Mobility Of Thorium Research Articles

The mobility of thorium, uranium and rare earth elements from Mid Ordovician black shales to acid waters and its removal by goethite and schwertmannite

Previous studies have addressed the occurrence of Acid Rock Drainage (ARD) affecting La Silva stream due to the generation of large dumps of Middle Ordovician black shales during the construction of a highway close to El Bierzo (León, Spain). This ARD was characterized by sulphated acid waters with high concentration of heavy metals and anomalies in dissolved thorium (Th) and uranium (U). In the present study, we analyse in depth black shales and water, streambed sediments and precipitates of La Silva stream and its tributaries using different petrographic, mineralogical and geochemical approaches. Black shales, with average Th and U contents of 20 and 3 μg/g respectively contain disseminated detritic micro-grains of high weathering-resistant minerals, such as monazite and xenotime, that present smaller amounts of yttrium and rare earth elements (REY) and other elements as Ca, U, Th, Si and F. Results of the affected waters by ARD show an enrichment in dissolved Th, U and REY of several orders of magnitude with respect to natural waters. Sampled precipitates were mainly schwertmannite (Fe8O8(OH)8-2x (SO4)xO16•nH2O) and goethite (α–Fe3+O(OH)) that showed an enrichment of Th (up to 798 μg/g) and REY, due to the presence of dissolved anionic species (e.g. Th(SO4)32−, REY(SO4)32−) that enables their adsorption. Furthermore, these black shales show a clear enrichment in REE (Rare Earth Elements) with respect to NASC (North American Shales Composite) normalized REE patterns. Likewise, normalized REE patterns of stream waters and precipitates clearly show convex curvatures in middle-REE (MREE) with respect to light- and something less than heavy-REE, indicating the trend towards MREE enrichment. These findings are essential to evaluate the impact of ARD of Mid Ordovician shales in the surrounding environment, and to start considering these site as potential source of REE and critical raw materials, activating a Circular Economy.

Thorium Metallogeny in U-Cu-REE bearing Singhbhum Shear Zone, Eastern India

Abstract The long arcuate Singhbhum Shear Zone (SSZ) of around 160 km length having roughly an E-W trend hosts many uranium deposits and working uranium mines viz., Mohuldih, Bandhuhurang, Turamdih, Narwapahar, Bhatin, Jaduguda and Bagjata from west to east in addition to Cu deposits viz., Rakha, Mosabani etc. REE is well known from Kanyaluka area. Recent sub-surface exploration for uranium by AMD unravelled occurrence of thorite (ThSiO4)-bearing bands in a number of locations in western, central and eastern sectors of uranium mineralisation in SSZ, spanning over the entire shear zone. Thorite is observed in various host rocks involving metapelites of Dhanjori and Singhbhum Group and also in the Soda Granite/ feldspathic schist unit emplaced along the shear zone at the contact between the two groups. The individual lithounits that host thorite-bearing bands are restricted along the Singhbhum Shear Zone and include feldspathic schists (possible derivative of Soda Granite), albite veins, quartz-chlorite schists, quartz-biotite schists and sericite/muscovite-quartz schists. The thorite bearing zones transgresses lithology, stratigraphy as well as uraniferous zones along the shear zone evidently placing them as epigenetic hydrothermal mineralisation possibly later to major uranium metallogeny. Thorite occurs as discrete, rounded as well as subhedral to euhedral grains in various metapelites. They also form veins of their own besides occurring as phases within veins of albite and magnetite-apatite along the shear zone. Such multiple modes of occurrence and varied associated mineralogy suggest hitherto unknown thorium related hydrothermal mineralisation in SSZ. Presence of secondary thorium phases such as brockite (Ca-Th-phosphate) as well as post tectonic vein-type occurrence, points towards the mobility of thorium under a hydrothermal regime as well. However, present study thus, for the first time, establish the occurrence of thorite along with REE-Th minerals showing definite evidences of thorium mobilisation in several sectors of the well know U-Cu province of Singhbhum Shear Zone. Thorium-REE mobility is a widely understudied domain and the present findings place the SSZ as an ideal ground for exploring the concept with more understanding of this metal.

Hydrogeochemical behavior of uranium and thorium in rock and groundwater samples from southeastern of El Bajío Guanajuatese, Guanajuato, Mexico

To evaluate the hydrogeochemical processes related to the presence, mobility, and transport of uranium and thorium in the southeastern Sierra de Guanajuato of the Bajio Guanajuatense, Mexico, the concentration of these elements in volcanic rocks and in groundwater were determined. Acidic volcanic rocks contained uranium concentrations of 1.04–6.88 ppm and thorium concentrations of 3.13–15.58 ppm. A basalt rock sample contained 2.58 and 4.07 ppm of uranium and thorium, respectively, and an andesite rock sample contained 4.07 and 8.7 ppm of uranium and thorium, respectively. Scanning electron microscopy with energy-dispersive X-ray spectroscopy showed that U and Th are disseminated throughout the matrix of felsic rocks; in addition, phosphate minerals (probably monazite) containing both elements are present. The concentration of uranium in water samples ranged from 2.23 to 10.3 ppb and of thorium ranged from 0.33 to 0.39 ppb. Geochemical modeling indicated that uranium was mobilized through the transport of the uranyl ions (UO22+) and their complexes, especially carbonates, although other elements such as Fe, Mg, HCO3, and Ca could also be involved in the mobility and transportation of uranium. The obtained results suggest that the mobilization of thorium is very low, almost negligible in some cases, so this element did not present a quantifiable hydrogeochemical pattern. In spite of the low concentrations of U and Th, the existence of high radon concentrations in several samples indicates that additional radioactive species could be naturally present in the hydrogeological environment.

