Producing iron from salt water and iron oxide

The iron and steel industry creates 7% of global carbon dioxide emissions, as much as all the world’s passenger vehicles, according to the International Energy Agency. A new low-temperature electrochemical process that produces metallic iron from iron oxide and saltwater could help clean up steelmaking’s act (Joule 2024, DOI: 10.1016/j.joule.2024.01.001).

Extracting iron from iron oxide ores—one of the first steps in steelmaking—typically involves roasting a mixture of the crushed ore and coke in a blast furnace at temperatures of up to 1,200 °C. Both the burning of coal to heat the furnace and the reactions that strip oxygen from ore produce CO₂.

Paul Kempler, a chemical engineer at the University of Oregon who developed the new low-temperature method, says the method could be driven by renewable electricity and use purified seawater as a source of salt. The by-products of the process, sodium hydroxide and chlorine gas, are also marketable, he says. “This is a scalable and cost-effective way to make iron without creating CO₂ emissions.”

The so-called chlor-iron process combines two known electrochemical methods. One reduces iron oxide into iron in a sodium hydroxide electrolyte. The other is the well-known chlor-alkali process, in which sodium chloride solution is electrolyzed to yield chlorine gas and NaOH.

The team made a Rubik’s cube–size reactor using the same readily available electrode materials and membranes employed in the chlor-alkali industry. The researchers added iron oxide powder to the cathode and aqueous sodium chloride solution at the anode. When they applied a voltage across the electrodes, sodium chloride got oxidized at the anode to create chlorine gas. Sodium ions passed through the membrane to the cathode, where they reacted with iron oxide, producing NaOH and high-purity metallic iron. The iron got plated on a copper collector as a solid film.

Electrolytic methods are important for reducing greenhouse gas emissions in iron production, says Rohan Akolkar, a chemical engineer at Case Western Reserve University. This novel approach “integrates efficient iron plating with the generation of value-added coproducts towards a process with tangible cost benefits.”