Environmental Radiological Impact Assessment Of Phosphorus Mining Area In Mabian,Sichuan

With the development of science,technology,industry and agriculture,the exploitation and utilization of phosphorus ores are also increasing day by day.The increase of exploitation of phosphorus ores has led to environmental problems in mines,and phosphorus ores are accompanied by radionuclides.The exploitation and utilization of phosphorus ores will cause radioactive environmental problems,which threaten the environment,ecology and human health.In this paper,Mabian Phosphate Mine is taken as the research object,and the content and morphological characteristics of radionuclides in soil and stream sediments of different media in the surrounding environment of the Phosphate Mine are analyzed by combining field measurement with data analysis.The correlation between U,Th and P elements and the migration and enrichment of radionuclides in different environmental media are also analyzed.The distribution of radionuclides in three sections was measured in the mining area,and the radioactivity level in the surface environment was discussed.On this basis,the prevention measures of environmental radioactivity in the mining area were summarized and put forward.The main results and conclusions are as follows:(1)During the exploitation of phosphate rock resources,the content of radionuclides in environmental media around the mining area has been affected to a certain extent.The average content of U and Th in the soil of mining area is 5.02 ug/g,ranging from 0.60 to 14.33 ug/g,and the average content of Th is 11.52 ug/g,ranging from 1.15 to 24.20 ug/g.The average content of U and Th is higher than the background values U(3.03 ug/g)and Th(13.75 ug/g)in the whole country.This shows that the phosphate rock affects the radionuclide content in the soil during the mining process.Distribution shows that the enrichment degree of U element increases obviously.The content of U and Th in stream sediments varies slightly.The average content of U element is 4.93 ug/g,ranging from 2.1 to 19.7 ug/g,which is higher than the background average value of elements in stream sediments of southern China(3.5 ug/g),and the average content of Th element is 8.23 ug/g,ranging from 1.9 to 14.2 ug/g,which is lower than that in stream sediments of southern China.The background mean value was 13.3 ug/g.It can be seen that the exploitation of phosphate ore is one of the reasons for the increase of radionuclides in the surrounding environmental media of the mining area,which may increase the radioactivity level of the mining area and have a certain radioactivity effect.(2)During the exploitation of phosphate rock resources,the distribution of radionuclides associated with phosphate rock has changed in different environmental media,and different degrees of migration and enrichment have taken place.Based on the analysis of the content and morphological characteristics of natural radionuclides U and Th in different environmental media in the mining area,it is concluded that the basic law of the migration and enrichment of radionuclides U in ores,soils and water is the following.The enrichment of nuclide Th in soil is higher than that in stream sediment.From the environmental medium of ore-soil-water system,it shows that nuclide U is more active than Th,and more likely to migrate and transform.(3)The average radioactivity concentrations of natural radionuclides U,Ra and Th in soil were 62.04 Bq/kg,62.49 Bq/kg and 46.79 Bq/kg.The average radioactivity concentrations of natural radionuclides in river sediments were 60.88 Bq/kg,61.32 Bq/kg and 57.65 Bq/kg.The average radioactivity concentrations of U and Ra were higher than the national average U=38.5 Bq/kg,Ra=37.6 Bq/kg,and the average radioactivity concentrations of natural radionuclides in soil were 60.88 Bq/kg,61.32 Bq/kg and 57.65 Bq/kg respectively.The specific activity concentration is lower than the national average,and the sediment in the river system is higher than the national average Th=54.6 Bq/kg.It can be seen that the exploitation of Mabian Phosphate Mine has less influence on the content of radionuclides in the environment.(4)The average specific activity concentration of natural radionuclides U,Ra,Th and K in rocks of phosphate mining area is 68.01 Bq/kg,68.51 Bq/kg,88.76 Bq/kg and 957 Bq/kg.The average absorbed dose rate of air at the height of 1 m above the surface of mining area is 128.15 nGy/s,which is higher than the national average of 81.5 nGy/h.The average annual effective dose rate is 157.17 uSv/a,which is less than the average of 460 uSv/a given by UNSCEAR in normal area.Therefore,the mining of Mabian Phosphate Mine has some influence on the content of radionuclides,but the radioactivity level in this area is still normal.