Influence Of The Soil Heavy Metal Deposition Form By Palygorskite Modified By Nanoscale Zero-valent Iron

With the rapid development of China’s industry and agriculture,the improper use of pesticides and fertilizers and the illegal discharge of industrial wastewater,so that China’s land heavy metal pollution problem is extremely serious,cadmium（Cd）,chromium（Cr）,copper（Cu）,nickel（Ni）,lead（Pb）and zinc（Zn）are more representative of the six heavy metals.Palygorskite is a clay mineral widely used in soil heavy metal restoration,which is cheap,easy to obtain and has large reserves,but the palygorskite quality in Gansu area is low,which affects the stabilization effect of palygorskite.Nanoscale zero-valent iron refers to zero-valent iron particles with particle size in the range of 1-100 nm,which can repair soil and groundwater pollution,but are prone to reunion and oxidation in the process of use.In this paper,Gansu Linze Banqiao town palygorskite as raw materials,according to the different quality ratio（Fe3+:palygorskite = 5:1,3:1,1:1,1:3,1:5）,through the liquid phase to restore the legal system to prepare five palygorskite modified by nanoscale zero-valent iron.The palygorskite,nanoscale zero-valent iron（nZVI）and five different proportions of palygorskite modified by nanoscale zero-valent iron were applied to the heavy metal contaminated soil by 4% cast-plus ratio,and the treatment group without adding any stabilizer was set up as a control group to carry out soil stabilization experiments and potted experiments.After applying the stabilizer to the soil for 30 d,the physical and chemical properties of the soil,the bio-efficient state of heavy metals and the chemical form of heavy metals were determined.After 30 days of stabilization,in which corn is sown,the biomass of the corn plant is measured 35 days after the date of seeding,and the abunding of heavy metals in the corn ground and underground parts is measured by dissolving the corn plant.Based on the data measured in the stabilization experiment and the potted plant experiment,the stabilization material of palygorskite modified by nanoscale zerovalent iron with the best effect on the stabilization effect of heavy metal contaminated soil was analyzed.The results are as follows:（1）After the stabilization agent was applied,the soil pH and cation exchange capacity（CEC）were significantly higher than the control group,and with the increase of the proportion of the palygorskite in the palygorskite modified by nanoscale zero-valent iron,the soil pH and CEC showed a trend of rising and then decreasing first,and both reached the maximum value in the NP13（Fe3+: palygorskite = 1:3）treatment group,which increased by 13.28% and 18.53%respectively compared with the control group.The electrical conductivity（EC）in the soil increased with the increasing proportion of the palygorskite in the palygorskite modified by nanoscale zero-valent iron,reaching the maximum value in the NP15（Fe3+: palygorskite = 1:5）treatment group.The NP15 treatment group increased by 211.723 compared to the control group.（2）Through X-ray diffraction analysis,palygorskite is mainly composed of attapulgite（A）,green mudstone（C）,dolomite（D）and quartz（Q）,the use of nanoscale zero-valent iron to the palygorskite modification,the characteristic peak of palygorskite did not change significantly,indicating that the use of nanoscale zero-valent iron modification did not destroy the structure of slope strands;Through scanning electron mirror analysis,it can be found that nanoscale zerovalent iron itself because of the characteristics of easy reunion,particles are connected to each other into a beaded shape.After the nanoscale zero-valent iron load is loaded on the palygorskite,the nanoscale zero-valent iron is gradually dispersed on the surface of the palygorskite,and the long string of nanoscale zero-valent iron becomes shorter,and the nanoscale zero-valent iron that exist alone appear;Fourier infrared transformation spectra show that with the increase of the proportion of palygorskite in palygorskite modified by nanoscale zero-valent iron,Si-O-Si telescopic vibration is gradually strengthened,and NP13 absorbs peaks the strongest when processed.（3）After applying PAL,nZVI and palygorskite modified by nanoscale zero-valent iron to the soil,the TCLP extraction state content,DTPA extraction state content,water-soluble content and CaCl₂ extraction state content were significantly reduced,and the content of the four extraction states increased with the increase of palygorskite of stabilization materials,showing a trend of first decline and then rise,and reached the minimum value in the NP13 processing group.The effective state content of palygorskite modified by nanoscale zero-valent iron continuously in Cu and Zn was significantly reduced,and the TCLP extraction state content in the NP13 treatment group was 80% and 69.35% compared with the control group,respectively.TCLP extraction content,DTPA extraction content,water soluble content and CaCl₂ extraction content of Ni all reached the minimum in the NP15 treatment group.TCLP extraction content,DTPA extraction content,water soluble content and CaCl₂ extraction content of Cd,Cr,Cu and Zn were significantly reduced after the application of palygorskite modified by nanoscale zero-valent iron compared with treatment groups applying PAL and nZVI alone.（4）The acid soluble content of Cd,Cr,Cu,Pb and Zn was significantly reduced,and the proportion of acid soluble content decreased and then increased,decreasing in the NP13 treatment group by 42.68%,62.69%,68.53%,68.23% and 44.50% compared with the control group,respectively.The residue content of Cd,Cr,Cu,Pb and Zn increased significantly compared with the control group,and as the proportion of the stabilization material increased first and then decreased,reaching the maximum in the NP13 treatment group by 55.49%,73.64%,97.90%,85.75% and 47.65% compared with the control group.The acid-soluble content of Ni reached a minimum in the NP15 treatment group and the residue content in the NP15 treatment group.（4）The acid-soluble content of Cd,Cr,Cu,Pb and Zn decreased significantly,and with the increase of the proportion of palygorskite in the passivated material,the tendency to decrease and then rise showed.The acid-soluble content of Cd,Cr,Cu,Pb and Zn was minimal in the NP13 treatment group,decreasing by 42.68%,62.69%,68.53%,68.23% and 44.50%,respectively,compared with the control group.The residual content of Cd,Cr,Cu,Pb and Zn increased significantly compared with the control group,and with the increase of the proportion of palygorskite in the passivation material,the maximum was reached in the NP13 treatment group,up 55.49%,73.64%,97.90%,85.75% and 47.65%,respectively.The acid-soluble content of Ni reached a minimum in the NP15 treatment group and the residue content in the NP15 treatment group.（5）The application of PAL,nZVI and palygorskite modified by nanoscale zero-valent iron in the soil is conducive to the growth of corn plants,compared to the control group,the application of different stabilizer treatment groups of corn plants plant height,root length,above ground and underground part of the fresh weight,above ground part and underground part of the dry weight are significantly increased,and with the increase in the stabilization material palygorskite proportion showed a tendency to rise and then decrease first,and all obtained the maximum value in the NP13 treatment group.The plant height,root length,above ground and underground part of the fresh weight,above ground part and underground part of the dry weight of the NP13 treated group rose 35.81%,35.21%,48.28%,80.00%,52.54% and41.88% compared with control groups,respectively.（6）After applying PAL,nZVI and nanoscale zero-valent modified palygorskite in the soil,the enrichment coefficient and transport coefficient of corn plants to Cd,Cr,Cu,Ni,Pb and Zn were less than 1 compared to the control group,which significantly inhibited the enrichment and transport of corn to heavy metals.The NP13 treatment group showed a significant reduction in the transport coefficient of corn plants on Cd,or 40.73% compared with the control group.The absorption stabilization ability of palygorskite is improved by the change of nanoscale zero-valent iron,and the problem of nanoscale zero-valent iron is easily oxidized and reunited.The experimental results can provide theoretical basis for the restoration of heavy metal pollution in soil by palygorskite modified by nanoscale zero-valent iron,and can also be used to facilitate the large-scale application of palygorskite in Gansu region.