Process for the production of calcium hydrogen phosphate dihydrate and/or anhydrous calcium hydrogen phosphate

摘要

Phosphoric acid, a water-soluble calcium salt and ammonia are brought into reaction, from the obtained suspension a precipitate is separated, which precipitate is processed into the product. Ammonia and a water-soluble calcium salt solution is recovered from the remaining solution by means of calcium oxide or calcium hydroxide, which ammonia and water-soluble calcium salt solution can be partly or totally returned into the process. A waste calcium chloride solution, which solution issues in the production of soda by the Solvay process, can be employed, either directly or after having been concentrated, as a water-soluble calcium salt, it being economical to interconnect a plant for manufacturing calcium hydrogen phosphate with a plant for manufacturing soda. Instead of starting from a water-soluble calcium salt and ammonia, one can also start from an ammoniacal calcium salt solution formed by the reaction of calcium oxide or calcium hydroxide with an ammonium salt solution. A part or the whole of the phosphoric acid and a part or the whole of the ammonia can be replaced by ammonium hydrogen phosphate and/or ammonium dihydrogen phosphate. In order to slow down the dehydration of the calcium hydrogen phosphate dihydrate and the hydrolysis of the anhydrous calcium hydrogen phosphate, it is useful to add stabilizers during the manufacture.