CN1978313A - Method for preparing fine calcium phosphate by weak acid leaching of triple super phosphate - Google Patents

Abstract

A method for preparing fine calcium phosphate salt by leaching heavy superphosphate with a weak acid, which is characterized in that the loose superphosphate after aging is used to leach the heavy superphosphate with a weak acid, wherein the weak acid refers to the process of leaching Add a small amount of inorganic acid, such as: sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid. The purpose of adding these acids is to increase the solubility of calcium dihydrogen phosphate in the system, which can dissolve the effective phosphorus pentoxide in double superphosphate to the greatest extent; at the same time, adding calcium soluble acid can also reduce the magnesium in double superphosphate. The ratio of ions entering the product ensures stable product quality in the event of changes in the source of heavy superphosphate.

Description

Method for preparing fine calcium phosphate salt by leaching heavy superphosphate with weak acid

1. Technical field

The technical field of application of the invention is the production of fine phosphates.

2. Background technology

The production methods of fine calcium phosphate salts (such as feed grade calcium hydrogen phosphate and toothpaste grade calcium hydrogen phosphate) are basically produced by wet process phosphoric acid or hot process phosphoric acid. The fine calcium phosphate salt produced by thermal phosphoric acid has good quality and high purity, but its production cost is relatively high. This process route is suitable for the use of phosphate with high value-added; while the phosphate produced by wet process phosphoric acid needs to remove phosphoric acid. Only by impurity purification can we produce qualified fine phosphate products, but this kind of process route is often more complicated, the investment of engineering equipment is high, the floor area is large, and there are many shortcomings such as many factory operators. At present, in the process of using double superphosphate as a phosphorus source to produce fine calcium phosphate salts, the patent application number CN98115729 uses clear water to leach heavy superphosphate, and the obtained clear liquid is neutralized with soda ash to obtain a solid ——Common calcium superphosphate, add sodium salt to the liquid phase to remove fluorine, filter, and neutralize the clear liquid with lime to obtain feed grade calcium hydrogen phosphate. The disadvantage of this process is: leaching with process water, the liquid-solid ratio is too high Low (2:1), it is difficult to completely leach the effective phosphorus pentoxide in double superphosphate, and in the defluorination process, it is difficult to remove the fluorine only by adding sodium salt (according to sodium hexafluorosilicate or potassium Solubility graph data of salt), product quality is also difficult to reach HG2636-2000 standard. And the patent that application number is 85102375 (authorization number 1011583) is to leaching common calcium superphosphate with clear water, and liquid-solid ratio is also 2: 1, and the advantage of this patent is that technique is simple and easy, and shortcoming is the effective five in common calcium superphosphate The leaching rate of phosphorus oxide is not high, and a large amount of calcium sulfate hemihydrate (CaSO ₄ ·1/2H ₂ O) needs to be treated. This kind of gypsum has fine crystals and has low efficiency in industrial equipment filtration. In addition, the above two patents do not provide a technical route for producing qualified products using high-magnesium double superphosphate and ordinary superphosphate as raw materials.

The present invention utilizes double superphosphate to produce fine calcium phosphate salt, which can change the disadvantage of high investment in wet-process phosphoric acid for current calcium phosphate salt, and at the same time, dilute acid is used to leach double superphosphate, and the pentoxide in it can be more perfectly utilized. Diphosphorus, to prepare high-purity calcium hydrogen phosphate (CaHPO ₄ ·2H ₂ O) products (such as feed grade calcium hydrogen phosphate). When producing fine calcium phosphate salt, the raw material used is loose heavy superphosphate after ripening, which can reduce product cost more effectively. In addition, the present invention has a wide range of applications. For example, the present invention also provides a solution to double superphosphate or common superphosphate with higher magnesium content. Therefore, utilize the process of the present invention to produce fine calcium phosphate salt (such as feed grade calcium hydrogen phosphate), no matter what kind of raw material is used, its product quality can reach or be better than the requirement of feed grade calcium hydrogen phosphate (HG2636-2000).

3. Contents of the invention

The purpose of the present invention is to provide a kind of weak acid leaching heavy superphosphate to prepare the technology of fine calcium phosphate salt in view of the deficiencies in the prior art. Its characteristic is to use the matured loose superphosphate to leach the superphosphate with weak acid, wherein weak acid refers to adding a small amount of inorganic acid during the leaching process, such as sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid. There are two purposes of adding these acids, one is to increase the solubility of calcium dihydrogen phosphate in the system, and the other is to increase the content of calcium ions in the system, thereby preventing the precipitation of magnesium ions into the product. Wherein these chemical reaction formulas are as follows:

