Experimental Study On Migration And Transformation Characteristics Of Heavy Metals During Incineration Of Oily Sludge

Oily sludge（OS）contains heavy metals and highly toxic and carcinogenic substances such as PAH,which is prone to cause serious environmental hazards.Among the methods for OS treatment,the incineration is believed to be the most effective way to achieve the reduction,innocuity and recycle of OS through carbonizing the harmful substances in the OS.However,with the characteristic of volatility and instability seriously,heavy metals seriously restricts the development of OS incineration technology.In this paper,the effects of incineration temperature,Ca O,mineral compounds on heavy metals transformation such as Cu,Cr,Zn,Pb,As,Cd during OS incineration were carried out based on the experimental study.The total amount,the form distribution and leaching characteristics of heavy metals were analysed by using combined methods including HNO₃-HF-HCl O₄ disintegration and the acetic acid buffer solution as well as the BCR continuous extraction method.Also,the morphological characteristics,elemental components and mineral components of the OS bottom ash were conducted by using the SEM,EDS and XRD.This paper will not only provide important basic data and theoretical support for the source control of heavy metals in the process of OS incineration,but help to realize the harmless treatment of OS and promote the development of OS incineration technology.Firstly,the study on the effects of different incineration temperatures（800°C～1000°C）on heavy metals transformation was conducted.According to the results,the higher boiling point and the lower incineration temperature led to the higher concentration of the heavy metals.For heavy metals with higher residual rate such as Cr,Cu,Zn,the higher the incineration temperature,the lower the leaching concentration;But for As,Pb and Cd,which had lower residual rate,the incineration temperature showed little effect on their leaching characteristics.The rise of incineration temperature could promote the volatilization of exchangeable and the reducible,the residual had better thermal stability,which was unable to decompose.Secondly,the incineration bottom ash of OS with Ca O was carried out.Ca O can not only reduce the emission of SO₂ during high-sulfur OS incineration,but also increase the chemical adsorption surface to absorb heavy metals through reacting with them at high temperatures and form stable compounds.The results presented that the adsorption effect of Ca O on Pb was most obvious,the next were Cu,Cd,As,Cr and Zn.The addition of Cao in OS brought about great decline on the heavy metals leaching concentration in the bottom ash,especially of Cu,Zn,and Pb.At the same time,it was found that Ca O could promote the oxidizable of Cr and the residual and oxidizable of the Cu at a lower temperature;And at a higher temperature,it enabled the exchangeable of Cr and the oxidizable of the Zn.Finally,the effects of different mineral compounds such as Fe₂O₃,Al₂O₃ and Mg O on heavy metals transformation during OS were studied.The results indicated that Fe₂O₃ showed better adsorption effect on Cu,As,and Cd.Mg O absorbed well on Cd.And in heavy metals with strong volatility such as Pb and As,Al₂O₃ adsorbed well.In addition,different mineral compounds showed different effects on heavy metals leaching concentrations.As for Cu:Ca O>Fe₂O₃>Al₂O₃>Mg O;For Pb:Al₂O₃>Ca O>Mg O>Fe₂O₃;For As:Al₂O₃>Fe₂O₃>Ca O>Mg O;And for Cr,Cd and Zn:Al₂O₃>Mg O>Fe₂O₃>CaO.