Distribution Of Thorium Research Articles

Geochemical Distribution of Lanthanum, Thorium, and Uranium in Surface Soils. Case Study: Mitrovica Region, Republic of Kosovo

ABSTRACTThe aim of this study is to investigate the distribution of lanthanum, thorium, and uranium content in soils from the Mitrovica region in the Republic of Kosovo. For this purpose, 156 samples of topsoil (0–5 cm) were considered in a sampling network of 1.4 × 1.4 km2. The soil samples were prepared using the aqua regia digestion method and analyzed using inductively coupled plasma mass spectrometry. The contents of La, Th, and U in the soil of the study area were determined to be 19, 4.8, and 0.84 mg/kg, respectively. The enrichment factor values for La, Th, and U ranged from 3.8 to 7.9, 3.2 to 7.0, and 2.0 to 7.0, respectively, indicating moderate to substantial enrichment. The geo‐accumulation index values of all elements were less than zero, indicating uncontaminated levels. The spatial distribution patterns of La, Th, and U content showed that the values are elevated in the north‐eastern and western parts of the study area, where Miocene latites and quartz latites predominate (average contents of 35, 2.4, and 2.1 mg/kg, respectively). These areas are located in rural areas, suggesting that the high La, Th, and U contents in the soil are related to the lithology of the study area and there is no influence of possible anthropogenic sources. This study contributes to the database of La, Th, and U contents in the soils of the Mitrovica region and allows an assessment of the relationship between geochemistry and ecosystem health.

A multi-disciplinary approach for uranium exploration using remote sensing and airborne gamma-ray spectrometry data in the Gebel Duwi area, Central Eastern Desert, Egypt

Uranium exploration plays a pivotal role in meeting global energy demands and advancing nuclear technology. This study presents a comprehensive approach to uranium exploration in the Gebel Duwi area of the Central Eastern Desert of Egypt, utilizing remote sensing and airborne gamma-ray spectrometric data. Multispectral remote sensing techniques, including Principal Component Analysis (PCA), Minimum Noise Fraction (MNF), and Band Ratioing (BR), are employed to identify lithological units and hydrothermal alteration zones associated with uranium deposition, such as iron oxides, argillic, propylitic, and phyllic alterations. Additionally, airborne gamma-ray spectrometry data provide insights into the spatial distribution of radioelements, including uranium (eU), thorium (eTh), and potassium (K), as well as radioelement ratios (eU/eTh, eU/K, and eTh/K). The uranium migration index map (eU-(eTh/3.5)) and the F-parameter map (K*(eU/eTh)) have been generated to investigate the movement of uranium within various geological zones and characterize anomalous uranium concentrations. Statistical analyses, including mean (X), standard deviation (S), and coefficient of variability (C.V.), are conducted to identify uranium-rich zones. The integration of these datasets enables the generation of a uranium potential map highlighting areas of elevated concentrations indicative of uranium mineralization. Field observations and mineralogical analyses of collected samples validate our findings, confirming the presence of minerals associated with uranium mineralization in mapped high-potential areas. The significance of minerals like Fe-Chlorite, Fe-Mg-Chlorite, ferrihydrite, goethite, calcite, muscovite, dolomite, actinolite, vermiculite, and gypsum in indicating potential uranium mineralization processes underscores the importance of our results.

Control and surveillance of redox potential for 233Pa dissolution in 2LiF-BeF2 molten salt.

233Pa, the precursor nuclide of 233U in the thorium-uranium conversion is prone to reductive deposition in 2LiF-BeF2 (66 : 34 mol%, FLiBe) molten salt. We explored the adjustment and control of the redox potential of the FLiBe melt to avoid the 233Pa reduction deposition. The experimental data indicated that the deposited 233Pa can be completely dissolved and reentered into the molten salt with the addition of oxidant NiF2, and the distribution and behaviour of uranium, thorium, neptunium, and most fission products did not have any significant change in the NiF2-oxidised FLiBe molten salt, showing the feasibility of this manner to make 233Pa exist stably in the melt. The effects of NiF2-addition on the behaviour of the fission products 95Nb and 131I in the FLiBe molten salt were also investigated. It was found that 131I could be used as a redox indicator to monitor the redox potential of the oxidation-enhanced FLiBe molten salt. All the information drawn from this study could provide significant support for the control and surveillance of the redox potential of the FLiBe molten salt in the upcoming thorium molten salt reactor (TMSR).

