Experimental Study Of Coal Gangue As Vegetation Substrate Combined With MICP Technology For Vegetation Restoration

Coal mine is an important energy source in China,and coal gangue is a kind of solid waste formed in the production and treatment of coal mines,and its production volume accounts for about 10%-15% of the raw coal output.According to incomplete statistics,the accumulative stacking of coal gangue in the country has exceeded 7 billion tons,and about 1,500 to 1,700 gangue hills have been formed,covering an area of more than 200,000 mu,with an emission of about 500 million to800 million t/a.increase yearly.A large amount of coal gangue accumulation has not only caused serious pollution to the ecological environment of the mining area,but also brought a great threat to people’s production and life.At the same time,coal mining will cause a large number of pits and subsidence areas,which will easily cause serious damage to the surrounding cultivated land,water,soil,vegetation and human environment.In order to solve the above problems,this paper proposes using waste coal gangue to fill mine pits and combining microbial mineralization technology to carry out experimental research on vegetation restoration.The paper employs the Microbial-Induced Calcium Carbonate Precipitation(MICP)method to solidify and improve coal gangue particles while planting rye grass.Through a combination of macroscopic mechanical tests and microscopic mechanism analysis,the feasibility and reinforcement effect of solidifying coal gangue particles under different MICP treatments are explored.In addition,experimental studies are conducted on vegetation restoration using coal gangue particles as planting material and combining with MICP technology from the perspectives of the germination characteristics and growth features of rye grass.The main research contents and achievements are as follows:(1)Through the activation and cultivation of Sporosarcina pasteurii,we have mastered the preservation and proliferation cultivation technology of the bacteria,monitored the bacterial concentration and enzyme activity of the bacterial liquid during the bacterial culture,and obtained the growth curve trend chart of Sporosarcina pasteurii.Grasp its biological characteristics in each growth period,and determine that 24 ～ 40 hours is the best period of activity.At the same time,the influence of temperature and concentration of cementing fluid on the hydrolysis of urea by Sporosarcina pasteurii was studied,and the results showed that Sporosarcina pasteurii could survive at a temperature of 5℃ to 40℃,and the optimum culture temperature was 30℃;The calcium carbonate yield decreased with the increase of the cementation solution concentration.(2)According to the above test parameters,the MICP solidified coal gangue particle test was carried out,and physical and mechanical tests such as wind blowing erosion,water retention,penetration,and calcium carbonate content determination were carried out on the samples treated with different MICP.The test results showed that: The sample can effectively reduce wind erosion,and at the same time improve the water retention,and the surface of the sample also has a certain strength to improve its stability..(3)The microscopic tests of coal gangue particles reinforced by MICP were carried out: XRD(X-ray diffraction test)and SEM(scanning electron microscope test).According to the X-ray diffraction test(XRD)results,the use of MICP technology successfully generated calcium carbonate(calcite and vaterite in two crystal forms)around coal gangue particles,and played a key role in soil reinforcement.In addition,the results of the SEM scanning electron microscope test showed that there were calcium carbonate deposits on the surface and pores of the soil particles in each group of samples.When the calcium carbonate completely covers the soil particles,a large amount of calcium carbonate is distributed in the pores between the particles,and the surrounding soil particles are cemented into an aggregated state.At this time,the reinforcement effect of the sample is the best,which can significantly improve the wind erosion resistance,water retention and penetration damage resistance of coal gangue particles.(4)We conducted a pot experiment with rye grass based on coal gangue particles as a vegetative substrate and combined with MICP technology for treatment.The experiment explored rye grass germination characteristics(germination rate,survival rate,germination index,vigor index,and germination potential)and growth characteristics(root length and seedling height,biomass,and root-shoot ratio)from two aspects,and studied the effects of cementation solution concentration and cementation times on the growth and development of rye grass.The results showed that under the condition of coal gangue particles as a vegetative substrate,rye grass could grow smoothly.After MICP treatment with low cementation solution concentration and low cementation times,both rye grass germination and growth characteristics were improved,indicating that MICP technology has a promoting effect on the growth of rye grass to a certain extent.