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ENIntroduction
The availability of green carbon and pre-processed iron rich bauxite residue (red mud) can take steelmaking one step further from just employing renewable energy carriers (hydrogen, electrical power) and extend the sustainability of the processes and the products.
Green carbon: Organic materials can be pyrolysed to biochar as a carbon carrier which can find application for two different purposes in the steel production: first, the reduction of iron oxides remaining in direct reduced iron (DRI) and second, the carburisation of iron to form hot metal or steel.
Pyrolysis units from Next Generation Elements GmbH can process different input materials into high quality biochar. This will be an essential input material in the steel industry after the phase out of fossil carbon carriers. The demand for biochar will also facilitate the development of pyrogenic carbon capture and storage (PyCCS).
Ermafa Environmental Technologies GmbH as the other cooperation partner in this project developed the REDREC-Technology, which separates bauxite residue into an iron rich fraction as iron ore for steelmaking and a calcium and magnesium rich fraction with potential use for CCS (Carbon Capture and Storage).
This allows us developments in the following processes:
Leaching offers a further refinement step of bauxite residue to recover valuable components before it is transferred to one of the follow-up processes. A charge material of even higher iron content may be achieved which will further raise the downstream process efficiency.
HYFOR-Smelter (see Project 2.2 and 2.6) is a process where the iron rich product from bauxite residue can be used as a new iron source. Research of this process route is conducted for a sustainable production of crude iron. HYFOR employs fluidised bed technology for direct reduction of iron oxide via green hydrogen in combination with the electric Smelter furnace for production of blast furnace-like hot metal and slag.
The Hydrogen Plasma Smelting Reduction (HPSR) in the project SuSteel Follow-up can utilise the iron-rich bauxite residue fraction in a direct steelmaking route. Iron oxides are reduced and melted by hydrogen plasma and alloyed with biochar to steel for an efficient and sustainable single step production.
Carbonatisation can store CO2 in the calcium and magnesium rich fraction of the bauxite residue to facilitate an alternative path for CCS (Carbon Capture and Storage).
Objectives and Motivation
- Circular economy through upcycling of problematic, landfilled red mud from bauxite processing
- Recovery of valuable metals
- Alternative source of iron carrier complementary to classic iron ores
- Use of secondary carbon carriers like biochar in metallurgical processes for reduction of DRI and carburisation of hot metal
- Cross-Linking of multiple in-development processes to share knowledge
- Alternative path for Carbon Capture and Storage
Methodology
- Hydrogen Plasma Smelting Reduction (HPSR) of processed iron rich bauxite residue for steel production
- Hydrogen based direct reduction in a fluidised bed (HYFOR) for DRI production
- Electrical smelting (Smelter) of DRI with secondary carbon carriers for green hot metal
- Investigation of secondary carbon carriers and their reactivity in metallurgical processes
- Leaching to recover valuable metallic components e. g. Fe, Al, Ti, Na, and rare earth elements from bauxite residue of various origins
- Carbonatisation of iron poor residue for long-term storage of CO2 by valorisation of Ca and Mg rich waste material
- Laboratory and pilot scale trials to prove the feasibility of secondary carbon and iron sources as well as technological synergies and effective structural cooperation
Results and Application
Within the scope of this project, the suitability of biochar as secondary carbon carrier and mechanically processed bauxite residues from selected sources will be evaluated for their feasibility in HPSR, HYFOR, Smelter, carbonatisation and leaching processes. The results can directly lead to upscaled trials of iron rich bauxite residue and biochar as carbon carrier in a large, continuous HYFOR-Smelter demonstration plant. Once both materials can be used at industrial scale, they will not only be seen as sustainable input materials, but also as a major step towards circular economy in the aluminium sector and sustainable carbon sources. The expected product quality has to match to the current industry standards.