1.67
Canadian Mineralogist Vol. 31, pp. 167-171(t993)
SYNTHESISOF LIEBIGITEAND ANDERSONITE, ANDSTUDY OFTHEIRTHERMAL BEHAVIOR AND LUMINESCENCE
RENATID VOCHTEN I' Inboratorium voor chemischeenfusische mineralogie, Ilniversiteit Antwerpen(RUCA), Middelheimlann B - 2020AntwerPen, Belgium
LAURENTVAN HAVERBEKE 1, Laboratoriumvoor anorganischechtmie, UniversiteitAnwerpen (RUCA),Groenenborgerlaan 17 B - 2020AnwerPen, Belgium
KARELVAN SPRINGEL I' Iaboratorium voor chemischeenfusische m.ineralogie, Universiteit Annverpen (RUCA)' Middelheimlaan B - 2020AntwerPen, Belgium
ABS'IRAC|
TheirH2o content, Andersoniteand liebigite weresynthesized starting from tetrasodiumuranyl tricarbonate[NaaUO2(CO3)3]. a bandgapenergy studiedby thermatanal/sis, is estimatedto be 10.5and 6 moles,respectivet. From the fluorescencespectr4 of approximately2.5 eV wascalculated. It is not affectedby temperature' Keywords:liebigite, andersonite,syntheses' thermal behavior, fluorescence'
SOMMAIRE
Leur teneuren Nous avonssynth6tis6 I'andersonite et la liebigite i partir du tricarbonateuranyl6 de sodiumfNaaUO2(COr)rl' l'6nergie H2O,6tudi& pal. uoulyr" thermique,serait de ldj et 6moles, respectivement.n!nO| les spectresde fluorescence, caicul6ede lai6paration entrebandes serait d'environ 2.5 eV. Elle ne semblepas affect6e par la temp€rature'. (Traduit Parla R6daction)
Mots-cl6s:andersonite, liebigite, synthbses,comportement thermique, fluorescence'
INTRODUC"I]ON Germany(Walenta 1977) andin the orebody of theTono mine,Gifu, Japan@4atsubwa1976). Several syntheses ofliebigite andandersoniie have been described starting In theuranyl carbonate system, the liebigite groupcan from oure chemicals (Blinkoff 1906, Axekod et al' be representedby the generalformula: R[UO2(CO3)3]' 1951,Bachelet et al. 1952,Meyrowitz & Ross 1961, nH2O.In this formula, R representsNarCa in anderson- Meyrowitzet al. 1963,dejka 1969,Coda et al. -1981)- ile, Ca, in liebigite, CaMg in swartzite, and Mg2 in in the presentpaper, a new methodof s;'nthesisof bayleyite,and n has a correspondingvalue of 6' 10 or andersoniteand liebigite is described,starting from the 11,12 wtd18, respectively. On thebasis of thestability complex tetrasodium uranyl trigSrbonqe diagrams(Alwan & Williams 1980),it may be expected Naa[UOr(CO3)r].This methodof synthesisallows-the that liebigite and andersonitecan coexist.Associations preparationof sufficientquantities of both minerals. The of liebigite and andersonitehave been found at the iOentityof the specieswas verified by X-ray diffraction Hillside mine,Yavapai County, Arizona (Axelrod el a/. andby chemicaland thermogravimetricanalyses. 1951) and at Stripa, Vdstrnanland,Sweden (Wellin 1958). Andersoniteoccurs by itself in the gypsum depositsof Myrthengraben,Semmering' Austria (Tufar SYNTmSIS 1967) and Jachymov,Czechoslovakia (Cejka & Ur- banec 1988).Liebigite also occurs at Shinkolobwe' ShabaZaire (Deliens 1985), Miillenbach, BlackForest, In this section,we discussthe synthesisof tetraso- 168 T}IE CANADIAN MINERALOGIST
dium uranyl tricarbonate (NauTC) and its further rA3Lr1. cHErdrcArrcoMposrrroNoFsyNxEETrcLrEBrcrrEAND conversion into liebigite and andersonite EBSoNITE
Synthesisof tetrasodiumuranyl tricarbonate Lieblgtte A!demDlte
rc. of atomlc m. of atodc NaUTC wassynthesized atroom temperatureaccord- atoml mtlo atom0 mdo ing to the method of Blake et al. (1956), slightly cao' r5,29 0,2128 X.93 Nr2O 9.80 0.1580 2.06 modified to obtain pure crystals.These were washed UO: 39.60 0.1384 0.98 CaO 8.S2 0.1590 1.03 coz 18.97 0.40U 3.05 UO3 M.29 0.1548 1.00 with 2M NaCl. In this way, crystalsfree of any Na2CO3 f,zo 28.53 ' caz 20.10 0.4568 2.58 were obtained. The residual NaCl was subsequentlv E2o 78,72 Tolal 100.39 removedby dissolutionin a 50/50ethanol-water mix- 9S.83 ture. The identity of the air-dried NaUTC crystalswas . verified by chemicalanalysis and by comparisonof the ca2lUO2(co3)31 X0-11820 N%caIUo2(co3)31.8s2o X-ray-diffraction data with those given by Douglas (1956). I t! spight S. I Ume tO4.
