Study On Stabilization Of Lead-contaminated Soil Treated By Phosphate And Lime Together

In recent years,heavy metal pollution in soil has become a global environmental problem.In the new context of establishing the“Green Water and Mountains are treasures”and striving to move towards a new era of socialist ecological civilization,the search for a fast,efficient,green,and economical method for the repair of heavy metals in soil has become a great challenge faced by environmental scientisis.Among the various repair technologies,soildification/stabilization method has received great attention at heavy metal contaminated sites due to the fast peiformance,high efficiency and economic advantages.In this study,two kinds of stabilisation reagents of phosphate and lime were used together to treat the lead contaminated soil.The feasibility and economy aspects of the reagents,and also their effects on plant growth were investigated in this study,with an aim to explore the possibility of a compound that could be potentially used in large-scale projects.The main research contents and research conclusions were as follows:?1?Results of lime and sodium dihydrogen phosphate?MSP?treated lead-contaminated soil showed that the application of both reagents can improve the stability efficiency of lead in the soil with a maximum stabilizing efficiency of 97.67%for MSP and 85.55%for lime,respectively.Results BCR sequential extraction method showed that MSP effectively reduced the amount of acid extractable lead in soil by 27.91%,and improved the residual content of lead by 40.58%.Basides,the addition of MSP also facilitated the soil lead to transfer from active to stable state,which improved the stability of lead in soil,while lime showed no significant effect on the speciation of lead in soil.XRD showed that Pb?H₂PO₄?₂,Pb₄O?PO₄?₂,and Pb₉?PO₄?₆ were generated in soil by MSP,while CaPbO₄,Pb₃Cl₄?OH?₂ and other substances were produced by lime.BET test results revealed that the application of lime can effectively improve the adsorption capacity of the soil sample.SEM showed that the surface of the soil sample after the application of the reagent became much smoother and the structure was denser.Results also showed that the adsorption of Pb²⁺on lime fitted to the Freundlich model?R²=0.984?.In the experiments to explore the optimal mix ratio for MSP and lime,the highest concentration of 0.25 mg/L as field control limit value in the Pollution Control Standard for Domestic Garbage Landfill was used as an evaluation index,The optimal compounding formula of sodium dihydrogen phosphate and lime was determined to be MSP:lime=1:6 with the addition amount to be4%.In the long-term experiment,it was found that the TCLP-Pb of soil samples within 1to 15 days fluctuates minimally with TCLP-Pb value kept at 0.194±0.016mg·L^-1.Obviously,the soil samples with the treatment of the optimal compound formula have a better stability.The use of MSP and lime together to treat lead-contaminated soil is therefore feasible,and has some potential application values.?2?In the study bioavailability?BA?of lead in contaminated soil,the BA of five soil samples were firstly measured by PBET and SBET method.Results showed that the BA measured by the two methods showed little differences in value,and the BA value of 5 soil samples ranges from 55.55%to 109.16%.There was no obvious correlation between the content of lead in soil samples and their BA,and the SBET method was more conservative than the PBET.By studying the influence of reaction conditions on BA,it was found that the retention time,reaction temperature,ratio of soil to liquid,and pH of simulated gastric juice all had a certain effect on the BA of soil samples,and the simulated gastric juice pH had the greatest influence.The application of MSP,lime,and C reagents can both reduce the BA of lead in soil samples and the effects of the three reagents on the BA of soil samples awere in an order of C reagents>MSP>Lime.?3?The pot experiment was used to explore the effect of soil lead concentration and application of stabilizing reagents on the growth of broad beans.The results showed that:when the soil lead content was kept in between 0ppm²500ppm,it had only slight effect on the biomass of broad beans,but a greater influence on the absorption of lead by broad beans,The lead content in various organs was in an order of root>embryo shell>leaf>stem.The concentration of lead in soil sample had some differences in the enrichment coefficient?EC?and translocation factors?TF?of each organ of broad bean,and the EC of each organ of broad bean was in an order of:root>embryo shell>leaf>stem.The TF did not show correlation with the soil lead concentration.The application of MSP and lime had a certain effect on the biomass of broad bean,with the effect of MSP higher than lime,while the effect of C reagents on the biomass of broad bean was minimal.After the application of the three reagents,the root absorptions of lead were inhibited and the inhibition effect was in an order:C reagents>MSP>lime.The application of reagents can affect the EC and TF of lead in various organs of broad bean.The addition of MSP can increase the EC of leaves and stems,and reduce the EC of embryo shell and root,while C reagents can reduce the EC of lead in various organs of broad bean.The TF of broad bean to lead was increased by the application of three reagents.In summary,the use of MSP and lime together to treat lead-contaminated soil can effectively reduce the migration and potential toxicity of lead in the environment and reduce the BA of lead.The treated soil showed little effect on the growth of broad bean,and can inhibit the absorption of lead from the soil by the broad bean,and therefore the co-use of the reagents is superior to the single application of MSP or lime.