 volumetric ratio The pH was keptconstant at 115 by the simultaneous addition of 2M NaOHThe suspension was aged at 65∘C for 24 h after the additionof metallic salts had been complete The solid productswere separated by centrifugation and washed severaltimes with deionized water until pH 7-8 The synthesizedhydrocalumite sample was subjected to an elemental analysisbased on which its approximate chemical formula wasestimated to be Ca

4Al2(OH)12Cl171

(OH)029sdot343H

2O

(MM = 5435 gmol) very close to the theoretical formula(Ca4Al2(OH)12Cl2sdot6H2O)

22 Calcination andRegeneration Procedure Thesynthesizedhydrocalumite was calcined for 2 h in a muffle furnace underambient atmosphere at the temperatures ranging from 400to 1500∘C with an increasing step of 100∘C The calcinationproductswere cooled to room temperature in a container pre-viously filled with allochroic silica gel as desiccant The massof the samples wasmeasured before and after calcinationTheregeneration procedure for the calcined hydrocalumite wasperformed by reacting with deionized water in polyethylenebottles at a constant temperature of 25∘C for 24 hours

23 Characterization Techniques The solid samples dried inoven of 50∘C were characterized by an XrsquoPert PRO DY2198diffractometer with Cu K120572 radiation and the XRD patterns

Table 1 Mass loss of hydrocalumite samples calcined at differenttemperatures

119879 (∘C) Mass loss ()

400 266

500 277

600 318

700 319

800 349

900 314

1000 391

1100 380

1200 407

1300 416

1400 358

1500 408

were recorded in the 120579-2120579 mode between 5∘ and 65∘ with a2120579 step of 0033∘ Their Fourier transform infrared spectra(FT-IR) were obtained using a FTIR Equinox 55 Brukerspectrometer with a scan range of 400ndash4000 cmminus1 and aresolution of 4 cmminus1 The KBr pellet technique was usedto prepare the sample that was introduced into the FT-IRcell The calcined hydrocalumite samples together with thoseundergoing regeneration procedures were also analyzed witha FEI Quanta200 Scanning Electron Microscope (SEM)equipped with an Energy Dispersive X-Ray (EDX) analyticalcapability for morphology crystallinity and elemental com-position Both SEM and EDX analyses were taken at 20 kVexcitation

3 Results and Discussion

31 Mass Loss of Calcined Products In general the mass lossof calcined product increases as the calcination temperaturerises except for three samples heated at 900 1100 and 1400∘Cshowing anomalously low mass losses The possible reason isthe rehydration of these samples during their cooling to roomtemperature The mass loss of hydrocalumite upon calcina-tion at 400∘C is 266 (Table 1) very close to 233 a theo-retical value corresponding to the calcination process duringwhich all interlayer water molecules including OHminus andClminus break away from the hydrocalumite structure as otherinvestigators had noticed [14 15] In this case the calcinedproduct could spontaneously reconstruct its original struc-ture with water molecules upon exposure to atmosphereThecalcination products obtained at temperatures higher than500∘C however can only regenerate the layered hydrocalu-mite structure by incorporating anions in aqueous solutionAt temperatures higher than 1000∘C the mass loss of hydr-ocalumite upon thermal decomposition is approaching400 a value indicating that it broke up into mayenite(Ca12Al14O33) and lime (CaO) [15] The formation of these

Journal of Chemistry 3

100 200 300 400 500 600

M

M

MM

M

M

M

M

M

M

MMM

M

M

CcCc CC

LL

L

L

HpHp

CH900

CH800

CH700

CH600

CH500

CH400

Rela

tive

inte

nsity

2120579

(a)

100 200 300 400 500 600

M

M MM

L

M

M C

L

LLp

L

L

Hp CH1500

CH1400

CH1300

CH1200

CH1100

CH1000

Rela

tive

inte

nsity

2120579

(b)

100 200 300 400 500 600

H

H

H

H

H

HH H H HH HH

HCH900

HCH800

HCH700

HCH600

HCH500

HCH400

Rela

tive

inte

nsity

2120579

(c)

100 200 300 400 500 600

CA

CA

CA

CACA

CA

CACACACACACACA

HCH1500

HCH1400

HCH1300

HCH1200

HCH1100

HCH1000

Rela

tive

inte

nsity

2120579

HH

H

HH

H

H

H H

HHH

(d)

Figure 1 XRD patterns of hydrocalumite samples calcined over a temperature range of 400ndash1500∘C and their rehydrated products (a)Hydrocalumite samples calcined at temperatures ranging from 400 to 900∘C (b) hydrocalumite samples calcined at temperatures rangingfrom 1000 to 1500∘C (c) rehydrated samples corresponding to those in Figure 1(a) (d) rehydrated samples corresponding to those inFigure 1(b) C calcite CA tricalcium aluminate hexahydrate Cc calcium chloride hydroxide H hydrocalumite Hp hydrophilite L limeM mayenite I tricalcium aluminate

mixed metal oxides can be expressed as the following reac-tion

Ca4Al2(OH)12Cl171(OH)029sdot 343H

2O

997888rarr 014Ca12Al14O33+ 229CaO

+ 171HCl + 872H2O

(1)