2Ca(H ₂ PO ₄ ) ₂ ·H ₂ O+H ₂ SO ₄ ==Ca(H ₂ PO ₄ ) ₂ ·H ₂ O+2H ₃ PO ₄ +CaSO ₄ ·2H ₂ O↓

2Ca(H ₂ PO ₄ ) ₂ ·H ₂ O+2HNO ₃ ==Ca(H ₂ PO ₄ ) ₂ ·H ₂ O+2H ₃ PO ₄ +Ca(NO ₃ ) ₂

2Ca(H ₂ PO ₄ ) ₂ ·H ₂ O+2HCl==Ca(H ₂ PO ₄ ) ₂ ·H ₂ O+2H ₃ PO ₄ +CaCl ₂

Ca(H ₂ PO ₄ ) ₂ ·H ₂ O+CaO+2H ₂ O＝＝2CaHPO ₄ ·2H ₂ O↓

The solubility of calcium dihydrogen phosphate in water is only 1.8g/100g solution (30°C), while the solubility in phosphoric acid can be increased to 7.7g/100g solution (phosphoric acid solution containing P ₂ O ₅ 1.2%). According to the solubility characteristics of calcium dihydrogen phosphate, when leaching heavy superphosphate, the liquid-solid ratio of leaching is controlled at 3:1 to 9:1, and the temperature is controlled at 40° C. according to the grades of heavy superphosphate. ~60°C, the leaching time is 0.5~3.0 hours, the standard for controlling the amount of acid added is: according to the difference of double superphosphate used, the final pH value in the system is 2.4~3.2. Under these technological conditions, the leaching rate of phosphorus pentoxide (P ₂ O ₅ ) in double superphosphate is above 85%. The leaching solution is neutralized with milk of lime, the neutralization temperature is 30-60°C, the neutralization time is 0.5-4.0 hours, and the neutralization terminal pH value is 4.0-7.0. After the reaction is finished, filter and dry the filter cake to obtain the product.

In addition, when the content of magnesium ions in double superphosphate is enough to affect the product quality, adding calcium soluble acids other than phosphoric acid and sulfuric acid can increase the content of calcium ions in the system, thereby reducing the entry of magnesium ions in double superphosphate. ratio in the product. The calcium-soluble acid here refers to an acid that can form a large amount of soluble calcium salt with calcium ions, such as nitric acid, hydrochloric acid, acetic acid, etc. This is because the concentration ratio of calcium ion and magnesium ion co-precipitation is about ([Mg ²⁺ ]/[Ca ²⁺ ]) about 5.7. Theoretically speaking, when the ratio of the concentration of magnesium ions to the concentration of calcium ions in the system is greater than or equal to 5.7, magnesium ions will precipitate into the product together with calcium ions. In order to control the precipitation rate of magnesium, a certain amount of calcium exists in the system ions are required.

The core technology of the present invention is: in the process of producing fine calcium phosphate salt by using heavy superphosphate, a certain amount of free phosphoric acid is ensured in the system, the purpose of which is to increase the solubility of calcium dihydrogen phosphate in the system, and to dissolve heavy calcium phosphate to the greatest extent. Effective phosphorus pentoxide in superphosphate; at the same time, adding calcium soluble acid (calcium soluble acid here refers to the acid that can form a large amount of soluble calcium salt with calcium ion, such as nitric acid, hydrochloric acid, acetic acid, etc.) The proportion of magnesium ions in calcium phosphate entering the product ensures stable product quality in the event of changes in the source of double superphosphate.

In the prior art, the shortcoming of the technique of utilizing hot-process phosphoric acid to produce fine calcium phosphate is: the production cost of the product is higher, and market competitiveness is low; The investment payback period is longer, and the patent application number is CN98115729, the heavy superphosphate leaching solution is neutralized with soda ash, and its production cost will be very high. Sodium salt solubility theoretically, its implementation possibility is very low; And the patent that application number is 85102375 (authorization number 1011583) is to leach common calcium superphosphate with clear water, because contain a large amount of hemihydrate gypsum in common calcium superphosphate, It is necessary to filter a large amount of leaching residue with fine crystals, which is difficult to realize in large-scale industrial installations. In addition, among the existing patents, none of the patents propose technical solutions for high-magnesium raw materials.

The object of the present invention is achieved by the following technical measures, wherein the parts of raw materials are parts by weight unless otherwise specified.

