Stabilization Remediation Of Heavy Metals In Soils By Palygorskite Modified By Ca（H₂PO₄）₂

With the rapid development of China’s economy,the industrial manufacturing and agricultural production have caused serious damage to the soil,and the soil environmental quality in China is deteriorating day by day.The soil is seriously polluted by heavy metals,and the prevention and control situation is grim.Soil heavy metal pollution is related to food safety and human survival and development.As a kind of clay mineral,palygorskite has good stabilization and adsorption ability to heavy metals in soil due to its special crystal structure,and is often used as a stabilization material in soil stabilization and remediation projects.The soil heavy metal pollution is extremely complex,often Shared by many heavy metals pollution,a single palygorskite in repair when compound pollution of soil heavy metals tend to reach the ideal effect,the palygorskite stabilization materials combining with others through the modification or can improve the repairing effect of palygorskite,so choose good stabilization material preparation for repair of soil heavy metals compound pollution,reduce the heavy metals.Environmental risks,reducing the toxic effects of heavy metals on the ecosystem and restoring the original functions of soil are of great significance.In this study,palygorskite was modified by Ca（H₂PO₄）₂,and the stabilization remediation effect of modified stabilization material on contaminated soil in mining area was studied.Seven kinds of modified stabilization materials were prepared by mixing 0%,5%,10%,15%,20%,25%and 30%Ca（H₂PO₄）₂with palygorskite according to dry matter weight,respectively.4%of the heavy metal contaminated soil was applied.After 30 days of stabilization experiment,pot experiment was carried out.The effects of modified stabilization materials on physicochemical properties,biologically available state,chemical morphology of heavy metals,plant growth and enrichment of heavy metals in contaminated soil were studied.The main research conclusions are as follows:（1）The addition of different modified stabilization materials significantly increased the soil p H compared with the control group.The soil electrical conductivity（EC）was increased,and the cation exchange capacity（CEC）was increased.（2）The addition of different modified stabilization materials significantly reduced the content of heavy metals in water soluble,TCLP extracted,DTPA extracted and CaCl₂extracted states in contaminated soil,compared with single palygorskite（AC0）,all of them were reduced.With the addition of AC25,the water extracted,CaCl₂extracted,TCLP extracted and DTPA extracted states of Cd and Ni were the lowest.The TCLP extraction content of Cd and Ni decreased most significantly compared to the control group,decreasing by 56.86%and 40.21%,respectively.With the addition of AC30,the water extracted,CaCl₂extracted,TCLP extracted and DTPA extracted states of Cu,Cr,Pb and Zn were the lowest.The contents of DTPA,TCLP,CaCl₂,Pb and Zn decreased by 45.12%,48.64%,48.75%and 39.18%,respectively.The addition of modified stabilization materials significantly reduced the bioavailability of heavy metals in contaminated soil.（3）After adding different modified stabilization materials,the changes of heavy metal speciation contents in contaminated soil were different.The acid-soluble state,reduction state,oxidation state and residual states of Cd,Cu,Cr,Pb,Zn and Ni are decreased in acid-soluble and reduction state,and increased in oxidation and residual states.Among them,the acid-soluble states of Cd,Pb and Ni decreased greatly.The residual states percentage content of Cu,Cr,Pb and Zn increases with the increase of the ratio of Ca（H₂PO₄）₂,the reduction and oxidation state contents of Cu,Cr and Ni have little change.（4）The addition of different modified stabilization materials significantly affected the growth indexes of corn.After the stabilization treatment,the stem length,root length,fresh weight and dry weight of corn were significantly increased compared with the control group,stem length and root length increased 45.87%and 64.02%for control,and fresh and dry weight increased 1.49g and 0.23g for control.and the stem length,root length,fresh weight and dry weight of corn reached the maximum under the addition of AC30.（5）The addition of different modified stabilization materials significantly affect heavy metal content in aerial part and underground part of corn plant enrichment,after stabilization treatment of maize plants on the ground and underground part of the enrichment of heavy metals content decreased significantly,under the treatment of AC25,the enrichment of Cd and Ni in the aboveground and underground parts of maize plants were the lowest,The above-ground enrichment content of Cd was 55.73%and 41.15%lower than the control group,and Ni was 45.09%and 32.76%lower from the control group.For ground and underground enrichment of Cu,Cr,Pb and Zn with Cu,Cr,Pb and Zn,The ground and underground enrichment of Cu was 33.93%and 20.83%lower than the slope treatment,and the Cr decreased most significantly,51.21%and 42.06%lower than the control group.The enrichment amount of heavy metals in maize plants was positively correlated with the water-soluble,CaCl₂-extracted,TCLP extracted,DTPA extracted,acid-soluble and reduced state of heavy metals,and negatively correlated with oxidation state and residual state of heavy metals.（6）The addition of different modified stabilization materials significantly reduced the enrichment coefficient and transport coefficient of aboveground and underground parts of maize,under AC25 treatment,the enrichment and transport coefficients of Cd and Ni in maize plants were the lowest,0.497 and 0.48,respectively.under AC30 treatment,the enrichment and transport coefficients of Cu,Cr,Pb and Zn in maize plants were the lowest,0.549,0.442,0.438 and 0.51,respectively.The results showed that the bioavailability of heavy metals,the chemical forms of heavy metals and the absorption and enrichment of heavy metals by corn in the contaminated soil in the stabilizated mining area were effectively reduced by the Ca（H₂PO₄）₂modified palygorskite stabilization material.