Electrokinetic stabilization of heavy metals in MSWI fly ash after water washing

Abstract

This study assessed the feasibility of combining the water washing and electrokinetic (EK) treatments for the removal of Pb, Cd, Cr, and Cu from two municipal solid waste incineration (MSWI) fly ashes. Two approaches were compared: a direct electrokinetic (DEK) treatment and a combined method using water washing before the electrokinetic (WEK) treatment. The following experimental EK parameters were evaluated: electric current, pH, and treatment time (168 h). The analytical results from a toxicity characteristic leaching procedure (TCLP) showed that one fly ash sample was within the regulatory limits after either approach. However, the second fly ash sample was only within the limits following the WEK technique because the WEK technique was able to decrease the high Pb level of 58.6% in the exchangeable and carbonates fractions to 9.5% in this sample. The water washing step first extracted the soluble salts KCl, NaCl, SiCl4, and CaClOH and decreased the interference from the large chloride concentration, thereby promoting the ability of the subsequent EK treatment to stabilize heavy metals as less reactive complexes. Therefore, the WEK technique is recommended over the DEK technique for treating fly ash. © 2014 American Institute of Chemical Engineers Environ Prog, 33: 1235–1241, 2014