There are two potential ways to separate iron from the oxygen in iron ore – traditionally using chemical reductants such as hydrogen or carbon (coal/coke) in a blast furnace, or using electrolysis to reduce the iron ore to iron.

A conventional blast furnace uses coke and limestone to reduce iron ore at high temperature, and emits a vast volume of carbon monoxide (CO). Iron ore is sintered or pelletised and mixed with coke and limestone (flux) to remove impurities (gangue) to form slag which floats on the iron. Hot air at about 1,000°C blows into the furnace, igniting the coke to produce intense heat and CO. As the material descends, the iron ore is reduced from iron oxides to metallic iron. The molten iron and slag collect at the bottom of the furnace, where they are drained off periodically (tapped) from separate openings. The iron is then cast into ‘pigs’ or transferred for steelmaking. A blast furnace typically produces 1.8 tonnes of CO₂ for every tonne of steel made.

Electrolysis
By comparison, in one high temperature electrolysis technique the iron ore is dissolved in a solvent of silicon dioxide (SiO₂) and calcium oxide (CaO) at 1,600°C, and an electric current passed through. Negatively charged oxygen ions migrate to the anode, and oxygen bubbles off. While positively charged iron ions migrate to the cathode where they are reduced to pure iron. If the electricity comes from renewable sources (or nuclear), the iron produced is carbon-free without CO₂ emissions.

Although electrolysis has been demonstrated at laboratory scale it has only recently reached industrial-scale pilots.

A low temp electrolysis approach
The EU-funded ULCOS project investigated prospects for electrolysis-based ironmaking through the ULCOWIN initiative, as part of the Horizon 2020 programme. The Siderwin project was led by steelmaker ArcelorMittal, with 11 European partners. It looked at using low temperature electrolysis with a water-based electrolyte in a pilot located at Maizières-lès-Metz, France, which produced 4 kg iron samples at technology readiness level 4 (TRL 4).

Subsequently, ArcelorMittal teamed up with Belgian engineering company John Cockerill in 2023 to develop the world’s first industrial scale, low temperature iron electrolysis plant: Volteron. Although the location has not been selected yet, depending on access to renewable energy and other factors, the plant could produce 10,000–40,000 t/y of iron in its first pilot plant. Once proven at this scale, the technology will be ready to boost production to a 1mn t/y facility.

‘The Volteron process is one of the most disruptive technologies to produce steel sustainably with minimum CO₂ emissions, in a global trend towards electrification,’ says Anderson Morelato, Head of Decarbonisation for the Group CTO team at ArcelorMittal.

This fully electrified process can produce 99% pure iron directly from iron ore using clean electricity. The iron ore fines of hematite (FE₂O₃) or magnetite (Fe₃O₄) are prepared by beneficiation (flotation and regrinding) to remove waste and produce an emulsion with 10–20% concentrate with 1% SiO₂ for electrowinning/electrolysis in a 50% caustic soda (NaOH) electrolyte, at just 110°C. The 1 metre x 1 metre plates created during electrolysis are then processed in an electric arc furnace (EAF).

‘Volteron is a highly innovative, modular and cost-effective solution for iron production,’ remarks Morelato. He recognises that the process is ‘cost intensive’ compared to the economics of a conventional blast furnace with access to cheap coal. However, as well as the environmental benefits, there are significant savings as the process avoids the need to build a pellet, coke or sintering plant and the associated infrastructure. It also avoids the high infrastructure costs associated with hydrogen for iron ore reduction or the costly infrastructure demands of carbon capture.

‘The process has strong scalability and modularity. It’s a revolutionary technology for tackling hard-to-abate carbon emissions, with high energy efficiency compared to other low-carbon steel manufacturing technologies. But like most of these new technologies, it will depend on the level of carbon tax, the regulatory environment and the input prices to determine the viability of using the process in certain locations,’ he says.

‘We have developed a very competitive energy consumption ratio compared to other approaches. However, there is no magic wand,’ continues Morelato. ‘Some solutions will be available in the short-term, some medium-term and some long-term.’ Indeed, ArcelorMittal has also been looking at smart carbon and innovative direct reduced iron (DRI) solutions.

Currently, blast furnaces account for about 70% of iron output worldwide, with the rest from EAFs which melt scrap at lower temperatures; whereas the US mixes 30% blast furnaces with 70% EAF because of plentiful scrap iron availability to produce steel with a minimum carbon footprint. The International Energy Agency (IEA) forecasts that 14% of steel production could be carried out by electrolysis by 2050.

‘Energy-wise, we think Volteron can be more competitive than using hydrogen for reduction in terms of energy efficiency,’ says Morelato. ‘Iron ore electrolysis has a relatively simple flowsheet, as you are replacing coal with electrons to produce pure iron plates, replacing scrap in an EAF. Provided you use low-carbon electricity, this is an effective low carbon process.’

