Volatilization characteristic and solidification of Pb, Zn, Cd and as during cement kiln co-processing of solid waste

Abstract

Cement kiln co-processing always became one of the predominate approaches to dispose hazardous solid waste containing heavy metals. The volatilization and morphology of heavy metals should be paid to more concern during the cement production due to the environmental risk of heavy metals. In this study, the volatilization characteristics and the solidification effect of heavy metals (Pb, Zn Cd and As) during cement kiln co-processing were explored by the lab and pilot scale experiments. At same experimental conditions, the volatilization rate followed as As > Pb > Cd > Zn. Both limestone and cement raw meal have been demonstrated the capability to mitigate the rates of heavy metal volatilization. Notably, cement raw meal displays a more pronounced effect compared to limestone in suppressing volatilization processes. Over 50% of heavy metals were transformed into residual state at 1400 °C, and Cd, As and Zn were easy to be solidified than Pb. A pilot scale experiment proved that more than 80% of heavy metals was solidified, and Zn reached nearly 100%. Moreover, around 80% of Cd, As and Zn were remained in clinker and the rest was distributed in kiln dust particles, only very few amount was released into the exhaust flue gas. This study provides a comprehensive and extensive understanding of the volatilization characteristics and migration patterns of heavy metals in the cement kiln environment. It offers theoretical support for the control of heavy metals during the co-processing of hazardous solid waste in cement kilns.