| Lead is a heavy metal element that is harmful to human health,and has a significant impact on children's physical development and nervous system.With the rapid development of industrialized soil and urbanization in China,soil lead?Pb?pollution is becoming more and more common.Lead in polluted soil can enter the human body through various ways such as food chain transmission and direct contact,which will cause harm to population health.Remediation of lead-contaminated soils has received increasing attention.A lot of research work has been carried out on methods and technologies for remediation and rehabilitation.Technical measures such as physical remediation,bioremediation,and chemical remediation have been proposed.These technologies have their own advantages and scope of application,and they also exist.Certain disadvantages and limitations.Among them,the chemical repair method has the advantages of low repair cost,economy,high efficiency,and wide application range.Chemical stabilization treatment has been widely used in the remediation of site soil pollution.The key to this method is to select the selection of high-efficiency stabilizers and optimize the stabilization conditions.The use of phosphorus-containing materials to stabilize lead-contaminated soil has attracted much attention because of its low cost and good repair effect.Different kinds of phosphorus-containing materials have different compositions,and they have different stabilizing ability and suitable stabilization conditions for soil lead.However,there are not many systematic comparative studies on the stabilization effects of these materials.At the same time,the environmental risks following the stabilization of contaminated soils have not received sufficient attention at present,such as the sustained stability of lead in different phosphorus-containing materials,and the releasability of phosphorus.Therefore,in this study,through indoor simulation experiments,potassium dihydrogen phosphate?MPP?,superphosphate?SSP?,calcium magnesium phosphate fertilizer?CMP?were investigated for purple soil-grey brown purple soil widely distributed in southwest China.Phosphorus ore fines?PR?4 kinds of phosphorus-containing materials,under different doses of Pb contaminated soil stabilization effect,and its long-term stability and P leaching of environmental risks were studied.The main results are as follows:?1?The four phosphorus-containing materials tested had a significant stabilization effect on soil Pb,and both could significantly reduce the leaching concentration of Pb in the purple soil.The degree of reduction was related to the type of material and the concentration of soil Pb pollution.When the P:Pb?molar ratio?is 1,the relative order of the stability efficiency is:MPP>SSP?CMP>PR.When the soil Pb pollution concentration is 600 mg·kg-1?HJ350-2007B?,after four kinds of phosphorus-containing materials are stabilized for 7 days,the Pb leaching concentration of the soil can be rapidly reduced to below the TCLP standard limit,and with stability With the prolongation of chemical treatment time,the leaching concentration of soil Pb can further decrease slowly and tend to balance,and the stability efficiency is more than 80%.When the soil Pb pollution concentration reaches1200 mg·kg-1,the MPP whose P:Pb ratio is 1 can still make soil Pb leaching concentration meet the standard in 7 days,the stable efficiency of 80.49%,while the SSP and CMP respectively need to stabilize the treatment for 30 or 60 days in order to meet the basic requirements,the stability efficiency of 46%to 50%Between;PR treatment Even after 60 days stabilization treatment,Pb leaching concentration still can not meet the requirements.?2?With fixed Pb concentration of 1200 mg·kg-1,the effects of phosphorus-containing materials on stabilizing Pb were affected by the dose.The effect of stabilizing Pb pollution in soils with four phosphorus-containing materials increased with increasing dosage.MPP shows good results.When P:Pb=0.6,MPP is stabilized for 7 days.The leaching concentration of Pb in soil is lower than the standard limit.When the amount of stabilizer is increased to P:Pb=1,it is stable.The leaching concentration of Pb in the soil for 3 days has fallen below the standard limit.The effect of stabilization of PR is the worst.When the molar ratio of P:Pb is as high as 4 and the stabilization treatment for 30 days still fails to meet the leaching standard limits.The stability of SSP and CMP treatment capacity is not much different,and the stabilization capacity of Pb in soil is between MPP and PR.When stabilized for 30days,the appropriate P:Pb ratios for SSP and CMP to meet the leaching toxicity requirements are 1.5 and 2;When the stabilization time is 15 days,SSP and CMP meet the leaching toxicity standard limits at P:Pb of 2 and 4,respectively.?3?Phosphorus-containing materials affect the distribution of lead in purple soils.Phosphorus-containing stabilizers can convert lead into less bioactive forms and reduce its leachability.The effects vary with the type,amount of stabilizer,and lead contamination level in soil.Different.With the increase of soil lead pollution,the percentage of exchangeable lead has increased,and the addition of a series of phosphorus-containing stabilizers has significantly reduced the percentage of exchangeable lead in the soil,and the percentage of residual lead has increased significantly and become the major The morphology and the iron-manganese oxidation state also increased.The proportion of residual lead in MPP treatment was the largest,followed by SSP and CMP.With the increase of the amount of phosphorus-containing material,the percentage of residual state