The Study On Soil Pollution Analysis And Ecological Restoration Of Bayan Obo Mine

After more than 60 years of surface mining,stacking and transportation activities,Bayan Obo mine has polluted the local and surrounding ecological environment to some extent.Some plants stopped growing even to dying,and the health of animals and human beings were threatened.Most scholars focus on the heavy metal pollution in mines,but few scholars study the combined pollution of heavy metal,light rare earth and radionuclide systematically.For the ecological restoration,most scholars focus on using the plant or microorganism as the single repair technology,but there are few researches on plant,microorganism and animal collaborative remediation technology.Firstly,based on the theoretical knowledge of mining engineering,soil science,botany,landscape ecology and mathematical statistics,the contents of heavy metals,light rare earth elements and radionuclides in soil of mining area were measured systematically,and their distribution characteristics were analyzed.Secondly,the methods of Nemero index,geo-accumulation index,principal component analysis and random forest analysis were used to study the distribution characteristics of soil pollutants in mining area.Thirdly,the plant species in the fence of Bayan Obo mine were investigated and the hypertolerant plants which could absorb the three kinds of pollutants were screened.Finally,collaborative technology called"tolerant plant and mycorrhizal fungi and tolerant earthworm"was used in mine soil remediation.Furthermore,the effect of soil ecological restoration was evaluated by AHP and fuzzy comprehensive evaluation method.Then the ecological restoration strategy of Bayan Obo Mining Park was updated and designed.The innovations of this paper are both studying the pollution characteristics of heavy metals,light rare earth elements and radionuclides in soil systematically,and using the"plant and microorganism and animal"innovative technology of collaborative to repair the soil compound pollution.The study results were as follows.1.The contents of heavy metals,light rare earth elements and radionuclides in the soil of sampling points in the mining area were measured respectively.The results showed that Pb,Cu,Mn and Zn in the soil around the main mine,East Mine,West Mine and dump of Bayan Obo mine in Inner Mongolia exceeded the standard seriously as the mining activities and the related elements of the mine pit.The contents of La,Ce,Pr,Nd,Sm and Eu in soil exceeded the standard seriously.In the sampling area,the variation law of its contents was that the surface soil contents were higher than the deep soil,the north were higher than the south and the east were higher than the west.Radionuclides ²³⁸U,²³²Th,²²⁶Ra and ⁴⁰K were found in the soil,which did not exceed the middle level of natural radiation level in Inner Mongolia.2.By using the methods of Nemero index,geo-accumulation index,principal component analysis and random forest analysis,the pollution degree,accumulation degree and sources of main pollutants were obtained,and the eight main pollution elements in the mining area were determined.Nemero comprehensive analysis results showed that heavy metals and light rare earth elements in soil were in moderate to severe pollution,and radionuclides in soil were light pollution.Geo-accumulation analysis showed that heavy metals pollution in soil was serious pollution,light rare earth pollution was mild to severe pollution,and radionuclides pollution was non pollution.Principal component analysis showed that Pb,Zn,La,Ce,²³⁸U and ²³²Th were the main pollutants in soil.According to the above three evaluation methods,the main pollutants of the sampling area soil were Pb,Cu,Mn,Zn,La,Ce,²³⁸U and ²³²Th.Random forest method was used to analyze the eight major pollution elements,and it was found that mining activities such as ore mining and dumping sites were the sources of pollutants.3.The diversity of plant species in the fence of Bayan Obo mine was investigated.27species of plants belonging to 24 genera and 15 families were found,accounting for 15.79%,6.32%and 3.20%of the total plant families,genera and species in Baotou city.They were rare.Five dominant plants were selected from the local plants,namely Stipa breviflora,Artemisia carvifolia,Astragalus adsurgens,Saussurea nivea and Elymus dahuricus.The contents of heavy metals,light rare earth elements and radionuclides in these plants were measured,and the ability of enriching heavy metals,light rare earth elements and radionuclides was studied.The results showed that the enrichment coefficient,transport coefficient and root retention coefficient were all less than 1.Therefore,they could not be directly used as hypertolerant plants for remediation.4.The collaborative remediation technology named"tolerant plant and mycorrhizal fungi and tolerant earthworm"was used to carry out pot experiment.It was found that the removal rate of pollutants in soil could be effectively improved.Through AHP and fuzzy comprehensive evaluation method,the optimal restoration scheme of"Pinus and Boletus luridus and tolerant earthworm"was selected.The ecological restoration strategy of Bayan Obo Mine Park was updated and designed.The vegetation biomass,soil pollution,meteorology,soil fertility and other information data were collected systematically and pertinently.This paper laid a foundation for scientific and effective guidance of mine ecological restoration.It provided theoretical basis and technical support for ecological restoration of mine soil environment and green mine construction.