| Rare-earth is important mineral resources and our country's reserves of rare earth materials and products in export volume are ranking first in the world. Because of its superior performance, the rare earth elements have been widely used in atomic energy, rocket technology, laser, color TV, radio electronics, steel, metallurgy, machinery, petrochemicals, glass, ceramics, agricultural, and medical and health industries. Especially in the high-tech fields, it has infiltrated into the military, energy, environmental protection, information and other cutting-edge science and frontier science, linked human life more and more closely and has made a significant contribution to China's modernization and national economic development.But the rare earth mineral raw materials used in production are often associated with uranium, thorium and other natural radionuclides, accumulated in some intermediate products and waste, resulting the natural radioactive pollution in the workplace and the surrounding environment. At the same time, because of different areas of rare earth mineral and different processing technology of rare earth materials, it led to a difference on the content of natural radioactive nuclides in products.Meanwhile the radionuclides contained by waste gas, wastewater and solid waste will bring radioactive contamination to environment and also bring harm to human beings.Therefore, the domestic and foreign scholars are particularly concerned about its impact on human health and regularity that the radioactive distribution of rare earth materials and the transfer of radionuclides to crops in waste.This paper, with the project of "Radioactive pollution and its countermeasures in rare earth production ", firstly elaborated the topic based and research Significance, introduced the production of radioactive rare earth and rare earth radionuclide migration, describes the current research status ,research ideas,contents of the radionuclide's migration in rare earth andenvironmental issuesin Rare earth resources development utilization. Then it is followed by a discussion of the decay law of imbalanced thorium series and the theoretical basis of radioactivity measurements in the production process. Finally the choice of the analysis and measurement method is discussed ,and the gamma spectrometry is applicated to determine the specific radioactivity of maternal and long-lived daughter nuclide in thorium series and thorium contents in rare earth ore, concentrate, decomposition products, intermediate products, enrichment and waste samples,and the distribution and migration of radioactivity in rare-earth mineral processing, ore decomposition, smelting and extraction process were studied,the following conclusions were got:1. In the rare-earth minerals in the processing and utilization, the radionuclides have been enriched in Rare Earth Concentrate. But regardless of acid or alkali, about 8% of the thorium have accessed to products, more than the standard, "non-ferrous metal mineral products of natural radioactive limit GB 20664-2006", on the earth chloride and rare earth oxide rare earth products in the total radioactivity and its strength exceed requirements of1000Bq/kg.2. Radioactive thorium enriched in the slag, which are close to or higher than average concentration limit exemption; and total radioactivity of solid waste is between the 10~4-10~5Bq/kg, not more than 4×10~6Bq/kg.In the light of "national standard: radioactive waste GB9133-1995" standard, they should be low-level radioactive waste.3. In the processing and utilization of rare-earth minerals, radioactive thorium series is in radioactive equilibrium basic state in raw ore, concentrate and mineral processing tailings, but in the rare earth products, enrichment, Ce-rich slag and smelting waste, the thorium series is non-radioactive state . The share of the transfer of Thorium in various substances, are depending on the thorium'scontent of rare earth ore and the production and processing technology.4. Thorium content of rare earth products exceeded the average national standard' requirements that any child physical activity≤10~3 Bq/Kg, (40)~K≤1.0×10~4 Bq/Kg in the natural radionuclides (238)~U, (226)~Ra, (232)~Th decay series for metal minerals.5. 8% of the radioactive thorium into the product in the rare earth production, on average only 80% , recovered,into the thorium Concentrate. Compared with the reported recovery of more than 90%, there had been a certain gap, which is one of the reasons that radioactivity of our country's rare earth products is out of limits... |
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