Changes in physicochemical properties of α-spodumene by mechanochemical treatment

379

Materials Chemisfry and Physics, 17 (1987) 379-389

tT2HANms INPHYSIaxmmI

CALPFQPEWXES OF wSPODWD4E BYMECWlICAL

IlwmMEm

H.J. GR8AUA, E.F. .%GUEITI,J.M. POKID IQPEZ and E. PEREIBA Centm de Tecnologfade BecursosMineralesy Certica (~C) C.C.49, (1897)M-B.-et

(CIC-CCNICET).

@rgentinaf

receivedNove&er 11, 1986: acceptedDece&er 18, 1986.

Texturaland structuralchangesinducedin wspodusene (Li2A12Si4012) by impactandfrictimmillingare studiedusingXBD, IRspectroscopy,IXCA,SEM and~ti~exchangec~citydete~ati~s.T~mecfianochernicaltreatnent pr~~sa~uti~of~cle

sizetogetherwithan increaseof E&T surface

area, andachange in tIx crystal&ape. &moveraprogressivedistortimof the crystallinenetwxk affectedt&a spectroscopic propertiesof the material, and enhancedits chemicalreactivityto acid dissolutim. Changesin its phase transformation sequenceunderthemaltreatmntaxe

also observed.The phase

y-spodmene, which is not observedin the sequence~8, appearsat 800°Cwhen nw&anicallytreatedwspc&mneis

Tlxs

usedas a startingrmterial.

reducticmof particlesize,using frictionand inpactmills s~taneous-

lyprcduces st~~lc~~s,~ch~f~~yas~iat~~~~

anurphi-

sationof the crystallinenetwrk. This phencmnon is know as ttx?nechanochemicaleffect,and developashigh energy surfaceswith simultaneous in

changes

texturaland structuralpamneters [l-2]; The~aticm

ofthasemcbanoc~cal

phencmma showstwo closelyrelated

aspects.The first one concernsthe texturalchanges,i.e. particlesize, specificsurfacearea, porosity,etc.; the secondaspextdeals with the producticm of newchemical and stmctural properties,throughtba generatim of particleswithhighenergy.These cWmnstanceslead tothe formatianof a ~~d~ch,al~~h~v~g~ ~~a~ffe~tp~i~c~~. 0254-0584/87,‘$3.50

sane stoichimetryas thaoriginal cne,

0 ElsevierSequoia/Printed inThe Netherlands

380 Thistypeoftreatmnt

has been studiedwith variousinorganicsolids [3-61

and clay minerals [7-81. Spcdmeneisalithim

alurti~umsilicate(cl-Li~$.12Si4012) which crystallizes

in tlxammxlinic systemand transfcrmstoatetragonalphase called B-spcdmxne at 1050°C. The first study of machanochemical phanomsnacm spcdmeue was carriedout by Samscmovaet al. [9] anddescribesthe effectsthatcccurduringthemillingof this mineralin a planetarymill. In thepresentpaper,changes in texturalandphysiaxhemical prcpertiesof a-spcdmene during impactand frictionmillingare studied.The study is extendedto the structuralc~gesthatther?echanochanicaltrea~tinducedinthe mineral.Also, changesin phase transformations by heat treatmentare evaluated. EXPEPJMENTAL Materialsand Techniques The rawmterialwas

cl-spcdumnefranSan LuisProvince (Argentina). The

mineralwas milled and then floatedin tetrabmxmethane (6=2.964g/an3);with these operaticmsmurities likequartz andkaolinitemre eliminated.The purifiedcl-spodmenehad tba followingchemicalcanposition: Si02=58.9%;A1203= 32.9%:Lii2"6.25%;X20 + Na20 + C&=1.95%. These cmtents of inpurities(alkaline oxides)had no influencecm the propertiesstudied. Ths mineraltreatmnt (milling) was carriedout in a Hermg -00

mill. The

atromtof a-spedmane used for each run was 30g. Grindingwas made at mtinous interv?& of 2Os, beWeen which the mineralwas mixed. The initialparticlesize was the fracticmcxxqxisedbe+mzenAS!IMsievesNo60 and 35 (zpr370~). Smples withdifferenttreatmenttimes~reobtained. The X-ray diffractcgrmswere obtainedusing a Philipsmodel PWll40/00.PadiationKc of Cu(3\=1.542 i) was used for all analyses,at 40 kV and 20 I-IA. Differentialthermalanalyses (DIR)were m&a in a Netzschequipmentusins 150 mg of samplewith OFA1203as referenceand a heatingrate of lO'C/miu. Infraredspec~a~~~edonKBrdisks,

