CS271694B1 - Method of pure hydrate or/and water-free calcium hydrogen phosphate production - Google Patents

Abstract

The following substances are led into this reaction: Solution of a water-soluble calcium salt that was eventually cleared by alkalisation and filtration of water non-soluble surplus, and raw material containing hydrogen carbonate anion or/and carbonate anion or/and raw material or materials containing carbon dioxide, and ammoniac; The originated coagulate of calcium carbonate is separated from the suspension, it is washed and dried, or it is by heat processing converted to calcium oxide. The obtained powder material is in a dry form or in the form of a suspension, mixed with a trihydrogenphosphoric acid solution. The originated calcium hydrogen phosphate is processed into the product that is suitable for use in food or the cosmetic industry.

Description

The invention relates to a process for the production of pure dicalcium phosphate for the food, cosmetic, pharmaceutical and electrical industries.

The technologies used in production can be divided into two groups. One includes precipitation technologies based on partially / neutralized trihydrogenphosphoric acid and calcium salt solution. These technologies place high demands on the purity of the calcium salt, which in some cases is achieved by a special purification operation. However, the main disadvantage of the precipitation processes is the formation of the secondary salt, in the form of a relatively dilute solution, for which it is not applicable. The second group comprises processes in which the trihydrogenphosphoric acid is neutralized with ground limestone, lime hydrate or directly calcined lime. These processes also require the use of very pure calcium raw material. The nature of the particles of the product obtained in this case depends on the shape of the particles and the representation of particles of different dimensions in the calcium raw material. The reaction time is then conditioned by the reaction of the largest particles. In these respects, it would be advantageous if the grains of the calcium raw material were of regular shape and that their size fell within a narrow range. The raw materials used do not meet these criteria.

Thus, as is evident, the drawbacks of the methods used hitherto are that a by-product is formed or that the calcium raw material particles have an irregular shape and a greatly different size. According to the invention, the process for producing pure calcium dihydrate and / or anhydrous dibasic calcium phosphate is eliminated by reacting a water-soluble calcium salt which has been optionally purified by alkalinizing and filtering off the water-insoluble residue and a raw material containing an anionic bicarbonate and / or the carbonate and / or carbon dioxide-containing raw material and / or ammonia and / or ammonium hydroxide, the resulting precipitate of calcium carbonate is separated from the suspension, washed and dried, or, by heat treatment, partially or completely converted to calcium oxide or in the form of a suspension is mixed with a solution of the trihydrogenphosphoric acid or a solution of the acid and calcium dihydrogenphosphate or with a suspension comprising this acid and calcium dihydrogenphosphate and / or calcium hydrogenphosphate The resulting precipitate of dicalcium phosphate is worked up to give the product.

According to a further feature of the invention, the particle size distribution of the precipitated calcium carbonate particles is adjusted, for example by milling or controlled recrystallization.

According to a further feature of the invention, substances are added during the production which, directly or / and after reacting, retard the dehydration of the hydrate form or the hydrolysis of the anhydrous salt.

The basic effect of the process according to the invention is that a product with a well-developed crystal structure is obtained in a narrow particle size range. These properties have a significant effect on product quality. As a result, the production method according to the invention becomes significantly more advantageous than the previously known production methods.

In the production process, for example, the water-soluble calcium salt solution is made alkaline with ammonia gas, the resulting precipitate containing impurities is filtered off and the purified calcium salt solution is reacted with an ammonium carbonate solution. The resulting calcium carbonate precipitate is separated, for example, by filtration, washed, dried, or further heat-treated. An aqueous suspension is prepared from powdered calcium carbonate to which food grade trihydrogenphosphoric acid is metered. Additives which directly or after the reaction retard the dehydration of the calcium hydrogen phosphate dihydrate, or the hydrolysis of the anhydrous salt, are advantageously metered into the suspension during the reaction or into the wet product, for example by optionally adjusting its particle size by grinding. Any excess of Н ^ РОд over stoichiometry can be recycled to production.

The production method according to the invention is described in more detail below with reference to a specific embodiment.

CS 271 694 lil

Example

The waste solution produced in the drums during the recovery of ammonia from ammonium chloride-containing lyes containing 10% by weight, calcium chloride and 7% by weight, sodium chloride was reacted in the flow reactor at 80 ° C with the mother liquor leaving the pure liquor sodium bicarbonate. The resulting calcium carbonate precipitate was filtered off, washed with water, dried at 120 ° C and heated at 550 ° C for 2 hours. From the calcium carbonate thus obtained, 1 liter of a 20¾ aqueous suspension was prepared, which was used to partially neutralize a 30% by weight solution of phosphoric acid. The neutralization was carried out in a stirred batch reactor at temperatures not exceeding 30 ° C. The resulting dibasic calcium phosphate dihydrate was collected by filtration and dried at 45 ° C.

The powder product obtained contained 80% of particles differing by a maximum of - 50% from the mean size. It is suitable for use in the food or cosmetics industry.

Claims (3)

SUBJECT OF THE INVENTION A process for the production of pure dihydrate and / or anhydrous dibasic calcium phosphate, characterized by reacting a water-soluble calcium salt which has been optionally pre-purified by alkalinizing and filtering off a water-insoluble residue and a feedstock containing an anionic bicarbonate and / or carbonate and / or feedstock or raw materials containing carbon dioxide and ammonia and / or ammonium hydroxide, the resulting calcium carbonate precipitate from the suspension separates _t washed and dried or heat treatment converted partially or completely into calcium oxide, the obtained powder material in a dry form or as suspension mixed with a solution of trihydrogen phosphate or a solution of this acid and calcium dihydrogen phosphate or a suspension containing the latter and calcium dihydrogen phosphate and / or calcium hydrogen phosphate and the resulting hydrogen phosphate precipitate The calcium nano is processed into the product. 2. A process according to claim 1, characterized in that the granulometry of the precipitated calcium carbonate particles is adjusted, e.g. by grinding. 3. Process according to claim 1 or 2, characterized in that substances are added during the production which, directly or / and after the reaction, delay the dehydration of the hydrate form or the hydrolysis of the anhydrous salt.