Study On Passivation Effect Of Stabilitying Materials On Heavy Metals In Municipal Pipeline Sludge

With the development of society and industrial,the municipal pipeline sludge is the inevitable outcome through human life,and the amount of the municipal pipeline sludge will increase significantly.Untimely cleaning up it will block the municipal pipe network.If the municipal pipeline sludge is disposed improperly after cleaning up,it will cause secondary environmental pollution.The municipal pipeline sludge is useful for agricultural production because of the sludge containing higher amount of N,P,K,organic matter and other inorganic nutrients.Nevertheless,municipal pipeline sludge contains higher level of heavy metals to some extent,it will cause the heavy metal pollution in farmland soil if applied directly into the soil.Generally,the activity of heavy metals in sludge may be reduced by adding the different kinds of passivating agents to the pipe network sludge,furthermore,the risk of heavy metal pollution on the environment,especially the soil environment will be controlled effectively.In this paper,the effects of different passivating agents on the fractionation and DTPA-extractable heavy metals in the municipal pipeline sludge were studied by adding five kinds of passivation agents,i.e.desulphurized gypsum,fly ash,phosphate rock,bentonite and sepiolite into the municipal pipeline sludge in proportion to 3%,7% and 10%,respectively.Moreover,the mechanism of deactivation of heavy metals in municipal pipeline sludge was also speculated by analyzing the electron microscope and infrared spectrum of different kinds of passivation agents and municipal pipeline sludge.There will be the important theoretical and practical significance for avoiding the risk of heavy metal pollution in the process of applying into farmland.The results were as following:(1)The contents of carbonate-bound and Fe-Mn oxide bounds of Cu,Zn,Pb and Cd in the sludge decreased significantly under adding the five passivating agents.Meanwhile the five passivating agents can reduce the content of the exchangeable As and that of carbonate-As also reduce except desulphurized gypsum.Therefore,the five kinds of passivating agents can reduce the activity of Cu,Zn,Pb,Cd and As through dereasing the contents of the exchangeable and carbonate of heavy metals.Meanwhile,the different passivating agents made the activity of mercury in municipal pipeline sludge decrease through dereasing the contents of the water-soluble,hydrochloric acid extractable and humic acid-bound.(2)The results from the contents of heavy metals extracted with DTPA in municipal pipeline sludge showed that the content of DTPA-extracted heavy metal decreased significantly with increasing amount of adding different passivating agents For the different passivating agents,bentonite can significantly reduce the content of extractable Cu and Pb;fly ash can obviously reduce the content of DTPA-extractable Zn,followed by bentonite.For the different adding ratio,fly ash can significantly reduce the content of DTPA-extractable Cd and Hg for the ratio of 7%,bentonite can reduce the content of DTPA-Cd and Hg for the adding ratio of 3% and 10%,sepiolite can reduce the content of DTPA extractable As more significantly than bentonite for the ratio of 3% and 10%,however,bentonite is more significant than that of sepiolite for the ratio of 10% passivation agent.(3)The passivation mechanism of heavy metals in the sludge according to the electron microscope and infrared spectrum of different kinds of passivation agents and municipal pipeline sludge may be that: adding the passivating agents to municipal pipeline sludge can increase the specific surface area of the sludge particles and produce more adsorption sites for heavy metal;phosphates,carbonates,sulfates and silicates contained in passivating agents can precipitate with heavy metals,and the change of the organic functional properties of the sludge,caused heavy metal ions to produce more stable complexes.