Study On Soil Heavy Metal Pollution Characteristics And Environmental Risk In Hongqiling Nickel Mining Area

The heavy metal pollution degree of soil samples with different levels of tailings contamination in the nickel-mining area of hongqiling,Jilin province was evaluated using the single factor evaluation method,nemero comprehensive index method and potential ecological hazard index method.Single extractant（EDTA and NH₄OAc）,Tessier continuous extraction method,combined with risk assessment code method（RAC）and secondary phase to primary phase distribution ratio method（RSP）were used to investigate the morphological distribution and bioavailability of heavy metals in soil.Through adsorption experiments,X-ray diffraction（XRD）and Fourier transform infrared spectroscopy（FTIR）analysis,the migration and accumulation patterns of heavy metals Cd and Ni in soil were studied,and the adsorption mechanism of Cd and Ni in soil was discussed.The main research results are as follows:1.The average contents of Cr,Ni,Cu,Zn,Cd and Pb in the surface soil of nickel mining area of Jilin province were 68.13,321.29,79.22,75.34,1.04 and 27.41mg·kg^-1,respectively,which were 1.46,15.01,4.63,0.94,10.36 and 0.95 times of the soil background values of Jilin Province.Except Zn and Pb,the average content of other heavy metals all exceeded the background value of soil environment in Jilin Province,and there were different degrees of accumulation.The contents of Ni,Cu and Cd all significantly exceeded the standard specified in"screening value of agricultural land soil pollution risk",indicating the presence of heavy metal pollution in the soil in the study area.2.The results of single-factor pollution index analysis showed that the soil samples far away from the study area and tailings pond（3km）had pollution indexes less than 1.0,which were still at the clean level.In the soil samples close to the tailings pond（1km）,the pollution indexes of Ni and Cd are all greater than 3.0,which is at the level of severe pollution.The results of comprehensive pollution index analysis showed that the soil samples far from the study area to the tailings pond all had pollution indexes less than 0.7,which were at the safe level.The pollution index of soil samples close to the tailings pond was greater than 3.0,which was at the level of severe pollution.RI showed that soil samples C1 and C3 were slightly polluted,while soil samples C2 and C4 were moderately polluted.3.The extraction amount of EDTA in the one-step extraction method was greater than that of NH₄OAc.The results of Tessier continuous extraction and analysis showed that Cr,Cu,Zn and Pb pollution was relatively light,and the residue content was relatively high.The contamination of Ni and Cd was heavier,and the contents of exchangeable state and carbonate binding state were higher.Risk assessment coding method（RAC）and secondary phase to primary phase distribution ratio method（RSP）indicated that the biological availability and environmental risk of Ni and Cd in nickel mining areas were high.Among the three factors,soil p H,organic matter content and total heavy metal content in soil,the total heavy metal content in soil was the main factor affecting the distribution of heavy metal morphology in mining areas.4.The study of adsorption kinetics showed that the whole adsorption process of Cd and Ni on the soil could be divided into two stages,namely the rapid adsorption stage of 0-60 min and the slow equilibrium stage of 60-1440 min.The results of adsorption thermodynamics showed that the adsorption reaction of Cd and Ni on soil was an endothermic process,and the adsorption amount of Cd and Ni on soil increases with the increase of temperature.X-ray diffraction（XRD）and Fourier infrared spectroscopy（FTIR）analysis indicated that the mineral and organic matter components in the soil played an important role in the fixation of heavy metal Cd and Ni.