Tessy Vincent

Extraction of UO22+ into Ionic Liquid Using TTA and TBP as Extractants

Thenoyltrifluoroacetone and Tributyl-phosphate have been used for extraction of UO22+ into Ionic Liquid 1-Butyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide. Increasing acidity of uranyl solution from 0.01 to 3 mol L−1 HNO3 for TTA in IL, the distribution ratio (DU) and extraction efficiency (%E) both decreased. Further increment in acidity shows reversal of trend. Similar behavior is observed for TBP. With increasing concentration of TTA, %E increases stabilizing at 0.5 mol L−1 TTA. Adding methanol to TTA increased the DU due to active enolic formation. The developed kinetic model estimates the overall mass transfer coefficient (Ka) as 3.6 x 10−2 s−1. Synergistic effect has been observed for combination of TTA + TBP resulting in enhanced DU.

Removal of ruthenium from high-level radioactive liquid waste generated during reprocessing of spent fuel

AbstractRadio-ruthenium (Ru) due to its existence in the form of complexes with varied oxidation state, larger fission yield and relatively long half life is an extremely troublesome nuclide during reprocessing and subsequent waste management. In the process of the concentration of high-level waste (HLW), containing many nitrates of fission products and nitric acid, Ru is oxidised to volatile tetroxide RuO4, which is reduced to its dioxide (RuO2) at the inner surface of the equipment and is deposited there. As a result, the radiation dose of the plant equipments keeps increasing. A process was developed for the separation of Ru from HLW stream by volatilisation using KMnO4 (potassium permanganate) and O3 (ozone) as oxidising agent and its subsequent trapping on adsorbent material polyether ether ketone pellets. Various parameters like acidity, Ru concentration, temperature, time period of reaction and type of adsorbent were studied. The sorption behaviour was examined with various isotherms like Langmuir,...

Catalytic reduction of U(VI) to U(IV) using hydrogen with platinum loaded on alumina and silica

During the reprocessing of spent nuclear fuel, uranium (U) and plutonium (Pu) are together extracted by employing tri-n-butyl phosphate (TBP)/dodecane mixture and their partitioning is achieved by adding uranous nitrate. The partitioning agent, uranous is conventionally produced by the electrolytic reduction of uranyl nitrate. An alternate route for the reduction of U from (VI) to (IV) using hydrogen (H2) as reductant was developed using platinum (Pt) based catalyst. Improvements in the development of the catalyst have been carried out in order to reduce the requirement of Pt without affecting the reduction performance. Experiments using 2 wt% Pt loaded on alumina beads and alumina powder have been performed and results are discussed. As the catalyst supported on alumina was found to be unstable in acidic environment, Pt loaded on silica powder has also been developed. Pt loaded on alumina and silica substrates have been tried to envisage the reduction behaviour using H2 as reductant in presence of hydrazine nitrate which acts as U(IV) stabiliser as well as reductant. Parametric studies have been carried out to optimise the process parameters namely pressure, temperature, U concentration, free acidity, hydrazine concentration and catalyst to U (C/U) ratio. 2 wt% Pt loaded on silica has been selected for further scale up studies for making uranous.

Reduction of uranium (VI to IV) by hydrogenation using Adams’ catalyst

AbstractPlutonium uranium reduction extraction using U(IV) as universal reductant for Pu partitioning is the only technology practiced internationally to recover U and Pu from spent nuclear fuels. Uranous requirement of Indian reprocessing plants is met by the electrolytic reduction of uranyl nitrate with 50–60% conversion. Though the current requirement can be met with this method, it increases the load on uranium purification cycle. In addition, it is a batch process with slow kinetics. In order to achieve higher conversion of uranyl nitrate to uranous nitrate, catalytic reduction method using hydrogen in presence of Adams’ catalyst (PtO2) was tried. Parametric studies have been performed in an autoclave to evaluate the effect of U(VI) concentration, the role of hydrazine nitrate and pressure. It is observed that kinetics is improved at higher pressures. The studies revealed that near total conversion of uranium from (VI to IV) can be achieved by the catalytic reduction route.

Microbial community modulates electrochemical performance and denitrification rate in a biocathodic autotrophic and heterotrophic denitrifying microbial fuel cell

A comparison of autotrophic (AD) and heterotrophic (HD) cathodic denitrification in a Microbial Fuel Cell (MFC) was made in this study. Denitrifying microbial consortia were developed from cow manure and soil and acclimatized under AD and HD conditions. The AD MFC supported the power output of 4.45 W m-3 while removing nitrate nitrogen (NO3--N) at the rate of 0.118 kg NO3--N m-3 d-1. Significant power output (3.02 W m-3) and nitrate removal rate (2.06 kg NO3--N m-3 d-1) were achieved in HD MFC. Further, 16S rDNA based community analysis revealed higher diversity in HDMFC. The genus Thauera and Pseudomonas were predominant in ADMFC while genus Klebsiella and Alkaliphilus were abundant in HDMFC. The abundance of the denitrifying genes namely narG, nirS, and nosZ were assessed with the help of quantitative PCR and presence of all the genes in both the conditions ensured the necessary molecular requirements for complete denitrification.

Denitration of High Nitrate Bearing Alkaline Waste Using Two Stage Chemical and Biological Process

During the operation of radio-chemical plants, low and intermediate level alkaline waste streams containing nitrates is generated. Some of these waste streams contain large concentrations of nitrates exceeding 100,000 ppm and is of highly alkaline nature. To remediate such wastes, a two stage denitration process was developed—with chemical denitration as the first stage, followed by biological denitrification. The chemical denitration process was developed using catalytic reduction technique for destructing the nitrates and converting them to harmless nitrogen gas using a suitable reductant, in the presence of bimetallic Pd-Cu catalysts. The reductant used was formalin (37–41 % formaldehyde) for the experimental work and different reaction parameters were determined to yield a higher reduction. For studies at laboratory scale, approx. 97 % nitrate reduction of synthetic waste prepared using sodium nitrate was achieved in 5 h and denitration of simulated waste resulted in nitrate reduction of approx. 96 % in 6 h and the final nitrate concentration was near 5000 ppm for both cases. According to Indian standards, the maximum permissible limit of nitrate in water is set at 100 ppm and since the reduced concentration doesn’t match the environmentally safe limits, the biological denitrification process was used for further reduction. Biological process was developed for treating effluent containing approx. 5000 ppm of nitrate, formic acid and unreacted formaldehyde, traces of catalyst and NaOH. The bacteria used were denitrifying bacteria. A continuous anaerobic packed bed reactor was used for denitration process.

Uranous Nitrate Preparation by Catalytic Reduction: A Pilot Plant Facility

Abstract A nonelectrolytic method for uranous preparation, deploying catalytic reduction with hydrogen and leading to highly improved kinetics and near total conversion of uranyl nitrate to uranous nitrate, has been developed. Detailed experimental studies up to 5-ℓ scale, involving selection of stable supports for the platinum-based catalyst, optimized process parameters with regard to catalyst-to-uranium (C/U) ratio, acidity, hydrazine concentration, temperature, and pressures, have led to a deployable flow sheet, for near total conversion of uranyl nitrate to uranous nitrate. Based on the studies at various stages, a facility for making 70 ℓ of uranous per batch in 0.5-h duration has been installed, and the process has been demonstrated on a pilot scale. Active runs have been taken, with various C/U ratios, namely, 1:200, 1:250, 1:300, and 1:350, in a gas induction reactor with uranyl nitrate solution generated from the reprocessing plant.