Process for the manufacture of dicalcium phosphate

• Main Authors: RODIS FRANZ, CREMER JOSEPH
• Format: Patent
• Language: English
• Published: 21.11.1967
• Subjects: CHEMISTRY; COMPOUNDS THEREOF; FERTILISERS; INORGANIC CHEMISTRY; MANUFACTURE THEREOF; METALLURGY; NON-METALLIC ELEMENTS; PHOSPHATIC FERTILISERS

Dicalcium phosphate, CaHPO4, is produced by causing a primary and/or a secondary alkali metal phosphate and/or ammonium phosphate as hydrate or in water solution to react with gypsum, whilst being mixed and comminuted, the other product being ammonia or an alkali metal sulphate. The starting materials may contain impurities, e.g. an alkali metal sulphate, (NH4)2SO4, NaNO3 or KCl, provided these remain in solution on completion of the reaction. A suitable phosphate starting material is produced by interaction of a phosphate rock, a salt of a mineral acid, e.g. KCl, and another mineral acid, which is less volatile than the first, e.g. H2SO4, in about stoichiometric proportions, in a finely divided form, the resulting mass being heated to a temperature not greater than 1200 DEG C., e.g. 200 DEG C., and the soluble phosphate extracted and possibly recovered by evaporation. Gypsum may also be produced in this process and after part of it has been removed the resulting mixture may be used in the reaction of the invention without further addition or separation of gypsum. In carrying out the invention lime and/or limestone or Na2CO3 and/or NaOH solution may be added to the reaction mixture and if none of these is used it is preferable to start with a dialkali metal phosphate, prepared by neutralizing a mono alkali metal phosphate with NaOH. The reaction may be carried out at 0-60 DEG C., pH 4-8, and the product used as fertilizer without separation or the phosphate filtered off, washed with water and dried. In an example the dried dicalcium phosphate is granulated.