Study On Key Technologies Of Heavy Metal Migration And Barrier From Gully Type Fly Ash Dumps In Coal Industry Gathering Area

There are a large number of fly ash sites around the coal industry cluster area,and a variety of polluting heavy metals in the fly ash sites are easy to migrate to the surrounding environment through various ways.Among them,gully type fly ash sites（which have no direct contact and connection with underground water layer,water holding mainly depends on natural precipitation infiltration,are usually in an unsaturated state,and internal cracks may be caused by strong heterogeneity.The heavy metals in the percolated water are discharged from the bottom through the leachate）after natural leaching out,they migrate to the surrounding soil and rivers and spread to the surrounding ecological environment.Although the concentration is relatively low,the total amount of heavy metals in the storage yard is large,and the pollution time is long（10-20 years）.Heavy metals accumulated in the environment for a long time will cause a series of ecological hazards and security risks.Therefore,aiming at the typical gully-type fly ash dump in Tunlan mining area,Gujiao City,Shanxi Province,this study studied the occurrence state,release and migration rule of nine heavy metals（copper,zinc,lead,chromium,cadmium,manganese,nickel,arsenic and mercury）in the dump,and explored the key technologies of heavy metal migration barrier in leachate.Finally,an osmotic adsorption wall structure is designed to prevent the heavy metal pollution in the leachate of gully type fly ash landfill from migrating to the surrounding soil and groundwater for a long time,which provides reference for the practical application of long-term control of heavy metals in the leachate of gully type fly ash landfill.The relevant conclusions of this thesis are as follows:（1）In the leaching experiment,the concentration of heavy metal elements in the leaching solution of sampling holes with different heights on the leaching column was high at the initial stage,and then gradually decreased and tended to be stable.The p H value in the leached solution fluctuates within a certain range（5.5-7.5）.The concentration of heavy metals in the leached solution is similar.After 120 days of leaching,it was found that the proportion of the stable state of various heavy metal elements in the packing samples with different depths increased significantly,which made the properties of heavy metal elements in the packing more stable and reduced the harm to the environment.（2）From the perspective of micro-interface electrical compatibility,it is proved that the interface self-assembly of Cu_xS and attapulgite can be realized at room temperature,and the synthesized ATP@Cu_xS material has suitable hydrophobicity,strong mechanical stability,good dispersion stability and suitable settlement performance,which is conducive to the rapid removal of Hg²⁺from the leachate.The mass ratio of Cu_xS to attapulgite was 3:1（T₂）in batch water treatment experiment.At the same time,it was found to have strong p H adaptability（4-11）,high mercury-removal ability at room temperature,resistance to various anions interference,obligate Hg²⁺absorption and high adsorption capacity（746.48 mg/g）.After a total of 8 cycles of adsorption and desorption,the adsorption efficiency in the final time is still as high as 70.8%,indicating that the adsorbent has excellent and stable recycling performance.In the long-term treatment of a large number of low concentration mercury-containing wastewater,it is proved that the adsorbent can achieve long-term control of mercury pollution in leachate and achieve standard discharge（<1μg/L）.（3）A variety of characterization methods were used to study the structural characteristics of ATP@Cu_xS adsorbent and its adsorption mechanism of mercury.XRD patterns showed that Cu_xS synthesized on ATP@Cu_xS surface were mainly Cu₂S and Cu S.XPS analysis shows that S exists in the form of S^2-,and Cu exists in the form of Cu²⁺and Cu⁺.The two elements combine to form Cu_xS,and the XPS diagram of adsorbent after adsorption of mercury can prove the existence of Hg-Cu-S,which proves that Cu_xS and Hg²⁺in the wastewater complex reaction.SEM results showed that mercury was successfully captured by ATP@Cu_xS.FT-IR spectra confirmed the existence of Cu-S bond and acted on the adsorption of mercury.（4）A permeation and adsorption wall structure was designed to block the migration of heavy metals in the leachate of gully type fly ash landfill,with low cost,simple construction technology,which can provide reference for the practical application of long-term control of mercury-containing leachate of gully type fly ash landfill.