Fluorimetric determination of uranium in certain refractory minerals,environmental samples and industrial waste materials

Summary A simple sample decomposition and laser fluorimetric determination of uranium at trace level is reported in certain refractory minerals, like ilmenite, rutile, zircon and monazite; environmental samples viz. soil and sediments; industrial waste materials, such as, coal fly ash and red mud. Ilmenite sample is decomposed by heating with ammonium fluoride. Rutile, zircon and monazite minerals are decomposed by fusion using a mixture of potassium bifluoride and sodium fluoride. Environmental and industrial waste materials are brought into solution by treating with a mixture of hydrofluoric and nitric acids. The laser induced fluorimetric determination of uranium is carried out directly in rutile, zircon and in monazite minerals and after separation in other samples. The determination limit was 1 μg ^. g^-1 for ilmenite, soil, sediment, coal fly ash and red mud samples, and it is 5 μg ^. g^-1 for rutile, zircon and monazite. The method is also developed for the optical fluorimetric determination of uranium (determination limit 10 μg ^. g^-1) in ilmenite, rutile, zircon and monazite minerals. The methods are simple, accurate, and precise and they require small quantity of sample and can be applied for the routine analysis.     

Micro-PIXE Analysis of Monazite from the Dora Maira Massif, Western Italian Alps

Quantitative micro-PIXE and electron microprobe analyses, as well as micro-PIXE compositional mapping of trace elements were performed on monazite [(Ce, La, Nd, Th)PO₄] inclusions in pyrope megablasts from Dora Maira Massif, Western Italian Alps for petrological and geochronological purposes. Monazite was studied by SEM-BSE imaging and by X-ray qualitative compositional maps of major elements; further WDS electron microprobe analyses were carried out in areas showing different BSE intensity in order to quantify chemical zoning. Finally, micro-PIXE compositional maps and quantitative analyses were performed on selected spots and areas. EPMA data indicate that the Dora Maira monazite is Ce- and Th-rich with homogeneous concentrations of LREE, but with a significantly heterogeneous distribution of Th, as well as of Y, Sr, U and Pb as displayed by micro-PIXE compositional mapping. HREE mostly occur in concentrations below the detection limit for standard quantitative EPMA. Th–U–Pb zoning suggests two monazite growth events, dated at 35 (±7 Ma) and 60 Ma (±10 Ma), respectively. While the younger age of 35 Ma found in high-Th monazite areas corresponds to the thermal and baric peak of the UHP metamorphism in the Dora Maira Massif, in agreement with previous literature data, the older ages of 60 Ma found in low-Th areas have to be confirmed by U–Th–Pb isotopic data.     

Uranium uptake from acidic solutions using synthetic titanium and magnesium based adsorbents

Uranium uptake from acidic solutions is comprised practically in this study into three main steps namely; adsorbent synthesis, uranium uptake procedure, and desorption step. In this respect, two uranium adsorbents were synthesized from mineral processing of ilmenite and talc. Titanium phosphate adsorbent (TP) was deposited from titanium sulfate solution obtained from ilmenite sands processing. On the other hand, magnesium silicate adsorbent (MS) is prepared by sodium metasilicate neutralization of the acidic magnesium bearing waste solution resulted from talc whitening process. Structurally and chemically the two adsorbents were investigated by XRD, IR and SEM-EDX analyses. The studied factors affecting the uranium uptake onto TP and MS adsorbents were uranium concentration (10–1000 ppm), acidic pH range (1–6), contact time, shaking time and solid to liquid ratio. The uranium analysis was determined spectrophotometrically using arsenazo(III) dye where SEM-EDX analysis confirmed the uranium uptake by adsorbents. The optimum conditions obtained were applied to uranium bearing, highly mineralized granite samples (5200 ppm U) and black shale (40 ppm U). The uranium uptake was more than 98% for the mineralized granite samples and more than 97% for shale. The loaded uranium was recycled by using 0.5 and 1M HNO₃ in case of TP and MS with percentage recovery of 96 and 98% respectively.     

