Batch and dynamic extraction of uranium(VI) from nitric acid medium by commercial phosphinic acid resin,Tulsion CH-96

Batch and dynamic extractions of uranium(VI) in 10⁻³–10⁻²M concentrations in 3–4M nitric acid medium have been investigated using a commercially available phosphinic acid resin (Tulsion CH-96). The extraction of uranium(VI) has been studied as a function of time, batch factor (V/m), concentrations of nitric acid and uranium(VI) ion. Dual extraction mechanism unique to phosphinic acid resin has been established for the extraction of uranium(VI). Distribution coefficient (K _d ) of uranium(VI) initially decreases with increasing concentration of nitric acid, reaches a minimum value at 1.3M, followed by increases in K _d . A maximum K _d value of ∼2000 ml/g was obtained at 5.0M nitric acid. Batch extraction data has been fitted into the linearized Langmuir adsorption isotherm. The performance of the resin under dynamic extraction conditions was assessed by following the breakthrough behavior of the system. Effect of flow rate, concentrations of nitric acid and uranium ion in the feed on the breakthrough behavior of the system was studied and the data was fitted using Thomas model.     

Extraction with long-chain amines-II Extraction and colorimetric determination of chromate

Highly selective extraction of chromate from slightly acidic solutions (0.1-0.2M sulphuric acid) with a chloroform solution of trioctylamine (Alamine 336-S) or trioctylmethylammonium chloride Aliquat 336-S) is described. Many metals such as iron, nickel, cobalt, copper, alluminium, zinc, are not extracted, even if present in large concentrations. Coextraction of vanadium(V) and uranium(VI) is prevented by addition of sodium chloride. Traces of extracted molybdenum are scrubbed with ammonium oxalate. Final determination of chromium is based on measurement of the absorbance of the extract at 445-450 nm.     

Efficient uranium(VI) biosorption on grapefruit peel: kinetic study and thermodynamic parameters

The uranium(VI) biosorption by grapefruit peel was studied from aqueous solutions. Batch experiments was conducted to evaluate the effect of contact time, initial uranium(VI) concentration, initial pH, adsorbent dose, salt concentration and temperature. The equilibrium process was well described by the Langmuir, Redlich–Peterson and Koble–Corrigan isotherm models, with maximum sorption capacity of 140.79 mg g⁻¹ at 298 K. The pseudo second order model and Elovish model adequately describe the kinetic data in comparison to the pseudo first order model and the process involving rate-controlling step is much complex involving both boundary layer and intra-particle diffusion processes. The effective diffusion parameter D _i and D _f values were estimated at different initial concentration and the average values were determined to be 1.167 × 10⁻⁷ and 4.078 × 10⁻⁸ cm² s⁻¹. Thermodynamic parameters showed that the biosorption of uranium(VI) onto grapefruit peel biomass was feasible, spontaneous and endothermic under studied conditions. The physical and chemical properties of the adsorbent were determined by SEM, TG-DSC, XRD and elemental analysis and the nature of biomass–uranium (VI) interactions was evaluated by FTIR analysis, which showed the participation of COOH, OH and NH₂ groups in the biosorption process. Adsorbents could be regenerated using 0.05 mol L⁻¹ HCl solution at least three cycles, with up to 80% recovery. Thus, the biomass used in this work proved to be effective materials for the treatment of uranium (VI) bearing aqueous solutions.     

