Thorium In Solution Research Articles

Multidecadal Monsoon Variations during the Early Last Deglaciation Revealed by Speleothem Record from Southwestern China

The Asian monsoon (AM) has direct and profound effects on the livelihoods of residents in South Asia and East Asia. Modern observations have shown multi-decadal alternations of flood and drought periods in these regions, likely influenced by climatic processes such as the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation. However, our understanding of the multi-decadal variability of the AM under different climatic conditions remains uncertain. In this study, we collected an annually laminated and 780-mm stalagmite (sample number: BJ7) from Binjia (BJ) Cave in southwestern China, which is deeply influenced by the Asian monsoon system. Based on this sample, we established 6-year resolution and multi-proxy records for the Asian summer monsoon (ASM) variabilities during the early last termination, spanning from 18.2 to 16.1 ka BP. Measurements of five pairs of uranium and thorium solutions for 230Th dating were conducted using a multi-collector inductively coupled plasma mass spectrometer (MC-ICP- MS), and 374 pairs of stable isotope (δ18O and δ13C) analyses were run on a Kiel Carbonate Device connected with Finnigan MAT-253 at Nanjing Normal University. The chronology for this sample was established by annual layer counting anchored with 230Th dating results. Our BJ7 δ18O record replicates well with other Chinese δ18O records on the general trend, all of which are superimposed by frequent multidecadal-scale fluctuations at approximately 60 years periodicity. Inspection of the 60-year band in BJ7 δ18O and δ13C records and results of the cross-wavelet analysis indicate coherent changes in the ASM and biomass production/karst processes during most of the studied period. In addition, the 60-year band of BJ7 and NGRIP δ18O records are consistent, implying the impacts of the high-latitude North Atlantic or Atlantic Multidecadal Oscillation on the ASM. Our study suggests that the 60-year variability should be an intrinsic feature of the climate system regardless of glacial or interglacial backgrounds.

Separation of lead-212 from natural thorium solution utilizing novel sulfonamide dibenzo-18-crown-6.

The extraction of lead-212 (212Pb) from radioactive thorium (Th) waste is immensely important, as it serves to mitigate environmental risks associated with radioactive waste and provides a vital source for medical isotopes. To economically extract 212Pb from thorium, we synthesized a novel extractant known as 2,13-disulfonyldiethylamine dibenzo-18-crown-6 (DSADB18C6). We assessed its performance in isolating Pb(II) by employing stable lead and optimizing the parameters of the extraction system. The results showcased an exceptional ability to extract Pb(II) efficiently. Within 10 minutes, using 20 mmol of DSADB18C6 and under conditions of 10 mg L-1 lead concentration (HNO3 = 0.5 mol L-1), the extraction efficiency reached up to 96.1%. Even after four rounds of stripping with 0.4 mol L-1 ammonium citrate, the efficiency remained at 90.2%. Moreover, the extraction stoichiometry and thermodynamics revealed that DSADB18C6 exhibited superior extraction performance compared to the commercial extractant 4',4'',(5'')-di-(tert-butyldicyclohexano)-18-crown-6 (DtBuDC18C6), in line with the density functional theory (DFT) calculation result. Furthermore, we successfully separated 212Pb from the thorium nitrate solution, maintaining radioactive equilibrium with its progeny. Gamma-spectroscopy confirmed a recovery yield of extraction exceeding 85.7%. This study presents a viable approach, underscoring the potential of DSADB18C6 as a promising extractant for the effective separation of 212Pb from radioactive thorium sources.