gradually increased,the ability of MPP to promote the conversion of lead to residue state was the strongest,the carbonate bound state and the iron-manganese oxidation state changed little,the organic state was slightly There is an increase.The addition of SSP and CMP,similar to the addition of MPP,all increased the proportion of the residue state to varying degrees.The carbonate bound state and the iron-manganese oxidation state did not change much,and the organic state slightly increased.The addition of PR has a relatively small effect on the transformation of soil lead species.The XRD analysis of stabilized stabilizing bodies showed that there were new characteristic peaks in the XRD pattern after addition of SSP,MPP,CMP,and PR.After identification of the phases,these characteristic peaks were found to be heavy metal-P compounds.,mainly lead phosphate salt compounds,lead phosphate salt compounds,showing that phosphorus reduces lead contamination soil leaching toxicity and the formation of very low solubility compounds such as lead phosphate in the soil.?4?Addition of different phosphorus-containing materials may cause pH changes in the soil.After MPP treatment,the pH of the soil increases first and then decreases.CMP and PR both increase the pH of the soil,while SSP gradually decreases the pH of the soil.CMP and PR increased soil pH by 0.31 and 0.16 units,respectively,while SSP decreased soil pH by 0.39 units.The addition of MPP increased soil pH,increasing from 8.2 to 8.48,increasing the amount of soil,and the soil showed a trend of increasing first and then decreasing.The maximum value of pH reached 8.48 when the amount was 0.6.?5?In order to understand the sustained stability of phosphorus in the soil with lead,four phosphorus-containing materials were observed at a P:Pb molar ratio of 2 for a stabilization treatment of 1200 mg·kg-1 Pb-contaminated soil in 3,6 and 9 months soil Pb.Leach concentration and stabilize efficiency.The results showed that all the four stabilizers had long-term stability.The stability efficiency was above 97%in 9months,and no Pb release in soil was found.Comparing the leaching concentrations at the 6th and 9th months,it was found that the change was not significant.It can be seen that the stabilization process of Pb in the soil was basically completed after 6 months of stabilization treatment,indicating that the phosphorus-containing material can achieve the Pb of the soil.Sustained stabilization,with little risk of subsequent Pb release.?6?Phosphorus-containing materials increase the stabilization efficiency of Pb in soils as their usage increases,but phosphorus-containing materials themselves also have the risk of P leaching leaching.The stabilization of Pb-contaminated soils by the addition of 4 different phosphorous-containing materials?P:Pb=2?After 1,3,6 and 9months,the monitoring results of changes in soil P content?Olsen-P?indicated that Phosphorus significantly increased the effective P in the soil as compared to the control.At the same time,the effective P content in the stable soil increased slightly with time.Soil Pb-contaminated soils stabilized by MPP,SSP,CMP,and PR increased in effective P by 4.29%,29.89%,15.24%,and 22.43%,respectively,over 8 months,indicating that soils were stabilized in soil over time.The P has a certain trend of activation.According to relevant literature analysis,the pH of purple soil studied in this paper is8.16,and the available phosphorus content in soil treated with MPP,SSP,CMP,and PR is still stable after being treated for 9 months.The threshold value of phosphorus leaching is 113.8 mg·kg-1,which is far below the threshold value of phosphorus leaching in this type of soil.This shows that after four kinds of phosphorus-containing materials are stabilizing Pb-contaminated soil,the risk of P leaching is still low in a certain period.Its long-term dissolution risk still needs attention.In summary,the four phosphorus-containing materials have a significant stabilizing effect on soil Pb.Under the condition of P:Pb=1:1?molar ratio?,the order of the relative efficiency of stable efficiency is:MPP>SSP?CMP>PR.When the concentration of Pb pollution is less than 600 mg·kg-1,all five stabilizers can achieve the stabilization of Pb soil.When the concentration of Pb was over 1200 mg·kg-1,MPP still maintained high efficiency of stabilization,but PR could not meet the leaching standard.When the concentration of lead contamination was 1200 mg·kg-1,and the dose of phosphorus-containing material had different effects on the stabilization effect.MPP as a stabilizer,the leaching standard can be achieved after stabilization treatment for 3 days under the condition of P:Pb=1:1.While SSP and CMP could reach the leaching standard when the P:Pb is 1.5 and 2 after stabilization treatment for 30 days,and for PR it could be 60 days under the condition of P:Pb=4.The increasing dosage of stabilizer can significantly improve the stability rate of Pb in purple soil.After applying a series of phosphorus-containing stabilizer,the soil pH value increased except for SSP.And along with the stabilization time extended,?Exc-Pb?gradually decreased,while Residual state?Res-Pb?proportion gradually increased,and Carb-Pb,FeMnOx-Pb and OM-Pb were showed no obvious change trend.After 9 months of stabilization,the Pb leaching concentration remained at an extremely low level after the treatment,and it could meet the Pb leaching standard,meanwhile the effective P also remained within the P prime leaching threshold,which means that all the four stabilizers can meet the requirements of continuous stabilization and environmental risk control. |
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