Preconcentration of uranium(VI) and thorium(IV) from aqueous solutions using low-cost abundantly available sorbent

Olive cake as low-cost abundantly available sorbent has been characterized by N₂ at 77 K adsorption, porosity analysis, elemental analysis and IR spectra and has been used for preconcentrating of uranium(VI) and thorium(IV) ions prior to their determination spectrophotometrically. The optimum pH values for quantitative sorption of U(VI) and Th(IV) are 4–7 and 3–7, respectively. The enrichment factor for the preconcentration of U(VI) and Th(IV) were found to be 125 and 75 in the given order. The sorption capacity of olive cake is in the range of 2,260–15,000 μg g⁻¹ for Th(IV) and in the range of 1,090–17,000 μg g⁻¹ for U(VI) at pH 3–7. The sorbent exhibits good reusability and the uptake and stripping of the studied ions were fairly rapid. The elution of U(VI) and Th(IV) was performed with 0.3–1 M HCl/1–2 M HNO₃ and 0.3–0.8 M HCl/1 M HNO₃, respectively. The precision of the method was 1.8 RSD% for U(VI) and 2.5 RSD% for Th(IV) in a concentration of 1.00 μg mL⁻¹ for 10 replicate analysis. The influence of some electrolytes and cations as interferents was discussed. Separation of U(VI) and Th(IV) from other metal ions in synthetic solution was achieved.     

Mathematical modeling of solvent extraction of uranium from sulphate media employing 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A) and its mixture with trioctylphosphine oxide (TOPO) as extractants

The extraction of U(VI) from sulphate medium with 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A, H₂A₂ in dimeric form) in n-dodecane has been investigated under varying concentrations of sulphuric acid and uranium. Slope analysis of uranium (VI) distribution data as a function of PC88A concentration suggests the formation of monomeric species, viz. UO₂(HA₂)₂. This observation was further supported by the mathematical expression obtained during non-linear least square regression analysis of U(VI) distribution data correlating the percentage extraction (%E) and the acidity (H _i). A mathematical model correlating the experimental distribution ratio values of U(VI) (D _U) with initial acidity (H _i) and initial uranium concentrations (C _i) was developed: D_\textU = 12.98( ±0.90)/{ C_\texti ^{- 0.75( ±0.05)} ×[ H_\texti ]² } D_{\text{U}} = 12.98( \pm 0.90)/\left\{ {C_{\text{i}}^{ - 0.75( \pm 0.05)} \times \left[ {H_{\text{i}} } \right]^{2} } \right\} . This expression can be used to predict the concentration of uranium in organic as well as in aqueous phase at any C _i and H _i. The extraction data were used to calculate the conditional extraction constant (K _ex) values at different acidities (2–7 M H⁺), uranium (0.02–0.1 M) and PC88A (0.2–0.6 M) concentrations. These studies were also extended for the extraction of U(VI) using synergistic mixtures of PC88A and TOPO from sulphate medium.     

Liquid–liquid extraction of uranium(VI) using cyanex 272 in toluene from sodium salicylate medium

Liquid–liquid extraction and separation studies of uranium have been carried out from sodium salicylate media using cyanex 272 in toluene. Uranium was quantitatively extracted by 1 × 10⁻³ M sodium salicylate with 5 × 10⁻⁴ M cyanex 272 in toluene. The extracted uranium(VI) was stripped out quantitatively from the organic phase with 1.0 M hydrochloric acid and determined spectrophotometrically with arsenazo(III) at 660 nm. The effect of concentration of sodium salicylate, extractant, diluents, metal ion and strippants has been studied. Separation of uranium(VI) from other elements was achieved from binary as well as from multicomponent mixtures. The method was extended for the separation and determination of uranium(VI) in geological samples. The method is simple, rapid and selective with good reproducibility (approximately ± 2%).     

Liquid-liquid extraction of uranium(VI) by Cyanex 301/alamine 308 and their mixtures with TBP/DDSO

Quantitative extraction of uranium(VI) is observed from 0.2M HCl by 5% (v/v) Cyanex 301. The extraction decreases with increasing acid concentration. Mixtures of Cyanex 301 with tri-n-butyl phosphate (TBP), didecyl sulfoxide (DDSO) and Alamine 308 result in significant synergism in the extraction process, where a species of the type UO₂R₂. L is proposed to be extracted [RH=Cyanex 301 and L=TBP, DDSO or Alamine 308]. Significant extraction of uranium(VI) by 5% (v/v) Alamine 308 is observed at and above 2M HCl, which increases with further increase in acidity attaining a maximum at 6M, after which a slight decrease in extration is observed. Mixtures of Alamine 308 with TBP or DDSO result in a synergism, where a species of the type (R ₃ NH)₂ UO₂Cl₄. Lis extracted. [R ₃ N=Alamine 308, L=TBP or DDSO]. Mixtures of Alamine 308 and Cyanex 301 at 2M HCl result in a profound antagonism in the extraction of uranium(VI).     

