Di-n-hexyloctanamide Research Articles

Selective Separation of Neptunium from an Acidic Feed Containing a Mixture of Actinides Using Dialkylamides

ABSTRACTExtraction of Np(IV), Pu(IV), U(VI), and Np(VI) was studied using N,N-di-2-ethylhexyl derivatives iso-butyramide (D2EHIBA) and n-propanamide (D2EHPrA). D2EHIBA showed higher selectivity for U(VI) over Np(IV) and Pu(IV). A flowsheet for the separation of Np(IV) from a mixture of uranium, neptunium, and plutonium in 3 M HNO3 was developed exploiting the selectivity of D2EHIBA for U(VI) over the tetravalent actinides followed by the selective stripping of Np(IV) from the di-n-hexyl-octanamide (DHOA) medium using acetohydroxamic acid (AHA). The results indicated that >90% of the neptunium present in the mixture could be recovered at the final step with a decontamination factor >103.

Extraction of uranium(VI) from nitric acid solutions using N,N-dihexyloctanamide in ionic liquids: Solvent extraction and spectroscopic studies

ABSTRACTLiquid-liquid extraction studies of uranium(VI) were carried out from nitric acid medium using di-n-hexyloctanamide (DHOA) in several room-temperature ionic liquids (RTIL). The extraction of the metal ion as a function of nitric acid concentration showed different trends based on the alkyl substituents of the RTIL. While the DU values decreased with increasing HNO3 concentration (up to ca. 0.5 M) with [C4mim][NTf2] and [C6mim][NTf2], almost no change was seen with [C8mim][NTf2]. This suggested that while a cation-exchange mechanism is operative with the former diluents, which was to a much lower extent for the latter. The extracted species were found to contain about 2 molecules of DHOA from the feed solutions containing either 0.01 M and 4 M HNO3, which was arrived at from the ligand-concentration-variation experiments. Recycling studies were also performed by carrying out stripping and radiolytic stability studies. The nature of the extracted species as ascertained from the UV-visible spectrophotometry studies indicated similarity between the extracts obtained in RTIL medium, which were entirely different from that observed with n-dodecane as the diluent.

Studies on the Radiation Stability of Several Polymeric Flat Sheets used for Actinide Ion Separation from Radioactive Feeds

Radiolytic stability of polymeric flat sheet membranes was evaluated from surface morphology (SEM), contact angle and porosity data. The flat sheets made from PES (polyether sulfone), PP (polypropylene), PC (polycarbonate) and PVDF (polyvinylidenefluoride) were irradiated to varying extent using a 60Co gamma ray source and the physical characterization of the membranes was carried out using various techniques mentioned above. Subsequently, the transport efficiency of the irradiated flat sheets was evaluated by studying the mass transfer of Am3+ from a feed containing 3 M HNO3 in to a receiver phase containing 0.01 M HNO3 as the strippant while 0.1 M TODGA (N,N,N’,N’- tetraoctyldiglycolamide) +0.5 M DHOA (di-n-hexyloctanamide) in n-dodecane was used as the carrier extractant. Out of the flat sheet membranes, PC membranes were found to be more promising and transport studies were carried out using PC membranes up to an absorbed dose of 50 MRad which suggested very good transport of Am3+ without any deterioration of the membrane.

Comparison in the extraction behavior of uranium(VI) from nitric acid medium using CHON based extractants, monoamide, malonamide, and diglycolamide, dissolved in piperidinium ionic liquid

