What solution could I add to a solution of water with dissolved carbon dioxide in order to get the carbon to precipitate out? I believe the ions are H+ and HCO3-

Thanks, Jerid

  • 2
    $\begingroup$ There is no solution that is a solution, but, for example, magnesium metal will burn in carbon dioxide gas and produce carbon particles and magnesium oxide. Totally impractical energetically as a way to get the carbon back from carbon dioxide. $\endgroup$
    – Ed V
    Feb 16 '20 at 2:12
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    $\begingroup$ do you want to precipitate out the carbonate ions or do you actually want to obtain elemental carbon? $\endgroup$
    – Francis L.
    Feb 16 '20 at 2:16
  • $\begingroup$ Thank you for the replies. I am not trying to obtain the elemental carbon. I have a process where I have a high concentration of CO2 in a gas sample. The sample also contains 95% Nitrogen and a small amount of oxygen. I am able to extract the CO2 by dissolving the gas through water. This leaves the original gas with a much lower CO2 concentration which is the goal. I am trying to figure a way to get the CO2 out of the water without it returning to a gas state which I am doing now with electrolysis but it is not the ideal setup for this application. $\endgroup$ Feb 16 '20 at 3:16
  • $\begingroup$ I think you must explain your needs in more detail for a reasonable answer. Is this a batch process in a lab, or is it supposed to be a continuous process on an industrial scale? What sort of flow rate of the gas? What is the starting concentration of CO2 and what would be an acceptable final concentration of CO2 in the gas? Is this supposed to be economical somehow? Is humidity change of gas a problem? Do you really need to ppt the CO2 somehow, or just trap the CO2 in the solution? $\endgroup$
    – MaxW
    Feb 16 '20 at 10:52
  • $\begingroup$ You might also consider scrubbing the CO2 straight from the gas. There are many commercial CO2 scrubbers that work by flowing the gas over solid NaOH. That seems more efficient than going into solution and out again. $\endgroup$
    – Andrew
    Feb 16 '20 at 13:10

Adding aqueous Ca(OCl)2 to CO2/H2O will create a precipitate of CaCO3 and Hypochlorous acid (HOCl).

$\ce{Ca(OCl)2 + CO2 + H2O -> CaCO3 (s) + 2 HOCl}$


The dissolved calcium hypochlorite reacts with the free carbonic acid and half bound carbonic acid in the water and there is formed calcium carbonate, and at the same time free oxychlorid, which is known technically as hypochlorous acid.

  • $\begingroup$ Adding Ca(OCl)2 may no be the best idea, because this compound is not pure. It contains also a lot of CaCl2. $\endgroup$
    – Maurice
    Feb 16 '20 at 10:34
  • $\begingroup$ The question is 'what solution' and not what pure chemical compound. Here the presence of some dissolved CaCl2, as well, is not relevant. $\endgroup$
    – AJKOER
    Feb 16 '20 at 23:42

I would rather add chalk water, which is a solution of $Ca(OH)_2$. At least it will not create a new substance dissolved in water, because the reaction will be : $$Ca(OH)_2 + CO_2 -> CaCO_3 + H_2O$$ and $CaCO_3$ is an insoluble substance.

  • 2
    $\begingroup$ Of course it depends on how much $\ce{CO2}$ must be ppt'ed per liter of solution. $\ce{Ca(OH)2}$ isn't greatly soluble. $\endgroup$
    – MaxW
    Feb 16 '20 at 10:43

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