CS234950B1 - Method of dihydrate and water-free hydrogen calcium phosphate mixrure production - Google Patents

Abstract

From the water-soluble calcium salt solution with ammonia and carbon dioxide or ammonium carbonate, calcium carbonate is precipitated, which is converted into a precipitate by the phosphoric acid, which is separated from the suspension, washed, dried or partially dehydrated by heat treatment if its composition does not correspond to the desired product. Ammonium and calcium salts are recovered from the remaining ammonium salt solution by the addition of calcium oxide or hydroxide or a mixture thereof, which, together with the carbon dioxide produced by the reaction of the calcium carbonate with the phosphoric acid, is used as a recycle. It is advantageous to add stabilizers slowing dehydration and hydrolysis of the product during manufacture. It is also advantageous to add the hardness affecting substances during manufacture.

Description

The present invention relates to a process for the preparation of a mixture of dihydrate and anhydrous hydrogenphosphate. or a mixture thereof with hydroxylapatite and calcium phosphate or hydroxylapatite and calcium phosphate from trihydrogenphosphoric acid and calcium oxide using water-soluble calcium salt, ammonia and carbon dioxide as recycle.

Until now, the production of the above products is usually accompanied by the formation of by-products of lower value, which consume part of the feedstock. An example of such a technology is a process in which limestone is dissolved in trihydrogenphosphoric acid to form calcium dihydrogenphosphate from which the desired product is obtained by precipitation, for example with sodium hydroxide solution. After separation of the product precipitate from the resulting suspension, a solution containing sodium hydrogen phosphate remains.

Thus, as is evident, the lack of precipitation processes is primarily due to the fact that the starting materials are not quantitatively converted to the desired product.

According to the invention, this process is avoided by a process for producing a mixture of dihydrate and anhydrous dicalcium phosphate or a mixture thereof with hydroxylapatite or calcium phosphate and / or hydroxylapatite and calcium phosphate from trihydrogenphosphoric acid and calcium oxide using water-soluble calcium salt such as recycle ammonia and carbon dioxide.

The process consists in precipitating calcium carbonate from a solution of a water-soluble calcium salt with ammonia and carbon dioxide or ammonium carbonate, which is converted into a precipitate which is separated, washed, dried and partially dehydrated by heat treatment to the desired product. . Ammonia and calcium salt are recovered from the remaining solution containing the ammonium salt by the addition of calcium oxide or hydroxide or mixtures thereof, which are used as a recycle together with the carbon dioxide formed in the reaction of the calcium carbonate with the phosphoric acid.

According to a further feature of the invention, the dilution of the trihydrogenphosphoric acid or the solutions to be precipitated can be effected with water leaving the product precipitate and / or with a water-soluble calcium salt solution and / or with an ammonium salt solution.

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

According to another aspect of the invention, hardness adjusting agents such as sodium pyrophosphate may be added.

According to another aspect of the invention, the calcium carbonate can be precipitated from a solution of the water-soluble calcium salt with an ammonium bicarbonate solution.

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 a waste-free production cycle is achieved by transferring all of the incoming phosphorus, calcium and additives, except for technological losses, to the key product. As a result, the process according to the invention becomes considerably more economical than the known processes.

The manufacture may be continuous, discontinuous, or a combination of both. For example, a solution of water-soluble calcium salt at a concentration of 1 wt. % to saturated solution at a given temperature is a 1% by weight solution of ammonium carbonate. % of a saturated solution at a given temperature precipitates calcium carbonate, which with 1% w / w% trihydrogen phosphoric acid. % to 98 wt. at a temperature of 20 [deg.] C. up to the boiling point of the solution to the calcium hydrogen phosphate, in a single or sequential manner, or alternatively diluting the phosphoric acid can be carried out simultaneously. The resulting precipitate is collected, washed, dried and optionally partially dehydrated by heat treatment to the desired product. The remaining solution containing the ammonium salt is regenerated to ammonia and a water-soluble calcium salt by addition of calcium oxide or hydroxide or a mixture thereof in the solid state, optionally in aqueous suspension. The regeneration is preferably carried out at a temperature corresponding to the boiling of the regenerated solution. The solution of the water-soluble calcium salt, if necessary, is reused together with the ammonia and carbon dioxide resulting from the reaction of the calcium carbonate with the phosphoric acid trihydrate. It is advantageous to incorporate the wash water into the production cycle. It is advisable to add the additives to the solutions led to the precipitation or directly to the precipitation apparatus, to the still wet product, possibly in the event of a possible particle size adjustment by grinding.

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

Example 1

Of a 10% calcium chloride solution containing 1 wt. The magnesium chloride was precipitated in a batch stirred reactor with a 5% ammonium carbonate solution prepared by carbon dioxide uptake in an ammonia solution at 25 ° C calcium carbonate, which was further transformed with 10% by weight trihydrogenphosphoric acid containing 0.5% by weight. disodium phosphate, for dibasic calcium phosphate. The temperature was maintained at 45 ° C by internal 234950 h and external reactor cooling. The resulting precipitate was collected by filtration, washed and dried first at 40 ° C and then dehydrated by heating at 70 ° C. The filtrate and washings were fed together with calcium oxide, which was in a 0.5% excess over the stoichiometry relative to ammonium chloride, into the recovery plant. A temperature corresponding to the boiling point of the solution was maintained in the regenerator. The suspension leaving the regenerator was freed by filtration of mechanical impurities and the clear filtrate after concentration and cooling was. used together with regenerated ammonia and carbon dioxide, formed during the reaction of calcium carbonate with trihydrogen phosphoric acid, to precipitate again. The product thus prepared contained 60 wt. % dihydrate and 40 wt. anhydrous dibasic calcium phosphate. The product obtained is suitable for use as an enriching additive in animal feed.

Claims (6)

SUBJECT A process for the preparation of a mixture of dihydrate and anhydrous dicalcium phosphate, optionally in admixture with hydroxylapatite and / or calcium phosphate from trihydragenophosphoric acid and calcium oxide using water-soluble calcium salt, ammonia and carbon dioxide as recycle, characterized in that Ammonia and carbon dioxide or ammonium carbonate precipitate calcium carbonate, which is converted into a precipitate by the trihydrogenphosphoric acid, which is separated, washed, dried and partially dehydrated by heat treatment to obtain a composition corresponding to the desired product from the remaining ammonium salt solution. or calcium hydroxide or mixtures thereof regenerates ammonia and the calcium salt which, together with the carbon dioxide resulting from the reaction of calcium carbonate with phosphoric acid, is used recycling. 2. Process according to claim 1, characterized in that the dilution of the trihydrogenphosphoric acid or the solutions to be precipitated is carried out with water leaving the product precipitate and / or with a water-soluble calcium salt solution and / or with an ammonium salt solution. 3. A process according to claim 1 or 2, characterized in that stabilizers retarding dehydration and hydrolysis of the product, for example magnesium chloride, are added to the solutions leading to precipitation and / or separately to the precipitation step and / or to the precipitation of the product. 4. Process according to claim 1, characterized in that substances influencing 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. A process according to any one of claims 1 to 4, wherein the calcium carbonate is precipitated from the solution of the water-soluble calcium salt with an ammonium bicarbonate solution. 6. The method according to claims 1 to 5, characterized in that the precipitation and the neutralization are carried out together.