Conversionof NaUTC into liebigite and andersonite X-Rav CRYSTAIOGRAPHY Accordingto the stability fields of the mineralsof the liebigitegroup (Alwan & Williams 1980),andersonite X-ray-diffraction datawere recorded at 40 kV and20 can only be formed at a high NayCa} concentration mA usingCuKcrl radiation (1, = 1.540564).The diffrac- ratio, whereasliebigite is formed at a low Na*/Ca2* tion patternswere recorded by meansof a Guinier-Hiigg concentrationratio. This was confirmed in our experi- c,rmer4with a diameterof 100 mm. Silicon powder men$. (NBS640)was used as an intemal standard.The relative Two gramsof NaUTCwere dissolved in 100mL of intensitiesof the diffraction lines were measuredwitl a 0.04M CaCl2and left to evaporateat25oC in an open Carl ZeissJena MDl00 microdensitometer.Usine the vessel.After oneweek, well-formed hemimomhic crvs- cell parametersof liebigite(space group Bba2), .virth a tals of liebigite startedto grow. After 3 weetcs,typical 16.699,b 17.557and c 13.697A(Mereiter 1982), and cubic crystalsof andersonitewere formed as a result of thoseof andersonite(space group R3m), wrth a 17.902 the changedNa+/Ca2+ concentration ratio. andc 23.7344 (Codaet al. 1981),rhe powderpatierns The formationof liebigite can be written as: were indexed with the computer program of Visser (1969). 2Ca2++ [uo2(co3)3]4-+ l0H2o --> For both syntheticspecimens, all the observed Ca2[UO2(CO)3].10H2O reflectionscould be indexed,with AQo6,< AQd" (Ae The tranformationof liebigite into andersonitecan be 0.05'), in agreementwith PDF 20-1092and 1I-246. representedas: The densities of the two synthetic minerals were Ca2[UO2(CO)3].l0H2O+ 2Na+ --) measuredin tolueneat 25'C + 0. I by meansof a Cahn Electrobalance Na2Ca[UO2(CO)3].6H2O+ C*+ + 4H"O RG. The measureddensity of anderson- It should be mentioned that the formation of an ite is 2.834 t 0.005 g/cm3,which agreeswith the intermediatephase, consisting of lath-like crystals,was calculatedvalue of 2.860g/cm3, corresponding to Z = observed,as previously reportedby Meyrowia et al. 18.For liebigite,a densityof 2.416t 0.005g/cm3 was (1963).The study of theintermediate compound will be found,which corresponds to Z=8, the subjectof a separatepaper. The crystalsof liebigite The morphologyof andersoniteand liebigite crystals and andersonitewere handpicked. is shownin theelectron micrographs @igs. lA, B). The dimensionsof theliebigite crystals range from 0.1to 0.6 CnBnarcelCoMposmoN mm,whereas thoseof andersonite range from 0.051o0.1 mm.The crystalsof andersoniteare clearly pseudocubic, and thoseof liebigite have a pronOuncedhemimorphic The air-dried syntheticspecimens were dissolvedin morphology(Mereiter 1986). 6 M HCl. The Na2Oand CaO contentwas determined by atomicabsorption spectroscopy (AAS), whereasUO3 was determinedspectrophotometrically with Arsenazo Thermslbehavior Itr as the reagent,the optical densitiesbeing measured at662.5 nm (Singer & Matucha1962).Tl-rcH2O and CO2 Concerningthe water content of the two minerals, contentswere measured on separatesamples by thermo- there is some confusion in the literature. Synthetic gravimetric analysis.Table I summarizesthe results. liebigite having-10 moles of H20 was describedby From the compositionin terms of oxides,the chemical Frondel(1958), Cejka & Urbanec(1979) nd Alwan & formulae were calculated by the classic method of Williams(1980). Appleman (1956) and Meyrowitzet al. residualoxygen. (1963)suggested a watercontent ranging berween 10 SYNTHESISOF LIEBIGITE AND ANDERSOMIE t69
