A CRYSTAL PHASE STUDY OF ZINC HYDROXIDE CHLORIDE IN ELECTRIC-ARC-FURNACE DUST

Chemical analysis shows that electric-arc-furnace (EAF) dust obtained from 1 steelmaking factories in Taiwan is composed chiefly of Fe (15-37%), Zn (7-28%) and Mn (1.55-3.99%) and that the mineral composition is mainly (Mn, Zn) Fe2O4, ZnO and ZnCl2 . 4Zn(OH)2 . H2O. It was also found that EAF dust exists as irregular agglomerates from 3 to 20 mum in size and are made up of much smaller round particles from 0.3 to 1 mum in size. ZnCl2 gas in the dust condenses after passing through the EAF gas-cooler system binding small particles of Mn-Zn ferrite together. The agglutinative substance was identified as being ZnCl2 . 4Zn(OH)2 . H2O possibly arising from the interaction between ZnCl2 and ZnO adhering to the Mn-Zn ferrite particles; a conjecture supported by the fact that EAF dust dissolves easily in hydrochloric-acid solution leaving only loosely aggregated Mn-Zn ferrite material.