Spectrophotometric determination of uranium in process streams of a uranium extraction plant

This paper deals with the development and standardization of procedures for the determination of uranium on a routine basis in various process streams of a uranium extraction plant, covering a wide range of concentrations from 350 g 1(-1) down to 5 mg 1(-1) using only a spectrophotometric technique. The self-absorption of uranyl ion in dilute phosphoric acid and the violet-blue colour of the UO(2)(2+)-Arsenazo III complex in 4 M HC1 were exploited for high and low concentrations of uranium, respectively. The methods described were applied to samples of varying nature such as aqueous, organics and solids, involve minimal sample preparation and do not require prior separation of uranium from impurities. The interfering impurities in different process streams were also studied. Large quantities of silica as undissolved material poses a serious interference in the case of UNS and UNF. Considerable quantities of iron in UNS, UNF, UNR and UNRC cause interference. Possible remedies in these cases are suggested. Problems with the direct spectrophotometric measurement of organic samples is discussed. The effect of the presence of large quantities of ammonium nitrate and sodium nitrate in WD samples on the determination of uranium is also discussed. The results are compared with those obtained by volumetry and X-ray fluorescence spectrometry for higher concentrations of uranium and by extraction-spectrophotometry (ethyl acetate-thiocyanate method) for lower concentrations. Relative standard deviation of 1% and 5% for high and low concentrations, respectively, were obtained, which are adequate as far as process stream samples are concerned. The compared results are in fair agreement. The problems associated with the determination of uranium in these process streams are discussed. Experimental results for 10 different process streams normally encountered in a uranium extraction plant are tabulated.     

Organic solvent extraction of uranium from alkaline nuclear waste

There are proliferation issues with the Plutonium Uranium Redox Extraction process due to the possibility of recovering plutonium. The objective of this research was to evaluate different organic extraction ligands that can remove uranium from the nuclear waste and to determine the most effective organic solvent for extracting uranium only, from alkaline media. The results indicate that Alamine 336 in xylene has zero (0%) extraction capability for surrogate fission products at an optimum extraction time of 15 min. Aliquat 336 in xylene has an extraction percentage of 72% for uranium in 60 min. However, Aliquat 336 in toluene extracted 82% of the uranium from the feed solution after 30 min, decreasing to 76% after 60 min.

     

In-line phase separator for microfluidic solvent extraction of uranium

Experiments are carried out to study the separation of liquid-liquid dispersion generated at a microfluidic junction by using an in-line phase separator. The phase separator comprises a metallic mesh sandwiched between two flow channels. Dispersion generated at the microfluidic junction is fed to the upper flow channel of the in-line phase separator. Continuous phase permeates through the metallic mesh into the lower flow channel and gets separated from the dispersed phase. The effects of operating parameters (flow rates of the aqueous and organic phases), flow channel geometry and mesh properties (pore size and thickness) on phase separation are studied. After identification of operating window in which complete phase separation is achieved, mass transfer experiments are performed to demonstrate intensified uranium extraction using a micromixer and in-line phase separator.

     

Recovery of uranium and thorium from zirconium oxychloride by solvent extraction

A solvent extraction process is proposed to recover uranium and thorium from the crystal waste solutions of zirconium oxychloride. The extraction of iron from hydrochloride medium with P350, the extraction of uranium from hydrochloride with N235, and the extraction of thorium from the mixture solutions of nitric acid and the hydrochloric acid with P350 was investigated. The optimum extraction conditions were evaluated with synthetic solutions by studying the parameters of extractant concentration and acidity. The optimum separation conditions for Fe (III) are recognized as 30% P350 and 4.5 to 6.0 M HCl. The optimum extraction conditions for U (VI) are recognized as 25% N235 and 4.5 to 6.0 M HCl. And the optimum extraction conditions for Th (VI) are recognized as 30% P350 and 2.5 to 3.5 M HNO₃ in the mixture solutions. The recovery of uranium and thorium from the crystal waste solutions of zirconium oxychloride was investigated also. The results indicate that the recoveries of uranium and thorium are 92 and 86%, respectively.     

Selective actinide solvent extraction used in conjunction with liquid scintillation

New commercial liquid scintillation counters allow rapid / measurements. Associated with liquid-liquid extraction techniques, rapid and selective actinide analyses are possible. Uranium, thorium and americium extractions with tri-n-octylphosphine oxide (TOPO) in toluene have been investigated. Detection limits of 40 mBq·l^–1 for -emitters are currently obtained with a Packard 2550 TR/AB^TM liquid scintillation analyzer.     

Determination of alpha-emitting uranium isotopes in soft tissues by solvent extraction and alpha-spectrometry

A radiochemical procedure has been developed for the determination of alpha-emitting isotopes of uranium ((238)U, (235)U and (234)U) in soft tissues. Known amounts of sample are spiked with (232)U internal tracer and wet-ashed. Uranium is co-precipitated with iron hydroxide as carrier, and extracted into 20% trilaurylamine solution in xylene after dissolution of the precipitate in 10M hydrochloric acid. The uranium, after stripping into an aqueous phase, is electro-deposited onto a platinum disc and counted by alpha-spectrometry. The radiochemical recovery ranges from 60 to 85% for bovine liver samples. The average radiochemical recoveries for human tissues vary from 53 to 78%.     

