Experiments have been conducted to study the diffusion of iodide, cesium and strontium ions through intact and fractured rock samples of charnockite rock formation present at Kalpakkam, India. The diffusion coefficient (Di) of these ions for the intact and fractured rock samples has been evaluated and is found to be ranging from 0.76·10–14 to 6.25·10–14 m2/s and 0.67·10–9 to 84.6·10–9 m2/s, respectively. The study reveals that despite the sorbing nature of Cs and Sr, these ions diffuse comparatively faster than the iodide ion (non-sorbing) through the intact and fractured rock mass. The results have been validated vis-à-vis those reported in the literature and a good agreement has been noticed. This paper deals with details of the testing methodology developed to assess the radionuclide migration as well as the rock mass suitability for safe disposal of the radioactive waste.
The extraction behavior of uranium (VI) from chloride medium with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) in dodecane has been investigated under wide range of conditions. Attempts have been made to establish the extraction mechanism of uranium(VI) with PC-88A. Treatment of the distribution data by slope analysis technique showed the formation of a monomeric complex of the nature [UO2(A2H)2]. Formation of this species was also confirmed by non-linear least square regression of the distribution data to the mathematical expression correlating percentage extraction and acidity. In this investigation attempts have also been made to develop a mathematical model for the system (UO2Cl2-HCl-H2O-PC-88A-dodecane) using experimental data on the distribution of uranium against initial aqueous acidity at different initial metal concentration. The mathematical model D = 37.547±0.223/Ci1/2×[Hi]2 can be used to predict the concentration of uranium in organic as well as in aqueous phases at any initial concentration of uranium [Ci] and initial hydrogen ion concentration [Hi]. The extraction constant (Kex) has been calculated.
A new inorganic ion exchanger, zirconium hexacyanoferrate(III) prepared by adding potassium hexacyanoferrate(III) to zirconium oxychloride at 80°C has been found to be stable in acids and salt solutions. Distribution coefficient values determined for various metal ions show that the exchanger has a high affinity for bismuth. Binary separations of Bi(III) from a number of other metal ions at different concentrations were achieved on the column of the exchanger. Thus the exchanger has been found useful for the separation of bismuth from a large number of metals.
α-Hemihydrate was allowed to hydrate
in the presence of tartaric, succinic, malic or citric acids at room temperature
at a water/ binder ratio of 0.35. Hydration of hemihydrate leading to the
crystallisation of calcium sulphate dihydrate is an exothermic process. The
temperature rise during hydration was measured as a function of time using
a semi-adiabatic method. The temperature rise–time curves are similar
for all investigated systems but with different induction period. The results
showed that calcium sulphate dihydrate crystallisation is a nucleation controlled
process and different acids are chemisorbed at the surface of forming nuclei
to different extent. Processes taking place during nucleation may control
the morphology of resultant crystals. Infrared spectral and differential scanning
calorimetric studies confirmed the adsorption of carboxylic acids at the surface
of dihydrate crystals.
Authors:G. Singh, B. Baranwal, I. Kapoor, D. Kumar, C. Singh, and R. Fröhlich
Three hexamethylenetetramine (HMTA) metal nitrate complexes such as [M(H2O)4(H2O-HMTA)2](NO3)·4H2O (where M=Co, Ni and Zn) have been prepared and characterized by X-ray crystallography. Their thermal decomposition have been studied
by using dynamic, isothermal thermogravimery (TG) and differential thermal analysis (DTA). Kinetics of thermal decomposition
was undertaken by applying model-fitting as well as isoconversional methods. The possible pathways of thermolysis have also
been proposed. Ignition delay measurements have been carried out to investigate the response of these complexes under condition
of rapid heating.
Authors:Ms. Singh, C. Panda, V. Chakravortty, and K. Dash
Solvent extractions of thorium(IV) and uranium(VI) by a commercially available chelating extractant LIX-26 (an alkylated 8-hydroxyquinoline) or 8-hydroxyquinoline, benzoic or salicylic acid, dipentyl sulphoxide (DPSO) and their mixtures with butanol as modifier in benzene/methylisobutyl ketone (MIBK) as the diluent have been studied. Extraction of uranium(VI) by 10% LIX-26 and 10% butanol in benzene becomes quantitative at pH 5.0. The pH 0.5 values for the extraction of thorium(IV) and uranium(VI) are 4.95 and 3.35, respectively. Quantitative extraction of thorium(IV) by the mixture of 0.1 M oxine and 0.1 M salicylic acid in methylisobutyl ketone was observed at pH 5.0. The influence of concentration of various anions on the extraction of Th4+ by mixtures of LIX-26 and benzoic acid has been studied. Studies on extraction of thorium(IV) and uranium(VI) by mixtures of LIX-26 (HQ) and DPSO show that the extracted species are possibly of the type [ThQ2/DPSO/2/SCN/2] and [UO2Q2/DPSO/], respectively.
Authors:N. Singh, C. Zimmerman, L. Lewis, and M. Wrenn
A radiochemical procedure has been developed for the simultaneous determinations of alpha-emitting isotopes of uranium and plutonium in bovine bone. The radiochemical recoveries ranged from 61 to 93% with a mean of 80±10% for uranium and 57 to 88% with a mean of 75±11% for plutonium. The method was successfully used for human bone.
Authors:K. Krishnan, K. D. Singh Mudher, and N. C. Jayadevan
Double sulphates of uranium(IV) with Mg, Ni, Cu and Zn with the general formula MU(SO4)3·8H2O were prepared from their respective metal sulphates. All the four compounds are isostructural and belong to monoclinic system. The thermal decomposition at 850 °C results in a single phase of triuranates MU3O10 which on further heating above 980 °C decompose to give the metal oxide and U3O8 in case of Ni and Zn compounds and MUO4 for Mg and Cu compounds. The activation energy for dehydration of these four compounds has been calculated using non-isothermal thermogravimetric data.
Authors:R. C. Mehrotra, S. N. Varma, and B. K. Singh
DTA techniques were employed to study the thermal and structural characteristics of hydrated aluminium oxides and aluminous clays of the Pipra pelitic rocks from district Sidhi, India. Detailed microscopic investigations, X-ray and chemical analyses reveal that these clays were derived by the localized weathering of arkosic metasediments. The chemical and normative behaviours have confirmed their formation by the isochemical metamorphism of arkose, aided by a little granitization and followed by minor retrogression. A tentative correlation between the thermal and structural changes of these oxides and clay minerals at various transition temperatures has nicely displayed the presence of kaolinite, diaspore and gibbsite. The exothermic curves of kaolinite confirm the recrystallization. The presence of kaolinite in the clay fractions indicates the detrital origin.
Authors:R. K. Singh Raman, F. C. Parida, and A. S. Khanna
Although liquid sodium has proved to be a technologically superior and economically viable coolant in the heat-exchange circuits of fast reactors, it is fraught with the serious problems of fire hazards in the event of accidental leakages into the ambient air. For the rapid and effective suppression of sodium fires, sodium bicarbonate has emerged as a potential extinguishant. This paper attempts a description of the thermal decomposition behaviour of sodium bicarbonate fine powder in vacuum on the basis of thermogravimetry and differential thermal analysis. The analog percentage mass change data, transformed into dimensionless extents of reaction and calculated rates of reaction, are then analysed by a generalized computational technique. The results indicate that the most probable rate-controlling step is a process of three-dimensional contraction of the bicarbonate particle surface, with activation energyE=82.94 kJ mol−1 and frequency factorA=34.73×106 s−1. The decomposition temperature of sodium bicarbonate shows an upward trend with increasing heating rate.