Thorium anomaly on the lunar surface and its indicative meaning

The Moon has been divided into three terranes: Procellarum KREEP Terrane (PKT), Feldspathic Highland Terrane (FHT), and South Pole-Aitken Terrane (SPAT), using globally measured Th and FeO. Many lunar evolution models have predicted that a lunar magma ocean will produce a residual layer enriched in incompatible elements such as K, REE, and P (i.e., KREEP) in the late age of crystallization; and that the distribution of thorium can be used as a proxy for determining the global distribution of KREEP. The thorium distribution in these three terranes is inhomogeneous. The highest concentration of thorium is in PKT, the medium concentration of thorium is in SPAT, and almost none in FHT. Then what is the specific distribution in each of the terrane and what enlightenment can it tell us? Here we present and describe the detailed thorium distribution in PKT, SPAT, and FHT and provide some information for the origin of asymmetries on the lunar surface.

Predicted resource assessment of Central Kazakhsta ore districts based on airborne geophysical methods

Purpose. The research is aimed at creating a high-quality geophysical basis for the additional geological study of Central Kazakhstan in determining the geological structure of the study area, identifying promising areas for further geological exploration, as well as analyzing the anomalous distribution of various minerals. Methodology. The research uses the methods of aeromagnetic, airborne gamma-ray spectrometry and gravimetric (ground) surveys. The obtained new airborne geophysical data are used for additional study of the geological structure of the district and the creation of a model of the geological structure of the study area. Gamma-ray spectrometry data analysis is conducted for detailed mapping of intrusive complexes and study of their lithological heterogeneity. Findings. The processing and interpretation of the materials of the conducted field studies in combination with the results of the geological-geophysical data analysis made it possible to refine the geological structure and to present a model of ore-prospecting complexes in the study area. Areas with an anomalous distribution of potassium, uranium, and thorium have been identified, which make it possible to assess the structural heterogeneity of hidden magmatic massifs and to reveal a connection with gold, copper-polymetallic and rare-metal mineralization. Recommendations for further detailed geological exploration, including prospecting-exploration drilling, are given. Originality. Research has shown the high efficiency of airborne geophysical methods, such as aeromagnetic and airborne gamma-ray spectrometry surveys to study the geological structure of ore areas, and in combination with detailed gravimetric exploration to identify lithological heterogeneity of igneous and sedimentary rocks in the study area. New scientific-methodological techniques and the geological structure model based on them gave an opportunity to assess the prospect of the study area for ore mineralization. Practical value. The identified promising areas for mining of minerals are of interest for further research and exploration. The integrated use of geological-geophysical data will make it possible to determine more precisely the nature of radioactive anomalies and to reveal their relationship with ore-prospecting horizons. In general, the research results contribute to increasing the efficiency and reducing the geological survey costs.

Fabrication of crack-free oxidic thorium–cerium microspheres by an external gelation process

Thorium dioxide as an excellent matrix with stable properties is available for the direct incineration of plutonium, while (Th,Pu)O2 is a promising advanced fuel, which can be applied to a wide range of reactor types. In this study, cerium was used to simulate plutonium owing to their similar physicochemical properties. (Th1-xCex)O2 kernels were prepared by an external gelation process, which employs thorium and ceric ammonium nitrate as source materials, ammonium hydroxide as a neutralizing agent, polyvinyl alcohol as a thickening agent, and an ammonia gas ring for preliminary forming. The effect of the reaction temperature, reactant concentration, and pH on the feeding solution gelation properties was investigated. After the dispersive process, the aqueous (Th1-xCex)(OH)y·nH2O gel microspheres were washed and dried at 200 °C, calcinated and sintered. It was found that more than 99 % of the sintered microspheres maintained an excellent degree of sphericity and integrality when the parameters were properly controlled. It was found that the feeding solution preparation process was the most important and complex step to obtain uniform microspheres of good sphericity during the whole kernel fabrication process. The (Th1-xCex)O2 microspheres produced were characterized using thermogravimetric analysis, X-ray diffraction (XRD), scanning electron microscopy, and energy dispersive spectroscopy (EDS). The XRD analyses showed that all products appeared as a solid solution with a cubic fluorite structure when doped with cerium in the selective compositional range. The elemental scanning by EDS showed an excellent uniform distribution of thorium and cerium in the sintered microspheres.