Separation and solvent extraction of vanadium and uranium with n-propyl 2,3,4-trihydroxybenzoate

A spectrophotometric method is described for the separation and determination of trace quantities of vanadium(IV) and (V) from uranium(VI). Vanadium is selectively separated from uranium by extraction at pH 6.5 into n-propyl 2,3,4-trihydroxybenzoate (PTB) dissolved in t-pentanol. Up to 120 microg of vanadium can be determined by measuring the absorbance of the blue complex in the organic phase at 585 nm. Uranium(VI) remains in the aqueous layer and can be determined spectrophotometrically by its reaction with PTB in aqueous acetone to produce a brown-red colour at pH 7.6-8.8. Solutions containing 25-275 microg of uranium absorb at 370-380 nm according to Beer's law. By modification, this procedure can be used for the determination of the two metals in native phosphate rocks. The effects of diverse ions on the determination of vanadium and uranium have also been examined.     

Separation of rare earth elements from uranium by solvent extraction and ion exchange

The detection limit of⁹⁹Tc in (,) radio-activation analysis was determined in the presence of molybdenum and compared with that of⁹⁹Tc in pure materials in the previous paper. The isotopic ratio of molybdenum in a⁹⁹Mo–^99mTc generator column could be simultaneously determined by photon activation analysis.     

An absorbing microwave micro-solid-phase extraction device used in non-polar solvent microwave-assisted extraction for the determination of organophosphorus pesticides

A single-step extraction-cleanup method, including microwave-assisted extraction (MAE) and micro-solid-phase extraction (μ-SPE), was developed for the extraction of ten organophosphorus pesticides in vegetable and fruit samples. Without adding any polar solvent, only one kind of non-polar solvent (hexane) was used as extraction solvent in the whole extraction step. Absorbing microwave μ-SPE device, was prepared by packing activated carbon with microporous polypropylene membrane envelope, and used as not only the sorbent in μ-SPE, but also the microwave absorption medium. Some experimental parameters effecting on extraction efficiency was investigated and optimized. 1.0 g of sample, 8 mL of hexane and three absorbing microwave μ-SPE devices were added in the microwave extraction vessel, the extraction was carried out under 400 W irradiation power at 60 °C for 10 min. The extracts obtained by MAE-μ-SPE were directly analyzed by GC–MS without any clean-up process. The recoveries were in the range of 93.5–104.6%, and the relative standard deviations were lower than 8.7%.     

Determination of uranium in process stream solutions from uranium extraction plant employing energy dispersive X-ray fluorescence spectrometry

Energy dispersive X-Ray fluorescence (EDXRFS) method is developed and standardized for the determination of uranium on routine basis in various process stream solutions, covering a vide range of concentrations from 0.1 to 400?g?L^?1, from an Uranium Extraction Plant at Nuclear Fuel Complex. The method has been applied to aqueous stream samples. Except for dilution, no much sample preparation was involved in the analysis and accordingly the experimental parameters were optimized. The calibration curve in the range of 0.1?C10?g?L^?1 of U was drawn manually using synthetic standard solutions prepared from U₃O₈ powder and L?? (13.61?keV) line of uranium was used for the measurements. The results from EDXRFS method are compared with other methods and are found to be in good agreement. The EDXRFS measurements carried over a range of 0.1?C350?g?L^?1 of uranium have shown a RSD of ±1?C5%. Also, the limitations of reported methods in literature and the advantages of present method are highlighted in the paper.     

Insight of solvent extraction process: Reassessment of trace level determinations

Solvent extraction is hoary yet modern technique with great scope of research due to the various intriguing phenomena in the system. Tri-n-butyl phosphate (TBP) is a well known extractant which has been extensively used for separation of uranium matrix prior to elemental profiling. In this paper, one of the impurities namely Fe is being considered as it posed a challenge to the separation due to its co-extraction with TBP along with uranium. In these studies, for the first time, the existence of cation-cation inner sphere complexes between the UO₂²⁺and Fe³⁺ ions in both aqueous and organic phases have been establisted in addition to the selective separation of iron from uranium sample matrix using only TBP. The data from both spectrophotometric and thermophysical studies corroborated one another confirming the presence of cation-cation interactions (CCIs). The developed solvent extraction with only TBP showed almost no interferences on the iron extraction from matrix uranium and other co-ions like aluminum and copper. This has been the first time application of pure TBP for selective removal of iron from uranium samples. The procedure possessed excellent reproducibility and robustness.     

