Removal of Heavy Metals from Electric Arc Furnace Dust Recycling Process by Alkaline Extraction

Abstract

This work shows that the level of lead (Pb) and chromium (Cr) in Electric Arc Furnace (EAF) dust can be reduced to less than 1 ppm making it suitable for processing via electrowinning for the production of high-quality zinc and zinc alloys. EAF dust is a considerable by-product from the steel recycling process and can be recycled by pyro-hydrometallurgical processes. Zinc ferrite (ZnFe2O4) is the main phase in the EAF dust and is a good source of zinc for the production of zinc metal by electrowinning. However, it is very stable and needs to be transformed to zinc oxide prior to cementation. The EAF dust is mixed with lime and then calcined at elevated temperatures to convert the zinc ferrite to zinc oxide. The zinc is then leached by a mild NaOH solution. The leachant contains lead and chromium which hinders further processing. In the process, zinc cementation was applied in order to remove these heavy metals from the leachant. The optimum conditions were found to be; Zn/Pb mole ratio 3.0, temperature of 60oC and 900 rpm stirring speed.