Hello,

it's not quite easy to answer, but it's definitely an interesting problem. I must first state that the solubility of CaCO3 is low, but only in pure water. In an environment with the presence of CO2, the amount of CaCO3 dissolved is definitely not negligible and increases with increasing pCO2. Lowering pH has the same effect. Everything can be calculated.

In bacterial culture, it will be difficult. Bacteria can produce acidifying agents as well as intentionally modify the carbonate balance to obtain carbon, most likely as HCO3-. However, the dissolution of CaCO3 in a closed system must be limited as there will be an accumulation of products, ie Ca2 + or organic salts with Ca2 +.

In the past, various volumetric analysis methods have been used to determine CO2 or CaCO3. The volume or pressure of CO2 produced was determined. The question is whether the bacteria can do without the open atmosphere. It would also be interesting to monitor changes in pH or its differences compared to a purely inorganic system.

Some reading for inspiration:

Article Microbial dissolution of calcite at T=28°C and ambient pCO2

I think, by calculating the carbon dioxide emitted as a result of adding hydrochloric acid when using the calcimeter device, this method is used to calculate the percentage of calcium carbonate in the soil.

There is another issue concerning this question regarding the CaCO3 polymorph that you are trying to dissolve. There is a significant difference between the dissolution rate of calcite and aragonite, which are the most commom type of CaCO3. I would suggest you to first perform a x-ray diffraction analysis in your CaCO3 material in order to understand what is the polymorph that you are working with. I agree with Dalibor, there is not a easy way to do it since you will have to deal with many variables, especially if you do it in a close environment.

You might also measure the Ca in solution, and with some luck the ratios of the stable Ca isotopes may provide a clue.