Heavy metal leaching and distribution in glass products from the co-melting treatment of electroplating sludge and MSWI fly ash

Abstract

Melting is a common solidification treatment that concentrates and encapsulates heavy metals into a glass matrix for waste containing heavy metals (Chae et al., 2016). To control the risk of heavy metal leaching into the glass product, a reduction in the amount of heavy metal was achieved in a pilot-scale furnace by co-melting electroplating sludge (EPS) and municipal solid waste incineration fly ash (MSWI FA). Through the melting process, the chloride from MSWI FA led to heavy metals volatilization in the form of chlorine salts. The fly ash additionally increased heavy metals volatilization by 4%-91%. The highest volatilization ratios of Zn, Pb, Cu, Cd, Cr and Ni were 33%, 96%, 33%, 79%, 81% and 31%, respectively. The concentrations of Pb and Zn in the secondary fly ash were close to the Pb and Zn concentrations in lead-zinc ore that are required in smelting industry. Moreover, glass sand was produced after the melting treatment. With an increase in the fly ash mixing ratio, the leaching concentration of Zn and Cu decreased to 3.8 mg/L and 2.1 mg/L. The leaching concentrations of other heavy metals stayed below 1 mg/L in all cases. When the ratio of MSWI FA reached 10%, the glass sand contained the least amount of impurities and a large amount of phosphate and silicate, which were probably responsible for the stability of the heavy metals. Therefore, our results provided a promising approach to the stability of the waste by the recovery of heavy metals in the co-treatment of heavy metal-bearing wastes.

Keywords: Co-melting; Electroplating sludge; Heavy metals; MSWI fly ash; Vitrification.