Extraction of uranium(VI) and thorium(IV) from nitric acid solution by N-alkylcaprolactam

Extraction of uranium(VI), thorium(IV) from nitric acid has been studied with N-octylcaprolactam and N-(2-ethyl)hexylcaprolactam. Distribution coefficients of U(VI), Th(IV) and HNO₃ as a function of aqueous NHO₃ concentration, extractant concentration and temperature have been studied. The compositions of extracted species, thermodynamic parameters of extraction have been evaluated. Third phase formation in extraction of U(VI) has been studied. Back extraction behavior of U(VI) and Th(IV) from the organic phase has also been tested. The results obtained are compared with those obtained by using TBP under the same experimental conditions.     

Extraction of U(VI) and Th(IV) from nitric acid medium using tri(butoxyethyl) phosphate (TBEP) in <Emphasis Type="Italic">n</Emphasis>-paraffin

Extraction behavior of U(VI) and Th(IV) from nitric acid medium is investigated using organo-phosphorous extractant, tri(butoxyethyl) phosphate in n-paraffin at room temperature (27 ± 1 °C). The effect of diluents, nitric acid concentration as well as extractant concentration on extraction of U(VI) and Th(IV) are evaluated. Extraction of U(VI) and Th(IV) from nitric acid medium proceeds via solvation mechanism. Slope analysis technique showed the formation of neutral complexes of the type of UO₂(NO₃)₂·2TBEP and Th(NO₃)₄·3TBEP with U(VI) and Th(IV) respectively in the organic phase. The FTIR data showed shifting of P=O stretching frequency from 1,282 to 1,217 cm⁻¹ indicating the strong complexation of P=O group with UO₂ ²⁺ ions in the organic phase. Effect of stripping agents, other metal ions and their separation with respect to U(VI) extraction has also been investigated.     

Synergistic extraction of U(VI) and Th(IV) from nitric acid with 4-benzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-thione (HBMPPT) and tri-n-octylphosphine oxide (TOPO) in toluene

The extractant HBMPPT (4-benzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-thione) was synthesized from HBMPP. Its m.p. was 106–108°C. The synergistic extraction of U(VI) and Th(IV) from nitric acid solution by HBMPPT and TOPO in toluene was studied. The extraction ability of HBMPPT was not so high as that of its parent (HBMPP), but when a little tri-n-octylphosphine oxide (TOPO) was added the ability to extract U(VI) and Th(IV) was seriously improved. The synergistic extracted complexes may be presented as UO₂NO₃·BMPPT·TOPO and UO₂(BMPPT)₂·TOPO for U(VI), and Th(NO₃)₃·BMPPT·TOPO and Th(NO₃)₂(BMPPT)₂·TOPO for Th(IV) respectively.     

Extraction and thermodynamic behavior of U(VI) and Th(IV) from nitric acid solution with tri-isoamyl phosphate

The extraction behavior of U(VI) and Th(IV) with tri-isoamyl phosphate–kerosene (TiAP–KO) from nitric acid medium was investigated in detail using the batch extraction method as a function of aqueous-phase acidity, TiAP concentration and temperature, then the thermodynamic parameters associated with the extraction were derived by the second-law method. It could be noted that the distribution ratios of U(VI) or Th(IV) increased with increasing HNO₃ concentration until 6 or 5 M from 0.1 M. However, a good separation factor (D _U(VI)/D _Th(IV)) of 88.25 was achieved at 6 M HNO₃, and the stripping of U(VI) from TiAP–KO with deionized water or diluted nitric acid was easier than that of Th(IV). The probable extracted species were deduced by log D-log c plot at different temperatures as UO₂(NO₃)₂·(TiAP)_(1–2) and Th(NO₃)₄·(TiAP)_(2–3), respectively. Additionally, △H, △G and △S for the extraction of U(VI) and Th(IV) revealed that the extraction of U(VI) by TiAP was an exothermic process and was counteracted by entropy change, while the extraction of Th(IV) was an endothermic process and was driven by entropy change.     

N,N′-二乙(甲)基-N,N′-二苯基脲对铀(VI)和钍(IV)萃取行为的研究

目前国际上一般采用磷酸三丁酯(TBP)作为铀的萃取剂。TBP对铀有较强的萃取能力,但其耐辐照能力较差。酰胺的理化性质类似于TBP,与TBP相比降解产物易除去,“可完全燃烧”等优点而被认为是一种能取代应用于核燃料后处理的有前途的萃取剂。本文以二甲苯或三氯甲烷     

The solvent extraction of UO 2 2+ and Th4+ with petroleum sulfoxide

The influence of the concentration of nitric, hydrochloric and phosphoric acids, petroleum sulfoxides (PSO), salting-out agent, kind of diluent and temperature on the distribution ratio of U(VI) and Th(IV) has been systematically studied. It is found that the extraction regularity of PSO is similar to that of TBP. The distribution ratio in phosphoric acid is lower, but it increases with the increase of hydrochloric acid concentration and reaches a high value. The U(VI) exhibits the maximum distribution ratio at 3–4 mol/l HNO₃. The distribution ratio of U(VI) and Th(IV) increases rapidly in the presence of a salting out agent. The extracted compounds are determined to be UO₂(NO₃)₂2PSO and Th(NO₃)₄2PSO. The extraction enthalpies of U(VI) and Th(IV) with PSO were also calculated.     

