SU1416442A1 - Method of extracting fluorine phosphate raw materials - Google Patents

Description

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The invention relates to a method for the recovery of fluorine in the processing of fofat raw materials for complex fertilizers,

The aim of the invention is to increase the yield of fluoride in the product.

When phosphate raw material decomposes with concentrated nitric acid, fluorine in the form of calcium silicofluoride, together with the insoluble residue, transforms into the solid phase. From the solid phase, calcium silicate fluoride is extracted with water and separated from the insoluble residue. Calcium fluoride is precipitated from the extract during ammonization. The process of calcium fluoride release is based on the reaction:

CaSiF + 2Ca (NO3) 2+ j + ZHjO-i- solution

3CaF,

 +

Sio

sediment

For this reaction, a certain CaO / F ratio and pH of the solution is necessary. An aqueous extract of calcium silicate fluoride must necessarily contain calcium nitrate. This is accomplished by capturing the fluorine-solid phase of a portion of the mother liquor. But since the mother liquor, in addition to Ca {NOj), contains nitric and phosphoric acids, it is first necessary to neutralize the free acidity (pH 2-2.3) in order for the precipitation reaction to occur. The products of neutralization — nitrate and ammonium phosphate — have a high solubility and remain in the liquid phase. With an increase in pH to 2.5, the first crystallizing phase will be calcium fluoride, which has the lowest solubility of all salts formed in this system, which ensures an increase in the yield of fluorine in the final product.

I.

Example 1. 1000 g of apatite concentrate containing 3.1% of fluorine are treated with 2170 g of 60% nitric acid. The resulting slurry is concentrated to T: W 1: 0.6. This gives 193.4 g of a condensed mass containing 13.2% fluorine. This mass is treated with water, the insoluble residue is separated, and the extract is ammoniated to a pH of 2.5. The result is 95.0 g of a wet fluorinated concentrate containing 26.7% fluorine. The yield of fluorine in the product, CaFiji, is 82% of that introduced with the raw material.

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Q 5

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five

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50

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Example 2. 1000 g of apatite concentrate containing 3.1% of fluorine are treated with 2170 g of 60% nitric acid. The resulting slurry is concentrated to T: W 1: 0, .8. This gives 217.5 g of a condensed mass containing 12.4% fluorine. This mass is treated with water, the insoluble residue is separated, and the extract is ammoniated to a pH of 2.75 °. The result is 100.5 g of a wet fluoride concentrate. containing 26.9% fluorine. The yield of fluorine in the product, CaFj, is 87%.

Example 3. 1000 g of apatite concentrate containing 3, .1% of fluorine are treated with 2170 g of 60% nitric acid. The resulting pulp is thickened to T: W 1; 1. You get 241.8 g of a condensed mass containing 11.3% fluorine. This mass is treated with water, the insoluble residue is separated, and the extract is ammoniated to a pH of 3.0. As a result, receive. 101.0 wet fluoride concentrate containing 27% fluorine. Fluorine yield to the product - CaF "- 88% of the feed with the raw material.

In tab. 1 shows the dependence of the fluorine yield in the product on the T: W ratio (pH 2.5).

Table 1

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At T: L below 1: 0.6, the concentration of calcium nitrate - CaCNt a) - is insufficient for the precipitation of calcium fluoride to occur, therefore the yield of fluoride in the product decreases.

At T: W above 1: 1, an excess of trapped liquid phase promotes the formation of by-products, reducing the fluorine yield.

In tab. 2 shows the dependence of the yield of fluorine in the product on the pH at T; W 1: 0.8.

Table

ph

The yield of fluorine in the product,%

2.3

2.5

3.0

3.2

50.0 84 ,, 5 89.5 75.0

ten

At pH values below 2.5, the yield of fluorine decreases, since at these pH values only free acidity is neutralized and the CaFj precipitation reaction practically does not proceed. When the ammonization pH is above 3.2, calcium phosphates are formed, contaminating the final product, and the yield of fluorine is reduced.

The invention allows to increase the yield of fluorine in the product from 70.2-78.3 to 82.0-89.5%.

Claims (1)

METHOD FOR REMOVING FLUOR FROM PHOSPHATE RAW MATERIAL, including its decomposition by concentrated nitric acid, separation of the liquid phase, treatment of the solid residue with water and. the selection of a fluorine-containing product from an aqueous extract, which entails the fact that, in order to increase the yield of fluorine in the product, separation of the liquid phase is carried out to a ratio T: G »1: 0.6-1.0, and the aqueous extract ammonia to a pH of 2.5-3.0 with the release of calcium fluoride. ·>