https://newatlas.com/materials/carbon-negative-cement-sand-substitute-seawater-electricity-co2/
Concrete is the most widely used artificial material on the planet – which is a shame, because making it also happens to be one of the most polluting processes. Worse still, at a global scale it requires huge amounts of sand, which is getting harder (financially and environmentally) to mine from coasts, seafloors and riverbeds.
An unassuming new material from Northwestern could help solve both problems. Composed of calcium carbonate and magnesium hydroxide in different ratios, it's pretty simple to make – just take some seawater, zap it with electricity and bubble some CO2 through it.
The whole process is similar to how corals and mollusks build their shells, according to the team.
If you really want to get your thinking cap on, here's how they do it: two electrodes in the tank emit a low electrical current that splits the water molecules into hydrogen gas and hydroxide ions. When CO2 gas is added, the chemical composition of the water changes, increasing levels of bicarbonate ions. These hydroxide and bicarbonate ions react with other natural ions in seawater, producing solid minerals that gather at the electrodes.
The end result is a versatile white material that not only stores carbon, but can stand in for sand or gravel in cement, and also forms a foundational powder for other building materials like plaster and paint.
Intriguingly, the researchers found the material could be tweaked by adjusting the flow rate, timing and duration of the CO2 and seawater, and the voltage and current of the electricity. By tweaking the manufacturing process, the researchers can make the material with different properties for different purposes
"We showed that when we generate these materials, we can fully control their properties, such as the chemical composition, size, shape and porosity," said Alessandro Rotta Loria, lead author of the study. "That gives us some flexibility to develop materials suited to different applications."
This process is far greener than the usual method of making these building materials. Not only does it reduce the need to strip mine huge quantities of sand from the natural environment, but the only gaseous byproduct is hydrogen, which can itself be captured for use as clean fuel. The CO2 used to make the material could even come from emissions from regular cement production, in which case the process could make regular cement greener as a byproduct.
"We could create a circularity where we sequester CO2 right at the source," Rotta Loria said. "And, if the concrete and cement plants are located on shorelines, we could use the ocean right next to them to feed dedicated reactors where CO2 is transformed through clean electricity into materials that can be used for myriad applications in the construction industry. Then, those materials would truly become carbon sinks."
Journal Reference: https://doi.org/10.1002/adsu.202400943
(Score: 5, Interesting) by Barenflimski on Tuesday March 25, @03:34AM (4 children)
All of this sounds great. I'll always root for a solution without repercussions.
I'm not a chemist. How would this affect the pH of the ocean if done on an industrial scale? Lets assume for electricity we're plugged directly into a fusion reactor with zero loss. 100% efficiency from source to point, zero emissions.
(Score: 5, Informative) by Samantha Wright on Tuesday March 25, @05:14AM (1 child)
I don't think the method involves returning anything to the sea when they're done making the sand, but if they did, it would raise the pH, as they're removing hydrogen from the water and leaving behind hydroxides and bicarbonates, which are both protophilic species. Acidity is the presence of surplus hydrogen, and alkalinity is its absence, sometimes generalized to a surplus of negative charges (i.e., electron pairs that are available for binding.)
(Score: 5, Interesting) by Mykl on Tuesday March 25, @10:57AM
So, possibly win-win given that the ocean is becoming slightly more acidic at the moment due to CO2.
(Score: 5, Touché) by Thexalon on Tuesday March 25, @11:12AM (1 child)
There ain't no such thing, of course.
"Think of how stupid the average person is. Then realize half of 'em are stupider than that." - George Carlin
(Score: 4, Interesting) by JoeMerchant on Tuesday March 25, @02:19PM
Agreed, but the repercussions are less than the process it is replacing, so at least that's a kind of forward progress.
There's a lot of "green concrete" development going on, I wonder how much pushback the entrenched concrete interests are generating as opposed to embracing the new methods. The method which can be "slipstreamed" into current processes while improving profits is going to be the one that wins, and this one seems like it might be that in certain areas. I know around Florida sand is becoming a more valuable commodity, at least in those places where it is easily mined and transported - where it is in direct competition with "beach nourishment" projects.