100 Frc. 1. SEM micrographsof syntheticcrystals of liebigite (A) andandersonite (B). scale b4r: Fm.
and l l moles of HrO. For synthetic andersonite,the Na2Ca[UO2(CO3)3]'6H2O 25-150"C watercontent was studied by a numbe.rof investigators -tilroo'" (dejka1969, Urbanec & dejka1979,Cejkaet a/. 1987). Na2ca[uo2(cot3]'H2o Theseauthors accept a water contentranging between ------) 5.4 and5.8 molesof HrO. NarCa[UO2(CO)r] 300-1000'Coxides The thermalstability of both syntheticminerals was (TGA) investigated by thermogravimetric analyses Since liebigite does not **in *r.t'uf cavities (DSC). combinedwith differential scanningcalorimery (Mereiter l98t), and andersoniteis structurallycharac- was used, A DuPontDSC9IO and TGA95I apparatus ierized by the presenceof channelsalong the three-fold flow of N2 with an appliedheating rate of 5'C/min anda axis (Coda it al. l98l), the water molecules are atwhich of 30 mUmin. In orderto detectthe temperature structurallybonded in liebigite, whereasin andersonite, passed CO2is liberared,the outlet of the gas-streamwas zeolitic water may occur. througha solutionof Ba(OH)2.The results,summarized in Table 2, showthat syntheticliebigite andandersonite contain10.53 and 5.99 moles of H2O,respectively. Luminescencesqectra The decompositionof liebigite and andersoniteas be representedas: function of temperaturecan Both synthetic specimensfluoresce intensely blue- green bolh under short- and long-wave ultraviolet Caz[UOu(CO:)3]'llH2O 25-150'C iudiution. The fluorescencespectra were recordedby meansof a Perkin-Elmer MPS44B spectrofluorimeter Ca2[UO2(CO)3]'H2O 150-300"C at298 and77 K, with an excitationwavelength of 366 nm. CazlUOz(CO:)rl :OO-tOO0do*id", The slight differencesin the fluorescencespectra are -_---t characterizedby the modeof bonding of the U ator-nin the crystal structure.No phosphorescence.could.be detectedfor either specimensin a measuringinterval of 2 ms.The spectrafor syntheticliebigite andandersonite TABLX 2. BESULTS OF TSEAII@BAVIMSrBIC ANAI,YSES aI 298 and77 K are representedin Figures 2 aad 3, OI' SYNTBRTIC LIEBIGITE AND ANDEBSOMTE respectively.For both specimens,the maxima of tlle uranvlbands at298 and77Kate givenin Table3' The iloblgtto ABaleEoDlte soeciraof andersoniteand liebigite arevery similar' The approximately3 nm TEnp. wt.g sstg!- TuIr. wt.g Estga- soectrumof andersoniteis shifted lntervsl lost reut btonal lost reDt to higherwavelengths relatrve to thatof liebigite'T{ng fluo- 5.o2S2O into iccount the ipplied amplification, liebigite 25-100 24.W 9.53 E2O 2j.200 13.99 of 150-300 2.59 l'00 g2o 200-300 2.'IS o.s1 s/J rescesmore intensety than andersonite.The intensity 300-500 14.89 2,40 CO2 300-575 72,40 7,82CO2 fluorescenceat 298 K is muchlower thanat 77 K, which 600-850 3.06 0.49 CO2 5?5-6?5 2.65 0.40 CO2 effrciency 650-1000 1.02 0.16 CO2 6?5-1000 5.05 0,74CO2 canbe explarnedby the fact that the quantum of fluorescencedecreases with increasingtemperature' of the fact that the increased TeBtFmtuF ,ltsral ln oC. This is a con$equence t70 THE CANADTANMINERALOGIST
