Method for preparing polyphosphate from white phosphate fertilizer

Abstract

The invention relates to a method for preparing polyphosphate by using a white phosphate fertilizer, which comprises the following steps: uniformly mixing the white phosphate fertilizer with tap water, stirring and heating to 40-60 DEG C to prepare white phosphate fertilizer slurry; adding sulfuric acid, stirring and heating to 60-100 DEG C, and reacting for 60-120 minutes to obtain white phosphate fertilizer acidolysis slurry; filtering while hot to obtain a white phosphate fertilizer acidolysis filtrate and an acidolysis filter cake, and washing the acidolysis filter cake with hot water to obtain phosphogypsum and washing water; adding a neutralization regulator into the white phosphate fertilizer acidolysis filtrate, keeping the temperature during acidolysis, and stirring to react for 10-60 minutes to prepare neutralization regulation slurry; concentrating the neutralized and adjusted slurry until the water content is 30%, transferring to a polymerization reaction device, adding a condensing agent, heating to 110-250 DEG C, and reacting for 45-180 minutes to prepare polyphosphate; low-value citrate-soluble phosphorus in the white phosphate fertilizer can be converted into high-value polyphosphate, and a new way is provided for high-value utilization of the white phosphate fertilizer.

Description

Technical Field

[0001] The invention belongs to the technical field of phosphorus chemical industry, in particular to a method for preparing polyphosphate by utilizing white phosphorus fertilizer. Background Art

[0002] White phosphate fertilizer is a solid product obtained in the neutralization stage of the production of feed-grade calcium hydrogen phosphate using wet-process phosphoric acid. Its P2O5 content is about 20-35%, and it is enriched with most of the impurities such as Fe, Al, and F in wet-process phosphoric acid. White phosphate fertilizer takes away 15-30% of the total phosphorus in wet-process phosphoric acid, and its water-soluble phosphorus accounts for less than 5% in general. Its application range is extremely small, and its current market price is about 25% of conventional phosphate fertilizers with the same nutrients. The existence of white phosphate fertilizer has seriously restricted the development of the feed-grade calcium hydrogen phosphate industry. Finding new ways to utilize white phosphate fertilizer at a high value is of great practical significance to the healthy development of the phosphorus chemical industry. In practical applications, white phosphate fertilizer is generally directly physically mixed with other substances to make compound fertilizer, which does not substantially change the form and market value of phosphorus.

[0003] After searching, the Chinese patent publication number: CN104140088A discloses a method for producing fertilizer-grade monoammonium phosphate using white fertilizer, which mixes the acid hydrolyzed white phosphate with a large amount of wet-process phosphoric acid to reduce the content of metal cations such as iron, aluminum, magnesium, and calcium in the mixed system, then neutralizes it with ammonia, and dries it to obtain fertilizer-grade monoammonium phosphate, which meets the relevant national standards for products. However, due to the high cost of phosphoric acid and liquid ammonia, and the finished product is low-nutrient powdered ammonium, the market value is not high and the profit margin is small.

[0004] Chinese patent publication number: CN106477543B discloses a high-value application process for white fertilizer, which extracts and purifies the acid hydrolyzate of white phosphate fertilizer to separate metal impurities such as iron, aluminum and magnesium to obtain high-quality phosphoric acid. Due to the long process flow, complicated operation and high cost of this method, it has not yet been put into practical use.

[0005] Literature: "Research on the recovery of feed-grade calcium hydrogen phosphate from white fertilizer, Sichuan Chemical Industry 1997 No. A1 P10-121672-4887" uses wet phosphoric acid to leaching white phosphate fertilizer. The main content is: wet phosphoric acid is mixed with white phosphate fertilizer to convert the calcium hydrogen phosphate therein into calcium dihydrogen phosphate, and then neutralized to pH = 2.6 with ash milk without filtering and separation, and finally filtered and separated to obtain a clear liquid that can be used for the production of feed-grade calcium hydrogen phosphate. This method can recover free phosphoric acid and P2O5 combined with Ca in white phosphate fertilizer. The total amount of phosphorus in this part accounts for 20% of the total phosphorus in white phosphate fertilizer. Most of the P2O5 remains in the white phosphate fertilizer and is difficult to extract and utilize.

