Evaluation of assisting agents for electrodialytic removal of Cd, Pb, Zn, Cu and Cr from MSWI fly ash

Different assisting agents (0.25 M ammonium citrate/1.25 % NH3, 0.25 M Na-citrate, 2.5 % NH3, DI water) have been used as assisting agents for the removal of heavy met-als during electrodialytic treatment of municipal solid waste incineration (MSWI) fly ash. In this study, the effectiveness of the different agents was evaluated. The heavy metal speciation in solution was discussed and simulated at the different conditions using the geochemical equilibrium model Visual MINTEQ. The heavy metals examined were Cd, Pb, Zn, Cu and Cr. The 2.5 % NH3 solution was the best assisting agent for removal of Cd, probably due to formation of stable tetraammine complexes; whereas the best Pb removal was obtained with 0.25 M Na-citrate (Pb forms very stable chelates with citrate). The best compro-mise for removal of all five metals was obtained with the 0.25 M ammonium citrate/1.25 % NH3 solution.