УРАН И ТОРИЙ В СИСТЕМЕ ВОДА – ПОРОДА (НА ПРИМЕРЕ НЕФТЕГАЗОНОСНЫХ ОТЛОЖЕНИЙ СЕВЕРНЫХ РАЙОНОВ ЗАПАДНОЙ СИБИРИ)

The paper presents the first data on the distribution of uranium and thorium in the underground waters of Mesozoic sediments of northern regions of the West Siberian oil and gas basin. The studied waters are very diverse in chemical composition and the amount of total mineralization (from ultrafresh to weak brines). The contents of natural radionuclides vary in a wide range (mg/cu dm): U (4,90•10–7–5,14•10–3), Th (1,90•10–6–8,93•10–3). The Th/U ratio varies from 0.07 to 93.1 and its maximum values characterize the waters of the Valanginian aquifers. The Th/U ratio in water – resistant rocks is in a rather narrow range, it amounts to 1.82–5.24, with an average of 3.56. Against this background, rocks of the Bazhenov Formation are distinguished by the lowest values of Th/ U = 0.07–1.71, its nature of radioactivity is associated with uranium. The formation of the radionuclide composition of underground waters of oil-and-gas-bearing deposits with high Th/U ratios took place in a sharply reducing medium, where thorium has a greater migration capacity than uranium. The evolution of the sedimentary rock basin has led to the widespread development of erosion processes and the redistribution of U and Th in the water-rock system.

Radioactive (U, Th) elements in technogenic waters of tungsten deposits in Eastern Transbaikalia (Russia)

The peculiarities of distribution and migration of uranium and thorium in technogenic waters of seven tungsten deposits located in Eastern Transbaikalia have been studied. It has been established that elevated concentrations of uranium are found in all types of investigated waters, whereas the accumulation of thorium was recorded only in acidic waters (pH < 4). Maximum concentrations of elements were found in the areas of deposits localized in leucocratic and lithium-fluorine granitoids. In acidic waters, uranium and thorium migrate primarily in the form of sulfate and fluoride complex ions, while in neutral and weakly alkaline conditions, carbonate complexes come to the fore.

Radiometric mapping of the Berg River estuary

AbstractGeographic Information Systems (GIS) consists of various tools to perform spatial analyses in a wide variety of disciplines, including radiometric analysis to characterize the distribution of natural radionuclide concentrations. Recently, open‐source GIS has become popular among geospatial users because it can be freely used, and powerful tools are constantly developed to enhance software capabilities. Gamma‐ray spectroscopy was used to measure the concentrations of these natural radionuclides by dragging a Delta Underwater Gamma System (DUGS) among the sediment in the Berg River estuary located in Velddrif, South Africa. In this study, QGIS was used to visually illustrate and interpret the distribution of natural radionuclides, that is, potassium (K40), thorium (Th232), and uranium (U238). These concentrations can be used to investigate various geographical and geological phenomena, which include sediment processes. The data were then interpreted to derive sediment characteristics. Various features of tidal estuaries were demonstrated by the results.

Study of the composition and properties of the beneficiation tailings of currently produced loparite ores

The increase in demand for rare earth metals and the depletion of natural resources inevitably causes the need to search for alternative unconventional sources of rare metal raw materials. The article presents the results of a study of the composition and properties of the beneficiation tailings of currently produced loparite ores. Sieve, mineralogical, chemical, and radionuclide analyses were carried out. The average content of loparite in tailings was determined. Using scanning electron microscopy, minerals-concentrators of rare earth elements in the loparite ore beneficiation tailings were diagnosed. The distribution of valuable components and thorium in the tailings was determined depending on the particle size class. The radium-thorium nature of radioactivity was established, the values of the effective specific activity of the samples were calculated. We concluded that it is necessary to develop an integrated technology for processing the beneficiation tailings of loparite ore, due to the complex and heterogeneous mineral and chemical composition of the tailings material.

Importance of accessory minerals for the vertical distribution of uranium and thorium in soil profiles: A case study of durbachite from the Třebíč Pluton (Czech Republic)