ABSTRACTLiquid-liquid extraction of U(VI) from nitric acid medium was carried out using three different class of CHON based molecular extractants namely monoamide, malonamide, and diglycolamide present in 1-butyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide ([C4mpip][NTf2]) ionic liquid. The extractants investigated were di-n-hexyloctanamide (DHOA), N,N-dimethyl-N,N-di-octyl-2-(2-hexyloxylethyl)malonamide (DMDOHEMA) and N,N,N’,N’-tetra(ethylhexyl)diglycolamides (T2EHDGA). The extraction behavior of uranium(VI) in ionic liquid medium was investigated as a function of various parameters, such as the duration and temperature of equilibration, aqueous phase concentrations of feed acid, extractant, NaNO3, and ionic liquid cation, etc. The extraction of U(VI) observed in these systems were compared with each other and the distribution ratios of U(VI) decreased in the order T2EHDGA > DMDOHEMA > DHOA. The slope analysis of the extraction data was carried out to understand the mechanistic aspects of extraction. The extraction of U(VI) observed in [C4mpip][NTf2] ionic liquid was also compared with pyrrolidinium ([C4mpyr][NTf2]) and imidazolium ([C4mim][NTf2]) based ionic liquids under identical experimental condition.

Non-Dispersive Solvent Extraction of Neodymium using N,N,N’,N’-Tetraoctyl Diglycolamide (TODGA)

Hollow fiber contactor was used to study non-dispersive extraction (NDSX) of Nd3+ ions from aqueous solutions. N,N,N′,N′-tetraoctyl diglycolamide (TODGA) diluted with n-dodecane was used as the organic phase with di-n-hexyl octanamide (DHOA) as the phase modifier. The role of cations (H+/Na+) on the transport of Nd3+ ions has been investigated for this system. It was observed that H+ ion has a significant role to play in the Nd3+/TODGA complexation reaction. A mathematical model has also been developed to simulate the NDSX process in a hollow fiber contactor. A comparison has also been made between extraction profiles from the NDSX process and the hollow fiber supported liquid membrane (HFSLM) process. It was observed that NDSX gave comparatively faster rates of extraction in the presence of H+ ions but slower in the absence of H+ ions.

Mathematical Model for the Extraction of Metal Ions using Hollow Fiber Supported Liquid Membrane Operated in a Recycling Mode

The role of cations H+ and Na+ on the transport of Nd3+ ions was investigated using microporous Hollow Fiber Supported Liquid Membrane (HFSLM) contactor. Extractant N,N,N′,N′-tetraoctyl diglycolamide (TODGA) diluted with n-dodecane was used as the membrane phase. Di-n-hexyl octanamide (DHOA) was used as a phase modifier for the extractant. Transport of Nd3+ ions and HNO3 was studied at varying concentrations of NaNO3 and HNO3 while keeping total nitrate () concentration nearly constant at 3 M. The extraction equilibrium constant (K ex ) for the complexation reaction was experimentally measured for various conditions. The maximum rate of extraction of Nd3+ ions was observed at an equimolar concentration (1.5 M each) of HNO3 and NaNO3 in feed solution under otherwise identical conditions. A mathematical model has also been developed to simulate this system. Mass balance equations for both acid (HNO3) and TODGA were also incorporated in the model. It was observed that the model results are in good agreement with the experimental data when diffusivity of metal-complex (D m ) and acid-complex (D hm ) through the membrane phase in the pore is 6 × 10−12 m2/s and 1.2 × 10−10 m2/s. Once the values of D m and D hm are estimated by simulation for one set of data, there are no further fitting parameters in the model. The model can then be used in a truly predictive mode for all the remaining data sets.

A Novel Liquid Emulsion Membrane Containing TODGA as the Carrier Extractant for Am Recovery from Acidic Wastes

The recovery of Am has been investigated by Liquid Emulsion Membrane (LEM) containing 0.1 M N,N,N′,N′-tetraoctyl-3-oxapentane diamide (TODGA) + 0.5 M di-n-hexyloctanamide (DHOA) in n-dodecane as extractant. Span 80 (sorbitan monooleate) was used as the surfactant for making the emulsion while 3 M HNO3 and 0.1 M acetate buffer (at pH 4.75) were used as the external and internal phases, respectively. Optimized conditions indicated 2% Span 80 was required for making the emulsions. The effect of different experimental conditions such as varying feed acidity, varying volume ratio, different strippants, and varying TODGA concentration have been studied for the quantitative removal of Am from acidic solution. The higher transport rate has been observed which can be attributed to the higher surface area per unit volume available for mass transport. Demulsification was possible by heating the emulsions to 80°C. Actual acidic radioactive waste has also been tested for the recovery of americium. The results show the applicability of ELM for the removal of Am(III) from waste solutions with a faster rate of transport as compared to those reported previously.