Sequestration and recovery of thorium ions using a recyclable, low-cost, glutathione-based magnetic nanocomposite: Experimental study and statistical modeling

Efficient removal and recovery of thorium from water resources is necessary to resolve the problem of radioactive contamination. To address this issue, magnetically separable Glu@MNPs have been fabricated and efficiently utilized for the removal of Th(IV). 99.40 % removal of Th(IV) by Glu@MNPs could attain an equilibrium state within 10 min at a dosage level of 6 mg for 20 ml of 50 mg/L thorium solution at pH 4 and 25 °C. It obeys Langmuir isotherm with maximum adsorption capacity of 636.94 mg g−1, which is independent of temperature variation. Kinetically, the adsorptive performance of Glu@MNPs fits well in the pseudo-second-order equation. The high removal efficiency is due to the existence of several types of functional groups on the surface of Glu@MNPs, which provide electrostatic attraction, and vander wall forces between adsorbate and adsorbent. The optimum conditions obtained from Box-Behnken composite design model was well matched with batch adsorption studies. Further, the results obtained for removal of Th(IV) by UV–vis spectroscopy matched well with ICP-OES. The removal efficiency still remained high (85.65 %) even after 10 adsorption–desorption cycles. Thus, Glu@MNPs acts as a timesaving adsorbent for sequestration of Th(IV) from an aqueous media with excellent removal performance.

Isolation of 212Pb from natural thorium for targeted alpha-therapy

Targeted alpha-therapy (TAT) is increasingly attractive due to its extraordinary antitumor efficacy. However, the supply of α-emitters for TAT is insufficient and under control by a limited number of countries. 212Pb is a promising α-emitter with an optimal half-life (10.6 h) and favored decay chain. Of interest, 212Pb can be extracted directly from natural thorium, which may be abundant in the mining waste of rare-earth, uranium, etc. Indeed, radioactive thorium waste has been a longstanding environmental challenge that needs immediate action. Developing an on-demand and facile process to isolate 212Pb from natural thorium would be ideal to meet the above challenges, yet is difficult. In theory, the ratio of 212Pb to natTh is below 10−13 in commercially available thorium salts. As a pilot study, 2.2 MBq of 212Pb was successfully extracted from a 5 L solution of thorium nitrate by using a Pb-selective resin. The radiochemical purity of 212Pb is over 99.9% according to gamma-ray analysis. The purified 212Pb was applied to radiolabel a couple of peptides used in clinics (i.e. PSMA, TATE and FAPI-04), and the radiochemical yields are >85%. Of note, 212Pb can be repeatedly separated from the thorium solution every 2 days. In summary, a practical and scalable method was developed to isolate 212Pb for potentially clinical use, which may be of great importance as it does not require either cyclotron or nuclear reactor.

Nanofiltration Extraction of Uranium and Thorium from Aqueous Solutions

The behavior of uranium and thorium ions in nanofiltration (NF) from aqueous solutions has been studied. It was shown that the retention capacity (R) of the NF membrane for uranium and thorium depends on their state in aqueous solutions. In the case of uranium, the smallest values of R (82–83%) are observed when uranium is in solution as uranyl ions or oxyhydrate complexes at pH in the range from 2 to 6. In solutions with large pH values, the retention of uranium increases (R ≈ 95%) due to the formation of an insoluble U(IV) hydroxide and/or carbonate complexes. In the NF of aqueous solutions of thorium, R grows from 94 to 99% with pH increasing from 1 to 3.5, which is due to the hydrolysis of thorium ions to give oxyhydrate complexes of various compositions. At pH 3–9, the retention of thorium remains constant due to the formation of an insoluble thorium hydroxide. In alkaline solutions (pH > 9), values of R decrease because of the formation of negatively charged hydroxo and/or carbonate complexes. A conclusion is made that the nanofiltration is an effective method for wastewater purification to remove admixtures of uranium and thorium.

Purification of thorium by precipitation

A precipitation method was applied to produce high-purity thorium product from industrial grade Th(NO3)4·4H2O. The conditions of pH in the thorium solution, the contents of hydrogen peroxide, calcination temperature were investigated as well as calcination time. The hydrogen peroxide of 30% (v:v) was added into the thorium solution and was continually stirred. The concentration of hydrogen peroxide was exceeded over 0.1–0.5 mol/L after suitable reaction between Th(NO3)4·4H2O and hydrogen peroxide. The pH of the solution was maintained at 2 through adding ammonium hydroxide. The precipitation obtained in the form of Th2O7·4H2O. The high-purity thorium product was prepared after calcination for 2 h at 700 °C. The purity of the purified thorium product was above 99.8%.