The mineralogical character of a parent rock strongly affects the uranium (U) and thorium (Th) contents of soils. We have selected five representative soil profiles developed on amphibole–biotite to biotite durbachites in the Třebíč Pluton (eastern part of the Czech Republic) to characterize the radioactivity and variable-intensity weathering. The Endoskeletic Cambisols with a silt loam to loamy sand texture and a well-developed subsurface Bw horizon represented the most common product of the pedogenetic processes on durbachites. All studied soil profiles showed the evidence of pedogenetic alteration with intrasoil weathering. They were moderately deep (70–80 cm) with high rock-fragment concentrations within the B and C horizons. The predominant grain size fractions were silt (12% to 83%) or sand (8% to 87%), and the percentage of clay was up to 15%. A feldspar–quartz–vermiculite (biotite)–amphibole–kaolinite–Fe–Mn (oxy) hydroxide assemblage was typical for the most weathered parts of the profiles. Variation in the U and Th contents within the studied soil profiles resulted predominantly from the changes in the amounts of primary accessory minerals at different depth levels. Uraninite, monazite, thorite, allanite, zircon, thorogummite, REE-(Rare Earth Elements) fluorocarbonates, and minerals of the rhabdophane group were the main carriers of radioactive elements in the parent durbachite and overlying soil profiles. The gamma-ray spectrometry, geochemical and mineralogical analyses show that uraninite was stable only in the parent durbachite and disappeared at the rocks–C horizon interface. This process was followed by the gradual alteration of allanites, thorites, brabantites and secondary U- and Th-rich minerals (e.g., thorogummite, bastnäsite) toward the soil surface.

DISTRIBUTION OF THORIUM (IV) IONS IN AQUEOUS EXFOLIATING SYSTEM CONTAINING ANTIPYRINE AND SULFOSALICYLIC ACID

The possibilities of an aqueous delaminating system containing antipyrine (AP) and sulfosalicylic acid (SSA) for extracting macro - and microamounts of thorium (IV) were studied. The proposed extraction system eliminates the use of toxic organic solvents. The dependences of the distribution of metal from nitrate solutions between phases on the concentration of reagents, acidity of the medium, the amount of inorganic salting-out agent (NaNO3, NH4NO3, Na2SO4) and the volume of the aqueous phase are determined, and optimal conditions for extraction are found. It is shown that in the organic phase with a volume of 1.6 ml at room temperature, macro-and microamounts of thorium (IV) are extracted by 88 and 90%, respectively. The maximum extraction of the cation is achieved at the ratio of AP: SSA = 2.0 : 1.0 and their concentration, mol/l: 0.6: 0.3, while the acidity of the medium created by nitric acid should be equal to 0.015 mol/l (pHequ. = 1.8-1.9). The extraction of thorium (IV) becomes quantitative if inorganic salts (sodium sulfate, sodium nitrate) are introduced into the AP – SSA – 0,015 mol/l HNO3 – H2O system, which, by reducing the activity of water, increase the concentration of reagents in the aqueous phase. The concentration of salting-out agents should correspond to 1.0 and 2.5 mol/l. A mechanism for the distribution of a mixed thorium (IV) complex containing AP, SSA, nitrate ions, solvated with a salt of antipyrinium sulfosalicylate is proposed. The extract is mixed in any relationship with distilled water, providing the use of various instrumental methods of analysis. A method for extraction-photometric determination of thorium (IV) with a toron indicator has been developed. The limit for the fulfillment of the Bouguer-Lambert-Beer law is established. The apparent coefficient of light absorption is calculated (ε = 1.7∙104).

Early Results on Uranium and Thorium Distribution in the Natural Waters of the Baydar Valley (the Crimean Peninsula)

Early Results on Uranium and Thorium Distribution in the Natural Waters of the Baydar Valley (the Crimean Peninsula)

Early Results on Uranium and Thorium Distribution in the Natural Waters of the Baydar Valley (the Crimean Peninsula)

Early Results on Uranium and Thorium Distribution in the Natural Waters of the Baydar Valley (the Crimean Peninsula)

Trace Metal Fractional Solubility in Size‐Segregated Aerosols From the Tropical Eastern Atlantic Ocean

AbstractSoluble and total trace metals were measured in four size fractionated aerosol samples collected over the tropical eastern Atlantic Ocean. In samples that were dominated by Saharan dust, the size distributions of total iron, aluminum, titanium, manganese, cobalt, and thorium were very similar to one another and to the size distributions of soluble manganese, cobalt, and thorium. Finer particle sizes (< ~3 μm) showed enhanced soluble concentrations of iron, aluminum, and titanium, possibly as a result of interactions with acidic sulfate aerosol during atmospheric transport. The difference in fine particle solubility between these two groups of elements might be related to the hyperbolic increase in the fractional solubility of iron, and a number of other elements, during the atmospheric transport of Saharan dust, which is not observed for manganese and its associated elements. In comparison to elements whose solubility varies during atmospheric transport, the stability of thorium fractional solubility should reduce uncertainties in the use of dissolved concentrations of this element in seawater as a proxy for dust deposition, although this topic requires further work.