Radiation stability of several polymeric supports used for radionuclide transport from nuclear wastes using liquid membranes

In an attempt to evaluate radiation stability of several polymeric materials used as the support in supported liquid membrane studies for the transport of radionuclides from nuclear waste, flat sheets made from polytetrafluoroethylene, polysulfone, polyether sulfone, polyacrylonitrile and polyvinylidenefluoride were irradiated to varying extents using a 60Co gamma ray source and subsequently, the transport efficiency of the irradiated flat sheets were evaluated. The membrane integrity was assessed from the transport rates of Am3+ from a feed containing 3 M HNO3 into a receiver phase containing 0.01 M HNO3 as the strippant while 0.1 M TODGA (N,N,N′,N′-tetraoctyldiglycolamide) + 0.5 M DHOA (di-n-hexyloctanamide) in n-dodecane was used as the carrier extractant. The radiation stability of the membrane filters was evaluated after irradiating them up to 20 MRad absorbed dose in a gamma chamber.

Mathematical Model for the Extraction of Neodymium from Nitrate Media using Hollow Fiber Supported Liquid Membrane Operated in a Recycling Mode

A mathematical model for facilitated extraction of Neodymium (Nd3+) ions from nitrate media using microporous hollow fiber supported liquid membrane (HFSLM) operated in a recycling mode is presented. Extractant N,N,N′, N′-tetraoctyl diglycolamide (TODGA) diluted with n-dodecane was used as the membrane phase. Di-n-hexyl octanamide (DHOA) has been used as a phase modifier for the extractant. The model developed is not specific to the case considered and has a more general and wide applicability. The model has been developed using equilibrium-based approach. The complexation and de-complexation reactions were assumed to be fast and at equilibrium. Mass balance equations for both acid (HNO3) and TODGA were also incorporated in the model. It was observed that the model results are in good agreement with the experimental data when diffusivity of metal-complex (D m ) and acid-complex (D hm ) through the membrane phase in the pore is 6 × 10−12 m2/s and 1.2 × 10−10 m2/s. Once the values of D m and D hm are estimated by simulation for one set of data, there are no further fitting parameters in the model. The model can then be used in a truly predictive mode for all the remaining data sets.

Analytical application of DHOA for the determination of trace metallic constituents in U based fuel materials by ICP-AES

DHOA (Di-n-hexyl-octanamide) is one of the alternative extractants to TBP (tri-n-butyl phosphate) known for the extraction of uranium from moderate nitric acid medium without significant extraction of the fission products. Analytical application of DHOA was explored to develop a methodology for determination of trace metallic constituents in uranium based nuclear materials. This involved the separation of uranium matrix by 1.1 M DHOA-dodecane followed by the analysis of the raffinate for trace constituents by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). A systematic study showed that four contacts of 1.1 M DHOA-dodecane were required for quantitative extraction of U from 4 M HNO3 feed for the sample size of 1 g in 10 mL. The feasibility of using DHOA for extraction of U from trace metallic constituents in U based fuel materials without losing trace quantities of analytes of interest was studied by using synthetic samples after appropriate spiking of common impurities and critical elements at their required specification limits (common elements—5 ppm, critical elements—1 ppm). A systematic study was carried out to compare the analytical performance of DHOA with TBP, which revealed that DHOA could successfully be employed for the determination of 19 trace constituents with lower estimation limits of 5 ppm for common impurities and 1 ppm for critical elements.