Method for preparing fine calcium phosphate salt by leaching heavy superphosphate with weak acid:

1. Use inorganic acid to extract heavy superphosphate. According to the grade of heavy superphosphate, the liquid-solid ratio of leaching is controlled at 3:1 to 9:1, the temperature is controlled at 40°C to 60°C, and the leaching time is at 0.5 to 3.0 hours, the standard for controlling the amount of acid added is: according to the difference of double superphosphate used, the final pH value in the system is 2.4 to 3.2;

2. After filtration, the leaching solution is neutralized with milk of lime to produce fine calcium phosphate products. The neutralization temperature is 30-60°C, the neutralization time is 0.5-4.0 hours, and the pH value of the neutralization end point is 4.0-7.0;

3. The mother liquor after the production of fine calcium phosphate salt is neutralized with milk of lime or alkaline substances, the magnesium ions in the mother liquor are precipitated, and the purified mother liquor is recycled;

4. According to the requirement of claim 1, said inorganic acid mainly refers to sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid, etc.;

5. According to the requirements of right 1, the preferential reaction conditions for leaching heavy superphosphate with weak acid are: the liquid-solid ratio is controlled at 5:1 to 7:1, the temperature is controlled at 40°C-60°C, and the leaching time is 1.0-2.0 Hour;

6. According to the requirements of rights 1, 2, 3, 4, and 5, when the magnesium ion content in double superphosphate is enough to affect the product quality, add calcium soluble acid to increase the calcium ion content in the system;

7. According to the requirement of right 6, the addition of calcium soluble acid should be based on the product quality as the criterion. Generally speaking, when the TSP leaching of different sources, its addition should make the calcium ion and magnesium ion in the system The molar ratio is ([Mg ²⁺ ]/[Ca ²⁺ ]) 1:1 to 25:1;

8. According to the requirements of rights 6 and 7, calcium soluble acid refers to an acid that can form a large amount of soluble calcium ions with calcium ions, such as nitric acid, hydrochloric acid, acetic acid, etc.;

9. According to the requirements of claim 2, the preferential reaction conditions for the milk of lime to neutralize the leaching solution are as follows: the neutralization temperature is 40-50°C, the neutralization time is 0.5-1.0 hours, and the pH value of the neutralization end point is 5.0-6.2;

10. According to the requirements of rights 3, 6, 7, and 8, after the fine calcium phosphate salt is produced, the magnesium ions in the mother liquor are precipitated with milk of lime (or other alkaline substances), and the preferential reaction conditions are: neutralization temperature at 30- 50°C, the neutralization time is 0.5-1.0 hours, the end point pH is 8.0-10.0, and the purified mother liquor is recycled.

The present invention has the following advantages:

Compared with the prior art, the present invention can directly utilize heavy superphosphate to produce fine phosphate products, such as calcium hydrogen phosphate, etc., and has changed the previous process route of producing fine calcium phosphate salts with wet-process phosphoric acid as raw material, thus effectively reducing the The total investment of engineering installations. Taking the 10kt/a feed-grade calcium hydrogen phosphate engineering device as an example, the project investment of preparing feed-grade calcium hydrogen phosphate by traditional wet-process phosphoric acid is 10 million yuan, while the project investment of preparing feed-grade calcium hydrogen phosphate by double superphosphate method is It is only 4.5 million yuan, and the depreciation alone can reduce the production cost by 50 yuan. If labor production costs and power consumption are added, the production cost can be reduced by 110 yuan per ton of products. In addition, compared with the patent with the application number CN98115729 and the patent with the application number 85102375 (authorization number 1011583), the present invention can more effectively extract the effective phosphorus pentoxide therein, and the extraction rate of the phosphorus pentoxide is as high as more than 85%. The weight of leaching slag is reduced greatly like this, has alleviated the filtration pressure of leaching slag. In addition, the addition of calcium soluble acid can reduce the proportion of magnesium ions in heavy superphosphate entering the product, and ensure stable product quality when the source of heavy superphosphate changes.

4. Description of drawings

Fig. 1 is the flow block diagram of fine calcium phosphate salt prepared by weak acid leaching heavy superphosphate.

5. Specific implementation

The present invention is described in detail by the following examples, it is necessary to point out that this example is only used to further illustrate the present invention, but can not be interpreted as limiting the protection scope of the present invention, those skilled in the art can according to above-mentioned this invention Some non-essential contents in the invention are improved and adjusted.

Example 1

Weigh _2000g of heavy superphosphate (including total _P2O5 % _44.6 , effective _P2O5 % 42.9, free _P2O5 % 4.2, MgO% 1.42), mix with 16775g _water , leaching at 50°C, The leaching time was 2 hours. Afterwards, adjust the pH with wet-process phosphoric acid (P ₂ O ₅ 20%), share 425g of phosphoric acid removal, control the pH end point to be: pH=2.65, filter, filter residue (fertilizer grade calcium hydrogen phosphate) weight: 234.5g (containing P ₂ O ₅ 29.1%); the filtrate continues to be neutralized with milk of lime, the neutralization temperature is: ~45°C, the time is 1.5 hours, when pH=6.5, filter and dry to obtain 2281g of feed grade calcium hydrogen phosphate (38.7%P ₂ O ₅ ), the total yield of phosphorus pentoxide is: 90.35%.

