Immobilization of EAFD heavy metals using acidic materials

Abstract

This study was undertaken to determine the chemical and leaching characteristics of the Electric Arc Furnace Dust (EAFD) generated by a Greek plant and to investigate various acidic materials efficiency on the EAFD stabilization. In order to investigate how [OH⁻] neutralization influences EAFD heavy metals leachability, Na HCO₃ ⁻, HNO₃ and H₃PO₄ were used as acidic materials. The concentration of Pb in leachate was found between 40 and 3.7 × 10³ mg Pb/kg of EAFD, exceeding in all EAFD samples the maximum acceptable limit (MAL) 25 mg/kg for landfill disposal. Neutralization of [OH⁻] with HCO₃ ⁻ decreased Pb concentration in leachate at 350 mg Pb/kg of EAFD, while excess over a stoichiometry in HCO₃ ⁻ addition increased leachability of Pb, Cd, Cr, Cu as well as F. Using HNO₃ as an acidic material decreased leachability of almost all the parameters concerning the EC directive 33/19-01-2003 in a pH value up to 7.2, in exception of Zn. Zinc leachability showed a U shape curve as a function of pH value. The concentration of Zn was minimized in a concentration lower than 1 mg Zn/kg EAFD in a pH range 10.5 to 9 and exceeded the MAL 90 mg/kg at a pH value 7.2. However, the major disadvantage of HNO₃ was proved to be its leachability, since NO₃ ⁻ concentration in leachate was equal to HNO₃ dose. H₃PO₄ was found the most promising acidic material for the chemical immobilization of heavy metals, since it decreased their leachability in a concentration significantly lower than MAL at a pH value up to 7.1. Finally, the concentration of Cl⁻ ranged between 18 and 33 × 10³ mg Cl⁻/kg EAFD exceeding in all EAFD samples the MAL 17 × 10³ mg/kg. This high concentration of Cl⁻ is attributed to the scrap and it could be reduced only by modification of its composition.

Keywords:

• Metallurgical waste
• EAFD
• characterization
• chemical immobilization
• toxic metals
• leaching

Notes

¹See Table 2, column 2.