Zinc removal from metallurgical dusts with iron- and sulfur-oxidizing bacteria

The generation of currently partially recyclable metallurgical dusts during the steel production represents a challenge for the realization of a circular economy in this industrial sector. Due to a high iron concentration, the reutilization of blast furnace and cast house dusts in internal crude steel processes, is state of the art. However, heavy metal impurities such as zinc, act as an interference due to diverse negative effects. The aim of this study is to utilize Acidithiobacillus ferrooxidans, an iron- and sulfur-oxidizing bacteria, to solubilize zinc whilst retaining iron in the dust residue intended for reuse. To achieve this, the biooxidation of elemental sulfur is of crucial relevance. Two different strains of A. ferrooxidans (DSM 583 and CCM 4253) were cultivated and their leaching performances were compared to each other using a stirred tank reactor operated in a fed batch set-up, with a working volume of 3 L, at an operation temperature of 30 °C. The dust concentration was gradually increased until a maximum of 125 g/L, after which the reactors were left to run for three additional cycles to ensure replicability of results. For both strains, at a cast house dust concentration of 125 g/L paired with a leaching duration of two weeks, an average zinc removal of 56 % was achieved whereas solely an average of 4 % of iron was leached.