| In recent years,with the gradual depletion of mineral resources and other reasons,a large number of abandoned tailings ponds have been formed.Abandoned tailings pond is an abandoned industrial and mining land used to store mineral wastes.It not only occupies land resources,but also causes a series of environmental problems such as water pollution,soil pollution and air pollution when solid tailings waste is accumulated without timely treatment.One of the most noteworthy problems is the heavy metal pollution of mining soil.Heavy metals in solid wastes in mining areas can enter the surrounding environment through a series of human and natural activities.Heavy metals in tailings and solid wastes are dissolved and infiltrated into the soil under the action of rainwater,which poses a serious threat to the surrounding ecological environment.Moreover,heavy metals are enriched and will eventually cause great harm to human health through the food chain.In addition,when the tailings contaminated by heavy metals encounter acids,alkalis and other substances,the migration and concentration of heavy metal ions may be caused,which will further affect the safety and stability of the tailings dam along with the change of the physical and mechanical properties of the soil.Therefore,it is of great practical significance and theoretical value to explore the release and migration characteristics of heavy metal pollutants in tailings abandoned land and its correlation with physical and mechanical indexes.Based on the background of a copper,lead and zinc co-existing abandoned tailings pond in Hanling Town,Liaoyang County,Liaoning Province,considering the stratification characteristics of the abandoned tailings soil,this paper uses a large soil column model made by ourselves to stratify the tailings and carry out simulated rainfall experiments in the laboratory.The dissolution,release and vertical migration characteristics of heavy metal pollutants Cu,Pb and Zn in the soil contaminated by layering waste tailings were investigated under the influence of various factors such as different rainfall p H value,rainfall intensity and rainfall duration.Direct shear tests were conducted to further explore the influence of leaching on the shear strength of tailings and the correlation between the content of heavy metal pollutants and the shear properties of layered tailings soil.The following conclusions are drawn:(1)During the whole leaching process,the leaching p H values of 18 soil columns in 6 groups were almost the same,the p H value of the leached liquid of each soil column increased from bottom to top along the water outlet of the soil column.And the leaching p H values were all neutral or weakly basic.In general,the influence of leaching intensity on total leaching is greater than leaching time.(2)The ionic concentrations of heavy metals Cu,Pb and Zn in the leaching solution decreased with the increase of p H of rainfall.The concentration of heavy metals at the bottom outlet remained the maximum and decreased from bottom to top.The leachate from the overflow mouth of each soil column has a slight leaching effect on the stratified polluted soil and the concentration of heavy metals is not 0.In general,the leaching concentrations of heavy metals Cu,Pb and Zn increased with the increase of rainfall intensity.Under acid rainfall,the longer the rainfall time,the higher the concentration of Cu,Pb and Zn in the leaching solution of each outlet;However,under weak alkaline leaching,the opposite is true.(3)Under different rainfall p H values,the variation trends of Cu and Zn were similar: after rainfall leaching,they mainly accumulated in the soil surface(0-20cm).The contents of Cu and Zn in the soil decreased significantly in the depth of 0～20cm under acid rainfall,but increased slightly under alkaline leaching.In the same soil column,the concentration of Cu,Pb and Zn ions decreases with the increase of stratification depth,but the content of each layer has little difference in general.With the increase of rainfall intensity,the seepage of leachate was accelerated,and the contents of Cu,Pb and Zn increased with the increase of rainfall intensity.The concentration of Cu,Pb and Zn ions in stratified contaminated soil changed roughly with the increase of leaching time.Compared with the initial level,the concentration of Cu,Pb and Zn ions decreased significantly,but there was no accumulation of Pb in the surface layer.(4)With the increase of p H value,the overall shear strength of polluted soil decreases.The internal friction Angle φ of the shear strength index gradually increases,and the cohesion C gradually decreases.Leaching can effectively increase the shear strength of tailings.The shear strength of tailings after leaching was positively correlated with rainfall intensity.The shear resistance of tailings after leaching was also positively correlated with rainfall duration.However,the increase of shear strength of tailings flow group is less than that of time group.The shear strength of tailings after leaching is inversely proportional to the content of heavy metal pollutants.In other words,under the same leaching condition,with the increase of the content of heavy metal pollutants in layered soil from surface to bottom,the shear strength decreases,the cohesion gradually increases,and the Angle of internal friction gradually decreases.(5)The layered soil filling in the soil column leaching test is used to simulate the actual abandoned tailings pond soil layer.It is found that the release law and vertical migration characteristics of heavy metals in the in-service tailings ponds are also applicable to abandoned tailings ponds,but they are slightly different.Through direct shear tests,this study further explored the influence of leaching on the shear strength of tailings and the correlation between the content of heavy metal pollutants and the shear characteristics.This part is a pioneering work,and the conclusions obtained can provide reference for guiding the reasonable and effective treatment and utilization of abandoned tailings ponds and improving the engineering properties of heavy metal contaminated tailings soil. |
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