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  • Author: Dipti Shah x
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Complexing behaviour of three dihydroxybenzenes (DHB) namely, hydroquinone, resorcinol and catechol with Th(IV) along with their protonation constants were studied in 1 M NaClO4 medium at 23 ± 0.5 °C, using pH titration technique. Both protonation and metal-ligand equilibrium constants of dihydroxybenzenes were computed using advance software suite of program HYPERQUAD. Logarithmic values of overall protonation constants (log β1H and log β2H) were found to be 11.47 ± 0.05 and 21.45 ± 0.06, for hydroquinone, 11.76 ± 0.04 and 20.98 ± 0.04 for resorcinol and 12.58 ± 0.03 and 21.87 ± 0.08 for catechol respectively. Complex formation has been investigated in the pH range 2 to 4. The logarithmic values of metal-ligand equilibrium constants obtained in the present work were β13-1=48.51 ± 0.67 and β14-1=64.86 ± 1.25 for hydroquinone, β110=16.98 ± 0.16, β13-1=46.46 ± 0.18 and β14-2=59.65 ± 0.20 for resorcinol and β11-1=14.06 ± 0.10 for catechol. The literature values were reviewed.

Abstract

The study demonstrates the accomplishment of single step, direct supercritical fluid carbon dioxide (SC CO2) dissolution and extraction of uranium from crude matrices viz. yellow cakes (>90%) and rock phosphate ores (70%) employing adducts of trialkyl phosphates and nitric acid, thus avoiding free acid usage and eliminating number of process steps. Rock phosphate ore was made amenable for supercritical fluid extraction (SFE) system by unique strategy of pyrohydrolytic removal of fluorine. Pressure and temperature conditions, which were found to influence uranium extraction efficiency, were optimized at 150 atm. and 323 K. Two milliliter of adduct amount was found to be adequate. Adducts of branched alkyl phosphate, tri-isoamyl phosphate and tri-ethyl hexyl phosphate (TEHP), yield better purity in comparision to straight chain tri-butyl phosphate (TBP).

The determination of fluoride from diverse matrices at front and back end of nuclear technology and some studies from this laboratory on optimizations of different experimental parameters differing with multiple fuels and reactor materials, have been reviewed. The most useful techniques such as fluoride ion selective electrode (F-ISE) and ion-chromatography (IC) widely adopted as routine methods for fluoride determination in nuclear industry have been discussed. The effect of various buffer strengths on the response of the fluoride ion selective electrode has been examined. The ion chromatographic studies on mobile phase concentration, medium of sample, sample injection volume etc. to get distinct fluoride peak within optimum time in presence of other anionic species in diverse concentrations have been reported. The results of various sample matrices such as UO2, PuO2, (U,Pu)O2, Pu-alloy, thoria, zircaloy, slag, HLLW, LLLW etc., analyzed after matrix separation using pyrohydrolysis setup, for both solid and liquid samples and without matrix separation by masking potentially interfering ions of liquid samples, have been presented.

Abstract

Pyrohydrolysis method was studied for the separation of Cl and F from U-Zr and U-Pu-Zr alloy nuclear fuels and determination by ion chromatography. A detailed study was performed on pyrohydrolysed products of U-Zr alloy, obtained on heating in moist argon and oxygen atmospheres using X-ray powder diffraction (XRD) and thermogravimtric methods. Using oxygen as the carrier gas pyrohydrolysis performed at 900 ℃ was complete within 30 min. It was found that, moist oxygen as carrier gas only could open the matrix completely within stipulated time. This was attributed to the formation of α-U3O8, which was not possible in moist argon heating for 30 min. The pyrohydrolysis in moist Ar required 60–90 min for complete removal of halides. The method was then successfully extrapolated to U-Pu-Zr alloys. The results showed recovery up to 90% or above for the optimized conditions.