SORPTION BEHAVIOUR OF MOLYBDENUM ON DIFFERENT METAL OXIDE ION EXCHANGERS

The thermal desorption of molybdenum(VI)-oxide from an inorganic adsorber matrix is an efficient new procedure for the final purification of fission molybdenum from inorganic and organic impurities. The investigations presented in this paper served to find out suitable thermally resistant inorganic ion exchangers and practical loading conditions for the preceding chromatographic sorption of molybdate anions from the process solution, in batch distribution experiments the influence of HN0₃-molarity, Mo-concentration and molybdenum loading on the Mo-sorption of Al2O₃, SnO₂, MnO₂ and Sb₂O₅ is described in terms of their retention capacities and distribution coefficients. It could be confirmed that the retention capacity - as expected -depends strongly on the specific surface area, crystallinity and acidity of the oxide. AL₂O₃ and SnO₂ with capacities of 30 and 4.7?mg Mo/g ion exchanger, respectively, proved to be superior to MnO₂ and Sb₂O₅ owing to their faster Mo-sorption and better stability against abrasion.

In further distribution experiments the co-sorption of relevant fission products like Ce, I, Ru, Sn, Te and Zr on SnO₂ - the moste suitable material for a Mo-sorption over a wide range of nitric acid molarity - has been determined.     

EXTRACTION STUDY FOR TRUEX PROCESS USING SHORT-LIVED RADIONUCLIDES PRODUCED BY NEUTRON IRRADIATION OF URANIUM

The extraction behavior of short-lived fission products and neptunium was studied by using octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide under the conditions of the transuranic elements extraction (TRUEX) process. The short-lived fission products and neptunium were produced by neutron irradiation of UO₂ of natural uranium, and the extraction behavior of ⁹³Y, ⁹⁹Mo, ⁹⁷Zr, ¹²²Sb, ¹³²Te, ¹³³I, ¹⁴³Ce, and ²³⁹Np was simultaneously studied, where ¹²²Sb was produced by neutron irradiation of antimony metal. The extraction of fission products and Np under the conditions of the PUREX process was also studied for comparison. The extraction of nuclides in the presence of large amounts of uranium(VI), and the presence of oxalic acid was examined. The conditions and performance of the TRUEX extraction were discussed by considering the obtained results.     

A TBP/BTBP-Based GANEX Separation Process – Part 3: Fission Product Handling

A Group ActiNide EXtraction (GANEX) separation system for transmutation has been developed, combining CyMe₄-BTBP with TBP and cyclohexanone. This new GANEX solvent has proven efficient in actinide extraction but also been found to extract some undesired fission products and corrosion products. Three major fission products were primarily selected for the study: Mo, Zr, and Pd. There are three main strategies for handling the extraction problem, all of which have been investigated and discussed; these are Pre-extraction, Suppression, and Scrubbing. The only strategy that was found to control the behavior of all three main fission products was suppression by the combination of two water-soluble complexing agents bimet and mannitol.     

Actinide Partitioning with a Modified TODGA Solvent: Counter-Current Extraction Studies with Simulated High Level Waste

Actinide partitioning studies with improved N,N,N',N'-tetraoctyl diglycolamide (TODGA) solvent (0.05 M TODGA + 5% iso-decanol in n-dodecane) has been explored in order to achieve better decontamination from fission products. The distribution behavior of various metal ions, viz. Am, Pu, U, Eu, Sr, Pd, Cs, Tc, Fe, and Mo with improved TODGA solvent was investigated. Lower concentration of TODGA (0.05 M as compared to previously proposed 0.1 M or 0.2 M) exhibited required extraction properties for actinide partitioning from pressurized heavy water reactor high level waste (PHWR-HLW). Counter-current extraction studies with simulated PHWR-HLW spiked with different radio-tracers (viz. ²⁴¹Am, ¹⁵²Eu, ¹³⁷Cs, ^85,89Sr, ⁵⁹Fe, ¹⁰⁶Ru, ¹⁰⁹Pd, ⁹⁵Zr, and ⁹⁹Mo) suggested that > 99.9% of the trivalent actinides and lanthanides could be extracted in six stages and stripped in four stages. The decontamination factor for various fission products with respect to Am was: 3918 (Cs), 2990 (Sr), 1150 (Zr), 1407 (Ru), 1185 (Pd), and 3250 (Mo). The counter-current extraction studies with the irradiated solvent (500 kGy) reflected a significant amount of Mo extraction.     