32 X-Ray Diffraction The X-ray diffraction patterns of thecalcined hydrocalumite samples obtained at different temper-atures as well as their rehydrated products were presentedin Figure 1 When calcined over a temperature range of400ndash500∘C hydrocalumite was transformed into an amor-phous phase and its crystalline structure totally collapsed asdemonstrated by the very broad and indistinct XRD peaks(Figure 1(a)) As the calcination temperature increases from600 to 900∘C hydrocalumite was converted to mayenite(Ca12Al14O33) and lime (CaO) Several small peaks of cal-

cite (CaCO3) were also observed The formation of calcite

(CaCO3) is due to the fact that mixed CaOCa

12Al14O33solid

can act as an effective CO2adsorbent at temperatures of 700ndash

1000∘C Mayenite as an inert binder prevented the sinteringof CaO during the calcination process and strengthened the

incorporation of CaO with atmospheric CO2[19] When the

calcination temperature was not less than 1000∘C the CO2

capture reactivity of calcined products declined evidently asrevealed by the decrease in mass ratio of calcite which isattributed to the conversion of CaO to tricalcium aluminate(Ca3Al2O6) at higher temperatures [20] In Figure 1 the XRD

peaksmarkedwith ldquoIrdquo are very close to the standard peaks ofboth mayenite and tricalcium aluminate but they wereconsidered to be the latter in view of the positive correlationbetween their intensity and calcination temperature Theabove-mentioned processes were described below

Ca12Al14O33+ 9CaO gt1000

∘C997888997888997888997888997888997888rarr 7Ca

3Al2O6

(2)

CaCO3

gt1000

∘C997888997888997888997888997888997888rarr CaO + CO

2

(3)

Moreover a trace of hydrophilite (CaCl2) and calcium

chloride hydroxide (Ca(OH)Cl) were identified from thecalcination products as well suggesting that not all interlayerchloride ions escaped during the dehydroxylation processand some of themwere combinedwith calcium in the originalhydrocalumite structure to form hydrophilite or calciumchloride hydroxide Vieille et al [15] denoted that after the


release of structural water molecules of chloride-intercalatedhydrocalumite driven by calcination the interlayer chlo-ride anions are closer to the calcium atoms on the layersimproving the possibility of their incorporation It is alsoworth noting that all the XRD peaks of minerals in thecalcined samples generally become sharper with increasingcalcination temperature reflecting that better crystallinity ofcalcined products could be acquired at higher temperatures

Upon mixing with deionized water the calcined hydro-calumite could totally or partially recover its original layeredstructure as reflected by the XRD evidence Hydration is thedriving force for the structural reconstruction of hydrocalu-mite just like other types of LDHs for example hydrotalciteandmeixnerite [21] In Figure 1(c) where the XRD patterns ofthe rehydrated hydrocalumite samples that were previouslycalcined at temperatures below 900∘C were presented onlytypical peaks for hydrocalumite can be recognized It impliesthat the original structure of hydrocalumite was sufficientlyrecovered as expressed by the following reactions

CaO +H2O 997888rarr Ca2+ + 2OHminus (4)

Ca12Al14O33+ 33H

2O

997888rarr 14Al(OH)4

minus

+ 12Ca2+ + 10OHminus(5)

4Ca2+ + 2Al(OH)4

minus

+ 4OHminus + 119909Mminus2119909 + nH2O

997888rarr Ca4Al2(OH)12M119909sdot 119899H2O

(6)

where the Mminus2119909 could be OHminus Clminus and CO3

2minus with OHminusbeing dominant in this experimental study In contrastFigure 1(d) shows the characteristic peaks for both hydroca-lumite and tricalcium aluminate indicating that the hydro-calumite samples calcined at temperatures not less than1000∘C could be only partially rehydrated Furthermore theintensities of the XRD peaks for the reconstructed hydroca-lumite decrease with the increase in calcination temperaturesuggesting that the structural regeneration ability of hydro-calumite can be impaired significantly by calcination at veryhigh temperatures The reason is that Ca

3Al2O6in the cal-

cination products could be immediately converted to a stablecompound upon exposure to water over 35∘C tricalcium alu-minate hexahydrate (Ca

3Al2O6sdot6H2O) [20] In this study the

rehydrated solid samples were dried at 50∘C which offeredan enough environmental temperature for the formation ofCa3Al2O6sdot6H2O

Finally it is interesting to compare the interlayer spacingvalues of the regenerated hydrocalumites with that of theoriginal one It is obvious that the intercalation of OHminusresulted in the decrease in d-spacing of the primary XRDpeak (003) of the hydrocalumites recovered from the solidsamples calcined at 500 1000 and 1500∘C (Figure 2) sinceOHminus has a smaller crystallographic radius (0137 nm) thanClminus (0168 nm) The hydrocalumite obtained via 500∘C cal-cination followed by rehydration shows less reduction ofinterlayer spacing probably as a result of the incorporation ofa trace of carbonate ions with much larger radius (0189 nm)[22]

100 105 110 115 120

d = 0784nm

d = 0783nmd = 0786nm

d = 0788nm

HCH500HCH1000HCH1500HRe

lativ

e in

tens

ity

2120579

Figure 2 119889-spacing of the primary XRD peaks (003) of originalhydrocalumite and those regenerated from the samples calcined at500 1000 and 1500∘C

