Synthetic Aluminum.pdf

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TI{E AMERICAN MINERALOGIST, VOL. 52, JULY-AUGUST, 1967

PROPERTIES OF A SYNTHETIC MAGNESIUM-ALUMINUMCARBONATE HYDROXIDE AND ITS RELATIONSHIP TOMAGNESIUM-ALUMINUM DOUBLE HYDROXIDE, MA-NASSEITE AND HYDROTALCITE1

G. J. Ross ,lxn H. KooeueSoil Researchnstitute. Canad.aDepartment of Agriculture,Ollowa,Onlorio.Assrnecr

A synthetic mineral prepared by titrating a mixed solution of MgClz and AlCl: withNaOH in a COz-free system and then diaiyzing the suspension for 30 days at 60'C was ahydrated Mg-AI carbonate hydroxide with the formula MgoAlzCOa(OH)re.4HzO andproperties of manasseite and hydrotalcite. The synthetic mineral is hexagonal witha:6.14t, c:15.6lz A and Z:1. Dehydration and corresponclingcontraction of basalspacingswere reversibleup to 300"C and irreversible above 450'C. Above 300'C both OHwater and COzwere evolved, and at 450'C the structure was destroyed.A one-dimensionalstructure analysis indicates a structure consisting of brucitic layers alternating withhydrous aluminum layers.INrnooucrroN

When a solutioncontainingMgClz and AlCh is ti trated with NaOH, adouble hydroxide of Mg and AI is formed having a characteristic struc-ture (e.g.,Feitknecht,1942;Feitknechtand Gerber,1942).Theseauthorsshowed hat other divalent ions such as Ca, Co, Mn, Cd in solutionwithAl or Fe3+ lsogive doublehydroxidesupon the addition of a base.Mort-land and Gastuche(1962) a\alyzedprecipitates prepared n this way andfound that with a molar ratio of 0.7 Mg/(Mgf AD


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SYNTHETIC MAGNESIUM-ALUMINUM CARBONATE HYDROXIDE IO37Pnrpan.qtoN ol' mr Pnocpnetr

The precipitate was prepared by titrating with 1N NaOH a solution consistingof AlChand MgCls having a total concentration of 0.1M and a Mg/(MgfAl) molar ratio of 0.8The molar ratio of 0.8 was selected because preliminary experiments showed that at thismolar ratio a precipitate free of brucite or gibbsite was obtained. The NaOH was added in astepwise manner and the pH was measured after each addition to give a titration curve. Astream of COrfree nitrogen was passed through the solution during the titration to mini-mize contamination of the precipitate with COz.For comparisona solution of MgCl: wastitrated with NaOH in a similar way.

The buffering at pH 9.5, obtained when MgCl2 alone was titrated with NaOH, was dueto the precipitation of Mg(OH): (t'ig. 1, curve 1) . The buffering between pH 4.0 and 4.5,obtained with the MgClz and AlCl3 mixture, was due to the precipitation of AI(OH)3(curve 2) . The secondbuffering range betweenpH 7.7 and 8.5 was more than one pH unitbelow that obtained when Mg(OH)z was precipitated. This bufiering range corresponds tothat obtained under similar conditions by Turner and Brydon (1962) and may be due to

me NoOHFrc. 1. Titration curves of 0.1M solutions of magnesium chloride

and aluminum-masnesium chloride.


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1038 G -T. ROSS AND IT. KODAMAadsorption bonding betrveen he hyclroxidesof Mg and Al with the latter as the negativecompound (Treadwell and Bernasconi, 1930)

The suspension,obtained from the titration of the solution containing both AICI3 andMgClz, was transferred to a polyethylene bag and dialyzed for one month at 60'C againstdistilled rvatel which was changed ctaily. The suspensionwas then freeze-driedand the re-sulting powclerused for the remainder of the study.Cunrrrcar,ANerysus

