The Use of 24-Crown-8's in the Solvent Extraction of CsNO3 and Sr(NO3)2

Abstract

The feasibility of a solvent extraction process for removing strontium and cesium from acidic high activity nuclear waste is shown. Both strontium and cesium can be extracted from an aqueous HNO₃ phase containing the metal nitrates into an organic phase containing kerosene or CCl₄ as a diluent and complexing agents dissolved in the diluent. The most promising results obtained thus far have required the use of a mixture of three metal complexing agents: tributyl phosphate, di-2-ethylhexyl phosphoric acid, and 4,4′(5′)-di-tert-butylbenzo-24-crown-8. The highest distribution coefficients obtained (organic/aqueous) were 1.45 ± 0.05 for Cs⁺ and 200 for Sr²⁺. The extraction is reversible and is strongly dependent on the pH of the aqueous phase. The metal can be removed from the organic phase by lowering the pH to 1, while raising the pH above 3 causes the metal to return to the organic phase. The utility of this extraction technique for nuclear processing will depend on the radiation stability of the complexing agents and the degree of selectivity obtained when extracting strontium and cesium from mixed fission products.     

Extraction of Cs+ and Sr2+ from HNO3 Solution Using Macrocyclic Polyethers

Abstract

A series of crown compounds has been studied in connection with the development of a solvent extraction process for removing Cs⁺ and Srs²⁺ from acidic high activity nuclear waste. Crown compounds were investigated because of their ability to form organic soluble complexes with the alkali metals and the alkaline earth metals. The solvent (tributyl phosphate and kerosene) was chosen because of its compatibility with the Purex process currently used at the Savannah River Plant for plutonium and uranium purification. The crown compounds were found not to be sufficiently strong complexing agents to extract these metals from an aqueous phase with an inorganic anion such as nitrate or chloride. However, the use of large organic soluble anions which also functioned as liquid ion exchangers made it possible to extract Cs⁺ from 3 M HNO₃ while leaving Sr²⁺ and La³⁺ behind. The use of .02 M bis-(4,4′(5′)-[q-hydroxyheptyl]-benzo)-18-crown-6 in 0.076 M (5 vol-%) didodecylnaphthalene sulfonic acid (DNS)-27 vol-% TBP-68 vol-% kerosene gave the most favorable results for cesium extraction. The two phases separated cleanly and rapidly, yielding a distribution coefficient of 2.0 org/aq from 3 M HNQ₃. Strontium and lanthanum did not extract significantly at this acid concentration. The distribution data in the low acid region (10^?4 M) are best explained by steric hindrance effects. The lanthanum did not extract at any acid concentration while the strontium extracted very well by a liquid ion-exchange mechanism but the addition of the crown compound did not improve the distribution. The addition of the crown compound improved the Cs⁺ distribution markedly in the low acid region even though the Cs⁺ diameter is larger than the 18-crown-6-crown cavity while Sr²⁺ should fit very well.     

Extraction of strontium ion from sea water by contained liquid membrane permeator

To develop a liquid membrane permeator that extracts strontium ion from sea water effectively and continuously, we investigated the extraction of strontium ion from artificial and natural sea water in a contained liquid membrane permeator. The permeator consists of a liquid membrane and two cells for aqueous solutions. The liquid membrane containing D₂EHPA(di-2-ethylhexyl-phosphoric acid) and DCH18C6(dicyclohexano-18-crown-6) is trapped between two hydrophobic microporous polyethylene films and separates sea water and the 0.2 M H₂SO₄ aqueous stripping solution. The effects of various operating parameters on the extraction of strontium ion were experimentally examined. The extractant of DCH18C6 -D₂EHPA mixture in kerosene had a synergistic effect on the extraction of strontium ion. The permeator extracted strontium ion from sea water effectively and continuously with long membrane lifetime.     

Influence of the Extractant on Strontium Transport from Reprocessing Concentrate Solutions through Flat-Sheet Supported Liquid Membranes

