Abstract: [Objective]The paper was intended to measure the contents of light rare earth elements in the soil and the contents of La and Ce and their distributions in plant in a light rare earth tailings in north China, Biological Transfer Coefficient (BTC) and Biological Absorption Coefficient (BAC) of the plants for La and Ce absorptions were calculated for the selection of La and Ce hyper-tolerant plants, in order to provide a scientific basis for landscape restoration in the tailings.[Method]Study site was selected at the edge of the rare earth tailings and 12 sampling plots were set up in 4 directions of south-east, north-west, north-east, and south-west according to the wind direction at 50, 100 and 300 m from the mine pit. Firstly, the 0 to 20 cm surface soil samples were collected using the 5-points collection and quarter-division method, and plant samples were collected from the above-ground organs and the roots of the trees planted by the rehabilitation program (Haloxylon ammodendron, Caragana microphylla, Hedysarum scoparium, Lespedeza bicolor, Nitraria tangutorum, and Populus tomentosa). Secondly, the contents of light rare earth elements La, Ce, Pr, Nd, Sm, Pm, and Eu in the soil and the contents of La and Ce in the plants were measured by ICP. Furthermore, the average of the single factor pollution index of soil in the surrounding areas of the tailings was analyzed with the N. L. Nemerow comprehensive index method. Lastly, the plant transfer efficiency was evaluated by the BTC and the plant absorbing ability of La and Ce was evaluated by BAC.[Result]The average contents of La, Ce, Pr, Nd, Sm, Pm, and Eu in the soil of the light rare earth tailings were 2 762.46, 5 440.42, 1 308.42, 1 604.11, 133.96, 28.12 and 40.53 mg·kg^-1 respectively, and the contents of La and Ce accounted for 72% of total contents. The order of these contents in the surface soil of all directions was south-east > north-east > south-west > north-west, all the values of which were 25.10 to 230.56 times higher than the geometric mean value (background value) of Inner Mongolia. Also, the single factor pollution indices of all directions were greater than 3, which could ascertain that the surrounding areas of the light rare earth tailings were seriously polluted. Then, the average values of the single factor pollution index in the south-east direction were 69.06 to 544.10, which were the highest. By contrary, the values in northwest were 5.99 to 19.75, which were the lowest. Meanwhile, the values in the north-east and south-west directions were similar. On the one hand, the La and Ce contents of the above-ground organs of H. ammodendron, L. bicolor and N. tangutorum were all higher than those in the roots. On the other hand, the La and Ce contents of the roots of C. microphylla, H. scoparium and P. tomentosa were all higher than those in the above-ground organs. At last, the BTC of La and Ce of H. ammodendron, L. bicolor and N. tangutorum ranged from 1.03 to 1.76. The BAC of La and Ce of L. bicolor ranged from 1.00 to 1.72. Only the BTC and BAC of L. bicolor were both greater than 1.[Conclusion]L. bicolor was the hypertolerant plant of La and Ce, which might be significant for the remediation of light rare earth polluted soil. The other 5 plant species can be used as tolerant to light rare earth elements.

Key words: light rare earth tailing, La, Ce, hypertolerant plant