Thermoacidophilic Bioleaching of Industrial Metallic Steel Waste Product

The continuous deposition of hazardous metalliferous wastes derived from industrialsteelmaking processes will lead to space shortages while valuable raw metals are beingdepleted. Currently, these landfilled waste products pose a rich resource for microbialthermoacidophilic bioleaching processes. Six thermoacidophilic archaea (Sulfolobusmetallicus, Sulfolobus acidocaldarius, Metallosphaera hakonensis, Metallosphaerasedula, Acidianus brierleyi, and Acidianus manzaensis) were cultivated on metal wasteproduct derived from a steelmaking process to assess microbial proliferation andbioleaching potential. While all six strains were capable of growth and bioleachingof different elements, A. manzaensis outperformed other strains and its bioleachingpotential was further studied in detail. The ability of A. manzaensis cells to break downand solubilize the mineral matrix of the metal waste product was observed via scanningand transmission electron microscopy. Refinement of bioleaching operation parametersshows that changes in pH influence the solubilization of certain elements, which mightbe considered for element-specific solubilization processes. Slight temperature shiftsdid not influence the release of metals from the metal waste product, but an increasein dust load in the bioreactors leads to increased element solubilization. The formationof gypsum crystals in course of A. manzaensis cultivation on dust was observed andclarified using single-crystal X-ray diffraction analysis. The results obtained from thisstudy highlight the importance of thermoacidophilic archaea for future small-scale aswell as large-scale bioleaching operations and metal recycling processes in regardto circular economies and waste management. A thorough understanding of thebioleaching performance of thermoacidophilic archaea facilitates further environmentalbiotechnological advancements.