CS236293B1 - Process for the preparation of calcium hydrogen phosphate dihydrate - Google Patents

Abstract

From the calcium chloride solution formed during the regeneration of ammonia from soda lye with milk of lime, or from this solution after reducing the concentration of sodium chloride, calcium carbonate is precipitated with a soda solution, which is converted into calcium hydrogen phosphate dihydrate with trihydrogen phosphoric acid. The precipitate is separated from the resulting suspension, washed and dried. The remaining solution containing sodium chloride and * the resulting carbon dioxide can be used to produce soda by the ammonia process. It is advantageous to add stabilizers during production to slow down dehydration and hydrolysis of the product. It is also advantageous to add substances affecting the hardness of the product during production. The product is suitable for use in the cosmetic, food and pharmaceutical industries.

Description

The present invention relates to a process for the production of calcium hydrogen phosphate dihydrate or a mixture thereof with hydroxylapatite or calcium phosphate and / or hydroxylapatite and calcium phosphate from trihydrogenphosphoric acid, calcium chloride and sodium carbonate.

To date, the production of the above products is usually accompanied by the formation of less valuable products that consume part of the feedstocks. Sodium hydrogen phosphate solution remains after separation of the product precipitate from the resulting suspension.

Thus, as is evident, the drawback is primarily that the starting phosphorus feedstock is not quantitatively converted to the desired product.

This disadvantage is overcome by the process according to the invention for producing calcium hydrogen phosphate dihydrate or a mixture thereof with hydroxylapatite or with calcium phosphate and / or with calcium phosphate and hydroxylapatite from trihydrogenphosphoric acid, calcium chloride and sodium carbonate.

The principle of the method is that from a solution of calcium chloride formed during the regeneration of ammonia from sodium hydroxide solution with lime milk, or from this solution after a reduction in the

- 3 236 293 sodium chloride precipitates calcium carbonate with a soda solution. The latter is then converted into tricalcium phosphate dihydrate into calcium hydrogen phosphate dihydrate, which is separated, washed and dried. The remaining solution containing sodium chloride and the resulting carbon dioxide can be used to produce soda by the ammonia process.

According to a further feature of the invention, the dilution of the trihydrogenphosphoric acid can be carried out with the effluent water of the product precipitate.

In a further aspect of the invention, stabilizers such as magnesium salts may be added to retard dehydration and product hydrolysis.

According to a further feature of the invention, hardness controlling agents such as sodium pyrophosphate may be added.

According to another feature of the invention, precipitation and neutralization can be carried out together.

The basic effect of the process according to the invention is that by combining the production of dibasic calcium phosphate dihydrate with soda production, a waste-free technology is achieved which makes it possible to utilize all the phosphorus in the feedstock to produce the desired product. It is also preferred that the calcium chloride solution used as a source of calcium ions in the proposed process is one of the undesirable products in the soda production by the ammonia process, and the carbon dioxide and sodium chloride solution formed can be used in this process.

The manufacture can be continuous, discontinuous, or cobinating both. For example, calcium carbonate is precipitated from a 1 wt.% To saturated solution of calcium chloride at a given temperature, which is converted to calcium hydrogen phosphate dihydrate at 5-50 ° C at a temperature of 5-50 ° C. this can be done once or sequentially, or it is also possible to simultaneously dilute trihydrogenphosphoric acid. A precipitate of dibasic calcium phosphate dihydrate formed

- 4 -

23B 293 Oe is separated, washed and dried at a temperature not exceeding 100 C. The remaining solution containing sodium chloride and carbon dioxide formed can be used to produce soda by the ammonia process. It is advantageous to incorporate the wash water into the production cycle. It is advisable to add the additives to the solutions to be precipitated, or directly to the precipitation apparatus, to the still moist product, or possibly to adjust the particle size of the product by grinding.

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

Example

From a 10% calcium chloride solution containing 10% magnesium chloride, a 5% sodium bicarbonate solution at 25 ° C was precipitated in a stirred tank reactor at 25 ° C for a longer period of time with a ig% wt. Sodium diphosphate, for calcium hydrogen phosphate dihydrate. The temperature was maintained at 35 ° C by internal and external reactor cooling. The resulting precipitate was collected by filtration, washed and dried at 40 ° C. The product obtained is suitable for use in the cosmetics, food and pharmaceutical industries.

Claims (5)

A process for the production of calcium hydrogen phosphate dihydrate optionally with hydroxylapatite or calcium phosphate from trihydrogenphosphoric acid, calcium chloride and sodium carbonate, characterized in that from a calcium chloride solution resulting from the regeneration of ammonia from soda lyes or from this milk. solution after reducing the content of sodium chloride with a solution of sodium carbonate is precipitated calcium carbonate which is orthophosphoric acid was converted to the dicalcium phosphate dihydrate, which is of the resulting suspension is separated off, washed and dried, the remaining solution containing chloride sod, NY and the resulting carbon dioxide-use ¹ · k soda production by the ammonia process. 2. A process according to claim 1, wherein the dilution of the phosphoric acid is effected with water leaving the product precipitate. 3. The method according to claim 1 and 2 _t wherein the stabilizers are added, slowing dehydration and hydrolysis of the product, such as magnesium chloride to the solution led to the precipitation and / nebp separately to the precipitation stage and / or to precipitate the product. 4. Process according to claim 1, characterized in that substances which influence the hardness of the product, for example sodium pyrophosphate, are added to the solutions to be precipitated and / or separately to the precipitation steps and / or to the product precipitate. 5. The process according to any one of claims 1 to 4, wherein the precipitation and neutralization are carried out together.