Behaviour of radionuclides in the presence of superplasticiser

Superplasticisers improve the flow properties of fresh cement and offer undoubted benefits to the construction sector. There is concern in the nuclear industry, however, that the presence of a superplasticiser in grout or backfill cement may increase the solubility of radionuclides in the cementitious pore water and/or reduce their adsorption from solution. This paper describes the effect of a commercial, polycarboxylated, polyether comb type superplasticiser on the behaviour of selected metals in blended cements through a series of batch and monolith leach experiments. Results of batch experiments show that the presence of free superplasticiser in solution reduces uptake of nickel (63Ni) and europium (152Eu) by both blast-furnace-slag- and pulverised-fly-ash-modified ordinary Portland cement. Further, metal bound in the presence of free superplasticiser is readily remobilised on exposure to fresh cement solution. Conversely, metal uptake is almost complete and appears irreversible when exposed to hardened cements prepared with superplasticiser as part of the original mix. Monolithic slag cement samples prepared with superplasticiser suffer from bleed, with the surplus water containing a significant proportion of the metals added, including uranium and thorium. Digital autoradiography reveals heterogeneous distribution of radioactivity in the monoliths and demonstrates that the dissolved metals have not been effectively immobilised throughout the specimen. The mobility of thorium may indicate similar behaviour by other tetravalent actinide species, notably Pu(IV) and Np(IV).

Mobilization of thorium, radium and radon radionuclides in ground water by successive alpha-recoils

Abstract Alpha-recoil is an important way for the mobilization of α-decay daughters in ground water. The processes of decay and recoil from 238U to 222Rn and from 232Th to 220Rn are successive. The release rates of successive recoils in this study are quantitatively estimated under two extreme conditions: complete absorption; and no adsorption of recoil elements by the porous medium. The recoil probability, recoil embedding and effective surface area are considered during the analysis. The result of this study shows that the recoil supply rates in the porous medium decrease down the decay chains. For the isotopes within the same decay chains, recoil emanation ratios of daugthers to parent are usually greater than 1 under both end-member conditions. This is consistent with the higher daughter to parent ratios observed in the field measurements. It is also found that the emanation ratios of Th, Ra and Rn show little change with the change of porosity in general. Radon emanation is most efficient at 15–20% porosity under the condition of complete adsorption. The calculated radioactivity ratios of daughters to parents from this study can provide a partial explanation for the disequilibrium of radioactivity of daughters relative to parents observed in natural water. Because of the low solubility of thorium, radium and radon, the emanation rates calculated under the condition of complete adsorption are closer to the natural conditions.

Determination of Barium and Selected Rare-Earth Elements in Geological Materials Employing a HpGe Detector by Radioisotope Excited X-Ray Fluorescence

The laterite material (geological) from Cerro Impacto was first studied by air radiometric techniques in the 1970's and was found to have an abnormally high radioactive background. Further studies showed this deposit to be rich in thorium, columbium, barium and rare-earth elements (mostly La, Ce, Pr and Nd). A similar work (1) has been reported for the analysis of Brazil’s lateritic material from Morro do Ferro to determine elemental compositions (including barium and rare-earth elements) and its relationship to the mobilization of thorium from the deposit using a Co-57 radioisotope source.

Some Aspects of The Influence of Surface and Ground Water Chemistry on The Mobility of Thorium in the “Morro Do Ferro” - Environment.

Information concerning the migration of thorium in natural environments is of interest in studies related to impact evaluations of mining and milling operations, to geochemical prospecting and at some point, to predict the long-term behavior of critical waste nuclides.

The mobility of thorium in natural waters at low temperatures

Thermodynamic properties of 32 dissolved thorium species and 9 thorium-bearing solid phases have been collected from the literature, critically evaluated and estimated where necessary for 25°C and 1 atm pressure. Although the data are incomplete, especially for thorium minerals and organic complexes, some tentative conclusions can be drawn. Dissolved thorium is almost invariably complexed in natural waters. For example, based on ligand concentrations typical of ground water ( ΣCl = 10 ppm, ΣF = 0.3 ppm, ΣSO 4 = 100 ppm, and Σ PO 4 = 0.1 ppm), the predominant thorium species are Th(SO 4) 0 2, ThF 2+ 2, and Th(HPO 4) 2 0below pH ≈ 4.5; Th(HPO 4) 2− 3 from about pH 4.5 to 7.5; and Th(OH) 0 4 above pH 7.5. Based on stability constants for thorium citrate, oxalate and EDTA complexes, it seems likely that organic complexes predominate over inorganic complexes of thorium in organic-rich stream waters, swamp waters, soil horizons, and waterlogged recent sediments. The thorium dissolved in seawater is probably present in organic complexes and as Th(OH) 0 4. The tendency for thorium to form strong complexes enhances its potential for transport in natural waters by many orders of magnitude below pH 7 in the case of inorganic complexing, and below about pH 8 when organic complexing is important. The existence of complexes in addition to those formed with hydroxyl, is apparent from the fact that measured dissolved thorium in fresh surface waters (pH values generally 5–8) usually ranges from about 0.01 to 1 ppb and in surface seawater (pH = 8.1) is about 0.00064 ppb. This may be contrasted with the computed solubility of thorianite in pure water which is only 0.00001 ppb Th as Th(OH) 0 4 above pH 5. Although complexing increases the solubility of thorium-bearing heavy minerals below pH 8, maximum thorium concentrations in natural waters are probably limited in general by the paucity and slow solution rate of these minerals and by sorption processes, rather than by mineral-solution equilibria.