US 7,101,522 B2Granted

Production of dicalcium phosphate or monocalcium phosphate

OwnerJan Christoffel De Waalinventor

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Abstract

A process is provided for the production of dicalcium phosphate form a phosphate source material in which a solution of phosphoric acid is produced by the action of a suitable mineral acid, generally sulphuric acid, on a phosphate source material. Calcium fluoride is precipitated at a pH of between 3.5 and 4.5 followed by hydrolyzing the solution by diluting it with water to a ratio of approximately 1:7 to about 1:10 monocalcium phosphate to water at a temperature of approximately 40 degrees Centigrade to form a primary precipitate containing substantially all of the fluoride present as CaF2 together with some dicalcium phosphate and a primary calcium and phosphate containing solution. The primary precipitate is dissolved, the pH adjusted to form 3.5 to 4.5 and the hydrolyzation repeated to form a secondary precipitate containing substantially all of the fluoride present as CaF2 together with some dicalcium phosphate and a secondary calcium and phosphate containing solution. The secondary precipitate can optionally, if required, by again processed in the same way to recover more phosphates. The product dicalcium phosphate is recovered from the combined calcium and phosphate containing solutions.

Claims12

Dependent claims

A process for the production of dicalcium phosphate from a phosphate source material comprising the steps of:

(a) preparing a solution of phosphoric acid by the action of a suitable mineral acid on a phosphate source material;
(b) optionally separating the solution from residual solid materials;
and
(c) treating the solution with suitable alkaline, calcium material to adjust the pH of the solution to between 3.0 and 4.5;
(d) hydrolyzing the solution by diluting it with water to a ratio of approximately 1:7 to about 1:10 monocalcium phosphate to water to form a primary precipitate containing substantially all of the fluoride present as CaF2 together with some dicalcium phosphate and a primary calcium and phosphate containing solution;
(e) separating the primary precipitate formed in step (d) from the primary calcium and phosphate containing solution;
(f) dissolving the primary precipitate with phosphoric acid and repeating steps (c), (d) and (e) containing substantially all of the fluoride present as CaF2 together with some dicalcium phosphate and a secondary calcium and phosphate containing solution;
(g) optionally repeating step (f) one or more times to produce a tertiary, quaternary, etc. precipitate and tertiary, quaternary, etc. calcium and phosphate containing solution;
(h) combining the calcium and phosphate containing solutions and adjusting their pH to above about 5.5 to precipitate dicalcium phosphate;
and
(i) recovering the product dicalcium phosphate.

8 more elements

Dependencies are inferred from the claim text.