Characteristics Of Soil Rare Earth Pollution And Stabilization Remediation In Bayan Obo Mining Area

Bayan Obo mine is a polymetallic symbiotic deposit in Inner Mongolia,which has the largest light rare earth reserves in the world.Many years of mining have released a large number of rare earth elements into the surrounding environment of the mine,leading to serious ecological damage and environmental pollution.In this study,the surface soil samples of five different functional areas in Bayan obo mining area were sampled,and the content of rare earth elements in the soil samples was measured.The spatial distribution of rare earth elements in the mining area and surrounding soil was analyzed by inverse distance spatial interpolation method,and the normalized distribution pattern of the rare earth elements in the soil was discussed.At the same time,the soil rare earth pollution degree and ecological risk were evaluated by soil accumulation index method,corrected pollution degree method,pollution load index method and potential ecological risk index method.Using biochar,bone and montmorillonite to stabilizing treatment of pollution of rare earth elements in soil,adopt the method of combining static culture and pot experiment,to clarify the three kinds of materials of rare earth pollution of soil physical and chemical properties,fertility,healing effect and affect the effectiveness of the plant,in order to provide theoretical basis for mining rare earth soil in situ bioremediation.The main research results and conclusions are as follows:(1)Affected by rare earth mining,rare earth elements in soils around Bayan Obo mining area are enriched to varying degrees.The order of REE content in soil is similar to that in Bayan Obo ore and the order of REE abundance in earth crust.Light rare earth elements(LREE)occupy the absolute superiority in the total rare earth elements,and LREE is enriched.The total rare earth content(ΣLREE)and light rare earth content(HREE)of different functional areas are far more than the average level of background values in Inner Mongolia,and all present a consistent law,that is,mining > dump >residential area > industrial area > tailings pond.The high value areas of total rare earth elements are mainly concentrated in the vicinity of the main,east and west mining areas,and the distribution of rare earth elements is very uneven and the spatial variability is strong.The distribution curves of rare earth elements in each functional area have good consistency,and all tilt to the right.The fractionation of heavy and light rare earth elements is obvious,and the fractionation of light rare earth elements is more significant.There is a significant correlation between all the rare earth elements,and the order and content of all the rare earth elements in the soil are consistent with the parent rocks,indicating that all the rare earth elements in the soils of Bayan Obo mining area may have similar sources,which is mainly caused by mining operations.The soil pollution of rare earth elements in the study area was evaluated by geoaccumulation index,corrected pollution degree,pollution load index and potential ecological risk index.Due to the influence of mining activities,the whole Bayan Obo mining area is polluted to different degrees.The pollution degree and ecological risk of mining area and dump are much higher than that of other functional areas.Ore mining and processing activities are the main pollution sources,and the related pollution control and remediation work need to be strengthened.(2)The cation exchange capacity(CEC),organic matter content(OM),redox potential(Eh)and electrical conductivity(EC)of the rare earth contaminated soils in the mining area were increased to varying degrees after the addition of the three remediation materials.The p H value of the soil treated with bone meal decreased,and the p H value of the soil treated with biochar and montmorillonite increased.After montmorillonite treatment,the soil was still infertile,while after biochar and bone meal treatment,the soil fertility reached medium level.The application of biochar in soil is beneficial to the formation of good soil aggregates,and the increase of large aggregates(0.2～2mm)is the largest,and the increase of large micro-aggregates(0.02～0.2mm)with montmorillonite is significant.The La and Ce loads of sandy soil(0.002～0.02 mm)and clay(<0.002 mm)in the soil treated with bone meal increased,and the corresponding environmental risks also increased.From the perspective of the leaching characteristics and available states of La and Ce,biochar treatment has the best stabilization effect.(3)When Lolium perenne L.and Medicago sativa L.were planted in the soil stabilized by remediation materials,the plants treated with biochar had the best growth,the highest biomass,the lowest contents of La and Ce in plants,and the least toxic effects on plants.The soil treated with bone meal showed a slight hardening phenomenon,which to some extent inhibited the growth of plants,and the contents of La and Ce in vivo were higher than those in the control group.When the remediation materials were applied to the soil contaminated by rare earth elements,both the surface and cells of the plant root tips changed to a certain extent,and the toxic effects of rare earth elements on the plant roots were slowed down to a certain extent.