inwhichtheguantityof samplewas

maintainedccnstantthroughallthe experiments. APerkin-Elmer

spectrom3W

nudel577wasused. Micropbtographswenao~inedwithaJEOLJ~-35CFScanningElec~Microscope. Dissolutiontests were nm in vesselsat 60°C with lN sulfuricacid during1 minute.Lithimwasdeterminedby flampImta&cry. Aluminimdissclutim was evaluatedthmughtheEDTAccqlexomstricmatimd. Caticm exchangecapacity@EC) was determinedusing the anmnium acetate tecbique at pH=8 PO]. SpecificsurfaceaxeawasdetenaInedwiththsBfirrWhcd.

381

RESULTS AS in

AND DISCUSSICN a

conventional grinding,the treatmantof cl-spoduaene in thiskindof

mill producesa reductionin particlesize.This decreasein size reachesan averageminimm value of 15~. (Lasergranulcmker CILAS 715).This effect is observedafter10minutesof treatmant;in samplestreatedat longer

tim=sno

reductionof particlesize beyond 15)nn was observed.Despitethe great harheSS of ol-spcdumne@ohs Scale 6-7) this mineralhas a fragilebehaviourwhen submitted to impactand frictionforces.At short times (< 10 min), a reductionin particlesize occurs;afterwards,a slightagglcmrationof the dispersed particlestakes place. The specificsurfacearea (BET)determinations show that startingfrm a mineralwithoutmeasurablesurface,it reachesa value of 8 m2/g for tbs sarqle treatedduring3Ominutes. This behaviourisnotconsistentwiththe reduction of particlesize. It is evidentthat during the treatnentan appreciable superficial porosityis generated. This changein the particletexturecan be observedin micrographs(Fig.1). The originalparticleslose their originalshape and good crystallinity and after 20 minutesof treatn-ent, the particlesare round-edgedwith a rugged surfaceand great porosity. The cationexchangecapacity (CEC:usual test for clay minerals)determinations starts frcxnzero (original cr-spodmane) reaching20 rmaq/lOOg for the sampletreatedduring30minutes.~hanicaltreatn~ntleads to an increasein the quantityof sites accessibleto ions, in this case NH: and Na+. These sites, whichmaybe regardedas non-saturated residualchargesfor the purposeof CEC determinations, are due to breakageof the crystalsand the apparitionof defectsand dislocations. In Fig.2, the X-ray diffractogramof tba samplesobtainedat differenttreata-cant timas are shmm. A progressivedecreaseof peak intensitiesis observed, but after 30 min of tnaatnentthe principalplanesof cr-spcduaene still persisted.Millinginduceda loss of networkorder and an amrphisaticnof the mineraltcok place.The structuraldisorderis not relatedto alterationsin plane spacings. The integratedarea of tbs (020)peak was measuredas a faction of the treatmet tine.

This

parametercan ke associatedwith the variaticmof crystallinity.

Figure3 (cuma a) shows that crystallinity(originalcl-spcduzen~ 100) demaased abruptlyupto15 minoftreatnent; observed. This

thereafterno changeswaxe

dbinuticm in crystallinity is acccqqnied with a reductionof crystal

size.Crystalsize was measuredwith the Sckxrer formulausing the (020)pak of cl-spcdumne(d=4.21;) and the (100)plane of quartz (d=4.26i) as reference.

382

Fig. 1. Scanning elect-

microscopy.

A:

or@ginal wqmdme.

treatedduring 20minutes (scalebar fsequivalenttolym).

B:

cwqodme

383

1

I

m

60

5s

so

1s

LO

3s

30

1

25

20

,

fS 10 s '2e(cuw

Fig. 2. X-ray diffractoqrams of a-spoduseneobtainedat differenttreataxmt times.

The originalwspodumene has a crystalsize greaterthan 0.2 urn.This value is consideredas infinitefor the measuringtechniquesused (broadening of DRX peaks);at 5 minutesof txeatnent

this

value decreasedto 360 i and a constant

value of 200 i was observedfor sanplestreated10, 15, 20 and 30 minutes. Figure 4 shows the IR spectraof the treatedsamples.In the same fiqurethe originala-spodumane and the B-spodurrene phase have been included.The @-spodumene phase was obtainedthroughthermaltreatmentat 11OO'Cof the cl-form. Roth w and B- phaseshad the characteristic IR bands of thesemineralsas re~rted in tba literature19, 11-123 . The treatedsamplesshow the effectof millingon the stretchingbands of M-0, which are originallycenteredat 1080 and 103Oan-l these bands becamebroad and shiftedto higherwavenwrbers(1090and 1030 cm-') transforming to a uniquebroad band similarto that of silicagel. This fact is explainedthroughthe dama* sufferedby the fSi206),chains.The same effect can baobservedintheSi.-Obanding zone,where the bandat 465 an-' bSCW?SS broad and shiftsto 490 cm-' after 30 minutesof treatru?nt. The symmetricbendinqs @i-O) at 400 and 368 an-' almostdisappeared.

