Study On Soil Environmental Characteristics Around Rare Earth Tailings Pond And The Adsorption Of Soil Colloid To Ce(ⅲ)

Rare earth elements（REE）are a kind of extremely special elements,which are widely used in various advanced industries and important support of national economy.China is a country with the largest quantity and supply of rare earth minerals.In recent years,the extraction and smelting of rare earth minerals have caused huge environmental problems.The long-term stacking of tailings may lead to the migration of toxic and harmful substances,such as rare earth,sulfate radical and chloride ions,into the environment,and the ecological risk is aggravated year by year.The study area is located in the northwest of China,and the special soil environment may have changed.At the same time,soil colloid exists widely in the soil,and its adsorption capacity of rare earth elements may also affect the spatial distribution of rare earth elements,so relevant research is urgent.Soil samples were collected from the surface layer（0～20 cm）,the middle layer（20～40 cm）and the deep layer（40～60 cm）of 12 distribution sites in the southeast of a rare earth tailings pond area in the north of China.The rare earth elements in soil samples in the study area were tested and analyzed,and their occurrence characteristics,differentiation characteristics,spatial distribution,control factors and environmental sources were systematically discussed.The results show that the total amount of rare earth elements in the study area ranges from 138.27 to5823.51mg/kg,with an average value of 1035.48mg/kg,showing strong spatial variability and REE enrichment.The average contents of light rare earth elements（LREE）and heavy rare earth elements（HREE）are 1002.90mg/kg and 32.58mg/kg respectively.The results of chondrite standardization show that the rare earth elements in the study area show different degrees of Ce and Eu relative deficit,indicating that Ce and Eu have migrated to the environment.The results of inverse distance weighted interpolation（IDW）analysis and correlation analysis further indicate that the rare earth elements in the soil of the study area are generated by the accumulation of tailings and transported by wind diffusion and atmospheric deposition.Under the background of global warming,the rare earth elements in the soil of the study area showed the characteristics of"more in summer and less in winter".In addition,the physical and chemical properties of soil samples in the study area were tested and analyzed,and the spatial distribution of each index was predicted by Kriging interpolation method.It was found that the soil in the study area was barren and not suitable for vegetation growth.The contents of nitrogen（N）and available potassium（K）ranged from 0.50 to 1.22 mg/kg and 195.55 to 490.50 mg/kg.The available iron（Fe）content is 2.58-28.84 mg/kg,and the exchangeable manganese（Mn）content is 11.33-51.27mg/kg.The contents of calcium and magnesium ranged from 6.29 to 39.85mg/kg and 4.63to 9.81 mg/kg,respectively.These indexes were in line with the vertical distribution of nutrient elements and showed uneven spatial distribution.In addition,the soil in the study area is seriously salinized and belongs to the level of saline soil,with the content of Cl^-ranging from 15.30 mg/kg to 2286.00 mg/kg and the content of SO₄^2-ranging from 187.67mg/kg to 3059.00 mg/kg.The soil colloid extracted from the soil in the study area was selected as the adsorption main body,and Ce（Ⅲ）with the highest content of rare earth elements in the soil in the study area was selected as the adsorption object.The soil colloid was characterized by BET,SEM,XRD and FTIR,and the isothermal adsorption,adsorption kinetics and adsorption thermodynamic characteristics of Ce（Ⅲ）were studied.In addition,the environmental stability of rare earth elements was simulated in the laboratory under freeze-thaw cycles,high salinity and alkali conditions,and the addition of mineral dressing agents.The results show that soil colloid is a kind of mesoporous material,and the adsorption of rare earth element Ce（Ⅲ）is a homogeneous surface reaction process involving both physical and chemical adsorption.Freezing and thawing affect the adsorption effect of soil colloid on Ce（Ⅲ）,and the adsorption effect is positively correlated with the number of freezing cycles,and negatively correlated with freezing temperature.Beneficiation agents and soil salinization are also negative factors of adsorption effect.This study provides reference for the source control of rare earth pollution and the ecological management of the surrounding area of tailings pond.