Part of the freeze-dried amplewas dissolved n dilute nitr ic acid andAl was determinedby the aluminon method (Robertson,1950)and Mgby the atomic absorption method. The Cl content was determined byX-ray spectromelryand CO: and H:O by dr1-combustionusing WO3 oensurecompletecombustion (Steyermark, 96t).The compositionof the precipitate prepared n this study is close othose of the two polymorphs manasseiteand hydrotalcite with theformula,Mg6AhCOr(OH)16.4HrO Table 1) . The prec ip i ta te ad re la-tively high CC)2ontent,which presumablywas ncorporated rom the airduring dialysisand after freezedrying, Brandenberger 1933)and Mump-ton, et al. (1965),have noted the rapid carbonationof relatedminerals.The CI content was negligible,unlike the considerableCl contents ofsomedouble hydroxides eportedb;, Feitknecht (1942).

X-n.rv AN,rr,vsrsX-ray diffraction polvderpatterns were obtained using Fe-fi l teredCoradiation with a 114.7mm camera containing the specimen n a thin-walledglass apil lary (Table 2). SomeX-ray i ine broadeningwas evidentwhich s attr ibuted to small particlesizeand imperlect crystal linity of theprecipitate and to statistical distr ibution of COs n its structure, dis-

cussedn a later section.Except for small differencesn (001) eflections(which are shownbelow to be dependenton relativehumidity) the pow-der data of the precipitateare very close o those eportedby Mortlandand Gastuche 1962).As to the values or manasseite nd hydrotalcite,the powder data of the precipitate prepared n this study agreemorecloselywith thoseof manasseitehan with thoseof hydrotalcitc indicat-ing that the precipitate belongs o the hexagonal ather than to therhombohedral group. The X-ray powder diffraction l ines of the pre-cipitate. therefore,were preliminari ly indexed n the hexagonalsystemusing he uni t -ce l ldata for manassei te, :6 .13 A and c:15.37 A. 1 lheunit-cell dimensionsof the precipitate,calculatedusing a pair of well-definedsmall spacings 1.541and 1.498A; of tLe indexed pattern, area:6.14rA and c:15.6 lzA. ' f t re data in Table 2 showgood agreementbetween he observedQr,pvalues (Qu"t:l /d'or) and the pmzvaluescal-culatedon the basisof the derived cell dimensions.


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SYNTHETIC MAGNESIUM-ALUMINUM CARBONATE HYDROXIDE 1039TaerE 1. Cnonrcel ANALYSES

Wt.''k* Precipitater Manasseite2 Manasseiter HydrotalciteaMgO 38.2 36.76 39.38 39 84Fero: o .2o o.21 o 90AlzOs 16.5 19 65 16.59 15 16C O z 6 . 4 0 . 3 ) 6 . 9 8 7 4 8 7 2 6c l 0 . 1 + 0 . 0 1 )H:O 38.4 36.13 36.34 3tr .83R e m . 0 . 3 5 0 . 1 4Total 99.6 100.07 100.00 100.13

* Based on air-dry weight.I Precipitate prepared in this laboratory.2 Sample from Snarum, Norway. Pure sample, but contains gibbsite. Rem. is SiOz.Frondel (1941)3Analysis of sample 2 recalculated to 100/s after deduction oI0.350/6 SiOz and 6.38/6gibbsite (on the basis of 6 Mg atoms per cell). Frondel (1941).a Sample from Snarum, Norway. Presumed to be a mixture of hydrotalcite and manas-seite. Rem. is insoluble. Manasee (1915).

Tnonlral Awar,vsrsThe thermal stabil i ty of the precipitatewas nvestigatedby DTA andTGA. The DTA was carriedout at a heating rate of lO'C/min (Moritaand Rice, 1955).The TGA was obtained at a hea ting rate of 5"C/minwith an analytical balance and a Fisher Balance Assembll 'mountedover a cylindrical urnacecontaining a suspendedPt dish. The balancewas calibratedwith an equal weight of calcined ample.The DTA curve of the precipitate s similar to that given for hydrotal-cite (Mumpton, et al., 1965,p. 1904),although its endothermpeaksareSomewhatdifferent in magnitude and occur at sl ightly different tem-

T.tnn 3. Cnr-r CoNrnNrsPrecipitatel Manasseite2 Mg6ALCOa(OH)16.4H2O

MgAICHo

6 . 02 . O0 . 92 4 . 42 3 . O

6 02 . O1 . 12 4 . 92 3 . 6

61I

2423I Calculated from analysis 1, Table 1.2 Calculated from analysis 3, Table 1.