33 Infrared Spectroscopy (FT-IR) The FT-IR spectra of theoriginal hydrocalumite the calcined products obtained at dif-ferent temperatures and the rehydrated samples are shown inFigure 3 For the original hydrocalumite the absorption bandat 3639 cmminus1 represents the stretching vibrations of latticewater together with surface-adsorbed water while the strongband at 3477 cmminus1 is related to the OH stretching vibrationsin the portlandite-like layers of hydrocalumite The band at1621 cmminus1 is assigned to theHndashOndashHbending vibrations of theinterlayer water molecules and that at 1433 cmminus1 can bedesignated to electrostatically adsorbed CO

2on the surface

of hydrocalumite micrograins or interlayer carbonate anionsindicating that the as-prepared hydrocalumite is not totallycarbonate free Moreover the absorption bands at 789 cmminus1535 cmminus1 and 425 cmminus1 indicative of metal hydroxides werealso detected The stretching and deformation vibrations ofAlndashOH are reflected by the band at 789 cmminus1 whereas thoseof CandashOH CandashOndashCa and OndashCandashO bonds are reflected bythe broad bands at 535 cmminus1 and 425 cmminus1 [7] The FT-IRspectra of uncalcined hydrocalumite clearly demonstrate itslayered structure composedmainly of [Ca

2Al(OH)

6]+ which

match well with the XRD resultsUpon calcination at different temperatures the FT-IR

spectra of hydrocalumite were changed evidently The bandat 3639 cmminus1 disappeared from the spectra of all calcinedhydrocalumite samples indicating a total loss of interlayerwater molecules However the absorption bands representa-tive of other functional groups were still present even afterhydrocalumite had been calcined at 1500∘C (Figure 3(b))but show a decrease in intensity and a shift in wavenumberIt is in agreement with the fact that the expected escapeof interlayer anions (eg chloride) during calcination wasactually prevented by the formation of new minerals asindicated by the XRD analyses In the low-wavenumberregion of the FT-IR spectra the shifts in the absorptionbands generally increase as the calcination temperature risesimplying a progressive collapse of the layered structure ofhydrocalumite [15] However it is noted that for the sampleobtained at 500∘C a strong band at 1418 cmminus1 is presented inits FT-IR spectra indicating the formation of certain


Tran

smitt

ance

()

4000 3500 3000 2500 2000 1500 1000 500

Wavenumbers (cmminus1)

3639

3477

3473

3446

3443

1621

1624

1627

1631

1489

1491

1433

1418

1415

1413

789

797

844

838

535

538

569

569

425

425

457

455

CH500

CH1000

CH1500

H

(a)

3639

3660

3632

3646

3477

3474

3468

3469

1621

1623

1623

1625

1022

1413

1413

1433

1429

789

789

789

792

876

535

534

530

531

422

423

425

424

Tran

smitt

ance

()

4000 3500 3000 2500 2000 1500 1000 500


HCH500

HCH1000

HCH1500

H

(b)

Figure 3 IR spectra of hydrocalumite samples calcined at 500 1000 and 1500∘C (a) and their rehydrated products (b) The IR spectra of anoriginal hydrocalumite sample were presented in the figures for comparison

carbonate-bearing mineral (very likely to be calcite takingaccount of the XRD evidence) The existence of a weak bandat around 1415 cmminus1 for the samples calcined at 1000 and1500∘C is indicative of possible CO

2capture by CaO during

the cooling of calcined products to room temperatureAfter contact with deionized water the band corre-

sponding to lattice water molecules (at around 3632 cmminus1)reappeared suggesting different extents of reconstruction ofthe hydrocalumite structure Nevertheless the FT-IR spectraof the rehydrated hydrocalumite samples that had been previ-ously calcined at 1000 and 1500∘Cshowed less similarity to theoriginal hydrocalumite as compared to that calcined at 500∘Cdemonstrating that the hydrocalumite structure cannot betotally regenerated after being calcined at temperatures over1000∘C This is in agreement with the XRD results as wellIt is worth noting that the FT-IR vibrations indicative ofcarbonate still existed in the rehydrated samples althoughthere are no peaks for any carbonate mineral in the XRDpatterns of these samples

34 Scanning Electron Microscope and Energy Dispersive X-Ray (SEM-EDX) Analysis The selected samples were alsosubjected to SEM-EDX analysis for a better understanding ofthe effects of calcination-regeneration process on the surfacemorphology and elemental composition of hydrocalumiteAs shown in the SEM image the original hydrocalumitesample presents a hexagonal platy structure (Figures 4(a)and 4(b)) After a treatment of calcination at 400∘C andsubsequent rehydration the hexagonal lamellar structure ofhydrocalumite was totally reconstructed (Figure 4(c)) Moreimportantly the regenerated sample shows more completeand larger crystals as compared to the original hydrocalumite(Figure 4(b)) As for the sample calcined at 1000∘C andrehydrated in deionized water less hexagonal hydrocalumitecan be identified (Figure 4(d)) implying that only parts of thesample could recover its original structure In comparisonthe sample regenerated from the calcination product at

Table 2 Results of EDX analysis for elemental composition of origi-nal hydrocalumite and regenerated samples (in atomic percent)Thelocations where the EDX analyses were made are shown in Figure 4(points 1 2 3 and 4)

