BACKGROUND OF THE INVENTION Calcium phosphate, Ca3 (PO4) 21 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 (H2PO4) 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, CaHPO4, 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 care 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 : Ca3 (PO4k + 6HCl i / (recycled) 3CaC12 + 2H3P04 l 1 Yi \ +3H20 +2CaO (recycled) in W I 3CaO + 6HCl 2CaHP04H20/ ---11, In the other instance : Ca3 (P04) 2 + 3H2SO4 i / (recycled) 3CaS04 + 2H3P04 '\ , - + 6NaOH (recycled) 2Ca HP04 + 4H,, O 1/\ z /i I (recycled) 3Na2S04 + 3Ca (0H) 2/ // r 11 electrolysis 6H, 0"*" (recycied) \ 1 H, S04 + 6NaOH

Apart from the calcium hydrogenphosphate, a small amount of excess calcium oxide is 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 for lime (CaO and Ca (OH) 2).

In another aspect of the invention, a method of producing monocalcium phosphate from calcium phosphate ore comprises those steps disclosed in Appendix"A"attached hereto. The monocalcium phosphate may further be processed to produce edible monocalcium phosphate and edible dicalcium phosphates using the methods disclosed in Appendices"B","C"and "D"attached hereto.

The specific reactions and steps disclosed in the attached Appendices"A","B","C"and"D"are intended to be illustrative of aspects of the invention and are not intended to be limiting of the scope of the invention in any manner.

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.

APPENDIX'A' PRODUCTION OF MONOCALCIUM PHOSPHATE FERTILIZER USING THE Na2SO4 -electrolytic method Ore : Foskor 80 M concentrate (South Africa) Ore + H2S04 = Ca(H2PO4)2 + CaSO4 + H20 (Mono calcium phosphate) 1. 62 1. 117 1 1. 549 0. 53 Add : equivalent (HCOOH) , (Oxalic acid) (HCOOH)2 - Ca(HCOO)2 + H3P04 + CaS04 + H, 0 0. 385 0. 547 0. 838 1. 549 0. 53 Decant and wash.

0. 72 H3PO4 + 0. 522 80M Ore = 1. 183 (Ca (H2P04) 2 Therefor : 0. 838 H3PO4 + 0. 608 80M Ore = 1. 377 Ca H2PO4)2 Ca (H2PO4)2 - Mono calcium phosphate-is the product Thus : 2. 228 80M Ore + 1. 117 H2S04 = 1. 377 Ca H2PO4)2 + 1. 549 CaS04 + 0. 53 H2O 0. 547 Ca (HCOO)2 + 0. 419 H2SO4 = 0. 581 Ca SO4 + 0. 385 (HCOOH), (Calcium Oxalate) Consumption : Ore 2. 228 ton 80M Ore H2SO4(1.117 + 0. 419) = 1. 536 H2SO4 Products : Ca (H2PO4)2 1.377 CaS04 (1. 549 + 0. 581) = 1. 159 Ca (OH) 2 (CaSO4 + 2NaOH = Ca OH), + Na2SO4) Na2SO4 = 2Na+ + SO4 = = 2NaOH + H2SO4 (-) 3H20 + 3H2 + 30 Note : All products are contaminated by Fluorine.

APPENDIX'B' Edible Mono Calcium Phosphate : Raw material : Mono Calcium Fertilizer (which has been produced in previous description) Ca (H2PO4)2 + 2 (CH, COOH) = Ca (CH3C00) 2 + 2H, PO, (Acetic Acid) (Calcium Acetate) Decant Add equivalent (HCOOH) 2-Ca (HC00 2 + 2H, PO, + 2 (CH3COOH) (Oxalic acid) (Calcium osalate) (Acetic acid) Filter Distill 2H3PO4 + 2 (CH3COOH) + H, 0 In distilling, H, O is distilled off and Acetic acid is concentrated for re-use in the above mentioned process.