Interaction of powdery Al, Zr and Ti with atmospheric nitrogen and subsequent nitride formation under the metal powder combustion in air

The combustion process in air for aluminum nanopowders (nAl), micron-sized powders of aluminum (μAl), titanium (μTi) and zirconium (μZr) was accompanied by the predominant reaction of the metals with N₂ and the subsequent stabilization of the nitride phases (from 38 wt.% of ZrN for μZr combustion to 72 wt.% of AlN for nAl combustion) in the condensed combustion products (CCP). The combustion process, composition and structure of CCP of nAl, μAl, μTi, and μZr were studied. Scanning electronic microscopy (SEM), X-ray diffraction (XRD), energy dispersive (X-ray) spectroscopy (EDX), and chemical analysis were performed on both initial powders and CCP. The combustion mechanism for the studied metal powders was experimentally proved. The formation of a large amount of non-equilibrium products (AlN, ZrN, TiN) instead of oxides in air is the special feature of the above mentioned experimental conditions. Nitride formation in air was defined by high temperatures and high burning rates during combustion of powdery Al, Ti and Zr.     

Surface strengthening of Ti3SiC2 through magnetron sputtering of Mo and Zr and subsequent annealing

Magnetron sputtering deposition of Mo and Zr and subsequent annealing were conducted with the motivation to modify the surface hardness of Ti₃SiC₂. For Mo-coated Ti₃SiC₂, Si diffused outward into the Mo layer and reacted with Mo to form molybdenum silicides in the temperature range of 1000–1100 °C. The MoSi₂ layer, however, cracked and easily spalled off. For Zr-coated Ti₃SiC₂, Si also diffused outward to form Zr–Si intermetallic compounds at 900–1100 °C. The Zr–Si compounds layer had good adhesion with Ti₃SiC₂ substrate, which resulted in the increased surface hardness.     

Development of a TODGA based Process for Partitioning of Actinides from a PUREX Raffinate Part I: Batch Extraction Optimization Studies and Stability Tests

Abstract

The extractant, N,N,N′,N′‐tetraoctyl diglycolamide (TODGA) has been evaluated for the separation of actinides(III) and lanthanides(III) from a high active raffinate (HAR). The effect of oxalic acid and HEDTA complexant on the extraction of actinides(III), lanthanides(III), and important fission products (e.g. Mo, Pd, Sr, Zr, Ru etc.) from synthetic HAR has been studied with 0.2 mol/L TODGA in TPH. With an extractant mixture of TODGA and tributyl phosphate (TBP) the amount of oxalic acid can be reduced to less than 0.3 mol/L for the effective complexation of zirconium, whereas the distribution ratios of actinides(III) and lanthanides(III) are still high for the separation from HAR. Furthermore the maximum loading of lanthanides (e.g. Nd) can be significantly increased by adding TBP to the extractant. However, the extraction of oxalic acid and nitric acid also increased by the addition of TBP, which can lead to problems during back extraction of the loaded extractant. Extraction studies after radiolysis and hydrolysis reveal that the TODGA+TBP mixture is a sufficient stable extraction system suited for further process development studies.     

