Geochemistry and thermodynamics of transuranium elements in ultrafine interstice under deep geosphere.

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Investigation of the chemical behavior of lanthanides and actinidesin the geosphere is important for the safety assessment of high-level radioactive waste disposal. However, determination of speciation for lanthanides and actinides is difficult, because it is too hard to distinguish between metal ion and colloidal metal in aqueous solution. Laser-induced breakdown spectroscopy (LIBS) can detect both ions and microparticles of metals in aqueous solution, especially, high-sensitive to microparticles. In this study, we analyzed Eu(III) ion and Eu_2O_3 particle in aqueous solution by LIBS, and measures the hydrolysis behavior of Eu(III) in aqueous solution. Furthermore, we tried to detect the plasma emission of Eu(III) ions sorbed on TiO_2 particles.Plasma emission of Eu was observed at 420.505 nm both in Eu(III) aqueous solution and in Eu_2O_3 suspended solution. The emission line was generally used for quantitative analysis of Eu. The plasma emission intensity of Eu_2O_3 was higher than … More that of Eu(III) ions when Eu concentration was same, and absorption band of Eu(III) ions was observed in LIBS spectrum of Eu(III) apeous solution. These results indicated Eu(III) ions can be distinguished from Eu_2O_3 particles in aqueous solution by LIBS.The plasma emission intensity of Eu increased with Eu concentration. The intensity vs. concentration plot showed a good linearity in low concentration range (approximately 10^<-2> to 10^<-1> mol/dm^3 and 1O^<-5> to 10^<-4> mol/dm^3 for Eu(III) ions and Eu_2O_3 particles, respectively).The plasma emission intensity of Eu increased with pH of Eu(III) aqueous solution, and drastic increase of emission intensity was observed above pH=6. The tendency was similar with solubility curve of Sm(OH)_3, which calculated using stability constants in litrature[1]. This result suggested that LIBS is useful for measurement of hydrolysis and precipitation behavior of Eu(III) in aqueous solution.From plasma emission of Eu(III) ions sorbed on TiO_2 particles, it was found that only Eu(III) ions on TiO_2 may be detected by LIBS.because the emission from Eu(III) ions in solution was not observed. We also have tried to use time-resolved LIBS to analyze sorption form of Eu(III) ions.[1] K.A.Gschneider, Jr., L.Eyring, eds. "Handbook on the Physics and Chemistry of Rare Earths, Vol.15" Elsevior Science (1991) 431 Less