Radiolytic Degradation of Uranyl-Loaded Tributyl Phosphate by High and Low LET Radiation

Understanding and characterizing the radiolytic degradation of solvents used for treatment of used nuclear fuel is an ongoing topic of research. In the work presented here, degradation constants for the radiolysis of tributyl phosphate (TBP) as a function of various process variables, such as the inclusion of nitric acid and uranyl ions on the TBP, were determined. Degradation constants were determined for both high linear energy transfer (LET) and low LET (gamma) radiation exposure. Results indicate that susceptibility to gamma radiolysis is roughly twice that of high LET and that acid uptake by TBP has little effect on the overall degradation for both high and low LET irradiations. The inclusion of a metal ion affects the degradation of TBP by forming complexes that absorb a portion of the energy deposited by radiation. These TBP–metal complexes break down during irradiation, and the degradation constants for the complex were found to be higher compared to free TBP, for both high and low LET radiations suggesting that the TBP–uranyl complex is more susceptible to radiation than free TBP.     

NMR study of the gamma radiolysis of poly(dimethyl siloxane) under vacuum at 303 K

The structural changes which occur on the γ-radiolysis of poly(dimethyl siloxane) (PDMS) under vacuum at 303 K have been investigated using ²⁹Si and ¹³C NMR. New structural units consistent with main chain scission and crosslinking through both H-linking and Y-linking reactions have been identified. The results obtained at various absorbed doses have been used to calculate the G-values for scission and crosslinking. G-values for scission of G(S)=1.3±0.2, for H-linking of G(D^CH₂-R)=0.34±0.02 and for Y-linking of G(Y)=1.70±0.09 were obtained for radiolysis under vacuum at 303 K. Thus crosslinking predominates over scission for radiolysis of PDMS under these conditions, and, by contrast with previous studies, Y-links have been shown to be the predominant form of crosslinks.     

Radiolysis of Diisodecyl Phosphoric Acid and its Effect on the Extraction of Neptunium

Radiolysis of diisodecyl phosphoric acid (DIDPA) in n-dodecane containing tributyl phosphate (TBP) was examined by analyzing concentrations of acidic extractants and H₃PO₄, and its effect on the extraction of neptunium was studied from the aspect of the extraction rate. For the solvent containing 0.5 M DIDPA and 0.1 M TBP irradiated in the absence of HNO₃, G-values for degradation of DIDPA and for production of dibutyl phosphoric acid (DBP) were found to be 0.47 and 0.14, respectively. For the solvent irradiated in stationary contact with 0.5 M HNO₃, G-value for DIDPA degradation was found to be 0.73, which was 1.7 times larger than the value for the solvent irradiated in the absence of HNO₃.

In the experiment on the extraction of neptunium initially in the pentavalent state from the solution containing 0.5 M HNO₃ and 0.5 M H₂O₂, it was found that the extraction rete tas determined by the concentration of MIDPA forted by radiolysis when the solvent was irradiated with lower dose than 1 MGy in the absence of HNO₃. When the solvent absorbed higher dose or was irradiated in the presence of HNO₃, the extraction rate was influenced by the other radiolysis products. Even in this case, when the solvent contained TBP, the rate varied little until absorbed dose increased over 0.5 MGy.     

RADIOLYSIS OF DIISODECYL PHOSPHORIC ACID AND ITS EFFECT ON THE EXTRACTION OF NEPTUNIUM

Radiolysis of diisodecyl phosphoric acid (DIDPA) in n-dodecane containing tributyl phosphate (TBP) was examined by analyzing concentrations of acidic extractants and H₃PO₄, and its effect on the extraction of neptuniua was studied froi the aspect of the extraction rate. For the solvent containing 0.5 fi DIDPA and 0.1 1 TBP Irradiated in the absence of HNO₃, G-values for degradation of DIDPA and for production of dibutyl phosphoric acid (DBP)were found to be 0.47 and 0.14, respectively. For the solvent irradiated in stationary contact with 0.5 M HNO3, G-value for DIDPA degradation was found to be 0.78, which ras 1.7 tines larger than the value for the solvent irradiated in the absence of HNO₃.     

