Tributyl Phosphate Degradation Research Articles

Radiolysis of Tributyl Phosphate by Particles of High Linear Energy Transfer

Tributyl Phosphate (TBP), used in chemical separation processes for used nuclear fuel, is susceptible to radiolysis causing losses in process performance. We have studied its degradation by exposing dry 1M TBP/n-dodecane solutions to gamma radiation from a cesium-137 source and in a mix of low and high linear energy transfer (LET) radiation by irradiating samples in the UC Irvine TRIGA® reactor and utilizing the 10B(n,α)7Li reaction. In a 1 M solution of TBP in n-dodecane the degradation of TBP (G−TBP) was found to be 0.36 and 0.14 μmol/J for low and high LET radiation, respectively. The formation of dibutyl phosphoric acid, DBP, (G+DBP) in this solution was found to be 0.18 and 0.047 μmol/J for low and high LET radiation, respectively. In samples exposed to low LET as well as a mix of low and high LET a variety of TBP degradation products containing phosphorus were observed indicating that other degradation products than DBP and the monobutyl diacid (MBP) were formed. Our results for both low and high LET radiation compare well with previous studies on these systems indicating that high LET degrades TBP to a lesser extent than gamma radiation. Available data for high LET is not as abundant as for low LET making such comparisons challenging. Nevertheless, our method yields a value for G+DBP that agrees well with previous alpha radiolysis studies indicating that our method shows promise for studying high LET radiolysis in liquid-liquid extraction systems.

Tributyl phosphate biodegradation to butanol and phosphate and utilization by a novel bacterial isolate, Sphingobium sp. strain RSMS

A Sphingobium sp. strain isolated from radioactive solid waste management site (RSMS) completely degraded 7.98g/L of tributyl phosphate (TBP) from TBP containing suspensions in 3days. It also completely degraded 20mM dibutyl phosphate (DBP) within 2days. The strain tolerated high levels of TBP and showed excellent stability with respect to TBP degradation over several repeated subcultures. On solid minimal media or Luria Bertani media supplemented with TBP, the RSMS strain showed a clear zone of TBP degradation around the colony. Gas chromatography and spectrophotometry analyses identified DBP as the intermediate and butanol and phosphate as the products of TBP biodegradation. The RSMS strain utilized both TBP and DBP as the sole source of carbon and phosphorous for its growth. The butanol released was completely utilized by the strain as a carbon source thereby leaving no toxic residue in the medium. Degradation of TBP or DBP was found to be suppressed by high concentration of glucose which also inhibited TBP or DBP dependent growth. The results highlight the potential of Sphingobium sp. strain RSMS for bioremediation of TBP and for further molecular investigation.

Biodegradation of tributyl phosphate using Klebsiella pneumoniae sp. S3

Tributyl phosphate (TBP) has enormous applications in the field of extraction, fuel reprocessing, as defoamers and/or plasticizers. Excessive usage of this organophosphorus compound, poses an environmental threat. The present study deals with microbial degradation of TBP using Klebsiella pneumoniae S3 isolated from the soil. Diauxic growth curve pattern explains a preferential utilization of TBP. The strain S3 was able to biotransform TBP (1,000 mg L⁻¹) to dibutyl phosphate within 48 h and showed higher tolerance towards TBP up to 17.0 g L⁻¹. Toxicity of the parent as well as degraded product was assessed using comet assay. Generation of reactive oxygen species elaborates the oxidative stress imposed upon the bacterial strain by TBP. The antioxidant defense mechanism was studied using various biomarkers namely catalase, glutathione-S-transferase, and superoxide dismutase. The present study describes a faster and eco-friendly alternative for disposal of TBP.

Tributyl phosphate degradation in batch and continuous processes using Pseudomonas pseudoalcaligenes MHF ENV

Tributyl phosphate (TBP) degradation was carried out in a batch process using free and immobilized cells of Pseudomonas pseudoalcaligenes MHF ENV and the effect of immobilization on TBP degradation and cell growth was investigated. Immobilization was found to enhance the rate and onset of TBP degradation. The initial degradation rate for immobilized cells was 2.8 times higher than for free cells and was attributed to the enhanced growth rate of the immobilized cells. Continuous TBP degradation was then carried out in a packed bed reactor using agarose immobilized cells of P. pseudoalcaligenes MHF ENV and the effect of flow rate on TBP degradation was studied. With 75 mg l−1 TBP as feed, degradation efficiency of 100, 96 and 47% and degradation rates of 75, 100.8 and 70.5 mg l−1 h−1 were achieved at the flow rate of 15, 21 and 30 ml h−1 respectively. Although the flow rate of 15 ml h−1 could achieve total degradation of TBP, flow rate of 21 ml h−1 was found to achieve maximum TBP degradation rate. This is the first study on continuous degradation of TBP, using a stable bacterial pure culture where TBP served as the sole source of carbon.

A Comparison of Low and High LET (Linear Energy Transfer) Induced Radiolysis of Solvent Extraction Processes

Reagents used in chemical separation processes for used nuclear fuel are susceptible to radiolysis. Here we investigate the 10B(n,α)7Li reaction for inducing high linear energy transfer (LET) radiolysis. A solution of tributyl phosphate (TBP) in n-dodecane, representing the PUREX solvent, was irradiated by gamma rays from a137Cs source and by high LET particles from the 10B(n,α)7Li reaction in the UC Irvine TRIGA reactor. TBP degradation and Dibutyl phosphate (DBP) formation were quantified by gas chromatography. Our data show a significantly larger formation of DBP in the presence of gamma radiation compared to high LET radiation.

Photocatalytic performance of combustion synthesized β-Ga2O3 for the degradation of tri-n-butyl phosphate in aqueous solution

Nanostructures of β-Ga2O3 were prepared by solution combustion route using urea as the fuel. Transmission electron microscopic measurements and powder X-ray diffraction measurements confirmed the crystalline nature of β-Ga2O3 with particle size in the range of 10–15 nm. Surface area measurements indicated that the synthesized semiconductor catalyst had a specific surface area of 30 m2/g. In this work, photocatalytic degradation studies of tri-n-butyl phosphate using nano sized β-Ga2O3 is presented. A cylindrical photoreactor was used for the degradation studies and gas chromatographic estimation was adopted to follow the extent of degradation. Complete degradation of tributyl phosphate could be achieved in less than 40 min using 10 mg of photocatalyst and 0.5 mL of H2O2 for 1000 mL of 400 ppm TBP. Degradation of TBP was found to follow pseudo first order kinetics and the rate of TBP degradation was found to be superior for β-Ga2O3 photocatalyst compared to P-25 TiO2.

Degradation of Tributyl Phosphate Using Nanopowders of Iron and Iron–Nickel under the Influence of a Static Magnetic Field

A novel method for the degradation of tributyl phosphate was investigated through the use of nanopowders of iron and iron–nickel. A combination of magnetic field and sonication was used to induce degradation. Using a tributyl phosphate concentration of 300 ppm at pH 4, the Fenton reaction was initiated in the presence of sonication and a reduction in organic carbon content of up to 50% could be created under an induced magnetic field of 0.7 T. The magnetic properties of powders after sonication treatment, in the presence and absence of a magnetic field, were observed to be different. Different degradation mechanisms were proposed under the influence of varying induced magnetic field for iron and iron–nickel.

Study on cleaning solvents using activated alumina in PUREX process

Abstract The PUREX process is used to extract uranium and plutonium from dissolved solutions (spent nuclear fuel liquor). The extractant is 30% tributyl phosphate in n-dodecane, which is known to be degradable by radiation and nitric acid. Tributyl phosphate degradation products can generally be washed in alkali solutions like sodium carbonate solution; however, it is more difficult to remove n-dodecane degradation products using this method. A method of cleaning solvents using activated alumina is discussed in this study. A degradation sample of 30% TBP/n-dodecane was prepared by irradiating (1.6 MGy) with a 60Co gamma-source. The degradation products were then qualitatively analyzed using a gas chromatography-mass spectrometer (GC-MS). After being irradiated the solvents were cleaned with activated alumina, and a phase separation test with performed in evaluating the cleaned solvent. This resulted in the discovery of a procedure for the removal of n-dodecane degradation products of dodecanol and dodecanone, with about 70% of the degradation products, and the phase separation performance could be clearly improved through use of activated alumina.

Biodegradation of tributyl phosphate by novel bacteria isolated from enrichment cultures

Tributyl phosphate (TBP) is an organophosphorous compound, used extensively (3000-5000tonnes/annum) as a solvent for nuclear fuel processing and as a base stock in the formulation of fire-resistant aircraft hydraulic fluids and other applications. Because of its wide applications and relative stability in the natural environment TBP poses the problem of pollution and health hazards. In the present study, fifteen potent bacterial strains capable of using tributyl phosphate (TBP) as sole carbon and phosphorus source were isolated from enrichment cultures. These isolates were identified on the basis of biochemical and morphological characteristics and 16S rRNA gene sequence analysis. Phylogenetic analysis of 16S rRNA gene sequences revealed that two isolates belonged to class Bacilli and thirteen to β and γ-Proteobacteria. All these isolates were found to be members of genera Alcaligenes, Providencia, Delftia, Ralstonia, and Bacillus. These isolates were able to tolerate and degrade up to 5mM TBP, the highest concentration reported to date. The GC-MS method was developed to monitor TBP degradation. Two strains, Providencia sp. BGW4 and Delftia sp. BGW1 showed respectively, 61.0±2.8% and 57.0±2.0% TBP degradation within 4 days. The degradation rate constants, calculated by first order kinetic model were between 0.0024 and 0.0099h(-1). These bacterial strains are novel for TBP degradation and could be used as an important bioresource for efficient decontamination of TBP polluted waste streams.

ＭＯＸ燃料再処理における溶媒劣化 Ｐｕ精製工程における溶媒劣化とその影響

A solvent including tributyl phosphate (TBP) has been used for extraction of uranium (U) and plutonium (Pu) from nuclear spent fuel at Tokai Reprocessing Plant (TRP). TBP is said to be degraded by radiolysis, hydrolysis, and reactions catalyzed by extracted elements. One of the problems caused by TBP degradation is transfer of Pu into U stream caused by strong chemical binding between Pu and dibutyl phosphate (DBP), which is a degradation product of TBP. TBP degradation kinetic equations were developed based on degradation experiments using Pu samples with different alpha-ray emission rates that were taken from actual processes at TRP. The influence of degradation on Pu stripping characteristics was investigated. Diluted nitric acid alone could not readily strip Pu when DBP concentration was on the order of 103 mg/L, but a reduction agent, i.e., U (IV) with hydrazine, drastically improved the efficiency of Pu stripping. TRP has recently started to reprocess mixed oxide (MOX) spent fuel from the heavy water reactor FUGEN that includes Pu with higher alpha-ray emission. However, DBP concentration was still sufficiently low for stable solvent extraction operation. In addition, even after retention of Pu in the solvent for 20 days during a temporary suspension of the solvent extraction process, no Pu transfer into U stream was observed.

A Pulse Radiolysis Investigation of the Reactions of Tributyl Phosphate with the Radical Products of Aqueous Nitric Acid Irradiation

Tributyl phosphate (TBP) is the most common organic compound used in liquid-liquid separations for the recovery of uranium, neptunium, and plutonium from acidic nuclear fuel dissolutions. The goal of these processes is to extract the actinides while leaving fission products in the acidic, aqueous phase. However, the radiolytic degradation of TBP has been shown to reduce separation factors of the actinides from fission products and to impede the back-extraction of the actinides during stripping. As most previous investigations of the radiation chemistry of TBP have focused on steady state radiolysis and stable product identification, with dibutylphosphoric acid (HDBP) invariably being the major product, here we have determined room temperature rate constants for the reactions of TBP and HDBP with the hydroxyl radical [(5.00 +/- 0.05) x 10(9), (4.40 +/- 0.13) x 10(9) M(-1) s(-1)], hydrogen atom [(1.8 +/-0.2) x 10(8), (1.1 +/- 0.1) x 10(8) M(-1) s(-1)], nitrate radical [(4.3 +/- 0.7) x 10(6), (2.9 +/- 0.2) x 10(6) M(-1) s(-1)], and nitrite radical (<2 x 10 (5), <2 x 10(5) M(-1) s(-1)), respectively. These data are used to discuss the mechanism of TBP radical-induced degradation.

Tributyl phosphate degradation by Rhodopseudomonas palustris and other photosynthetic bacteria

Tributyl phosphate (TBP) is widely used in nuclear fuel processing and other waste generating chemical industries. Although TBP is bacteriostatic, some microbes are resistant to it and may degrade it. Under dark aerobiosis, purple non-sulfur photosynthetic bacteria degraded up to 0.6 mM TBP, initially present at 2 mM, within 3 weeks and under photosynthetic conditions, Rhodopseudomonas palustris degraded 1.6 mM TBP within 3 weeks. The curing of the Rhodopseudomonas palustris endogenous plasmid demonstrated that the genes involved in the TBP degradation are chromosomal.

Tributyl phosphate degradation by Serratia odorifera.

Several strains from tributyl phosphate (TBP)-polluted soils were isolated and screened for their ability to degraded this widely used organophosphorus compound. The most active strain, identified as Serratia odorifera, degrades up to 600 microM TBP (initially present in the medium at 2 mM) during its growth phase, within 8 h from inoculation. However, this bacterium could not utilize TBP as the sole carbon and/or phosphorus source but nevertheless is a good candidate for bioremediation of TBP-polluted industrial sites.

Phosphate and Phosphate Analogue Complexes of Uranyl Nitrate

In the Purex process the selective uranium and plutonium extraction (and back extraction) from nitric acid into 30% tri butyl phosphate/ odourless kerosene is used to separate uranium and plutonium from each other and fission products in spent nuclear fuel recycle process. The presence of dibutyl phosphate (a tributyl phosphate degradation product) can inhibit the uranium (and plutonium) back extraction process by forming very stable solvent phase complexes with these actinides. However, the types of complexes that exist and prevent back extraction have not been fully characterised. A model compound approach has been adopted in which the co-ordination chemistry of UO22+ with a range of P=0 and P(0)OH ligands have been studied. These complexes have been characterised using spectroscopic techniques including IR, Raman, UV7 vis, 31NMR NMR, and by single crystal X-ray diffraction to assess their utility in identifying molecular species under extraction conditions. We report full structural characterisation of [UO2(NO3)2(MDPhP)2], [UO2(NO3)DppmO2] and [UO2(Dpp)2(MeOH)] where MDPhP = methyl diphenyl phosphine oxide, Dpp = diphenyl phosphate and DppmO2 = Bis(diphenyl phosphino) methane dioxide

Improved determination of tributyl phosphate degradation products (mono- and dibutyl phosphates) by ion chromatography

Tributyl phosphate (TBP) is a very important compound in the nuclear industry, particularly in the area of nuclear fuel reprocessing. This compound is used in the PUREX (plutonium and uranium refining extraction) process which consists of the extraction of uranium and plutonium from an aqueous nitric acid phase, for the purpose of recycling. But TBP may be degraded to dibutyl phosphate (DBP) and monobutyl phosphate (MBP) by dealkylation of one or two butoxy groups, respectively. We have compared and evaluated the capacity of two resins manufactured by Dionex (AS11 and AS5A) in the separation and measurement of these two degradation products. AS11 generates two interferences: nitrite/DBP and carbonate/MBP. The first one is the most serious. So, we have developed a method for oxidising nitrite ions to nitrate ions which have no trouble over the measurement. The second resin tested, AS5A, allows a very efficient separation between DBP and NO 2 − ions and a good separation between MBP and CO 3 2− in comparison with the AS11. The detection limits for the AS5A column are 0.13 μ M for MBP and 0.71 μ M for DBP (injection loop=50 μl).

Nonphosphate Degradation Products of Tributyl Phosphate and Their Reactivities in Purex Media under Extreme Conditions

The chemical degradation of tributyl phosphate (TBP) in liquid systems, where TBP was in contact with aqueous solutions containing nitric acid and/or uranyl nitrate, was studied experimentally to clarify the mechanisms of the formation and successive reactions of nonphosphate products under atmospheric pressure. Butyl nitrate, propionic acid, acetic acid, butric acid, and butyl alcohol were formed as the nonphosphate butyl products derived from the butyl-groups of TBP in an open system. The total amount of these products almost equals the amount of the major intermediate phosphate products reduced, i.e., di- and monobutyl phosphates and phosphoric acid. Butyl alcohol was found to be the precursor of the other nonphosphate products.Even when the extremely degraded solvent was further contacted with 10 M nitric acid at 90°C, no significant heat evolution was observed at atmospheric pressure. Only butyl alcohol changed into carboxylic acids by exothermic oxidative reactions.

Stabilisation of tributyl phosphate-biodegradative ability of naturally-occurring pseudomonads using ampicillin

The biodegradation of tributyl phosphate (TBP) by a mixed microbial culture was demonstrated but growth on TBP and its catabolism were erratic. Pseudomonads isolated from the culture initially degraded TBP but were unstable and irreversibly lost this ability. Maintenance of cultures in the presence of ampicillin or growth in the presence of the antibiotic stabilised, and in some cases enhanced, TBP degradation, suggesting a central role for plasmid-borne activity.

Degradation of Tributylphosphate in Highly Radioactive Liquid Waste of Nuclear Fuel Reprocessing

Degradation of Tributylphosphate in Highly Radioactive Liquid Waste of Nuclear Fuel Reprocessing

Destruction of Emulsions Stabilized by Precipitates of Zirconium and Tributyl Phosphate Degradation Products

In solvent extraction for nuclear fuel reprocessing, a stable emulsion called crud is formed at the interface between the organic and aqueous phases. Crud is an emulsion stabilized by finely dispersed solids. Process disturbances are often induced by crud. Accordingly, crud should be eliminated from the interface in the extractors. The eliminated crud is stable and highly radioactive; thus, the treatment of this crud may be difficult. Complexes of zirconium and tributyl phosphate (TBP) degradation products, such as phosphoric acid (H{sub 3}PO{sub 4}) and mono-n-butyl phosphate (H{sub 2}MBP), are one source of the fine particles that stabilize emulsions in the extraction process. In this paper a chemical treatment method to demulsify crud stabilized by precipitates of Zr-H{sub 3}PO{sub 4} and Zr-H{sub 2}MBP is studied.

Degradation of Tributylphosphate in Plutonium Nitrate Solution

Degradation of tri-n-butylphosphate (TBP) dissolved in aqueous nitrate systems containing Pu was investigated under various conditions. The difference of degradation rates of TBP observed in reprocessed Pu streams and in nitric acid is discussed. The followings were elucidated: (1) The degradation of TBP in plutonium nitrate solutions depends upon the Pu concentration although it indicates first-order kinetics. (2) The half life of TBP increases linearly with HNO3 concentration in plutonium nitrate solutions. The retardation by undissociated HNO3 is almost independent of Pu concentration. (3) No significant effect of HNO2, generated by radiolysis, on the TBP degradation rate was observed. (4) The retardation of the degration of TBP can be described only with the concentrations of Pu and HNO3. (5) The G-values of TBP in plutonium nitrate solutions extremely decrease with increasing the concentrations of HNO3 and Pu. (6) Plutonium other than undissociated HNO3 would be involved in the retardation due to OH radical scavenging because Pu(III) and Pu(IV) give different degradation rates of TBP.