Study On Geochemical Characteristics And Heavy Metal Element Migration Of Coal Gangue Backfilling Material

As China attaches great importance to environmental protection and the utilization of solid waste resources,it is urgent to study the control of pollution components in surface discharge and underground filling process.When coal gangue is piled up on the surface or filled into the goaf in a large scale,the heavy metal elements contained therein are in the state of secondary enrichment.Under the joint actions of high temperature,high pressure and mine water in the goaf,heavy metal elements will be released continuously,which will have certain impact on the groundwater environment.Based on the analysis of the regional distribution and geological age distribution of coal gangue producing areas in China,this paper studies the difference of distribution of heavy metal elements in coal gangue,the causes of element enrichment and its migration behavior in the floor by means of field investigation,laboratory testing,theoretical analysis and numerical simulation.The migration distance of heavy metals in floor is predicted by numerical calculation.The main research results are as follows:(1)On the basis of investigating the regional distribution and geological age distribution of coal gangue in China,the contents of Hg,Pb,Cd,Cr,As,Cu,Zn,Mn,Se and Be in coal gangue were measured by ICP-MS and AFS.Cluster analysis of heavy metal elements was carried out by statistical method.According to the results of cluster analysis,the heavy metal elements in coal gangue were divided into four categories.(2)The ecological risk assessment and content of difference analysis of heavy metals in coal gangue were carried out,and the average ecological hazard index and enrichment factor of different heavy metals in different gangue producing areas and geological ages were obtained.Based on the total sulfur content and geological origin of coal gangue,the reasons for the enrichment of heavy metals and the differences in their distribution were explained.(3)Based on the analysis of migration path and influencing factors of heavy metal elements in backfill goaf,the evolution law of permeability under different stress and lithology of floor was studied,and the change law of permeability stress sensitivity was analyzed.According to the results of permeability stress sensitivity test,five kinds of function relations of permeability with stress were fitted.(4)Based on the permeability stress sensitivity test,a numerical simulation model for the migration of heavy metal elements under seepage-stress coupling conditions was established using COMSOL Multiphysics.Taking Mn element as an example,the concentration distribution and seepage law of heavy metal elements in the floor under different stress states and different lithology conditions were analyzed,and the diffusion distance of heavy metal elements in 100 years was predicted.There are 42 figures,20 tables and 113 references in this paper.