The chemical compositions of iron ore used for iron making are mainly hematite (Fe
2O
3), magnetite (Fe
3O
4) and goethite (FeOOH). The uranium (U) and thorium (Th) of natural radioactive elements are contained with mg/g or ng/g levels as impurity elements in these iron ores. The purpose of this study was to develop on analytical method for the determination of radioactivities for U and Th isotopes in iron ore by an
α spectrometry. The certified reference material of iron ore (JSS-805-1, hematite of BMR iron ore) was used as analytical samples in this work. The concentrations of U (3.4±0.2 mg/g) (
238U radioactivity : 42.0±2.5 mBq/g) and Th (0.35±0.03 mg/g) (
232Th radioactivity : 1.4±0.1 mBq/g) in the reference material had been determined by an instrumental neutron activation analysis. After the iron ore samples were dissolved by a microwave method, U and Th were separated from the matrix elements by several chemical processes. Chemical processes to remove matrix elements were mainly Fe(OH)
3 coprecipitation, Fe(OH)
3 dissolution, NdF
3 coprecipitation, NdF
3 dissolution, Nd(OH)
3 coprecipitation and Nd(OH)
3 dissolution. After these chemical processes, U and Th were only separated by two steps : anion?exchange chromatography. Further, a Sm(III) carrier as an internal standard was added in the U fraction or the Th fraction, and SmF
3 coprecipitation was performed with a HF solution. These precipitation samples were measured by an
α spectrometer system. The Th standard solution was added in the dissolved solution of the iron ore samples. The
α peaks of
238U,
234U,
232Th,
230Th,
228Th and
147Sm were determined from the
α spectra of these fraction.
147Sm as an internal standard is a natural
α emitter. As results, the chemical yields of U and Th were 90±6% and 103±2%, respectively. Also, it was found that the relation of the radioactivity of
238U-
234U was radioactive equilibrium, and that the relation of the radioactivity of
238U-
230Th was none-radioactive equilibrium.
View full abstract