Transport Of Thorium Research Articles

A fractional derivative model for nuclides transport in heterogeneous fractured media

Nuclide transport in fractured media involves the advection, dispersion, adsorption, etc. The dispersion and adsorption properties of the rock matrix have spatial variability, which results in an anomalous transport of nuclides. In this study, a time-fractional advection-diffusion equation (t-FADE) model is utilized to capture the sub-diffusion transport behavior with heavy-tail property, including the breakthrough curves (BTCs) of uranium and thorium transport in granite plates. Moreover, hydrodynamic dispersion of tritiated water, strontium and cesium in granite fractures are also studied. The results indicate that BTCs of nuclides transport in the granite fractures are unimodal and asymmetric. The decrease of the fractional order α reflects the stronger sub-diffusion. Furthermore, small initial velocity enhances sub-diffusion effect of nuclides and lengthens the breakout time of BTCs, which results in obvious heavy-tail phenomena. The analysis results demonstrate that the t-FADE model can accurately describe sub-diffusion behavior of nuclides transport. At last, the advantages of the t-FADE model in prediction and remediation of nuclides contamination are put forward.

Membrane assisted transport of thorium (IV) across bulk liquid membrane containing DEHPA as ion carrier: kinetic, mechanism and thermodynamic studies

Abstract Extraction and carrier mediated transport of thorium (IV) ions through bulk liquid membrane containing di-2-ethylhexyl phosphoric acid (DEHPA) in kerosene as metal ion carrier. The feed comprised of thorium (IV) ions solutions containing various concentrations of hydrochloric acid, while sulfuric acid solutions of different concentrations are used as a stripping agent. Various parameters about thorium (IV) ion extraction and transport were investigated: the feed solution acidity, initial metal ions aqueous solution concentration, carrier concentration and stripping agent concentration. More than 85% thorium (IV) is recovered in 960 min using 0.2 M DEHPA/kerosene as carrier and 1.5 M H2SO4 as stripping agent from the 0.0001 M HCl solution containing 50 mg L−1 thorium (IV) as feed. Assuming a consecutive, irreversible extraction and back-extraction (stripping) reactions a simple kinetic model was proposed for estimating the reaction rate constant or reaction rate coefficient under the investigated experimental conditions. The activation energy values of extraction and back-extraction reactions were calculated to be 29.94 kJ mol−1 and 20.55 kJ mol−1, respectively, which indicates that the extraction process was controlled by the mixed regime (both kinetic and diffusion), and the back-extraction process was mainly controlled by diffusion process.

Recovery and transport of thorium(IV) through polymer inclusion membrane with D2EHPA from nitric acid solutions

Recovery and transport of thorium(IV) from HNO3 medium using a polymer inclusion membrane (PIM) containing di (2-ethylhexyl) phosphoric acid (D2EHPA) as the carrier, and polyvinyl chloride (PVC) as polymer were studied. Taguchi L-16 orthogonal array was used to evaluate the effects of the membrane’s carrier content, pH, strip phase type and concentration, and initial concentration of Th(IV) on the cation transport. Using a 45% (m/m) D2EHPA-55% (m/m) PVC PIM, Th(IV) is completely separated from a number of common metal cations. Studies on the transport kinetics and the stability of the membranes were also performed. The results showed that the PIM has excellent stability.

Modeling and experimental validation of the steady-state counteractive facilitated transport of Th(IV) and hydrogen ions through hollow-fiber renewal liquid membrane

In this study, a new mathematical model was proposed to analyze the permeation of thorium across the hollow fiber renewal liquid membrane (HFRLM). Diluted solutions of bis (2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272) and H2SO4 were used as the carrier and strip phases, respectively, in a one-through mode of operation. A one-dimensional (longitude direction) and time-independent model was developed based on the mass conservation equations and considered not only the transport of thorium but also the counter-transport of hydrogen ions on both sides of the module. The set of obtained algebraic and ordinary differential equations was numerically solved, and the comparison between the calculated results and the experimental data was performed. Experimental results were obtained at various operating conditions such as the lumen side fluid flow rate, carrier concentration, initial pH of the feed phase, initial solute concentration of the donor phase, and the module scale. Modeling results show that the developed model could predict the experimental data as well.