Accountancy for intrinsic colloids on thorium solubility: The fractionation of soluble species and the characterization of solubility limiting phase

The extensive hydrolysis of tetravalent actinides leads to polynuclear formations through oxygen bridging facilitating the formation of colloids as end products. The pH, ionic strength has phenomenal effects on Thorium colloids formation. The quantitative estimation of colloids facilitates the fraction of soluble fraction into ionic, polymeric and colloidal forms of thorium. The colloids accountability and precipitate characterization explains the discrepancies in estimated solubility limits. The supernatants of long equilibrated (∼3 years) saturated thorium solution under various pH (5- 11) and ionic strengths (0–3 M NaClO4) were analysed by Inductively Coupled Plasma Mass Spectrometer (ICP-MS) and Ion Chromatography (IC) to determine total and ionic thorium respectively. Laser Induced Breakdown Detection (LIBD) was employed to determine the colloid size and concentrations. The precipitates were characterized by calorimetry and XRD to determine the solubility limiting phase. The results of pH, IC, ICP-MS, and LIBD measurements on the aged thorium samples are discussed with regard to the mechanism of the formation of thorium colloids. The results revealed the formation of colloids having particle size (10–40 nm) at concentrations (109-1011 particles/mL). The colloids accountancy resulted in estimated solubility products to 2–4 orders lower than their inclusion as soluble thorium. The soluble thorium was fractionated quantitatively into ionic, polymeric and colloidal forms of thorium. The precipitates formed are found to be semi amorphous.

The development of 228Ac isotopic generator

The paper describes a method of recovery of 228Ac tracer from an old thorium salt through sequential separation of 228Ra by sorption onto the MnO2-CTA disk from thorium solution followed by Ac/Ra separation using the Axionit 507 extraction chromatographic resin. It was shown that the optimal conditions of radium separation from thorium nitrate solution are pH 4.7–6.1 and EDTA as a complexing agent for thorium stabilization as Th4+ form at Th/EDTA molar ratio of 1:1. Since both 228Ra and 224Ra are separated from thorium solution, 25 days were calculated as the minimal time necessary for obtaining pure fraction of 228Ra. Separation of 228Ac from 228Ra generator solution by the Axionit 507 resin is possible at pH 2.4–2.9; actinium desorption can be performed by 4–10 mL of any mineral acid solution at pH 1–1.5. High selectivity of the Axionit 507 resin provided additional decontamination of 228Ra generator solution from 228Th. The 228Ac eluate with the average radionuclide purity of 98.8% containing no organic compounds and/or complexing agents was obtained.

Selective Sorption of Radium with Inorganic Sorbents from Solutions of Thorium with Trilon B

A generator of radium-224 based on a neutral solution of thorium with Trilon B with EDTA : thorium molar ratio of 4 : 1 was suggested. The properties of the generator were examined and its efficiency for obtaining radium-224 as a radioactive tracer was demonstrated.

Sorption of Radium from Tap Water with Inorganic Sorbents

Radium-224 isolated from a generator having the form of a solution of thorium and Trilon B with pH 6.5–7.0 (molar ratio 4 : 1) was used to examine the sorption of radium from tap water by inorganic sorbents of T-3A, T5(400), and T5 (MnO2) brands under dynamic and static conditions.

Thorium Oxo-Clusters as Building Blocks for Open Frameworks.