Extraction relationship of Li+ and H+ using tributyl phosphate in the presence of Fe(III)

ABSTRACT

During the extraction of lithium from high Mg-containing salt lake brines by tributyl phosphate (TBP) in the presence of Fe(III), H⁺ is used to stabilize Fe(III). However, the distribution ratio of H⁺ (D_H) is 4–6 times higher than that of Li⁺ (D_Li), which affects the extraction of Li⁺ significantly. In this study, the competition mechanism between H⁺ and Li⁺ was investigated by spectral analysis and thermodynamic equilibrium. The extracted species are determined as HFeCl₄ · 2TBP and LiFeCl₄ · 2TBP for H⁺ and Li⁺, respectively. The apparent equilibrium constants are K_H = 799.8 and K_Li = 120.6, respectively. Both equilibrium constants and the distribution ratios for H⁺ and Li⁺ extraction show that extraction of H⁺ is stronger than Li⁺.     

DEGRADATION OF TRUEX-DODECANE PROCESS SOLVENT

The hydrolysis and radiolysis of TRUEX-dodecane process solvent (0.2 M octyl(phenyl)N,N-diisobutycarbamoylmethylphosphine oxide (CMPO)-1.2 M tributylphosphate (TBP) in n-dodecane) has been Investigated in a series of experiments conducted in a biphasic mode involving contact with aqueous nitric acid solutions. The stability of the principle extractant (CMPO) is observed to be considerably greater than that reported previously for similar studies in chlorinated diluents. The concentration profiles for the degradation products determined by capillary gas chromatography have been successfully fit assuming pseudo-first order kinetics and mechanistic information derived from these fits.     

The Solvent Extraction of Heptavalent Technetium by Tributyl Phosphate

Abstract

The solvent extraction of heptavalent technetium from aqueous nitric or hydrochloric acid by tributyl phosphate in n-dodecane (TBP-NDD) has been studied over a wide range of TBP and acid concentrations at 25, 50, and 60°C. The extraction was found to proceed according to the reaction 3TBP + H⁺ + TcO₄ ^? → (HTcO₄ · 3TBP). A discussion of possible reaction mechanisms is presented, along with values for ΔG, ΔH, ΔS, and the equilibrium constant for the extraction reaction. Finally, evidence for the coextraction of technetium by uranyl ions is discussed.     

Radiolytic and hydrolytic degradation of the hydrophilic diglycolamides

The stability of different hydrophilic diglycolamides against acid degradation and radiolysis was studied. Tetraethyldiglycolamide (TEDGA) was found to undergo degradation in nitric acid at high reaction rates at elevated temperatures with a maximum of a ~8% decrease per hour at 65°C in 4 mol L^–1 HNO₃. The radiolysis was studied for tetramethyldiglycolamide (TMDGA), TEDGA, methyl-tetraethyldiglycolamide (Me-TEDGA), and dimethyl-tetraethyldiglycolamide (Me₂-TEDGA). The degradation rates decreased with increasing molecular weight, following the trend TMDGA > TEDGA > Me-TEDGA ≥ Me₂-TEDGA. Degradation products were identified by mass spectrometric techniques and were found to be comparable to those previously reported for the radiolysis of lipophilic diglycolamides in dodecane. Significant insight into the degradation mechanism in water was gained using pulse radiolysis experiments. The ^?OH radical was identified as the most important reactive species and predominant mechanism of radical reaction is one of electron transfer rather than H-atom abstraction.     

Diglycolamic Acid Functionalized CNTs for Preferential Selection of Eu(III) over Am(III) Ion: Density Functional Theoretical Modelling Validated by Experiments

We report the structure, bonding, energetic, and thermodynamic parameters of Eu³⁺ and Am³⁺ with diglycolamic acid functionalized CNTs at BP86 and B3LYP functional level of theory using SVP and TZVP basis set. The free energy of extraction, ΔG_ext, of Eu³⁺ and Am³⁺ was computed using standard thermodynamical procedure in conjunction with COSMO (conductor like screening model) model. The value of ΔG_ext for Eu³⁺ ion was found to be higher than that of Am³⁺ as observed in the extraction experiments. The HOMO-LUMO analysis indicates that Eu³⁺ ion is harder than Am³⁺ ion leading to stronger interaction with hard donor based DGA-CNT.     

