Electrodialytic upgrading of municipal waste incineration fly ash for reuse: optimization of time and energy consumption

As incineration becomes a more widespread means of waste treatment, volumes of incineration residues increase and new means of handling become a demand. Municipal Solid Waste Incineration (MSWI) fly ash is hazardous material, which is presently disposed off as such; primarily due to its high content of water soluble, mobile salts and heavy metals. It was shown that the mobility of salts and toxic elements can be significantly reduced by extraction with electrodialysis in stack [1, 2]; and that treated MSWI fly ash may potentially be utilized as a substitute for cement in concrete [3].
In order to optimize the process and reach the lowest possible leachability of target constituents (As, Ba, Cd, Cr, Cu, Mn, Ni, Pb, Zn, Cl, Na and SO4) at minimum time and energy consumption, the present work gives results of 10 pilot scale (8 kg MSWI fly ash each) electrodialysis experiments at different current densities and with three different types of fly ashes (semi-dry, dry and wet fluegas cleaning). Continuous monitoring of voltage, pH and conductivity of the diluate (MSWI fly ash) solution and the concentrate is reported. Sampling of the treated fly ash was made during and after each experiment to investigate the leachability of salts and toxic elements as a function of treatment time and current density.
Results show that a delicate balance between pH and treatment-time exist and that continuous monitoring of pH and conductivity may be used for controlling of the process at an industrial scale.
References
[1] Jensen, P. E., Ferrira, C. M. D., Hansen, H. K., Rype, J.-U. R., Ottosen, L. M., Villumsen, A. Electroremediation of air pollution control residues in a continuous reactor. Journal of Applied Electrochemistry, 40, 1173-1181 (2010).
[2] Kirkelund, G. M.; Jensen, P. E.; Villumsen, A.; Ottosen, L. M. Test of electrodialytic upgrading of MSWI APC residue in pilot scale: focus on reduced metal and salt leaching. Journal of Applied Electrochemistry, 40, 1049-1060 (2010).
[3] Kirkelund, G. M.; Geiker, M. R.; Jensen, P. E. Feasibility test of electrodialytically upgraded MSWI APC residue utilization in mortar. In: Proceedings of 3rd International Conference on Engineering for Waste and Biomass Valorisation, Beijing, China, (2010).