frequencyof collision atelevatedtemperatures improves the probability for deactivationby externalconversion. In comparisonwith the spectraat 298 K, thereexists a supplementarysmall band at 610 nm at 77 K.T\e spectrumof andersoniteat 298 K is not quite identical to the one shownby Tufar (1967),as no weakpeak at 407nm couldbe detectedin our spectrum. Basedon the relationE = hc/tr (hc = 1.9863x 104 Jm) (1 eV = 1.6021x l0re D, E canbe expressedin eV as 1.24x l0-6/1,.With this relation,the bandgap energy Eg between the conduction and valence band was calculatedat the mostintensive peak at 298 and77 K for both syntheticspecies. The Eg valuesfound for ander- soniteare 2.45 eV (298K; l, = 506nm) md2.46ey (77 ( 503 nm).For liebigite,Eg valuesof 2.46ey (298K; FIc. 2. Fluorescencespecrra at 298 K. A. Syntheticliebigite 503nm) and2.48eV (77 K;500 nm)were obtained. For (amplification factor 0.1). B. Syntheticandersonite (ampli- both specimens,the bandgapenergy is not affectedby ficationfactor 3.0). temperature.Based on the Eg values,we may conclude that liebigite and andersonitemust be consideredas mineralswith insulatorproperties.
Drscussrox
Liebigite and andersoniteare easily formed from NaUTC in aqueousmedium. The latter can only be obtainedfrom a strongly alkaline Na2CO,solution of polynuclearuranium hydroxides by a continuousinput of CO2. The synthesisofliebigite andandersonite is donewith an initial concentrationof 0.04 M NaUTC and 0.M M CaClr. Initially, liebigite is formed becausethe ratio Ca'*A\la* is equal to one. Later, ttre Ca2+ArIa*value diminishes,and andersoniteappears. The formation of liebigiteand andersonite can be explained by a two-stage process.Fi$t, the [UO2(CO3)3]4-complex is formedin a stronglyalkaline medium. Subsequently, this complex forms both minerals when sufficient Ca2+ions are Ftc. 3. Fluorescencespectra at 77 K. A. Synthetic liebigite present. (amplificationfactor 0.05). B. Syntheticandenonite (am_ In natural plifi cationfactor 0.3). environments,the UO?+ions necessaryfor the formationofthe tricarbonatecdnnplex are geneiated by oxidation and acid leachingofprimary pitchblende. If the migration of the UO!+ ions takes place in limestone-bearingsediments, the two minerals can be formed with secondarygypsum. This is observedin most of the depositsin which theseminerals occur. In some deposits,however, only liebigite is found. This cannotbe explainedby a differencein solubility ofthese TABLE 3. FLUOBESCEI{CS MAXIIdA Or'SYNTSETIC TIEBIGITE two minerals.It can only be explainedby an initial AND ANDERSONITE AT 298 AND 7? K Caz+/\la+ratio that is larger than unity. The synthesisof these minerals indicates that Tsnfr. Sp€d@ an Fluorc@@ naxlna (m) intermediatephase is formed.This consistsof lathJike 2S8 Ltsbigtte 486 503 525 548 5?5 crystalswith a well-definedcomposition. Up to now, no AndEeDlts 480 506 528 551 6?8 suchintermediate phase is reportedto be presentas an 77 Ltsbigtte 482 500 622 54 5?0 accessory mineral with liebigite and andersonite. AldemDits 485 503 6 647 574 Whetherthis intermediatephase is formed in a natural environmentremains unclear. SYNTHESISOF LIEBIGITE AN'D ANDERSONNE t7l