Fundamental understanding of tetravalent actinide chemistry is essential to optimize many steps of the nuclear fuel cycle, as well as to predict actinide speciation in the environment. Herein, we report synthesis and structure of three open inorganic frameworks composed of Th4+ -oligomers and sulfate anions. The compounds [Th10 O4 (OH)8 (SO4 )12 (H2 O)18 ]⋅28 H2 O (1), [Th9 O4 (OH)5 (SO4 )12 (H2 O)18 ]⋅ 1 TMA⋅18 H2 O (2), and [Th8.5 O4 (OH)4 (SO4 )12 (H2 O)18 ]⋅2 TMA⋅n H2 O (3) were obtained by slow evaporation of aqueous Th4+ -SO42- solutions, with variable SO42- :Th4+ ratios (SO42- :Th4+ =1:1, 1.5:1 and 2:1 for 1, 2, and 3; TMA=tetramethylammonium). The structure of 1 features a neutral open framework architecture with two interpenetrating networks, built from Th6 O4 (OH)412+ hexamers and Th2 (OH)26+ dimers, linked by sulfate anions. The complex anionic framework of 2 is built from hexamers, dimers, and monomers, with charge-balancing TMA cations. Compound 3 is very similar to 2, but it is constructed only from hexamers and monomers. Small angle X-ray scattering (SAXS) of the reaction solutions reveals pre-assembled hexamer building units in the presence of sulfate, and underlines the key role of the sulfate-oxoanion ligand on thorium polymerization processes.

Solution and Solid State Structural Chemistry of Th(IV) and U(IV) 4-Hydroxybenzoates.

Organic ligands with carboxylate functionalities have been shown to affect the solubility, speciation, and overall chemical behavior of tetravalent metal ions. While many reports have focused on actinide complexation by relatively simple monocarboxylates such as amino acids, in this work we examined Th(IV) and U(IV) complexation by 4-hydroxybenzoic acid in water with the aim of understanding the impact that the organic backbone has on the solution and solid state structural chemistry of thorium(IV) and uranium(IV) complexes. Two compounds of the general formula [An6O4(OH)4(H2O)6(4-HB)12]· nH2O [An = Th (Th-1) and U (U-1); 4-HB = 4-hydroxybenzoate] were synthesized via room-temperature reactions of AnCl4 and 4-hydroxybenzoic acid in water. Solid state structures were determined by single-crystal X-ray diffraction, and the compounds were further characterized by Raman, infrared, and optical spectroscopies and thermogravimetry. The magnetism of U-1 was also examined. The structures of the Th and U compounds are isomorphous and are built from ligand-decorated oxo/hydroxo-bridged hexanuclear units. The relationship between the building units observed in the solid state structure of U-1 and those that exist in solution prior to crystallization as well as upon dissolution of U-1 in nonaqueous solvents was investigated using small-angle X-ray scattering, ultraviolet-visible optical spectroscopy, and dynamic light scattering. The evolution of U solution speciation as a function of reaction time and temperature was examined. Such effects as well as the impact of the ligand on the formation and evolution of hexanuclear U(IV) clusters to UO2 nanoparticles compared to prior reported monocarboxylate ligand systems are discussed. Unlike prior reported syntheses of Th and U(IV) hexamers where the pH was adjusted to ∼2 and 3, respectively, to drive hydrolysis, hexamer formation with the HB ligand appears to be promoted only by the ligand.

Analysis of the effects of stirring condition of separation of thorium in the elution process of monazite partial solution by solvent impregnated resin method

Monazite is a natural mineral which contains abundant valuable element such as Radioactive Element and Rare Earth Element(REE). In this experiment, it is proven that solution of residual Thorium Sulfate from Monazite mineral process, can be seperated selectively by using extracting method of Solvent Impregnated Resin(SIR), with the elutant solution HNO3. In the earlier process, Thorium solution is conditioned at PH 1 by using H2SO4. Then REE, Thorium and Uranium elements are seperated. This seperation is conducted by using adsorption method by Amberlite XAD-16 Resin, which has been impregnated by Tributhyl Phosphate extractant. It is continued with elution process, which is aimed to obtain Thorium solution of a higher level of concentration. This elution process is conducted by using HNO3, with the elution variables of the lenght of mixing and amount concentration elutant. Based on this experiment, SIR extracting method is able to dissolve Thorium solution until 63,2%grade and a higher level of %grade about 92,40%. It can be concluded that this SIR method can extracted Thorium elements selectively, improve extracting process recovery, and determine optimum stripping condition in the 45th minutes with elutant concentration of 1,0M HNO3.

