8 ms·

Yep, exactly! The world needs CaO for cement. We have a carbon neutral process for making it. It's actually overall negative as not all carbonates we extract ar

Yep, exactly! The world needs CaO for cement. We have a carbon neutral process for making it. It's actually overall negative as not all carbonates we extract are usable in cement production. But as far as cement producers are concerned it's carbon neutral.

hwillis 5y ago
why does removing carbonates cause the ocean to absorb more CO2, though? Calcium and magnesium oxide aren't just floating around the ocean waiting to absorb more CO2. Removing salts does not lower oceanic acidity.
- marcuslima 5y ago
  The ocean and the atmosphere exist in an equilibrium there is a 'balance' of relative concentration of CO2. Because CO2 can dissolve in water as CO3 and HCO3 the concentration is skewed to a higher concentration in oceans. When we take out CO2 from the oceans we lower the relative concentration, so we shift it out of balance. So the entire ocean becomes the surface area for re-absorbing CO2 from the atmosphere to re-establish that balance!
  - hwillis 5y ago
    But the re-absorbed CO2 will come from new limestone dissolving into calcium bicarbonate, not from atmospheric CO2. You'll be adding more CO2 to the air -increasing oceanic acidification- while increasing the ocean's ability to dissolve more CaCO3. Far from fighting global warming it sounds like this will put exactly as much CO2 into the atmosphere and double the leaching impact on shellfish and coral. I am shit at chemistry and would really like cement to not release CO2, but I don't understand this.
    - PeterisP 5y ago
      Wait, no, why? As far as I understand the process of limestone dissolving into oceans is the long term (on the scale of millions of years) process and is based on rivers dissolving limestone so would not be affected by the ocean changes; in the short term (days/years/centuries) it would be balanced simply by CO2 exchange between the atmosphere and what's dissolved in the ocean.
      - marcuslima 5y ago
        Yeah absolutely, the CO2 balance comes from re-equilibration with the atmosphere. The rivers replenish calcium content on a longer time scale. But as you point out we're in no danger of running out of calcium in the oceans
    - flyingsilverfin 5y ago
      Same question! As I understand it: CO2 pulled out of the ocean is replenished by atmospheric CO2, because limestone in the ocean dissolves too slowly to make up for the imbalance and it more readily comes in from the air. But if that's true, then the calcium will actually not be replenished quickly in the ocean (not sure what the significance of this is)! If it were true that the calcium is dissolved fast enough to replenish, then there must also be CO2 released from underwater limestone? Which means extracting Ca and CO2 will not remove any atmospheric CO2 really. Alternatively, we do end up extracting Ca from the ocean that is not replenished (there's probably so much we don't care) and rely on the atmospheric CO2 to correct ph balance of the ocean?
deleted 5y ago
[deleted]
brilee 5y ago
A followup question... how do you regenerate the alkaline sorbent? It gets acidified in the process of extracting CaO from the water and needs to be made alkaline again somehow.
- twic 5y ago
  He mentions producing hydrogen as another product, so I would guess they use electricity to turn protons into hydrogen gas, so removing acidity.
froh 5y ago
so there is no more additional burning of limestone needed? instead your process directly produces the lime, CaO? and that then binds the CO2 when curing? to my limited understanding cement production emits CO2 in two ways: by splitting limestone into lime and co2 and by burning carbon based fuels to split the limestone. your method addresses both sources of co2 from cement production? or just one of them?
- tablespoon 5y ago
  > so there is no more additional burning of limestone needed? instead your process directly produces the lime, CaO? and that then binds the CO2 when curing? The OP says they'll make money by selling synthetic limestone ("We make money from selling synthetic limestone to cement producers..."), so I think the CO2 still needs to be burned off of it before the cement is produced. However they say they already (indirectly) pulled that same CO2 out of the air, instead of the ground, so overall the process is carbon neutral.
  - robinsoh 5y ago
    > they say they already (indirectly) pulled that same CO2 out of the air, instead of the ground, so overall the process is carbon neutral. I find that difficult to understand. If the output is CaCO3 that still needs to kilned to make CaO, then CO2 gets emitted. Even if that volume of CO2 was obtained from dissolved CO2 in the ocean, one would have had to expend energy to extract that CO2 from the ocean and that energy would have generated emissions as well. If the output of this is just CaCO3 again, then I fail to see how this is a better solution than carbon capture using a clay geopolymer technique that goes directly to a concrete like structural material. What I mean is, wouldn't it be better to just skip all of this and go focus on rediscovering the technology for "creating" rock like what was possibly achieved at Cuzco (Hatun Rumiyoc) or Pumapunku? Or more realistically in the short term, using fly ash and silica flume or slag to make concrete without requiring CaO?
    - tablespoon 5y ago
      > one would have had to expend energy to extract that CO2 from the ocean and that energy would have generated emissions as well. I suppose they could planning to use renewable energy? > If the output of this is just CaCO3 again, then I fail to see how this is a better solution than carbon capture using a clay geopolymer technique that goes directly to a concrete like structural material. I don't have a horse in this race, but one possibility is that concrete is a better understood material than some novel "concrete like structural material," so it's more acceptable in safety critical situations (e.g. people know how it fails, how to detect failures, how to remediate problems, etc.).
robinsoh 5y ago
I'm probably missing something obvious. > The world needs CaO for cement. We have a carbon neutral process for making it vs > We make synthetic limestone using atmospheric CO2, such that when it is used to make cement, the process is carbon neutral. Do you make CaO or CaCO3?
- marcuslima 5y ago
  We make CaCO3, I mention CaO here because that's what cement producers ultimately need. They heat up limestone (CaCO3) to make CaO
  - coryrc 5y ago
    Is there a reason not to make quicklime instead of limestone?
m12k 5y ago
A way to help explain this to people is that it's the equivalent of rapidly growing trees and burning those for fuel instead of burning fossil fuels. You do the same with limestone, rapidly creating it by capturing atmospheric CO2 (indirectly, via the ocean) so it can then be burned in cement production instead of the naturally occurring kind. In both cases, CO2 is released into the air at the end when the product is burned, but because the released CO2 had just now been sucked out of the air anyway (instead of having previously been sequestered in natural limestone) you're not adding to the total amount of CO2 in circulation in the system, making the process neutral.
- _nalply 5y ago
  Additionally governments could buy limestone and not use it. Carbon sequestration. The money could come from a CO2-tax. I really hope this is scalable worldwide.