Chromatographic separation of uranium(VI) from other elements using L-valine and poly[dibenzo-18-crown-6]

A selective and effective column chromatographic separation method has been developed for uranium(VI) using poly[dibenzo-18-crown-6]. The separation was carried out in L-valine medium. The adsorption of uranium(VI) was quantitative from 1.0 × 10⁻⁴ to 1 × 10⁻¹ M of L-valine. Amongst various eluents 2.0–8.0 M hydrochloric acid, 1.0–4.0 M sulfuric acid, 1.0–5.0 M perchloric acid, 6.0–8.0 M hydrobromic acid and 5.0–6.0 M acetic acid were found to be efficient eluents for uranium(Vl). The capacity of poly[dibenzo-18-crown-6] for uranium(VI) was 0.25 ± 0.01 mmol/g of crown polymer. Uranium(VI) was separated from number of cations and anions in binary mixtures in which most of the cations and anions show a very high tolerance limit. The selective separation of uranium(VI) was carried out from multicomponent mixtures. The method was extended to determination of uranium(VI) in geological samples. The method is simple, rapid and selective with good reproducibility (approximately ∼2%).     

Solvent extraction of uranium(VI) and molybdenium(VI) by Alamine 310 and its mixtures from aqueous H3PO4 solution

Liquid-liquid extraction of uranium (VI) from aqueous phosphoric acid solution by triisodecylamine (Alamine 310), tri-n-butyl phosphate (TBP), di-n-pentyl sulfoxide (DPSO) and their mixtures in benzene in the range 1–10M aqueous H₃PO₄ shows that extraction is maximum (80%) in the higher acidity range 6–8 M. Extraction of this metal ion by bis(2,4,4-trimethylpentyl)phosphinicacid (Cyanex 301) and its mixtures studied in the range 0.2–1.0M aqueous H₃PO₄ is far from being quantitative. Antagonism in extraction by mixtures of extractants is observed in most of the cases. Extraction of molybdenum(VI) under identical conditions shows that it is quantitative in the lower acidity range upto 2M H₃PO₄. Separation of uranium(VI) from molybdenum(VI) is feasible by Alamine 310, TBP and DPSO, the order of efficiency being TBP>DPSO>Alamine 310.     

Extraction of molybdenum by a supported liquid membrane method

This is a report on the extraction of molybdenum(VI) ions using a supported liquid membrane, prepared by dissolving in kerosene, the extractant Alamine 336 (a long-chain tertiary amine) employed as mobile carrier. A flat hydrophobic microporous membrane was utilised as solid support. Appropriate conditions for Mo(VI) extraction through the liquid membrane were obtained from the results of liquid-liquid extraction and stripping partition experiments. The influence of feed solution acidity, the carrier extractant concentration in the organic liquid film and the content of strip agent on the metal flux through membrane were investigated. It was established that maximal extraction of metal is achieved at a pH 2.0 if sulphuric acid is used in the feed solution and at a pH value over 11.0 if Na₂CO₃ is used as strip agent. Moreover, the molybdenum extraction through membrane is enhanced when a 0.02 mol l⁻¹ content of the amine carrier in the organic phase is used. The present paper deals with an equilibrium investigation of the extraction of Mo(VI) by Alamine 336 and its permeation conditions through the liquid membrane, and examines a possible mechanism of extraction.     

