Impact of temperature and gas composition on hydrogen-based zinc recovery from electric arc furnace dust

Steel galvanization, essential for corrosion protection, results in zinc-enriched waste streams during recycling, presenting both environmental challenges and opportunities for resource recovery. Electric arc furnace dust (EAFD), generated at rates of 15–25 kg per ton of recycled steel, contains up to 40 % Zn and represents a significant secondary Zn resource. The current industrial practice relies on the Waelz process, which successfully recovers Zn but fails to recover Fe, generates substantial slag (700 kg per ton EAFD), and emits over 2000 kg CO₂ per ton of recovered Zn.

Here, we demonstrate that hydrogen-based direct reduction of EAFD enables efficient Zn recovery while significantly reducing environmental impact but requires precise temperature control between 900 and 1200 °C. This research is the first to systematically explore the temperature and gas composition dependencies in hydrogen-based EAFD reduction, offering novel insights into optimizing recovery processes. Through a systematic investigation of reduction kinetics and microstructural evolution, we demonstrate that reaction rates decrease by two orders of magnitude within a narrow 50 °C temperature window due to particle sintering and micro-pore collapse. These findings reveal a critical trade-off between kinetic enhancement and structural degradation.

The identified mechanisms indicate that optimal reduction requires a precise balance between kinetic acceleration below 1150 °C (showing a five-fold increase in mass loss rates) and the prevention of structural degradation above this critical threshold. Process efficiency is further controlled by reaction-generated H₂O, creating local thermodynamic barriers that require careful management. These findings establish temperature control as the key parameter for maximizing Zn and Fe recovery efficiency, providing critical guidance for the industrial implementation of hydrogen-based EAFD treatment.