Effects of limestone addition and sintering on heavy metal leaching from hazardous waste incineration slag

Hazardous waste incineration (HWI) in rotary kilns and the disposal of the residual slag on landfills play an important role in German waste treatment. In order to save disposal costs the elution behaviour of HWI-slag should be further optimised. Quality-improved slag may be disposed off on cheaper landfill sites still applying to landfill regulations. In a new process-integrated approach hazardous waste is mixed with limestone, which initiates chemical reactions with heavy metals in the rotary kiln yielding new compounds of different solubility. In this work HWI-slag/limestone mixtures are thermally treated and then examined by elution tests. Experimental data indicate that the heavy metals pertinent to landfill class assignment of a HWI-slag share a solubility minimum at a CaO-content of about 15%. Such improved HWI-slags are allowed to be disposed off on cheaper landfill sites. Furthermore, a new combination of thermodynamic calculation methods is applied to predict heavy metal solubility for different process conditions. Used models hold the opportunity to explain the tendencies of heavy metal leaching and propose plausible chemical reactions. With it, a new tool to examine the impact of temperature treatment and slag composition on heavy metal elution from HWI-slag is presented.