Abstract

The influence of the extractant on strontium transport through a flat-sheetsupported liquid membrane from nuclear fuel reprocessing concentrate solutions to demineralized water has been studied using two crown ethers of different lipophilicity: dicyclohexano-18-crown-6 (DC18C6) and di-tert-butylcyclohexano-18-crown-6 (DtBuC18C6). The distribution coefficients of strontium showed that DC18C6 is a better strontium extractant than DtBuC18C6 in the entire range of crown-ether concentration studied. No effect of association between the DC18C6 molecules was observed even at high concentrations. However, the strong lipophilic character of DtBuC18C6 led to a distribution coefficient of this extractant 10 times higher than the distribution coefficient of DC18C6. Thus, the membrane concentration of DtBuC18C6 was approximately 10 times higher than that of DC18C6. This leads to greater strontium permeability for DtBuC18C6, even though DC18C6 had a greater capacity for strontium extraction and a higher diffusion coefficient in the membrane due to the smaller molar volume of this crown ether. The precipitation of a white solid was observed when the synthetic concentrate was mixed with an organic phase containing DtBuC18C6 dissolved in n-hexylbenzene (0.7 mol·L^?1 isotridecanol), causing a decrease of strontium permeability. In this case, DC18C6 had the greatest strontium permeability.     

Removal of 230Th by solvent extraction from high grade uranium ore liquid tailings to arrest 226Ra production in the tailings

Primene JM‐T, D2EHPA and TBP were used as solvents to extract ²³⁰Th from sulphuric acid uranium leachate and barren solutions from a Saskatchewan, Canada uranium mill. This was done with the objective of eliminating the source for ²²⁶Ra production in the tailings in perpetuity. A 0.1 vol% Primene JM‐T, 5 vol% isodecanol (modifier), and kerosene diluent mixture was found to completely remove thorium from the solutions. The thorium was stripped from the loaded organic with a 15 wt% ammonium carbonate solution.     

A Recovery Process of Strontium from Acidic Nuclear Waste Streams

Abstract

A process combining liquid–liquid extraction with ion exchange for strontium traces removal in the presence of an excess of sodium concentrations is described. In this continuous process, strontium is extracted from acidic (0.9 M) solution using a substoichiometric amount of dicyclohexano-18-crown-6 (0.1 M in CHCl₃). Extracted strontium is readily stripped from an organic phase with water and concentrated onto an ion exchanger. This process allows a high strontium decontamination factor (250) with a very important extraction factor (5000).     

A NOVEL STRONTIUM-SELECTIVE EXTRACTION CHROMATOGRAPHIC RESIN*

ABSTRACT

The effect of nitric acid concentration on the selectivity of a novel extraction chromatographic resin consisting of an octanol solution of 4,4′(5′)-bis(t-butyl-cyclohexano)-18-crown-6 sorbed on an inert polymeric support for strontium over a number of alkali, alkaline earth, and other metal cations was evaluated. The effect of macro quantities of selected elements on strontium retention by the resin was also examined. The resin is shown to exhibit excellent selectivity for strontium over nearly all of the test elements; only lead and tetravalent neptunium, polonium, and plutonium show significant affinity for the material. In addition, concentrations of calcium or sodium ion up to ～ 0.1 M. are shown not to diminish the sorption of strontium appreciably. Several useful radiochemical separation schemes devised on the basis of the results obtained are described.     

Efficient co-extraction of strontium and cesium from nitric acid medium by mixtures of di-tert-butylcyclohexano-18-crown-6 and 1,3-di(2-propoxy)calix[4]arene-crown-6 in n-octanol

The co-extraction of strontium and cesium from nitric acid medium by di-tert-butylcyclohexano-18-crown-6 (DtBuCH18C6) and 1,3-di(2-propoxy)calix[4]arene-crown-6 (iPr-C[4]C-6) in n-octanol was studied. The effects of contact time, nitric acid concentration, extractant concentration and temperature on the co-extraction behavior were systematically investigated. Effective extraction of the two metals was achieved under a variety of conditions. The co-extraction from a simulated high-level liquid waste (HLLW) was also conducted, and strontium and cesium could be selectively extracted in the presence of a large number of other metals. Results in this work illustrate the feasibility of partitioning radioactive strontium and cesium simultaneously from HLLW by a mixture of DtBuCH18C6 and iPr-C[4]C-6 in n-octanol.     

