Bioleaching and Selective Precipitation for Metal Recovery from Basic Oxygen Furnace Slag

Decreasing ore grades and an increasing consumption of metals has led to a shortage of important primary raw materials. Therefore, the urban mining of different deposits and anthropogenic stocks is of increasing interest. Basic oxygen furnace (BOF) slag is produced in huge quantities with the so-called Linz-Donawitz process and contains up to 5.2, 0.9, 0.1, and 0.07% of Mn, Al, Cr, and V, respectively. In the present study, sulfur-oxidizing Acidithiobacillus thiooxidans and iron- and sulfur-oxidizing Acidithiobacillus ferridurans were applied in batch and stirred tank experiments to investigate the biological extraction of metals from BOF slag. In the batch experiments, up to 96.6, 52.8, 41.6, and 29.3% of Cr, Al, Mn, and V, respectively, were recovered. The stirred tank experiments, with increasing slag concentrations from 10 to 75 g/L, resulted in higher extraction efficiencies for A. ferridurans and lower acid consumption. Selective metal precipitation was performed at pH values ranging between 2.5 and 5.0 to study the recovery of Mn, Al, Cr, and V from the biolixiviant. Selective precipitation of V and Cr was achieved at pH 4.0 from A. thiooxidans biolixiviant, while Fe and V could be selectively recovered from A. ferridurans biolixiviant at pH 3.0. This work revealed the potential of BOF slag as an artificial ore for urban mining and demonstrated that combining bioleaching and selective precipitation is an effective method for sustainable metal recovery.