Study On The Occurrence Forms And Influencing Factors Of Heavy Metals In Soil Of A Tailing Affected Area In Eastern Inner Mongolia

Soil heavy metal pollution is a very serious environmental problem that needs to be solved urgently;The tailings produced in the development and utilization of mineral resources will cause heavy metals to enter the surrounding soil and water bodies through dust settlement and rainwater leaching during the long-term stacking process,causing pollution to the ecological environment.Heavy metals exist in different forms in soil and water,and their migration behavior in the environment and their harm to the environment are very different.It is of great significance to study the occurrence of heavy metals in soil to clarify their migration and transformation behavior in the environment and potential risks to the environment.The addition of different kinds of humic acid and iron-manganese oxide to soil can change the occurrence of heavy metals and their migration and transformation behavior in soil-water bodies and plants,and change their ecological risk to the environment.Taking the 0-20 cm soil around a lead-zinc tailings in eastern Inner Mongolia as an example,25 sampling points were laid around the tailings reservoir based on local geographical characteristics to determine the total amount of heavy metals,and the pollution level was comprehensively evaluated by using the single-factor index method and the ground accumulation index method,and then the accumulation form of heavy metals was extracted to clarify their ecological risk and migration capacity to the environment.Finally,the effects of different kinds of humic acid and iron-manganese oxide on the occurrence of heavy metals were explored by exogenous addition,and the results showed that:(1)The soil in the study area is alkaline or weakly alkaline,and the soil organic matter and cation exchange capacity are low;The physical and chemical properties of soil were different and at the level of strong variation.Zn > Pb > As > Cu in soil,and the cumulative average content was 31.39 times,23.60 times,16.12 times and 12.50 times higher than the background value,respectively.The overall pollution level in the study area is As > Zn >Pb > Cu.(2)Occurrence forms of heavy metals in the soil of tailings affected area The four kinds of heavy metals mainly occur in the residual state and the oxidation state of iron and manganese.In addition to these two forms,the contents of carbonate bound copper,primary sulfide and carbonate bound zinc,organic bound arsenic and carbonate bound lead in soil are also large.The effective state was used to evaluate soil heavy metal pollution as low risk and medium risk,and the effectiveness of zinc was the highest and the lowest in arsenic in the study area.(3)Exogenously added humic acid can increase the adsorption sites in soil and enhance the stability of heavy metal ions in soil.Heavy metals mainly exist in the form of iron and manganese oxidation state and residue state.The effects of different humic acids on the occurrence forms of heavy metals in soil are different.After adding total humic acid,the available states of Zn and As increased,while the available states of Pb and Cu decreased.After adding fulvic acid,humic acid and humin,the available states of Zn,Pb and Cu decreased,while the available states of arsenic increased.The available states of various heavy metals decreased with the increase of humic acid concentration.After adding humin and humin acid,the available Pb and Cu in soil will increase with the increase of aging time,while the available As in the soil with adding fulvic acid and humin will increase.It can be seen that the addition of different types of humus acid has different effects on the occurrence forms of heavy metals in soil.(4)After the exogenous addition of Fe and Mn oxides,the available states of the four heavy metals all showed a downward trend,indicating that Fe and Mn oxides could significantly reduce the ecological risk of heavy metals in soil.In the orthogonal experimental design,the effects of various factors on the available content of lead were as follows: aging time > concentration of iron and manganese oxides > humic acid concentration;The effect of zinc available state content was as follows: aging time > humic acid concentration > ferric manganese oxide concentration;The effect of the available copper content was as follows: humic acid concentration > aging time > ferric manganese oxide concentration;The effect of available arsenic content was as follows: humic acid concentration > ferric manganese oxide concentration > aging time.In summary,the spatial difference of soil physical and chemical properties in the tailing mining area is large,and the content of heavy metals zinc and lead is high.Most of the four heavy metals exist in the oxidation state and residual state of iron and manganese.After the addition of humic acid and iron and manganese oxides,the heavy metals exist in a stable form in the soil medium,and their potential available and non-available state contents are high,which is not easy to migrate and transform,which is conducive to the solidification of heavy metals.Arsenic is the main pollution in this study area,and its pollution level,potential ecological risk and availability are higher than other heavy metals.