Binding Of Thorium Research Articles

Carboxyl-functionalized UiO-66-NH2 for efficient capture of Th(IV) in aqueous solution: Experimental and DFT study

Thorium is an excellent alternative to uranium as a potential nuclear fuel due to the gradual depletion of uranium resources. Therefore, the separation and enrichment of thorium from tailing wastewater is of great significance. In this study, a novel adsorbent, UiO-66-NH-PMA, was prepared by grafting pyromellitic acid (PMA) onto UiO-66-NH2 composite via a simple amination reaction for the separation and enrichment of thorium from aqueous solution. The presence of a significant number of –COOH functional groups on PMA provides an abundance of adsorption sites for thorium binding. Under acidic conditions (pH = 3.0), UiO-66-NH-PMA exhibited a theoretical maximum adsorption capacity of 168.38 mg/g. Moreover, the adsorbent reached adsorption equilibrium within 150 min. After five cycles of adsorption-elution experiments, UiO-66-NH-PMA retained 84.6 % of its first-time thorium adsorption, demonstrating excellent regenerative performance. Additionally, the mechanism of UiO-66-NH-PMA complexed with Th(IV) was analyzed in detail by combining XPS, FT-IR, XRD and DFT calculation. This work demonstrates the high efficiency of carboxyl-functionalized UiO-66-NH2 for disposal of thorium-containing nuclear wastewater, and offers new insights into the mechanism of thorium adsorption on the adsorbents containing carboxyl groups.

Reversibility of uranium and thorium binding on a modified bauxite refinery residue: The effects of aging temperature

The effects of aging on the pH-dependence and reversibility of uranium and thorium binding by a modified bauxite refinery residue (MBRR) were studied in laboratory uptake/leaching experiments. Natural uranium and thorium isotopes (predominantly 238UVI and 232ThIV) of 0.4, and 0.2mM were loaded for an 8-day period at the natural equilibrium pH of the MBRR (approximately 8.5) and were allowed to age for 6months in humid sealed containers at 4, 23, and 65°C. After aging, anthropogenic 232UVI and 229ThIV were added as exchange isotopes and the pH decreased stepwise from 8 to 3 over several hours in pH dependent experiments. The relative concentrations of the isotope pairs (i.e. 238UVI and 232UVI; 232ThIV and 229ThIV) indicated that irreversibility of UVI and ThIV binding by the MBRR increased with aging and was dependent on the aging temperature and surface actinide loading. Linear combination fitting of the EXAFS data for the uranium loaded materials indicated that at low uranium concentrations sorption to minerals (particularly hematite) was a prime uranium removal mechanism, but at higher concentrations precipitation dominated. The data suggest that increased irreversibility and incorporation of UVI during aging is associated with re-crystallisation of precipitates.

The pH-dependence and reversibility of uranium and thorium binding on a modified bauxite refinery residue using isotopic exchange techniques

The pH-dependence and reversibility of uranium and thorium binding onto a modified bauxite refinery residue (MBRR) were studied in laboratory uptake/leaching experiments. Natural 238U and 232Th isotopes were contacted with MBRR in an 8 day loading period (equilibrium pH ≈ 8.5) then leached in pH-dependent experiments, where the pH was decreased from 8 to 3 over several hours following addition of exchange isotopes 232U and 229Th. Relative concentrations of the thorium isotope pair ( 232Th and 229Th) indicate that Th is very strongly bound to MBRR, and although at pH 3, some de-sorption is observed 232Th (≈3%) and 229Th (≈2.5%), released thorium is partially re-adsorbed during an overnight equilibration. During the initial equilibration, approximately 50% of the 238U was adsorbed, and a U adsorption maximum occurs between pH 5 and pH 6, where <0.5% of the U remains in solution. However, at a pH between 5 and 3, some 60% of the bound U releases, hence the pH range of maximum U retention on the MBRR is relatively narrow. When equilibrated overnight, the MBRR releases additional U, suggesting a kinetically controlled de-sorption linked to mineral dissolution. Plots of U isotope exchange between 232U and 238U are linear, and suggest that U adsorption is mostly reversible. Data for adsorption in mixed systems of U and Th suggest that Th and U compete for similar binding sites.