Element Point 1 Point 2 Point 3 Point 4Ca 1316 2234 527 2453Al 849 1647 383 2037O 7170 4704 6293 5509Cl 665 1416 202 mdash

1500∘C is characterized by much more rhombic dodecahe-dron crystals (Figure 4(e)) These crystals have an elementalcomposition very close to that of tricalcium aluminate hex-ahydrate (Ca

3Al2O6sdot6H2O) as shown in Table 2 (point 4)

The results of the SEM-EDX analyses are generally in accor-dance with the XRD results suggesting that with the increaseof calcination temperature the mass ratio of hydrocalumitedecreased while that of tricalcium aluminate hexahydrateincreased after the calcination-regeneration treatment

35 Summarization of Calcination-Regeneration Process ofHydrocalumite and Its Comparison with Hydrotalcite This isthe first systematic study on the rehydration of hydrocalumitecalcined over a wide temperature range (400ndash1500∘C) Theresults of this study show that hydrocalumite heated attemperatures below 500∘Ccan be rehydrated since its positivecharged structure ([Ca

2Al(OH)

6]+) remained after calcina-

tion while those calcined at and above 600∘C can be totallyor partially regenerated in water as a result of dissolutionof mayenite and lime as well as subsequent reprecipitationof hydrocalumite To the best of our knowledge only themechanism for structural reconstruction of hydrocalumitecalcined over a low-temperature range (80ndash400∘C) wasclarified in published literatures Another new point worthbeing addressed here is that calcite a secondary calcinationproduct of hydrocalumite was detected in this experimental


+Point 1

(a) (b)

+Point 2

(c)

+Point 3

(d)

+Point 4

(e)

Figure 4 SEM images of original hydrocalumite at two different magnifications (a and b) and the rehydrated products of calcinedhydrocalumite at 400∘C (c) 1000∘C (d) and 1500∘C (e)

study It was formed through an effective sorption of CO2by

mayenite-bound lime above 600∘CIt is interesting that other types of layered double hydrox-

ides typically hydrotalcite [23 24] can reconstruct theirdestroyed structure by calcination in solution via dissolution-reprecipitation as well However as compared to calcinedhydrocalumite that can be rehydrated immediately upon

exposure to water and restore its original structure within 24hours the calcination product of hydrotalcite shows muchslower kinetics in structural restoration It was reported byRocha et al [25] that hydrotalcite previously calcined at 650and 750∘C could be recovered completely after 72 hours ofrehydration The distinctly different reconstruction rates ofcalcined hydrocalumite and hydrotalcite are probably due to


the much higher solubility of Ca(OH)2(159 gL at 25∘C) as

compared to Mg(OH)2(002 gL at 25∘C) [26] Furthermore

the calcination-regeneration process of hydrocalumite can bedivided into three stages in terms of calcination temperaturewhereas only two different stages can be identified for hydro-talcite as confirmed by previous studies Miyata et al [27]suggested that the calcination of hydrotalcite at temperaturesranging from 350 to 800∘C causes the formation of periclase-like MgndashAl oxide solid solution capable of recovering itslayered structure via being treatedwith purewater or aqueoussolutions In contrast it has been proved [17 28 29] thatthe heating of hydrotalcite at higher temperatures producesspinel (MgAl

2O4) resulting in a partial regeneration of

calcined hydrotalcite upon contact with water It means thathydrotalcite would recover its original structure totally onlyif calcined at temperatures not higher than 800∘C while thiscritical calcination temperature for hydrocalumite is 900∘C

4 Conclusions

The results obtained in this study demonstrate that the ther-mal decomposition behavior of hydrocalumite varies at dif-ferent temperaturesThe extents of structural regeneration ofcalcination products in deionizedwater are also differentThehydrocalumite samples calcined over a temperature range of400ndash900∘C could totally recover their layered structure uponcontact with deionized water However for those calcined attemperatures not less than 1000∘C and reacting with deion-ized water later both tricalcium aluminate hexahydrate andhydrocalumite were identified in the rehydrated samplesThat is only parts of the samples heated over 1000∘C canbe converted to hydrocalumite through reaction with waterFinally it is noted that all the rehydration experiments in thisstudy were conducted using deionized water Research intoappraising the rehydration process of calcined hydrocalumitein aqueous solution containing different types of harmfulanions (eg B(OH)

4

minus CrO4

2minus AsO2

minus MoO4

2minus and SeO4

2minus)is urgently needed for determining optimal temperatures atwhich hydrocalumite can be calcined and used to removethese anions from solution most efficiently

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This study was financially supported by the FundamentalResearch Fund for National Universities (nos CUG120505andCUG120113) and theOpen Fund for Teaching Laboratoryof China University of Geosciences (Wuhan) (SKJ2012107)The helpful comments of an anonymous reviewer are grate-fully acknowledged

References

[1] J V Bothe Jr and P W Brown ldquoPhreeqC modeling of Friedelrsquossalt equilibria at 23 plusmn 1∘Crdquo Cement and Concrete Research vol34 no 6 pp 1057ndash1063 2004

[2] TMatschei B Lothenbach and F PGlasser ldquoTheAFmphase inPortland cementrdquo Cement and Concrete Research vol 37 no 2pp 118ndash130 2007

