Synthesis and characterization of uranium and thorium bearing monazites
Description
The objective of this research thesis was to determine parameters governing the introduction of uranium and of thorium into minerals with a monazite-type structure, under temperature and pressure conditions corresponding to those of its crystallisation in geological environments. The study is performed in hydrothermal environment, in function of different physical-chemical parameters such as the chemical composition of the aqueous liquid phase, and the temperature. After some generalities about the LaPO4 monazite (synthesis methods, chemical and physical properties), the author reports an experimental study of the solid solution between LaPO4 and (Ca0.5U0.5)PO4 at 780 C and 200 MPa, an analogue experimental study with thorium instead of uranium, and an experimental study of solid solutions of the same compounds at 300 C and 200 MPa. The author also reports the study of Raman spectra of actinide-bearing monazites, and the application of Raman spectroscopy to the study of natural monazites. He discusses the orthorhombic structure of (Ca0.5U0.5)PO4, and reports the study of the stability of the solid solution of LaPO4-(Ca0.5U0.5)PO4. Geological implications are finally discussed
Abstract (French)
Les composes (La1-2x[U,Th]xCax)PO4 ont ete synthetises par voie hydrothermale a 780 deg. C et 200 MPa, en milieu [H3PO4]=30 m, pour des fractions molaires x comprises entre 0 et 0,5. Le principal mecanisme d'insertion des radioelements dans la monazite est: LaPO4 + x[U,Th]4+ + xCa2+ = (La1-2x[U,Th]xCax)PO4 + xLa2O3. La stabilite des composes (La1-2xUxCax)PO4 diminue lorsque la temperature decroit de 780 a 300 deg. C, alors que les composes (La1-2xThxCax)PO4 restent stables dans un domaine de temperature compris entre 500 et 780 deg. C, 200 MPa et [H3PO4]=30 m. Les composes obtenus cristallisent dans le systeme monoclinique et forment deux solutions solides completes entre LaPO4-Ca0,5U0,5)PO4 et LaPO4-(Ca0,5Th0,5)PO4. Leurs parametres cristallins diminuent lineairement lorsque le taux d'insertion des radioelements augmente. Le compose (Ca0,5U0,5)PO4, synthetise a 500 deg. C, 200 MPa et [H3PO4]=30 m, cristallise dans le systeme orthorhombique, groupe d'espace Pnma et les parametres cristallins sont a=13,926(4)A, b=6,958(3)A et c=6,136(2)A. L'etude par microspectroscopie Raman des monazites synthetiques U et Th montre que la distribution des atomes dans le site cationique est aleatoire: Le deplacement des bandes de vibration est directement lie a l'augmentation du taux d'insertion des radioelements dans la monazite. L'etude des monazites naturelles par spectroscopie Raman permet de caracteriser semi-quantitativement certaines proprietes physico-chimiques de ces mineraux, telles que la zonation ou la metamictisation. A l'issue de ce travail, une nouvelle approche des mecanismes de fractionnement des terres rares par les monazites naturelles basee sur la valeur moyenne du rayon ionique des terres rares dans le site cationique est proposee. Les parametres controlant et limitant l'insertion des radioelements dans la monazite cristallisant dans un magma sont la solubilite et la diffusion des terres rares, ca, Th et U dans les liquides silicates. (auteur)Files
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Additional details
Additional titles
- Original title (French)
- Synthese et caracterisation des monazites uraniferes et thoriferes
Publishing Information
- Imprint Pagination
- 237 p.
- Report number
- FRNC-TH--14716
INIS
- Country of Publication
- France
- Country of Input or Organization
- France
- INIS RN
- 54091830
- Subject category
- S58: GEOSCIENCES; S11: NUCLEAR FUEL CYCLE AND FUEL MATERIALS;
- Resource subtype / Literary indicator
- Thesis
- Descriptors DEI
- AQUEOUS SOLUTIONS; CHEMICAL COMPOSITION; CHEMICAL REACTION KINETICS; CRYSTALLIZATION; CRYSTALLOGRAPHY; FRANCE; GEOCHEMISTRY; GEOLOGY; HYDROTHERMAL SYSTEMS; MICROSTRUCTURE; MONAZITES; PETROGENESIS; RAMAN SPECTROSCOPY; RESEARCH PROGRAMS; SYNTHESIS; TEMPERATURE DEPENDENCE; THORIUM; URANIUM
- Descriptors DEC
- ACTINIDES; CHEMISTRY; DEVELOPED COUNTRIES; DISPERSIONS; ELEMENTS; ENERGY SYSTEMS; EUROPE; GEOLOGY; GEOTHERMAL SYSTEMS; HOMOGENEOUS MIXTURES; KINETICS; LASER SPECTROSCOPY; MATERIALS; METALS; MINERALS; MIXTURES; PETROLOGY; PHASE TRANSFORMATIONS; PHOSPHATE MINERALS; RADIOACTIVE MATERIALS; RADIOACTIVE MINERALS; REACTION KINETICS; SOLUTIONS; SPECTROSCOPY; THORIUM MINERALS; WESTERN EUROPE
Optional Information
- Notes
- 107 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses