Dibutyl Phosphoric Acid Research Articles

The influence of dibutyl phosphoric acid on zirconium extraction with diluted tributyl phosphate and the role of uranyl nitrate

The influence of dibutyl phosphoric acid on zirconium extraction with diluted tributyl phosphate and the role of uranyl nitrate

The influence of tributyl phosphate on molybdenum extraction with solutions of dibutyl phosphoric acid

Comparative investigations were carried out to study the influence of TBP on Mo extraction by HDBP solutions in xylene and TBP in xylene. The dependences of DMo on HNO3 concentration for both HDBP and D2EHPA have minima at about 3 mol/L HNO3. This shows similar extraction properties of HDBP and D2EHPA. The presence of TBP in the solvent results in the reduction of Mo extraction and in an increase in the formal slopes of the falling and rising parts of the logDMo — log[HNO3] curve from −0.5 and +2 up to −2 and +4.

Effects of Ligand Structure on Reactive Vapor−Liquid Distribution Ratio and Selectivity for C6-Olefin Isomers

Vapor−liquid equilibrium experiments are performed to evaluate the suitability of π-complexing silver of various phosphoric and sulfonic acids for application as functionalized solvents in Reactive Extractive Distillation to separate 1-hexene from other C6-olefin isomers. The effect of solvent structure is investigated by testing five different ligands, di (2-ethylhexyl) phosphoric acid (D2EHPA), di (butyl) phosphoric acid (DBPA), mono (2-ethylhexyl) phosphoric acid (MEHPA), di (nonyl) naphthalene sulfonic acid (DNNSA), and dodecyl benzene sulfonic acid (DBSA), for a variety of C6-olefin isomers (1-hexene, 2-methyl-1-pentene, n-hexane, 1,5-hexadiene, trans-2-hexene). The introduction of silver in the solvent increases the solvent selectivity for 1-hexene. At equal silver concentration the ligand size does not influence the selectivity of chemically similar components (1-hexene/2-methyl-1-pentene) but increases that of chemically different components (1-hexene/n-hexane). A lower pressure, a higher silver concentration, or higher solvent-to-feed (S/F) ratio are beneficial for the 1-hexene selectivity. The highest selectivity is obtained for Ag−DBPA (20 wt % Ag, S/F-ratio of 3): 1.23 for 2-methyl-1-pentene and 1.42 for n-hexane, relative to 1.04−1.06 for unreactive solvents.

Radiation Chemical Behavior of Tributyl Phosphate, Dibutylphosphoric Acid, and Its Zirconium Salt in Organic Solutions and Two-Phase Systems

Radiation-induced and hydrolytic decomposition of HDBP and its zirconium salt in organic solutions and two-phase aqueous-organic systems in the presence of TBP and nitric acid is studied. The yields of radiation-induced decomposition of HDBP and temperature dependences of its hydrolysis rate constants are determined. Kinetic equations for radiation-induced decomposition of HDBP are derived.

Efficient Strategies for Partitioning Actinides from Alkaline Wastes

Actinide losses to alkaline wastes during reprocessing (or partitioning) can be significant, especially as higher burn-up fuels are processed. These losses result from the fact that radiolysis degrades neutral extractants into acidic species (e.g., mono- and dibutylphosphoric acids in Purex), which are themselves powerful extractants. Sodium carbonate is used to remove these acidic degradation products, but actinides and fission products also transport into the aqueous phase. The alcohol extraction process described here uses 2-ethylhexanol to extract the degradation products away from the actinides and fission products, which may then be returned to the aqueous phase for recovery and purification using neutral extractants.

Mathematical Simulation of Steady-State Concentration Profiles in Extraction Cascades for Reprocessing NPP Spent Fuel Using TBP-Compatible Processes (SUPERPUREX)

A mathematical model is proposed for calculating distribution coefficients of NPP spent fuel components in extraction systems with 30% TBP in a hydrocarbon diluent and dibutylphosphoric acid zirconium salt in 30% TBP. The model is based on the semiempirical extraction equations. A computer code has been developed for simulation of the steady-state concentration profiles throughout the extraction cascade. Comparison of the predicted and experimental data showed that the code is well applicable to simulation and optimization of the SUPERPUREX process.

Effect of TBP on Extraction of REE and TPE from Nitric Acid Solutions with Dibutylphosphoric Acid and Its Zirconium Salt

Solvent effect on extraction of REE and TPE with dibutylphosphoric acid is studied. Over the HNO3 concentration range 0.1-0.5 M, HDBP is a good extractant for REE and TPE, whereas addition of TBP suppresses the extraction. The effect of excess HDBP is similar to the previously observed effect of TBP on extraction of REE. Evidently, free HDBP, like TBP, can enter the solvation shell of a lanthanide with formation of fairly complex, probably polymeric species.

Effect of TBP on Extraction of REE and TPE with 4d Element Salts of Dibutylphosphoric Acid

Extraction properties of 4d element (Ti, Zr, and Hf) salts of dibutylphosphoric acid (HDBP) are examined. In extraction of Eu from nitric acid solutions, the optimal [HDBP]/[M] ratio depends on the presence of TBP and a diluent in the extraction system and also on the HNO3 concentration in solutions. With decane used as a diluent instead of xylene, the distribution coefficients of the extracted elements increase, and the extracting properties of the Zr and Hf salts become more similar. The extraction characteristics of these salts are similar over the entire examined range of HNO3 concentrations. At the same time, the difference between the Zr and Hf salts in the extractive power applies to all the lanthanides. The extraction properties of the Ti salt strongly differ from those of the Zr and Hf salts. Thorough study of the behavior of the Ti salt is complicated by its limited solubility in organic solvents.

Partitioning of High-Level Waste with an Extractant Based on Chlorinated Cobalt Dicarbollide and Dibutylphosphoric Acid Zirconium Salt

A new extractant allowing full partitioning of high-level waste was developed. It consists of chlorinated cobalt dicarbollide, dibutylphosphoric acid zirconium salt, and polyethylene glycol, dissolved in a polar diluent, mononitrobenzotrifluoride. This extractant recovers from the Purex process raffinate REE, TPE, Cs, Sr, Mo, and Zr. The component ratio ensuring maximal recovery of REE and TPE was found. The majority of the above-mentioned elements are extracted by the cation-exchange mechanism, with the recovery increasing as the aqueous phase acidity is decreased. The composition of the extractable species and the stoichiometry of extraction exchange reactions with REE and TPE were studied.

Disposal of spent tributylphosphate by gliding arc plasma

The gliding arc in humid air is a relevant source of free radicals and strongly oxidising species such as HO (shown by emission spectroscopy), which are able to degrade organic wastes. This feature was used in a new process for mineralising spent tributylphosphate (TBP) which is an important waste from nuclear industry. The degradation kinetics is examined by monitoring the conversion of TBP into phosphoric acid in a batch reactor. The kinetics exhibits three steps and especially an overall zero-order linear step with a rate of 10 mmol h −1 at the beginning of the treatment. This zero-order step agrees with a surface oxidation process. After a 13.7 h treatment, about 45% of the TBP is converted into inorganic phosphorus compounds, with phosphoric acid as the major product (63% of inorganic phosphorus compounds), and at least 19.5% is not degraded. Dibutylphosphoric acid (HDBP) was identified as the main by-product by a nuclear magnetic resonance technique, infrared spectroscopy and gas chromatography.

Compounds of Hexavalent Uranium and Dibutylphosphate in Nitric Acid Systems

Storage tanks at the Savannah River Site (SRS) contain highly enriched uranium (U) and dibutyl phosphoric acid (HDBP), formed from the hydrolysis and radiolysis of tributylphosphate (TBP) in the PUREX process. Highly enriched dibutyl phosphoric acid, a relatively strong acid with a pKa (acid dissociation constant) of about one, forms insoluble compounds with U and other actinides in acid solutions. Accumulation of solids in these storage tanks presents a criticality hazard and must be avoided. In this work, U and HDBP compounds were formed from batch reactions in 0.2–6.0 M nitric acid (HNO3) and two HDBP concentrations, forming either a homogenous or heterogeneous solution based on solubility. A 4:1 HDBP:U ratio was used in all experiments. The chemical composition of the compounds was characterized using liquid scintillation, ion chromatography, and stannous chloride reduction. The physical characteristics of the U and HDBP compounds were characterized using a combination of infrared spectrometry (IR), electronic spectrophotometry (UV/Vis), and Phosphorous‐31 Nuclear Magnetic Resonance (31P NMR). The physical appearance of the solids ranged from a pale yellow powder at 0.2 M HNO3 loading to a bright yellow gel at 6.0 M HNO3, with constant modifications as the acid concentration increased. The U and HDBP precipitate from 0.2 M HNO3 was characterized as UO2(DBP)2 (a polymer with ten units) in homogenous U and HDBP solutions and UO2(DBP)2(HDBP) x (where x = 1 or 2) in heterogeneous U and HDBP solutions. Indications of nitrate complexation appeared in precipitates from 0.8 M HNO3 for both HDBP loadings, however a 1:1 uranium: nitrate ratio was not reached at that acid concentration. UO2(NO3)(H(DBP)2)(HDBP)2 precipitated from ≥ 3.0 M HNO3 with high HDBP concentrations. This compound was not formed until 6.0 M HNO3 was used in lower HDBP concentrations. It is assumed that the change in physical characteristics and addition of nitrate coincides with the breakdown of the UO2(DBP)2 polymer. Supporting data for these findings are presented and discussed.

Extraction of transplutionium and rare-earth elements, molybdenum and iron with zirconium salt of dibutyl phosphoric acid

Zirconium salt of dibutyl phosphoric acid (ZS-HDBP) dissolved in dilute tributyl phosphate (TBP) is proposed as a solvent for separation of transplutonium and rare-earth elements (TPE, RE), including yttrium, from high-level waste in the presence of molybdenum and iron. The optimum HDBP:Zr ratio is 9 for RE and TPE extraction and is 12.5 for Mo. IR spectra indicate formation of Zr(DBP)4(HDBP)4 complex as a base of solvation. HNO3 depresses RE and TPE extraction, while Mo extraction is characterised by a minimum at 2.5 mol/L HNO3. Presence of TBP in the solvent, independently of the used diluent, leads to reduction of the distribution coefficients, but ZS-HDBP extraction capacity for the above elements is increased, as well as solubility of their solvates.

TPE/REE separation with the use of zirconium salt of HDBP

Partitioning of long-lived radionuclides (minor actinides, fission products) is considered as TBP-compatible ZEALEX-process for extraction separation of transplutonium elements (TPE) and rare-earth elements (REE), as well as Y, Mo, Fe and residual amounts of Np, Pu, U. Zirconium salt of dibutyl phosphoric acid (ZS-HDBP) dissolved in 30 % TBP is used as a solvent. The process was tested in multistage centrifugal contactors. Lanthanides, Y and TPE, as well as Mo, Fe were extracted from high-level Purex raffinate, Am and ceric subgroup of REE being separated from the polyvalent elements by stripping with HNO3. TPE/REE partitioning was achieved in the second cycle of the ZEALEX-process using DTPA in formic acid media. The integral decontamination factor of Am from La and Ce after both cycles is >200, from Pr and Nd 20–30 and from Sm and Eu 3.6; REE strips in both cycles contained <0,1% of the initial amount of TPE.

SISAK Liquid-Liquid Extraction Experiments with Preseparated 257Rf

The SISAK liquid-liquid extraction system was used to extract 4.0-s 257 Rf. The 257 Rf was produced in the reaction 208 Pb( 50 Ti, 1n) 257 Rf with 237-MeV beam energy on target, separated in the Berkeley Gas-filled Separator (BGS) and transferred to a gas jet using the Recoil Transfer Chamber (RTC). The activity delivered by the gas jet was dissolved in 6-M HNO3 and Rf was extracted into 0.25-M dibutyl-phosphoric acid in toluene. This was the first time a transactinide, i.e., an element with Z ≥ 104, was extracted and unequivocally identified by the SISAK system. Thus, this pilot experiment demonstrates that the fast liquid-liquid extraction system SISAK, in combination with liquid- scintillation detectors, can be used for investigating the chemical properties of the transactinides. The extraction result is in accordance with the behaviour shown by the Rf group IV homologues Zr and Hf. and output. 2-4 During recent years, work has been undertaken to deploy SISAK in studies of the chemical properties of the transactinide elements (Z ≥ 104). 2, 5, 6 The only suitable detection method found was liquid-scintillation (LS) detection. 7 This was mainly because of the rather high flow rates (0.5-2.0 mL/s) encountered in the SISAK system. Other detection methods usually require either thin, dry samples or very thin liquid films. No suitable method was found to prepare such samples without an unac- ceptable time delay between separation and detection. LS counting has high efficiency, but suffers from relatively poor energy resolution (about 300-keV FWHM at 7-MeV α en- ergy) and is sensitive to β particles and γ rays. This puts very stringent demands on the separation system, because most of the β- and γ-emitting contaminants are produced with orders of magnitude higher yield than the transactinide under study. A huge effort was made to develop methods for LS detection of very low levels of α activity under these conditions. The most important techniques implemented are: • Pulse-shape discrimination is used to reduce the β back- ground in the α spectra by a factor >1000. Without this tech- nique the β- and γ-induced background from the surroundings and from nuclides produced in the target will interfere with the α spectrum to such an extend that it becomes useless. 8 • Real-time scintillation-yield monitoring by continuous mea- surement of the Compton edge of 662-keV 137 Cs γ rays. The position of the Compton edge is used to automatically adjust the energy calibration. Based on this adjustment the event gates used for switching the detection cells between mother and daughter mode (open or closed valve, respectively) will always be set on the correct energy range. 9

Extraction Properties of Dibutylphosphoric Acid Zirconium Salt in Recovery of Transplutonium and Rare-Earth Elements from Nitric Acid Solution

The structures of dibutylphosphoric acid zirconium salt (Zr-DBP) and of the complexes formed in the organic phase in extraction of rare-earth elements with Zr-DBP were suggested on the basis of the extraction and IR data. The influence exerted by the acidity, Zr-DBP concentraiton, and degree of extractant saturation with the metal on the structure of the complexes was examined. The contributions of various extraction mechanisms for all the rare-earth elements and also for Am and Cm were revealed by mathematical simulation. Irrespective of the diluent, addition of TBP to Zr-DBP decreases the distribution factors of Ce, Eu, and Am but increases the extractant capacity for rare-earth elements by a value that considerably exceeds the extraction of the elements with TBP taken separately.

SOLUBILITY LIMITS OF DIBUTYL PHOSPHORIC ACID IN URANIUM-NITRIC ACID SOLUTIONS

The Savannah River Site has enriched uranium (EU) solution that has been stored since being purified in its solvent extraction processes. The concentrations in solution are approximately 25mM U and 0.1 M nitric acid. Residual tributylphosphate in solution has slowly hydrolyzed to form dibutyl phosphoric acid (HDBP) at concentrations averaging 0.14–0.2450 mM. Dibutyl phosphoric acid, in turn, is in equilibrium with (HDBP)2 and DBP−. Uranium can form compounds with the dibutylphosphate ion (DBP−) which have limited solubility, thereby creating a nuclear criticality safety issue. Literature reports and earlier SRTC tests have shown that it is feasible to precipitate U-DBP solid during the storage and processing of EU solutions. As a result, a series of solubility experiments were run at nitric acid concentrations from 0–4.0 M HNO3, uranium at 0–378 mM, and temperatures from 0–30°C. The data show temperature and HNO3 concentration dependence consistent with what would be expected. With respect to uranium concentration, U-DBP solubility passes through a minimum between 25 and 50 mM U at the HNO3 concentrations and temperatures studied. However, the minimum shows a slight shift toward lower uranium concentrations at lower HNO3 concentrations. The shifts in solubility are strongly dependent upon the overall ionic strength of the solution. These data also reveal a shift to higher DBP solubility above 0.5 M HNO3 for both 25 mM and 50 mM uranium solutions. Analysis of U-DBP solids from the tests identified distinct differences between precipitates from <0.5 M solutions and those from >4 M acid. Analyses identified UO2(DBP)2 as the dominant compound present at low HNO3 concentrations in accordance with literature reports. As the acid concentration increases, the crystalline UO2(DBP)2 shows molecular substitutions and an increase in amorphous content.

