Mechanism of hydrothermal alteration of natural self-irradiated and synthetic crystalline titanate-based pyrochlore

Pöml, P.; Menneken, Martina; Stephan, T.; Niedermeier, D; Geisler, Thorsten; Putnis, Andrew

doi:10.1016/j.gca.2007.03.031

Cited by 49 publications

(25 citation statements)

References 40 publications

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“…For the same reason described above this again would possibly result in dissolution of some albite explaining the coarse porosity within the intergrowth zones. A similar scenario was also proposed for the metastable formation of aeschynite during hydrothermal alteration of titanite-based pyrochlore (Pöml et al 2007) and of CeO 2 during the replacement of Y-stabilized zirconia-ceria ceramics (Plümper et al, in prep.). The metastable formation of monazite during the experimental replacement of fluorapatite by hydroxyapatite (Harlov et al 2005) may be related to the same phenomenon.…”

Section: Discussionsupporting

confidence: 52%

The replacement of plagioclase feldspars by albite: observations from hydrothermal experiments

Hövelmann

Putnis

Geisler

et al. 2009

Contrib Mineral Petrol

184

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Oligoclase and labradorite crystals have been experimentally replaced by albite in an aqueous sodium silicate solution at 600°C and 2 kbars. The replacement is pseudomorphic and is characterised by a sharp chemical interface which progresses through the feldspar while preserving the crystallographic orientation. Reaction rims of albite, up to 50 lm thick, can be readily achieved within 14 days. Re-equilibration of plagioclase in an 18 O-enriched sodium-and silica-bearing solution results in oxygen isotope redistribution within the feldspar framework structure. The observed characteristics of the reaction products are similar to naturally albitised plagioclase and are indicative of an interface-coupled dissolution-reprecipitation mechanism. Chemical analyses demonstrate that the albitisation is accompanied by the mobilisation of major, minor and trace elements also including elements such as Al and Ti which are commonly regarded as immobile during hydrothermal alteration. The results contribute to developing our understanding of the close association between large-scale albitisation and secondary ore mineralisation which is common in nature.

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Section: Discussionsupporting

confidence: 52%

The replacement of plagioclase feldspars by albite: observations from hydrothermal experiments

Hövelmann

Putnis

Geisler

et al. 2009

Contrib Mineral Petrol

184

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“…Interestingly, most of the line-scans revealed a presence of a layer depleted in both uranium and titanium (local minimum on the line-scans). Such feature usually marks the position of the reaction front and the presence of porosity that facilitates the transport of the lixiviant into the mineral surface and dissolution of the parental phase (Pöml et al, 2007). The elemental maps and the EDX analyses of the leached particles showed that the residues consisted mostly of uranium-titanium oxide ( Figure 12 and Figure 13) with some titanium oxide.…”

Section: Chemical Compositionmentioning

confidence: 99%

Leaching of brannerite in the ferric sulphate system. Part 2: Mineralogical transformations during leaching

2016

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT AbstractBrannerite, UTi 2 O 6 , is the most common refractory uranium mineral and is the most important uranium ore mineral after uraninite and coffinite. In order to develop an effective treatment method for the hydrometallurgical extraction of uranium from ores containing brannerite, it is necessary to understand the chemistry of the leaching process. Part 1 of this series described the results of a study of the chemical reaction mechanisms of brannerite under conditions similar to those used industrially. In this paper, the mineralogical data obtained from samples collected during the leaching work is used to derive further insight into the transformations that take place during leaching. Detailed characterisation of the brannerite feed specimen and leach residues were carried out using surface imaging and X-ray diffraction techniques. It was shown that the brannerite specimen is heterogeneous, consisting of at least two phases. The brannerite phase was metamict and showed signs of natural alteration to fine-grained (10-20 nm) crystalline anatase. Comparisons between the feed and residues showed that the X-ray amorphous material, in particular lead and silicon enriched areas identified near the anatase were most susceptible to leaching while the crystalline material was relatively resistant to leaching. These results demonstrate that the extent of brannerite alteration and its texture are important considerations to the hydrometallurgical behaviour of a particular ore along with the typical concerns such as grade, liberation size and gangue mineralogy.

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“…2). The relatively high O data and textural observations, Pöml et al (2007) concluded that the alteration products deposited on the pyrochlore surfaces precipitated from solution.…”

Section: Formation Of Secondary Phasesmentioning

confidence: 99%

“…Various studies show that the alteration of Ti-bearing pyrochlore supergroup minerals under natural or laboratory conditions, at temperatures 100-550 o C, led to the formation of various products that include TiO 2 (rutile, anatase), aeschynite, columbite, Nb-goethite, liandratite, uranpyrochlore, Nb-Ta oxide, and Y-REE phases (Lumpkin and Ewing, 1996;Wall et al, 1996;Nasraoui and Bilal, 2000;Xu et al, 2004;Geisler et al, 2005a,b;Pöml et al, 2007;Pöml et al 2011). In the samples analyzed here, no TiO 2 phases were observed.…”

Section: Formation Of Secondary Phasesmentioning

confidence: 99%

“…Most of these phases form micro-and nanoparticles deposited on the pyrochlore surface, along grain boundaries, pores and along fractures forming secondary veins. In several cases, the alteration of pyrochlore under hydrothermal conditions led to its recrystallization (Xu et al, 2004;Geisler et al, 2005a;Leturcq et al, 2005;Pöml et al, 2007, Pöml et al, 2011.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Role of vein-phases in nanoscale sequestration of U, Nb, Ti, and Pb during the alteration of pyrochlore

Deditius

Smith

Utsunomiya

et al. 2015

Geochimica et Cosmochimica Acta

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Mechanism of hydrothermal alteration of natural self-irradiated and synthetic crystalline titanate-based pyrochlore

Cited by 49 publications

References 40 publications

The replacement of plagioclase feldspars by albite: observations from hydrothermal experiments

The replacement of plagioclase feldspars by albite: observations from hydrothermal experiments

Leaching of brannerite in the ferric sulphate system. Part 2: Mineralogical transformations during leaching

Role of vein-phases in nanoscale sequestration of U, Nb, Ti, and Pb during the alteration of pyrochlore

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