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Fz. Ft s . 3

z -ol w

a -c d qb 0 h. = >o >

A A

SVNTHETIC MAGNNSIUM-ALUMINUM CARBONATE HYDROXIDN 1041

O N N N N N N *

o c o o \ o q q q a o q - o o o N \ o q q Nr O N N i H F

N . -- - | ! o Na a . N

{ - iO H N N N N N CO O O O N N N N N +

+ N O \ N O 4 + 1 N O \@ e n * r + r O N N i ON m : o o . + r N o @ N \ O + r i oN Q Q N N N N N

o 4 r Di N

s < . q i o r < i dO O i N N N N N

' d -o I 9: iEH l l i ir rN i N T D 4N O \ H O \ O O \ r4 + r + S N O , a

i : d i i o o

"-i aE 7 H V >o.'e=ir O\4 4 O c } 1 @N N N i i

oo

dk

F

- a ( = ; 6 ; 6 V V V N e o i H : * H d

i o \N N :

HHF

oPr

H(.)tslts

zFza3tsO14

/,oruotsz3O

xNt4FlF

@r od N

{q

e i ll l ^

d J

@I Ir >

' N


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G. "T.ROSS AND H KODAMA

T.rp.rotrr" "l600 7oo 8oo

Frc. 3. Thermogravimetric and difierential thermogravimetric analysis curvesof the precipitate.

slides o different temperatures n the furnace of a TGA apparatusat arate of S"C/min. After cooling over P2Os, he oriented specimenswereX-rayed at close o 0 percentrelativehumidity with a Phil ips Difiractom-eter.As shown n Figure 5, an increasen relativehumidity from 40 percentto 85 percent at 25oCsignificantly ncreased asal spacings.Heating to

180oC auseda sl ight decreasen basal spacing,but at 150"Cand 180"Can additional first-order reflection appearedat a lower basai spacing-.From 220'C to 300"C only one first-orderbasal eflectionat about 6.6 Awas present.After heating at 450oC,no peaks were evident in the dif-fractograms ndicating destruction of the crystal structure.After heating, the oriented specimenswere rewetted, dried overnightat room temperature,and then X rayed at room temperatureand 40 per-

*coI


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SYNTH]JTICMAGNESIUM-ALUMINUMCARBONATE YDROXIDE 1043cent relativehumidity. AII the specimens, xcept he oneheated o 450oC,gave first-orderbasal reflectionsat the originai spacingwith no loss nintensity (Fig. 5).

These results ndicate that the amount of water of crystal l izationde-termines he basal spacingbetween7.9 A and O.OA. the 7.9 A spacingrepresents he fully hydrated phase,and the 6.6 A spacingcharacterizesthe fully dehydrated phase.Dehydration appears o be completedbe-tween 180"C and 220"C and is reversible up to 300oC ndicating no ap-preciabledestructionof crystal structure at this Lemperature. randen-T,q.eln 4 ONr-DrurNsroxer, Srnucrunn F.qcrops (Fcor) eNo rnr Drntl'u ANnOnsrnltnl IntnNsnrns lon eN Ioeer, Moorr,t or rnB Pnoposnl Srnuctuln

F""r" I I cosz201"'r" - (F*r")'sin29 osdf -

0020040060080 . 0 . 1 00 . o . 1 20 . 0 . 1 40 . 0 . 1 6

- 5 9 . 2+88 .5+91 8+39 9- 6 . 0+ 1 1 3 . 4-39 .9+61 8

100532320.037I3

10060406*65+

* Includes intensity of a prismatic reflection.f Based on the chemical formula Mg6AlzCO:(OH)ro.4HuO

berger (1933) also concluded hat the X-ray diffraction propertiesof asimilarhydrated Ca-AI doublehydroxidevaried with its content of waterof crystal l ization.