Liquid-liquid extraction of uranium(VI) from aqueous acidic solutions using Alamine, TBP and CYANEX systems

Liquid-liquid extraction of uranium(VI) (UO₂ ²⁺) from aqueous acidic (HCl and HNO₃) solutions into a co-existing organic phase containing Alamine 308 (triisooctyl amine), TBP (tri-n-butyl phosphate) or CYANEX 302 (bis(2,4,4-trimethylpentyl) monothiophosphinic acid) and diluent (toluene) was studied at isothermal conditions (298.2 K) at aqueous phase acidity varying in the range 0.5-6 mol/dm³. All solvent systems exhibit a maximum distribution ratio restricted in the acidity range 3-4 mol/dm³. An obvious difference in extraction behavior through amine system has been observed for two acids, HCl and HNO₃, distinguishing the divergent interactions attributed to the different mechanism of complexation depending on the acidic medium. The high degree of separation of UO₂ ²⁺ from HNO₃ solution is feasible through a complex formation with extractants ranging in the order CYANEX 302 > TBP > Alamine 308. The results were correlated using various versions of the mass action law, i.e., a chemodel approach and a modified version of the Langmuir equilibrium model comprising the formation of one or at least two U(VI)-extractant aggregated structures.     

<Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-Butylcalix[8]arene loaded silica gel for preconcentration of uranium(VI) via solid phase extraction

This paper reports silica gel loaded with p-tert-butylcalix[8]arene as a new solid phase extractor for determination of trace level of uranium. Effective extraction conditions were optimized in column methods prior to determination by spectrophotometry using arsenazo(III). The results showed that U(VI) ions can be sorbed at pH 6 in a mini-column and quantitative recovery of U(VI) (>95–98%) was achieved by stripping 0.4 mol L⁻¹ HCl. The sorption capacity of the functionalized sorbent is 0.072 mmol uranium(VI) g⁻¹ modified silica gel. The relative standard deviation and detection limit were 1.2% (n = 10) for 1 μg uranium(VI) mL⁻¹ solution and 0.038 μg L⁻¹, respectively. The method was employed to the preconcentration of U(VI) ions from spiked ground water samples.     

Extraction behavior of U(IV) from nitric acid medium using di-isodecyl phosphoric acid dissolved in dodecane

Solvent extraction of U(VI) with di-isodecyl phosphoric acid (DIDPA)/dodecane from nitric acid medium has been investigated for a wide range of experimental conditions. Effect of various parameters including nitric acid concentration, DIDPA concentration, temperature, stripping agents, and other impurities like rear earths, transition metal ion, boron, aluminum ion on U(VI) extraction has been studied. The species extracted in the organic phase is found to be UO₂(NO₃)(HA₂)·H₂A₂ at lower acidity (<3.0 M HNO₃). Increase in temperature lead to the decrease in extraction with the enthalpy change by ∆H = −16.27 kJ/mol. Enhancement in extraction of U(VI) from nitric acid medium was observed with the mixture of DIDPA and tri butyl phosphate (TBP). The stripping of U(VI) from organic phase (DIDPA–U(VI)/dodecane) with various reagents followed the order: 4 M H₂SO₄ > 5% (NH₄)₂CO₃ > 8 M HCl > 8 M HNO₃ > Water. High separation factors between U(VI) and impurities suggested that the use of DIDPA for purification of uranium from multi elements bearing solution.     

Extraction and separation of uranium(VI) and protactinium(V) with 1-(4-tolyl)-2-methyl-3-hydroxy-4-pyridone

Summary The extraction of uranium(VI) from aqueous hydrochloric or nitric acid, and the extraction of protactinium from hydrochloric acid by 1-(4-tolyl)-2-methyl-3-hydroxy-4-pyridone (HY) dissolved in chloroform has been studied. At pH >4, uranium (VI) is quantitatively extracted while at pH < 1 practically all the uranium remains in the aqueous phase. At hydrochloric acid concentrations lower than 1M, protactinium(V) is quantitatively extracted while at hydrochloric acid concentration higher than 5M practically all the protactinium remains in the aqueous phase. This difference in extraction of uranium and protactinium was utilized for their separation. From 0.5M hydrochloric acid, protactinium is quantitatively extracted, and separated from uranium.The composition of the extracted uranium(VI) and protactinium (V) complexes was studied. A uranium complex with the formula UO₂Y₂ · HY was isolated from the chloroform solution. The solution of this complex in chloroform has a maximum absorbance at 319 nm and the molar absorptivity is 3.1×10⁴ l · mole^–1 · cm^–1. Owing to this property uranium can be determined spectro-photometrically directly in the organic phase.