[0006] Literature: "Technical Scheme for Producing Compound Fertilizer Using Fertilizer-Grade Calcium Hydrogen Phosphate" (Phosphate Fertilizer and Compound Fertilizer. 2001, (04)) describes that white phosphate fertilizer is mixed with phosphoric acid and sulfuric acid and then reacted with liquid nitrogen to generate NPK compound fertilizer. Due to the presence of a large amount of CaSO4 in the product, its water solubility and nutrient content are both low, which has great defects and low economic value.

[0007] Therefore, the key issue is how to convert the citrate-soluble phosphorus in white phosphate fertilizer into water-soluble phosphorus while reducing the mass fraction of iron, aluminum and magnesium. Summary of the invention

[0008] The purpose of the present invention is to overcome the shortcomings of the prior art, provide a method for preparing polyphosphate using white phosphate fertilizer, and develop and utilize the white phosphate fertilizer at low cost and high value.

[0009] The present invention solves the technical problem by adopting the following technical solutions:

[0010] A method for preparing polyphosphate using white phosphate fertilizer comprises the following steps:

[0011] S1. Evenly mix white phosphorus fertilizer and tap water, stir and heat to 40-60° C. to prepare white phosphorus fertilizer slurry;

[0012] S2. Add sulfuric acid to the white phosphorus fertilizer slurry, stir and heat to 60-100° C., react for 60-120 minutes, and obtain white phosphorus fertilizer acidolysis slurry;

[0013] S3, filtering the white phosphate fertilizer acidolysis slurry while hot to obtain white phosphate fertilizer acidolysis filtrate and acidolysis filter cake, and washing the acidolysis filter cake with hot water to obtain phosphogypsum and washing water;

[0014] S4, adding a neutralizing agent to the obtained white phosphate fertilizer acid hydrolysis filtrate, maintaining the temperature at the acid hydrolysis temperature, stirring the reaction for 10 to 60 minutes, and obtaining a neutralization adjustment slurry;

[0015] S5. Concentrate the obtained neutralized and adjusted slurry to 30% water content, transfer it to a polymerization reaction device, add a condensation agent, raise the temperature to 110-250° C., react for 45-180 minutes, and obtain polyphosphate.

[0016] Moreover, the white phosphate fertilizer described in step S1 is a neutralization byproduct of feed-grade calcium hydrogen phosphate production, wherein the dry basis P2O5 content is 25-35wt%, and the water-soluble P2O5 accounts for 0%-15% of the effective P2O5 content.

[0017] Moreover, the concentration of sulfuric acid added in step S2 is 60%-98%, and the ratio of the amount of S in sulfuric acid to the amount of P in white phosphate fertilizer is 0.8-2.0.

[0018] Moreover, the neutralizing adjusting agent in step S4 is at least one of liquid ammonia, urea, sulfuric acid, ammonium sulfate, urea sulfate, urea phosphate, and ammonium phosphate, so as to maintain the mass ratio of nitrogen to phosphorus in the neutralizing adjusting slurry at 0.2-0.5 and the mass ratio of sulfur to phosphorus at 0.5-1.0.

[0019] Furthermore, the pH value of the neutralized slurry obtained in step S4 is 2.0 to 2.5.

[0020] Moreover, the condensing agent in step S5 is at least one of ammonium sulfate, melamine, urea and dicyandiamide.

[0021] Moreover, the amount of the condensing agent added is 0.05-1 wt % of the neutralized adjustment slurry.

[0022] Moreover, the polyphosphate obtained in step S5 has a water-soluble phosphorus content of 50% to 95% of the available phosphorus, a phosphorus polymerization rate of 20% to 95%, a product pH value of 2 to 5, and a polymerization degree of 2 to 5.

[0023] The advantages and positive effects of the present invention are:

[0024] 1. This method uses a simple and easy-to-industrial process to convert low-value white phosphate fertilizer into high-value water-soluble phosphorus and polyphosphate, creating a new source of profit for related companies.

[0025] 2. The present invention effectively protects phosphorus resources and achieves green recycling of phosphorus by efficiently utilizing phosphorus in white phosphate fertilizer.