溶剂萃取动力学的研究 II: 三辛基氧化膦从盐酸体系中萃取铀(IV)的速率

The kinetics of the oxtraction of U(IV) chloride in the TOPO-HCl system has been studied using the single drop technique, The effects of the concentrations of U(IV, TOPO and HCl on the extraction rate for U(IV) have been examined. The extraction rate measured were found to be of first order with respect to (U(IV)) and (TOPO) (0). Moreover, the rate varied with (HCl)^3^/^2 between 2-7M hydrochloric acid. The extraction rate equation can be written as R=K(U(IV))(TOPO)(0) The rate constant K was evaluated to be 3.7X10^-^5 at 3M HCl and 15`C. The extraction rate was increased with increasing temperature. The apparent activation energy was found to be 10.8 kcal/mol between 15 to 45`C. It is suggested that the rate-controlling step may be the chemical reaction of UCl4 with TOPO at the interface and the formation of the interfacial complex UCL4.TOPO.     

Separation of high purity gadolinium for reactor application by solvent extraction process

A solvent extraction process for the production of nuclear grade Gd₂O₃ for its applications in pressurized heavy water reactor (PHWR) from a crude concentrate of rare earths containing ~70 % Gd₂O₃ has been developed and tested on bench-scale and continuous counter-current operations. The separation of gadolinium from other rare earths with similar chemical properties has been successfully accomplished by adopting a dual cycle solvent extraction employing 2-ethylhexylphosphonic acid, mono-2 ethylhexyl ester (EHEHPA) as an extractant. Taking advantage of the extraction order of rare earths with EHEHPA, in the first cycle, heavy rare earths including Tb, Dy and Y were separated in the product strip solution, while gadolinium was separated in the raffinate solution along with samarium and neodymium. In the second cycle, gadolinium was purified to the extent of >99.5 % with respect to other rare earths. Effects of process variables such as aqueous acidity, phase ratio, metal concentration in the aqueous feed, scrubbing and stripping acidity etc. on separation of terbium and other heavy rare earths in the first cycle and upgrading the purity of Gd₂O₃ in the second cycle have been investigated. The experimental conditions were optimized using computer simulation and validated by bench scale counter-current operations. Under optimized conditions of process parameters, continuous operations of mixer settler yielded kilogram quantity of nuclear pure Gd₂O₃ which was subsequently converted to gadolinium nitrate for PHWR application. The overall recovery was found to be >98 %.     

Some solvent effects on the solvent extraction of 8-quinolinol

The distribution constants of 8-quinolinol between water and a series of substituted aliphatic hydrocarbons, at 25 degrees , are reported. The results are discussed in terms of dielectric constant and solubility parameter of the solvents. For 8-quinolinol, and possibly for its chelates, bromochloromethane, dibromomethane and chloroform seem to be about the best solvents, in that order. Among the solvents studied, chloroform shows significantly higher values than expected; the deviation may be explained as a specific interaction of the hydrogen- bonding type.     

Determination of optimum process conditions for solvent extraction of thorium using Taguchi method

Solvent extraction of thorium was studied using Taguchi method. The effect of various parameters such as acid types (sulfuric, nitric, hydrochloric, sulfuric + nitric) and their concentrations from 0.001 to 4 M, initial thorium concentration (0.0001, 0.001, 0.01, 0.1 M) and solvent type (TBP, D₂EHPA, Cyanex921, Cyanex272) in the ranges of 0.001 to 1 M on thorium extraction efficiency were investigated. The maximum extraction of thorium was obtained while 0.001 M hydrochloric acid, 0.001 or 0.01 M thorium and Cyanex272 were used. Under these optimum conditions, the extraction percent and distribution coefficient of thorium were 98.7% and 73.8, respectively. Compared with the hydrochloric aqueous solution, the nitric acid system showed less variation in the extraction of thorium. The proposed process has been applied for the separation of Th(IV), U(VI), La(III), and Ce(III) from synthetic solution same as thorium ores (monazite).     

柴胡中柴胡皂甙a的超声辅助溶剂提取

以溶剂提取法为基础,以超声波为辅助手段,对柴胡中的有效成分进行了提取.通过对提取液中柴胡皂甙a量的测定,研究了超声功率、提取温度、提取时间和样品浸渍时间等条件对提取效果的影响,优选出超声辅助溶剂提取的最佳条件为超声功率50%、提取温度50 ℃、提取时间20 min、样品浸渍时间24 h.实验结果表明,超声辅助溶剂提取比普通的溶剂提取具有更高的提取效率.     

Development of a micro-mixer-settler for nuclear solvent extraction

Nuclear solvent extraction was traditionally performed with packed columns, pulse columns, mixer-settlers and centrifugal extractors. However for rapid separations at micro-flow level, micro mixer-settlers were desired and in the past, few of them were actually designed and operated in nuclear solvent extraction research. In the current era of micro-reactor and microchannel devices, there is a renewed interest for micro-mixer-settlers for costly solvents and specialty solutes where small flow-rate is not an issue. In this article, development of a simple but effective micro-mixer-settler for nuclear solvent extraction is reported. The developed unit was tested with 30% TBP/n-dodecane/nitric acid system and in both the regimes of mass transfer c → d (mass transfer from continuous phase to dispersed phase, also written as c → d) and d → c (mass transfer from dispersed phase to continuous phase, also written as d → c) nearly 100% efficiency was observed in extraction as well as stripping modes of operation.