Effects Of Soil Heavy Metal Compounds On The Structure And Stability Of Microaggregates In Kafang Tailings Pond

As the structural foundation of soil,the structure and stability of soil microaggregate greatly affect the strength of soil structure.The stability of tailing pond soil is affected by various factors,and the study of microaggregates in the soil can more reasonably reflect the overall stability of the soil.Heavy metal compounds can promote the process of soil agglomeration,especially in the soil of tailings pond.In this study,the soil microaggregates and heavy metal compounds（As₂O₃,Co₃O₄,Cr₂O₃,CuO,Ni O,ZnO）in the Kafang tailings pond of Yunxi Company,Gejiu City,Yunnan Province were used as the test objects,and drilling sampling sites were set up to collect and determine the physical and chemical properties of soil.The distribution characteristics of soil water-stable microaggregates were determined by sedimentation test,and the structural character of soil microaggregates was determined by compression test.The effects of heavy metal compounds on the structure and stability of soil microaggregates were studied.The study has reached the following important conclusions:（1）In the study area,the soil sand content was 44.82%,the silt content was 49.8%,the clay content was 5.38%,the soil texture was silty loam,and the soil organic matter content was only 0.14 g·kg^-1.The variation coefficient of the content of heavy metal compounds in the soil was CuO at the highest（0.661）,and Co₃O₄ at the lowest（0.502）,all showing moderate variability.（2）The semivariance model with 6 heavy metal compounds at different depths was mainly Gaussian model.The spatial heterogeneity and total variation of heavy metal compounds were low and the spatial dependence was strong.The content distribution of heavy metal compounds in different soil depths was quite different.The content of As₂O₃and Ni O in tailing pond decreased layer by layer.The contents of CuO and ZnO in the tailings pond decreased first and then increased layer by layer.The content of Co₃O₄ and Cr₂O₃ showed a relatively uniform distribution in the upper soil of the tailings pond,and then increased in the lower layer.（3）The content of soil microaggregates in the study area was 96.74%.The MWD and GMD of water-stable microaggregates in the depth of[0,5]m were about 2.1 times that in the depth of(5,15]m.The fractal dimension of soil microaggregates was unevenly distributed at different depth,which is the largest in the depth of(5,8]m and the smallest in the depth of(2,5]m.（4）Scanning electron microscopy（SEM）was used to observe the compact structure of microaggregate in the depth of[0,5]m soil layer,and the porous structure in the depth of(5,15]m soil layer.The structural parameter curve drawn by compression test presents two kinds of laws.The curve of soil microaggregates in the[0,5]m soil layer showed a downward trend as a whole,and the decline rate was fast and then slow.The curve of the(5,15]m soil layer rises to a peak at the initial loading and then falls back,and the overall change is relatively gentle.（5）The heavy metal compounds that mainly affect the structure and stability of microaggregates in the soil of the study area are CuO and ZnO.The contribution level of CuO to the structure and stability of soil microaggregates was twice that of ZnO in the depth of[0,8]m soil layer,and both of them contribute the same level to the structure and stability of soil microaggregates in the depth of(8,15]m soil layer.In summary,the content of CuO and ZnO in soil will affect the structure and stability of the microaggregates,of which CuO has the highest contribution to the structure and stability of the microaggregates.The results of this study are of great significance to further explore the influence of heavy metal compounds on the overall stability of the tailings pond soil.