The Utilization of Mswi Fly Ashes in Cement Production and Its Impact on Heavy Metal Contents in Cement

SUMMARY: The disposal of fly ashes from municipal solid waste incineration (MSWI) is becoming a growing environmental issue in Europe. In order to avoid landfilling and recycle MSWI fly ashes, initiatives aim to recycle them in cement production. While numerous studies have analyzed the impact of MSWI ashes application on the concrete quality and the leaching of potentially hazardous heavy metals from MSWI ash amended concretes, only few studies have determined the consequential heavy metal content in cements if MSWI ashes would be added in large scale in cement production. Therefore, the aim of this study is to determine the inputs of selected heavy metals (Cd, Cr, Hg) into cement production and the heavy metal contents of cements after application of MSWI fly ashes on a national level, taking the case study of cement production in Austria. In order to do so, data on cement production and corresponding consumption of primary and secondary raw materials and fuels in Austria is retrieved from the environmental reports of the Austrian cement industry. Afterwards, concentrations of heavy metals in the primary and secondary raw materials (and fuels) are retrieved from literature. Both are inserted in a material flow analysis (MFA) model using the STAN freeware in order to calculate the heavy metal concentrations in cements currently produced. Afterwards, a scenario is drafted, assuming that all MSWI fly ashes in Austria are used in the cement industry without prior treatment. The result of the calculation gives the final heavy metal content of cements after application of untreated MSWI fly ashes. Results show that the application of untreated MSWI fly ashes will significantly increase the Cd content by a factor of five. Hg contents will rise by a factor of three, while the increases of Cr contents are low. Though a pre-treatment of MSWI fly ashes is required due to the salt contents of MSWI fly ashes, it will either only remove some fractions (neutral washing), or be relatively expensive (acidic washing). These results suggest that the secondary raw material value of MSWI in cement production is quite low, particularly if compared to other secondary raw materials currently used.