[3] F Delorme A Seron B Vergnaud P Galle-Cavalloni VJean-Prost and J Manguin ldquoEvidence of the influence of thecationic composition on the anionic affinity of layered doublehydroxidesrdquo Journal of Materials Science vol 48 no 15 pp5273ndash5279 2013

[4] M Zhang and E J Reardon ldquoRemoval of B CrMo and Se fromwastewater by incorporation into hydrocalumite and ettringiterdquoEnvironmental Science and Technology vol 37 no 13 pp 2947ndash2952 2003

[5] Q H Guo and E J Reardon ldquoCalcined dolomite alternative tolime for minimizing undesirable element leachability from flyashrdquo Industrial and Engineering Chemistry Research vol 51 no26 pp 9106ndash9116 2012

[6] P Zhang G R Qian H S Shi X X Ruan J Yang and RL Frost ldquoMechanism of interaction of hydrocalumites (CaAl-LDH) with methyl orange and acidic scarlet GRrdquo Journal ofColloid and Interface Science vol 365 no 1 p 540 2012

[7] P Zhang G Qian H Cheng J Yang H Shi and R L FrostldquoNear-infrared and mid-infrared investigations of Na-dode-cylbenzenesulfate intercalated into hydrocalumite chloride(CaAl-LDH-Cl)rdquo SpectrochimicaActaAMolecular and Biomol-ecular Spectroscopy vol 79 no 3 pp 548ndash553 2011

[8] Q Guo and J Tian ldquoRemoval of fluoride and arsenate fromaqueous solution by hydrocalumite via precipitation and anionexchangerdquo Chemical Engineering Journal vol 231 pp 121ndash1312013

[9] K Chibwe andW Jones ldquoIntercalation of organic and inorganicanions into layered double hydroxidesrdquo Journal of the ChemicalSociety Chemical Communications no 14 pp 926ndash927 1989

[10] T Werpy T Kwon and T J Pinnavaia ldquoAdvances in thesynthetic design of pillared layered silicate clay (LSC) andlayered double hydroxide (LDH) catalystsrdquo Abstracts of Papersof the American Chemical Society vol 198 p 18 1989

[11] D Yang Z Song and X Qian ldquoAdsorption of abietic acid fromcolloidal suspension by calcined MgAl hydrotalcite com-poundsrdquo Industrial and Engineering Chemistry Research vol 52no 21 pp 6956ndash6961 2013

[12] K L Erickson T E Bostrom and R L Frost ldquoA study ofstructural memory effects in synthetic hydrotalcites usingenvironmental SEMrdquoMaterials Letters vol 59 no 2-3 pp 226ndash229 2005

[13] S Narayanan and K Krishna ldquoHydrotalcite-supported palla-dium catalysts part I preparation characterization of hydro-talcites and palladium on uncalcined hydrotalcites for COchemisorption and phenol hydrogenationrdquoApplied Catalysis AGeneral vol 174 no 1-2 pp 221ndash229 1998

[14] E Lopez-Salinas M E L Serrano M A C Jacome and I SSecora ldquoCharacterization of synthetic hydrocalumite-type[Ca2

Al(OH)6

]NO3

sdot119898H2

O effect of the calcination tempera-turerdquo Journal of PorousMaterials vol 2 no 4 pp 291ndash297 1996

[15] L Vieille I Rousselot F Leroux J P Besse and C Taviot-Gueho ldquoHydrocalumite and its polymer derivatives 1 Rever-sible thermal behavior of Friedelrsquos salt a direct observation by


means of high-temperature in situ powder X-ray diffractionrdquoChemistry of Materials vol 15 no 23 pp 4361ndash4368 2003

[16] F Rey V Fornes and J M Rojo ldquoThermal decomposition ofhydrotalcites an infrared and nuclear magnetic resonancespectroscopic studyrdquo Journal of the Chemical Society FaradayTransactions vol 88 no 15 pp 2233ndash2238 1992

[17] T S Stanimirova G Kirov and E Dinolova ldquoMechanism ofhydrotalcite regenerationrdquo Journal of Materials Science Lettersvol 20 no 5 pp 453ndash455 2001

[18] R Segni N Allali L Vieille C Taviot-Gueho and FLeroux ldquoHydrocalumite-type materials 2 Local order intoCa2

Fe(OH)6

(CrO2minus4

)05

sdotnH2

O in temperature studied by X-rayabsorption and Mossbauer spectroscopiesrdquo Journal of Physicsand Chemistry of Solids vol 67 no 5-6 pp 1043ndash1047 2006

[19] J Mastin A Aranda and J Meyer ldquoNew synthesis methodfor CaO-based synthetic sorbents with enhanced properties forhigh-temperature CO

2

-capturerdquo in Proceedings of the 10th Inter-national Conference on Greenhouse Gas Control Technologiesvol 4 pp 1184ndash1191 2011

[20] Z S Li N S Cai and Y Y Huang ldquoEffect of preparation tem-perature on cyclic CO

2

capture and multiple carbonation-calcination cycles for a new Ca-based CO

2

sorbentrdquo Industrialamp Engineering Chemistry Research vol 45 no 6 pp 1911ndash19172006

[21] F Cavani F Trifiro and A Vaccari ldquoHydrotalcite-type anionicclays Preparation properties and applicationsrdquo CatalysisToday vol 11 no 2 pp 173ndash301 1991

