[LeifCarrotson]

I understand that calcium salts and bicarbonate ions are common in the ocean, and are increasingly common as the oceans become more acidic, but have no idea how common that is.

How much seawater do you need to get one kg of CaCO3 precipitate?

[marcuslima]

We're actually working on figuring this out. Our current calculations assume we need to process a huge amount of seawater (11,000 tonnes per tonne of CO2), if the CO2 is the limiting factor (2000 umol). However our R&D suggests undersaturated seawater re-absorbs CO2 from the air surprisingly quickly. Might be able to get this 10x lower

[ephbit]

Wow .. 11,000 tonnes of seawater per tonne of CO2 is indeed huge.

Assuming that the new process stochiometrically generates CaO according to the amount of CO2 taken up from the ocean you'd produce 1.27 tonnes of CaO per tonne of CO2. (molar masses of CO2 and CaO: 44 g/Mol and 56 g/Mol)

Cementa website states [1] an annual output of 2.7 million tonnes of cement.

So in order to produce what is only a portion of Sweden's (a comparatively small country) annual demand for cement, Heimdal's process would require processing of ~ 23 billion tonnes of seawater.

That's 23 billion cubic metres or 23 cubic kilometres per year or ~ 730 litres of seawater per second.

[1]: https://www.cementa.se/en/about-cementa

[liketochill]

.73 m^3/s of seawater is only a pipe of 1m diameter with water traveling at 1 m/s. Not that big a pipe in the grand scheme of things!

[ephbit]

True. Not that big.

But let's not forget that it's not about merely pumping the water around. All this water must be processed. And I figure the process is a little more involved than simple reverse osmosis for seawater desalination.

In the desalination business 1 m diameter pipes with water traveling at 1 m/s and the resulting volumetric flow rate isn't a big thing .. but I'd guess for more complex processes it indicates huge/expensive apparatuses.

[twic]

Is it surprising? Carbon dioxide equilibrates between salty water and air fast enough to keep every single terrestrial animal on the planet alive, after all.