From hazardous waste incineration (HWI) in rotary kilns ashes are generated as solid residues. In this thesis the effect of limestone addition to HWI-ashes was examined for the elution behaviour of heavy metals after a temperature treatment. Experimental results were compared to theoretic modelling. After treatment at 1200°C, the typical temperature for hazardous waste incineration, a minimum of heavy metal leaching from HWI-ashes was found at CaO-contents between 15 and 20%. On the one hand, lower melting temperatures of the ashes were measured after limestone addition. The melting process may lead to immobilisation of heavy metals in glassy phases of the ash. On the other hand, thermodynamic equilibrium calculations prove the decrease of the solubility of heavy metals as for example zinc, lead and chromium due to a changed chemical speciation. In future a HWI-ash optimised with regard to heavy metal leaching could be disposed off to lower landfilling costs, so that the incineration costs of hazardous waste in rotary kilns may also decrease.