[22] J D Phillips and L J Vandeperre ldquoAnion capture with calciumaluminium and iron containing layered double hydroxidesrdquoJournal of Nuclear Materials vol 416 no 1-2 pp 225ndash229 2011

[23] L Moyo N Nhlapo and W W Focke ldquoA critical assessment ofthe methods for intercalating anionic surfactants in layereddouble hydroxidesrdquo Journal of Materials Science vol 43 no 18pp 6144ndash6158 2008

[24] W Tongamp Q Zhang and F Saito ldquoPreparation of meixnerite(Mg-Al-OH) type layered double hydroxide by a mechano-chemical routerdquo Journal of Materials Science vol 42 no 22 pp9210ndash9215 2007

[25] J Rocha M Del Arco V Rives and M A Ulibarri ldquoRecon-struction of layered double hydroxides from calcined precur-sors a powder XRD and 27A1 MAS NMR studyrdquo Journal ofMaterials Chemistry vol 9 no 10 pp 2499ndash2503 1999

[26] M Rajamathi G D Nataraja S Ananthamurthy and P VKamath ldquoReversible thermal behavior of the layered doublehydroxide of Mg with Al mechanistic studiesrdquo Journal of Mate-rials Chemistry vol 10 no 12 pp 2754ndash2757 2000

[27] SMiyata ldquoAnion-exchange properties of hydrotalcite-like com-poundsrdquoClays amp ClayMinerals vol 31 no 4 pp 305ndash311 1983

[28] F M Labajos V Rives andM A Ulibarri ldquoEffect of hydrother-mal and thermal treatments on the physicochemical propertiesof Mg-Al hydrotalcite-like materialsrdquo Journal of Materials Sci-ence vol 27 no 6 pp 1546ndash1552 1992

[29] V Rives ldquoCharacterisation of layered double hydroxides andtheir decomposition productsrdquo Materials Chemistry andPhysics vol 75 no 1ndash3 pp 19ndash25 2002

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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anion decomposition These processes may overlap witheach other in different extents [16] Upon cooling to roomtemperature in ambient atmosphere low-temperature cal-cined hydrocalumite (lt280∘C) can recover its initial layeredstructure spontaneously and the reaction rate depends on airhumidity and other experimental conditions [15] In compar-ison the amorphous compounds obtained via calcination at400∘C have an ability to reconstruct the original structure ofhydrocalumite when exposed to aqueous solution of KCl Inthe relevant literatures the conversion of calcined productsto layered hydrocalumite was referred to as different termssuch as regeneration reconstruction and rehydration whilethe whole process was reported as ldquocalcination-rehydrationprocessrdquo or ldquostructurememory effectrdquo [17] Although the ther-mal decomposition of hydrocalumite has been investigatedat comparatively low temperature there is so far a lack ofsystematic studies on the thermal behavior and structurememory effect of hydrocalumite at higher temperaturesThisstudy focuses on the structural and compositional changesof hydrocalumite upon calcination over a much wider tem-perature range (400ndash1500∘C) The rehydration process of thecalcination products obtained at different temperatures indeionized water was also evaluated

2 Experimental

21 Synthesis of Hydrocalumite Hydrocalumite was preparedby the coprecipitation method that has been describedelsewhere [18] Typically the synthesis was carried out at65∘C under vigorous magnetic stirring A mixed solutionof 066M CaCl

2sdot2H2O and 033M AlCl

3sdot6H2O was added

dropwise to a beaker filled with a mixture consisting of waterand ethanol in a 2 3 volumetric ratio The pH was keptconstant at 115 by the simultaneous addition of 2M NaOHThe suspension was aged at 65∘C for 24 h after the additionof metallic salts had been complete The solid productswere separated by centrifugation and washed severaltimes with deionized water until pH 7-8 The synthesizedhydrocalumite sample was subjected to an elemental analysisbased on which its approximate chemical formula wasestimated to be Ca

4Al2(OH)12Cl171

(OH)029sdot343H

2O

(MM = 5435 gmol) very close to the theoretical formula(Ca4Al2(OH)12Cl2sdot6H2O)

22 Calcination andRegeneration Procedure Thesynthesizedhydrocalumite was calcined for 2 h in a muffle furnace underambient atmosphere at the temperatures ranging from 400to 1500∘C with an increasing step of 100∘C The calcinationproductswere cooled to room temperature in a container pre-viously filled with allochroic silica gel as desiccant The massof the samples wasmeasured before and after calcinationTheregeneration procedure for the calcined hydrocalumite wasperformed by reacting with deionized water in polyethylenebottles at a constant temperature of 25∘C for 24 hours

23 Characterization Techniques The solid samples dried inoven of 50∘C were characterized by an XrsquoPert PRO DY2198diffractometer with Cu K120572 radiation and the XRD patterns

Table 1 Mass loss of hydrocalumite samples calcined at differenttemperatures

119879 (∘C) Mass loss ()