Continuous bulk liquid membrane technique for thorium transport: modeling and experimental validation

A continuous bulk liquid membrane technique “three-phase flow layered bulk liquid membrane (TPFLBLM)” is proposed. Aspects related to TPFLBLM were studied in thorium removal by D2EHPA as the carrier. The mass transfer coefficients were determined and experimental correlations were developed to determine the local mass transfer coefficients. The results showed that the thorium transport increases with increase in the membrane and acceptor phases flow rates. Based on the developed correlations, more than 90% Th(IV) transfer is achieved after 30 min of the TPFLBLM system continuous operation with a surface-to-volume ratio of 375 containing 600 mL acceptor phase, 42.5 mL organic phase, and 30 mL donor phase circulating with the flow rates of 300, 274 and 78 mL min−1, respectively.

Measurement of 232Th(n,f) and 232Th(n,γ) reaction rates in thorium powder cylinder bombarded with D-T neutrons

ABSTRACTIn order to provide reference for the evaluation of thorium parameters for the conceptual design of fusion–fission hybrid energy reactor, a dedicated integral experiment was carried out in a thorium powder cylinder bombarded with D-T neutrons. Thorium capture and fission rates in the 0° direction to the incident D+ beam were obtained using the activation method followed by the off-line gamma-ray technique, experimental uncertainties were ∼3.1% for thorium capture rate, and were 5.5%, 8.1%, and 6.3% for thorium fission rates based on fission products 85mKr, 143Ce, and 87Kr, respectively. The thorium fission rate based on 85mKr agreed well with the simulation employing ENDF/B-VII.0 library data. The influence of the oxygen contained in the thorium oxide powder and the scattering neutrons from the experimental hall was also evaluated. MCNP simulations employing ENDF/B-Ⅶ.0, JENDL-4.0 library data agreed with experiment within uncertainties except that employing ENDF/B-Ⅶ.1 (6.0%) and CENDL-3.1 (7.9%) for thorium fission rate, while for thorium capture rate, simulation employing JENDL-4.0 agreed with experiment best. The influence of reaction channels of thorium transport medium employing different library data on the thorium reaction rates could be neglected according to the simulation. The thorium capture to fission ratio demonstrated that the fuel breeding efficiency is quite low and energy production plays a leading role under the neutron spectra in this experiment.

Selective and Efficient Ligandless Water-in-Oil Emulsion Liquid Membrane Transport of Thorium(IV) Ions

The present paper concerns on the selective and very efficient transport of thorium(IV) ions from aqueous solutions through an emulsion liquid membranes composed by paraffin and a surfactant, without carrier requirement. The influence of pH of the external aqueous phase, the surfactant concentration in the membrane phase, the type, and concentration of the acid used in the receiving phase, the emulsification and mixing speed on the process efficiency were examined and discussed. The optimized conditions were: liquid paraffin as diluent, 5% surfactant (nonionic polyamine surfactant span-80), emulsification rate 5250 rpm, 15 min of stirring at 750 rpm in the extraction step, pH 5, oil/aqueous ratio of 3 in emulsions and using 0.3 M solution of sulfuric acid as stripping phase. Under optimized experimental conditions, thorium ions were selectively and quantitatively transported from its mixture solution with lanthanides La(III), Sm(III), Eu(III) and Er(III). The concentration of thorium ions, in single component transport experiment, was measured spectrophotometrically using ArsenazoIII as the indicator at 655 nm, and the analysis of metal ions in competitive experiments was performed by an ICP-OES instrument under recommended conditions provided by the instrument’s manufacturer.

