Selective dissolution and kinetics of leaching zinc from lime treated electric arc furnace dust by alkaline media

Abstract

The EAF steelmaking process generates 10–20 kg of dust per ton of steel, containing 15–30% zinc, making it a valuable secondary zinc resource. In this work, selective dissolution and kinetics of leaching zinc from lime (CaO) treated EAF dust using NaOH, KOH, and LiOH alkaline solutions were investigated. By reacting with CaO, insoluble ZnFe2O4 in EAF dust is converted to soluble ZnO and stable Ca2Fe2O5. Optimal zinc leaching conditions were achieved after 2 h at 70 °C and a S/L ratio of 1/300 (mg/ml). Among the alkaline solutions used, the zinc leaching rate was highest using 2 M NaOH solution at 99% zinc recovery. On the other hand, thermodynamic solubility calculations indicate that KOH is a better candidate for practical extraction as it can dissolve 6–8 times more zinc than NaOH. The prevailing rate-controlling mechanisms when using NaOH, KOH, and LiOH solutions were found to be the same. From 25 °C to 50 °C, chemical reaction was primarily rate-limiting. In contrast, from 50 °C to 70 °C, the controlling step later shifted to a product layer diffusion control – implying that higher temperatures and finer particle size are vital to achieving high zinc leaching rates. Finally, a solid by-product containing Ca2Fe2O5 and CaO only, which can be recycled in the iron and steelmaking process, was obtained via calcination at 500 °C.