Extraction and separation of Th(IV) and U(VI) from nitric acid media using PIA-8 and HDEHP

Extraction behavior of Th(IV) and U(VI) has been investigated with bis(2-ethylhexyl) phosphinic acid (PIA-8) and bis(2-ethylhexyl) phosphoric acid (HDEHP) from nitric acid media in toluene. The optimum conditions for extraction of these metals have been established by studying various parameters like acid concentration, pH, reagent concentration, diluents and shaking time. The extraction of Th(IV) was found to be quantitative with 0.3-2.5M HNO₃ by 2.5^.10^-2M HDEHP and in the pH range 0.1-2.5 with 2.3^.10^-2M PIA-8 in toluene. U(VI) was completely extracted in the acidic range of 0.1-2.0M HNO₃ with 2.2^.10^-2M HDEHP and in the pH range of 1.0-3.0 with 2.0^.10^-2M PIA-8 in toluene. The probable extracted species have been ascertained by log D-log c plot as UO₂ R₂ ^.2HR with both the reagents and Th (NO₃)₂R₂ ^.2HR with PIA-8 and Th (NO₃)₃R^.3HR with HDEHP, respectively. Temperature dependence of the extraction equilibrium is examined by the temperature variation method. Separation of U(VI) and Th(IV) was also carried out from commonly associated metals.     

LIX 84 as an extractant for throium(IV), uranium(VI) and molybdenum(VI)

The extraction order of Th(IV), U(VI) and Mo(VI) based on pH_0.5 values is Mo(VI)>U(VI)>Th(IV). Quantitative extraction has been observed for U(VI) by mixture of 10% (v/v) LIX 84 and 0.1M dibenzoylmethane at pH 4.2 and by mixture of 10% LIX 84 and 0.05M HTTA in the pH range 5.5–7.3 and for Mo(VI) by 10% LIX 84 from chloride media at pH 1.5. The order of extraction of Mo(VI) from 1N acid solutions is HCl>H₂SO₄>HNO₃>HClO₄ and extraction decreases very rapidly with increase in the concentration of HCl as compared to that from H₂SO₄, HNO₃ and HClO₄ acid solutions. The diluents C₆H₆, CCl₄ and CHCl₂ are found to be superior ton-butyl alcohol and isoamyl alcohol for extraction of Mo(VI). Influence of concentration of different anions on the extraction of U(VI) and Mo(VI) has been studied. Very little extraction has been observed in case of Th(IV) by LIX 84 or its mixtures with other chelating extractants or neutral donors.     

Synergistic effect of HBMPPT with PSO, DOSO and TBP on the extraction of U(VI) and on the separation of U(VI) and Th(IV)

Some popular neutral extractants (PSO-petroleum sulfoxide, DOSO-di-n-octyl sulfoxide, TBP-tributylphosphate etc.) were chosen as synergist to study the synergistic effect on the extraction reaction with HBMPPT (4-benzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-thione) for U(VI), and the synergistic separation ability of HBMPPT for U(VI) and Th(IV). The synergistic extraction ability shown by the studied systems for U(VI) is as follows: PSO>DOSO>TBP, and the same sequence was also verified for the separation coefficient of U(VI) and Th(IV). The synergistic complexes may be presented as: UO₂NO₃·BMPPT·S and UO₂(BMPPT)₂·S for U(VI) (S is PSO, DOSO or TBP).     

Solvent extraction of uranium(VI) and thorium(IV) by N,N′-di-p-tolylpyridine-2,6-dicarboxamide from nitric acid solution

Synthesis and characterization of N,N′-di-p-tolylpyridine-2,6-dicarboxamide (DTPDA) was carried out and used for extraction of U(VI) and Th(IV) from nitric acid solutions. The processes of extraction were determined by the slope analysis and by analyzing a function that allows the simultaneous treatment of all the experimental points obtained in different conditions. The different factors affecting the extraction distribution ratio(D) of U(VI) and Th(IV) (extraction concentration, concentrations of nitric acid, salting-out agent NaNO₃ concentration, equilibration time and temperature) were investigated. The results obtained indicated that the extraction species of U(VI) and Th(IV) are mainly extracted as UO₂(NO₃)₂·1.5DTPDA and Th(NO₃)₄·1.5DTPDA. The related thermodynamic functions were calculated. Back-extraction of U(VI) and Th(IV) from organic phases was also studied.     