DISTRIBUTION BEHAVIOUR OF U(VI), Th(IV) AND Pa(V) FROM NITRIC ACID MEDIUM USING LINEAR AND BRANCHED CHAIN EXTRACTANTS

ABSTRACT

The extraction behaviour of 1M solutions of tri-2-ethylhexyl phosphate (TEHP), di-2-ethyl hexyl isobutyramide (D2EHIBA), tri-n-butyl phosphate (TBP) and di-n-hexyl hexanamide (DHHA) in n-dodecane towards U(VI), Th(IV) and Pa(V) in the presence of 220 g/L of Th from nitric acid medium has been studied. The limiting organic concentrations (LOC) of thorium (g/L) for 1 M TBP and 1 M DHHA are evaluated as 31, 20 ( at 1 M HNO₃) and 25,13 (at 4 M HNO₃) respectively. The distribution ratio (D) values of U(VI), Th(IV) and Pa(V) in the presence of thorium (220 g/L) at. 1 M HNO₃ suggest that branching in the alky group of amides suppresses the extraction considerably. In view of the selective extraction of U over Th by 5 % TBP in THOREX process at 4 M HNO₃, distribution behaviour is also studied employing a lower concenfration (0·18 M) of extractant for comparison purpose, Separation factor (S. F.) values for U(VI) over Th(IV) under different experimental conditions consistently varied in the order: D2EHIBA > DHHA > TEHP > TBP. The quantitative extraction of ²³³U from a synthetic mixture containing ²³³U (10^?5 M). ²³³Pa (10^?11 M) and thorium (220 g/L) at 1 M HNO₃ using 1 M solution of D2EHIBA in n-dodecane is achieved in three stages, Stripping and reusability studies of D2EHIBA have also been carried out.     

Tuning the Extractive Properties of Purex Solvent using Room Temperature Ionic Liquid

An Aliquat-336 based ionic liquid, namely, tri-n-octylmethylammonium bis(2-ethylhexyl)phosphate ([A3636]⁺[DEHP]^?) was prepared and studied for the extraction of U(VI), Pu(IV), and Am(III) from nitric acid medium. Since the ionic liquid, [A336]⁺[DEHP]^? was miscible in n-dodecane (n-DD), the extraction of these actinides in the PUREX solvent, 1.1 M tri-n-butylphosphate (TBP) in n-dodecane (n-DD), was investigated in the presence of small concentrations of ionic liquid. The distribution ratio of U(VI) and Am(III) in 0.03 M [A336]⁺[DEHP]^?/n-DD decreased with increase in the concentration of nitric acid; whereas the extraction of Pu(IV) initially increased, it reached a maximum at 4 M nitric acid followed by the decrease. The extraction of actinides in ionic liquid medium decreased in the order Pu(IV) > U(VI) >> Am(III), indicating the feasibility of modifying the extractive properties of TBP/n-DD to favor Pu(IV) extraction. Therefore, the extraction of Pu(IV) in a solution of TBP – [A336]⁺[DEHP]^? in n-DD was also studied. The distribution ratio of Pu(IV) increased with increase in the concentration of ionic liquid and decrease in the concentration of TBP in organic phase. The distribution ratio of Pu(IV) determined in the presence of small concentration of ionic liquid in 1.1 M TBP/n-DD was always much higher than that observed in 1.1 M TBP/n-DD. In contrast to this, the distribution ratio of U(VI) decreased by the addition of ionic liquid and Am(III) was inextractable even in the presence of ionic liquid.     

Hydrogen Production in the Radiolysis of Dodecane and Hexane

The yields of molecular hydrogen, H₂, have been measured in the radiolysis of dodecane and hexane following radiolysis by γ-rays and a variety of heavy ions. Measured yields with γ-rays are found to be slightly higher than literature values and decrease by about 25% on aeration of the sample. Increasing the linear energy transfer (LET) from γ-rays to radiolysis with protons results in a decrease of H₂ yields by about 15% due to the increased importance of second-order H atom combination reactions. A further increase in LET results in a slight increase in H₂ yields.     

