IL142209A

IL142209A - Production of calcium hydrogenphosphate or monocalcium phosphate from calcium phosphate

Info

Publication number: IL142209A
Application number: IL14220998A
Authority: IL
Inventors: Jan C De Waal
Original assignee: Willem P D De Waal
Priority date: 1998-09-23
Filing date: 1998-09-23
Publication date: 2004-06-20

Abstract

A method for the manufacture of dicalcium phosphate from calcium phosphate comprising: (a) reacting the calcium phosphate with a suitable mineral acid to form the corresponding calcium salt and phosphoric acid; (b) hydrolyzing the calcium salt of step (a) to form the corresponding calcium alkali and the mineral acid of step (a) or its salt; (c) where the salt of the mineral acid is formed in step (b), electrolyzing such salt to form the corresponding mineral acid together with an alkali; (d) recycling the mineral acid of steps (b) or (c) to step (a); and (e) reacting the calcium alkali of step (b) with the phosphoric acid of step (a) to form dicalcium phosphate.

Description

VSV) ypt?n ODt sι*ρυ-*τη ΊΚ ODPI "n -m» PRODUCTION OF CALCIUM HYDROGENPHOSPHATE OR MONOCALCIUM PHOSPHATE FROM CALCIUM PHOSPHATE Applicant: Willem P. D. De Waal DEW A 90117/2.1 PRODUCTION OF CALCIUM HYDROGENPHOSPHATE OR MONOCALCIUM PHOSPHATE FROM CALCIUM PHOSPHATE FIELD OF THE INVENTION The present invention relates to methods for the manufacture of calcium hydrogenphospate from calcium phosphate. It also relates to methods for the manufacture of monocalcium phosphate fertilizer, edible monocalcium phosphate and edible dicalcium phosphates.

BACKGROUND OF THE INVENTION Calcium phosphate, Ca3(P04)2, occurs in nature as rock phosphate ore, for example and is used as such as a source of fertilizer. It can also be converted with sulphuric acid to a mixture of calcium sulphate and phosphoric acid, or calcium dihydrogen phosphate, Ca(H,P04)2, the latter also being known as monocalcium phosphate. Calcium phosphate has a relatively low phosphorous content (20% m:m) while monocalcium phosphate, while having a much higher phosphorous content (26.5% m:m), is difficult to manufacture, and also expensive mainly because one of the by-products of the reaction by means of which it is so prepared, calcium sulphate, has to be discarded as a waste product.

Calcium hydrogenphosphate, CaHP04, also known as dicalcium phosphate, has a relatively high phosphorous content (22.8% m:m) and may be used as a fertilizer. It is also used in animal licks as well as in the manufacture of certain toothpastes.

Therefore, there is a need in the art for an economical method of producing calcium hydrogenphosphate from calcium phosphate. There is a further need in the art for an economical method of producing monocalcium phosphate fertilizer from calcium phosphate and further producing edible products from the resultant fertilizer.

SUMMARY AND DESCRIPTION OF THE INVENTION In accordance with one aspect of the invention, a method of producing calcium hydrogenphosphate from calcium phosphate comprises the following steps: a) reacting the calcium phosphate with a suitable mineral acid to form the corresponding calcium salt and phosphoric acid; b) hydrolysing the calcium salt produced by step a) to form the corresponding calcium alkali and the mineral acid of step a), or its salt; c) if the salt of the mineral acid is formed in step b), electrolysing said salt to form the corresponding mineral acid together with an alkali; d) recycling the mineral acid of steps b) or c) to step a); e) reacting the calcium alkali of step b) with the phosphoric acid of step a) to form calcium hydrogenphosphate.

In one embodiment of the invention, the mineral acid comprises hydrochloric acid, so that calcium chloride is the calcium salt formed. The calcium chloride is then treated with water at an elevated temperature, preferably in the range of 1000 to 1200°C, to form calcium oxide and hydrochloric acid. Preferably, the aforesaid hydrolysation of the calcium chloride is carried out in a suitable cyclone.

