Experimental Study On Solidification/Stabilization Of Heavy Metal Contaminated Soils In Typical Mining Areas Based On MICP Technology

In recent years,a large number of mining enterprises have been shut down or relocated,and improper disposal methods and accidental leakage of waste from abandoned industrial sites have led to a large number of heavy metal pollution sites.At the same time,China has issued a series of guidelines,standards and policies and regulations for the contaminated sites in mining areas,put forward the requirements of sustainable development and green development,and explored the sustainable restoration of the contaminated sites with heavy metals,so as to meet the requirements of both environmental safety and redevelopment,utilization and construction.In this paper,the application of microbe induced mineralization technology is a new type of biological mineralization technology,its rapid response,artificial control,green environmental protection,has been more and more used in soil reinforcement.However,the solidification/stabilization of heavy metal contaminated soils in typical mining areas remains to be researched and proved.Based on where the technology and the introduction of biochar additive,was prepared in laboratory microbial induced mineralization specimen,study after repair the unconfined compressive strength of the soil,heavy metal leaching concentration,durability,and to evaluate the long-term stability of the repair effect of fixing agent,metal repair provides the basis for the field test data.The test results are as follows:（1）Microbial induced mineralization（MICP）technology is used to solidify/stabilize the heavy metal contaminated soil,and the optimal mineralization conditions are:Cemented nutrient solution was NH₄Cl 10g/L,nutrient broth 3.0g/L,NaHCO₃ 2.12g/L,UREA 42.0g/L,CaCl₂.2H₂O 88.42g/L,and curing time was 10d.The indoor unconfined compressive strength of the restored soil meets the requirement of the lower limit of 0.35MPa stipulated by the state,and is up to 2.69times.The leaching concentration of lead decreased by 44.8%and that of zinc decreased by 46.8%compared with untreated.（2）Based on microbe induced mineralization technology（MICP）technology combined with adsorption materials to solidify/stabilize heavy metal contaminated soil,three different adsorption materials were added,which were rice activated carbon,porous silicon,and corn stalk concentrated stalk activated carbon.The results showed that when 10%porous silicon was added,the indoor unconfined compressive strength of the restored soil reached the highest of 1021kPa,and the degradation effect of lead was very good,and the leaching concentration of lead was 67.8%lower than that of the untreated soil.When 20%rice straw biochar was added,the leaching concentration of Zn in all adsorbent materials reached the minimum value of2.66mg/L in the three groups,which decreased by 66.9%compared with that without treatment.（3）With the addition of porous silicon（DKG 10%）and rice straw biochar（SDT）as raw materials,the unconfined compressive strength gradually decreased with the increase of the addition of rice straw biochar,and the minimum compressive strength was 931.5kPa,and the leaching concentration of lead was 2mg/L.The leaching concentration of zinc was 52.38%,73.71%,46.51%and 73%lower than that of MICP alone and 2.31mg/L respectively.（4）Curing/stabilization mechanism:The mineralization products are mainly calcite and aragarite by SEM and XRD analysis.The urease produced by Bacillus pasteurii in the metabolism process can decompose urea to form NH₄⁺and CO₃^2-.Due to the special structure of the cell wall of the bacterium,the surface of the bacterium is negatively their large specific surface area and rich micropores on the surface.Heavy metal ions may be adsorbed on their surface or may enter into their pores through diffusion.Bacillus basiensis produces enzymatic characteristics during its growth and reproduction,and deposits and mineralizes Ca2+,Zn2+and Pb2+ions from the surrounding environment in the form of carbonate.（5）Based on microbe induced mineralization（MICP）technology combined with adsorption materials to solidify/stabilize the heavy metal contaminated soil,showing good resistance to freeze and thaw cycles.When no adsorbents were added,the solidified/stabilized heavy metal contaminated soil could withstand 7 freeze-thaw cycles,and the combined treatment of heavy metal contaminated soil based on MICP technology and adsorbents could withstand 15 freeze-thaw cycles.In addition,compared with the adsorption material,it has a better freeze-thaw cycle resistance in terms of unconfined compressive strength and toxic leaching.