| China is a big country of rare earth, and the reserves of rare earth mining industry of Baotou in Inner Mongolia are even ranked the first in the country( accounting for 83.6% of the total reserves). Driven by the economic interests, the rare earth mining industry has been developing rapidly which adds many burdens to the social environment. Besides a small dose of radiation produced by some rare earth elements, it is often accompanied with natural radionuclides which are higher than that in the background surroundings, such as radioactive thorium isotopes.In this paper, Inner Mongolia Baotou Rare Earth ore is the major study object. Based on a detailed investigation of the geological background, we took rapid in-situ gamma-ray spectrometry measurement to identify the Baotou Rare Earth mining radionuclide distribution. And a reasonable assessment of the potential radiation hazards to the environment caused by rare earth minerals was also carried out. The study shows that:(1) 232 Th is the most important radioactive contaminant element in the survey area of Baotou and Bayan Obo. The concentration of radioactive contamination in Baotou District is mainly concentrated in the tailings dam and the Baotou Steel Company’s Concentrator, which is mainly derived from the mining, dressing and smelting of Bayan Obo iron ore. And the concentration of radioactive contamination in Bayan Obo District is mainly concentrated in mining area( West Ore Body, Main Ore Body and East Ore Body), tailings dam and the surrounding rare earth enterprises.(2) Based on the data acquired by gamma-ray spectrometry, we can draw the following conclusions: 232 Th is concentrated in tailings in Baotou Dam. The 232 Th concentration at the sites inside of the tailings dam ranges from 293.9×10-6 to 354.8×10-6, with a mean value of 320.8×10-6±30.7×10-6. The concentration of 232 Th in the soil around the Baotou tailings dam is increasing, which is approximately 1.5 times higher than the global average. In Bayan Obo District, the concentration of 232 Th is a little lower than that recorded in Baotou district( with a mean value of 275.9×10-6±0.57×10-6). Radioactive anomalies are found in the vicinity of the Bayan Obo tailings transportation pipeline and a pile of coal. And uranium and potassium are normal and uniform either in ore, tailings or in soil.(3) Based on the data of radioactive risk assessment, we can draw the following conclusions: in the rare earth tailings dam of Baotou District, the average of air-absorbed dose rate(Dr), annul effective dose equivalent(AEDE) and the excess lifetime cancer risk(ELCR) was 841.2±84.7nGy/h, 1.03±0.10 mSv/y and 3.1×10-3±0.3×10-3, respectively. The data of radioactive risk assessment in Baotou tailings dam are higher than the corresponding standard limit value, regarded as highly radioactive contaminated area. In addition, the berm of Baotou tailings dam and the slag in a workshop also have high radioactivity risk. Affected by the Bayan Obo iron ore, the mining areas of Bayan Obo Mine and the tailings dam of Bayan Obo District are also viewed as highly radioactive contaminated areas. |
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