GB2159510A

GB2159510A - Process for the production of calcium hydrogen phosphate dihydrate and/or anhydrous calcium hydrogen phosphate

Info

Publication number: GB2159510A
Application number: GB08512556A
Authority: GB
Inventors: Vladimir Glaser; Jan Vidensky
Original assignee: Vysoka Skola Chemicko Technologicka V Praze
Current assignee: Vysoka Skola Chemicko Technologicka V Praze
Priority date: 1984-05-25
Filing date: 1985-05-17
Publication date: 1985-12-04
Also published as: HU201496B; IT1183673B; GB2159510B; NL8501303A; YU87585A; DE3517608A1; IT8520868A0; FR2564817A1; FR2564817B1; HUT39685A; GB8512556D0

Abstract

Phosphoric acid, a water-soluble calcium salt and ammonia are brought into reaction, from the obtained suspension a precipitate is separated, which precipitate is processed into the product. Ammonia and a water-soluble calcium salt solution is recovered from the remaining solution by means of calcium oxide or calcium hydroxide, which ammonia and water-soluble calcium salt solution can be partly or totally returned into the process. A waste calcium chloride solution, which solution issues in the production of soda by the Solvay process, can be employed, either directly or after having been concentrated, as a water-soluble calcium salt, it being economical to interconnect a plant for manufacturing calcium hydrogen phosphate with a plant for manufacturing soda. Instead of starting from a water-soluble calcium salt and ammonia, one can also start from an ammoniacal calcium salt solution formed by the reaction of calcium oxide or calcium hydroxide with an ammonium salt solution. A part or the whole of the phosphoric acid and a part or the whole of the ammonia can be replaced by ammonium hydrogen phosphate and/or ammonium dihydrogen phosphate. In order to slow down the dehydration of the calcium hydrogen phosphate dihydrate and the hydrolysis of the anhydrous calcium hydrogen phosphate, it is useful to add stabilizers during the manufacture.

Description

SPECIFICATION Process for the production of calcium hydrogen phosphate dihydrate and/or anhydrous calcium hydrogen phosphate This invention relates to a process for the production of calcium hydrogen phosphate dihydrate and/ or anhydrous calcium hydrogen phosphate and/or a mixture thereof and/or in mixture with hydroxyapatite and/or calcium phosphate and/or calcium carbonate.

Due to their simplicity, the precipitation methods are the most widely employed methods for the preparation of the above mentioned products.

Most commonly one starts when carrying them out, from waste, water-soluble calcium salts which salts are purified, according to need, or these salts are prepared by decomposition of limestone with the respective acid, high demands being mostly made on the purity of the starting calcium raw material. A by-product of the precipitation is the ammonium or the alkali metal salt.

As is thus evident, a drawback of the up to currently employed production processes consist above all in that the quality of the product depends on the purity of the starting calcium raw material and that there results a secondary waste in form of a diluted solution which waste can be utilized with difficulty only.

These disadvantages are avoided by the process for the production of calcium hydrogen phosphate do hydrate and/or anhydrous calcium hydrogen phosphate and/or a mixture thereof and/or in mixture with hydroxyapatite and/or calcium phosphate and/or calcium carbonate which process is characterized in that it starts from trihydrogen phosphoric acid, a water-soluble calcium salt and ammonia and/or ammonium hydroxide which are brought into reaction, from the obtained suspension the precipitate is removed which precipitate is processed into the product, from a part or all of the remaining solution ammonia and/or ammonium hydroxide and a water-soluble calcium salt solution is recovered by means of calcium oxide and/or calcium hydroxide or a mixture thereof or a mixture of these substances with magnesium oxide and/or magnesium hydroxide, a part or all of the water-soluble calcium salt solution and/or the ammonium hydroxide being, if desired, returned into the process.

According to a further feature of the invention, a solution which issues from the recovery of ammonia from lyes arising in the production of soda by the Solvay process, which solution contains mainly calcium chloride, is employed as a water-soluble calcium salt.

According to a further feature of the invention, instead of the solution of calcium chloride issuing from the recovery of ammonia from lyes arising in the production of soda, this solution is employed after concentrating and/or concentrating and reducing the sodium content thereof.