[0026] 3. The raw material white phosphate fertilizer used in this method contains a certain proportion of trace elements required by plants, such as calcium, magnesium, iron, manganese, and copper. The generated polymerized phosphorus is a slow-release component that can chelate a certain amount of metal ions and activate them, thereby converting insoluble trace elements into soluble ones that can be absorbed by plants, thereby realizing the high-value utilization of industrial by-products.

[0027] 4. The present invention decomposes phosphates in white fertilizer by adding sulfuric acid to obtain phosphoric acid, and precipitates calcium in white phosphorus fertilizer slurry in the form of calcium sulfate, thereby reducing the content of water-insoluble matter in the acidolysis solution; and by washing the filter cake with water, the water-soluble phosphorus on the filter cake is recovered into the system as much as possible, thereby improving the phosphorus recovery rate of the entire process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0030] Example 1

[0031] A method for preparing polyphosphate using white phosphate fertilizer comprises the following steps:

[0032] S1. Take white phosphate fertilizer, the wet basis nutrient composition is N: 0%, total P2O5: 28.32%, effective P2O5: 27.80%, water-soluble P2O5: 3.66%, the ratio of total water-soluble phosphorus to total effective phosphorus is: 13.16%, and the water content is 8.68%; sulfuric acid is an industrial by-product; take 400g of tap water in a beaker, start stirring, quickly add 200g of white phosphate fertilizer (water content 8.68%), beat the water, the water content is 69.56%, and the temperature is raised to 50°C to obtain white phosphate fertilizer slurry.

[0033] S2. After adding 80 g of concentrated sulfuric acid to the white phosphorus fertilizer slurry, the temperature was raised to 85° C. and the acid hydrolysis reaction was carried out for 60 minutes to obtain white phosphorus fertilizer acid hydrolysis slurry.

[0034] S3, filter the white phosphate fertilizer acidolysis slurry while hot to obtain 410.55g of white phosphate fertilizer acidolysis filtrate (containing 10.15% phosphorus pentoxide and 2.42% sulfur trioxide) and an acidolysis filter cake; use 400g of 85°C tap water to rinse the filter cake while filtering, and drain to obtain 259.25g of phosphogypsum (drying weight 92.93g, on a dry basis, containing 1.57% phosphorus pentoxide and 51.82% sulfur trioxide) and 410.2g of wash water (containing 3.29% phosphorus pentoxide and 0.16% sulfur trioxide).

[0035] S4, take 100g of the acid solution of white phosphate fertilizer in S3, add 8.2g of urea and 12.5g of concentrated sulfuric acid, stir and react for 10min to obtain a neutralized adjusted slurry;

[0036] S5. After the neutralized and adjusted slurry is concentrated to about 30% water content, 0.05 g of histidine is added and mixed, and the mixture is transferred to an oven for polymerization reaction at a reaction temperature of 150° C. for 210 min. After cooling and crushing, 28.87 g of polyphosphate is obtained.

[0037] The nutrient composition is: N: 9.35%, effective P2O5: 35.16%, water-soluble P2O5: 28.13%, the ratio of total water-soluble phosphorus to total effective phosphorus is: 80.00%, polymerized phosphorus accounts for 75.52% of the effective phosphorus content, and the pH value is: 2.3.

[0038] Example 2

[0039] A method for preparing polyphosphate using white phosphate fertilizer, the steps are as follows:

[0040] S1. Take white phosphate fertilizer, wet nutrient composition N: 0, total P2O5: 28.32%, effective P2O5: 27.80%, water-soluble P2O5: 3.66%, the ratio of total water-soluble phosphorus to total effective phosphorus is: 13.16%, water content is 8.68%; sulfuric acid is an industrial by-product, with a concentration of 98%; ammonium phosphate is 55 powdered ammonium (nutrient 11-44);

[0041] S2. Take 200 g of the wash water obtained in step S3 of Example 1 into a beaker, start stirring, quickly add 100 g of white phosphate fertilizer, slurry, the moisture content is 65.78%, raise the temperature to 60°C, add 210 g of the white phosphate fertilizer acidolysis filtrate obtained in Example 1 and 40 g of concentrated sulfuric acid, stir and heat to 85°C, acidolysis reaction for 60 minutes, and obtain white phosphate fertilizer acidolysis slurry.