Mineralogical role on natural radioactivity content in the intertidal sands of Tamilnadu coast (HBRAs region), India

Activity concentration and mineralogical characterization in the intertidal sand samples of Tamilnadu coast, India have been analyzed. From the gamma spectral analysis, the average value of ²³⁸U, ²³²Th and ⁴⁰K in the intertidal sand samples are 12 ± 4, 59 ± 4 and 197 ± 26 Bq kg⁻¹ respectively. The average value of ²³²Th alone is slightly higher than the world average value. From XRD and FTIR analysis, monazite, zircon, ilmenite, magnetite, hematite, quartz, witherite, calcite, nacrite, microcline feldspar, orthoclase feldspar, gibbsite and organic carbon are identified. Of these minerals, monazite and microcline feldspar are the most associated with the presence of ²³²Th and ⁴⁰K respectively.

     

Radiogenic heavy minerals in Chhatrapur beach placer deposit of Orissa, southeastern coast of India

The beach placer deposit at Chhatrapur coast of Orissa state, southeastern coast of India, has a significant concentration of radiogenic heavy minerals. The average activity concentrations of radioactive elements such as ²³²Th, ²³⁸U and ⁴⁰K were measured by gamma ray spectrometry using a HPGe detector, and found to be 2650±50, 400±30 and 120±30 Bq/kg, respectively, for the bulk sand samples. The activity concentrations in monazite and zircon sands are found to be 305,000±2000 and 2000±150 Bq/kg for the ²³²Th and 21,500±300 and 3450±250 Bq/kg for the ²³⁸U. Electron probe microanalysis results of monazite sands show the average ThO₂ and UO₃ concentrations to be 10.42 wt.%, and 0.32 wt.%, respectively. The major contributors for the enhanced level of radioactivity are monazite and zircon sands. These heavy mineral sands were derived from the nearby source areas such as Eastern Ghats Group of rocks.     

Synthesis and characterization of radiation sensitive TiO<Subscript>2</Subscript>/monazite photocatalyst

A TiO₂/monazite photocatalyst was prepared by embedding TiO₂ nanoparticles into a monazite substrate surface. TiCl₄ hydrolysis/citric acid chelating procedure under acidic conditions were used to synthesize the nanophase TiO₂ particles. The anatase TiO₂/monazite photocatalyst surface area, morphology, crystalline and elemental concentrations were characterized using Brunauer-Emmett-Teller (BET) method, scanning electron microscopy (SEM), X-ray diffraction (XRD), and inductively coupled plasma-atomic emission spectrometry (ICP-AES). Monazite contains a large amount of Ce-, La-, Nd- and Th-PO₄ compounds; it has been known as a natural mineral material with minor radioactivity. TiO₂-CeO₂ composite is a kind of radiation sensitive photocatalyst in which the radiations of thorium nuclides give energy to trigger TiO₂ and cerium ions which play an energy absorber with charge separator. The result showed that methylene blue and phenol were spontaneously photocatalytic decomposed by TiO₂/monazite composite even in a dark environment. A synergistic effect was also examined with applied exterior UV or ⁶⁰Co irradiation. A hybrid mechanism is proposed; according by the radioluminescence (RL) from excited Ce ion by γ-radiation soliciting CeO₂/TiO₂ heterojunction (HJ). This seems to be a possible mechanism to explain this self-activated photo-catalytic behavior.     

Thermal Study of the Ceramic Pigments CoxZn(7−x)Sb2O12

Using the Pechini method, pigments with spinel structure (Zn₇Sb₂O₁₂)were synthesized by substitution of the cation Zn²⁺ by Co²⁺, in compounds with different concentrations of Sb₂O₃. The doping resulted in Co_xZn_(7–x)Sb₂O₁₂ phases(x=1–7) that were isomorphs to spinel, denominated as samples A and B. After thermal treatment at 400°C for 1 h, the powders were characterized by thermogravimetry(TG) and differential thermal analysis (DTA). The results indicate a different behavior whena higher amount of Sb₂O₃ is used, due to the presence of a secondary phase (ilmenite). This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of individual rare earth elements in Vietnamese monazite by radiochemical neutron activation analysis

