Dennis Krämer

• This study addresses the influence of siderophores on the geochemical behavior of critical metals in rocks, ores and aqueous solutions. Rare earth elements and Y, the platinum group elements as well as other high field strength elements such as Zr, Hf, Th and U are presently referred to as high technology metals with many of them classified as critical metals. These critical metals are facing a distinct supply risk due to high production concentration and/or processing issues but are, however, essential for the development of state-of-the-art industries. Today’s industries rely on a steady supply of these metals for their economic development and the industry’s demand as well as the linked anthropogenic input of these metals will likely increase significantly in the near future. Siderophores are produced by a variety of microbes and plants in Fe-deficient environments to solubilize sparingly soluble Fe. However, siderophores also complex a range of other polyvalent metal ions. This study elucidates the mechanisms and the geochemical implications behind leaching with the hydroxamate siderophore desferrioxamine B (DFOB) and focuses on the siderophore-promoted mobility of ‘immobile’ high field strength elements. The second goal of this thesis was to elaborate to what extent siderophores can be used for processing and extraction of high technology metals from mineralogically complex ores like oxidized Platinum Group Element (PGE) ores or deep-sea ferromanganese nodules and crusts. Leaching of rocks and particle-rich aqueous solutions with siderophores leads to a significant mobilization of the ‘immobile’ high field strength elements like rare earth elements, Zr, Hf, Th and U and to distinct features in REY patterns. Bulk-rock normalized REY patterns of leaching solutions with DFOB showed a very distinct positive Ce anomaly and a depletion of La and other light REY relative to the middle REY, with a concave downward pattern between La and Sm. The “siderophore redox pump” that is first described in this thesis leads to a preferential enrichment of redox-sensitive Ce and U relative to redox-insensitive dissolved LREY and Th during siderophore leaching due to changes in the redox equilibrium and preferential complexation of oxidized species by DFOB. The observed fractionation patterns and decoupling of Ce and U by siderophore-induced oxidation might be helpful in constraining the presence of siderophores or chemically similar metal-specific organic chelating agents present during weathering and might be used as a bio-proxy for paleoenvironmental research. Furthermore, a leaching process was developed and is presented in this thesis that uses siderophores for the extraction of Pt and Pd from oxidized (weathered) Platinum-Group Element (PGE) ores of the Great Dyke, Zimbabwe. Current mining operations focus on the recovery of PGE from pristine and unweathered ore material from the Main Sulfide Zone (MSZ). The oxidized PGE ores are currently not mined, because recoveries using conventional processing techniques render this uneconomic. The data presented in this study indicates chemical extraction of Pt and Pd at alkaline conditions as (Pt,Pd)HDFOB and/or (Pt,Pd)H2DFOB+ complexes. Up to 80% Pt were mobilized using the developed leaching process. Siderophores also represent viable reagents for the hydrometallurgical extraction of high technology metals from ferromanganese nodules and crusts. Deep-sea ferromanganese deposits contain a wide range of high technology metals and are considered an important future resource, but extraction techniques, especially with respect to high technology metals, are still not established. The data on leaching of ferromanganese nodules and crusts presented in this thesis showed that the high technology metals Li, Mo, Zr, Hf, Nb and Ta are significantly extracted using siderophores, whilst base metals are not mobilized to large extents. This study highlights the importance of siderophores for the mobility and fractionation of certain high technology metals in the environment. The data presented in this study shows that siderophores like desferrioxamine B not only enhance the solubility and mobility of Fe(III), but also strongly enhance the mobility of ‚immobile‘ high field strength and highly siderophile elements such as the rare earth elements, Zr, Hf, Th, U and Pt and Pd. Additionally, siderophores or similar specific metal-binding organic ligands have a promising potential in future processing technologies of oxide deposits like those investigated in this study.