SELECTIVE SEPARATION OF URANYL ION FROM TRU'S IN A COMBINED SOLVENT EXTRACTION PROCESS USING TETRAHYDROFURAN-2,3,4,5-TETRACARBOXYLICACID

ABSTRACT

Selective partitioning of uranyl from transuranic elements in a solvent extraction system which employs a neutral organophosphorus extractant and an aqueous complexant has been demonstrated in a previous report. The extractant solution combines octyl(phenyl)-N,N-diisobutylcarbamoylrnethylphosphine oxide (CMPO), diamyt(amyl)phosphonate (or tributylphosphate), and di(t-butylcyclohexano)-18-crown-6 in Isopar L, and is designed for simultaneous removal of strontium, technetium, lanthanides and actinides from radioactive wastes. The aqueous complexant is tetrahydrofuran-2,3,4,5-tetracarboxylic acid (THFTCA). In this report, the separation of UO₂ ²⁺ from Np(IV), Eu(III), Am(III), and Pu(IV) using the Combined Process Solvent has been optimized. Potentiometric titration and NMR spectroscopic results describe the distribution of THFTCA into the organic phase as a function of acidity and [THFTCA]. Further potentiometric titration experiments have determined the stoichiometry and stability of uranyl complexes in the aqueous phase. The thermodynamic data indicate that the uranyl complexes are anomalously weak which partially accounts for the selectivity. Ternary complexes involving, UO₂ ²⁺ CMPO, and THFTCA in the extractant phase also appear to play a role.     

EXTRACTION OF CESIUM NITRATE FROM CONCENTRATED SODIUM NITRATE SOLUTIONS WITH 21-CROWN-7 ETHERS: SELECnVITY AND EQUILIBRIUM MODELING

ABSTRACT

The extraction of cesium nitrate from a high concentration of sodium nitrate by a family of 21-crown-7 ethers in 1,2-dichloroethane has been investigated. Dibenzo-21-crown-7 (DB21C7) and bis[4(5),4′(5′)-rm-butylbenzo]-21-crown-7 (BtBB21C7) ethers have higher selectivity for cesium but lower extraction efficiency than dicyclohexano-21-crown-7 (DC21C7) ether. As measured by the distribution coefficient ratio D_cs/D_Na, the cesium selectivity averaged 78 and 93 for DB21C7 and BtBB21C7, respectively. However, in the case of DC21C7, the cesium selectivity was lower and decreased approximately three-fold from 10 to 3 as cesiüm loading increased. Alkyl substitution on the benzo group has only a small effect on the extraction behavior. It was shown by use of the equilibrium modeling program SXLSQI that the extraction of sodium and cesium could be adequately modeled by augmenting the previously determined cesium nitrate equilibrium model with a 1:1 Na⁺:crown organic-phase complex. No evidence for a mixed-metal species was found. In accord with our previous study, cesium nitrate extraction entails formation of a 1:1 Cs⁺:crown complex, but a minor 1:2 complex also forms in the case of DC21C7. Although the sodium and cesium made possible by the U. S. Department of Energy Postgraduate Research Program administered by the Oak Ridge Associated Universities.     

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.     

Influence of Membrane Solvent on Strontium Transport from Reprocessing Concentrate Solutions through Flat-Sheet-Supported Liquid Membranes

Abstract

The influence of membrane solvents on strontium transport from nuclear fuel reprocessing concentrate solutions to demineralized water through a flat-sheet-supported liquid membrane has been studied using dicyclohexano-18-crown-6 as the extractant and Celgard 2500 as the solid support. Even though the highest values of the distribution coefficients of strontium were obtained with nitrated compounds as membrane solvents, strontium permeabilities were determined only when a membrane solvent was used for which stable SLMs were obtained. Among the latter, the use of 4-nonylphenol as a phase modifier is not satisfactory for long-term strontium transport experiments due to its reactivity with the nitric acid of the aqueous feed solution. We achieved a good correlation between strontium permeability and two parameters of the membrane diffusion coefficient (molecular weight and viscosity of the membrane solvent) for aromatic solvents modified with isotridecanol or 1-decanol. The best results were obtained with n-hexylbenzene (0.7 mol·L^?1 isotridecanol) which should lead to a high strontium decontamination by hollow-fiber-supported liquid membranes. The transport of nitric acid and nonradioactive cations through the membrane was not greatly influenced by the membrane solvent used.     

磷酸三丁酯/甲基异丁基酮萃取锂的特性

为从含有Li和Mg的水溶液中选择性地萃取Li,在FeCl3存在的条件下,以磷酸三丁酯(TBP)为萃取剂,以煤油为稀释剂,在萃取平衡时出现第3相的情况下研究了有机相中Li和Fe的浓度,结果表明萃合物主要集中在中间有机相.针对萃取过程中的分相问题,以TBP为萃取剂,比较了甲基异丁基酮(MIBK)、乙酸乙酯和煤油作为稀释剂对...     