0 Al

3t

A Li ‘+

0

10

20

30

SO

40

TREATMENT

TIME

(min)

Fig, 3. Crystallin~ty detewiked by XRD &xrve a) and ~~~~ extractionuuder sZmElardBsolutlcaz amditima

and lithium

(cmcvesbaudcf

as

a function

oftrea+nx?nttime.

Vibrationsof alumfnlurn octahedr a (AlO6)comespond to the bands at 916, 860, 630 and 590 an-'. Ats~rttrea~ttines (5 and IOminutesl these bands increasedtheir absorpti~XIs slightly,dua probablyto the reducticpl in size of the fSi2061,chains,which muld bring about a greaterpossibilityof vibratim toAl-O?.xmds.Atlongertreatmanttims adkninutim of these the slmilderat 860 cm-l dsappeared .

bandsoccurred:

and tbs bands at 916, 630 and 590 cm-l

shiftedto 920, 636 and 586 cm-l respectively. The bandwbich appears at531m-l

isattributedto theLi-Ooctakdral

bonds.This baud graduallyreducesand disappmrs under the Si-0 (490an-l) band, as thetroatmnttime increases. In wspodumene Al06 andLiO6octahadraare padkedbetweensilicatecbains. The ruptureand deformationof these chainsgeneratesa randcmpackingof Si04 tetrakdra, similarto the silicagel structum, which affectsthe Al and Li coxdination conditions. Tbs cksnkal reactivityof the seriesof sampleshas been evaluated.All san@eswredissolvedTn

sulfuricaoidintb? same~rimntalccMitions.

In

385

n

$3 I

ia0

us9

3 ‘

mm#ar SW

I

1

*

1

900 700 64) 500

‘

,

400300

WAVENI;IMBER ~~6’)

Fig.4. IR spectra of Hp&mne

and a-s&mdum?netreatedat differentmilling

tinE?s.

Fig. 3, curvesb and c, the percentsof Al and Li extractedfrom the original a-qodwmeandfromthe

~lestreatedd~~gvariablet~sare

&mm.

The

increaseof caticmextractioncannotke explainedonly throughan increaseof specificsurfacearea. The high reactivityobservedmst be attributedmainlyto tk structuralCLeterioraticPl of the mineral. DIAzz.hmsthatthe structuralalteraticmsinducedbythem&ancxzhemical processgeneratedmdificatims on sub-t

thermaltransformaticm.In Fig.5

386

\ 1

600

I

700

1

9m

I

1

900

1000

TEMPERATURE

1

1100 (‘C 1

Fig. 5. DTA of the originala-spodumeneand of the samplesc%ta.ined at different millingtixes. the +zkn?lograms of the orIgina cl-spodwe and of tlxxe obtainedat 5, 10, 15, 20 and 30 minuteshave keen superpz~sed. The raw originalcr-spodweneshowsa uniqueendothermicpeak at 1050°C due to the @yxzphic

transfonraticn CM. The

increasingofthetreatrznttiiz leads to adisplacenvzkof this

peak tolowsr

temperatures and to a reductionin the anrxmtof heat necessary for this transformation(peakarea).At the sm the, an exotherhc peak that gradually increasesits area appears at 810°C,suggestingthat a new structuralchange takes place. In Fig.6, the diffractqramsof samplesof cl-spcdLn'@zne Itkxhanically

387

1

6s

60

I

I

5s

so

LS

40

3s

30

2s

I

20

15

10 ‘28

5

(Cu Kc)

Fig. 6. Diffractograms of a-spodumanetreatedduring 30 minutes,and heated during lhr. at differentterr&xaratures.

treatedduring 30 minutesand i-eattreatedafterwardsare skwn. At 8OO'C it transformsto the phase ~-~F&REIE, the presenceof which is relatedto the exothermicpeak (ETA).Fxkhcl and 5 phases have the sane chamicalcomposition (Li2Al2Si4012). 'Ik phase y or s+xdme

III has ken studied by Chi-TangLi [13,14],whc

preparedthis phase by themaaltmatnxmt of a vitreoussolid consistingof a quenchedmalt of cl-m-e.