Mechanisms of Cell Killing Response from Low Linear Energy Transfer (LET) Radiation Originating from 177Lu Radioimmunotherapy Targeting Disseminated Intraperitoneal Tumor Xenografts

Radiolabeled antibodies (mAbs) provide efficient tools for cancer therapy. The combination of low energy β⁻-emissions (500 keV_max; 130 keV_ave) along with a γ-emission for imaging makes ¹⁷⁷Lu (T_1/2 = 6.7 day) a suitable radionuclide for radioimmunotherapy (RIT) of tumor burdens possibly too large to treat with α-particle radiation. RIT with ¹⁷⁷Lu-trastuzumab has proven to be effective for treatment of disseminated HER2 positive peritoneal disease in a pre-clinical model. To elucidate mechanisms originating from this RIT therapy at the molecular level, tumor bearing mice (LS-174T intraperitoneal xenografts) were treated with ¹⁷⁷Lu-trastuzumab comparatively to animals treated with a non-specific control, ¹⁷⁷Lu-HuIgG, and then to prior published results obtained using ²¹²Pb-trastuzumab, an α-particle RIT agent. ¹⁷⁷Lu-trastuzumab induced cell death via DNA double strand breaks (DSB), caspase-3 apoptosis, and interfered with DNA-PK expression, which is associated with the repair of DNA non-homologous end joining damage. This contrasts to prior results, wherein ²¹²Pb-trastuzumab was found to down-regulate RAD51, which is involved with homologous recombination DNA damage repair. ¹⁷⁷Lu-trastuzumab therapy was associated with significant chromosomal disruption and up-regulation of genes in the apoptotic process. These results suggest an inhibition of the repair mechanism specific to the type of radiation damage being inflicted by either high or low linear energy transfer radiation. Understanding the mechanisms of action of β⁻- and α-particle RIT comparatively through an in vivo tumor environment offers real information suitable to enhance combination therapy regimens involving α- and β⁻-particle RIT for the management of intraperitoneal disease.     

A 31P-NMR study of peroxo species formed during oxidation of cyclohexene with hydrogen peroxide in tri-n-butylphosphate catalyzed by heteropolyacids

In the oxidation of cyclohexene with H₂O₂in monophasic tri-n-butylphosphate (TBP) solution catalyzed by Keggin-type 12-heteropolyacids, i.e., H₃PMo_12-xW _x O₄₀(x=0–12), several peroxo species were observed by ³¹P-NMR spectroscopy in lower field than the original heteropolyacids. Their composition varied regularly with that of the starting catalyst. The P-containing peroxo species formed was deduced as [PM₄O₈(O₂)₈]^3-(M = Mo, W). The peroxo species formed more easily with a decrease in the W content, x of H₃PMo_12-xW_xO₄₀. It was further indicated from the reactivity with cyclohexene and the comparison with catalytic performance that W-rich peroxo species were catalytically more active than Mo-rich peroxo species for the oxidation of cyclohexene in this reaction system.     

A rheology study of high‐energy radiolysis of a semicrystalline ethylene‐propylene copolymer containing DOP mobilizer

The radiolysis of a poly(ethylene‐co‐propylene), Elpro grade P 750 J, marketed by Thai Polypropylene Co. Ltd. for the manufacture of medical goods, was investigated at ambient temperature and melt rheology measured. The roles of calcium stearate, blended with the Elpro as a processing aid, and dioctyl phthalate (DOP), added in various amounts as a radical scavenger, were assessed. Following radiolysis, G′ and the viscosity of the polymer melts at 453 K both decreased with increasing radiation dose, even when the mobilizer was present. The results indicated that although the DOP did scavenge radicals, it did not protect the polymer from net chain scission in a low‐dose regimen. The value of (G_S ? 4G_X) was approximately 0.6–0.7. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3437–3441, 2006     

