Phosphoric Acid → Calcium Sulfate, Hemihydrate
Reaction equation
P(=O)(O)(O)[OH:2].[S:6](=[O:10])(=[O:9])([OH:8])[OH:7].[S].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O.[F-].[Ca+2:28].[Ca+2].[Ca+2].[Ca+2].[Ca+2]>>[OH2:2].[S:6]([O-:10])([O-:9])(=[O:8])=[O:7].[Ca+2:28].[Ca+2:28].[S:6]([O-:10])([O-:9])(=[O:8])=[O:7]Participants
Procedure
Also, the present inventors have previously proposed in Japanese Patent Sho 45-10408 (U.S. Pat. No. 3,653,826) a process for the filtration and hydration of the hemihydrate in which calcium sulfate hemihydrate is formed during a digestion step and filtered off, then calcium sulfate dihydrate of good quality is obtained by hydration during a hydration step and, finally, highly concentrated phosphoric acid is recovered. In this process, easily filterable agglomerate crystals of calcium sulfate hemihydrate can be obtained in the following manner: Phosphate rock is digested under specified conditions, i.e., it is first mixed with phosphoric acid, and then sulfuric acid is added into the mixture, whereby 70-80% of the CaO existing in the phosphate rock combines with sulfur to form calcium sulfate hemihydrate and the other 20-30% of the CaO is transformed into calcium dihydrogen phosphate [Ca(H2PO4)2 ]. Then more sulfuric acid is added to the mixture, in order to turn the calcium phosphate into calcium sulfate hemihydrate and phosphoric acid under conditions such that 2-3% of free sulfuric acid will be present in the reaction vessel. The present inventors found that agglomerate crystals of calcium sulfate hemihydrate having good filtrability can be obtained by recycling a part of the slurry formed into a digestion system. Thus, a method using hemihydrate filtration and hydration has become industrially practical.
Sources & evidence
- ORD record
- ord-3b6a9588ecd5423fafc4076c12c0c938
- Source dataset
- uspto-grants-1978_07
- Patent number
- US04101638
Reaction notes
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