Radiotracer study of thorium complexation with humic acid at pH 2–11 using free-liquid electrophoresis

Free-liquid electrophoresis was used for the study of thorium complexation with Aldrich humic acid (HA) in aqueous solutions of 0.01 M (NaClO 4 + HClO 4 or NaOH) with dependence on pH and concentration of thorium (< 10 ―9 ―10 ―5 M, labelled with 234 Th) and HA (0.1―10 mg/L). The abundances and the mean electrophoretic mobilities of thorium humate complexes were calculated from the electrophoretic mobilities of thorium measured. It has been found that negatively charged humate complexes dominate in the solutions of pH 2―11 containing 1―10 mg/L HA and up to 0.001 M HCO 3 ― . Experimental evidence was given of the formation of Th(OH) 4 HA y― complex at pH 8―11 and its stability constant was determined. New conclusions about spontaneous association of HA molecules at pH 2-6 and about binding of thorium by non-dissociated carboxyl groups of HA were drawn.

Uranium and thorium sequestration by a Pseudomonas sp.: Mechanism and chemical characterization

The mechanism and chemical nature of uranium and thorium sequestration by a Pseudomonas strain was investigated by transmission electron microscopy, energy dispersive X-ray (EDX) analysis, FTIR spectroscopy and X-ray diffractometry. Atomic force microscopy (AFM) used in the tapping mode elucidated the morphological changes in bacterial cells following uranium and thorium binding. Transmission electron microscopy revealed intracellular sequestration of uranium and thorium throughout the cell cytoplasm with electron dense microprecipitations of accumulated metals. Energy dispersive X-ray analysis confirmed the cellular deposition of uranium and thorium. EDX and elemental analysis of sorption solution indicated the binding of uranium and thorium by the bacterial biomass via displacement of cellular potassium and calcium. The strong involvement of cellular phosphate, carboxyl and amide groups in radionuclide binding was ascertained by FTIR spectroscopy. X-ray powder diffraction (XRD) analyses confirmed cellular sequestration of crystalline uranium and thorium phosphates. Overall results indicate that a combined ion-exchange–complexation–microprecipitation mechanism could be involved in uranium and thorium sequestration by this bacterium. Atomic force microscopy and topography analysis revealed an undamaged cell surface with an increase in cell length, width and height following radionuclide accumulation. The arithmetic average roughness ( R a) and root mean square (RMS) roughness ( R q) values indicated an increase in surface roughness following uranium and thorium sequestration.

Binding of thorium(IV) to carboxylate, phosphate and sulfate functional groups from marine exopolymeric substances (EPS)

Th(IV) isotopes are important proxies in oceanographic investigations, and are used as tracers of particle dynamics and particulate organic matter (POC) fluxes out of the euphotic zone through the use of 234Th/POC ratios. These approaches rely on empirically determined and variable POC to 234Th ratios, which might be controlled, in parts, by the abundance of exopolymeric substances (EPS). EPS contain acidic polysaccharides (APS) and are excreted by both phytoplankton and bacteria. To this end, radiotracer experiments with EPS from microbial cultures were conducted to determine the binding environment of 234Th(IV)-binding ligands in colloids and suspended particles in marine systems. In these experiments, the 234Th distribution during isoelectric focusing (IEF) and polyacrylamide gel electrophoresis (PAGE) was related to the functional group composition of EPS and of colloidal organic matter (COM) isolated from the Gulf of Mexico (GOM) using cross-flow ultrafiltration. EPS was extracted from phytoplankton ( Emiliania huxleyi and Synechococcus elongatus) and bacteria ( Sagittula stellata and Roseobacter gallaeciensis) cultures by repeated alcohol precipitation. Phosphate and sulfate concentrations were determined using ion chromatography (IC). IEF profiles indicated that 49% to 65% of the 234Th-labeled EPS from plankton and bacteria as well as COM samples from the GOM was found concentrated below pH of 4, near an isoelectric point, pH IEP, of about 2. The carboxylic acid maxima for extracted EPS and COM samples appeared close to the pH IEF of 234Th(IV). The phosphate maximum appeared at the same pH IEF as 234Th(IV) for EPS from R. gallaeciensis and S. elongatus. The sulfate maximum was found at the same pH IEF as 234Th(IV) for EPS from S. elongatus and COM. The molecular weight (MW) of the strongly Th(IV)-binding ligand varied from 1 to 14 kDa, depending on the species, but was about 10 kDa in COM. Thus, depending on the species of plankton or bacteria, the MW and specific functional group composition of the strongly 234Th(IV)-binding amphiphilic biomolecule can vary. Therefore, different acidic functional groups can, at times, contribute to the binding of Th(IV) to the EPS chelating ligand, which can also have different MWs. This implies that the binding environment for Th(IV), which is present at total concentrations at least a million times lower than the acid functional groups, consists of strong polydentate chelate complexes in clustered structures of carboxylate, sulfates and/or phosphates. The combination of strongly chelating groups and amphiphilicity gives this biomolecule the unique properties of a “sticky” ligand.