Preparation and evaluation of nano-crystalline titania as sorbent for 99Mo/99mTc generator

In the presented work, nano-crystalline titania (TiO₂) was synthesized and evaluated as a novel chromatographic sorbent for the preparation of the medical ⁹⁹Mo/^99mTc generator. TiO₂ was synthesized by dissolving TiCl₄.6H₂O with isopropyl alcohol to form a semisolid mass that was extensively dried and washed. The physicochemical parameters and surface area of the synthesized nano-crystalline TiO₂ were evaluated. TiO₂ was packed as a chromatographic column to study the sorption of ⁹⁹Mo-polymolybdate (VI) anionic solution by dynamic equilibrium. The maximum sorption capacity of ⁹⁹Mo was ~141±2mg Mo/g TiO₂, thereby confirming its suitability for using low specific activity ⁹⁹Mo for the preparation of ⁹⁹Mo/^99mTc generator. The elution performance of the prepared ⁹⁹Mo/^99mTc generator based on Ti-⁹⁹Mo was evaluated. It showed high radiochemical purity (≥ 97% TcO₄^?), high radionuclidic purity (≥ 99.99%^99mTc) and high chemical purity; all of these specifications show the suitability for use in nuclear medicine applications.     

Polymeric Titanium Oxychloride Sorbent for 188W/188Re Nuclide Pair Separation

Abstract

The chemical synthesis conditions (TiCl₄: iPrOH reagent ratio and reaction temperature scheme) were optimized for the preparation of polymeric titanium oxychloride sorbent which met the requirements for clinically useful ¹⁸⁸W/¹⁸⁸Re generator production, such as high W-adsorption capacity, high ¹⁸⁸Re-elution yield, low ¹⁸⁸W-breakthrough, and good mechanical stability. This polymeric material was formed by polycondensation of titanium-oxychloride units, the chemical formula of which was supposed as [OTiO (Ti₄₀ Cl₈₀ (OH) ₈₀ (TiO₂)₉₅.60H₂O) OTiO]_n. The effect of the W-content of tungstate solution on the WO₄ ^2? ion adsorption (with minimizing the poly-tungstate ion adsorption) and its covalent bonding with the Ti metal atoms in the polymeric matrix were justified with respect to the optimal W-adsorption conditions for the preparation of a useful ¹⁸⁸W/¹⁸⁸Re generator column. The high W-adsorption capacity of about 515.6 mg W/g sorbent and ¹⁸⁸Re elution yield of higher than 85% wereachieved. The large difference in the distribution ratio values found for alumina and polymeric titanium oxychloride sorbent in 0.005% NaCl solution (D_{W, Re-188} = 50 and D_{W, Re-188} = 1.0, respectively) offered an advantage for the preparation of a consecutive-elution based ¹⁸⁸Re generator system which combined both ¹⁸⁸Re elution and ¹⁸⁸Re concentrating processes in one portable system. This generator system is of a tandem column type which consists of a polymeric titanium oxychloride sorbent coupled to an alumina column. This system gave a ¹⁸⁸Re concentration factor of approximately 10. The overall ¹⁸⁸Re yield achieved from this system was >80%. ¹⁸⁸W isotope and elemental tungsten breakthrough were not detected in its ¹⁸⁸Re eluate. This system thus offers a potential application for clinically useful ¹⁸⁸Re production using low specific radioactivity ¹⁸⁸W (around 500 mCi/g) producible in a medium neutron flux reactor.     