Radiochemical neutron activation analysis (RNAA) has been applied for determination of rare earth elements (REE) in Vietnamese monazite. The chemical separation procedure used is based on the chromatographic elution of rare earth groups, after the separation of²³³Pa(Th) in irradiated monazite samples by coprecipitation with MnO₂, the rare earth elements were retained by Biorad AG1×8 resin column in 10% 15.4M HNO₃-90% methanol solution. The elution of heavy rare earth (HREE) and middle rare earth (MREE) groups was carried out with 10% 1M HNO₃-90% methanol and 10% 0.05M HNO₃-90% methanol solution, respectively; while the light rare earths (LREE) were eluted from the column by 0.1M HNO₃ solution. The accuracy of the method was checked by the analysis of granodiorite GSP-I and the rare earth values were in good agreement.     

Na<Subscript>x−y</Subscript>H<Subscript>y</Subscript>Ti<Subscript>2−x</Subscript>Fe<Subscript>x</Subscript>O<Subscript>4</Subscript>·nH<Subscript>2</Subscript>O nanosheets with lepidocrocite-like layered structure synthesized by hydrothermal treatment of ilmenite sand

Na_x−yH_yTi_2−xFe_xO₄·nH₂O nanosheets with lepidocrocite-like layered structure were produced through alkaline hydrothermal treatment at very low temperatures (130°C) from ilmenite sand. The crystal structure, morphology and optical properties were investigated by X-Ray diffraction, transmission electron microscopy, selected area electron diffraction, energy dispersive spectroscopy and UV-Vis spectroscopy. The product shows leaf-like nanosheet morphology with thickness <30 nm and lengths <1 μm. Three lepidocrocite-like titanates (Imm2 space group) with similar a and c lattice parameters but different interlayer distances (b/2) were identified. This appears to be the first preparation of lepidocrocite-like layered nanosheets by a simple, energy efficient (low temperature) and low cost (starting from mineral sand) procedure.     

Determination of 231Pa in Monazite and Other Streams of the Thorium Production Cycle

Monazite (chief source of thorium) which is available in plenty in the beach sands of Kerala, India, contains uranium in the range of 0.25% to 0.35%. An attempt has been made to estimate ²³¹Pa in monazite and the corresponding process stream samples of the thorium production cycle. This paper reports the ²³¹Pa activity in these samples, after coprecipitation of ²³¹Pa on MnO₂ carrier and estimation by -ray spectrometry. The estimation shows about 1000 Bq/kg of ²³¹Pa in monazite. This is the first reported estimate of ²³¹Pa in monazite.     

Solid-state synthesis of monazite-type compounds LnPO4 (Ln = La to Gd)

This work is devoted to the synthesis of monazite-type compounds LnPO₄ (with Ln = La, Ce, Pr, Nd, Sm, Eu and Gd) by solid–solid reaction between a lanthanide oxide and a phosphate precursor NH₄H₂PO₄. Starting mixtures and resulting powders were characterized by coupling different techniques, in particular thermal analysis, X-ray diffraction and MAS ³¹P NMR. Results are presented according to the valence state of the lanthanide element in its oxide form. The intermediate chemical reactions occurring during the firing of starting reagents are described for the first time in the case of monazite with one or several cations. It has been highlighted that the solid-state route is an efficient way in order to obtain very pure and very well crystallized monazite powder. Optimum synthesis conditions are 1350 °C–2 h. The synthesis of monazite powders containing several lanthanides appears to be more difficult, because all the lanthanides do not react at the same temperature, leading to the formation of heterogeneous powders.     

Extraction study of uranium(VI) and thorium(IV) salicylates with triphenylarsine oxide

Triphenylarsine oxide is proposed as an extractant for the solvent extraction of uranium and thorium salicylates. The optimum extraction conditions are established by studying the various parameters such as pH, sodium salicylate concentration, triphenylarsine oxide concentration, diluents and shaking time. The probable extracted species as ascertained by logD-logC plots are UO₂(Hsal)₂·2TPAsO and Th(Hsal)₄·2TPAsO. The method is simple, fast, precise and permits the determination of uranium and thorium in monazite sand samples.     