Dating kaolinite from the Neogene Içá Formation and overlying laterites, central Amazonia, Brazil: Constraints for a stratigraphic correlation

The Neogene Içá Formation is a major sedimentary deposit in central Amazonia (Brazil) that is critical to the understanding and modeling of the evolution of the Amazon Basin. However, its chronostratigraphy is poorly defined, mostly because it is not fossiliferous and it does not contain volcanic ash levels. This study is the first attempt at the absolute dating of the sediments and overlying soils of the Içá Formation by electron paramagnetic resonance (EPR) of radiation-induced defects in kaolinite (RIDs). Four profiles of unconsolidated sediments overlaid by lateritic soils from the Barcelos region (Amazonia, Brazil) were studied. The concentration of RIDs was assessed from EPR spectra through a simplified procedure on a selected set of samples, excluding those showing too strong of interference from the signal of trace vanadyl complexes. It is shown that in such sedimentary material, both the microscopic distribution of thorium (together with uranium) and the origin of kaolinite, either detrital or authigenic, are critical for kaolinite dating. Considering an argued authigenic origin and two scenarios of Th distribution, it appears that most of the present chronologic data support the stratigraphic correlation with the Madre de Dios sedimentary Formation in Peru previously proposed in the literature for the Içá Formation (9.5–2.5 Ma). This study also shows a rejuvenation process of kaolinite both in the uppermost soil and at depth of the profiles. This rejuvenation occurred during paleoclimatic periods already revealed in other weathering covers from the Amazon Basin and possibly resulted from downward weathering in the topsoil and water table or lateral weathering at depth.

Distribution and Bioaccumulation of Uranium and Thorium in Natural Soil and Wild Plants of Wadi El-Missikat, Central Eastern Desert, Egypt

Uranium and thorium concentrations were determined in soil and wild plant samples collected from Wadi El Missikat, Central Eastern Desert, Egypt. The U and Th contents are similar to those in Gebel Qattar soil (North Eastern Desert, Egypt) but higher than their corresponding levels in the Earth’s crust. The results obtained indicate that the Fagonia boveana plant uptakes and accumulates both elements but uptakes of Th is higher than for U. Fagonia sp. can absorb and accumulate uranium element with 150 times more than the average of world plant uptake. The Zilla spinosa plant was also found to be hyper-accumulator for U and Th and can absorb and accumulate uranium with 48 times more than the average world plant Analyses of the studied plants show that they are considered as hyper-accumulators for uranium and thorium and could be used as candidates for exploration for these elements and phytoremediation of radionuclide-contaminated soils.

Uranium and thorium contents in soils and bottom sediments of lake Bolshoye Yarovoye, western Siberia

The uranium and thorium contents in the soils and bottom sediments of the Lake Bolshoye Yarovoye natural system correspond to the data for the steppe climate zone and are noticeably lower than the background values for the Altai Territory as a whole. Factors that reduce the content of uranium and thorium are: 1 - lighter grain size distribution of the substrate, and, accordingly, the soils in this area; 2 - low content of organic matter (high ash content at 600 °C); 3 - the presence of significant quantities of quartz and calcite; 4 - general salinization of soils and the development of the solonchak process; 5 - remoteness from the region of material removal from the Altai mountains with its uranium-thorium-bearing granites and various mineraliszation.The distribution of uranium and thorium in the soils of the catchment area is heterogeneous. Minimum contents are observed in the soils of the boggy eastern coast and in its southern part in connection with the development of the solonchak process. This part of the catchment is characterized by high salinity (HCO3−- Na+) of water extracts in soils. Under subalkaline and alkaline conditions (pH 7.1–8.4) in soil waters, an increase in the content of these ions facilitates the transition of uranium to the liquid phase and its migration to the lake. In this part of the water area, the maximum uranium content in bottom sediments is observed.The results of cluster analysis indicate a change in the correlation of uranium and thorium during their redistribution from soils to bottom sediments. In soils, there is no correlation between uranium and thorium; in the bottom sediments, a strong positive correlation is observed between them (correlation coefficient 0.9). Uranium in soils has only a bond with Cr and possibly with Mn. The absence of a correlation with the elements of the mineral component of the soil confirms it finding, mainly in soluble form. In bottom sediments, both elements are associated with the mineral component.The established features of the distribution of uranium and thorium in the soils and bottom sediments of Lake Bolshoye Yarovoye indicate the need for detailed geochemical studies in lakes of a similar type. This will help to avoid ecological risks when choosing such lakes as anthropogenic objects.