This authoralso obtaineda solidwith ccanposition

Li20.A1203.3Si02 startingfrom a fusedmixtureof the oxides,concludingthat bth the tm were membersof a seriesof solid solutionswith -sitions rangingfrom Li20.A1203.2Si02 tc Li20.A1203.4Si02 , andwbse XRDpattems are very

similar.

Samscnovaet al. [9] observedthe sama transitionby thermaltreatrentof a-spodumeneqromd in aplanetarymill. Hcwaver,thay assignedtl-ka new phase to a B-eucryptite(Li2A12Si208) structure,forminga solid solutionwith silica.

388

The appeamnceofthis intermdiatephase (y-spkiunene) can beexplained consideringthatthelossofcrystallinityinducedbyrrcillingproduae~a vitreousstructurescarewfiatsimilartothatpreparedby~-TangLi. During~nechanochemicalproa?ssct-spod~e

storedenergyin different

forms:reductim of particlesize, increaseof surfacearea, structuraldmage, etc.. In thiscase, the appearancE!ofthephasey-spodmenemuldba

acampanied

byapartiallikeraticmofthis storedenergy,throughtbaexothexmictransfomation ctjy,as seen by DIPA. Anotherexplanationfor this

behavioramld be theassumptionthat the

structuralalterationsobservedin the treatedsamplescould providefavorable sites from which tbs nuoleaticnand growthof the y-phasetakesplace.

when cmpodmme

is grouud throughirqactand frictionforces,particlesize

diminishesto a limit value of 15 m; then aggloneratimof particlestakes place.This is accmpanied by an increaseof surfacearea, and externalporosity as indicatedby SEX The surfacedamge causedthe apparitim of residualcharges,fbEtexistence of which was cxmfimed throughthe CRC detenninatims. Structureis also affected;it can be seen throughXRD and IR techniques. A loss of crysMlli.nity and a reductionof crystalsize is observedby XPD. The infraredspectrasbmxl a prcgressiveloss of definition,reflectingthe deterXoraticm of the crystallinestructure. Tba amx-phisaticm resultedin agreater reactivityofthe solid.Aciddissolutionof alurnikfmand lithiumat constantoperatingccmditicm increased withthem

ofrrechanicaltreatmmt.

Tha milledmineralchangesits phase tiansformticm under theme1 treatsent. DTA indicatesthe appariticmof a new in-izexmdiate phase.This phase,identified byXRD,isy~~,vlhichwas~~~lytoappearwhenafused

fvitreous)

mixtureof tbs oxides is heated,. This type of treatrent,which affectsthe physicochemical behaviorof crystalline solids,could be considerednot only as a mans ofenhancingtheirreactivibut also fromthepointof ty, thus helpingprccessasof mineralbsneficiation, view of the preparaticgl of materialswith new and/or predeteminedproperties. REJZRENCES

1 V.V.Roldyrevand E.G. Awakurmv, RussianChemicalReviews,40 (10) WW 2 P.Yu. Rutyagin,RussianchemicalI&views,40 (11) (1971)901. 3 T.G. F%rton,Trans. Inst. CYkm. F&g., 44 (1966)37. 4 M. Shinozaki and M. Senua, Ind. Wg. C&IX. Fundsm.,20 (1981159.

847.

389

F.W.Dynysand J.W. Halloran, J. Am. Ceram. Sot., 64 (4) (1981) C62. A.N.Scian,E.F. Rglietti, J.M. Pox-toI&z and E.Pereira, Rev. Lat. Am. Ing. ~ufin.Qufm. Apl., 14 (11 (19841 51. V. Mingelgrin, L. Klfger, M. Gal and S. Saltzmn, Clays Clay Miner., 26 (4) (1978) 299. E.F. Aglietti, J.M. Port0 L&m (1986) 125.

and E. Pereira, Int. J. Miner. Proc., 16

T.I. Samsonova, M.I. Tatarintseva, I.A. Poroshina, V.V. Boldyrev, Izv. Sib. Otd. Akad. Nauk SSSR, Ser. Khim. Nauk, 1 (1981) 67. 10 W.E. mrrall, Trans. Brit. Ceram

Sec., 62 (6) (19631 477.

11M. Krishna IQrthy, E.N. Kirby, J. Am. Ceram. See., 45 (7) (19621 324. 12 P. Tarte, SpectrochimicaActa, 23 A (1967) 2127. 13 Chi+t'angLi, Z. Krist., 132 (5) (1970) 128. 14 &-Tang

Li, Z. Krist., 127 (1968) 327.