WO2004076348A1

WO2004076348A1 - A process for the manufacture of feed grade dicalcium phosphate

Info

Publication number: WO2004076348A1
Application number: PCT/IN2003/000039
Authority: WO
Inventors: Visweswara Rao Abburi
Original assignee: Visweswara Rao Abburi
Priority date: 2003-02-27
Filing date: 2003-02-27
Publication date: 2004-09-10
Also published as: AU2003303978A1

Abstract

This invention relates to the preparation of feed grade dicalcium phosphate from a source containing monocalcium phosphate such as super phosphate, concentrated super phosphate and the like. The first step consists of leaching water soluble mono calcium phosphate therefrom with water or recycle wash water from one of the subsequent steps. The supernatant liquid treated with a frist quantity of hydrated lime to precipitate impurities such as Fe, Al and F. The filtrate obtained after removing the precipitate is further treated with hydrated lime to raise the pH till mono calcium phosphate present therein gets converted into dicalcium phosphate which crystallizes out wash water from the second and the third stages are recycled to the system. By-product obtained is gypsum, which is used in cement industry or as a fertilizer filter.

Description

"A PROCESS FOR THE MANUFACTURE OF FEED GRADE DICALCIUM

PHOSPHATE"

Dicalcium phosphate known, as DCP is a commonly used animal feed supplement and it is desirable to obtain dicalcium phosphate free of contaminants, particularly fluoride containing compounds. Feed grade dicalcium phosphate has a chemical formula CaH P0₄ 2H₂P wherein phosphorus expressed as P is 18% and calcium expressed as Ca is at least 23%. Maximum fluorine content is 0.16%.

Rock phosphates and bone ash are natural sources of calcium phosphate in the form of tricalcium phosphate of the chemical formula Ca₃ (P0₄)₂. Acidification of tricalcium phosphate with mineral acids yields phosphates and phosphoric acids. Acidification of rock salt with hydrochloric acid also produces mono calcium phosphate which remain in solution which is treated to remove fluorides as precipitates. The supernatant liquid containing monocalcium phosphate is treated with lime to obtain dicalcium phosphate and calcium chloride wliich is discarded as a by-product. Phosphoric acids which are obtained on acidification of natural phosphates are purified and then neutralized to produce dicalcium phosphate.

In the US patent no.6183712 a process wherein calcium phosphate is reacted with a mineral acid and the product thus obtained is hydrolyzed to form a corresponding calcium salt has been reported. This patent also discloses a process wherein naturally occurring phosphate is reacted with phosphoric acid and the product is treated with acetic or oxalic acid. DISCLOSURE OF THE INVENTION:

Dicalcium phosphate substantially free of fluorides is prepared by a novel process which particularly avoids production of unwanted calcium chloride as a byproduct. This simple process produces high grade dicalcium phosphate and is energy efficient. The reaction steps are carried out at ambient temperature and no heat input is required except for the drying step.

The first step in this process is in the production of single super phosphate generally known as SSP, triple super phosphate (TSP) a well known fertilizer and a super phosphate of a grade between SSP and TSP. Tricalcium phosphate present in rock phosphate or any other natural sources of phosphates on treatment with sulphuric acid or phosphoric acid gets converted into mono calcium phosphate according to the following reaction.

Ca₃(P0₄)₂ + H₂80₄ → Ca(H₂PG₄)₂ + CaSQ₄ n H₂0 CaaCPO^ + H_aP0₄ → Ca<H₂P0₄)₂

During this reaction a fraction of the fluorides present in the starting mat rial escapes as reaction vapours. However, the monocalcium phosphate produced is still contaminated with fluorides. This product obtained is known as green super in the industry and has a very high unreacted free acid content. Green super on keeping gets cured and the unreacted free acid as well as the excess of phosphoric acid formed during the reaction and the unreacted calcium phosphate present therein slowly react with each other to yield more of mono calcium phosphate. Soluble fluoride content of this product depends on the available free acid when cured frilly, single super phosphate contains approximately 1.2 to 2.2% of free acid content. This fully cured product is treated with water or recycle liquor from a subsequent process step to dissolve mono calcium phosphate present therein. Solid impurities are separated and the filtrate containing free acid is treated with a solution of hydrated lime to increase its pH and to precipitate out impurities such as iron, aluminum and fluorine containing compounds. Monocalcium phosphate solution free from such contaminants is further treated with a solution of hydrated lime to neutralize and to produce dicalcium phosphate free of fluoride ions. If required a mixture of mono and dicalcium phosphate may also be produced by adjusting the quantity of hydrated lime. This product is found to have at least 18% or more P than normal dicalcium phosphate and exhibits higher digestibility when used as a feed additive.

This invention relates to a process for the preparation of feed grade dicalcium phosphate substantially free of fluorides from a source containing monocalcium phosphate such as simple super phosphate, concentrated super phosphate or fertilizer grade phosphate which comprises the steps of (a) leaching out soluble monocalcium phosphate therefrom with water or recycle wash water from at least one subsequent steps, (b) adding a first quantity of a solution of hydrated lime thereto to precipitate ά j≤frørat© contaminants like iron, aluminum arid fluorine containing ompoundi. therefrom (c) adding a further quantity of hydrated lime to the filtrate containing monocalcium phosphate to produce dicalcium phosphate as precipitate which is separated washed and dried, wash water from steps (b) and (c) being recycled to step (a) to leach out further monocalcium phosphate.