As for industrial scale effects on the oceans - removal of calcium carbonate seems like it may have negative effects on corals, shellfish and other species which use calcium carbonate from the water to build their bodies. On the other hand, the ocean is really big, and complex, and reduction of CO2 in the overall system may be more beneficial to those same species (increasing ocean pH, lowering acidity). Because the ocean is so big, local effects from industrial scale mining of the calcium should dilute fairly quickly, especially where strong currents are nearby.
🌻🌻🌻 [google.com]
(Score: 1, Insightful) by Anonymous Coward on Tuesday March 25, @12:22PM (3 children)
(Score: 3, Interesting) by Sourcery42 on Tuesday March 25, @03:58PM (2 children)
Approximately a metric fuckton of power per ton of sand. Water is a happy molecule. It takes a lot of energy to get it to split apart into its components.
I don't have the data to compare mining and transporting sand to this electrolysis method, but in general, studies like this tend to assume an efficient green grid with a rose-colored glasses mix of wind, solar, and nuclear.
This is a cool way to sequester CO2. I've just seen way too many reports that are very...forward leaning on the abundance of electrical power and its CO2 footprint. There's a whole lot of electrification ideas out there that fit the someday it might be a great idea but today, not so much mold.
I'm not trying to disparage the research. This could be a great tool in the toolbox someday. Maybe it is now for all I know, but I've seen enough to be skeptical.
(Score: 1, Informative) by Anonymous Coward on Tuesday March 25, @04:15PM
Coral, shellfish etc do something like this. They don't do it superfast though: https://www.researchgate.net/figure/Growth-of-giant-clams-Tridacna-crocea-T-derasa-T-maxima-and-T-squamosa-over_fig4_259422585 [researchgate.net]
So that's why I'm curious on how much energy/power. e.g. if you put in 1kW how many mg per second can it make.
(Score: 4, Interesting) by chucky on Tuesday March 25, @08:08PM
Abundance of electricity… maybe we could use this to “waste” excess power from solar/wind. Producing too much? Okay, let’s make some sand.
(Score: 3, Informative) by Covalent on Tuesday March 25, @08:18PM (2 children)
It totally works, with 2 very important asterisks:
1. You have to be careful not to make chlorine at the anode. The paper hand waves this away by saying you can sell the chlorine. That's true, but the chlorine is super toxic, super corrosive, and super reactive. You are FAR better off not making it at all, but that involves fancy anodes.
2. You have to actually provide the electricity to do this. If you do it with fossil fuels...well that's just dumb.
In theory, though, you could design an anode that is durable and oxidizes water to oxygen instead of chloride to chlorine (hard) and then hook it up to a nuclear reactor (also hard) to suck gigatons of carbon out of the air. Actually, for that much you'd need several nuclear power plants. But one step at a time.
You can't rationally argue somebody out of a position they didn't rationally get into.
(Score: 3, Insightful) by gnuman on Tuesday March 25, @10:35PM (1 child)
You'd want to use solar for that actually, as it's the cheapest option.
But the problem is that sand costs like $5/ton. And sand is used as a filler because cement is *expensive*. So, how are we coming up with a cheaper filler involving precipitates from sea water? Yeah, I don't think so. Coal ash is being used to make cinder blocks. But that stuff is *free* or at negative cost as it's generally considered a pollutant. So making your own concrete filler with electricity is a little ... crazy. It's going to cost far more than $5/ton or even $50/ton. And when the filler costs more than the concrete, it's kind of pointless.
https://concretecaptain.com/when-did-cinder-blocks-come-out/ [concretecaptain.com]
(Score: 1) by lars_stefan_axelsson on Wednesday March 26, @07:47AM
And to add insult to injury the most polluting part of concrete production is making the cement. Not mixing it with sand and water.
So while this is cool and all, it doesn't address the elephant in the room which is emissions from cement production. In short that's done by heating limestone (calcium carbonate) to very high temperatures, often using fossil fuels, to scare away the CO2 (adding yet more CO2 emissions). This so you end up with lime (calcium oxide) which is then further processed.
In short, the sand, while often a limited natural resource, is not the main problem when making concrete.
Stefan Axelsson