J Radioanal Nucl Chem 2013 Li.pdf

Distribution of thorium in soils surrounding the rare-earth tailings reservoir in Baotou, China Rou-yu Li ? Qiang Li ? Sheng Chen ? Feng-chang Wu ? De-zhi Sun ? Hai-qing Liao Received: 15 August 2013  Akade?miai Kiado?, Budapest, Hungary 2013 Abstract Thorium distribution was investigated in the soils surrounding the rare-earth (RE) tailings reservoir near the Baotou grassland of Inner Mongolia, northern China. Totally 77 soil samples were collected from 8 different directions in the periphery of the RE tailings reservoir, and then were determined for 232Th. The 232Th activity degree ranges from 9.1 to 307.1 Bq kg-1 with an average value of 42.4 Bq kg-1. In some samples, the degree is higher than that of global average, showing that these soils were polluted by thorium. There is a high linear correlation coefficient between the thorium diffusion coefficient parameter and the wind intensity parameter which indicates that the distribu- tion of 232Th is mainly correlated with wind speed and direction. The geo-accumulation index method was used to evaluate the level of thorium pollution, and the Kriging method was applied to estimate the land area at each level. By calculation, result shows that the area at each pollution level is 2.10 km2 with medium-strong pollution, 38.29 km2 with medium pollution, and 47.19 km2 with slight pollution. The remaining 738.63 km2 of land investigated is clear from thorium pollution. Keywords Baotou  Tailings reservoir  Soils  Thorium  Distribution Introduction Bayan Obo deposit, located near Baotou in China’s Inner Mongolia, has the largest repository of rare-earth (RE) resources in the world. It has been recorded as a mixed type RE deposit of monazite and bastnaesite. There monazite contains a high concentration (*3 %) of naturally formed thorium [1], which is much enough to change the compo- sitions of radionuclides in natural soil, thereby exerting an impact on terrestrial ecosystems [2–6]. A previous study shows that in Brazil,