Effects Of Modified Lignite On Radial Migration Of Lead And Cadmium In Calcareous Soil

As the processing of industrialization in our country,the problem of heavy metal pollution in the soil has been very serious,and heavy metals will pollute water through the surface runoff and rain,affecting our daily life.In this study,lignite was modified as raw material to prepare nitrated lignite,demineralized lignite,lignite-based activated carbon,sulfonated lignite,lignite-based humic acid,graft copolymer of lignite-based humic acid,resin of lignite-based humic acid,seven kinds of modified materials.We analyze the release of lead and cadmium in the leachate and their radial migration and occurrence patterns by soil leaching,evaluating the fixed effects of different modified materials on the soil.Research shows that:1.In the deionized water leaching,the radial movement distribution and morphological changes of heavy metals in calcareous soils were studied by simulated rainfall conditions.The content of Cd in the leachate was lower and the threat to the environment and groundwater was smaller than the blank control.However,the content of Pb was higher and the threat to the environment and groundwater was higher.Compared with the blank,all kinds of modified materials can effectively fix Cd and Pb,which shows that the release of Cd and Pb in the soil leaching solution is obviously decreased after the application of the modified materials,and the contents of Cd and Pb in the deep soil are lower than CK.However,the immobilization effect of the modified materials on the Cd and Pb was different,the lignite,humic acid,graft copolymerization and resin treatment had the best passivation effect on Cd,and the total release was decreased by 94.48%,94.28%,95.80%and 95.38%,respectively.Lignite,demineralization and sulfonation treatment had the best passivation effect on Pb,and the total release was decreased by 95.60%,96.38%and 96.05%,respectively.After the eluviation,the treated soil column surface(0-5cm)of Pb and Cd with iron and manganese oxidation state and the residual state as the main form,tend to lower the form of active transformation,and Pb and Cd of deep soil are dominated by residue state.2.CaCl2 solution can simulate the ionic strength of natural soil solution when leaching with CaCl2,which reflects the effect of soil solution on the migration of heavy metals.The addition of modified materials significantly reduced the concentration of Pb and Cd in the leachate,and the contents of Pb and Cd in the deep soil were significantly lower than CK,and the contents of the modified materials were different.Among them,lignite,nitrification,sulfonation and humic acid significantly enhanced the stability of cadmium in soil column soil,the total release of Cd was decreased by 92.67%,94.09%,92.69%and 92.72%,respectively the effect of demineralization,activated carbon and humic acid on Pb were better,the total release of Pb was decreased by 95.91%,95.50%and 95.77%,respectively.After leaching,the heavy metal lead and cadmium contained in the surface layer 0-5cm of the soil treated with the modified material are mainly present in the state of iron and manganese oxidation and the residual state,and tend to shift to a relatively stable form,which is not easy to migrate,which is not easily absorbed by plants,while Pb and Cd of heavy metals in deep soil are mainly in the residual state.3.EDTA solution can decompose heavy metals of the soil,through the degree of analysis of heavy metals of the addition of modifier compared with no modification,you can understand what kind of soil additives can be combined with heavy metals morcloser,not easier to elute.The content of Pb and Cd in the leaching solution was decreasing with the modified material,but the EDTA had a strong leaching effect on heavy metals,and most of the modified materials were less obvious.The reduction of humic acid grafting and humic acid resin was the most obvious,Pb decreased to 52.81%,53.11%,and Cd decreased to 51.53%,51.59%,respectively.In summary,lignite and its modified materials applied to heavy metal pollution of soil,the heavy metals Pb and Cd have played a fixed role,and reduce their radial migration.By contrast,the application of lignite-based humic acid,graft copolymerization of humic acid,resin of humic acid can improve the heavy metals Pb,Cd stability in the calcareous soil and reduce the radial migration,they are better than other modified materials,and the combinations with the heavy metals are not easy to release into the soil.