Direct Selective Extraction of Actinides (III) from PUREX Raffinate using a Mixture of CyMe4BTBP and TODGA as 1-cycle SANEX Solvent Part III: Demonstration of a Laboratory-Scale Counter-Current Centrifugal Contactor Process

The direct selective separation of the trivalent actinides americium and curium from a simulated Plutonium Uranium Refining by EXtraction (PUREX) raffinate solution by a continuous counter-current solvent extraction process using miniature annular centrifugal contactors was demonstrated on a laboratory scale. In a 32-stage spiked test (12 stages for extraction, 16 stages for scrubbing, and 4 stages for Am/Cm stripping), an extractant mixture of CyMe₄BTBP and TODGA in a TPH/1-octanol mixture was used. The co-extraction of some fission and corrosion product elements, such as zirconium and molybdenum, was prevented by using oxalic acid. Co-extracted palladium was selectively stripped using an L-cysteine scrubbing solution and the trivalent actinides were selectively stripped using a glycolic acid-based stripping solution. It was demonstrated that a selective extraction and high recovery of > 99.4% of the trivalent minor actinides was achieved with low contamination by fission and corrosion products. The product contained 99.8% of the initial americium and 99.4% of the initial curium content. The spent solvent still contained high concentrations of Cu, Cd, and Ni. The experimental steady-state concentration profiles of important solutes were determined and compared with those from computer-code calculations.     

EXTRACTION OF Am FROM NITRIC ACID BY CARBAMOYL-PHOSPHORYL EXTRACTANTS: THE INFLUENCE OF SUBSTITUENTS ON THE SELECTIVITY OF Am OVER Fe AND SELECTED FISSION PRODUCTS

A number of neutral extractants containing the P(0)(CH₂)_nC(0)N raolety were evaluated for their ability to extract Am from nitric acid and their selectivity for Am over Fe and selected fission products. Extractants containing alkoxy, alkyl, and aryl substltuents were evaluated. Tetrachloroethylene was used as a diluent. Fission products selected for study were Y, Zr, Mo, Tc, Ru, Rh, Pd, La, Ce, Pr, Nd, Sra, and Eu. The conclusions drawn were that the most efficient and selective Am extractant contains a single carbon bridging group, one or two phenyl groups attached to the phosphorus atom and l9obutyl groups attached to the amide nitrogen.     

Synthesis,characterization and evaluation of Ni–Mo/Zr–Al2O3 catalyst for hydro-conversion of lignite-based heavy carbon resources

NaOH depolymerized products (SDP) of Shengli lignite was used as lignite-based heavy carbon resources in this study. Hydrotreatment of SDP over Ni–Mo/Al₂O₃ and Ni–Mo/Zr–Al₂O₃ catalysts was investigated. It was found that the incorporation of Zr to Ni–Mo/Al₂O₃ catalyst results in the easy reduction of metal oxides and the increase of the stacking degree and length of MoS₂ slabs. Both of Ni–Mo/Al₂O₃ and Ni–Mo/Zr–Al₂O₃ catalysts show better performance for hydrogenation of SDP and can be used repeatedly. The incorporation of Zr to Ni–Mo/Al₂O₃ catalyst significantly inhibits the formation of tetrahydrofuran insolubles (THFI), promotes the formation of two-ring aromatics and increases HS yield compared to that over Ni–Mo/Al₂O₃ catalyst.     

Electrochemical and morphological properties of zirconium conversion coating in the presence of nickel ions on galvanized steel

A hexafluorozirconic acid-based conversion coating was applied on a galvanized steel substrate and the influence of nickel ion from nickel sulfate solution (in zirconium solution and in a separate solution) on the corrosion resistance behavior and morphology of zirconium conversion coating was investigated. Electrochemical impedance spectroscopy and DC polarization were conducted in 3.5 wt% NaCl solution in order to optimize practical conditions of zirconium conversion coating and NiSO₄ solution on the galvanized steel substrate. Field emission scanning electron microscopy and X-ray photoelectron spectroscopy were employed to study the morphology and composition of the coated surfaces. Results revealed that the conversion coating obtained from solution containing zirconium and nickel ions (Zr + Ni) did not improve corrosion resistance and uniformity of the coating in comparison with Zr conversion coating in optimized condition. However, a positive effect was obtained from samples coated with separate solutions of zirconium and nickel (Zr–Ni). Improved corrosion resistance and morphology of Zr-based conversion coating were observed in Ni²⁺ concentration, pH, and immersion time of 10 g/L, 6 and 300 s, respectively. Morphology and surface composition analysis proved that two separate layers of conversion coating containing zirconium, zinc, and nickel oxide/hydroxide compounds were formed in the case samples that were treated by separate solutions. This led to better uniformity and higher thickness of the coating. Finally, adhesion strength of epoxy organic coating on galvanized steel with and without conversion coating was investigated by pull-off measurement. Zr–Ni conversion coating in optimum conditions had a positive effect on adhesion of organic coating in comparison with blank sample and samples pretreated with Zr and Zr + Ni conversion coatings through increased surface roughness and physical interlocking.     