Extraction of uranium(VI) and thorium(IV) ions from nitric acid solutions by N,N,N′,N′-tetrabutyladipicamide

A new symmetrical diamide, the straight-chain alakyl substituted neutral tetrabutyladipicamide (TBAA) has been synthesized, characterized and used for the extraction of U(V) and Th(IV) from nitric acid solutions in a diluent composed of 50% 1,2,4-trimethylbenzene (TMB) and 50% kerosene (OK). Extraction distribution coefficients of U(VI) and Th(IV) as a function of aqueous nitric acid concentration, extractant concentration and temperature have been studied. Back-extraction of U(VI) and Th(IV) from organic phases by dilute nitric acid has been undertaken. From the data, the compositions of extracted species, equilibrium constants and enthalpies of extraction reactions have also been calculated.     

Extraction of U(VI), Zr(IV) and Th(IV) from perchlorate media, by PC-88A

Extraction of U(VI), Zr(IV) and Th(IV) has been investigated from perchlorate media using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) dissolved in toluene. The extraction of U(VI), Zr(IV) and Th(IV) was found to be quantitative in the pH range 1.6 to 3.2, 2.0 to 4.7 and 2.3 to 3.8, respectively, with 3.0^.10^-3, 5.6^.10^-4 and 1.0^.10^-2M PC-88A dissolved in toluene. U(VI) was stripped with 4.0M HCl, Zr(IV) with 2.5M NaF and Th(IV) with 8.0M HCl from the metal loaded organic phase containing PC-88A dissolved in toluene. The probable extracted species have been ascertained by plotting log D vs. log [HR] as UO₂R₂ ^.2HR, ZrR₄ ^.2HR and ThR₄ ^.4HR, respectively. U(VI) was separated from Zr(IV) and Th(IV) and from other associated metals. This method was proved by the determination of U(VI) in some real samples.     

Synergistic extraction of uranium(VI) and thorium(IV) with mixtures of Cyanex272 and other organophosphorus ligands

The extraction of thorium(IV) and uranium(VI) from nitric acid solutions has been studied using mixtures of bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex272 or HA), and synergistic extractants (S) such as tri-butylphosphate (TBP), tri-octylphosphine oxide (TOPO) or bis(2,4,4-trimethylpentyl)thiophosphinic acid (Cyanex301). The results showed that these metallic ions are extracted into kerosene as Th(OH)₂(NO₃)A·HA and UO₂(NO₃)A·HA with Cyanex272 alone. In the presence of neutral organophosphorus ligands TBP and TOPO, they are found to be extracted as Th(OH)₂(NO₃)A·HA·S and UO₂(NO₃)A·HA·S. On the other hand, Th(IV), U(VI) are extracted as Th(OH)₂(NO₃)A·HA·2S and UO₂(NO₃)A·HA·S in the presence of Cyanex301. The addition of neutral extractants such as TOPO and TBP to the extraction system enhanced the extraction efficiency of both elements while Cyanex301 as an acidic extractant has improved the selectivity between uranium and thorium. The effect of TOPO on the extraction was higher than other extractants. The equilibrium constants of above species have been estimated by non-linear regression method. The extraction amounts were determined and the results were compared with those of TBP. Also, it was found that the binding to the neutral ligands by the thorium–Cyanex272 complexes follows the neutral ligand basicity sequence.     

New extractants for reprocessing of spent Th-U fuel

A study on solvent extraction of U(VI), Th(IV) and HNO₃ from nitric acid media by DEHSO is described. Extraction coefficients of U(VI), Th(IV) and HNO₃ as a function of aqueous HNO₃ concentration, extractant concentration and temperature have been studied. From the data the compositions of extracted species, equilibrium constants and enthalpies of extraction reaction have been evaluated. Back-extraction of U(VI) and Th(IV) from the organic phase by dilute nitric acid has also been tested. All studies on DEHSO are compared with TBP.     

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.     

Solvent Extraction Separation of Th(IV) and U(VI) with PC-88A

Liquid-liquid extraction of Th(IV) and U(VI) has been investigated by commercial extractant PC-88A in toluene. The optimum conditions for extraction of these metals have been established by studying the various parameters like acid concentration/pH, reagent concentration, diluents and shaking time. The extraction of Th(IV) was found to be quantitative with 0.1–1.0M HNO₃ acid and in the pH range 1.0–4.0 while U(VI) was completely extracted in the pH range 1.0–3.5 with 2.5·10^–2M and 2.·10^–2M PC-88A in toluene, respectively. The probable extracted species have been ascertained by log D-log C plot as ThR₄·4HR and UO₂R₂·2HR, respectively. The method permits separation of Th(IV) and U(VI) from associated metals with a recovery of 99.0%.     

