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posted by janrinok on Wednesday February 07, @08:25AM   Printer-friendly

https://www.science.org/content/article/electrifying-new-ironmaking-method-could-slash-carbon-emissions

By extracting metallic iron without producing carbon dioxide, the new process could even be carbon negative, at least for part of the world's iron production

Making iron, the main ingredient of steel, takes a toll on Earth's delicate atmosphere, producing 8% of all global greenhouse gas emissions. Now, a team of chemists has come up with a way to make the business much more eco-friendly. By using electricity to convert iron ore and salt water into metallic iron and other industrially useful chemicals, researchers report today in Joule that their approach is cost effective, works well with electricity provided by wind and solar farms, and could even be carbon negative, consuming more carbon dioxide (CO2) than it produces.

"It's a very clever approach," says Karthish Manthiram, a chemical engineer at the California Institute of Technology who was not involved with the study. He notes that the process has other advantages, including working at a low temperature, and being amenable to working with intermittent renewable electricity. "It checks all the boxes."

Iron is one of the most abundant elements on Earth, but in its natural state is bound to oxygen in the various minerals that make up iron ore. To extract metallic iron from this ore, workers typically mix it with a high-carbon form of coal called coke and heat the combination to about 1500°C in a blast furnace. At that temperature, the carbon atoms strip the oxygen atoms from the iron, producing CO2 that wafts into the atmosphere and leaves behind the molten metal. Steelmakers then combine this iron with a small amount of carbon and other trace metals to forge steel.

Although this way to make iron and steel is cheap and time tested, it produces significant amounts of CO2. The world mines 2.5 billion tons of iron every year, and reducing it to iron emits as much CO2 as the tailpipes of all passenger vehicles combined. So, scientists are looking for economically viable ways to produce metallic iron that don't generate greenhouse gases.

To that end, Paul Kempler, a chemical engineer at the University of Oregon, and colleagues wondered whether an industrial process for making chlorine from saltwater could be repurposed for ironmaking. In this "chlor-alkali" process, water containing sodium-chloride is placed in an electrochemical cell resembling a battery that contains two electrodes submerged in a liquid electrolyte. The positively charged electrode, the anode, pulls electrons from chloride ions, causing chlorine atoms to pair up into chlorine gas. At the same time, electrons flowing in from the cathode split water molecules into pieces that pair with the sodium ions and one another to make sodium hydroxide and hydrogen gas.

To tweak the setup to purify iron, Kempler's team added iron oxide particles to its cathode. Now, the electrons sent to it would also release the oxygen atoms from iron oxide and again form sodium hydroxide—as well as leave behind solid metallic iron. The process is highly efficient, the researchers claim. In fact, they estimate that selling the chlorine and some of the sodium hydroxide at current market prices should enable the overall process to produce iron at roughly the same price as making it in blast furnaces. And because sodium hydroxide can bind CO2 and convert it into carbon-based minerals, the process could be used to help capture CO2, making it carbon negative.


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  • (Score: 3, Insightful) by khallow on Wednesday February 07, @01:48PM (8 children)

    by khallow (3766) Subscriber Badge on Wednesday February 07, @01:48PM (#1343508) Journal
    I think the bit about being a water-based reaction is particularly interesting. That means far lower operating temperatures (even if the water is kept as water by very high pressure) and backs their assertion that the reaction can be turned on and off to match variable power sources like wind power.

    Also sodium hydroxide has some utility as a carbon-trapping mechanism and chlorine can be similarly used in PVC plastic (from memory, I don't have time to look for links). So there's some additional potential for trapping CO2.
    • (Score: 0) by Anonymous Coward on Wednesday February 07, @03:59PM (2 children)

      by Anonymous Coward on Wednesday February 07, @03:59PM (#1343520)
      Where's the part that says it's kept as water by very high pressure? Or is that just some random stuff you added?
      • (Score: 3, Insightful) by Anonymous Coward on Wednesday February 07, @05:37PM

        by Anonymous Coward on Wednesday February 07, @05:37PM (#1343530)

        I don't defend khallow very often, but in this case it is chemistry 101 to suggest higher temperatures to increase a reaction rate. The simple way to raise boiling point of water is to put it under pressure (like the coolant in most IC car engines, which is ~half water).