Behavior of Molybdenum (VI) in {DMDOHEMA–HDEHP/nitric acid} Liquid–Liquid Extraction Systems

The EXAm (extraction of americium) process was developed for americium recycling in future nuclear fuel cycles. In this solvent extraction system, a combination of two extractants, N,N′-dimethyl-N,N′-dioctyl-hexylethoxy malonamide (DMDOHEMA) and di-2-ethylhexyl phosphoric acid (HDEHP), in TPH (hydrogenated tetrapropylene) is used to extract americium in the first step of the process at high acidity (HNO₃ 5–6 M). Americium is co-extracted with light lanthanides and other fission products like molybdenum, iron, ruthenium, etc.. Molybdenum is selectively scrubbed during the second step at low acidity using citric or glycolic acid as a buffer and complexing agent. The speciation of Mo(VI) in aqueous solutions is highly dependent on acidity and Mo concentration. In this article, a simple thermodynamical model is proposed for Mo(VI) scrubbing based on batch extraction experiments (with pH and cation concentration variations) and stoichiometries of complexes formed in the organic phase according to electrospray ionization mass spectrometry (ESI-MS) experiments and published data on Mo(VI) speciation. At high acidity ([HNO₃] > 1 M), the MoO₂²⁺ species is strongly extracted by the solvent DMDOHEMA–HDEHP according to a solvate mechanism. At lower acidity ([HNO₃] < 1 M), cation exchange mechanisms become predominant and DMDOHEMA does not participate to the extraction Mo(VI) anymore. During Mo scrubbing at pH higher than 1, the extraction of Mo as neutral species (like MoO₃) and anionic species (like MoO₄^2–) has to be taken into account in the model to predict the “bell-shape” of Mo distribution ratio evolution as a function of pH. This model was then implemented in the PAREX simulation code developed by the CEA to build the flowsheet for the “Mo scrubbing” section of EXAm process and predict Mo concentrations profiles in batteries of mixer-settlers during pilot-scale tests.     

Development of Mo recovery and concentration column processes for production of 99Mo from accelerator-driven irradiation of aqueous uranyl-sulfate solution

ABSTRACT

Recovery and concentration columns were designed for separation of Mo from highly concentrated uranyl–sulfate solution. Molybdenum uptake on titania sorbent, from concentrated uranium solutions, is superior to alumina and enables use of low-enriched uranium (LEU, <20% U-235) for ⁹⁹Mo production. Compared to highly enriched uranium (HEU), LEU requires five times more uranium to produce the same amount of Mo. Isotherm parameters were examined for Mo, Te, and Tc. The VERSE (VErsatile Reaction SEparation) model was used to generate profiles for metal ion concentrations in the columns and determine the minimum column length required for 99.9% Mo capture. Column designs were verified with an irradiated uranyl sulfate solution in a pilot-scale process, where 1.4 Ci of ⁹⁹Mo was produced, recovered, and purified. Partitioning of fission products on titania columns is also presented.     