Synthesis and characterization of N,N,N′,N′-tetraalkyl-4-oxaheptanediamide as extractant for extraction of uranium(VI) and thorium(IV) ions from nitric acid solution

Tridentate ligand N,N,N′,N′-tetraoctyl-4-oxaheptanediamide(TOOHA) and other three analogous diamides have been prepared and characterized by using NMR spectra and element analysis. The extraction of UO₂ ²⁺ and Th⁴⁺ with the present extractants was investigated at 293 ± 1 K from nitric acid solutions. n-Octane was found to be the most suitable diluent in the present study compared with other diluents tested. Extraction distribution ratios (D) of U(VI) and Th(IV) have been studied as a function of aqueous concentrations of HNO₃, extractant concentrations. The results indicated that U(VI) is mainly extracted as UO₂(NO₃)₂·2TOOHA. In the case of Th⁴⁺ ion, the possible compositions of extracted species in organic phase were presumed to be Th(NO₃)₄·2TOOHA and Th(NO₃)₄·3TOOHA. In addition, the influence of concentration of sodium nitrate as salting-out agent on the distribution ratio of U(VI) and Th(IV) with TOOHA was also evaluated.     

Adsorptive removal of U(VI) and Th(IV) from aqueous solutions using polymer-based electrospun PEO/PLLA fibrous membranes

Fibrous membranes based on poly(ethylene oxide) and poly(l-lactide) fabricated by electrospinning were evaluated for the first time as substrates for the adsorption of tetravalent thorium (Th(IV)) and hexavalent uranium (U(VI)) from aqueous media. The membranes consisted of microfibers with diameters of approximately 2 μm as revealed by scanning electron microscopy. The adsorption of Th(IV) and U(VI) on the membrane was investigated as a function of pH, ionic strength and initial metal concentration under normal atmospheric conditions. The experimental data indicated increased affinity of the membrane for Th(IV) and U(VI), which was pH depended and reaches maximum values (>90 %) for Th(IV) and U(VI) at pH 3 and pH 6.5, respectively. The maximum adsorption capacity (q _max) at optimum conditions was evaluated from the Langmuir isotherm and was found to amount 50.08 and 9.3 mmol kg^?1 for Th(IV) and U(VI), respectively. In addition, studies on the effect of ionic strength on the adsorption efficiency did not show any significant effect indicating that the adsorption of Th(IV) and U(VI) on the membrane was most probably based on specific interactions and the formation of inner-sphere surface complexes. The significantly higher adsorption efficiency of the membrane for Th(IV) in acidic media (pH ≤ 3) could be utilized for a pH-triggered, selective separation of Th(IV) from U(VI) from aqueous media.     

Uptake of actinides and lanthanides from nitric acid by dihexyl-N,N-diethylcarbamoylmethylphosphonate adsorbed on chromosorb

Batchwise uptake of Am(III), Pm(III), Eu(III), U(VI) and Pu(IV) by dihexyl-N,N-diethylcarbamoylmethylphosphonate (CMP) adsorbed on chromosorb (CAC) at nitric acid concentrations between 0.01 to 6.0M has been studied. The difference between the uptake behavior of Pu(IV) as compared to other actinides and lanthanides is discussed. The Am(III) and U(VI) species taken up on CAC were found to be Am(NO₃)₃·3CMP and UO₂(NO₃)₂·2CMP, respectively. The equilibrium constants for the formation of these species have been evaluated and compared with those of similar species formed in liquid-liquid extraction. Batchwise loading of Pm(III) on CAC from 3.0M HNO₃ has also been studied.     

N,N,N′,N′-tetrabutylsuccinylamide as a new extractant in n-dodecane for extraction of uranium(VI) and thorium(IV) ions

N,N,N,N-tetrabutylsuccinylamide (TBSA) was synthesized, characterised and used for the extraction of U(VI) and Th(IV) from nitric acid solutions into n-dodecane. Extraction distribution coefficients of U(VI) and Th(IV) as a function of aqueous nitric acid concentration, extractant concentration and temperature have been measured and found that n-dodecane as diluent was superior to 50% 1,2,4-trimethyl benzene (TMB) and 50% kerosene, (OK) system for extraction of U(VI) and Th(IV). The compositions of extracted species, equilibrium constants and enthalpies of extraction reactions have also been calculated. The formation of the 121 complex of uranyl(II) ion or the 141 complex of thorium(IV) ion, nitrate ion and TBSA and extracted species was further confirmed by the IR spectra of saturated extract of U(IV) and Th(IV).