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Zusammenfassung Die Extraktion von Uran(VI) aus wäßriger Salzsäure oder Salpetersäure sowie die Extraktion von Protaktinium aus Salzsäure mit 1-(4-Tolyl)-2-methyl-3-hydroxy-4-pyridon (HY) in chloroformischer Lösung wurde untersucht. Bei pH > 4 wird U(VI) quantitativ extrahiert, während bei pH < 1 praktisch alles Uran in der wäßrigen Phase bleibt. Bei Salzsäurekonzen-trationen unter 1-m wird Protaktinium (V) quantitativ extrahiert, während bei Salzsäurekonzentrationen über 5-m praktisch alles Pa in der wäßrigen Phase bleibt. Dieser Unterschied bei der Extraktion der beiden Elemente wurde für deren Trennung benützt. Pa wird aus 0,5-m Salzsäure quantitativ extrahiert und so von Uran getrennt.Die Zusammensetzung der extrahierten U (VI)- und Pa (V)-Komplexe wurde untersucht. Ein Urankomplex der Formel UO₂ · Y₂ · HY wurde aus der Chloroformlösung isoliert. Die Lösung dieses Komplexes in Chloroform hat ein Absorptionsmaximum bei 319 nm und eine molare Extinktion von 3,1 · 10⁴ l · mol^–1 · cm^–1. Auf Grund dieser Eigenschaft kann Uran spektrophotometrisch direkt in der organischen Phase bestimmt werden.

     

Poly(cyclotriphosphazene-co-phloroglucinol)PCPP as a solid phase extractant for preconcentrative separation of uranium(VI) from aqueous solution

Poly(cyclotriphosphazene-co-phloroglucinol) (PCPP) microspheres, a new solid phase extraction for extracting uranium(VI), synthesized via one-pot precipitation copolymerization. The PCPP microspheres were characterized by FT-IR, SEM/EDS, zeta potential and N₂ adsorption/desorption isotherms. Through the extraction experiment to evaluate the extraction behavior of the PCPP microspheres for uranium(VI). The extractant can achieve the optimal effect under the conditions of contact time with 60 min, pH = 3.5, initial concentration 100 mg L⁻¹ and extractant dosage 0.70 g L⁻¹. The extraction behavior obeyed with the pseudo second-order model and Langmuir isotherm model.

     

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.

     

Solvent extractions of zirconium and niobium from HCl solutions by Aliquat 336/Alamine 336 and DOSO mixtures

Liquid-liquid extractions of zirconium(IV) from aqueous HCl solutions by mixtures of Aliquat 336 or Alamine 336 and diocytl sulfoxide (DOSO) in the diluent benzene has been found to be always higher than that by any single extractant. While the cationic extractants extract Zr(IV) above 6M HCl, DOSO extracts from 4M onwards. Synergism has been observed in all cases. With any of these extractants extraction becomes almost quantitative at and above 10M HCl, but with mixtures of the cationic and neutral extractants, extraction is quantitative in the range 8–9M HCl. Although the extracted species with DOSO alone seems to be ZrCl₄·DOSO, with the mixture of extractants, however, the extracted species appear to be Q₂ZrCl₆·DOSO where Q is R₃ ⁺NH (for Alamine 336) and R₃ ⁺N(CH₃) (for Aliquat 336). Studies on separation of⁹⁵Zr–⁹⁵Nb pair from aqueous HCl media by Alamine 336 or DOSO and their mixtures in benzene exhibit preferential extraction of⁹⁵Nb leaving behind⁹⁵Zr in the aqueous phase, and extractions have been found to depend both upon the extractant and HCl concentrations.     

