Development of a sustainable zinc process for recycling of cemented carbides using gaseous zinc

WC-Co cemented carbides are indispensable engineering materials for cutting, drilling, forming, and wear-resistant applications. Their production, however, depends on tungsten and cobalt, both of which are classified as critical raw materials and are associated with increasing supply risk and geopolitical dependencies. Efficient recycling routes are therefore of growing ecological, economic, and strategic importance. Among the available options, the zinc process represents the most important direct recycling route, since it enables the recovery of reusable powder while largely preserving the original WC-Co material system. At the same time, the conventional process is associated with high temperatures, long treatment times, and an energy-intensive distillation step. The present cumulative dissertation addresses the further development of a sustainable zinc process for recycling cemented carbides using gaseous zinc. The work combines process-metallurgical fundamentals, experimental setup development, and systematic investigations of both zinc-induced disintegration and subsequent zinc removal. Particular emphasis is placed on the role of material composition, microstructural design, and the process conditions governing the efficiency of the overall recycling route. The results show that gaseous zinc provides a promising basis for a more selective and potentially more efficient disintegration process than conventional liquid-based treatment. At the same time, zinc-induced disintegration was found to be strongly material dependent and governed by a coupled interaction of reaction and transport processes rather than by a single limiting mechanism. This demonstrates that uniform treatment schedules are not suitable for all cemented carbide grades and that process duration must be adapted to the material being treated. In addition, the work shows that recyclability is influenced not only by the principal WC-Co composition, but also by alloying additions and microstructural features that affect binder reactivity, interfacial behavior, and crack-assisted transport. A further central outcome concerns zinc removal from the disintegrated material. Experimental and thermodynamic investigations demonstrate that substantial zinc removal can already be achieved under moderate vacuum conditions. This indicates that the conventional high-vacuum strategy should be reconsidered and supports a more differentiated interpretation of the distillation step. Overall, the dissertation establishes a coherent process-metallurgical concept for a more sustainable zinc process based on gaseous zinc disintegration, material-specific process control, and staged zinc removal. In this way, it provides an improved scientific basis for the more efficient recovery of tungsten and cobalt from cemented carbide scrap while largely preserving the original material system.