Metal Recovery and Exploitation of Lignite Ashes by Combined Physicochemical and Biotechnological Approaches

Ashes from lignite combustion for power generation contain strategic metals, metalloids and rare earth elements and may thus be a potential source of industrially demanded metals. The presented project focuses on the assessment and exploitation of this potential raw material. Lignite ash assessment showed that largest ash amounts for potential exploitation are available in the Lusatia district, Saxony. Mechanical ash pre-treatment in principle provided enriched fractions by different methods but still suffered from low yields of enriched fractions. Thermal ash processing showed multiple significant phase changes compared to original ash. Subsequent chemical leaching using HClaq resulted in high metal extraction. Alternatively, bioleaching was applied using acidophilic Fe (II) and S-oxidizing or Fe (III)-reducing microorganisms (MO) as well as heterotrophic MO. The results indicated likewise high and partly specific metal mobilizations. Industrial ash exploitation was accomplished by direct reaction with acids resulting in Al-Fe-solutions which potentially can be applied in water treatment.