Single super phosphate may be prepared by treating tricalcium phosphate with an acid such as sulphuric acid or phosphoric acid. BRIEF DESCRIPTION OF DRAWING:

Fig.I attached herewith shows different stages of the process schematically. This figure also shows utilization of wash water in a continuous process of producing dicalcium phosphate according to this invention.

BEST METHOD OF CARRYING OUT THE INVENTION:

The following non-limitive examples illustrate this invention.

Example 1:

Fully cured single super phosphate is agitated thoroughly with water or wash water recycle for about an hour to dissolve all water soluble components. pH of this solution is found to be between 2.2 to 2.6. This solution contains monocalcium phosphate and is marked as filtrate 2 in the flow diagram. pH of the filtrate is raised by adding a small quantity of hydrated lime solution. Impurities like iron, aluminum and fluorides are precipitated. This precipitate is separated, washed with water to recover phosphate therefrom. This mainly consists of gypsum and is used in eenisnt industry or fertilizer industry. The solution obtained after separation of the precipitate contains monocalcium phosphate underpH3.2, the filtrate has 5.2% of P and 0.0153% ofF.

A fiirther quantity of hydrated lime is added to the filtrate obtained after the separation of solids to raise the pH to 6.5 to 6.7. Dicalcium phosphate crystallises out from the solution. This is separated by filtration and the filtrate is recycled particularly to wash the filter cake obtained after the first addition of hydrated lime. The precipitated dicalcium phosphate is washed and dried. On analysis this product conformed to the following analysis.

P 18.17% Ca 24.45% F 0.12%

Example 2:

Single super phosphate containing 16.5% of water soluble P₂0₅ and 1.3% of free acid expressed as P₂O_s is used for this experiment. 250gm of this cake is taken and agitated with lOOOg of water for half an hour and then filtered. The filter cake is washed with water in two lots of 250g each.

Total water soluble F₂ s 41.25g

Water added lOOOg

Filtrate obtained 982g

The filtrate contains pH 2.39

P₂0₅ 3.45%

F content 0.030%

P₂0₅ in gm 33.S7gm

Quantity of wash 456g

P₂0₅ content 1.1%

P₂O_s content in gm 5.06g

Total P₂O_s recovered 38.93g

% yield of P₂0₅ 93.8%

This clearly shows that substantial quantity of P₂O_s has been recovered. Example 3:

900gm filtrate containing 3.45% of P₂O_s and a P/F ratio of 49.8 is treated with a solution of hydrated lime to raise the pH to 2.9. Contents are separated by filtration and the P₂0₅ and F value assessed. In 900gm of solution

P₂0₅ content of the solution 3.45%

Total P₂0₅ input 31.05g

Weight of the filtrate 891 gm

P₂O_s of the filtrate 3.41%

P/F ratio of the filtrate 148

This experiment shows that treatment of the filtrate with lime removes impurity and fluorine therefrom.

800gm of the filtrate is further heated with hydrated lime to raise the pH till 6.88 and the contents are then filtered to separate dicalcium phosphate therefrom. The solution and the products are analyzed and the results are given below.

Dicalcium phosphate on a dry basis 63.8-g

P content of DCP 18.1%

F content of DCP 0.076%

Total P₂0₅ recovered 30.8g

P₂0₅ content of the filtrate 0.12%

Weight of the filtrate 760g This confirms that dicalcium phosphate of high purity is obtained on further addition of hydrated lime to monocalcium phosphate containing filtrate.

The flow diagram clearly shows how wash water obtained in the second and third stage can be effectively recycled to leach out monocalcium phosphate and to wash the filter cake containing gypsum which is a by-product.

The appended claims do not exclude obvious equivalents and alteration known to persons skilled in the art from their scope.

Claims

CLAIMS:

1. A process for the preparation of feed grade dicalcium phosphate substantially free of fluoride from a source containing monocalcium phosphate such as superphosphate, concentrated super phosphate and fertilizer grade phosphate which comprises the steps of (a) leaching out monocalcium phosphate therefrom with water or recycle wash water from at lest one subsequent steps, (b) adding a first quantity of a solution of hydrated lime thereto to precipitate and separate contaminants like iron, aluminum and fluorine containing compounds therefrom, (c) adding a further quantity of hydrated lime to the filtrate from step (b) which contains monocalcium phosphate to produce dicalcium phosphate as precipitate, which is separated, washed and dried, wash water from step (b) and (c) being recycled to step (a.) to leach out further monocalciu phosphate.

2. The process as claimed in claim 1, wherein superphosphate is obtained by treating tricalcium phosphate with an acid such as sulphuric acid or phosphoric aci and then allowing the green super produced thereby to cure automatically.

3. The process as claimed in claim 1, wherein in step (b) said first quantity of hydrated lime is added to raise the pH from 2.2/2.6 to 2.9/3.2 and to precipitate impurities such as iron, aluminum and fluorides therefrom.

4. The process as claimed in claim 1, wherein said filtrate from step (b) containing monocalcium phosphate is treated with hydrated lime to raise the pH to 6.5 and above till dicalcium phosphate crystallizes out therefrom.

5. Dicalcium phosphate whenever prepared by a process as claimed in claims 1 to 4.