Zirconium tetra-n-butylate modified with different organic acids: Hydrolysis and polymerization of the products

In this work, (a) complexation reaction of zirconium tetra-n-butylate, Zr(OBu ⁿ )₄, with MAc and different organic acids, (b) the hydrolysis reaction of modified Zr species, and (c) the polymerization reaction of complex products are studied. Zr(OBu ⁿ )₄ was reacted with different mole ratios of methacrylic acid (MAc) at room temperature and the maximum combination ratio was found to be 1:2 [Zr(OBu ⁿ )₄:MAc] by FT-IR. The modification of zirconium tetra-n-butylate with the acid mixtures [methacrylic acid-acetic acid (MeCOOH), methacrylic acid-propionic acid (EtCOOH), methacrylic acid-butyric acid (PrCOOH)] was made for a combination ratio of 1:1:1 [MAc:RCOOH:Zr(OBu ⁿ )₄; R: Me, Et, Pr] and the products were characterized by¹H-NMR, FT-IR, and UV spectroscopies. Following their synthesis, hydrolysis of the complexes with various amounts of water and polymerization with benzoyl peroxide were realized. The hydrolysis and polymerization products of the complexes were studied by Karl-Fischer coulometric titration and thermal analysis, respectively. Methyl ethyl ketone(MEK) and chloroform were chosen as solvents.     

Densification,microstructure, elastic and mechanical properties of reactive hot-pressed ZrB2–ZrC–Zr cermets

In this study, cermets composed of zirconium diboride and zirconium carbide with intergranular zirconium were sintered by reactive hot-pressing. Relative density exceeding 97% was obtained for the sintered cermets having four distinct compositions varying in concentration of excess Zr. Their densification behaviour was examined by monitoring displacement during sintering. The microstructure was characterized by scanning electron microscopy and X-ray diffraction, and the elastic and mechanical properties were evaluated at room temperature. The effects of Zr concentration on the densification and mechanical properties were assessed. The ZrB₂ and ZrC micron-grains coarsened with increasing amount of Zr starting material. In addition, the cermets exhibited high flexural strength (546–890 MPa) and fracture toughness (6.63–10.24 MPa m^1/2), which simultaneously increased with increasing Zr concentration. However, the elastic moduli and hardness (11–18 GPa) decreased with increasing Zr. The shear modulus and Young's modulus were in the range of 150–190 GPa and 360–440 GPa, respectively.     

Zirconium tetra-n-butylate modified with different organic acids: Hydrolysis and polymerization of the products

In this work, (a) complexation reaction of zirconium tetra-n-butylate, Zr(OBu ⁿ )₄, with MAc and different organic acids, (b) the hydrolysis reaction of modified Zr species, and (c) the polymerization reaction of complex products are studied. Zr(OBu ⁿ )₄ was reacted with different mole ratios of methacrylic acid (MAc) at room temperature and the maximum combination ratio was found to be 1:2 [Zr(OBu ⁿ )₄:MAc] by FT-IR. The modification of zirconium tetra-n-butylate with the acid mixtures [methacrylic acid-acetic acid (MeCOOH), methacrylic acid-propionic acid (EtCOOH), methacrylic acid-butyric acid (PrCOOH)] was made for a combination ratio of 1:1:1 [MAc:RCOOH:Zr(OBu ⁿ )₄; R: Me, Et, Pr] and the products were characterized by¹H-NMR, FT-IR, and UV spectroscopies. Following their synthesis, hydrolysis of the complexes with various amounts of water and polymerization with benzoyl peroxide were realized. The hydrolysis and polymerization products of the complexes were studied by Karl-Fischer coulometric titration and thermal analysis, respectively. Methyl ethyl ketone(MEK) and chloroform were chosen as solvents.     