400 266

500 277

600 318

700 319

800 349

900 314

1000 391

1100 380

1200 407

1300 416

1400 358

1500 408

were recorded in the 120579-2120579 mode between 5∘ and 65∘ with a2120579 step of 0033∘ Their Fourier transform infrared spectra(FT-IR) were obtained using a FTIR Equinox 55 Brukerspectrometer with a scan range of 400ndash4000 cmminus1 and aresolution of 4 cmminus1 The KBr pellet technique was usedto prepare the sample that was introduced into the FT-IRcell The calcined hydrocalumite samples together with thoseundergoing regeneration procedures were also analyzed witha FEI Quanta200 Scanning Electron Microscope (SEM)equipped with an Energy Dispersive X-Ray (EDX) analyticalcapability for morphology crystallinity and elemental com-position Both SEM and EDX analyses were taken at 20 kVexcitation

3 Results and Discussion

31 Mass Loss of Calcined Products In general the mass lossof calcined product increases as the calcination temperaturerises except for three samples heated at 900 1100 and 1400∘Cshowing anomalously low mass losses The possible reason isthe rehydration of these samples during their cooling to roomtemperature The mass loss of hydrocalumite upon calcina-tion at 400∘C is 266 (Table 1) very close to 233 a theo-retical value corresponding to the calcination process duringwhich all interlayer water molecules including OHminus andClminus break away from the hydrocalumite structure as otherinvestigators had noticed [14 15] In this case the calcinedproduct could spontaneously reconstruct its original struc-ture with water molecules upon exposure to atmosphereThecalcination products obtained at temperatures higher than500∘C however can only regenerate the layered hydrocalu-mite structure by incorporating anions in aqueous solutionAt temperatures higher than 1000∘C the mass loss of hydr-ocalumite upon thermal decomposition is approaching400 a value indicating that it broke up into mayenite(Ca12Al14O33) and lime (CaO) [15] The formation of these


100 200 300 400 500 600

M

M

MM

M

M

M

M

M

M

MMM

M

M

CcCc CC

LL

L

L

HpHp

CH900

CH800

CH700

CH600

CH500

CH400

Rela

tive

inte

nsity

2120579

(a)

100 200 300 400 500 600

M

M MM

L

M

M C

L

LLp

L

L

Hp CH1500

CH1400

CH1300

CH1200

CH1100

CH1000

Rela

tive

inte

nsity

2120579

(b)

100 200 300 400 500 600

H

H

H

H

H

HH H H HH HH

HCH900

HCH800

HCH700

HCH600

HCH500

HCH400

Rela

tive

inte

nsity

2120579

(c)

100 200 300 400 500 600

CA

CA

CA

CACA

CA

CACACACACACACA

HCH1500

HCH1400

HCH1300

HCH1200

HCH1100

HCH1000

Rela

tive

inte

nsity

2120579

HH

H

HH

H

H

H H

HHH

(d)




2O

997888rarr 014Ca12Al14O33+ 229CaO

+ 171HCl + 872H2O

(1)




12Al14O33solid








∘C997888997888997888997888997888997888rarr 7Ca

3Al2O6

(2)

CaCO3

gt1000

∘C997888997888997888997888997888997888rarr CaO + CO

2

(3)







Ca12Al14O33+ 33H

2O


minus

+ 12Ca2+ + 10OHminus(5)

4Ca2+ + 2Al(OH)4

minus



(6)



3Al2O6in the cal-





100 105 110 115 120

d = 0784nm

d = 0783nmd = 0786nm

d = 0788nm


lativ

e in

tens

ity

2120579



2on the surface


2Al(OH)

6]+ which




Tran

smitt

ance

()

4000 3500 3000 2500 2000 1500 1000 500


3639

3477

3473

3446

3443

1621

1624

1627

1631

1489

1491

1433

1418

1415

1413

789

797

844

838

535

538

569

569

425

425

457

455

CH500

CH1000

CH1500

H

(a)

3639

3660

3632

3646

3477

3474

3468

3469

1621

1623

1623

1625

1022

1413

1413

1433

1429

789

789

789

792

876

535

534

530

531

422

423

425

424

Tran

smitt

ance

()

4000 3500 3000 2500 2000 1500 1000 500


HCH500

HCH1000

HCH1500

H

(b)













2Al(OH)




+Point 1

(a) (b)

+Point 2

(c)

+Point 3

(d)

+Point 4

(e)












4 Conclusions


4

minus CrO4

2minus AsO2

minus MoO4

2minus and SeO4




Acknowledgments


References















Al(OH)6

]NO3

sdot119898H2








Fe(OH)6

(CrO2minus4

)05

sdotnH2



2



2


2




















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


100 200 300 400 500 600

M

M

MM

M

M

M

M

M

M

MMM

M

M

CcCc CC

LL

L

L

HpHp

CH900

CH800

CH700

CH600

CH500

CH400

Rela

tive

inte

nsity

2120579

(a)

100 200 300 400 500 600

M

M MM

L

M

M C

L

LLp

L

L

Hp CH1500

CH1400

CH1300

CH1200

CH1100

CH1000

Rela

tive

inte

nsity

2120579

(b)

100 200 300 400 500 600

H

H

H

H

H

HH H H HH HH

HCH900

HCH800

HCH700

HCH600

HCH500

HCH400

Rela

tive

inte

nsity

2120579

(c)

100 200 300 400 500 600

CA

CA

CA

CACA

CA

CACACACACACACA

HCH1500

HCH1400

HCH1300

HCH1200

HCH1100

HCH1000

Rela

tive

inte

nsity

2120579

HH

H

HH

H

H

H H

HHH

(d)




