Zn recovery from steel mill EAF dusts: A two-step biotechnological approach

• Leaching of EAF dusts was demonstrated using a biogenic lixiviant produced by A. thiooxidans . • At 30°C, 100 g L -1 pulp density, and at a leaching duration of 10 minutes, 76.67 % of Zn were extracted from the dust while only 0.02 % of Fe went into solution, indicating a good leaching selectivity. • To purify the leaching solution, 48 % Fe was precipitated by adjusting the pH to 3.8 using NaOH. • 99.9 ± 0.1 % of Zn was recovered from the purified leachate using a microbial electrolysis cell (MEC) with a purity of 99 %. The growing demand for recycling strategies intended for electric arc furnace (EAF) dusts to recover secondary raw materials, calls for innovative approaches aligning with environmentally compatible practices. For recovery of Zn, biogenic sulfuric acid was produced utilizing A. thiooxidans in a reactor in fed-batch mode. The acid was then used in leaching experiments endeavoring to determine optimal leaching parameters for an efficient Zn extraction whilst retaining Fe in the dust matrix. At 30°C, 100 g L -1 pulp density, and at a leaching duration of 10 minutes, a concentration of 30 g L -1 of Zn equivalent to leaching efficiency of 76.67 % were found in the leachate while only 0.02 % of the Fe went into solution, indicating a good separation of these two metals. To purify the leaching solution, 48 % Fe was precipitated by adjusting the pH to 3.8 using NaOH. The extraction of Zn from the leachate was then achieved using a microbial electrolysis cell (MEC) with a two-chamber H-cell setup, the chambers being separated by a proton exchange membrane. The average Zn recovery from the leachate was 99.9 ± 0.1 % and a final Zn purity on the electrode of 99.2 % was achieved.