[OH-].[Ca+2:2].[OH-].[NH3:4].C(=O)=O.O.C(=O)=O.[C:12](=[O:15])([O-:14])[O-:13].[NH4+].[NH4+].[S:18]([O-:22])([O-:21])(=[O:20])=[O:19].[Ca+2]>>[C:12](=[O:13])([O-:15])[O-:14].[Ca+2:2].[S:18]([O-:22])([O-:21])(=[O:20])=[O:19].[NH4+:4].[NH4+:4]The existing technology for preparation of nano calcium carbonate is bubbling carbon dioxide into a calcium hydroxide slurry to obtain nano calcium carbonate, while the present invention is injecting carbon dioxide into a calcium sulfate slurry containing ammonia to obtain nano calcium carbonate with byproduct ammonium sulfate. The principle of the present invention is as follows: due to the calcium hydroxide is more alkaline than ammonia, the reaction formula (1) cannot be carried out; instead, according to the reaction formula (2) and (3), the carbon dioxide is firstly reacted with ammonia to generate ammonium carbonate, and then ammonium carbonate and calcium sulfate react to get calcium carbonate and ammonium sulphate. The nano calcium carbonate can be obtained by controlling the speed of the formation of calcium carbonate. CaSO4+2NH3+2H2O→(NH4)2SO4+Ca(OH)2 (1) 2NH3+CO2+H2O→(NH4)2CO3 (2) (NH4)2CO3+CaSO4→(NH4)2SO4+CaCO3 (3)
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