2O

997888rarr 014Ca12Al14O33+ 229CaO

+ 171HCl + 872H2O

(1)




12Al14O33solid








∘C997888997888997888997888997888997888rarr 7Ca

3Al2O6

(2)

CaCO3

gt1000

∘C997888997888997888997888997888997888rarr CaO + CO

2

(3)







Ca12Al14O33+ 33H

2O


minus

+ 12Ca2+ + 10OHminus(5)

4Ca2+ + 2Al(OH)4

minus



(6)



3Al2O6in the cal-





100 105 110 115 120

d = 0784nm

d = 0783nmd = 0786nm

d = 0788nm


lativ

e in

tens

ity

2120579



2on the surface


2Al(OH)

6]+ which




Tran

smitt

ance

()

4000 3500 3000 2500 2000 1500 1000 500


3639

3477

3473

3446

3443

1621

1624

1627

1631

1489

1491

1433

1418

1415

1413

789

797

844

838

535

538

569

569

425

425

457

455

CH500

CH1000

CH1500

H

(a)

3639

3660

3632

3646

3477

3474

3468

3469

1621

1623

1623

1625

1022

1413

1413

1433

1429

789

789

789

792

876

535

534

530

531

422

423

425

424

Tran

smitt

ance

()

4000 3500 3000 2500 2000 1500 1000 500


HCH500

HCH1000

HCH1500

H

(b)













2Al(OH)




+Point 1

(a) (b)

+Point 2

(c)

+Point 3

(d)

+Point 4

(e)












4 Conclusions


4

minus CrO4

2minus AsO2

minus MoO4

2minus and SeO4




Acknowledgments


References















Al(OH)6

]NO3

sdot119898H2








Fe(OH)6

(CrO2minus4

)05

sdotnH2



2



2


2




















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





Ca12Al14O33+ 33H

2O


minus

+ 12Ca2+ + 10OHminus(5)

4Ca2+ + 2Al(OH)4

minus



(6)



3Al2O6in the cal-





100 105 110 115 120

d = 0784nm

d = 0783nmd = 0786nm

d = 0788nm


lativ

e in

tens

ity

2120579



2on the surface


2Al(OH)

6]+ which




Tran

smitt

ance

()

4000 3500 3000 2500 2000 1500 1000 500


3639

3477

3473

3446

3443

1621

1624

1627

1631

1489

1491

1433

1418

1415

1413

789

797

844

838

535

538

569

569

425

425

457

455

CH500

CH1000

CH1500

H

(a)

3639

3660

3632

3646

3477

3474

3468

3469

1621

1623

1623

1625

1022

1413

1413

1433

1429

789

789

789

792

876

535

534

530

531

422

423

425

424

Tran

smitt

ance

()

4000 3500 3000 2500 2000 1500 1000 500


HCH500

HCH1000

HCH1500

H

(b)













2Al(OH)




+Point 1

(a) (b)

+Point 2

(c)

+Point 3

(d)

+Point 4

(e)












4 Conclusions


4

minus CrO4

2minus AsO2

minus MoO4

2minus and SeO4




Acknowledgments


References















Al(OH)6

]NO3

sdot119898H2








Fe(OH)6

(CrO2minus4

)05

sdotnH2



2



2


2




















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Tran

smitt

ance

()

4000 3500 3000 2500 2000 1500 1000 500


3639

3477

3473

3446

3443

1621

1624

1627

1631

1489

1491

1433

1418

1415

1413

789

797

844

838

535

538

569

569

425

425

457

455

CH500

CH1000

CH1500

H

(a)

3639

3660

3632

3646

3477

3474

3468

3469

1621

1623

1623

1625

1022

1413

1413

1433

1429

789

789

789

792

876

535

534

530

531

422

423

425

424

Tran

smitt

ance

()

4000 3500 3000 2500 2000 1500 1000 500


HCH500

HCH1000

HCH1500

H

(b)













2Al(OH)




+Point 1

(a) (b)

+Point 2

(c)

+Point 3

(d)

+Point 4

(e)












4 Conclusions


4

minus CrO4

2minus AsO2

minus MoO4

2minus and SeO4




Acknowledgments


References















Al(OH)6

]NO3

sdot119898H2








Fe(OH)6

(CrO2minus4

)05

sdotnH2



2



2


2




















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


+Point 1

(a) (b)

+Point 2

(c)

+Point 3

(d)

+Point 4

(e)












4 Conclusions


4

minus CrO4

2minus AsO2

minus MoO4

2minus and SeO4




Acknowledgments


References















Al(OH)6

]NO3

sdot119898H2








Fe(OH)6

(CrO2minus4

)05

sdotnH2



2



2


2




















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of







4 Conclusions


4

minus CrO4

2minus AsO2

minus MoO4

2minus and SeO4




Acknowledgments


References















Al(OH)6

]NO3

sdot119898H2








Fe(OH)6

(CrO2minus4

)05

sdotnH2



2



2


2




















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






Fe(OH)6

(CrO2minus4

)05

sdotnH2



2



2


2




















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

Research Article Thermal Decomposition of Hydrocalumite over a...

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Transcript of Research Article Thermal Decomposition of Hydrocalumite over a...