Sulfate Ion → Calcium Sulfate, Hemihydrate

Reaction equation

[S:1](=[O:5])(=[O:4])([OH:3])[OH:2].[S:6]([O-:10])([O-:9])(=[O:8])=[O:7].[Ca:11].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O.[F-].[Ca+2].[Ca+2].[Ca+2].[Ca+2].[Ca+2]>>[OH2:2].[S:6]([O-:10])([O-:9])(=[O:8])=[O:7].[Ca+2:11].[Ca+2:11].[S:1]([O-:5])([O-:4])(=[O:3])=[O:2]

Participants

Reactant 4

HCID 1117Sulfate Ion3×

HCID 1118Sulfuric Acid

HCID 5460341Calcium

HCID 10207414Fluorapatite (Ca5F(PO4)3)

Product 1

HCID 3033839Calcium Sulfate, Hemihydrate

Procedure

Sulfuric acid is added in amounts such that the sulfate content of the added acid and the sulfate content of the added rock is equivalent to about 90% to about 100% (more preferred 93-99.5%) of the stoichiometric amount of sulfate required to react with calcium added in the phosphate rock to form calcium sulfate hemihydrate.