      • (Score: 1) by khallow on Thursday February 08, @02:08AM

        by khallow (3766) Subscriber Badge on Thursday February 08, @02:08AM (#1343567) Journal

        Where's the part that says it's kept as water by very high pressure? Or is that just some random stuff you added?

        As the AC replier noted, higher temperature means faster reaction. High pressure is relevant when one side of the reaction has much lower volume than the other side - high pressure biases towards the lower volume state. Here, I think that works against the scheme unless there's some way to remove the high volume chlorine (and hydrogen gas maybe?) produced. You get some reduction in volume from the iron ore turning into iron and water. Rust is notorious as being significantly higher volume than iron and steel. It causes expansion of corroding rebar in concrete for example.

    • (Score: 2) by JoeMerchant on Wednesday February 07, @05:46PM (3 children)

      by JoeMerchant (3937) on Wednesday February 07, @05:46PM (#1343531)

      Certainly the C in PVC stands for chloride. Meanwhile: https://phys.org/news/2023-12-pvc.html [phys.org]

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      • (Score: 1) by khallow on Thursday February 08, @12:55AM (2 children)

        by khallow (3766) Subscriber Badge on Thursday February 08, @12:55AM (#1343564) Journal
        I guess the war on chlorine continues. IMHO, if exposure to vinyl chloride is a problem (note that the exposure examples they give in the article are extreme and not at all indicative of dosage from use in PVC water lines) then reduce exposure to vinyl chloride. Don't ban vital products just because some of their supply chain is moderately dangerous.
        • (Score: 2) by JoeMerchant on Thursday February 08, @02:33AM (1 child)

          by JoeMerchant (3937) on Thursday February 08, @02:33AM (#1343570)

          There is a particular spot on I95 which has the smell of melted/burning PVC every workday as I passed on my commute. The closest building is over 100 yards away across a service road and the various spaces and parking lot between. That is one of no doubt thousands of operations where overexposure (for the people who spend 40+ hours a week in that cloud) is a problem. Not a dying this year problem, more of an expensive healthcare for decades to come problem.

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          • (Score: 1) by khallow on Thursday February 08, @02:47AM

            by khallow (3766) Subscriber Badge on Thursday February 08, @02:47AM (#1343571) Journal

            There is a particular spot on I95 which has the smell of melted/burning PVC every workday as I passed on my commute. The closest building is over 100 yards away across a service road and the various spaces and parking lot between. That is one of no doubt thousands of operations where overexposure (for the people who spend 40+ hours a week in that cloud) is a problem.

            Sounds like you ought to hold your breath when you drive through there. I take it the war on chlorine goes poorly?

    • (Score: 2, Interesting) by khallow on Thursday February 08, @01:23AM

      by khallow (3766) Subscriber Badge on Thursday February 08, @01:23AM (#1343566) Journal

      Also sodium hydroxide has some utility as a carbon-trapping mechanism and chlorine can be similarly used in PVC plastic (from memory, I don't have time to look for links). So there's some additional potential for trapping CO2.

      BTW, the source [soylentnews.org] for closely related discussion.

      [Covalent:] I analyzed the possibility of using solar power to electrolyze ocean water. The by-products are aqueous calcium hydroxide and chlorine gas. You collect the chlorine gas and sell it to offset part of the cost (or use it to chlorinate city water or water from your desalination plant...it was an involved project!)

      The aqueous calcium hydroxide absorbs CO2 from either the water or the air, producing insoluble calcium hydrogen carbonate, which sinks to the bottom of the ocean. This is essentially artificial seashells. This also has the desirable side effect of raising the pH of the ocean, which is currently being acidified by so much CO2.

      You can do a similar thing with the sodium hydroxide generated by this process though it's soluble in water and would have to be put somewhere else unless you're interested in altering ocean PH to make it less acidic.

  • (Score: 2) by darkfeline on Friday February 09, @10:57AM

    by darkfeline (1030) on Friday February 09, @10:57AM (#1343701) Homepage

    They aren't making iron. They're smelting it, or alternatively refining or extracting it. We have a lot of iron, so there's no need to make more of it, although breakthroughs in nuclear fusion are welcome.

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