Zirconium tetra-n-butylate modified with different organic acids: Hydrolysis and polymerization of the products

In this work; (a) complexation reaction of zirconium tetra-n-butylate, Zr(OBu ⁿ )₄, with MAc and different organic acids. (b) the hydrolysis reaction of modified Zr species, and (c) the polymerization reaction of complex products are studied. Zr(OBu ⁿ )₄ was reacted with different mole ratios of methacrylic acid (MAc) at room temperature and the maximum combination ratio was found to be 1∶2 [Zr(OBu ⁿ )₄∶MAc] by FT IR. The modification of zirconium tetra-n-butylate with the acid mixtures [methacrylic acid-acetic acid (MeCOOH), methacrylic acid-propionic acid (EtCOOH), methacrylic acidbutyric acid (PrCOOH)] was made for a combination ratio of 1∶1∶1 [MAc∶RCOOH∶Zr(OBu ⁿ )₄∶R∶Me. Et, Pr] and the products were characterized by¹H-NMR, FT-IR, and UV-spectroscopies. Following their synthesis, hydrolysis of the complexes with various amounts of water and polymerization with benzoyl peroxide were realized. The hydrolysis and polymerization products of the complexes were studied by Karl-Fischer Coulometric titration and thermal analysis respectively. Methyl-ethyl-ketone (MEK) and chloroform were chosen as solvents.     

Partial Oxidation of Isobutane Over Hydrothermally Synthesized Mo–V–Te–O Mixed Oxide Catalysts

Mo–V–O and Mo–V–Te–O catalysts were prepared by a hydrothermal synthesis route and tested for the oxidation of isobutane and isobutene. Characterization results (XRD, FT-IR, TPR, BET, and XPS) showed that the structure and property of Mo–V-based catalysts are considerably different depending on the presence of Te element and calcined temperature. Catalytic tests showed that the maximum selectivity of methacrolein (44.2%) can be achieved over a MoV_0.3Te_0.25-600 catalyst for the selective oxidation of isobutane. It is found that TeMo-containing phases are active and selective for the selective oxidation of isobutane to methacrolein.     

The use of various metal carbonyls as catalyst precursors for coal hydroliquefaction

The catalytic activity of metal carbonyl complexes of chromium, molybdenum, tungsten, manganese, iron, cobalt, and nickel in the liquefaction of coal (Illinois No. 6, Wandoan and Mi-ike) was investigated. The carbonyl compounds of molybdenum, tungsten, iron, cobalt, and nickel acted as highly active catalysts for the liquefaction of Illinois No. 6 coal, resulting in high coal conversion (>90%) and high oil yield (>32%), under hydrogen pressure of 50 kg cm^?1 in a nonhydrogen-donating solvent at 425°C for 60 min. Among the catalysts surveyed, Mo(CO)₆ gave the highest oil yield (57.7%) and the largest amount of hydrogen transferred to coal (3.1 wt.% of d.a.f. coal). However, the molybdenum and tungsten carbonyls did not exhibit high catalytic activity for low sulfur Wandoan coal in the absence of added sulfur. On the other hand, cobalt and nickel carbonyls showed high catalytic activity irrespective of the amount of sulfur in the reaction system. Fe(CO)₅Mo(CO)₆ binary catalyst promoted hydroliquefaction of Wandoan coal, resulting in increases in oil yield and transfer of hydrogen to coal in the presence of sulfur.     

Preparation of porous resin loaded with crystalline hydrous zirconium oxide and its application to the removal of arsenic

A porous resin loaded with monoclinic or cubic hydrous zirconium oxide was prepared by incorporation of ZrOCl₂·8H₂O into porous spherical polymer beads followed by hydrolysis and hydrothermal treatment of the zirconium salt. Hydrous zirconium oxide appeared to deposit inside the pores with relatively large diameter. The adsorption capacity and distribution coefficients for As(III) and As(V) were determined by batch procedures. The hydrous zirconium oxide-loaded resin (Zr resin) showed a strong adsorption for As(V) at slightly acidic to neutral pH region while As(III) was favorably adsorbed at pH around 9 to 10. The removal of low concentrations of arsenic from the model effluents to meet the demand of Japanese industrial effluent standard (0.1 ppm) was successfully achieved by the column operation packed with the Zr resin. The Zr resin was regenerated by treatment of the column with 1 M sodium hydroxide followed by conditioning with 0.2 M acetate buffer solution. The amount of zirconium leached out during the adsorption and regeneration cycles was negligibly small and the column can be used repeatedly.