Thorium impact on tobacco root transcriptome

Thorium is natural actinide metal with potential use in nuclear energetics. Contamination by thorium, originated from mining activities or spills, represents environmental risk due to its radioactivity and chemical toxicity. A promising approach for cleaning of contaminated areas is phytoremediation, which need to be based, however, on detail understanding of the thorium effects on plants. In this study we investigated transcriptomic response of tobacco roots exposed to 200μM thorium for one week. Thorium application resulted in up-regulation of 152 and down-regulation of 100 genes (p-value <0.01, fold change ≥2). The stimulated genes were involved in components of jasmonic acid and salicylic acid signaling pathways and various abiotic (e.g. oxidative stress) and biotic stress (e.g. pathogens, wounding) responsive genes. Further, up-regulation of phosphate starvation genes and down-regulation of genes involved in phytic acid biosynthesis indicated that thorium disturbed phosphate uptake or signaling. Also expression of iron responsive genes was influenced. Negative regulation of several aquaporins indicated disturbance of water homeostasis. Genes potentially involved in thorium transport could be zinc-induced facilitator ZIF2, plant cadmium resistance PCR2, and ABC transporter ABCG40. This study provides the first insight at the processes in plants exposed to thorium.

N-benzoyl-n-phenylhydroxylamine (n-BPHA) carrier – mediated selective transport of thorium using bulk liquid membrane

The carrier activity of n-benzoyl-n-phenylhydroxylamine (n-BPHA) was examined for the possibility of selective transport of thorium across a bulk liquid membrane system, in the present work. The bulk liquid membrane setup based on the Schulman Bridge contained 25 ml of 10 4 M carrier solution in chloroform, as the membrane phase (M) that was connecting the two spatially separated aqueous feed (5mL containing 1M of metal ion solution) and receiving (10 mL of suitable stripping agent like dilute acid, dilute sodium fluoride and EDTA) solutions. The feed solution was maintained at an optimum pH of 3. The optimum pH of the feed solution was 3. It was found that the extraction efficiency for the different stripping agents followed the order of NaF>EDTA>HNO3and with NaF as stripping agent, the transport was achieved within 1 h. The studies were carried out in the presence of other ions and the interference from most of the ions could be effectively reduced using a masking agent in the feed.

Reactive transport modeling of thorium in a cloud computing environment

Despite the long standing interest in modeling the fate and environmental impacts of radionuclides, simulations addressing the fate and transport of rare earth elements (REEs) and thorium (Th) have received comparably little attention. This study presents an architecture that enables reactive transport modeling and parameter sensitivity analysis on cloud computing platforms. We adapted an existing groundwater modeling framework to perform some of the computationally most expensive steps within a cloud environment based on Microsoft Windows Azure. The cloud computing architecture was evaluated and validated through the development of a schematic, cross sectional model along a transect across a tailings impoundment at a REE mine tailings site in northwest China. The model framework employs a suite of flow, solute transport and reactive transport simulation tools, i.e., MODFLOW, MT3DMS, and PHT3D. On the basis of our model simulations, the collection-trench for the impoundment constructed above the ground surface appears to collect a substantial portion of the leachate fluxes, but the remainder will bypass the trench and migrate downstream. Those bypassed leachate fluxes will subsequently interact with downstream fluviolacustrine aquifers and eventually discharge into the Yellow River south of the study site under the idealized simulation environment. Further investigations of the hydraulic parameters of the aquifer system and the impoundment dam, and other geochemical characteristics are needed to elucidate the fate and transport of thorium and improve the reliability of the numerical model. Although the discussion and analysis of this study is tailored to thorium reactive transport modeling of a REE tailings impoundment, such a framework can also be applied to deploy different types of scientific modeling applications on Azure Cloud.

