Effects Of Modified Lignite On Calcareous Soil Aggregate Size Composition And Chemical Speciation Of Pb?Cd

In recent years,heavy metal pollution of soil has become a hot topic.To be able to more accurately understand and fix the northwest of Henan a soil heavy metal pollution,this study uses humic acid-rich lignite as raw material,which from Zhaotong City,Yunnan Province.Through a variety of modified,study prepared(lignite-based humic acid,demineralized lignite,calcium-loaded lignite,lignite-based activated carbon,nitration lignite,sulfonated lignite,resin of lignite-based humic acid,graft copolymer of lignite-based humic acid)8 kinds of modified materials.Through pot experiment and soil aggregate culture experiment,we study the effect of modified materials on the bioavailability of heavy metals in soil and the effect of soil aggregate composition and the forms of heavy metals in soil.Fully understanding the mechanism and influencing factors of the availability and mobility of heavy metals in soil.Research shows:1.Lignite,humic acid,demineralization,calcium-loaded and activated charcoal significantly reduced DTPA-extractable Pb,with the increasing of additives,the amount of DTPA-extractable Pb content decreased gradually in the soil,in addition to lignite,these materials significantly lower magnitude of DTPA-extractable Pb,which were 4.67%-7.97%,5.92%-11.46%,5.90%-11.80% and 11.69%-26.43% respectively;adding nitration,sulfonation,resin and graft copolymerization in the soil increased the amount of Pb which was extracted by DTPA,resin and graft copolymerization significantly increased the DTPA-extractable Pb by 5.82%-32.12% and2.55%-24.76%.Modified lignite significantly reduced or increased the DTPA-extractable Pb than the unmodified lignite,decreased most with activated carbon treatment,increased most with the resin and the graft copolymerization treatments.with the increase of lignite,humic acid,demineralization,activated charcoal,graft copolymerization,the content of DTPA-extractable Cd state gradually reduce in soil,activated charcoal and graft copolymerization significantly reduced DTPA-extractable Cd in the range of 5.41%-13.51% and 5.18%-27.70%;nitration,sulfonation,resin significantly improved DTPA-extractable Cd with the amplitude of7.92%-20.13%,5.74%-21.05% and 21.30%-44.63% respectively.increased with the increase of the dosage of DTPA-extractable Pb/Cd.Lignite based materials can significantly change the effective form of lead and cadmium in calcareous soil,significantly inhibited the growth of lettuce,but there is no positive correlation between the DTPA-extractable Pb or Cd content of soil with content and accumulation of Pb or Cd in the upper part of the lettuce.There is a difference between the effects of several kinds of repair agents on the DTPA-extractable Pb and Cd,and there should be a consistent effect of repair agent in the remediation of contaminated soil.Humic acid,demineralization and activated charcoal have influence on the DTPA-extractable Pb and Cd in the same role,that is,to reduce the effective state of the two,and resin to improve the effective content of DTPA-extractable Pb and Cd in soil.3.Soil pH and soil organic matter content of serious impact soil environment.Because of the impact on soil p H and soil organic matter content,modified lignite affected the soil aggregate composition and the transformation of Pb and Cd in soil.4.By the soil dry sieving method,in addition to calcium-loaded treatment,other treatments can significantly reduce <0.053 mm aggregates content,lignite,humic acid,mineralization,nitrification,sulfonation,resin,graft copolymerization treatment could increased the content of soil R0.25,humic acid,mineralization,resin,graft copolymerization treatment significantly enhanced the mechanical stability of the soil;By the soil wet sieved,in addition to resin and graft copolymerization process,soil water-stable aggregates mainly concentrated in <1 mm size fractions of water-stable aggregates.Lignite,humic acid,mineralization,activated carbon,nitration,resin,graft copolymerization processing can increase content of soil water-stable R0.25.Brown coal,humic acid,mineralization,resin,graft copolymerization of reinforced soil anti erosion ability.The mechanical stability and the anti erosion ability of humic acid,mineralization,resin,and graft copolymerization were enhanced.5.Applied modified lignite and soil culture after 150 days,the soil Pb speciation distribution: Fe-Mn oxide > carbonate fraction > residual > exchangeable > weak organic fraction > strong organic fraction;soil Cd speciation distribution: Fe-Mn oxide > carbonate fraction > exchangeable > residual > weak organic fraction >2.Lignite,humic acid,demineralization,calcium-loaded,activated charcoal andgraft copolymer could increase the biomass of lettuce,nitration,sulfonation and resin treatment decreased the biomass of lettuce,the biomass of aboveground part was negatively correlated with the content of DTPA-extractable Pb and Cd in soil andagglomeration degree and stability were improved;the >0.25 mm and <0.053 mm particle sizes of water-stable micro aggregate Pb and Cd are extracted from each state enrichment coefficient is the largest,followed by 0.053-0.25 mm particle level.Applying humic acid,mineralization,activated charcoal to make >0.25 mm and<0.053 mm size water stable aggregates Pb/Cd exchangeable,carbonate fraction content reduce,Fe-Mn oxide,weak organic fraction,strong organic fraction and residual increased;applied to mineralization,activated charcoal to make 0.053-0.25 mm size water stable aggregates Pb/Cd exchangeable,carbonate fraction content reduce,Fe-Mn oxide,weak organic fraction,strong organic fraction and residual increased.After the modified lignite was added to the soil,the soil aggregate composition and the distribution of heavy metals were affected.By comparison,the agglomeration degree and stability of calcareous soil aggregates,and passivation of heavy metals Pb,Cd were the best by applying lignite-based humic acid and demineralized lignite.