| Bayan Obo deposit is the largest light rare earth deposit in the world.A large number of heavy metals are accumulated in the surrounding environment due to long term mining activities,which leads to serious pollution of the local soil environment.In order to develop effective protection measures,this study investigated and analyzed the concentration,spatial distribution,pollution sources,leaching and leaching characteristics of heavy metals in the Bayan Obo mining area,and evaluated the environment-human health risks of heavy metals.Through the construction of ecological risk model,the risk areas of ecological environment in mining area were divided.The main conclusions are as follows:(1)The contents of Mn,Cu,Zn,Pb,Cd,As,Hg and Cr in soil were determined.The average values were 3662.57,26.20,289.22,123.00,0.75,12.69,0.05 and 57.98mg/kg,respectively.Except Cr and As,the contents of other heavy metals in the study area were significantly higher than the background values of Inner Mongolia Autonomous Region and the control point area,indicating that the local mining and industrial activities caused the accumulation of heavy metals in the soil.(2)The geo-accumulation index,potential ecological risk assessment and Risk Assessment Code(RAC)were used to evaluate the heavy metal pollution of local soil.The results showed that all areas of Bayan Obo were seriously polluted by heavy metals.The pollution degree and ecological risk of Cd were much higher than other heavy metals.The speciation analysis showed that the heavy metals were mainly residual,relatively stable.The results of human health risk assessment showed that the local total carcinogenic risk and non-carcinogenic risk were acceptable.(3)The spatial distribution map based on GIS showed that the high-value areas of Cu,Zn,Mn,Cd and Pb were mainly located in the mining area,the high-value areas ofAs and Cr were mainly distributed in the west of the mining area,and the Hg was mainly distributed in the industrial area.Five methods of spatial variation coefficient,accumulation coefficient,correlation analysis,principal component analysis(PCA)and positive matrix factorization(PMF)were used to analyze heavy metal sources,and it was finally determined that Hg was mainly from industrial activities and coal burning;Cu was mainly from mining activities;Mn and Pb were mainly from transportation;Cd and Zn were composite sources of mining and transportation activities;Cr and As were mainly from natural sources.(4)The results of soil leaching experiments showed that the concentration of heavy metals in the leaching solution was related to the total amount in the soil,except Pb.The leaching experiment showed that the concentration of heavy metals increased rapidly and then decreased slowly with the leaching process,and the lower the pH of the leaching solution,the higher the concentration of heavy metals after leaching.The concentration of heavy metals in uncontaminated soil column was analyzed.It was found that Cu and Cd were easy to migrate to the lower soil layer,while Zn,Pb and Cr were opposite.(5)According to the field investigation and literature research,heavy metals and rare earth elements were selected as the stress factors of local pollution,and the local pollution situation was evaluated based on the comprehensive fuzzy mathematics method,and the ecological risk evaluation model based on the characteristics of the Bayan Obo mining area was constructed.The ecological threshold values of some stress factors were determined with the help of the U.S.eco-soil screening system(Eco-SSL).Meanwhile,the clustering analysis and superposition analysis functions in GIS software were used to divide the local ecological risk prevention and control areas by combining the surface biomass factors and the selected stress factors,which provided a scientific basis for the treatment of heavy metals in the Bayan Obo mining area... |
PDF Full Text Request