Concentration of arsenic in soil samples collected around the monazite processing facility, Thailand

Arsenic (As) in soil is a contaminant originated from human activities including pesticide use, mining and ore processing operations. In this work, As concentration in soil samples collected around the monazite processing facility, Pathum Thani, Thailand, was investigated. The collections of 24 soil samples were collected from the monazite processing area and 7 soil samples were collected from the control area without the processing activity of the same facility. Soils were digested with the mixture of HNO₃, HClO₄ and HF using a microwave digester. Inductively coupled plasma mass spectrometer (ICP-MS) equipped with an octopole reaction system (ORS) was used to determine the concentration of As in soils after the acid digestion. JB-3 (igneous rock) was the standard reference material used to check the accuracy of the method. It was found that the analytical results showed good agreement with the certified values. As concentration in soils collected from the monazite processing area ranged from 3.85 to 36.01 mg kg^?1 with the mean of 13.06 mg kg^?1. The concentration of As higher than the US EPA cancer soil screening level (22 mg kg^?1) was observed for only one sample. The control area showed As concentration varied from 9.59 to 14.19 mg kg^?1 with the mean of 11.97 mg kg^?1. The obtained results from this work were compared with the contaminated soil data of Amphoe Ron Phibun, Nakhon Si Thammarat, Thailand.     

Determination of rare earth elements in Taiwan monazite by chemical neutron activation analysis

Taiwan monazite is a unique mineral obtained from the heavy sand found in the river floor of Tzuo-suei river and En-suei river. Both rivers are flowing parallel with separated narrow area into the sea at southwestern coast of Taiwan. The characteristic of monazite is that it contains considerable rare earth elements (REEs). REEs are considered very useful elements in the local industries and scientific researches such as ceramic, semiconductors, and glass optics. In this study, chemical neutron activation analysis (CNAA) was used to determine the contents of REEs in Taiwan monazite. A few milligram of monazite was digested in the microwave oven for 25 minutes with mixed acid (conc. HNO₃ and HClO₄). REEs were preconcentrated by hydrated magnesium oxide and CNAA was performed.     

Production from ilmenite of TiO2-supported catalysts for selective catalytic reduction of NO with NH3

Economic production of titanium dioxide (yield >98 %) from ilmenite has been achieved by use of a modified sulfate reduction process. A series of samples were prepared by varying the concentration of titanium dioxide nuclei (0.2, 0.3, and 0.6 %) and further impregnation with antimony and vanadia. The structural and acidic properties of the samples were comprehensively studied by X-ray diffraction (XRD), transmission electron microscopy, BJH pore size distribution, and temperature-programmed desorption of NH₃. The XRD results revealed the presence of intense peaks from anatase titanium dioxide. Enhancement of surface area was observed for second-time filtered samples, possibly because of loss of iron from the bulk. As a result, formation of additional micropores was apparent from N₂ adsorption and desorption isotherms. Among all the antimony and vanadia-doped samples, the first-time filtered sample with the low concentration of nuclei (0.2 %) had the highest catalytic activity at low temperatures, owing to its larger pore size and abundant acidic species.     

Interactions between the iron and the aluminum minerals during the heating of Venezuelan lateritic bauxites. II. X-ray diffraction study

Four samples of Venezuelan lateritic bauxites were heated to 300, 600 and 1000°C and the thermal reactions were studied by X-ray diffraction (XED) and by chemical extractability of silica and alumina. Gibbsite was converted to boehmite at 300°C, to an amorphous phase at 600°C and partly to corundum at 1000°C, with isomorphic substitution of Fe for some of the Al in the corundum structure. Goethite was converted to protohematite at 600°C and the hematite at 1000°C, with isomorphic substitution for Al for some of the Fe in both α-Fe₂O₃ varieties. Ti contributed by ilmenite is also occluded by the hematites. The occlusion of Ti takes place at 1000°C during the decomposition of the ilmenite and concomitant recrystallization of α-Fe₂O₃.     