hwillis 5y ago

why does removing carbonates cause the ocean to absorb more CO2, though? Calcium and magnesium oxide aren't just floating around the ocean waiting to absorb more CO2. Removing salts does not lower oceanic acidity.

marcuslima 5y ago
The ocean and the atmosphere exist in an equilibrium there is a 'balance' of relative concentration of CO2. Because CO2 can dissolve in water as CO3 and HCO3 the concentration is skewed to a higher concentration in oceans. When we take out CO2 from the oceans we lower the relative concentration, so we shift it out of balance. So the entire ocean becomes the surface area for re-absorbing CO2 from the atmosphere to re-establish that balance!
- hwillis 5y ago
  But the re-absorbed CO2 will come from new limestone dissolving into calcium bicarbonate, not from atmospheric CO2. You'll be adding more CO2 to the air -increasing oceanic acidification- while increasing the ocean's ability to dissolve more CaCO3. Far from fighting global warming it sounds like this will put exactly as much CO2 into the atmosphere and double the leaching impact on shellfish and coral. I am shit at chemistry and would really like cement to not release CO2, but I don't understand this.
  - PeterisP 5y ago
    Wait, no, why? As far as I understand the process of limestone dissolving into oceans is the long term (on the scale of millions of years) process and is based on rivers dissolving limestone so would not be affected by the ocean changes; in the short term (days/years/centuries) it would be balanced simply by CO2 exchange between the atmosphere and what's dissolved in the ocean.
    - marcuslima 5y ago
      Yeah absolutely, the CO2 balance comes from re-equilibration with the atmosphere. The rivers replenish calcium content on a longer time scale. But as you point out we're in no danger of running out of calcium in the oceans
  - flyingsilverfin 5y ago
    Same question! As I understand it: CO2 pulled out of the ocean is replenished by atmospheric CO2, because limestone in the ocean dissolves too slowly to make up for the imbalance and it more readily comes in from the air. But if that's true, then the calcium will actually not be replenished quickly in the ocean (not sure what the significance of this is)! If it were true that the calcium is dissolved fast enough to replenish, then there must also be CO2 released from underwater limestone? Which means extracting Ca and CO2 will not remove any atmospheric CO2 really. Alternatively, we do end up extracting Ca from the ocean that is not replenished (there's probably so much we don't care) and rely on the atmospheric CO2 to correct ph balance of the ocean?