Studies on the use of N,N,N′,N′-Tetra(2-Ethylhexyl) Diglycolamide (TEHDGA) for Actinide Partitioning II: Investigation on Radiolytic Stability

N,N,N′,N′-tetra(2-ethylhexyl)diglycolamide (TEHDGA) was found to be a promising extractant for actinide partitioning from high-level waste (HLW) (Part I). In order to evaluate the applicability of TEHDGA to the HLW partitioning process, investigations on its radiolytic stability were carried out. The present work deals with the studies on the uptake of americium by γ-irradiated 0.2 M TEHDGA/n-dodecane in the absence and presence of phase modifiers—di(n-hexyl)octanamide (DHOA), isodecanol and n-decanol—against the absorbed dose up to 1 × 106 Gy in the presence of nitric acid at varying concentrations. The addition of phase modifiers suppressed the radiolysis of TEHDGA in n-dodecane and DHOA was found to be the most effective radiolysis suppressor. Investigations were also carried out on the degradation of neat TEHDGA by γ-irradiation, and it was attempted to isolate and identify its degradation products by instrumental analysis. The radiolysis study showed that the degradation products were formed by the cleavage of the –C-N bond, to eliminate an ethylhexyl group, and the bond adjacent to the ether bond. The results obtained for TEHDGA radiolysis were compared with that of its straight-chain isomer TODGA, and TEHDGA was observed to be more resistant to radiation than TODGA. The changes in the physico-chemical properties of γ-irradiated TEHDGA against the absorbed dose were also investigated.

Studies on the Use of N,N,N´,N´-Tetra(2-ethylhexyl) Diglycolamide (TEHDGA) for Actinide Partitioning. I: Investigation on Third-Phase Formation and Extraction Behavior

Diglycolamides have emerged as an interesting class of extractants for actinide partitioning from high-level waste (HLW). N,N,N´,N´-tetraoctyl diglycolamide (TODGA) has been extensively studied for lanthanide-actinide co-extraction behavior. The present work deals with a branched isomer of TODGA, that is, N,N,N´,N´-tetra(2-ethylhexyl) diglycolamide (TEHDGA). TEHDGA was studied for the extraction of 241Am and third-phase formation. The effect of using different phase modifiers on the prevention of the formation of a third phase during nitric acid extraction by TEHDGA along with the acid uptake behavior by TEHDGA in the presence of the modifiers was studied. The modifiers used for this purpose were di(n-hexyl)octanamide (DHOA), isodecanol, and n-decanol. The effect of the modifiers on the uptake of 241Am as a function of acid concentration and as a function of modifier concentration was also examined. DHOA was found to be a suitable modifier, in spite of its high acid uptake. The uptake of lanthanides Ce, La, Eu, Gd, and Nd and elements such as Fe, Ni, Mn, Mo, Ru, Sr, and Cs with DHOA-modified TEHDGA–n-dodecane solvent systems were investigated. The results obtained indicated that, while DHOA-modified TEHDGA/n-dodecane extracted lanthanides and actinides, it did not show any significant uptake of other elements. Thus, the TEHDGA-DHOA/n-dodecane solvent system can be used effectively for the partitioning of lanthanides and actinides from HLW.

Separation of actinides using hollow fiber supported liquid membranes

Hollow fiber supported liquid membrane (HFSLM) studies were carried out using TODGA (N,N,N′,N′-tetraoctyl diglycolamide) — DHOA (di-n-hexyloctanamide) — NPH (normal paraffin hydrocarbon) and Cyanex-301-n-dodecane as carriers. The first carrier was employed to recover trivalent actinides and lanthanides from simulated high level waste (SHLW) of pressurized heavy water reactor (PHWR) origin. Subsequently, the mutual separation of the actinides and the lanthanides was demonstrated with the second carrier (Cyanex-301-n-dodecane). Quantitative transport of Am(III) and Nd(III) was observed in 45 min from a feed solution (500 mL) containing 1 g/L Nd spiked with 241Am at 3 M HNO3. Similarly, all the lanthanides (La, Ce, Pr, Nd and Sm) and tracer Am(III) were quantitatively recovered in 30 min from SHLW. No significant transport of other metal ions present in SHLW was observed. Quantitative and selective recovery of Am(III) was achieved by Cyanex-301-n-dodecane from feed solution containing 1 g/L total lanthanides spiked with 241Am tracer. The physical stability of HFSLM was reasonably good during continuous operation for over 72 h. Radiolytic stability of solvent and hollow fibre module up to 500 kGy dose was also satisfactory.

