Lime

which is mainly presented as CaO

is often used in sludge conditioning and stabilization.To study the effects of CaO on the fate of heavy metals in pyrolysis and sludge gasification process

the sludge pyrolysis and gasification experiments were conducted with a drop-tube furnace and a fixed-bed system.The content and speciation of typical heavy metals(Mn

Zn

Cu

Cr

Ni) were also analyzed.Samples included different sludges(raw sludge

CaO conditioned sludge)

their corresponding pyrolysis chars and gasification ashes.The results indicated that after CaO conditioning

the content of heavy metals reduced due to the dilution effect.Mn

Zn

Cr transformed to stable state.Some heavy metals ions reacted with OH-to form precipitate which then decomposed to produce oxide during sludge gasification process.In addition

CaO can increase the residual rate of heavy metals in solids

and also absorb HCl

SO2 and other acid gases from decomposition of chloride or sulfate to promote the formation of oxides at high temperatures.Subsequently

eutectic was generated in the reactions between these oxides and compounds such as Al3O2

SiO2

Fe2O3 and CaO

thus suppressing the release of heavy metals.