According to a further feature of the invention, in the preceding two processes, ammonia and/or am monium hydroxide is recovered in soda production from a part or all of the solution containing mainly ammonium chloride which remains after removing the precipitated product.

According to a further feature of the invention, instead of the water-soluble calcium salt and am monia and/or ammonium hydroxide, an ammonia cal calcium salt solution is employed, which solution is obtained in that calcium oxide and/or calcium hydroxide or a mixture thereof and an am monium salt solution are reacted, the remaining solid phase is removed and the obtained solution is ammoniacalized, if desired.

According to a further feature of the invention, a part or all of the trihydrogen phosphoric acid and a part or all of the ammonia and/or a part or all of the ammonium hydroxide is replaced, directly or after purification thereof, by ammonium dihydro gen phosphate and/or ammonium hydrogen phos phate.

According to a further feature of the invention, the dilution of trihydrogen phosphoric acid is car ried out by waste waters arising from washing the precipitated product and/or by a solution contain ing ammonium salt.

According to a further feature of the invention, stabilizers slowing down the dehydration of calcium hydrogen phosphate dihydrate and/or the hydrolysis of anhydrous calcium hydrogen phosphate are added.

The primary effect of the production process according to this invention consists in that it is not necessary to start from calcium raw materials of high purity, and that no undesirable salts, as byproducts, are formed. When combining the production of calcium hydrogen phosphate with the production of soda, a part of the machinery for producing both products can be shared what is, from the standpoint of investment, and operating costs, advantageous. In this manner, the production process according to this invention becomes, against other hitherto known processes, economically distinctly more advantageous.

The production can be continuous, discontinuous or a combination of both. One proceeds for instance so that a trihydrogen phosphoric acid solution having a concentration of 1% - 95% by weight, a water-soluble calcium salt solution having a concentration of 1% by weight to a saturated solution thereof, at a given temperature, and ammonia and/ or ammonium hydroxide are mixed together at the same time or successively, in one or more stages, a dilution being made at the same time if desired.

The temperature ranges in dependence of the required composition of the product from 0 C to the boiling point. The formed precipitate is removed for instance by filtration or centrifugation, washed and dried, if necessary partly or wholly dehydrated by thermal treatment to obtain the product of desired composition. Ammonia and the water-soluble calcium salt is recovered from the remaining solution containing the ammonium salt by means of calcium oxide or calcium hydroxide or a mixture thereof in solid state or in water suspension, for instance in form of burnt lime and/or hydrated lime or lime milk. Ammonia and/or ammonium hydroxide and the water-soluble calcium salt solution can be, after elimination of mechanical impurities, if need be, and after optional concentration and cooling, partly or wholly returned into the process.The washing waters can be incorporated into the production cycle. The additives slowing down the dehydration of calcium hydrogen phosphate dihydrate and/or the hydrolysis of anhydrous calcium hydrogen phosphate, for instance sodium diphosphate, are preferably dosed into the solutions led to the precipitation and/or directly into the precipitating apparatus and/or into the damp or dry product and/or in the optional adjustment of the particle size by grinding.

The process according to the invention is illustrated by the following examples.

Example I A 10% calcium chloride solution was mixed in an agitated batch type reactor with an equimolar quantity of trihydrogen phosphoric acid having a concentration of 85% by weight. The pH was adjusted by gaseous ammonia to 7. The temperature did not exceed 30"C. The resulting precipitate was filtered off, washed and dried at 40 C. The obtained product was calcium hydrogen phosphate dihydrate. The filtrate and the wash waters were introduced together with calcium oxide employed in an amount corresponding to an 0.5% excess over stoichiometry, as related to ammonium chloride, into a recovering apparatus. In said apparatus, a temperature of the boiling point of the solution was maintained.From the suspension leaving the recovering apparatus, mechanical impurities were removed, and clear filtrate, after having been concentrated and cooled, was employed together with recovered ammonia for the precipitation again.