U, Th, and K partitioning between metal, silicate, and sulfide and implications for Mercury's structure, volatile content, and radioactive heat production

AbstractThe distribution of heat-producing elements (HPE) potassium (K), uranium (U), and thorium (Th) within planetary interiors has major implications for the thermal evolution of the terrestrial planets and for the inventory of volatile elements in the inner solar system. To investigate the abundances of HPE in Mercury’s interior, we conducted experiments at high pressure and temperature (up to 5 GPa and 1900 °C) and reduced conditions (IW-1.8 to IW-6.5) to determine U, Th, and K partitioning between metal, silicate, and sulfide (Dmet/sil and Dsulf/sil). Our experimental data combined with those from the literature show that partitioning into sulfide is more efficient than into metal and that partitioning is enhanced with decreasing FeO and increasing O contents of the silicate and sulfide melts, respectively. Also, at low oxygen fugacity (log fO2 < IW-5), U and Th are more efficiently partitioned into liquid iron metal and sulfide than K. Dmet/sil for U, Th, and K increases with decreasing oxygen fugacity, while DUmet/sil and DKmet/sil increase when the metal is enriched and depleted in O or Si, respectively. We also used available data from the literature to constrain the concentrations of light elements (Si, S, O, and C) in Fe metal and sulfide. We calculated chemical compositions of Mercury’s core after core segregation, for a range of fO2 conditions during its differentiation. For example, if Mercury differentiated at IW-5.5, its core would contain 49 wt% Si, 0.02 wt% S, and negligible C. Also if core-mantle separation happened at a fO2 lower than IW-4, the bulk Mercury Fe/Si ratio is likely to be chondritic. We calculated concentrations of U, Th, and K in the Fe-rich core and possible sulfide layer of Mercury. Bulk Mercury K/U and K/Th were calculated taking all U, Th, and K reservoirs into account. Without any sulfide layer, or if Mercury’s core segregated at a higher fO2 than IW-4, bulk K/U and K/Th would be similar to those measured on the surface, confirming more elevated volatile K concentration than previously expected for Mercury. However, Mercury could fall on an overall volatile depletion trend where K/U increases with the heliocentric distance if core segregation occurred near IW-5.5 or more reduced conditions, and with a sulfide layer of at least 130 km thickness. At these conditions, the bulk Mercury K/Th ratio is close to Venus’s and Earth’s values. Since U and Th become more chalcophile with decreasing oxygen fugacity, to a higher extent than K, it is likely that at an fO2 close to, or lower than, IW-6 both K/U and K/Th become lower than values of the other terrestrial planets. Therefore, our results suggest that the elevated K/U and K/Th ratios of Mercury’s surface should not be exclusively interpreted as the result of a volatile enrichment in Mercury, but could also indicate a sequestration of more U and Th than K in a hidden iron sulfide reservoir, possibly a layer present between the mantle and core. Hence, Mercury could be more depleted in volatiles than Mars with a K concentration similar to or lower than the Earth’s and Venus’s, suggesting volatile depletion in the inner solar system. In addition, we show that the presence of a sulfide layer formed between IW-4 and IW-5.5 decreases the total radioactive heat production of Mercury by up to 30%.

Comprehensive Studies on Third Phase Formation: Application to U(VI)/Th(IV) Mixtures Extracted by TBP in N-dodecane

ABSTRACTPhase splitting of tributylphosphate (TBP)/n-dodecane organic phases resulting from the extraction of UO2(NO3)2, Th(NO3)4 and mixtures of both actinides from aqueous nitrate solutions has been investigated. Limiting organic concentrations (LOC) and metals distribution beyond third phase formation have been determined, with comparison between the cases of single metal-systems and metals mixtures. Simultaneous quantification of TBP and both metals was achieved through X-ray fluorescence (XRF) analyses. LOC studies reveal that thorium (IV) drives the third phase formation as it is the most destabilizing element in the solvent. After organic phase splitting, studies of the distributions of metals between the heavy organic phase (HOP) and the diluted organic phase (DOP) in the case of U(VI)/Th(IV) mixtures revealed that they are similar to those observed when both metals are alone in the solvent: Thorium (IV) has a strong affinity for the HOP, whereas uranium (VI) distributes both in HOP and in DOP. A supersaturation coefficient (NLOC) is proposed as a new tool to account for the data obtained in the present study. Furthermore, the approach was successfully applied to analyse available data in the literature regarding thorium (IV) distribution studies after phase splitting in various TBP-alkane solvents. Such a study beyond third phase formation paves the way for studying the mechanism involved in third phase formation, as the metal is clearly identified as the key parameter.