| Nano-iron was often used in restoration research due to its large specific surface area and high activity.However,some of its own shortcomings,such as stability,high synthesis cost and environmental friendliness of reagents,which limited its application in the environment.Palygorskite was a natural layer-chain hydrous aluminum-magnesium silicate clay mineral,which has high adsorption capacity for heavy metals owing to its unique crystal structure.However,the development and utilization of palygorskite were at a relatively low-level,which have caused the waste of resources,and there was little research on the remediation of soil that polluted by heavy metals with nano-iron-palygorskite composite materials.Therefore,carrying out some relevant researches can provide a theoretical basis and practical guidance for the current treatment of soil polluted by heavy metals.In this study,iron nanoparticles were synthesized by the extract of green tea,and loaded palygorskite,which produced in Linze,Gansu Province to synthesize a new type of nano-iron-palygorskite composite materials with different iron-to-palygorskite ratios(3:1,2:1,1:1,1:2,1:3,1:0,0:1).Analyzing the microscopic characteristics and element composition of the samples with XRD,SEM and FTIR.Then,the Nano-iron-palygorskite composite materials were applied at a dosage of 4% to soil polluted by heavy metals.The incubation and subsequent verification experiments(pot and seed germination experiments)were conducted to explore the influences of Nano-iron-palygorskite composite materials on the biologically available content and speciation distribution of heavy metals,stabilization efficiency and plant growth indicators to evaluate the stabilization remediation and ecotoxicity.The results suggested that:(1)Nano-iron was a granular substance formed on the outside of iron oxide with organic functional groups such as phenolic hydroxyl group,carboxyl group.The structure showed a relatively regular spherical shape,but some clusters have irregular shapes.Palygorskite was mainly composed of attapulgite and quartz,which structure was a cluster of crystal bundles composed of needle-shaped crystals and bundle-shaped aggregates.There were some groups both contained in nano-iron and palygorskite,which appeared in the nano-iron-palygorskite composite materials,indicating that they were well loaded,while with the proportion of palygorskite in the nano-iron-palygorskite composite materials increased,the material composition as attapulgite and quartz gradually increased.(2)The application of different stabilization materials can increase the pH,EC and CEC of the soil.the pH of the soil can be increased by 15.06% at the maximum;The application of different Nano-iron-palygorskite composite materials can increase the conductivity of heavy metal contaminated soil by 2.11?4.66 m S/m,respectively;The cation exchange capacity of the soil increased by 0.21?7.89 cmol/kg.The effect of nano-iron-palygorskite composite materials on CEC was more significant,compared with the impact on soil pH and EC.(3)The application of stabilization materials can significantly reduce the bioavailable content of heavy metals in the soil,which extracted by DTPA,TCLP and water with state of the nano-iron-palygorskite composite materials.It was lower than that with a single application of nano-iron and palygorskite.The stabilization materials have significant differences on the stabilization ability,which DTPA-extractable content on heavy metals followed as Pb > Ni >Cr > Zn > Cu > Cd,which was similar to the TCLP-extractable contents.(4)The application of different stabilization materials can reduce the acid-soluble content of heavy metals in the soil,and promote more active acid-soluble heavy metals transformed into more inactive oxidizable and residual speciation.After stabilization,the acid-soluble state and the residue state of the heavy metal Pb in the soil accounted for 2% and 65% of the total composition,respectively,which can realize the maximum conversion of the soil heavy metal Pb from the acid-soluble state to the residue state.The ability of nano-iron-palygorskite composite materials to promote the transformation of the speciation distribution of heavy metals in the soil is higher than the application of nano-iron and palygorskite.(5)The application of different stabilization materials can significantly promote the growth of corn plants,while the heavy metal content of shoot,biological concentration,transport factor and the biological uptaking factor of heavy metals in corn reduced,which against the toxic effect on plants.The increasing rate of seeds germination can against the stress of heavy metals on the growth of seeds,which can provide a better environment for seeds.Among them,the root length of corn with the application of nano-iron and palygorskite increased by 23.91% and 5.62%,respectively compared with the control group,and the shoot length of corn reduced by 5.88% and 9.79%,respectively.The root length of corn with the nano-iron-palygorskite composite materials increased from 7.01% to 66.16% compared with the control group,and the shoot length of corn was significantly increased.(6)The application of different stabilization materials can improve the stabilization efficiency and remediation ratio of heavy metals in the soil,while the potential ecological risk of heavy metals reduced,which has better effects on Pb,Ni and Cd.The application of nano-iron-palygorskite composite materials can increase the stabilization efficiency of Pb at 78.44%,which increased 49.87% and 76.03% respectively compared with application of nano-iron and palygorskite.At the same time,it can increase the remediation ratio of heavy metal Pb from5.15% to 65.22% in the control group.Therefore,using green synthetic materials prepared by palygorskite supported with iron nanoparticles can evidently improve the stabilization function of nanoparticles and palygorskite,and the nano-iron-palygorskite composite materials have the potential for large scale in-situ remediation of soils polluted by heavy metals. |
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