Radioactivity of metallurgical enterprises waste

Abstract

Abstract. Problem. The problem of obtaining environmentally friendly materials is especially relevant when using the wastes that concentrate natural radionuclides (NRN) dangerous for public health. The concentrators of radionuclides include dump and granular blast-furnace slags. Goal. The purpose of the work is to determine the radionuclide composition of the fractions of dump and granular blast-furnace slags from Ukrainian enterprises, their compliance with the radiation safety standards of Ukraine and international radiological indicators, and to identify the factors that determine the level of natural radioactivity of the slags. Methodology. The specific activity of natural slag radionuclides was determined by the gamma spectrometric method on a SEG-001 scintillation gamma spectrometer. The mineral composition of the crystalline component of the slag was determined using X-ray phase analysis performed on a Siemens D500 powder diffractometer. The elemental composition of blast furnace slag was determined by the method of electron-probe microanalysis on a JSM-6390 LV scanning electron microscope with an INCA micro-X-ray analysis system. The particle charge and electrokinetic potential were determined during macroelectrophoresis of suspensions. Results. The blast-furnace slag contains natural radionuclides: 226Ra, 232Th and 40K. The content of radionuclides varies by waste fractions. According to the contribution to the total activity value, NRN can be arranged in a row: 40К > 226Ra > 232Th. The most radiation-clear is the fraction > 20 mm of the “Zaporizhstal” dump slag, the radioactivity of the fractions 1.25‒2.5 mm for DMC, 5‒10 and 0.63‒1.25 for MMC and the “ArcelorMittal” granulated slag is increased. All investigated slags belong to the first class of radiation hazard (Сef 370 Bq/kg) and can be used in construction without restrictions. Originality. All investigated slags correspond to international radiological indicators: Raeq 370 Bq/kg, radiation hazard indices are Iγ, Iex, Iin and Iα 1, which indicates that there is no danger of increased gamma radiation and emanation of radon and the daughter products of its decay into the room air. The concentration of radon indoors does not exceed 200 Bq/m3. For the average sample and slag fractions <2.5 mm of “ArcelorMittal”, the activity utilization index which determines the safety of practical waste use is overestimated; the absorbed dose rate in the open air and the annual effective equivalent dose are higher than the world average values, they are, respectively, 58 nGy/h and 0.07 mSv, but at the same time below the value recommended by the IAEA for the population of 1 mSv/year. The excess lifetime carcinogenic risk for dispersed fractions of “ArcelorMittal” slag is higher than the world average: 0.29·10–3, but below the 0.05 limit set by the International Commission on Radiation Protection. A direct correlation between the acidity of the slag fractions and the increase in radiological parameters was determined. Practical value. An attempt has been made to relate the radioactivity of blast-furnace slag with the NRN sorption on the negatively charged surface of slag particles, which is more reliable for amorphous sorption-active granular slag.