抄録
The chemical compositions of iron ore used for iron making are mainly hematite (Fe2O3), magnetite (Fe3O4) and goethite (FeOOH). The uranium (U) and thorium (Th) of natural radioactive elements are contained with ppm level as impurity elements in these iron ore. The purpose of this study is a estimation U and Th isotopes behavior for in various iron ore by an α spectrometry. Samples were the iron ore from Australia, Brazil and India. After those samples were dissolved by a microwave method, U and Th were separated from matrix elements by the chemical processes were mainly a Fe(OH)3 coprecipitation method, a NdF3 coprecipitation method and a Nd(OH)3 coprecipitation method. Thereafter, U and Th were only separated by two steps anion–exchange chromatography. Further, Sm(III) carrier as an internal standard was added in U fraction or Th fraction, and a SmF3 coprecipitation was done with HF solution. These precipitation samples were measured by an α spectrometer system. The α peak of 238U, 234U, 232Th, 230Th, 228Th and 147Sm of these fraction were determined. As the results, U and Th isotopes in all of the iron ore were able to determine within 15% of RSD. And those were found that a relation of a radioactivity of 238U–234U was a radioactive equilibrium, and that a relation of a radioactivity of 238U–230Th was a radioactive disequilibrium. In addition, it was indicated that a positive association between their disequilibrium and the chemical compositions of ferrioxide in various iron ore.
