Results 1 - 10 of 1714
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[en] Here we study the homogeneity of Eu3+-doped La1-xGdxPO4 (x = 0, 0.11, 0.33, 0.55, 0.75, 0.92, 1) monazite-type solid solutions by a combination of Raman and time-resolved laser fluorescence spectroscopies (TRLFS) with complementary quasi-random structure-based atomistic modeling studies. For the intermediate La0.45Gd0.55PO4 composition we detected a significant broadening of the Raman bands corresponding to the lattice vibrations of the LnO9 polyhedron, indicating much stronger distortion of the lanthanide cation site than the PO4 tetrahedron. A distortion of the crystal lattice around the dopant site was also confirmed in our TRLFS measurements of Eu3+ doped samples, where both the half width (FWHM) of the excitation peaks and the 7F2/7F1 ratio derived from the emission spectra increase for intermediate solid-solution compositions. The observed variation in FWHM correlates well with the simulated distribution of Eu···O bond distances within the investigated monazites. The combined results imply that homogenous Eu3+-doped La1-xGdxPO4 monazite-type solid solutions are formed over the entire composition range, which is of importance in the context of using these ceramics for immobilization of radionuclides. - Highlights: •Homogenous Eu3+-doped La1-xGdxPO4 monazite-type solid solutions have been synthesized. •Solid solution formation is accompanied by slight distortion of the LnO9 polyhedron. •Raman and laser spectroscopic trends are observed within the monazite series. •Results are explained with atomistic simulations of Eu-O bond distance distribution.
[en] The pilot plant studies made to develop a process for helium recovery from monazite and its purification are described. The steps in the developed process are : (1) liberation of helium from monazite processing plant during caustic digestion of the ore, (2) collection of the crude gas (30-50% helium) after removal of condensables and drying, (3) removal of hydrogen by catalytic combination with oxygen to form water vapour using de-oxo catalyst bed, (4) removal of oxygen and nitrogen by condensation (helium content is raised 98% in this step) and (5) passing the gas over activated charcoal cooled by liquid nitrogen. In the final step, 99.995% pure helium is obtained. Trials have shown that the process is feasible. (M.G.B.)
[en] A process for yellow cake production from Thai-monazite by sulfuric acid method was developed. It was found in the experiment that uranium extraction could reach 96.307% by digestion -200 to +270 mesh ore with 90% sulfuric acid with acid to ore ratio 1.5:1 at 200 deg C for 1.5 hrs. Separation of rare earths and thorium was done by precipitation as oxalate salts with oxalic acid. Purification of uranium was achieved by using anion-exchange method with Amberlite IR A-400 resins. Elution shows the highest efficiency when nitrate solution was used as eluent. Ammonium diuranate could subsequently be precipitated from the uranium eluate by ammonium hydroxide solution at pH of 4.30-9.25. Calcined yellow cake products meet the Usaec specification with uranium content greater than 75.209% U3 O8
[en] Beaches are the main sources for economic heavy minerals (HM) like ilmenite rutile, monazite, zircon, garnet and sillimanite. The seasonal HM accumulations, colloquially called 'beach washings' are mined by IREL and KMML in Kerala and by IREL and several private enterprises in Tamil Nadu. These sediments are found to contain 85-90% THM. It is presumed that during the monsoon, the sea is agitated and the churning and spiralling action of water lifts HM-bearing sediments from the sea floor and transports in suspension and deposits on the beach berm, the backwash taking the relatively lighter part of the sediment load back into the sea. This process is thought to give rise to HM-enriched sand on the beach face and the swash plain. It is pertinent to understand the controls on these economically important and scientifically interesting processes. Beachface is the seaward section of a beach exposed to and shaped by the action of waves. The beach face is the zone of most active change. Berm is the terrace of a beach that has formed in the backshore, above the water level at high tide. Berms are commonly found on beaches that have fairly coarse sand and are the result of the deposition of material by low energy waves. On broad beaches there may be three or more sub-parallel berms, each formed under different wave conditions. Swash zone is defined as that part of the beach extending from a nearshore shallow depth to the limit of maximum inundation; is a relatively narrow region of great importance for the exchange of sediment between land and sea. Morphological processes such as storm-induced erosion, post-storm recovery, seasonal variation in foreshore shape, and evolution of rhythmic
[en] As early as 1886, monazite for Thorium was mined in Brazil from beaches in the Bahia region of Prado. This material was mostly exported to German and Austria amongst other European markets. It was used for Auer gas lamp net bags manufacturing. India and Brazil have vied for first ranking in thorium production from 1945. Prior to this India was the largest producer during the period 1915-1945 and Brazil up until 1915. As of 1955 the status of in situ identified monazite quantities in Brazilian resources is outlined in a table.
[en] This paper describes the study of various parameters of the fractionation process of didymium carbonate into light/medium and heavy rare earths concentrates by solvent extraction. These products constitute intermediate materials in the overall process to obtain high purity rare earth oxides, by solvent extraction, fractional precipitation and ion exchange techniques, presently being developed at IPEN. (author)