Understanding environmental leachability of electric arc furnace dust

Dust from production of steel in an electric are furnace (EAF) contains a m ixture of elements that pose a challenge for both recovery and disposal. Th is paper relates the leachability of six Canadian EAF dusts in four leachin g tests [distilled water, Ontario Regulation 347 Leachate Extraction Proced ure, Amount Available for Leaching (AALT), and pH 5 Stat] to their mineralo gy. Chromium and nickel contaminants in EAF dust are largely unleachable (< 5% available in AALT and pH 5 Stat), as they are found with the predominant spinel ferrite phase in EAF dust. However, even a small proportion of oxid ized chromium can result in significant leachate concentrations of highly t oxic chromate. The leachability of zinc (7-50% available), lead (2-17% avai lable), and cadmium (9-55% available) can be significant, as large fraction s of these contaminants are found as chlorides and oxides. The leaching of these metals is largely controlled by pH. The acid neutralization capacity of the EAF dusts appeared to be controlled by dissolution of lime and zinci te, and results from regulatory leaching tests can be misleading because th e variable acid neutralization capacity of EAF dusts can lead to very diffe rent final leachate pHs (5-12.4). A more informative approach would be to e valuate the total amounts of contaminants available in the long term, and t he acid neutralization capacity.