Reducing the Long-Term Hazard of Reactor Waste Through Actinide Removal and Destruction in Nuclear Reactors

Abstract

Public opposition to nuclear power has focused on the long-term risks from reactor waste. In the Purex process used in Europe, this waste is a concentrated nitric acid solution containing all nonvolatile fission products and the actinides Np, Am, and Cm, plus smaller amounts of U and Pu.

Techniques have recently been described which guarantee an absolutely safe containment of this high-active waste (HAW) for about 1000 years. At longer times, the risk to the biosphere is dominated by the actinides. If these actinides are isolated from the rest of the HAW and destroyed through nuclear incineration, the long-term risks of the HAW will be dramatically reduced.

This paper presents a detailed scheme for removing the actinides from the Purex-HAW solution. In principle, the process consists of three different solvent extraction cycles, using HDEHP and TBP in three successive steps. The scheme has been tested on a synthetic HAW solution containing all fission products and actinides (except Z ≥96, Cm) using laboratory-scale mixer-settler batteries. Results from runs on old Purex waste are also presented.

If applied to fresh Purex waste, the process will encounter problems due to radiation damage to the reagents. In practice, this difficulty can be circumvented by using short contact times in the solvent extraction process. Extremely rapid multistage solvent extraction separations can be carried out by the SISAK technique (i.e., batteries of static mixers and special centrifugal separators). This technique is also described.     

Compositional Characterization of Organic Phases after the Phase Splitting in the Extraction of Th(NO3)4 by 1.1 M Tri-n-butyl phosphate/n-Alkane

Third phase formation in the extraction of Th(IV) by 1.1 M solutions of tri-n-butyl phosphate (TBP) in n-decane and n-hexadecane from Th(NO₃)₄ solution in 1 M HNO₃ has been investigated as a function of equilibrium aqueous phase Th(IV) concentration ([Th(IV)]_aq,eq) to estimate the concentrations of Th(NO₃)₄, HNO₃, and TBP in the third phase (TP) and the diluent-rich phase (DP). In this connection, new methods for the estimation of TBP in the organic phases after the phase splitting have been developed by exploiting the linear relationships of the density and refractive index of the solvent, the limiting organic concentration (LOC) for the third phase formation in the extraction of Th(IV) from solution with near-zero free acidity with TBP concentration in the solvent. TBP concentrations estimated by the above-mentioned methods have been validated by nitric acid (8 M) equilibration method. Experimental values for the concentration of TBP in the TP and DP for 1.1 M TBP/n-alkane–Th(NO₃)₄/1 M HNO₃ systems have been compared with the values computed based on a model proposed earlier. In addition, the density of organic phases and the ratio of the volume of the DP to that of the TP have been measured for the above-mentioned systems as a function of [Th(IV)]_aq,eq at 303 K.     

Solvent Extraction of Au(I) from Auro‐Cyanide Solution with Cetyltrimethylammonium Bromide/Tri‐n‐Butyl Phosphate System using Column‐Shaped Extraction Equipment

Abstract

Solvent extraction of Au(I) from alkaline cyanide solution containing several milligram per liter of gold was investigated with column‐shaped extraction equipment using tri‐n‐butylphosphate (TBP) as extractant with addition of quaternary ammonium salt, cetyltrimethylammonium bromide (CTAB), directly into the aurous aqueous phase in advance. The influences of the volume of TBP and the NaCl concentration in the aurous aqueous phase on Au(I) extraction were investigated. The experimental results for treating 50 L of synthetic auro‐cyanide solution containing 10 mg/L Au(I) and for treating real auro‐cyanide leaching liquor by CTAB/TBP system were reported. The results obtained establish that the column‐shaped extraction equipment was suitable for extracting Au(I) from low content auro‐cyanide solution at high aqueous/organic phase ratio, and that more than 97% of gold(I) could be extracted while the Au(I) concentration in the raffinate was less than 0.3 mg/L. In addition, the stripping of Au(I) from the loaded organic phase and the recycle of the organic phase were also discussed.     