Ca (HCO0) 2 + H, SO4 = CaSO4 + (HCOOH) 2 2H3PO4 + Ca(OH)2 = Ca(H2PO4)2 Ca (H2PO4)2 - Mono calcium Phosphate-is the fluorine free product Thus : 1 Ca(H2PO4)2 + 0.419 H2SO4 = 1 Ca (H2PO4) + 0. 607 Na, SO, Note : _ the use of acetic acid to dissolve the phosphates without dissolving the CaF, _ the use of oxalic acid to overcome the buffer action of the Calcium acetate

APPENDIX'C' Edible Dicalcium phosphate Raw material is Monocalcium fertilizer (production already discussed above).

Ca H2PO4)2 + Ca(OH)2 = 2CaPO4 + 2H2O CaHPOA + 2 (CH, COOH) = Ca (CH, COO) 2 + H3PO4 (Acetic acid) (Calcium acetate) Ca (CH3COO)2 + 2 (HCOOH) = Ca(HCOO)2 + 2 (CH3COH) + H3PO4 (Oxalic acid) (Calcium oxalate) Thus : 1 Ca(H2PO4)2 + 0.316 Ca(OH)2 = CaHPO4 + 0. 54 H2O 1. 162 CaHPO4 + 1. 025 CH3COOH = 1. 35 (Ca H3COO)2 + 0. 837 H3PO4 1. 35 Ca H3COO)2 = 0. 769 HCOOH = 1. 094 Ca (HCOO) + 1. 025 CH3COOH + 0. 837 H3PO4 Filter Distill : 1. 025 CH3COOH + 0. 837 H3PO4 + H20 Water goes off as acetic acid is concentrated and re-used.

H3PO4 remains.

Ca HCOO)2, + H2SO4 = CaSO4 + (HCOOH) 2 1. 094 0. 838 1. 162 0. 769 CaS04 and H3PO, are all Fluorine free CaS04 + 2NaOH = Ca(OH)2 + Na2SO4 I. 162 0. 684 0. 632 1. 213 H3PO4 + Ca (OH)2 = CaHPO4 + H, 0 0. 837 0. 632 1. 162 CaHOP4 - Dicalcium phosphate-is the product

APPENDIX'D' Edible Dicalcium Phosphate. 2H20 CaHPO4-2 H20 Raw material : Monocalcium Fertilizer-of which the production has already been discussed.

Ca H2PO4)2 + Ca oh 2 = 2CaHPO4 CaHPO. + 2 (CH3COOH) = Ca(CH3COO)2 + H3PO4 (Acetic acid) (Calcium acetate) Add (HCOOH) 2 = Ca (HCOO) 2 + 2 (CH3COOH) + H3PO4 (Oxalic acid) (Calcium oxlate) (Acetic acid) Filter Distill : CH3COOH + H3PO4 + H2O Water goes off as acetic acid is concentrated and re-used.

H3PO4 remains.

Ca (HCOO) 2 + H2SO4 = CaSO4 + (HCOOH)2 CaSO, + 2NaOH = Ca(OH)2 + NaS04 Ca OH)2, + 2 (CH3COOH) = Ca (CH3CO0) 2 + H2O H3PO4 + 2NaOH = Na2HPO4 + H20 Na, HPO, + Ca (CH3COO)2 = CaHPO4. 2 H2O + 2Na CH3COO Cold Cold CaHPO4.2 H2O - Dicalcium Phosphate. 2H20-is the product 2Na CH3COO + H2SO4 = NaSO4 + 2 (CH COOH) Note : neutralizing action will cause heat in both the following reactions : H3PO4 + 2NaOH = Na2HPO4 + (heat) Ca (OH)2 + 2 (CH, COOH) = Ca HCOO)2, + H20 + (heat) After cooling down to below 60°C the endproducts, Ca (CH3COO)2 and Na2HPO4 can be combined resulting in CaHPO4, 2 H2O