| With the rapid development of industrialization and economic development,the situation of heavy metal-contaminated soils today is very serious.How to effectively and reasonably remediate the heavy metal-contaminated soils has become one of the most widely-reviewed global issues.Among the numerous remediation methods,chemical passivation technology is favored by many researchers because of its unique advantages.It is not only easy to implement,but also generally low cost.It can repair large-area farmland contaminated by heavy metals and its applicability is relatively wide.Chemical passivation repair technology is the way in which one or more passivation agents are added to the earth to make the harmful heavy metals and the added passivation agents complete a series of processes such as adsorption,redox,and complexation,which can reduce the biological toxicity of heavy metals in soil.Therefore,during the remediation of contaminated soil,it is of great significance to find a passivation agent with low price and strong passivation effect.In this paper,the passivation effect of copper and chromium in soil was studied by using the new passivation agent thiol modified nanoscale silica which is small secondary pollution and environment-friendly,and chemical passivation agent ammonium ferrous sulfate which can be used as fertilizer,which can be used as fertilizer,in order to provide a new idea for soil heavy metal remediation in the future.Heavy metal leaching toxicity test and morphological analysis are two commonly used evaluation indicators of soil remediation effect.Therefore,we use the thiol modified nanoscale silica to repair the artificially simulate Cu contaminated soil with different pollution levels(100 mg/kg,200 mg/kg,400mg/kg,(600 mg/kg,800 mg/kg),chromium(100 mg/kg,200 mg/kg,300 mg/kg,600 mg/kg),and the ammonium ferrous sulfate was used for artificially simulate chromium contaminated soil of different pollution levels(100 mg/kg,200 mg/kg,300 mg/kg and 600 mg/kg).The passivation effects of Cu contaminated soils with different levels of pollution were analyzed by using bioavailability(the first two steps of speciation analysis)as evaluation index for remediation.The passivation effect of chromium contaminated soil with different degree of pollution was analyzed by leaching toxicity test as the index of remediation evaluation.The amount of passivation agent,soil moisture content,pH and passivation timeeffect of the contaminated soils Cu and chromium;the modified tessier sequential extraction procedure was used to compare the speciation distribution of Cu and Cr in the soil before and after passivation.The effect of passivation agent on the distribution of Cu and Cr in soil was discussed.The main research contents and conclusions of this paper are as follows:(1)when thiol modified nanoscale silica was used to repair the Cu-contaminated soil with different polluted degrees,the passivation rate of polluted soil with different polluted degree could reach more than86% under the best passivation condition.However,the higher the level of pollution,the greater the amount of passivation agent needed to achieve the best passivation effect.And the optimum amounts of passivation agent for soils A,B,C,D,and E are 1%,2%,3%,4.5%,and 6.5%,respectively.The effect of soil moisture content on soils with different degrees of pollution was basically the same.The polluted soils of all groups had a relatively good passivation effect when the soil moisture content was 55%.the optimum passivation pH of Cu-contaminated soil was 6.5,and the passivation rate of Cu-polluted soil was relatively high when the passivation time was 3 days.and after that,with the passivation time continued to be prolonged,the passivation effect did not become worse,to a certain extent,this result shows that the passivation agent has a good stability for the repair of Cu-contaminated soil;After repairing the Cu-contaminated soil with thiol modified nanoscale silica,the proportion of organic binding state and residual state in soils was significantly increased,while the proportions of the other three forms with strong bioavailability were significantly reduced,this result shows that after the remediation,the toxicity and migration ability of Cu in soil was weakened,and the passivation agent is effective for the remediation of Cu in soil,and the remediation effect is pretty good.(2)when thiol modified nanoscale silica was used to repair the Cr-contaminated soil,the passivation rate of polluted soil with different polluted degree was relatively low under the best passivation condition.And the passivation rates under optimum conditions of soils A,B,C,D,and E were 54.21%,52.17%,43.70%,and 41.42%,respectively.For the Cr-contaminated soils of different degrees,when the passivation effect is relatively good,the optimum amounts of passivation agent required for soils A,B,C,and D were0.75%,1.25%,2%,and 5%,respectively;65% of the optimum soil moisture content,the optimum pH were6.5,the optimum passivation time were 3 days.In the repaired soils,the proportions of the organic bound state and the residual state increased,and the proportions of the other three forms decreased,but the overallchange in the proportion of five forms were small.This shows that the thiol modified nanoscale silica has certain effects on the repair of Cr-contaminated soil,but overall the repair effect is not ideal.(3)When ferrous ammonium sulfate was used to repair the Cr(?)-contaminated soil with different polluted degrees,the passivation rates under optimum conditions of soils A,B,C,D,and E could reach91.33%,95.76%,97.81%,and 98.06%,respectively.When the amount of ammonium ferrous sulfate was1.75 times that of the theoretical addition,soil moisture content was 65%,pH was 5.5,repair time was 3days,the passivation effect was relatively good.After repairing Cr(?)-contaminated soils with ferrous ammonium sulfate,the proportion of organic binding state and residual state in soils was significantly increased,the majority of Cr(?)in soil changed from the form with higher biological toxicity to the form with less toxicity.This further indicates that the reduction method is particularly effective in the remediation of Cr(?)contaminated soil,which is feasible;and with the passivation time continued to be prolonged,the passivation effect did not become worse,to a certain extent,this result shows that the passivation agent has a good stability for the repair of Cr(?)contaminated soil. |
PDF Full Text Request