Synergistic extraction and separation of Fe(III) and Zn(II) using TBP and D2EHPA

Waste chloride pickle liquors from hot-dip galvanizing plants, steel plants and flue dust contain reasonable amounts of heavy metals such as Zn, Cr, Ni, etc. Iron is invariably associated with most of these materials and comes into solution during leaching. Thus, the synergistic extraction of zinc(II) and iron(III) from leach solutions in tri-n-butyl phosphate (TBP)–di(2-ethylhexyl) phosphoric acid (D2EHPA) system diluted in kerosene was investigated. The Zn and Fe concentrations in the leach liquor used in the present study were 2 g/L. Experiments were carried out in the pH range of 0.5–4.0, temperature of 25°C, using sole D2EHPA, sole TBP and D2EHPA–TBP mixtures at different ratios. Results showed that the co-extraction of zinc(II) and iron(III) increased with increasing equilibrium pH using D2EHPA. It is demonstrated that the mixtures of TBP and D2EHPA are more efficient and selective than D2EHPA alone. At low pH values, the separation factor is low when pure D2EHPA is used as an extractant; however, using TBP as a synergist, the separation factor increases and results in a better separation of zinc from iron. Increasing TBP to D2EHPA ratios in the organic phase caused a slight shift to the right in the extraction isotherm of iron and a marked shift to the right in the extraction isotherm of zinc, and the maximum separation factor of 13.3 × 10³ was achieved at a TBP to D2EHPA volume ratio of 4:1 (0.58 M TBP: 0.12 M D2EHPA). Furthermore, the effect of equilibrium pH, organic to aqueous phase ratio and Cl^? concentration on the selective extraction was investigated. Using two extraction stages at the O/A ratio of 2:1 and pH_e (equilibrium pH) of 3 and 1 for zinc and iron, respectively, 99% of zinc(II) and 96.25% of iron(III) were extracted.     

Evaluation of the SREX Solvent Extraction Process for the Removal Of 90Sr and Hazardous Metals from Acidic Nuclear Waste Solutions Containing High Concentrations of Interfering Alkali Metal Ions

Abstract

The SREX process, which was developed at Argonne National Laboratories, has been evaluated for its effectiveness for the decontamination of radioactive liquid waste at the Idaho Chemical Processing Plant located at the Idaho National Engineering Laboratory. The extraction solvent consists of 0.15 M 4′,4′,(5′)-di-(t-butyl-dicyclohexo)-18-crown-6 in either 1.2 M TBP/Isopar L®. Suppressed extraction due to matrix interferences limits D_Sr values to the range of 3-4 in batch extraction experiments. The SREX solvent has been shown to be effective in the removal of non-radioactive Pb from liquid wastes, in addition to the extraction of ⁹⁰Sr. The information from this study has been used to develop a proposed flowsheet for the treatment of liquid waste in centrifugal contactors.     

Selective Separation of Gallium from Acidic Leach Solutions by Emulsion Liquid Membranes

Abstract

The separation and concentration of gallium from acidic leach solutions, containing various other ions such as iron, cobalt, nickel, zinc, cadmium, lead, copper, and aluminium, by an emulsion liquid membrane (ELM) technique using tributyl phosphate (TBP) as carrier has been presented. Liquid membrane consists of a diluent, a surfactant (ECA 4360J), and an extractant (TBP), and 0.1 M HCl or 0.1 M H₂SO₄ were used as the stripping solution. The important variables governing the permeation of gallium and their effect on the separation process have been studied. These variables were membrane type and composition, mixing speed, diluent type, surfactant concentration, extractant concentration, HCl concentration in the feed, acid type of stripping phase, feed concentration, and treatment ratio. The optimum conditions were determined. It was possible to selectively extract 96.0% of gallium from the acidic leach solutions, containing Fe, Co, Ni, Zn, Cd, Pb, Cu, and Al, at the optimum conditions.     

Batch Comparisons of Sr and Ba Retention and Capacities on AnaLig® Sr-01 and Eichrom Sr Resins

The isolation of strontium from aqueous media may be required for environmental monitoring or nuclear forensics sample analyses.^[1–4] The prevalent method is to use a strontium selective extraction chromatographic resin. Two such products are Eichrom Technologies Sr resin and IBC Advanced Technologies AnaLig® Sr-01 resin. Eichrom Technologies Sr resin utilizes a crown ether (4,4′(5′)-di-t-butylcyclohexano-18-crown-6) diluted in 1-octanol and coated onto Amberchrom^TM CG71 resin, and IBC Advanced Technologies AnaLig® Sr-01 resin features a proprietary extractant covalently tethered to a silica support. The use of each resin is reported in the literature; Eichrom Sr Resin specifications, including the resin’s weight distribution ratio and capacity factor for analytes, have been reported but no such data have been published for IBC Analig® Sr-01 resin. In this work, batch studies were completed to determine the capacity and weight distribution ratio of both AnaLig® Sr-01 and Eichrom Sr resins for strontium and barium. This work shows that both resins retained Sr from aqueous samples, but Eichrom Sr resin provided superior Sr/Ba separation compared with Analig® Sr-01 resin.