Removal Of Lead From Water And Solidification Of Lead In Contaminated Soil With Phosphorylated Zero-valent Iron

Lead,as a raw material,has been widely used in various fields,such as batteries,photographic materials and steel manufacturing.In recent years,the use of lead-containing substances has caused serious pollution in water and soil,which has threated survival and development of human beings.Thus,it is very urgent to remediate lead pollution.Zero-valent iron possesses the favorable characteristics for low cost,nontoxicity,high chemical activity and environmental friendliness,which has been widely used to remediate heavy metal.However,the surface of zero-valent iron is easily oxidized,and the formed iron oxide shell hinders the transmission of electrons from the core.As the thickness of the shell layer gradually increases,the activity of zero-valent iron decreases.Mechanical ball milling is a good method to modify zero-valent iron.The iron oxide layer on the surface of zero-valent iron can be effectively destroyed by the strong mechanical force during the ball milling process,which can increase the reactivity of zero valent iron.Furthermore,adding materials with specific functional groups in the ball milling process can achieve the regulation of the surface functional groups of zero-valent iron.In this study,phosphorylated zero-valent iron(P-ZVI BM)was prepared through a co-ball milling process of micron zero-valent iron with potassium dihydrogen phosphate.The removal effects of P-ZVIBM on lead pollution in water and soil were evaluated,and the mechanisms of enhanced lead removal was investigated.The main results are summarized as follows:(1)P-ZVIBM could remove lead from water rapidly and efficiently.The results indicate that the lead removal efficiency of P-ZVI BM was 110 times higher than unphosphorylated zero-valent iron(ZVI BM).Microscopic,crystal form,surface structure and micro-mechanism of the lead removal process reveal that the improvement of reactivity resulted from follow aspects:phosphorylated modification of zero-valent iron promoted the specific adsorption of lead ions.Phosphate,which is tightly bound on surface of zero-valent iron played a role in lead removal in coordination with zero-valent iron.In addition,the modified zero-valent iron enhanced the corrosion ability,which could promote the ability to removal lead ions by flocculation and precipitation(2)Soil batch tests were also conducted in this study.The results show that P-ZVIBM could effectively immobilize lead in soil.The leaching experiments revealed that the effect of lead remediation was significantly enhanced after phosphorylation.With the dosage of 4%P-ZVI BM(P-ZVI BM:experimental soil),the leaching concentration reaches the national standards and the stabilization efficiency is 95%after 48 days.Furthermore,sequential extraction analysis was used to analyze the speciation distribution of lead in soil.The results revealed that the acid-extractable state and reducible state of lead were reduced after remediation by P-ZVI BM,while the residual state was significantly increased.Moreover,the safety assessment of remediation soil revealed that the lead migration in water and acid solution and bioavailability were significantly reduced after remediation.These findings highlighted the potential of P-ZVI BM as a promising amendment for immobilizing lead in soil.