Carrier facilitated transport of thorium from HCl medium using Cyanex 923 in n-dodecane containing supported liquid membrane

Present studies deal with supported liquid membrane (SLM) technique for the separation of thorium from hydrochloric acid (HCl) medium using Cyanex 923 as a carrier. Effects of feed acidity, strippant, and membrane pore size and membrane thickness on the transport of thorium have been studied in detail. The optimized parameters were applied for separation of thorium from a radioanalytical waste. Stability of the membrane and membrane support was investigated. Transport of thorium increased from 78.3 to about 93.7 % with increase in acidity from 0.5 to 2 M using 0.3 M Cyanex 923 in n-dodecane as carrier and 2 M ammonium carbonate as stripping phase. The transport of thorium decreased above 2 M HCl. An attempt was made to model the physicochemical transport of thorium in SLM and understand the mechanism of thorium transport.

Carrier Mediated Transport of Thorium from Nitric Acid Medium using 2-Ethyl Hexyl Hydrogen 2-Ethyl Hexyl Phosphonate (PC88A)/N-Dodecane as Carrier

The present study deals with the application of supported liquid membrane (SLM) technique for the separation of thorium from nitric acid medium using 2-ethyl hexyl hydrogen 2-ethyl hexyl phosphonate (PC88A) as a carrier and aqueous ammonium carbonate as a receiving phase. The effects of feed acidity, nature of strippant, and membrane pore size and membrane thickness on the transport of thorium have been studied in detail. Transport behavior of uranium (233U) and fission products from a radioanalytical laboratory waste is also studied. Stability of the membrane against the leaching of the extractant and stability of the membrane support have been investigated. An attempt has been made to model the physicochemical transport of thorium in SLM and establish the mechanism of thorium transport. Transport of thorium increased from 25% to about 96% using 0.75 M PC88A in n-dodecane as carrier and 2 M ammonium carbonate as stripping phase as the feed acidity decreased from 4 M HNO3 to 0.5 M HNO3. Optimum conditions obtained from this study were applied to recover thorium and 233U from analytical waste generated in the laboratory.

The effect of EDTA on the groundwater transport of thorium through sand

The effect of the anthropogenic complexing agent EDTA on thorium transport in groundwater has been studied using sand-packed columns and flow rates in the range of 20–100 m y−1. The concentrations injected into the columns were in the range of 0.4–4 mM for Th and 4–40 mM for EDTA, and with EDTA:Th ratios in the range 1:1 to 10:1. The results show that EDTA can significantly increase Th transport, but two very different behaviours are observed at Th concentrations of 0.4 and 4 mM. At the lower concentration, Th breakthrough is retarded with respect to a conservative tracer, with a peak width that is consistent with a single Kd value, followed by a longer tail, and the behaviour is very sensitive to the flow rate. However at 4 mM Th, the breakthrough peak appears near to that of the tracer, and the width of the peak is consistent with a distribution of Kd values and/or a larger dispersivity than the tracer. Speciation and transport modelling have been used to interpret the data, and a model was developed that could explain the 0.4 mM behaviour. This suggests that ternary surface complexes are important in these systems, with at least two different species involved, although the complexity of Th speciation in these systems leads to significant uncertainty in the values of the equilibrium and kinetic parameters. For the 4 mM systems, the rapid transport observed could not be explained by a simple chemical model; instead it is likely that EDTA plays an important role in stabilising and transporting thorium colloids and clusters.

How does dynamical spatial variability impact 234Th-derived estimates of organic export?