‘The Volteron process is one of the most disruptive technologies to produce steel sustainably with minimum CO₂ emissions, in a global trend towards electrification.’ – Anderson Morelato, Head of Decarbonisation for the Group CTO team at ArcelorMittal.

High temp molten oxide electrolysis 
Research at the US Massachusetts Institute of Technology (MIT) led to the founding of Boston Metal, which commissioned its first prototype high temperature (1,500°C) molten salt-based cell in 2014 and has produced over 1,000 tonnes of metal. Boston Metal has now commissioned a multi-inert anode molten oxide electrolysis (MOE) industrial cell which produces ‘tonnage steel’ without CO₂ emissions.

This innovative process also simplifies steelmaking by replacing traditional multiple carbon-intensive steps with a single, electrified reaction, for a clean, viable alternative to traditional blast furnaces.

Conventional steelmaking emits 1.85t CO₂ on average per tonne of steel. Nevertheless, the steel sector has questioned the economic viability and scalability of carbon-free production. While hydrogen-based direct iron reduction (DRI) has been gaining traction, there have been serious issues around the lack of infrastructure for hydrogen production – and the hydrogen economy has not gained momentum at the pace anticipated in the energy transition. There are also issues around water usage and the high cost of carbon capture for a truly carbon-free steel sector. The products of DRI chemistry are typically 90–94% iron, including 83–89% metallic iron, up to 9% iron oxide, up to 2.5% carbon, 2–6% gangue, 0.09% phosphorus and 0.03% sulphur.

After decades of research since the 1980s, focused on developing an electrolytic cell to produce pure metal, there was a breakthrough. The core element is a proprietary electrified inert anode which heats an iron ore electrolyte to 1,600°C, splitting iron oxide bonds and releasing pure oxygen and liquid metal.

The MOE process eliminates the need for coke and bypasses the multi-step process in traditional steelmaking, which includes coke production from coal, sintering, pelletising, blast furnace reduction and oxygen furnace refinement. Blast furnace iron typically contains up to 5% carbon and a number of impurities, including silicon, sulphur, manganese and phosphorus, and must be refined during primary and secondary steelmaking.

MOE is a ‘one-step solution’ to decarbonise steel operations, reducing emissions and operational complexity by direct transformation of raw ore into finished metal, without process water, hazardous chemicals or rare metal catalysts. The cells are about the size of a school bus and can scale by adding more anodes. The process is powered by renewable electricity.

Boston Metal secured $400mn in financing, with investors including the ArcelorMittal XCarb Innovation Fund, Microsoft, Aramco Ventures, IFC and BMW Ventures. The pilot plant is located in Woburn, Massachusetts, and Boston Metals also owns a subsidiary in Brazil for recovering critical metals from mining and metallurgical waste. The company believes it has the potential to cut nearly 10% of the world’s carbon emissions – a bold ambition.

Aluminium processing
In 2018, Alcoa announced a joint venture with Rio Tinto called ELYSIS to develop and commercialise a ‘revolutionary’ aluminium smelting technology that eliminates GHGs but produces oxygen and aluminium using an inert anode. Aluminium electrolysis takes place at a significantly lower temperature than molten salt iron electrolysis.

Montreal-based ELYSIS has just started up a 450 kA designed inert anode cell at the end of the existing potline at the Rio Tinto smelter in Alma, Quebec. This is seen as a ‘defining moment’ in the transition towards large-scale, low-carbon aluminium production, with the first commercial-scale plant after years of R&D.

The company claims that ELYSIS technology has the potential to improve worker safety, reduce costs and enhance productivity. François Perras, President and Chief Executive Officer of ELYSIS says: ‘Today, we’re not just powering a new cell, we’re powering the future of aluminium.’

The process is designed for both newbuild and retrofit in existing aluminium smelters. It eliminates GHG emissions and seven other byproducts including perfluorocarbons (PFCs), carbon monoxide, sulphur dioxide, carbonyl sulphide, nitrogen oxides, polycyclic aromatic hydrocarbons (PAHs) and benzopyrene in the aluminium production process.

The technology features a newly developed proprietary electrode increasing process efficiency and enabling higher productivity, the company claims. While a typical carbon anode is replaced every 25 days, the ELYSIS anodes are expected to last several years without need for replacement. Furthermore, the vertical anode/cathode geometry is said to offer higher productivity for the same surface area. The first batch of metal was purchased by Apple.

ELYSIS technology has also been producing metal at the Alcoa Technical Center near Pittsburgh in the US since 2009. Starting with the new Quebec plant, the plan is to roll-out the process with global licensing agreements.

• Further reading: ‘Better policies and more action – getting steel on the path to net zero’. Rasmus Valanko, Managing Director, Systems Transformation, of the We Mean Business Coalition, calls for action on carbon and the steel production sector.
• ‘New BP and Thyssenkrupp venture to focus on decarbonising steel production’. Discover how the new BP and Thyssenkrupp Steel strategic collaboration aims to help accelerate decarbonisation of the steel industry, promoting policies to support the development of low carbon hydrogen and green steel in Europe.