Example 2

According to the method of example 1, with the raw material of example 1, weigh 5000g of superphosphate and 25000g of water to adjust the slurry, after leaching, adjust the pH with phosphoric acid by humidification method, control the end point pH to be 2.8, share phosphoric acid (P ₂ O ₂₀ % ) 450g. After filtering, fertilizer grade calcium hydrogen phosphate (containing P ₂ O ₅ 31.2%) weighed 2684g, and after further neutralization, 3724g of product (containing P ₂ O ₅ 39%) was obtained, and the total yield of phosphorus pentoxide was 62.6%.

Example 3

Weigh 2000g of heavy superphosphate (including total _P2O5 % _44.3 , effective _P2O5 % 42.5 _, free _P2O5 % 4.8, _MgO % 3.21), mix with 16775g water, leaching at 50°C, The leaching time was 2 hours. Afterwards, adjust the pH with nitric acid (65%), share 110g of nitric acid removal, control the pH end point: pH=2.7, filter, filter residue (fertilizer grade calcium hydrogen phosphate) weight: _315.2g (containing _P2O5 30.3%); filtrate Continue to neutralize with milk of lime, the neutralization temperature is: ~45°C, the time is 1.5 hours, when the pH=6.5, filter and dry to obtain 2012g of feed grade calcium hydrogen phosphate (38.9%P ₂ O ₅ ), phosphorus pentoxide The total yield is: 88.33%.

Example 4

Weigh 6000g of heavy superphosphate (including total _P2O5 % _44.3 , effective _P2O5 % 42.5, free _P2O5 % 4.8, MgO% 3.21), mix _it with _51000g water, leaching at 50°C, The leaching time was 2 hours. Afterwards, adjust the pH with sulfuric acid (93%), share 180g of sulfuric acid removal, control the pH end point: pH=2.76, filter, filter residue (fertilizer grade calcium hydrogen phosphate) weight: 930g (containing P ₂ O ₅ 31.3%); filtrate continues Neutralize with milk of lime, the neutralization temperature is: ~45°C, and the time is 1.5 hours. When the pH=6.5, filter and dry to obtain 5900g of feed grade calcium hydrogen phosphate (39.3%P ₂ O ₅ ), total phosphorus pentoxide Yield: 87.2%.

Claims (10)

1. The weak acid leaching coarse whiting prepares the method for fine calcium phosphate, it is characterized in that:

   1. adopt mineral acid leaching coarse whiting, grade difference according to coarse whiting, the liquid-solid ratio of leaching was controlled at 3: 1 to 9: 1, temperature is controlled at 40 ℃～60 ℃, leaching time was at 0.5～3.0 hour, the standard that control adds the acid amount is: follow the difference according to used coarse whiting, the final pH value in the system is 2.4～3.2.
2. 2. after filtering, leaching liquid utilizes milk of lime (or other alkaline matter) neutralization to produce the fine calcium phosphate product, and neutral temperature is at 30～60 ℃, in and the time be 0.5～4.0 hour, in and endpoint pH be: 4.0～7.0.
3. 3. the mother liquor behind the production fine calcium phosphate adopts the neutralization of milk of lime or other alkaline matter, the magnesium ion in the mother liquor of precipitation of ammonium, the mother liquid recycling after the purification.
4. 4. according to the requirement of right 1, said mineral acid mainly is meant sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid etc.
5. 5. according to the requirement of right 1, the preferential reaction conditions of weak acid leaching coarse whiting is: liquid-solid ratio was controlled at 5: 1 to 7: 1, and temperature is controlled at 40 ℃～60 ℃, and leaching time was at 1.0～2.0 hours.
6. 6. according to the requirement of right 1,2,3,4,5, when the magnesium ion content in the double superhosphate is enough to influence quality product, add calcium dissolvable acid with the calcium ion content in the increase system.
7. 7. according to the requirement of right 6, the addition of calcium dissolvable acid should be criterion with the quality product, and generally speaking, the double superhosphate of different sources when leaching, its addition should make that the mol ratio of calcium ion and magnesium ion is ([Mg in the system ²⁺]/[Ca ²⁺]) 1: 1 to 25: 1.
8. 8. according to the requirement of right 6,7, calcium dissolvable acid is meant the acid that can form the great amount of soluble calcium ion with calcium ion, for example nitric acid, hydrochloric acid, acetic acid etc.
9. 9. according to the requirement of right 2, in the milk of lime (or other alkaline matter) and the preferential reaction conditions of leaching liquid be: neutral temperature is at 40～50 ℃, in and the time be 0.5～1.0 hour, in and endpoint pH be: 5.0～6.2.
10. 10. according to the requirement of right 3,6,7,8, after producing fine calcium phosphate, mother liquor milk of lime (or other alkaline matter) precipitation magnesium ion wherein, preferential reaction conditions is: neutral temperature is at 30～50 ℃, in and the time be 0.5～1.0 hour, terminal point pH=8.0～10.0, the Recycling Mother Solution after the purification is used.