ACKNOWLEDGEMENTS structure of synthetic andersonite,Na2Ca[UO2(CO3)31' xH2O(x = 5.6).Acta Crystallogr.837,149G1500. We thank the National Fund for Scientific Research DELTENS,M. (1985): Une occurencede liebigrte, carbonate supportawarded to R. Vochten.We thank for financial d'uranyle et de calcium, h Shinkolobwe, Shaba Zalre. thereferees of this paperfor their consffuctivecriticism. MusCeRoyal d'ffique Centrale,Tervuren (Belqiqw)' Mr. J. Cillis of the Royal Belgian Institute of Natural Rapportannuzl 1981-1984,79-80. Sciencesis acknowledgedforthe SEM micrographs.We also areindebted to Mrs. V. Van Heurcken G. Thijs for DouGrAs, R.M. (1956): Tetrasodium uranyl uicarbonate, patiently ryping the manuscript.We also thank very NaaUO2(CO3)3.Anal. Chem-2.8, 1635. muchDr. J. eejka of Czechoslovakiafor thevery useful reprintson his work on uranyl carbonateminerals. FnononL C. (1958): Systematicmineralogy of uranium and thorium.u.S. Geol.Sun., BuII.106/.. RsmREI.{cEs MATsuBARA,S. (1976): The occurrenceof liebigite ftom the Tsukiyoshi orebody of the Tono mine, Gifu Prefecture' ALwAN,A.K. & WnrAMs,P.A. (1980): The aqueous chemistry Japan.Butl. Nat. Sci.Museum Tolqo, Ser. C: Geology2, of uraniumminerals, 2. Mineralsof the liebigitegroup. I I 1-l14. Mineral. Mag. 43, 665-667. MERETER,K. (1982): The crystal structure of liebigite, Aper.nMAN,D. (1956): Crystal structure of liebigite.Bull. Geol- Ca2UO2(CO3!.11H2O. TschermaksMineral. Petogr. Soc.Am.67, 1666 (abstr.). Mitt.30.n7-288.
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BLINKoFF,C. (1906): Bettragezur Kenntniskondensierter TwAR,W. (1967):Andersonit, ein neuerUranmineralfund aus ttranyl-Verbindungan.Thesis, Univ. of Bem, Bern, Swit- Osterreich.Neze s Jahrb.Mineral. Abh. lM,191-199. zerland;Phil. Diss.1906{7,46. UnsANEc.Z. & Cure, J. ( I 9?9): Thermalanalysis of synthetic CrJKA,J, (1969):To the chemistryof andenoniteand thermal andenonite.Comparison of various experimentaltechni- decompositionof dioxo-tricarbonatouranates.Co lle cti on of ques. /z Thermal 1979. Ptoc. 8th Conf. on Thermal Czech.Chenr Commw.34, 1635-1656. Analysis,213 (abstr.).
- & UnsANEc,Z. (1979)'rContribution to the thermal VIssER,J.W. (1969):Fully automaticpro$arn for finding the decomposilionof liebigite. easopisNdrodnlo Muzca'iada unit cell from powderdata. J. Appl. Crystallogr,2'89-95' pf i ro dov d ilnl 148(3| 4), l7 7- 180. WALEr.,rrA,K. (1977):Neue Funde sekun&irer Uranmineralien - & - (1988): Thermal and infrared specrum in mittleren und ndrdlichenSchwarzwald. Der Aufschlws analysesof natural and syntletic andersonites.J. Thermal 28.177-188. AnaI.33.389-394. WELLIN,E. (1958):Notes on the mineralogyof Sweden.1. dsre, J.,Jn. ( I 987): Contributionto the crystal Andersonite,liebigite and'schroeckingeritefrom Suipa, chemistryof andersonlte.Neues Jahrb. Mineral. Monatsh., Viistmanland.Arliv Mineral.Geol. 2(27)' 313-377. 488-501. Received.December I 0, t 99 I , revised manuscript accepted Cooe. A.. DELLAGtusrA, A. & Tpzau, V. (1981):The March27, 1992.