Triphenyltetrazolium chloride as a new analytical reagent for molybdenum(VI): Application to plant analysis

Solvent extraction of molybdenum(VI) ion associate with triphenyltetrazolium chloride (TTC) has been studied. TTC was proposed as reagent for the spectrophotometric determination of micro amounts of molybdenum(VI) at λ_max 250 nm. The optimum conditions for extraction of molybdenum(VI) as an ionassociation complex with TTC has been determined. Beer’s law is obeyed in the range of 0.5–10 μg/mL molybdenum(VI). The molar absorptivity of the ion-pair is 1 × 10⁶ L/mol cm. The sensitivity of the method is 9.6 × 10⁻⁵ μg/cm². The characteristic values for the extraction equilibrium and the equilibrium in the aqueous phase are: distribution constant K _D = 32.64, extraction constant K _ex = 2.19 × 10¹⁰ association constant β = 6.71 × 10⁸. The interferences of different cations, anions on molybdenum(VI) determination were also investigated. A sensitive and selective method for the determination of microquantities of molybdenum(VI) has been developed. The determination was carried out without preliminary separation of molybdenum. A novel procedure of molybdenum(VI) extraction and spectrophotometric determination in different plant samples was examined.     

Extraction studies of uranium into a third-phase of thorium nitrate employing tributyl phosphate and <Emphasis Type="Italic">N,N</Emphasis>-dihexyl octanamide as extractants in different diluents

Extraction behavior of 1 × 10⁻²–0.1 M U(VI) from aqueous phases containing 0.86 M Th(IV) at 4 M HNO₃ in 1.1 M tributyl phosphate (TBP) and 1.1 M N,N-dihexyl octanamide (DHOA) solutions in different diluents viz. n-dodecane, 10% 1-octanol + n-dodecane, and decahydronaphthalene (decalin) was studied. Third-phase formation was observed in both the extractants using n-dodecane as diluent. There was a gradual decrease in Th(IV) concentration in the third-phase (heavy organic phase, HOP) with increased aqueous U(VI) concentration [0.71 M (no U(VI))–0.61 M (0.1 M U(VI)) for TBP; 0.27 M (no U(VI))–0.22 M (0.1 M U(VI)) for DHOA]. The HOP volume in case of DHOA was ~2.2 times of that of TBP. Uranium concentration in HOP increased with its initial concentration in the aqueous phase [from 1.8 × 10⁻² M (0.01 M U(VI))–0.162 M (0.1 M U(VI)) for TBP; from 1.4 × 10⁻² M (0.01 M U(VI))–0.14 M (0.1 M U(VI)) for DHOA] suggesting that Th(IV) was being replaced by U(VI). An empirical correlation was developed for predicting the concentrations of uranium and thorium in HOP for both the extractants. No third-phase appeared during the extraction of uranium and thorium from the aqueous phases employing 10% 1-octanol + n-dodecane, or decalin as diluents, and therefore, were better choices as diluent for alleviating the third-phase formation during the reprocessing of spent thorium based fuels, and for the recovery of thorium from high-level waste solutions.     

Extraction of uranium (VI) from sulfuric acid solution with TOPO

The extraction of uranium(VI) from sulfuric acid medium with tri-octylphosphine oxide (TOPO) in n-heptane was studied. Accompanied with the increase in the concentration of H₂SO₄, the distribution coefficient of uranium(VI) increased in the region of dilute sulfuric acid. When the concentration of H₂SO₄ surpassed 3.5 mol·dm⁻³, the distribution coefficient of uranium(VI) was at maximum. This result was due to the competition extraction between uranium(VI) and H₂SO₄. From the data, the composition of extracted species and the equilibrium constant of extraction reaction have been evaluated, which were (TOPOH)₂UO₂(SO₄)₂ (TOPO) and 10^7.6±0.15, respectively.