Example 2 The process was operated in the same manner as in Example 1 except that instead of the 10% calcium chloride solution, a waste solution issuing from the recovery of ammonia from lyes arising in the production of soda, by means of lime which solution contains as main components calcium chloride, sodium chloride and magnesium chloride, was employed.

Example 3 The production process was the same as in Example 1 except that the temperature in the reactor was maintained at 80"C and the precipitate was dehydrated by heating at a temperature of 115 C.

The product was anhydrous calcium hydrogen phosphate.

Example 4 To a solution of ammonium chloride having a concentration of 10% by weight calcium hydrate was added in a quantity representing a 10% excess over stoichoimetry. The suspension was agitated in a closed vessel at a temperature of 70"C during 20 minutes whereupon it was cooled to 20"C and separated by filtration into a solution and a solid phase. A ciear ammoniacal calcium salt solution was mixed in an agitated batch type reactor with trihydrogen phosphoric acid having a concentration of 75% by weight in stoichoimetric ratio with regard to the production of calcium hydrogen phosphate. The temperature of the reaction was maintained at 300C. The resulting precipitate was filtered off, washed, mixed with a solution of sodium diphosphate, which contained 1% of said salt as related to the dry product weight, and dried at 40 C.

There was obtained calcium hydrogen phosphate dihydrate as product.

The obtained products are useful for use in cosmetics, foodstuffs and pharmaceuticals producing industries and as enriching additives in feeding mixtures for animals.

Claims

1. A process for the production of calcium hydrogen phosphate dihydrate and/or anhydrous calcium hydrogen phosphate and/or a mixture thereof and/or in mixture with hydroxyapatite and/or with calcium phosphate and/or with calcium carbonate, in which trihydrogen phosphoric acid, a water-soluble calcium salt and ammonia and/or ammonium hydroxide are reacted, from the obtained suspension a precipitate is separated, which precipitate is processed into the products, from a part or from the entire remaining solution ammonia and/or ammonium hydroxide and a water-soluble calcium salt solution is recovered by means of calcium oxide and/or calcium hydroxide or a mixture of said substances with magnesium oxide and/or magnesium hydroxide, a part or all of the water-soluble calcium salt solution and/or a part or all of the ammonia and/or a part or all of the ammonium hydroxide being, if desired, returned into the process.

2. A process according to claim 1, wherein a solution which issues from the recovery of ammonia from lyes arising in the production of soda by the Solvay process, containing mainly calcium chloride, is employed as the water-soluble calcium salt.

3. A process according to claim 2, wherein instead of the calcium chloride solution issuing from the recovery of ammonia from lyes arising in the production of soda, this solution is employed after its concentrating and/or its concentrating and reducing the sodium chloride content thereof.

4. A process according to claim 2 or 3, wherein ammonia and/or ammonium hydroxide is recovered in soda production from a part or all of the solution containing mainly ammonium chloride, which solution remains after removing the precipitated product.

5. A process according to any one of claims 1 to 3, wherein instead of the water-soluble calcium salt and ammonia and/or ammonium hydroxide, an ammoniacal calcium salt solution is employed, which solution is obtained in the recovery of ammonia from an ammonium salt solution in that calcium oxide and/or calcium hydroxide or a mixture thereof and an ammonium salt solution are brought into reaction, the remaining solid phase is removed and the obtained solution is ammoniacalized, if desired.

6. A process according to any one of claims 1 to 5, wherein a part or all of the trihydrogen phosphonic acid and a part or all of the ammonia and/or a part or all of the ammonium hydroxide is replaced, directly or after the purification thereof, by ammonium dihydrogen phosphate and/or ammonium hydrogen phosphate.

7. A process according to any one of claims 1 to 6, wherein the dilution of trihydrogen phosphoric acid is carried out by waste waters arising from washing the precipitated product and/or by a solution containing ammonium salt.

8. A process according to any one of claims 1 to 7, wherein stabilizers slowing down the dehydration of calcium hydrogen phosphate dihydrate and/or the hydrolysis of anhydrous calcium hydrogen phosphate are added.

9. A process according to claim 1 substantially as herein described with reference to Examples 1 to 4.