Brannerite

In most uranium ores the element is present in several, usually many diverse minerals. Some of these dissolve in sulfuric acid solutions under mild conditions, while others may require more aggressive conditions. Thus, while it may be comfortable to recover 90-95% of the uranium present, it may be tough or impractical to win the balance amount of a few percent economically. Some of the most difficult uranium minerals to leach are those of the multiple oxide variety, most commonly brannerite and davidite. These usually have U(IV) as well as U(VI), together with a number of other elements such as titanium, iron, vanadium, thorium, and rare earths. To extract uranium from these sources is not as easy as other relatively simpler commonly occurring sources. 

Effect of synthesis conditions on phase composition of Pyrochlore-Brannerite ceramics. Materials Research Society Symposium Proceedings, 663, 315-324. 

Fig. 4. SEM backscattered electron images of alteration in natural brannerite (a) Part of a large brannerite specimen showing minor alteration around the rim of the crystal and along fractures extending into the interior (b) Brannerite crystals showing extensive alteration along their rims, together with the presence of U-rich phases along cracks in the host rock.

Fig. 5. Scatter plot showing the number of Si atoms per formula unit and the U/Ti atomic ratio in a suite of natural brannerite samples, ( , unaltered areas , altered areas). In unaltered brannerite, the U/Ti ratio lies below the ideal value of 0.5 due to extensive substitution of Th, Ca, and minor REEs for U on the A-site.

Fig. 8. Plots showing the dependence of the elemental release rate on pH for U in brannerite, pyrochlore, and zirconolite at 75 °C (after Zhang et al. 200 b). Also shown are data for Ca in perovskite and Ba in hollandite (after McGlinn et al. 1995 Carter et al. 2002). Linear fits are shown for perovskite and hollandite, but the other curves are weighted fits used to illustrate the trends.

Fig. 9. Graph showing the change in U/Ti atomic ratio in the fluid (normalized to the stoichiometry of the starting material) after dissolution of synthetic brannerite acidic and basic fluids (after Zhang et al. 2003). The experiment at pH = 2 reveals a strong preferential release of U, reaching a steady-state normalized U/Ti atomic ratio of about 20 after several weeks.

Helean, K. B., Navrotsky, A. et al. 2003. Enthalpies of formation of U-, Th-, Ce-brannerite implications for plutonium immobilisation. Journal of Nuclear Materials, 320, 231-244. 

Lumpkin, G. R., Leung, S. H. F. Colella, M. 2000. Composition, geochemical alteration, and alpha-decay damage effects of natural brannerite. In Smith, R. W. Shoesmith, D. W. (eds) Scientific... 

Szymanski, J. T. Scott, J. D. 1982. A crystal structure refinement of synthetic brannerite, UTi206, and its bearing on rate of alkaline-carbonate leching of brannerite in ore. Canadian Mineralogist, 20, 271-279. 

Vance, E. R., Watson, J. N. et al. 2000. Crystal chemistry, radiation effects and aqueous leaching of brannerite, UTi206. Ceramic Transactions, 107, 561-568. 

Zhang, Y., Thomas, B. S., Lumpkin, G. R., Blackford, M., Zhang, Z., Colella, M. Aly, Z. 2003. Dissolution of synthetic brannerite in acidic and alkaline fluids. Journal of Nuclear-Materials, 321, 1-7. 

Fig. 8.9(b), ZnV20g is able to crystallize with the brannerite structure whose theoretical bond valences, calculated from the network equations ((3.3) and (3.4)) and shown in Fig. 8.9(b), already predict an out-of-centre distortion for the ion. ZnV20g thus adopts a bond graph that supports the electronically induced distortion. In this case the adoption of a lower symmetry bond graph is favoured because it is able to reduce the bond strain. 

Ziolkowski, J. (1983a). Catalytic properties of defective brannerite-type vanadates. II. A model of sites active in oxidation of propylene on the (201) and (202) planes J- Catal. 81, 311-27. 

Sedimentary Quartz-pebble conglomerates and associated formations Monazite, uraninite, brannerite Karnataka... 

U-mineralized shear zones Brannerite, xenotime, monazite Singhbhum Thrust Belt, Bihar... 

Of these, bastnasite is the only mineral worked primarily for rare earths and both monazite and xenotime are mostly by-products of mining ilmenite, rutile, cassiterite, zircon or gold. Apatite and some multi oxide minerals like pyrochlore, euxenite, brannerite and loparite (a niobium titanate) are also commercial sources of rare earths, but production of RE from these is limited. 

Canada and Australia are the world s largest producers of uranium. All Canadian production is from rich deposits in the Athabasca basin of northern Saskatchewan among those is the McArthur River mine, which has the world s largest high-grade deposit, estimated at 1.52 X 10 t of uranium from ore grading 15-18% uranium. These unconformity -type Saskatchewan deposits, which are also the principal deposit-type for Australian uranium production, contain mainly uraninite [UO2] with associated coffinite [U(Si04)i jc(0H)4j and brannerite [(U,Ca,Y,Ce)(Ti,Fe)206] (Plant et al, 1999). The chief uses of uranium are in nuclear power plants and weaponry. 

Oxides/Ions Pyrochlore Zirconolite Brannerite RutUe ... 

Corrosion of the Pu-doped pyrochlore-based ceramics is by incongruent dissolution and segregation of secondary phases [40], Leach rates in 1-year PCT-B tests were found to be (in g/(m xday) Ca - 10, Gd - 10, Pu - 10, Zr - <10. The leach rate of Pu is reduced by one order of magnitude - from lO" g/(m day) in short tests (1 to 7 days) to 10 g/(m xday) after 112-324 days of interaction with water [105], Introduction of 8 to 15 wt.% of oxides of typical contaminants (F, Cl, Na, Mg, K, Na, Si, Al, Ga, Mo, W, etc.) yielded extra glass, perovskite, and Ca-Al-Ti phase instead of brannerite [117]. This does not affect or even improve the chemical durability with respect to actinides. 

Melted (U,Pu)-bearing ceramics are composed of major pyrochlore and minor brannerite and rutile. Their grain size is from 20 to 200 microns which is one or two orders of magnitude larger than in ceramics produced by sintering. Leach rates (7-day MCC-3 test at 90 °C) of Ti, Zr, U, and Pu were found to be (2 -6)xl0 g/(m xday) [118,119]. 

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