Comparison of Pyrolysis and Microwave Acid Digestion Techniques for the Determination of Mercury in Biological and Environmental Materials

 Microwave digestion reduction-aeration and pyrolysis combined with cold vapour atomic absorption and cold vapour atomic fluorescence are compared for the determination of total mercury in several biological and environmental matrices. The biological samples were digested in a mixture of HNO₃/H₂O₂, the environmental samples in a mixture of HNO₃/HClO₄. After reduction with SnCl₂, the mercury was collected by two-stage gold amalgamation. After microwave digestion reduction-aeration, detection limits of 1.4 ng g⁻¹ and 0.6 ng g⁻¹ were obtained for cold vapour atomic absorption spectrometry (CVAAS) and cold vapour atomic fluorescence spectrometry (CVAFS), respectively, for 250 mg of environmental samples. For biological samples (500 mg) the detection limits were 0.7 ng g⁻¹ (CVAAS) and 0.4 ng g⁻¹ (CVAFS). After pyrolysis, detection limits of 3.5 ng g⁻¹ and 1.6 ng g⁻¹ for CVAAS and CVAFS, respectively, were obtained for a 10 mg sample. Pyrolysis can only be applied when the organic content of the sample is not too high. Accurate results were obtained for 8 certified reference materials of both environmental and biological origin. In addition, a real sludge sample was analysed. Author for correspondence. E-mail: richard.dams@rug.ac.be Received September 18, 2002; accepted December 3, 2002 Published online May 5, 2003     

Successive uranium and thorium adsorption from Egyptian monazite by solvent impregnated foam

The present work deals with uranium and thorium recovery from the Egyptian monazite sulfate leach liquor using the extraction chromatography technique (solvent impregnated material), where tributylamine (TBA) and di-n-octylamine (DOA) solvents were impregnated onto foam uranium and thorium separate recovery. The calculated theoretical capacities of the latter solvents were about 1.4 gU/g foam and 1.6 gTh/g foam, respectively. The attained uranium and thorium adsorption efficiencies (using ion-exchange columnar technique) were about 75 and 70% of its theoretical capacities, respectively. Using 1 M NaCl–0.1 M H₂SO₄ and 2 M H₂SO₄ as eluent solutions for uranium and thorium from the loaded solvents impregnated foam gave 95.8 and 98.7% elution efficiencies, respectively.     

Determination of uranium in liquid and solid samples by radioisotope excited XPR analysis using the ULα/ULγ ratio for matrix correction

A method for the exact determination of uranium in liquid and solid samples containing various main elements with Z≤29 is described. The method is based on simultaneous measurements of the excited LX fluorescent energies of uranium and the backscattered energies of the iodine target used for excitation. UL_α/UL_γ and (UL_υ/IK_αincoh)/U% peak intensities were found to be linearly dependent in samples of different chemical composition. Twenty eight liquid and solid samples of various matrices containing uranium in the range 0.3–30% were determined and a calibration line based on these measurements was obtained. Several samples containing different U concentrations were checked by this method and the average deviation of the calculated results from the known content is ±12.5%. The X-rays were excited using a 10 mCi²⁴¹Am/I source-target assembly and measured with 25 mm² Si(Li) detector.     

Catalytic combustion of methane over iron- and manganese-substituted lanthanum hexaaluminates

A series of hexaaluminates, LaMnFe _x Al_11−x O_19−δ samples (x = 1, 2, 4, 6, 8) as new catalysts were prepared by carbonate precipitation and calcined at high temperature. Fe and Mn ions were used as active components to replace part of aluminum ions in the hexaaluminate lattices. The structures and properties of these samples were characterized by XRD, BET, and XPS. The series of hexaaluminates exhibited significant catalytic activity and stability at high temperature. The LaMnFe₂Al₉O_19−δ retains a larger surface area and shows a good activity in methane combustion.