CS247432B1 - Method of dihydrate or/and anhydrous calcium hydrogen phosphate production - Google Patents

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for the production of calcium dihydrate or anhydrous calcium phosphate and / or. mixtures thereof.

For the sake of simplicity, widespread methods of manufacturing the above products are precipitation processes. They are mostly based on waste water-soluble calcium salts, which are purified as necessary or prepared by decomposing the limestone with the appropriate acid, whereby the purity of the starting calcium raw material is usually high. An ammonium salt or an alkali metal salt is formed as a by-product during precipitation.

As is clear, then. The drawbacks of the production processes used hitherto are mainly that the quality of the product depends on the purity of the starting calcium raw material and that a by-product, difficult to enforce, is obtained in the form of a dilute solution.

These disadvantages are overcome by a process for the production of calcium dihydrate or anhydrous calcium phosphate and / or a mixture thereof with trichloro-hydrogenphosphate and quicklime or lime hydrate or lime milk, more particularly. by separating the calcined lime and / or lime hydrate and / or lime milk and the ammonium salt solution, separating the solid phase, reacting the resulting ammoniacal calcium salt solution, if necessary, and reacting with phosphoric trihydrate and / or ammonium hydrogen phosphate; or and ammonium dihydrogen phosphate. The resulting suspension is a calcium phosphate salt and treated. to the desired product, the remaining ammonium salt solution is optionally recycled.

According to a further feature of the invention, part or all of the amount of water washings produced during the precipitation process is used to compensate for the operational losses of the ammonium salt and water during production.

According to a further feature of the invention, dihydrate retarding stabilizers and / or are added. hydrolysis of anhydrous dicalcium phosphate.

The basic effect of the production method according to the invention is that it is not necessary to start from highly pure calcium raw materials and that undesirable salts are not formed. As a result, the process according to the invention becomes considerably more economical than the known processes.

The manufacture can be continuous, discontinuity or co-ordination of both. For example, an ammonium salt solution of 1% strength to saturated solution at a given temperature is mixed with quicklime and / or calcium hydrate and / or lime milk. they zoom out undissolved. the solid phase and the ammoniacal solution of the calcium salt are precipitated with a trihydric acid solution having a concentration of 1 to 85% by weight. The temperature varies from 0 ° C to the boiling point, depending on the desired product composition.

The resulting phosphate salt or salt mixture is separated from the suspension, for example by filtration, washed and dried, optionally partially or completely dehydrated by heat treatment to obtain the product of the desired composition. The filtrate containing the ammonium salt, if desired mixed with some or all of the wash water, is returned to the start of production. It is advantageous to add the additives, for example sodium phosphate, to the solution of trichlorophosphoric acid and / or to the precipitation apparatus and / or to the wet or dry product and / or to optionally adjust the particle size of the product by grinding.

The production method of the invention is described in more detail below with reference to specific embodiments.

Example la dl

To a 10% w / w ammonium chloride solution was added lime hydrate in an amount of 10% excess over the reaction mixture. The suspension was stirred in a sealed vessel at 50 ° C for 20 minutes, then cooled to 50 ° C. 20 ° C and filtered to a solution and an undissolved solid phase, the clear amosiacal solution of calcium chloride was mixed in a stirred batch reactor with 75% by weight of phosphoric acid in a stoichiometric ratio to the formation of dibasic calcium phosphate. The reaction temperature was maintained at 30 ° C by vigorous cooling. The resulting precipitate was collected by filtration, washed, mixed with sodium phosphate solution containing 1% by weight of the salt relative to the dry product and dried at 40 ° C.

The product was dibasic calcium phosphate dihydrate.

Example 2

The production procedure was the same as in Example 1 except that the reactor temperature was maintained at 80 ° C and the precipitate was dehydrated by heating with steam at 95 ° C.

The product was anhydrous dibasic calcium phosphate.

Example3

The production procedure was the same as in Example 1 except that the reactor temperature was maintained at 65 ° C.

The product contained 60% by weight of dihydrate and 40% by weight of anhydrous dibasic calcium phosphate.

The products obtained are suitable for use in the cosmetic, food and pharmaceutical industries and as an enriching additive to compound feed in animal production.

Claims (3)

Process for producing dihydrate and / or anhydrous dicalcium phosphate optionally in admixture with hydroxylapatite and / or calcium phosphate, characterized by reacting quicklime and / or lime hydrate and / or lime milk and ammonium salt solution, separating the solid phase, the resulting ammoniacal calcium salt solution, after any ammoniacalization, is reacted with phosphoric acid and / or ammonium hydrogen phosphate and / or ammonium dihydrogen phosphate, the resulting calcium phosphate salt is separated from the resulting suspension, and the remaining ammonium salt solution is optionally returned as recycle. 2. A method according to claim 1, characterized in that part or all of the amount of washing water produced during the precipitate treatment is used to compensate for the operational losses of ammonium salt and water during production. 3. A process according to claim 1 or 2, characterized in that stabilizers retarding dehydration of the dihydrate and / or hydrolysis of the anhydrous dicalcium phosphate are added.