My phosphogypsum research notes. Part 6

Dissolving of calcium carbonate is going according to equation
CaCO3 + 2NH4NO3 --> Ca(NO3)2 + 2NH3 + CO2 + H2O
During the dissolution Ca ions accumulate in the solution and they stall the reaction.

Gases NH3 and CO2 should go to react with gypsum. And Ca ion concentration affects both reactions. Gypsum solution will have low Ca ion concentration and might not absorb NH3 and CO2. If it is not possible, then another idea might be possible.

The idea is to purify CaCO3. The process can be described:
1. Dissolve impure CaCO3
CaCO3(impure) + 2NH4NO3 --> Ca(NO3)2 + 2NH3 + CO2 + H2O
2. Precipitate pure CaCO3
Ca(NO3)2 + 2NH3 + CO2 + H2O --> CaCO3(pure) + 2NH4NO3

So, the reuse of phosphogypsum can be to process it into pure (NH4)2SO4 and pure CaCO3 instead of pure gypsum. This process will consume NH3 and CO2 or (NH4)2CO3. This means additional logistics costs.
Pure (NH4)2SO4 can be precipitated from mother liquor by adding (NH4)2CO3. I checked and it works.

But if we have pure ammonium sulfate and pure calcium carbonate can we obtain pure gypsum? Yes, it is possible by reaction
CaCO3 + (NH4)2SO4 --> CaSO4 + 2NH3 + CO2 + H2O
In this case extra logistics will be avoided.
The reaction is slow and a catalyst should be used, e.g. ammonium acetate.