Study On Heavy Metal Elements Release And Migration In Filling Reclaimation Materials In Mining Area

Filling reclamation technology has a significant function in restoring the goaf and subsidence areas caused by mining activities and improving the mining environment,which has been widely used in land reclamation in mining areas.The choose of backfill material and the release of pollutants in it under natural conditions have a profound impact on the mining area environment.This paper combines theoretical analysis,laboratory experiments,numerical simulation etc.to find a better filling material in coal mining areas and study the release and migration laws of heavy metal elements.Firstly,this article analyzed the constituent of coal gangue and fly ash,then fly ashes were mixed with gangues in different mass proportions 1:0.2,1:0.4,1:0.6 and1:0.8.By using the soil column leaching experimental device,the dissolution-release laws of five heavy metal elements including Cu,Zn,Pb,Cd,and Cr were studied.Then sequential extraction was used to study the changes in the occurrence status of heavy metal elements before and after leaching in different proportion samples.Hakanson ecological risk assessment method was introduced for heavy metal elements ecological risk assessment,combined with compaction rate analysis,the best proportion of materials was determined.Finally,the multi-physics simulation software COMSOL Multiphysics was used to simulate the release-migration laws of the studied heavy metal elements in order to predict the release-migration situation in long period.Conclusions reached in this article are as follows:?1?The content of heavy metal elements in coal gangue and fly ash samples with different proportions showed an upward trend with the increase of fly ash;?2?The concentration of heavy metal elements in the leaching solution of each sample was relatively high in the early release period,and it was leached in large quantities at the beginning,then gradually decreased and stabilized.The pH value in the leaching solution was large,showing strong alkalinity.The largest EC value occurred at the beginning of dissolution,then decreased rapidly with the increase of leaching time and gradually stabilized;?3?Elovich kinetic equation,double constant equation,polynomial equation,and parabolic equation can describe the release process of heavy metal elements under leaching,but the polynomial equation is more effective;?4?After mixing and leaching coal gangue and fly ash,the occurrence state changed greatly,the inert occurrence state,especially the residue state,has increased to varying degrees,and their releasing ability was effectively restricted;?5?The ecological risk assessment grades of four samples mentioned above were all middle and low grade,showing that the pollution degree to the environment was lower.Combined with the analysis of the smallest potential ecological risk and compaction rate,1:0.6 sample was considered as the best;?6?Natural precipitation affects the movement of water in the filling reclaimation material.The way water flows were seepage.Under simulated rainfall conditions,Cu²⁺,Zn²⁺,Pb²⁺have a longer release period,while Cr²⁺and Cd²⁺release periods are shorter.At the same time,the maximum concentration of each heavy metal element was at the bottom of the column.This thesis contains 30 figures,28 tables and 123 references.