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Abstract  

ThO2(cr) was dissolved in the solutions containing various carbonate ion concentrations, and the results were compared with thorium solubility in a domestic granitic groundwater having very low ionic strength. The soluble thorium concentration excluding colloids after phase separation increased with increasing carbonate concentration. However, the thorium concentration in the real groundwater was remarkably greater than that in the carbonate-containing solutions with a similar concentration of carbonate and pH condition. This might be attributable to other species as well as Th(OH)4(aq) and Th(OH)3(CO3). These species form colloids or precipitates, and their concentration can be reduced in the ultra-filtered solution by an aging effect.

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Abstract  

This work studied a way to reclaim uranium from contaminated UO2 oxide scraps as a sinterable UO2 powder for UO2 fuel pellet fabrication, which included a dissolution of the uranium oxide scraps in a carbonate solution with hydrogen peroxide and a UO4 precipitation step. Dissolution characteristics of reduced and oxidized uranium oxides were evaluated in a carbonate solution with hydrogen peroxide, and the UO4 precipitation were confirmed by acidification of uranyl peroxo–carbonate complex solution. An agglomerated UO4 powder obtained by the dissolution and precipitation of uranium in the carbonate solution could not be pulverized into fine UO2 powder by the OREOX process, because of submicron-sized individual UO4 particles forming the agglomerated UO4 precipitate. The UO2 powder prepared from the UO4 precipitate could meet the UO2 powder specifications for UO2 fuel pellet fabrication by a series of steps such as dehydration of UO4 precipitate, reduction, and milling. The sinterability of the reclaimed UO2 powder for fuel pellet fabrication was improved by adding virgin UO2 powder in the reclaimed UO2 powder. A process to reclaim the contaminated uranium scraps as UO2 fuel powder using a carbonate solution was finally suggested.

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-added chemicals [ 1 ]. Among the chemicals derived from glycerol, glycerol carbonate, which can be used as the solvent or reaction intermediate, is a high value-added product with many potential applications [ 2 – 6 ]. Glycerol carbonate can be prepared

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vacancies both in anionic and cationic sites which make these materials as highly effective ion exchange matrixes [ 1 ]. Carbonate apatites are the main mineral components of human and animal hard tissues (bones and teeth) [ 2 – 4 ]. It has been established

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Introduction Apatites are a large class of mineral compounds with the general formula M 10 (PO 4 ) 6 X 2 , where M is generally a divalent cation and X can be a hydroxyl, carbonate or a halide. They crystallise in the hexagonal

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distributed solar thermal power. The melting point of mixed nitrate used in the current stations is about at range of 150–200 °C, which can not meet the requirement of high storage temperature. However, mixed carbonate, with high melting point and larger

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, Hess law, and several equations derived from basic thermodynamic equations. In this study, this method was applied for determination of temperature equilibrium of CaCO 3 dissociation. Calcium carbonate dissociation is represented by reaction ( 1 ): 1

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Abstract  

Pressureless sintering of CaCO3 was carried out, with Li2CO3 (from 0.5 to 8 wt%) as an additive, under different pressures of CO2. Densification occurs between 600 and 700°C. Sintering above the eutectic temperature (T>662°C) leads to the decomposition of calcium carbonate and the materials become expanded. At 620° under 1 kPa of CO2, a relative density of 96% is reached. Li2CO3 enhances the densification process and grain growth of calcium carbonate. CO2 pressure slows down densification and grain growth kinetics. These results are explained by the influence of carbonate and calcium ion vacancies on the sintering mechanisms.

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. T. Nakamori 2001 Global carbonate accumulation rates from Cretaceous to Present and their implications for the carbon cycle model Island Arc 10

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can occur. Among these substitutions, the partial replacement of the F − and PO 4 3− ions by the carbonate ions presents a special interest generated by the similarity of the carbonated compounds with the natural apatites. There are two possibilities

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