Alterations of thorium oxalate morphology by changing elementary precipitation conditions

Oxalates of actinide elements are widely used in research and industry mainly due to their low solubility in aqueous solution and easy conversion to oxide. Although thorium oxide is worldwide mostly produced by the oxalate precipitation and conversion route, the powder morphology obtained through this process is known to inhibit the packing and sintering step of the pellet production. The presented work investigates the effects of oxalate precipitation conditions on the final powder morphology. Among the precipitation conditions considered are: pH of the thorium feed solution, concentration, temperature and the order of addition (thorium solution in oxalic acid solution and vice versa) known as reverse/direct strike. Herein, we show that the morphology of the final oxalate depends significantly on the above mentioned precipitation parameters.

Electrochemical behaviour of uranium and thorium aqueous solutions at different temperatures

The waste streams generated from thoria fuel cycle normally have thorium and uranium species, therefore, in the present studies, electrochemical techniques were used to determine their redox potentials in presence of each other. Uranium and thorium solutions in 1 M HClO4, with concentration ratios of 10:1, 2:1 and 1:1, were studied using cyclic-voltammetry, in the temperature range, 298–338 K. The data was used to determine diffusion coefficients of ionic species and rate constants, entropy changes and activation energies of reduction processes.

Ruling out accumulation of thorium in sulfuric acid solutions for leaching of phosphogypsum

It is shown that introduction of fluoride ions into recycled sulfuric acid solutions used for leaching of rare-earth elements from phosphogypsum precludes accumulation of thorium in these solutions, thereby making it possible to develop a technology for obtaining concentrates of rare-earth elements that rules out formation of intermediate and waste radioactive products.

Thorium-234 Electrodeposition Using Ionic and Aqueous Uranyl Solutions

The isotope 234Th is daughter from 238U natural decay, with a half-life of 24.1 days. Then, 234Th produces 234Pa/234mPa pair, which decay to 234U, with a half-life of 6.70 h, emitting an intense beta radiation in the order of 2.2 MeV [1]. This short-lived thorium isotope has been used as a tracer for a variety of transport processes in aquatic systems [2,3]. Pourbaix diagram for aqueous solution of thorium and uranyl, as presented in Figure 1, shows that Th4+ has pref-erential hydroxide formation if compared to (UO2)2+ in pHs greater than 3. For this, some beta/alpha ratio increase is fore-seen during uranyl electrodeposition. Considering lower pHs, there is a prevalence of ionic state for either cations Th4+ or (UO2)2+. [Figure 1 – Pourbaix Diagram for uranyl solution containing thorium in low concentration.] The present work made an extensive experimentation to obtain thorium precipitation as 234Th, which happens during uranyl reduction or hydroxyl precipitation. The experimental process was as indicated below:1. Acidic solutions of 50mM [U] in UO2(NO3)2 in 2˗propanol (ionic solution: 140 experiments) and 50mM [U] UO2(NO3)2 in bidistilled water (aqueous solution: 98 experiments) with pH~1; 2. Direct cathodic polarization galvanostatic set at ˗100mA (110 experiments); 3. Pulsed cathodic polarization galvanostatic set at ˗100mA during 70 ms (“on”-stage) followed by 10 ms (“off”-stage) with a frequency of 12.5 Hz (128 experiments). The 4-graph set in Figure 2 shows the main results of the 234Th electrodeposition by means of radioactive alpha and beta emission counting. From these results, it is re-markable that the direct polarization and aqueous solu-tion has no great effect in changing the beta/alpha ratio. The level of this ratio stayed under 10, which could be a sign of preferential electrodeposition of thorium as indi-cated in Pourbaix diagram. However, when 2˗propanol uranyl electrolyte was used associated with pulse polari-zation, the results showed drastic increase of beta/alpha ratio. It reached ratio levels above 100. [Figure 2 – Results of ratio, varying with pH, from electrodeposi-tion experiments taking into account the solution type (aqueous and ionic) and the electrodeposition method (direct and pulsed). Experiments: 238 in total; 98 aqueous and 140 ionic; 110 using direct polarization and 128 using pulsed polarization.] This association of pulse polarization and ionic electro-lyte under high cathodic polarization imposed variables that are important to build up the 234Th content obtained from uranyl-solution electrodeposition in very acidic 2-propanol media, under higher cathodic polarization. This occurrence might be linked to restrictions imposed by non-protonated process by using 2-propanol solution, hindrance of water electrolysis to produce hydroxyl near the cathode and H2 evolution4,5, which promotes very acidic media around the cathode and probable hydride formation in absence of hydroxyl. As a general idea, there is a likely co-reduction of Th4+ and U4+ co-reduction, forming hydride species. The co-reduction from uranium-VI (uranyl) to uranium-IV has a feasible condition under high acidic condition, low water electrolysis and non-equilibrium of high imposed cathodic polarization4,5. When there is an exhaustion of thorium deposition in the same solution, noticed by beta-counting decreasing, it is observed that uranium electrodeposition starts more promptly, discernible by alpha-counting increasing.