In this study we first evaluate the small-scale spatial variability of particulate export, using a set of synoptic thorium-234 activity observations sampled within a one-degree radius. These data show significant variability of surface thorium activity on scales of the order of 100km (∼270–550dpmm−3). This patchiness of export potentially affects the robustness of point observations and our interpretation of them. Motivated by these observations we subsequently couple an explicit model of thorium-234 dynamics to a coupled physical–biogeochemical basin model capable of resolving these small-scales. The model supports the observations in displaying marked thorium variability on spatial scales of the order of 100km and smaller, with highest values in the regions of large eddy kinetic energy and large primary productivity. The model is also used to quantify the impact of small-scale variability on export estimates. Our model shows that the primary source of error associated with the presence of small-scale spatial variability is related to the standard assumptions of steady state and non-steady state (>40% during bloom condition). The non-steady state method can misinterpret variations due to patchiness in thorium activity as temporal changes and lead to errors larger than those introduced by the simpler steady state approach. We show that the non-steady state approach could improve the flux estimates in some cases if the sampling was conducted in a Lagrangian framework. Undersampling the spatial variability results in further bias (>20%) that can be reduced when the sampling density is increased. Finally, errors due to the dynamical transport of thorium associated with small-scale structures are relatively low (<20%) except in regions of high eddy kinetic energy.

Transport of Thorium(IV) Across a Supported Liquid Membrane Containing N,N,N′,N′-Tetraoctyl-3-oxapentanediamide (TODGA) as the Extractant

The transport behavior of Th4+ was investigated from a feed containing 3.0 M HNO3 into a receiver phase containing 0.1 M oxalic acid across a PTFE flat sheet supported liquid membrane (SLM) which contained TODGA (N,N,N′,N′-Tetraoctyl-3-oxapentanediamide) in n-dodecane as the extractant. Effects of the nature of the strippant, extractant concentration, Th concentration in the feed, and feed acidity on the transport rates were investigated. The transport behavior apparently depended on the rate of extraction of the metal ion at the feed-membrane interface and was not diffusion controlled. Influence of Th concentration on flux was also investigated. Transport mechanism was elucidated and the diffusion coefficient was calculated to be 2.13 × 10−7 cm2/s. Solvent extraction studies at varying feed acidity and TODGA concentration were also carried out.

Transport of thorium from nitric acid solution by non-dispersive solvent extraction using a hollow fibre contactor

Membrane based non-dispersive solvent extraction (NDSX) of Th(IV) from aqueous nitric acid medium was carried out using di-n-hexyl octanamide (DHOA) in normal paraffin hydrocarbon (NPH) using a commercial hollow fiber module containing microporous hydrophobic polypropylene capillaries. The NDSX operation was carried out with pumping various concentrations of nitric acid (1–6 M) containing Th(IV) through the tube side and organic extractant (usually 1.1 M DHOA in NPH) through the shell side of the hollow fibre capillaries at aqueous and organic phase flow rates of 3.5 mL/s and 4.5 mL/s, respectively. Extraction studies were performed under different hydrodynamics conditions and the overall mass transfer was evaluated under cuonter-current flow condition. The percentage NDSX of Th(IV) increased with the increase in the extractant concentration (from 0.1 M DHOA to 1.1 M DHOA) as well as with nitric acid concentration (from 1 M to 6 M). Stripping studies were carried out using both distilled water as well as oxalic acid as the strippant. The possibility of the separation of U from Th was also evaluated.

Redistribution of uranium and thorium by soil/plant interaction in a recultivated mining area

During the recultivation of the uranium mining area of Kővágószőlős (Hungary), the tailings were covered with clay and loess soil layers having a thickness of 30 cm and 100 cm, respectively. In the loess covering layer, acacia ( Robinia pseudoacacia), poplars ( Populus × albus, Populus × canescens), oak ( Quercus pubescens), silver tree ( Eleagnus angustifolia) were planted between 1996 and 2004. In order to establish the extent of the uranium and thorium transport from the sludge to the leaves by uptake and translocation processes through roots with a length higher than 1.3 m results in a remarkable redistribution of these pollutants, a gray poplar tree, growing spontaneously in the last uncovered tailing, being selected as reference tree. The U and Th concentrations in the leaves of the above-mentioned trees, in the covering layers as well as in the original sludge were determined by inductively coupled plasma sector field mass spectrometry (ICP-SF-MS). Generally, the Th concentration of the soils was about 4 times higher than that of uranium, while uranium concentration was about 10–130 times higher than that of thorium in the leaf samples and its concentration ranged from 28 to 1045 ng g − 1 , the last value belonging to the poplar tree growing on the last uncovered tailing. In order to assume the mobility and bioavailability of uranium if the dry leaves fall down, the uranium species in the leaves of the poplar tree growing in the uncovered reservoir were determined applying ultrasound-assisted extraction with distilled water and ammonium acetate as well as high performance liquid chromatographic (HPLC)-ICP-SF-MS technique. About 20% of total uranium could be extracted in form of uranyl cations and a presumably negatively charged uranium compound. Estimations revealed that the annual increment of U in the soil surface layer due to the dead fallen leaves in case of the investigated gray poplar ( Populus × canescens) is about 1.2%.

