Hydration of hemihydrates
Hemihydrate takes place hydration reaction immediately after mixing with water
according to a through-solution route, first the hemihydrate dissolves and then the
dihydrate precipitates from the solution.
CaSO . H O H O CaSO H O 4 2 2 4 2 ⋅ 0 5 +1.5 → ⋅ 2 (1)
The hydration of two hemihydrates (α- and β-), produced from flue gas desulfurization
gypsum, from Knauf Gips KG was investigated. The particle size distribution that was
measured with Mastersizer 2000 is shown in Figure 1. Results show that the mean
particle size of α-hemihydrate is larger than that of β-hemihydrate, which is in line with
/9/ that α-hemihydrate consists of large primary particles while β-hemihydrate forms
flaky, rugged secondary particles with scanning electron micrograph method.