Abstract: The invention relates to the production of calcium compounds containing water of crystallization by means of a chemical reaction between an aqueous alkaline sodium aluminate solution and solid or dissolved or suspended calcium (hydr)-oxide in the presence of carbon dioxide or carbonate; and to the use of these compounds. The resulting precipitate is separated by sedimentation, dehydration, drying and/or clacination and/or grinding or suspending the resulting filter cake and reacted with at least one mineral acid and/or at least one salt of the same. The resulting precipitate, which contains water of crystallization, is separated by sedimentation, dehydration, drying and/or grinding.