deleted 5y ago

[deleted]

brilee 5y ago

A followup question... how do you regenerate the alkaline sorbent? It gets acidified in the process of extracting CaO from the water and needs to be made alkaline again somehow.

twic 5y ago
He mentions producing hydrogen as another product, so I would guess they use electricity to turn protons into hydrogen gas, so removing acidity.

froh 5y ago

so there is no more additional burning of limestone needed? instead your process directly produces the lime, CaO? and that then binds the CO2 when curing? to my limited understanding cement production emits CO2 in two ways: by splitting limestone into lime and co2 and by burning carbon based fuels to split the limestone. your method addresses both sources of co2 from cement production? or just one of them?

tablespoon 5y ago
> so there is no more additional burning of limestone needed? instead your process directly produces the lime, CaO? and that then binds the CO2 when curing? The OP says they'll make money by selling synthetic limestone ("We make money from selling synthetic limestone to cement producers..."), so I think the CO2 still needs to be burned off of it before the cement is produced. However they say they already (indirectly) pulled that same CO2 out of the air, instead of the ground, so overall the process is carbon neutral.
- robinsoh 5y ago
  > they say they already (indirectly) pulled that same CO2 out of the air, instead of the ground, so overall the process is carbon neutral. I find that difficult to understand. If the output is CaCO3 that still needs to kilned to make CaO, then CO2 gets emitted. Even if that volume of CO2 was obtained from dissolved CO2 in the ocean, one would have had to expend energy to extract that CO2 from the ocean and that energy would have generated emissions as well. If the output of this is just CaCO3 again, then I fail to see how this is a better solution than carbon capture using a clay geopolymer technique that goes directly to a concrete like structural material. What I mean is, wouldn't it be better to just skip all of this and go focus on rediscovering the technology for "creating" rock like what was possibly achieved at Cuzco (Hatun Rumiyoc) or Pumapunku? Or more realistically in the short term, using fly ash and silica flume or slag to make concrete without requiring CaO?
  - tablespoon 5y ago
    > one would have had to expend energy to extract that CO2 from the ocean and that energy would have generated emissions as well. I suppose they could planning to use renewable energy? > If the output of this is just CaCO3 again, then I fail to see how this is a better solution than carbon capture using a clay geopolymer technique that goes directly to a concrete like structural material. I don't have a horse in this race, but one possibility is that concrete is a better understood material than some novel "concrete like structural material," so it's more acceptable in safety critical situations (e.g. people know how it fails, how to detect failures, how to remediate problems, etc.).

robinsoh 5y ago

I'm probably missing something obvious. > The world needs CaO for cement. We have a carbon neutral process for making it vs > We make synthetic limestone using atmospheric CO2, such that when it is used to make cement, the process is carbon neutral. Do you make CaO or CaCO3?

marcuslima 5y ago
We make CaCO3, I mention CaO here because that's what cement producers ultimately need. They heat up limestone (CaCO3) to make CaO
- coryrc 5y ago
  Is there a reason not to make quicklime instead of limestone?

m12k 5y ago

A way to help explain this to people is that it's the equivalent of rapidly growing trees and burning those for fuel instead of burning fossil fuels. You do the same with limestone, rapidly creating it by capturing atmospheric CO2 (indirectly, via the ocean) so it can then be burned in cement production instead of the naturally occurring kind. In both cases, CO2 is released into the air at the end when the product is burned, but because the released CO2 had just now been sucked out of the air anyway (instead of having previously been sequestered in natural limestone) you're not adding to the total amount of CO2 in circulation in the system, making the process neutral.

_nalply 5y ago
Additionally governments could buy limestone and not use it. Carbon sequestration. The money could come from a CO2-tax. I really hope this is scalable worldwide.