Mobilização de tório em águas subterrâneas de águas da prata, estado de São Paulo

The paper describes and discusses results of the determination, by alpha spectrometry, of the natural thorium isotopes in groundwaters associated with different rock types in Aguas da Prata spa, state of Sao Paulo. The dissolved Thorium is relatively low (0.003 to 1.72 m g.L -1 for 232 Th), while the 228 Th/ 232 Th isotopic ratios for dissolved thorium were higher than unity (1.8 to 34). The thorium concentration in suspended solids of these waters ranged between 183 up and 3445 m g.g -1 and indicates that significant thorium transport occurs under this condition. The obtained results allowed to calculate the factor for preferential mobilizati on of thorium in particulate matter relative to the liquid phase, an important parameter for understanding the geochemical behaviour of this element in hydrosphere.

Role of Naturally Occurring Organic Matter on Thorium Transport in a Wetland

ABSTRACTA wetland located on the Savannah River Site in Aiken, South Carolina has become contaminated by a number of radionuclides as a result of operating a pilot-scale nuclear test facility. Sediment Th-232 concentration at the site exceed 700 mg/kg, whereas background concentrations are ∼7 mg/kg. The Th is relatively mobile, having moved &gt;300-m since 1958 and greatly exceeding contaminant transport model predictions. Studies were initiated to determine the chemical cause for the enhanced transport of Th. Particle-size fractionation studies showed that colloids alone were not likely responsible for all of the enhanced transport of Th. Sediment sequential extraction data showed that &gt;80% of the Th was associated with the sediment organic fraction. In an experiment in which varying soil amendments resulted in the release of dissolved organic carbon (DOC) to the aqueous phase, a significant correlation (r = 0.91; p ≤ 0.01, n = 8) was calculated between aqueous Th and DOC. Pore water Th partitioning to hydrophobic resins suggested that 33% of the aqueous Th was associated with organic matter. Together, these results provide indirect evidence support the notion that enhanced mobility of Th at the site may in part be due to the presence of Th-DOC complexes.

FACILITATED TRANSPORT OF Th(IV) ACROSS BULK LIQUID MEMBRANE BY DI(2-ETHYLHEXYL)PHOSPHORIC ACID

Di(2-ethylhexyl) phosphoric acid (DEHPA) has been successfully used as a carrier for the selective and efficient transport of Th(IV) across a bulk liquid membrane (BLM) of chloroform. The feed comprised of a solution of pure Th(IV) or a binary mixture of Th(IV) and a cation, such as Na+, K+, Ca2+, Mg2+, Cu2+, Pb2+, La3+, Fe3+, or UO2+ 2, in water maintained at pH 2, while 0.1 mol/L hydrochloric acid served as a stripping agent in the receiving compartment of the permeation cell. Greater than 99% of Th4+ selectively permeated across the membrane in less than 3 h, while the transport of other cations present along with thorium was less than 3% during the same time. Selectivity of the transport of thorium was greatly affected by the presence of Fe3+ and UO2+ 2 in the feed solution. Fe3+ could be effectively masked by the addition of SCN− or citric acid to the feed solution but the cotransport of UO2+ 2 could only be partially reduced by the addition of carbonate or thiocyanate to the feed solution.