| Under the leaching of rainwater,the coal gangue stacked in the open air releases a large amount of pollutants,which causes the permeability coefficient of the soil aeration zone in the lower part of the dumping area to change,which is beneficial to some toxic and harmful components entering the soil,jeopardizing the dumping area and the surrounding ecological environment.At present,most of the researches on soil-meteorite system in China use leaching and permeation experiments to explore the mechanism of permeability change.However,there are relatively few studies on the effects of mineral dissolution and sedimentation and microbial growth and propagation on soil permeability.Based on the National Natural Science Foundation of China?41372258?,this paper uses coal gangue in the Han cheng district of Shaanxi Province as the research object,analyzes the variation of soil pore and permeability coefficient by laboratory test and numerical simulation,and clarifies the changes of water chemical reaction and microbial permeability coefficient.The influence of the leaching on the permeability coefficient of the vermiculite-soil system is revealed.The results are as follows:1.There are significant differences in the permeability coefficients of different soil media under leaching.The average permeability coefficient of sand medium in the whole leaching cycle is 6.14×10-3cm/s.With the increase of leaching days,the permeability is further enhanced,up to 8×10-3cm/s;the mean permeability coefficient of silt medium It is 1.22 times of the empirical value,and the large change is mainly concentrated in the late stage of leaching;the clay has the smallest permeability coefficient with a mean value of 4.66×10-5cm/s due to its self-adhesive content and large specific surface area.2.In addition to significant changes in pores and permeability during leaching,there are significant differences in the release of anions and cations and the degree of mineralization of the leachate.Generally speaking,the larger the particle size of the soil,the larger the pores and the faster the release of the major components.However,due to the differences in the soil conditions and the environment in which the microorganisms grow and reproduce,the pores are blocked in different leaching times.The release of the points is not the same.The initial release of sand mineralization is 155mg/l.With the increase of leaching time,the salinity gradually increases;the silt mineralization varies from 252-2750mg/l;the clay mineralization shows initial release.The amount of high,medium-term reduction of late growth trend,the average release is 251.84mg/l.Combined with the total composition of the entire coal gangue-soil system,the general trend of silt>clay>sand is released.3,PHREEQC simulation results show that mineral dissolution and sedimentation changes are closely related to soil permeability coefficient changes.Under the leaching action,the substances released from the vermiculite clogging or leaching the soil pores under the water chemistry of the soil medium,causing the coal gangue-soil permeability coefficient to change.The dissolved and precipitated amount of sand in the sand is basically balanced under the action of water and rock,and there is a certain change in the late stage of leaching.The total sedimentation amount is 2.21×10-3mg/l;the mineral in the early stage of silty leaching is mainly sedimentation,and the later stage is dissolved.Mainly,the mineral dissolved precipitates changed dynamically in different time periods,and the overall sedimentation amount reached2.09×10-1 mg/l.The clay has a strong adsorption capacity due to its internal and external surfaces,which can effectively adsorb the sediment particles generated by the water chemical reaction and block the soil particles.Between the pores,the mineral dissolved and precipitated the largest amount,which is 2.68 times that of silt.4.Changes in soil permeability will not only be affected by changes in the dissolution and precipitation of minerals,but also by the growth and reproduction of microorganisms.Combined with the change of microbial bacteria content,the pores of sand media are mainly affected by Bacillus cereus,the number of reproduction is 88×104,accounting for 52.34%of the proportion of bacteria;the permeability of silt medium is mainly affected by yeast,the maximum reproduction The number is 13×104,and Staphylococcus is the main factor in the later stage;the permeability of clay medium is mainly affected by Bacillus cereus and Escherichia coli.The soil infiltration process provides the necessary nutrients for microbial growth.Under good infiltration conditions,the microorganisms multiply,and the propagated microorganisms block the pores between the soil particles and reduce the soil permeability.5.Through the correlation analysis and principal component analysis of various factors affecting the permeability coefficient,a multivariate regression equation was established.It was found that the permeability of sand medium is mainly affected by the porosity?ratio?,the amount of dissolved minerals,and the permeability of microorganisms.The influence is small;the porosity of silt medium and the influence of mineral dissolved sedimentation on soil permeability are basically in the same order of magnitude;while the microbial growth of clay medium has certain influence on its permeability,but the change of mineral precipitation is the main influencing factor. |
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