INln.{nno AssonprroN ANar,ysrsInfrared absorptionspectrawereobtainedwith a Perkin-Elmer Model21 Spectrophotometeron KBr pellets containing 0.20 percent of thesample.The spectrumof the precipitate (Fig. 6) is l ike the spectrumof

hydrotalcite publishedby Mumpton, et al., p. 1903 1965). n both pat-terns the stretching vibrations of water are representedby a band at 3480cm-1 and a shoulder at about 3000 cm-l; the stretching vibrations ofcarbonateare shown by bands at about 1480 cm-l and 1380cm-].

Car,curerroN ol STRUCTURALoRMULAThe formula of the precipitate was calculated using the data of chemi-cal and thermal analyses.Based on the break in the TGA and DTGAcurves at 200oC Fig. 3) and on the strong but reversible ontraction n


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1044 G. "T.ROSSAND H. KODAMA

T e m p e r o t u r e ( " C )Frc.4. Evolution of carbon dioxide from the precipitate heated to various temperatures.basalspacings etween180oCand 220"C (Fig.5), the weigh t lossbelow200oCwasattr ibuted to absorbedwater and water of crystal l ization,andthat above 200oC o OH water and COz.Because he amounts of ad-sorbedwater and water of crystal l izationwerenot accuratelyknown. theformula was first calculatedon the basis of the data in Table 1 recal-culated as percentof the sampleweight at 200oC.The weight lossbelowll0"C (3.27a)washen assigned o absorbedwater and excluded rom thecalculations.The weight lossbetween110oCand 200'C (l2.l7o) was at-tr ibuted to water of crystal l izationand corresponds o four H2O mole-cules n the formula. The calculated ormula for the precipitate(Table 3)agrees loselywith the experimental alues or manasseite nd they bothconform to the general ormula, MgoALCOg(OH)16.4HrO.

! q)o

UNo(JooG


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SYNTHDTIC MAGNESIUM-ALUMINLTM CARBONATE HYDROXIDE 1045

7.

7.30

6(-o).guoo-tt,ooloc,-ctoiI! It)(,

-oo6.90

Temperolure ( 'C)Fro. 5. Efiect of relative humidity (solid triangles), heating (solid circles) and rehydra-tion (open circles) on basal spacings of the precipitate. Data from difiractograms of oriented

specimens giving a regular sequence of basal reflections

Srnucruner, ANer,ysrsAs shown n Table 2, the largestbasal reflectionoccurredat the half

height of the c-dimension which indicates a hexagonal subcell with di-mensions, :6.14 A and c:7.79 A. l l t ir subcellcontains he half mole-cule MgaAI(OH)s(COt+.2H2Owhich requires he repetit ionof an equiv-alent atom array at a distance oI 7.79A and implies that the distr ibu-tion of COs ons must be statistical.The thermal data and the results of the dehydration experiment (Figs.2, 3 and 5) indicated that, except or the loss of H2O below 200oC, hethermal decompositionof the precipitate was similar to that of brucite in


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1046 G. -T. ROS.SAND II . KODAMAWAVETENGTHMICRONS}

FREQUENCYCM_')Frc. 6. Infrared spectra of the precipitate ancl hydrotalcite.

that the OH was evolvedbetween300oCand 450"C. When oxygen onsare n hexagonalclosestpacking, as in brucite, the hexagonalbasewithedge .2 A permits four oxygens n each ayer. Three layersof four close-packedoxgyenswould give a subcellheight of 7.20A as compared o theobserved7.79h value. A structural model was assumed, herefore,con-sistingof a brucitic laver containing3 n4g and 8 OH (two layersof close-packed oxygen ons) and a looselvstacked ayer containing 1 Al, + COaand 2 HzO per subcell.A diagram of this model is shown in Figure 7.Basedupon the proposed tructure,a one-dimensional tructureanaly-

4 0 H3Mg4 0 H

{_+_'8Fi

4 0 H3Mg

4 0 H

o{@v?P r- - - -

r - -o { _ -R"i@ t oTEJ_ iL

A+f(cor)+zHro

Al+ (COr)+zHrO

Al+f(CQ)+zH2OFrc. 7. Diagram of the proposed structure of the precipitate.


