Abstracting Zinc Flakes from Crude Zinc Oxide Through the Reclamation of Electric Arc Furnace (EAF) Dust

Abstract

In recent years, factories in Taiwan have successively installed dust processing equipment in electric arc steel smelting furnaces (EAF) to reclaim crude zinc oxide which is then sold for profit. The price of crude zinc oxide, however, is directly correlated to their purity, as lower purity requires downstream factories to install additional purification technology [1, 2]. A case is presented in which the low quality of zinc oxide flakes produced make it difficult for a firm to justify its initial investment. To raise the value of its product, the firm requires an efficient manufacturing process to turn crude zinc oxide into high-purity zinc flakes. In this study, hydrometallurgy technology was used to transform zinc oxide into high-purity zinc flakes through a three-step process including leaching, purification and electrodialysis. Results show that zinc dissolution reaches its highest rate after 48 h of stirring in 7 N-NaOH as the leach agent with a solid–liquid ratio of 1:10 at room temperature. Using a strong alkaline as the leach agent can prevent the dissolution of iron oxide; however, the leach solution still contains a large amount of lead which must be removed to avoid degrading the purity of the electrodialyzed zinc powder. Using sheet zinc recycled from batteries as a displacement for purifying leach solution yielded a level of quality comparable to commercial zinc powder, but at a cost only 1/30 of that for the zinc powder process. This process also yielded high purity lead slag as a byproduct, which adds to its value. The purified leach solution is then electrolyzed into zinc flakes and the zinc powder manufactured from the above flakes achieves a purity as high as 99.1 % [3–5].