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Wed Aug 28, 2019, 08:28 PM

Atmospheric Carbon Capture Performance of Legacy Iron and Steel Waste

The paper I will discuss in this post has the same title as this post. It can be found here: Atmospheric Carbon Capture Performance of Legacy Iron and Steel Waste Pullen et al, Environ. Sci. Technol. 2019 53 16 9502-9511)

It is, happily, open sourced. Anyone can read it.

All of the world's steel is made using coke, and all the world's coke, in turn, is made from coal. This is true of steel in buildings, in cars, bridges, and yes, that much hyped form of so called "renewable energy," wind turbine posts.

It's why it's appropriate to put the word "renewable" in quotations, as I almost always do.

If one travels to Bethlehem, PA, one can tour the abandoned steel plant from the historical Bethlehem Steel. It's worthwhile if one is interested in Engineering. Bethlehem Steel collapsed financially in 1995, after producing much of the steel for World War II ships, the Chrysler Building, the Golden Gate Bridge, etc. The town has done a credible job making the abandoned plant into an interesting tourist attraction, featuring among other things, a wonderful summer concert series in front of the hulking massive retorts.

Outside of town are the slag heaps. They are huge. I often wonder if they're toxic, but to my knowledge, they've not been tested.

It appears that some of the carbon dioxide associated with making steel can be sequestered using the slag at least according to this paper.

I won't spend a lot of time excerpting the paper, since it's open to anyone interested, but put in a few teasers:

In 2013, carbon dioxide concentrations in the atmosphere exceeded 400 ppm, a significant increase versus pre-Industrial Revolution levels (280 ppm).(1) This continuing anthropogenic influence has an increasing likelihood of severe, pervasive, and irreversible impacts for people and ecosystems.(2) A Special Report from the Intergovernmental Panel on Climate Change (IPCC) in 2018,(3) along with numerous scientific academies,(4−6) suggests that greenhouse gas removal (GGR) from the atmosphere is needed, coupled with an extensive reduction in greenhouse gas emissions to negate the worst of these effects. The amount of CO2 removal is significant, on the order of 100–1000 billion tons (Gt) of CO2 this century. Various GGR options have been proposed, including directly capturing greenhouse gases from the atmosphere,(7) biomass energy and carbon capture and storage,(8) and mineral carbonation.(9) The latter concept was first proposed in the 1990s(10,11) and mimics natural weathering processes in which calcium or magnesium (Mg) minerals are converted into carbonates.(12) This idea was extended to alkaline iron and steel slags in the following decade,(12−15) which also contain a significant source of Ca and Mg silicates and oxides. The minerals in slags (e.g., larnite, Ca2SiO4, and gehlenite, Ca2Al2SiO7) can react with atmospheric CO2 that has dissolved into solution, the products of which are thermodynamically stable.(11,16,17)





In eqs 1 and 2, captured CO2 is precipitated as solid carbonate minerals (“mineral carbonation”), e.g., calcite, or, if Mg is the cation, hydrated magnesium carbonates.(18) However, if the saturation state with respect to the carbonate mineral is insufficient to induce precipitation, the captured CO2 can be transported to the ocean in the form of dissolved carbonate (CO32–) or, more commonly, bicarbonate (HCO3–) ions (eqs 3 and 4), where it increases ocean alkalinity (“enhanced weathering”).(19)
World steel output exceeded 1600 Mt in 2017.(20) In the EU, steel production released ∼182 Mt of CO2(21) of greenhouse gases,(12,22) which equated to 4–5% of the EU’s total emissions. However, it is estimated that 470–610 Mt of slag was concurrently produced, which could negate some of these CO2 emissions.(23−25) Due to the reactive nature of some slag phases, e.g., larnite,(12) mineral CO2 sequestration is more rapid in slags than in natural silicates, e.g., forsterite (Mg2SiO4); thus, their utilization may incur lower energy consumption and costs.(26)

The authors note that slag apparently naturally only captures about 3% of the carbon it could capture, and propose processes for slag treatment that can raise that figure to values closer to the theoretical values.

In general, I do not favor sequestration because of its high energy intensity and its lack of a return on value, but have written extensively here and elsewhere about carbon capture and utilization.

In any case, it's an interesting little paper, and offers, if nothing else, some insight into the composition of slags.

If interested, enjoy it.

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