Generation of thorium ions by laser ablation and inductively coupled plasma techniques for optical nuclear spectroscopy

Single- and double-charged 232Th and 229Th ions were produced by laser ablation of solid-state thorium compounds and by inductively coupled plasma techniques with mass-spectrometry analysis from liquid solutions of thorium. The latter method was found to be more applicable for producing ions of radioactive 229Th for laser experiments when searching for the energy value of the isomeric nuclear transition.

Separation by competitive transport of uranium(VI) and thorium(IV) nitrates across supported renewable liquid membrane containing trioctylphosphine oxide as metal carrier

Supported renewable liquid membrane (SRLM) technique is investigated for the selective separation of uranium from thorium solutions. Trioctylphosphine oxide (TOPO) dissolved in dodecane is used as the metal carrier in the liquid membrane (LM) phase. The renewable LM configuration used is highly stable for consistent long run operations. Systematic investigations were carried out to investigate the transport of U(VI) across the SRLM under different experimental conditions such as, concentration of TOPO in the LM phase, concentration of U(VI), Th(IV) and nitric acid in the feed, receiving phase composition and hydrodynamic conditions across the polymeric membrane support. By combining the process of in situ precipitation of thorium carbonate in the receiving phase, an excellent separation of uranium from thorium with decontamination factor of the order of 350 could be achieved. The solid precipitate of thorium carbonate generated in the receiving phase did not create any hindrance to the transport of U(VI) across the SRLM. The parameters defining the transport mechanism of U(VI) across the SRLM are experimentally evaluated as; maximum permeability coefficient, PU=9.66×10−5cm/min, diffusion coefficient for U(VI) in the aqueous feed solution, Da=2.35×10−4cm2/min with length of the concentration depletion layer from membrane interface, da=4.17×10−2cm and membrane diffusion coefficient for UO2(NO3)2·2TOPO in the LM phase, Do=5.36×10−6cm2/min. The numerical model obtained with these parameters gives satisfactory concordance with the experimental results under given constraint of the concentrations of nitric acid, TOPO and U(VI). Selectivity of this separation process is tested by determining permeability of different metal ions across the SRLM under optimized conditions.

Thorium nanochemistry: the solution structure of the Th(iv)–hydroxo pentamer

Tetravalent thorium exhibits a strong tendency towards hydrolysis and subsequent polymerization. Polymeric species play a crucial role in understanding thorium solution chemistry, since their presence causes apparent solubility several orders of magnitude higher than predicted by thermodynamic data bases. Although electrospray mass spectrometry (ESI MS) identifies Th(IV) dimers and pentamers unequivocally as dominant species close to the solubility limit, the molecular structure of Th(5)(OH)(y) polymers was hitherto unknown. In the present study, X-ray absorption fine structure (XAFS) spectroscopy, high energy X-ray scattering (HEXS) measurements, and quantum chemical calculations are combined to solve the pentamer structure. The most favourable structure is represented by two Th(IV) dimers linked by a central Th(IV) cation through hydroxide bridges.