Characterization of zirconium complexes of interest in spent nuclear fuel reprocessing by electrospray ionization mass spectrometry

Liquid-liquid extraction of zirconium, one of the most important fission products, was followed using electrospray ionization mass spectrometry under conditions simulating reprocessing of nuclear spent fuel. Zr(IV) can precipitate from the organic phase after extraction by dibutylphosphoric acid (HDBP), the most common degradation product of tributylphosphate (TBP) radiolysis. Different complexes were detected with electrospray used in positive or negative ion modes, according to the extraction conditions such as the ligand/metal ratio. Stoichiometry of the Zr(IV) complexes was determined by combining isotopic labeling [H(15)NO(3)] of the aqueous phase in the extraction system and tandem mass spectrometry experiments. These results were compared with the species observed using other techniques reported in the literature. The mechanisms of ionization/desorption of these complexes are proposed depending on the organic ligand character (neutral (L) such as TBP, or acidic (HL') such as HDBP), and the ionization mode used. Copyright 2000 John Wiley & Sons, Ltd.

Thermal Decomposition of Nitrated Tributyl Phosphate

Extended contact between heated mixtures of trin-butyl phosphate (TBP) and aqueous solutions of nitric acid and/or heavy metal nitrate salts at elevated temperatures can lead to exothermic reactions of explosive violence. Most solvent extraction operations (e.g., Purex) are conducted at ambient conditions without heating TBP and have been performed safely for decades, but several explosions involving TBP have occurred in the United States, Canada, and the former Soviet Union. This investigation was undertaken to characterize the products of thermal decomposition of both single- and two-phase mixtures of TBP, nitric acid, and water under a variety of conditions. The data indicate that the extent of reaction and the rate of gaseous product formation are affected by the presence of Zr4+, distillation compared with reflux conditions, temperature, water/HNO3 and HNO3/TBP ratios, and whether the decomposition occurs under constant pressure or constant volume conditions. Higher reaction temperatures accelerate the rate of decomposition, but the extent of decomposition, as measured by the quantity of gaseous products, was greater at lower temperatures when the decomposition was performed under distillation conditions. Higher gas production occurs under reflux conditions, lower H2O/HNO3 ratios, and when a separate water-HNO3 phase is initially present. The major gaseous products include N2, CO, CO2, NO, and N2O. Measurable amounts of NO2 were not present in the final product mixture, although an orange color suggesting the presence of NO2 was observed in the early stages of decomposition. The major liquid products were dibutyl phosphoric acid, butyl nitrate, and water. Small amounts of C1-C4 carboxylic acids were also present. Because of the small sample sizes that were employed and the isothermal conditions of the decomposition, runaway reactions were not observed. Some possible reaction pathways are considered.

Radiation-induced decomposition of the tributyl phosphate-nitric acid system: Role of nitric acid

Radiation-induced decomposition of tributyl phosphate-nitric acid as a two-component system has been studied. Degradation products, dibutylphosphoric acid (DBP) and monobutylphosphoric acid (MBP), were determined by separation-extraction method. 0.59, 0.78 and 1.38 are the G (DBP) values and 0.15, 0.17 and 0.13 are the G (MBP) values obtained for pure TBP, TBP-3M HNO3 extract and TBP-5M HNO3 extract, respectively. G (−HNO3) values are 5.19 and 6.15 for 3M HNO3 and 5M HNO3 extracts. It is shown that nitric acid plays a significant role in enhancing the decomposition of TBP.

Processing of interfacial tension data in solvent extraction studies. Interfacial properties of various acidic organophosphorus extractants

AbstractBasically, the interfacial tension data can be plotted as a function of logarithm C where C denotes the concentration of any form of the surface active species considered. The various relationships y vs In C are discussed here from a mathematical point of view and it is shown that ambiguities may arise from the use of the interfacial tension curves versus the total extractant concentration for the interfacial tension data interpretation. The method recommended in this work is based on the computation of the whole surface excess curves (Γ vs concentration of individual species). This is achieved by matching various adsorption equations (e.g. Szyszkowski or Temkin relationships) or empirical equations to the interfacial tension data (y vs C). The term dy/dln C can then be analytically calculated and introduced into the Gibbs equation [Γ = −(1/RT)dy/dln C] to derive mathematical expressions for the surface excess curves. To exemplify our approach, interfacial data are interpreted for dibutylphosphoric acid (HDBP), di(2‐ethylhexyl)phosphoric acid (HDEHP), di(hexoxyethyl)phosphoric acid (HDHOEP), 2‐ethylhexyl‐2‐ethylhexylphosphonic acid (HEH[EHP]) and di(2‐ethylhexyl)phosphinic acid (H[DEHP]) at various liquid‐liquid interfaces.