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SYNTIIETICMAGNESIUM-ALUMINUMCARBONATE YDROXIDE 1047sis was used and the structure factors (F""r")and the intensities 1",r".)werecalculated.The agreement etween he 1".r".and 1o5". alues Table4) supports he validity of the proposedstructure.

CoNcrusroNsX-ray diffraction, chemical, thermal and infrared analysesshowedthat the precipitate preparedby ti trating mixed solutionsof AICL andMgCb and dialyzing the suspension Mortland and Gastuche,1962) was

not a pure hydrated Mg-Al doublehydroxide, as has generallybeen be-l ieved,but a hydrated Mg-Al carbonate ydroxidewith similarpropertiesand the same ormula asmanasseite nd hydrotalcite,MgaAlzCOa(OH)6.4H2O.

A one-dimensional tructure analysis ndicated a structure consistingof brucitic Iayers alternating with hydrous aluminum layers.

RrlrnlucesBn.q.NonNsnncrn,E. (1933) Kristallstructurelle Untersuchungen an Ca-Aluminatehydra-

ten. Schw,eiz M'inerol, Petrogr. Mift 13,569-570.Fnrtrnecnt, W. (1942) Uber die Bildung von Doppelhydroxyden zwischen zwei- und

dreiwertigen M etallen H el,o.Chim. A cta 25, 555-569.-- and M. Gerber (1942) Zur Kenntnis der Doppelhydroxyde und basischeDoppel-

salze. III Uber Magnesium-Aluminiumdoppelhl'droxyde. Heh. Chim. Acta 25, l3l-r37.l 'noNnnl, C. (1941) Constitution and polymorphism of the pyroaurite and sj6grenite

grotps. Amer. Mineral 26,295-375.Mawesse, E. (1915) Idrotalcite e piroaurite. Atti Soc lioscana Sc . Nat., Proc. Verb. 24 ,92-105.Monrtl, H aNo H. M Rrcn (1955) Characterization of organic substancesby differential

thermal analysis. Anal. Chem.27, 336 339.Montre.No, M. M aNo M. C. Gasrucux, (1962) Cristallisation d'hydroxides mixtes de

magn6siumet d'aluminium en milieu dialys6. C. R. Acad,.Sc i Pari's,255,2131-2133.Muumox, F. A., H. W. Je,r'rr, aNo C. S. Tnolrlsox (1965) Coalingite, a new mineralfrom the New Idria serpentine, Fresno and San Benito Counties, Ca\ifornia. Amer.Mineral,. 50, 1893 1913.

Roetnrson, G. (1950) The colorimetric determination of aluminum in silicate materials.I. Sci. Food.Agrie. l,59-63.

Snrru, J. V. (ed.) (1965) ndex (inorganic) tothePorvderDifiraction h'ile. Pub. Amer. Soc.Test.Moler. PDIS l5iSrrvrnu,trr, A. (1961) Quantitatioe Organi.cMicro Analysis. Second ed , Academic Press,New York.Tnnalwtr.l, W. D. aNo Eo. BnnNescoNr (1930)Versuchezur elektrometrischenTitration

von Aluminium- und Magnesiumion nebeneinander. Ilelt Chim. Acta 13, 500-509.Tunnen, R. C. eNo J E. Bnvoox (1962) Formation of double hydroxides and the titrationof clays. Science 136 (3521), 1052-1054.Manuscript receiaed,,uly 22, 1966; accepted.or publicotion, September8, 1966.

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