Radionuclide remediation using a bacterial biosorbent

Abstract A Pseudomonas strain, characterized as part of a project to develop a biosorbent for removal of toxic radionuclides from nuclear waste streams, was a potent accumulator of uranium (VI) and thorium (IV), with the metal sequestration process being unaffected by culture age, presence of carbon/energy source and metabolic inhibitor but sensitive to the composition of the growth medium. Further characterization of radionuclide biosorption using lyophilized biomass revealed rapid cation binding of >90% within 1– 10 min of contact and complete removal of U and Th was observed at initial concentrations up to 100 mg l −1 . Initial solution pH strongly affected radionuclide biosorption with an optimum at pH 4.0–5.0. High affinity, efficient and high capacity uranium and thorium binding was indicated, with maximum loading of 541 mg U g −1 dry mass or 430 mg Th g −1 dry mass. Good conformity of sorption data with the Langmuir model suggests monolayered U and Th binding. Sorption in presence of several interfering cations and anions indicates a specific U and Th binding by the biomass with significant antagonism offered only by iron (III). Transmission electron microscopy and energy dispersive X-ray fluorescence analysis of metal loaded biomass revealed intracellular U and Th sequestration. More than 90% of biomass-bound radionuclide was recovered using sodium or calcium carbonate. For continuous process application an immobilized biomass system was developed and tested with multiple cycles of sorption–desorption. Overall, the biosorbent appeared suitable for realistic bioremediation.

Biosorption of thorium (IV) by a Pseudomonas biomass

Lyophilized biomass of a Pseudomonas soilisolate adsorbed thorium (IV) (430 mg g−1 dry wt) optimally at pH 4, with 91% of equilibrium loading being reached in 1 min. Equilibrium metal sorption showing conformity to Langmuir isotherm model suggested a monolayered thorium binding. Thorium binding remained unaffected or slightly affected (< 20% inhibition) in presence of equimolar (430 μM) concentration of several interfering ions except Fe3+ (40% inhibition). More than 90% of loaded thorium could be recovered using 1 M CaCO3, though mineral acids and Na2CO3 were also effective.

Interaction of humic and fulvic acids with Th(IV)

The binding of Th(IV) to three humic and two fulvic acids has been studied using a solvent extraction technique. The results are interpreted to indicate the formation of two types of thorium binding sites in the humic polymer containing one or two carboxylate groups. High complex stability is observed and thorium humate binding constants increase with increasing ionization of the humic (fulvic) acid polyelectrolyte. The results are interpreted using a modified Born equation for electrostatic interaction. Thermodynamic results indicate that the great stability of these complexes is derived from a very favorable complexation entropy.

The Binding of Thorium(IV), Plutonium(IV), Americium(III) and Curium(III) to the Constituents of Bovine Cortical Bone In Vitro

By means of a gel filtration technique it has been shown that thorium (IV), plutonium (IV), americium (III) and curium (III) bind to five glycoprotein fractions isolated from bovine cortical bone and to certain other substances. The effects of pH on the binding of plutonium to poly-L-glutamic acid and to bone chondroitin sulfate and of curium to bone sialoprotein and chondroitin sulfate-protein complex are described. Plutonium, americium, and curium were found to bind to bone glycoproteins in the presence of a 30-fold greater mass of bone mineral than glycoprotein. Some experiments on the precipitation of calcium phosphate in vitro in the presence of plutonium and americium are also presented. These observations are discussed in the light of the hypothesis that certain actinide elements are localized at bone surfaces by binding to glycoproteins.