GB825976A - Production of phosphates - Google Patents

Abstract

Orthophosphates.-Dialkaline - earth - metal hydrogen orthophosphates are prepared by adding to a solution of phosphoric acid containing pyrophosphoric acid or a soluble pyrophosphate, an alkaline - earth - metal oxide, hydroxide, or salt of a weak, or easily displaced, or volatile acid, in an amount not substantially in excess of the stoichiometric amount required to precipitate the orthophosphate. The method is especially suited to the production of hydrated calcium and magnesium hydrogen orthophosphates. The pyrophosphate ions, which are preferably present as 1 to 6% by weight based on the phosphoric acid, may be provided as the pyrophosphates of aluminium, zinc, cadmium, tin, manganese, iron, and especially sodium, potassium, magnesium, calcium, and mixtures thereof. The temperature is preferably maintained between 10 DEG and 50 DEG C. Pyrophosphates.-The dialkaline-earth-metal hydrogen orthophosphates prepared as above may be converted to the pyrophosphates by heating, preferably to 400 DEG to 700 DEG C. The orthophosphates and pyrophosphates may be ground to any desired degree of fineness, and are suitable for use in dentifrices, either separately or in combination.ALSO:A dentifrice comprises a polishing agent which is an alkaline earth ortho- or pyrophosphate prepared by adding to a solution of phosphoric acid containing pyrophosphoric acid or a soluble pyrophosphate an alkaline earth metal oxide, hydroxide or salt of a weak, or easily displaced, or volatile acid, whereby the orthophosphate is precipitated, which may be converted to the pyrophosphate by heating (see Group III). Suitable dentifrice compositions contain 30-60% by weight of the pyrophosphate, 35-55% of aqueous glycerine and/or sorbitol solutions, 0.25-3% of a detergent, about 1% by weight of a stabilizing agent, and flavouring, colouring and preservative materials. Sodium, ammonium, aluminium, or stannous fluoride may be present in amounts to give a fluoride ion concentration of 0.05% to 0.2% by weight. Tooth powders generally contain 85-95% of the pyrophosphate, the remainder being made up of detergents, flavouring and fluoride compounds.