Transport of thorium from nitric acid solution by non-dispersive solvent extraction using a hollow fibre contactor

Membrane based non-dispersive solvent extraction (NDSX) of Th(IV) from aqueous nitric acid medium was carried out using di-n-hexyl octanamide (DHOA) in normal paraffin hydrocarbon (NPH) using a commercial hollow fiber module containing microporous hydrophobic polypropylene capillaries. The NDSX operation was carried out with pumping various concentrations of nitric acid (1–6 M) containing Th(IV) through the tube side and organic extractant (usually 1.1 M DHOA in NPH) through the shell side of the hollow fibre capillaries at aqueous and organic phase flow rates of 3.5 mL/s and 4.5 mL/s, respectively. Extraction studies were performed under different hydrodynamics conditions and the overall mass transfer was evaluated under cuonter-current flow condition. The percentage NDSX of Th(IV) increased with the increase in the extractant concentration (from 0.1 M DHOA to 1.1 M DHOA) as well as with nitric acid concentration (from 1 M to 6 M). Stripping studies were carried out using both distilled water as well as oxalic acid as the strippant. The possibility of the separation of U from Th was also evaluated.

Transport of uranium from nitric acid solution by non-dispersive solvent extraction using a hollow fibre contactor

Summary Membrane based non-dispersive solvent extraction (NDSX) of U(VI) from aqueous nitric acid medium was carried out using a commercial hollow fibre module containing microporous hydrophobic polypropylene capillaries. The NDSX operation was carried out by pumping U(VI) solutions at varying concentrations of nitric acid (1-5 M) through the tube side and organic solvent (di-n-hexyl octanamide (DHOA) in normal paraffin hydrocarbon (NPH)) through the shell side of the hollow fibre capillaries. Extraction studies were performed under different hydrodynamic conditions and the overall mass transfer was evaluated under counter-current flow conditions. Counter-current mode was found to be better as compared to the co-current mode. The U(VI) mass transfer rates were positively influenced by the nitric acid as well as DHOA concentrations.

Interfacial Tension Studies of N,N‐Dialkyl Amides

The interfacial tension (IFT) of 1 M solutions of N,N‐dialkyl amide in n‐dodecane against water and nitric acid has been measured at 303 K. Ten amides, namely, dibutyl hexanamide (DBHA), diisobutyl hexanamide (DiBHA), dibutyl octanamide (DBOA), dihexyl hexanamide (DHHA), dibutyl dodecanamide (DBDA), di n‐octyl butanamide (DOBA), diisooctyl butanamide (DiOBA), di n‐octyl isobutanamide (DOiBA), di n‐hexyl octanamide (DHOA), and di n‐octyl hexanamide (DOHA) were synthesized and used. The effect of concentration of DOHA on IFT against 3 M nitric acid was also studied. It was observed that the introduction of branching in an amide on either the acyl or the nitrogen side increases the IFT over its straight chain analogue, as in the case of DiOBA, DOiBA, and DiBHA. Increasing the carbon chain length on the acyl side, keeping the total carbon number constant, was found to increase the IFT considerably. Increasing the concentration of the amide resulted in a decrease in the IFT values, due to the lowering of the concentration of hydrophobic diluent. An increase in the uranium loading of the organic phase in the case of 1 M DOHA, was found to increase the IFT.