Studies on the Hydration of Natural Anhydrite

Abstract

The results of these are summarized as follows: It was understood to be difficult to hydrate the natural anhydrite (CaSO₄) and to get good crystals of hydrated gypsum (CaSO⋅2H₂O), than getting the gypsum from some byproduct anhydrite.
But, the good crystalized gypsum can be easily obtained by the recrystalization of the natural anhydrite with continuous stir in some solutions of NaCl, NaCl and K-alum, (NH₄)₂SO₄, NH₄NO₃ or NaNO₃. Especially, 15% solution of NH₄NO₃ was so effective that perfect hydrated granular gypsum was obtained by only 24, 36 horus reaction in this solution at room temperature.
The effects of concentration of solution, fineness of anhydrite, reaction temperatures and some effects of organic salts on these reactions were also discussed.
The plaster of paris made of the hydrated gypsum was found to have very good properties.