| The heavy metal pollution in soil has gradually become a global hot topic.There has been a lot of researches on the remediation of heavy metal contaminated soil.As one of the promising approaches,chemical passivation received great attention,due to its easy operation,low investment,short repair period and wide application.The common passivants included some alkaline substances(i.e.,lime and calcium carbonate),adsorbed substances(i.e.,biological carbon)and reactive substances(i.e.,organic chelating agents).However,these passivants usually suffered from the problems of unsteadiness,causing secondary pollution and changing the physicochemical properties of original soil.Therefore,it is extremely important to explore an efficient and green passivation agent for the remediation of contaminated soil.In this project,a new type thiol modified nanoscale silica,which was from the Research Center of Nanomaterials Engineering in Henan Province,was selected as passivant.The material not only contains thiol groups,which could react with heavy metal ions,but also possesses the environmentally friendly characterization and less secondary pollution.The toxic effects of heavy metals in environment is not only related to their total amount,but also related to the speciation of heavy metals in the soil.Thus,it is necessary to investigate the speciation distribution of heavy metals in soil.In this thesis,by using the thiol modified nanoscale silica as passivant,and the artificial soil contaminated with nickel,copper and zinc at the levels of 300 mg·kg-1(soil-A)and 600 mg·kg-1(soil-B)as research object,the optimal remediation parameters were investigated by fixing passivation time,water content and fixative dosage etc.Moreover,the speciation changes of heavy metals in soil before and after passivation were analyzed by a modified tessier sequential extraction procedure.The main results were listed as follows.(1)The optimal remediation conditions of nickel,copper and zinc were investigated by controlling variables of passivate time,water content in soils,the amount of passivant,as well as the bioavailable content of nickel,copper and zinc in soil before and after the passivation.For soil-A,the optimal remediation conditions were 3d of passivate time,55%of water content in soils(maximum field capacity)and 2%of the dosage of passivant.Under such conditions,the passivation rate of nickel,copper and zinc in soil-A reached 62.46%,61.90%and 48.03%,respectively.For soil-B,the optimal remediation conditions were 3d of passivate time,55%of water content in soils(maximum field capacity)and 5%of the dosage of passivant.Under such conditions,the passivation rate of nickel,copper and zinc in soil-B were up to 63.14%,56.86%and 57.79%,respectively.(2)Before the passivation,the speciation distribution of nickel was in the order of Fe-Mn oxides form>carbonates form>residual form>organic form>water soluble and exchangeable form,the distribution of copper speciation was in the order of organic form>Fe-Mn oxides form>carbonates form>residual form>water soluble and exchangeable form,and the distribution of zinc speciation was in the order of Fe-Mn oxides form>carbonates form>residual form>organic form>water soluble and exchangeable form.(3)The thiol modified nanoscale silica caused a certain influences on the distribution of nickel,copper and zinc speciation in soil.The dosage of such passivant could significantly decrease the water soluble and exchangeable form,carbonates form and Fe-Mn oxides form,and simultaneously increase the organic form and residual form,of nickel,copper and zinc.Based on the changes of the contents and the forms of nickel,copper and zinc in soil before and after passivation,the mechanism for the thiol modified nanoscale silica passivating heavy metals was speculated,that is,nickel,copper and zinc in soil reacted with the thiol(-SH)on the surface of nanoscale silica,to form coordination bonds and finally were immobilized. |
PDF Full Text Request