One of the biggest challenges of our time are the CO2 emissions resulting from the production of steel and cement (concrete), amongst the 2 most abundantly used construction materials on this planet. In the production of steel, the biggest challenge remains in splitting up the Iron and Oxygen atoms that are bound together in iron ore (oxides). Classically this is still done in a blast furnace, where coal (coke) is used to “steal” the O atoms in the ore and form Fe, but also CO and CO2. The most well known alternative routes are the ones using for example hydrogen as an alternative for cokes, as well as an electrometallurgical route, using electrolysis in a bath with molten material, similar to the process used in the production of aluminum. The majority of the initiatives related to reducing CO2 emissions from steel production presently being prepared on an industrial scale rely on a DRI route involving hydrogen gas. If the hydrogen itself is green, that indeed can be a CO2-neutral route. The production of H2 is however energy-intensive as well, so the overall energy footprint of the full proess can be relatively high.
An other potential disadvantage of the DRI-based route is more indirect: as for the melting an EAF is often proposed, this results in a very irregular consumption on the electrical grid, together with potential distortions. This means that the challenges ahead are not purely metallurgical in nature.
Other metals, like aluminum, copper and zinc are produced since ages using a more docile and continuous approach called “electrolysis”. The same process that can be used to produce hydrogen out of water. Recent advances show that a similar approach might be an option to be used in the production of iron as well. The technology hasn’t reached full industrial scale yet, but today 2 routes are being pursued:
⏩ A low-temperature one using an aqueous solution, like is the case in the production of copper and zinc
⏩ A high-temperature one using a molten salt, like in the case of aluminum
In the first one iron ores are first dissolved in a water-based liquid. Subsequently, using an electrical current, the iron is collected out of the liquid on one of the electrodes. Temperatures remain comfortably below 100°C. In the latter one the iron ore is molten into a liquid salt. Again an electrical current is used to reduce Iron ions into almost pure iron. In this case the temperatures need to be at least 1600°C.
Both techniques have advantages and disadvantages, but initial signs show that both can indeed serve as a viable alternative to a DRI-based production route. In order to evaluate properly, real numbers are required, and these are currently being generated by amongst others Boston Metal (molten salt) in the US and projects related to the SIDERWIN SPIRE project at the European side of the Atlantic (aqueous route). Again the availability of continuous power and or the ability to cope with increased fluctuations in green power sources will play a role in deciding what the most viable options are as well as where best to locate the plants.
Recently the US-based ARPA-E program announced funding of a number of additional potential alternative routes, these include:
⏩ A method based on exposing iron ore to hydrogen plasma, a state of matter also researched in nuclear fusion reactors
⏩ A few alternative methodologies for refining iron ores using hydrometallurgical processes and perform electrolysis at lower (< 100°C) temperatures in aqueous solutions
⏩ A bit further away from classical approaches: using very localized, very high temperatures resulting from irradiating the ore with high-energy laser light
Some of the processes before have already reached pilot scale deployment, so can be considered very promising. Next to these approaches also a number of projects focusing on technology already posted about before received support.
Exciting times ahead!
For those looking for more details:
- Argonne National Laboratory using hydrogen plasma
- Blue Origin using an Ouroboros approach also touched upon in Lunar applications
- Electra using low-temperature aqueous approaches
- Form Energy introducing a powder-to-powder process. Challenging!
- Georgia Institute of Technology focusing more on the application side, reducing weight
- Limelight Steel using heat injection through laser to break chemical bonds in the ore
- Penn State University will focus on electrochemical processes, looking for suited electrode materials
- Phoenix Tailings will try to modify the requirements imposed on electrodes by applying an arc
- Tufts University will introduce ammonia in the preprocessing step of the ore
- University of Minnesota will work on hydrogen plasma as well
- University of Nevada-Las Vegas will also follow an electrochemical route, using an impeller-accelerated reactor to influence kinetics
- University of Utah will also implement hydrogen, avoiding the need of a molten state in the first stages of the process
- Worcester Polytechnic Institute will also look at electrochemical routes to create iron powder