Bioweathering of metallurgical wastes: Insights into dissolution mediated by fungus Aspergillus niger

Laboratory incubation experiments are useful for deciphering the slag solubilization potential as well as the susceptibility of solids to abiotic and biotic dissolution. Here, the potential release of elements has been examined using fungus Aspergillus niger as biotic agent and sterile medium as abiotic control. As a ubiquitous environmental microorganism, A. niger produces organic acids that enhance acidification and dissolution of metal-bearing phases. Results show that at a pulp density of 10% and after 30 days of incubation, A. niger leached up to 30% of Cu and 57.4% of Zn compared to only 2.5% in the sterile medium. Overall, biotic incubation plays a more important role in the dissolution of amorphous slag, whereas its contribution to crystalline slag dissolution is more complex and strongly dependent on host minerals that accommodate major elements. Fungus enhanced the leaching of major elements by factors up to 2.5–4.2 while metal leaching was increased by factor up to 5.2 relative to abiotic conditions. Regardless of the type of slag, higher element leaching was observed when the biomass fraction was considered, enhancing the element yield by up to 4.1 × 10³-fold relative to the dissolved metal fraction in the biotic solution. These findings suggest that fungal bioleaching of Cu metallurgical slags is a promising approach for treating them as secondary resources although further optimization steps are still required.