Sulfate radical-based ferrous–peroxymonosulfate oxidative system for PCBs degradation in aqueous and sediment systems

Polychlorinated biphenyls (PCBs) in the environment pose long-term risk to public health because of their persistent and toxic nature. This study investigates the degradation of PCBs using sulfate radical-based advanced oxidation processes (SR-AOPs). These processes are based on the generation of sulfate radicals through iron (Fe(II), Fe(III)) mediated activation of peroxymonosulfate (KHSO₅, PMS) or persulfate (Na₂S₂O₈, PS). This study is the first instance for coupling of Fe(II)/Fe(III) with PMS for PCB degradation in aqueous and sediment systems. The high oxidation efficiencies of the free radicals (SO₄⁻), in combination with the slow rate of consumption of the oxidants, make these processes very effective for the degradation of recalcitrant organic compounds. The effectiveness of the process was evaluated based on the degradation of a model polychlorinated biphenyl, 2-chlorobiphenyl and total organic carbon (TOC) removal. The kinetics of 2-chlorobiphenyl degradation along with the effect of oxidant and catalyst concentrations on the degradation efficiency was studied. Near complete removal of 2-chlorobiphenyl was observed when Fe(II) was used with PMS or PS. Fe(II) acts as a sulfate radical scavenger at higher concentrations indicating that there is an optimum concentration of Fe(II) that leads to most effective degradation of the target contaminant. A chelating agent, sodium citrate, was used to control the quantity of iron in the solution for activation of the oxidant. For the first time, we studied the feasibility of the activation of PMS using iron citrate complexes for PCB degradation. In the presence of sodium citrate, increase in degradation efficiency was observed up to a metal:ligand ratio of 1:2, after which the increase in citrate concentration led to a decrease in removal efficiency. Fe(II)/PMS systems were found to be very effective in degrading PCB in a sediment-slurry system with more than 90% PCB removal being observed within 24 h.     

Mercury Extraction By The TRUEX Process Solvent: III. Extractable Species And Stoichiometry†

ABSTRACT

Mercury extraction from acidic aqueous solutions by the TRUEX process solvent, 0.2 M n-octyl(phenyl)N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO), 1.4 M tributylphosphate (TBP) in n-dodecane, has not been extensively examined, Research is currently in progress at the Idaho Chemical Processing Plant to evaluate the TRUEX process for actinide removal from several acidic waste streams, including liquid sodium-bearing waste (SBW), which contains significant quantities of mercury. Reactions for two mercury species, HgCl₂ and HgCl₄ ^?2, are reported. Classical slope analysis techniques were utilized to evaluate the stoichiometric coefficients of each Hg species independently for both CMPO and TBP. The slope analysis results indicate that even the HgCl₄ ^?2 species extracts as HgCl₂. The results also indicate that 1.9 to 2.2 moles of CMPO and 1.5 to 1.81 moles of TBP are required per mole of HgCl₂ extracted. A generic equation for mercury extraction into CMPO or TBP has been shown to be:

where x = 2 or 4, y = 0 or ?2, E = CMPO or TBP, a = the experimentally determined CMPO or TBP stoichiometry, and over lines indicate organic species. Equilibrium constants for HgCl₂ species were determined to be 295 when extracted by CMPO and 18.2 when extracted by TBP. Equilibrium constants for the HgCl₄ ^?2 species were found to range between 5.8 and 12.0 for the CMPO reaction and 0.13 to 0.27 with TBP.     

Study on the photocatalytic degradation of trichlorfon in suspension of titanium dioxide

In this paper, the photocatalytic degradation of trichlorfon, an organophosphorous pesticide, was studied by using TiO₂ as a photocatalyst. The effects of various parameters, such as the amount of the photocatalyst, illumination time, reaction temperature, electron acceptors, metal ions, anions, and initial pH value on the photocatalytic degradation of trichlorfon were investigated. The best conditions for the photocatalytic degradation of trichlorfon were obtained. The results show that the optimum amount of the photocatalyst used is 8.0 g L^− 1. The photodegradation efficiency of trichlorfon increases with the increase of the illumination time or reaction temperature. The photodegradation efficiency of trichlorfon is increased rapidly by adding a small amount of H₂O₂, K₂S₂O₈, KBrO₃, Fe³⁺ and Cu²⁺, however, with the addition of Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, Co²⁺ and Ni²⁺, or with the addition of trace amount of SO₄²⁻, Cl⁻, Br⁻, there are no obvious effects on the photocatalytic degradation reactions. Alkaline mediums are favorable for the photocatalytic degradation of trichlorfon. The possible roles of the additives on the reactions and the possible mechanisms of effect were also discussed.