Study On Radio-Thorium Nuclides Transfer Process And Its Radiation Effect On People

Rare-earth ore is one of the most important minerals resources in China. The quantities of reservation and export are the first in the world which make the marketing possess ratio over 70%. Rare-earth ore is usually accompanied by different natural radioactivity nuclides. The radioactivity nuclides is extracted in the progress of collected, melted and processed. The content of radioactivity is an important factor of export and application. After the entrance of the WTO, it become urgent and necessary for our export trade to make the radioactive level of the rare-earth materials meet the international standard. Recently, many Chinese enterprises had suffered great loss because of the above-mentioned reason. So the transfer of radioactive nuclides in products and environmental media becomes one of most important problems in environmental sciences and physics as well as chemistry.Due to the difference of source and treating process, the concentration of radio-nuclides in rare-earth materials vary greatly. At the same time, the radio-nuclides in the waste gas, water and solid discharge can pollute the environment and threaten the health of the human being. There are reports on radio-nuclides pollution cases during the extracting and refining process of rare-earth materials in China. So scholars all over the world pay special attention to the study of the regular and mechanism on human health, that come from the transfer ofradio-nuclides.We have investigated sixty two factories and analyzed about 850 samples to get 2220 data. We have carried out the profound the works focused on the transfer regulation of radio-nuclides and the radiation dose on human being. Therefore, the results of the research are foundation on theory and application in distribution of radio-nuclides in products and migration in environment medium as well as radiation impact of the public. The conclusions is of important scientific significance and application value in environment protection, quality controlling, soil protection and human health. At same time, the results supply theory and technical inquirment for exploring enriches Rare-earth resources properly, and promotes development of economy in our country.1) Determine the concentration of radio-nuclides and the radio level of total a, total a in rare-earth mine, rare-earth material products and its exhaust gas, waste water, solid discharges by using the Neutron Activation Analysis and a spectrum Analysis. The results indicate that in Panxi area, Sichuan, the natural thorium series is dominating the radio-nuclides in rare-earth mine. The concentration of radio-nuclides of Uranium series is lower about 12 times than that of Thorium series, while the ratio is 18 in Baotou area.2) Study the distribution of the radioactive material and its physical and chemical property in the acid processing of Rare-earth mine, and get processes of chemical reaction and processing condition by using Primary amine resins to separate Thorium. Molecule structure of Thorium is the difference in Rare-earth materials due to the difference of processes. The molecule structure of Thorium among product, solid waste, wastewater and mine are ThO2,ThCl4, Th(SO4)2·Na2(SO4)·6H2O, Th(OH)2, respectively. The concentration ratio of RECI3, REO, RE-ALLOY are (0.01~4.10)×103Bq.kg-1(0.09~2.86)×103Bq.kg-1 and(1.42-9.82) ×103Bq.Kg-1, respectively.The results show that separation ratio of Thorium is 90% by using Primary amine resins to separate Thorium. The process can decrease greatly radiation effect on human health and environment.3) Study the radionuclides distribution regulation in Rare-earth materials during mining, extracting and refining process to get the transfer coefficient of thorium. The results show that the transfer regulation of Thorium in the waste from Rare-earth mine exploring in Baotou area, Neimenggu province is:84.5% into mill tailing and 14.46% into the solid wastes, 0.92% into the slag.·0.06% into the air and 0.06% into the waste water.The transfer regulation of Thorium with acid-method in Rare-earth mine exploring in Panxi area, Sichuan province is:·0.08% into the waste water, 1.03% into the air and 1.98% into the the slag.·87.39% into the solid discharges and 9.52% into the products.4) Immersed experiment was done to study desorption from Rare-earth waste solid The results show that concentration of Thorium in water is more than 1Bq.kg-1 between 1day and 11 day. Modeling raining experiment was done to get the desorption coefficient of Thorium is 7.11 × 10-4 kgl-1 .Thorium releasing into water from one-kilogram waste solid is 40Bq.5) The adsorption coefficient and migration velocity of Thorium on various soil are difference. The result shows that the adsorption coefficient of Thorium is between 345.21 and 587.92.6) Get the transfer coefficient of thorium from soil to crops based on detecting the radioactive level of the soil near the factories. Thetransfer coefficient is (0. 4-11. 0) × 10-1.7) Build up the model to assess the radioactive level of the public through food chain and calculate the dose in the occupational operator and the public. The result shows that the maximum dose of the radioactive Thorium to the occupational worker is 1.74~11.50mSv.a-1 while 0.24~1.40mSv.a-1 to the public in the near area of Rare-earth material producing factories, which is higher than the public dose limit (1mSv.a-1).8) Propose the treatment of the radioactivity and suggest the pollution control method.