Soil-fixing Effect Of Grass Planting On Improved Coal Gangue Matrix And Its Regulation On Fe/Mn Leaching And Migratio

The coal gangue mountain is prone to soil erosion,and its heavy metal Fe,Mn leaching migration has an impact on the surrounding soil and water environment,due to the strong acidity,low nutrients and poor structure of the coal gangue,which is not conducive to the normal growth of plants,the coal gangue mountain vegetation restoration faces greater difficulties,therefore,this thesis by adding phosphogypsum and mycorrhizal residue to the coal gangue to improve the mixed vegetation substrate,in the potting conditions,planted ryegrass,Under potted conditions,ryegrass,tall fescue,alfalfa and white clover were planted to analyze the plant growth and physical properties of the substrate on the mixed substrate of coal ganguephosphogypsum-mycorrhizae,to compare and analyze the shear resistance of the root system of ryegrass,tall fescue,alfalfa and white clover with the mixed substrate of coal gangue,and finally to explore the regulatory effect of grass planting on the leaching migration of heavy metals Fe and Mn in the mixed substrate of coal gangue.The main conclusions are as follows:(1)The ryegrass on pure gangue can not grow normally,adding 10%～40%phosphogypsum and 10%～20% mycorrhizal residue to gangue for improvement can significantly improve the growth of ryegrass.Among them,adding 20% phosphogypsum and10% mycorrhizal slag is the preferred ratio of gangue-phosphogypsum-mycorrhizal slag mixed substrate suitable for ryegrass growth,under this preferred ratio,the effective phosphorus content increased by 4.53 times,the effective potassium content increased by 1.16 times,the natural water content increased by 18.88%,the total porosity increased by 14.18%,and the capillary porosity increased by 13.5% compared with the gangue mixed substrate with 10%mycorrhizal slag.The natural water content increased by 18.88%,total porosity increased by14.18%,capillary porosity increased by 13.12%,bulk weight decreased by 24.76%,ryegrass plant height increased by 42.75%,aboveground dry weight increased by 42.68%,root weight density increased by 124.90% and chlorophyll content increased by 25.99%.(2)The coupling effect of ryegrass root system and gangue-phosphogypsum-mycorrhizal slag composite can significantly improve the shear resistance of the mixed substrate.Compared with the mixed substrate without grass,the shear strength of the root system-mixed substrate increased by 26.04%,the cohesion and internal friction angle increased by 34.83% and 17.89%,respectively,at all levels of vertical loading.Among them,the shear resistance of the ganguephosphogypsum-mycorrhizal mixed substrate with 20% phosphogypsum and 10% mycorrhizal residue and ryegrass rhizosphere complex was the best,with the average shear strength of268.81 k Pa and the average cohesion and internal friction angle of 94.66 k Pa and 34.94 °,respectively,at all levels of vertical loading.(3)Different plant root systems and gangue-phosphogypsum-mycorrhizal mixed substrate complexes showed significant differences in improving the shear performance of the mixed substrate.Compared to the ungrown gangue-phosphogypsum-mycorrhizal mixed substrate,the shear strength of the gangue-phosphogypsum-mycorrhizal mixed substrate under the growth of ryegrass,tall fescue,alfalfa and white clover increased by an average of 30.51%,44.08%,14.29% and 11.40% under all levels of vertical loading,and the cohesion increased by an average of 57.30%,72.44%,25.41% and 17.84%,respectively.The average shear strength increased by 30.51%,44.08%,14.29% and 11.40%,the average cohesion increased by 57.30%,72.44%,25.41% and 17.84%,respectively,and the average internal friction angle increased by14.61%,24.75%,7.42% and 7.12%.Tall fescue showed the greatest increase in shear resistance to the gangue-phosphogypsum-mushroom residue mixed substrate,followed by ryegrass and the least by white clover.(4)Plant growth can significantly reduce the leaching migration of Fe and Mn in the mixed substrate of gangue-phosphogypsum-mycorrhizae,and the Fe and Mn contents in the leachate of the mixed substrate of gangue-phosphogypsum-mycorrhizae were reduced by37.39% and 44.75% on average under the growth of rye grass compared with the mixed substrate of gangue-phosphogypsum-mycorrhizae without grass.Compared with the mixed substrate of gangue-phosphogypsum-bacterial residue,the average content of Fe in the permeated water of gangue-phosphogypsum-fungal residue mixed matrix decreased by17.92%～90.85%,21.81%～95.48%,13.06%～84.66% and 10.78%～82.80%,respectively.The average content of Mn decreased by 30.69%～76.54%,37.48%～85.41%,21.52%～68.44% and20.29%～62.31%,respectively.High fescue had the best effect on the leaching migration of Fe and Mn in the gangue-phosphogypsum-bacterial residue mixed matrix,followed by ryegrass and white clover was the worst.