Dr. Efthymios Balomenos has spent almost two decades as a post-doc researcher at the National Technical University of Athens (NTUA). His career began with a post-doctoral project in 2010, when he helped install the METLEN pyrometallurgical pilot unit, which launched a long research journey in bauxite residue valorisation. Since then, he has worked between NTUA and METLEN, contributing to both fundamental metallurgical research and industrial-scale technology development. He is currently an Assistant Professor at NTUA (Tesmet group), teaching iron and steel metallurgy, non-ferrous metallurgy, thermodynamics, and high-temperature processes, while continuing to advise METLEN as an external expert in R&D.
What is your area of expertise, and what is your role within the HEPHAESTUS project?
I am a metallurgist by training, and for many years my work has centred on industrial residue valorisation , especially bauxite residue from the alumina production. More than ten years ago, I helped set up the pyrometallurgical pilot unit that METLEN still operates today. Within HEPHAESTUS, I assist the METLEN team that runs this pilot unit.
At the same time, I teach at the National Technical University of Athens. The university has strong lab-scale research capabilities and very skilled PhD students and researchers who can produce metallurgical innovations albeit at a low TRL level. In industry, there is often neither the time nor the manpower, nor the infastructure to explore such early-stage research. However, industry can scale up the technological innovation and test our concepts in real industrial conditions. When the two sides work together, the loop becomes very productive!
Could you tell us a bit more about the METLEN pyrometallurgical pilot plant?
METLEN brings an important asset: a fully operational pyrometallurgical pilot plant. It was installed more than ten years ago at the METLEN facilities in Greece. It is a smaller and simpler version of the Italian pilot operated by AIT, but it allows us to test different industrial residues with real operational flexibility.
Our pilot includes an Electric Arc Furnace (EAF) equipped with CleanTech technology. This system can treat fine materials directly, without pelletising, which is a significant advantage. In the past, we ran extensive campaigns on bauxite residue. Now, within HEPHAESTUS, we are testing other residues such as EAF dust, ferronickel dust, and ferronickel slag from the former LARCO plant in Greece. In this process, industrial waste is converted into pig iron ingots and slag that can be used in for mineral wool or cement production.
As I mentioned, the Italian partners of HEPHAESTUS are building a larger pilot plant with a more modern EAF that will serve as a higher-TRL demonstration line. There they will also implement the EZINEX process for zinc recovery.
Is there a big difference between processing bauxite residue and EAF dust?
Although the pilot was originally built for bauxite residue, the transition to steel-related residues came very naturally. At its core, the process is designed to treat low-grade iron materials. Whether the feed is bauxite residue, electric arc furnace dust, or ferronickel slag, the goal remains the same: to recover valuable metals while reducing waste.
Could you guide us through the tests performed so far in HEPHAESTUS and what they have revealed?
We have completed a full test campaign with ferronickel dust from LARCO, and the results were very successful. We managed to recover iron with a small amount of nickel, and we demonstrated that the dust can be treated directly without pelletising.
One of the key strengths of the CleanTech EAF is the speed of melting. Fine residues react quickly when they touch the molten metal bath, and the material forms only a very thin overburden layer. This is different from traditional submerged EAFs, where the overburden is thick and the processing scale much larger.
Another asset we have is an indirect rotary kiln that heats the material up to 900 degrees Celsius before it enters the EAF. When carbon is present in the feed, the reduction process already begins in the kiln. The hot, partially reduced material then enters the furnace, where the remaining iron oxides are converted into metallic iron. This pre-reduction step reduces the workload of the EAF and is particularly attractive when gas prices are lower than electricity prices. The rotary kiln runs on gas, while the EAF runs on electricity.
The furnace is tilting, so it pours the slag into one ladle and then the metal into another. The products are slag and pig iron.
While pig iron can be used in steel production, what can be done with the slag?
In the HEPHAESTUS process, we envisioned using the slag for mineral wool. This requires the slag to be poured hot into the fiberizer, so that we avoid reheating. However, the mineral wool market is already saturated, and transport is only cost-effective within roughly a 1000-kilometre radius. METLEN is a metal producer, so mineral wool is not part of our business plan. Another company, or perhaps a future HEPHAESTUS start-up, could take on mineral wool production from EAF dust.
Alternatively, slag can be used as a low-value filler in cement or in road construction. If cooled quickly, it can even become a high added value product, namely supplementary cementitious material, clinker substitute in cement with significant environmental benefits.
What is your view on the HEPHAESTUS technology?
I believe the HEPHAESTUS process has real potential. Recovering metals from EAF dust is already a proven concept, but integrating the EZINEX pilot makes the whole process even more attractive. When you imagine the Italian and Greek pilots working together, you see a flexible and cost-efficient system that turns waste into three valuable products with zero waste.
Italy produces a significant amount of EAF dust, so the technology is extremely relevant. We often speak about industrial symbiosis and zero waste, but HEPHAESTUS is one of the rare cases where this vision is actually being implemented in practice.