In the preferred embodiment, the calcium chloride/water solution is damped in and heated to its boiling point before it is introduced to the cyclone, with cave being taken to ensure that the resulting evaporation does not exceed a value commensurate with the solubility of calcium chloride in water. This ensures that there is sufficient water, in fact a slight excess, to take the reaction to completion.

In an alternative embodiment of the invention, the mineral acid used is sulphuric acid, so that calcium sulphate is the salt which is formed. In this embodiment, the hydrolysis of the calcium sulphate is carried out with an alkali metal hydroxide, such as sodium hydroxide, to form calcium hydroxide and the alkali metal sulphate. The latter is then electrolyzed to sulphuric acid together with the alkali metal hydroxide. The latter is then recycled for the aforementioned hydrolysis reaction.

The preferred source for the calcium phosphate starting material is calcium phosphate rock ore.

It may therefore be appreciated by a person skilled in the art that the overall reactants required for the method of the present invention are calcium phosphate and the hydrolysis reagent required in step b). The only other requirement is either the energy required for obtaining the elevated temperature for the hydrolysis step in the one instance, or the electrical energy required for the electrolysis step in the other instance.

The following equations represent the chemical reactions occurring in the aforesaid two instances. In either instance, the specific reactions are illustrative of the invention and are not intended to be limiting of the scope of the invention.

In the one instance: (re d) In the other instance: Ca3(P04)2 + 3H.S0, (recycled) 3CaS04 + 2H3P04 \ \ + 6Na0H (recycled) 2Ca HPO, + 4H,0 I (recycled) 3Na,S04 + 3Ca(0H)2 Velectrolvsis 6H,0 ^"~ ' (recycled) ^ - 3H,S04 + 6NaOH - D - Apart, from the calcium hydrogenphosphatc, a small amount of excess calcium oxide i s produced as a byproduct in the overall reaction in the one instance, and calcium hydroxide in the other instance, either of which can be used as a source of lime (CaO and Ca(OII)2) .

As will be apparent to those skilled in the art, various modifications, adaptations and variations of the within specific disclosure can be made without departing from the teachings of the present invention.

Claims

142209/2 " 6 " CLAIMS: The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for the manufacture of dicalcium phosphate from calcium phosphate comprising: (a) reacting the calcium phosphate with a suitable mineral acid to form the corresponding calcium salt and phosphoric acid; (b) hydrolyzing the calcium salt of step (a) to form the corresponding calcium alkali and the mineral acid of step (a) or its salt; (c) where the salt of the mineral acid is formed in step (b), electrolyzing such salt to form the corresponding mineral acid together with an alkali; (d) recycling the mineral acid of steps (b) or (c) to step (a); and (e) reacting the calcium alkali of step (b) with the phosphoric acid of step (a) to form dicalcium phosphate.

2. The method of claim 1 in which the mineral acid used in step (a) comprises hydrochloric acid, so that calcium chloride is the salt which is formed.

3. The method of claim 2 in which the hydrolysis of step (b) is carried out by treating the calcium chloride with water at an elevated temperature to form calcium oxide and hydrochloric acid. 142209/2 " 7 "

4. The method of claim 3 in which the elevated temperature is in the range of about l OOO.degree. to about 1200.degree. C.

5. The method of claim 3 in which the reaction between the calcium chloride and water at the elevated temperature is carried out in a cyclone.

6. The method of claim 5 in which the calcium chloride and water solution is damped in and heated to boiling point before it is introduced to the cyclone, care being taken to ensure that the resulting evaporation does not exceed a value commensurate with the solubility of calcium chloride in water in order to ensure that there is sufficient water (slight excess) to take the reaction to completion.

7. The method of claim 1 in which the mineral acid used in step (a) comprises sulphuric acid so that calcium sulphate is the salt which is formed in step (a).

8. The method of claim 7 in which the hydrolysis of step (b) is carried out by treating such calcium sulphate with an alkali metal hydroxide such as sodium hydroxide to form calcium hydroxide and the alkali metal sulphate.

9. The method of claim 1 wherein calcium phosphate rock ore is utilized as source of calcium phosphate. For the Applicant, Jeremy M. Ben-David & Co. Ltd. DEWA 90117/2.1