[0042] S3, filter while hot, wash the filter cake with 200g 85℃ hot water to obtain 415.3g white phosphate fertilizer acid hydrolysis filtrate (containing 11.54% phosphorus pentoxide and 3.56% sulfur trioxide), 129.50g phosphogypsum (drying weight 52.31g, on a dry basis, containing 1.37% phosphorus pentoxide and 51.24% sulfur trioxide) and 205.2g washing water (containing 3.68% phosphorus pentoxide and 1.0% sulfur trioxide).

[0043] S4. Take 100g of the acid hydrolysis filtrate of white phosphate fertilizer, add 26.23g of 55 powdered ammonium to the acid hydrolysis solution, and add 7.78g of urea and 13.27g of concentrated sulfuric acid thereto, react at 85°C for 10min to obtain a neutralized adjusted slurry.

[0044] S5. Add 0.1 g of arginine to the concentrated neutralized adjusted slurry and mix well. Transfer to an oven for polymerization reaction at a temperature of 200° C. for 60 min. After cooling and crushing, 60.0 g of polyphosphate is obtained.

[0045] The nutrient composition is: N: 9.88%, effective P2O5: 37.15%, water-soluble P2O5: 31.75%, the ratio of total water-soluble phosphorus to total effective phosphorus is: 85.46%, polymerized phosphorus accounts for 78.31% of the effective phosphorus content, and the pH value is 2.5.

[0046] Example 3

[0047] A method for preparing polyphosphate using white phosphate fertilizer, the steps are as follows:

[0048] S1. Take white phosphate fertilizer, wet basis nutrient composition N: 0, total P2O5: 28.32%, effective P2O5: 27.80%, water-soluble P2O5: 3.66%, the ratio of total water-soluble phosphorus to total effective phosphorus is: 13.16%, and the water content is 8.68%; sulfuric acid is an industrial by-product with a concentration of 98%; ammonium sulfate is industrial grade; take 200g of the wash water obtained in Example 2 in a beaker, start stirring, quickly add 100g of white phosphate fertilizer, beat with pulp, the water content is 64.12%, the temperature is raised to 55°C, and the acidolysis reaction is 60min to obtain white phosphate fertilizer acidolysis slurry.

[0049] S2, add 185g of the acid solution obtained in Example 2 and 40g of concentrated sulfuric acid, add 25g of tap water, stir and heat to 75°C, and acidolyze for 120min to obtain white phosphate fertilizer acidolysis slurry;

[0050] S3, filter while hot, wash the filter cake with 200g of 75℃ hot water to obtain 417.6g of white phosphate fertilizer acid hydrolysis filtrate (containing 11.55% phosphorus pentoxide and 3.65% sulfur trioxide), 126.70g of phosphogypsum (drying weight 52.54g, on a dry basis, containing 1.32% phosphorus pentoxide and 51.45% sulfur trioxide) and 205.7g of washing water (containing 3.72% phosphorus pentoxide and 1.1% sulfur trioxide).

[0051] S4. Take 100g of the acid hydrolysis filtrate of white phosphate fertilizer, add 3.0g of urea and 10.5g of ammonium sulfate, react at 75°C for 20min, and obtain a neutralized adjusted slurry.

[0052] S5. Add 0.1 g of histidine to the concentrated neutralized adjusted slurry and mix well. Transfer to an oven for polymerization reaction at a temperature of 180° C. for 70 min. After cooling and crushing, 31.30 g of polyphosphate is obtained.

[0053] The nutrient composition is: N: 10.55%, effective P2O5: 36.89%, water-soluble P2O5: 30.14%, the ratio of total water-soluble phosphorus to total effective phosphorus is: 81.70%, polymerized phosphorus accounts for 68.52% of the effective phosphorus content, and the pH value is 2.4.

[0054] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for preparing polyphosphate using white phosphate fertilizer, characterized in that: The steps include: S1. Evenly mix white phosphorus fertilizer and tap water, stir and heat to 40-60° C. to prepare white phosphorus fertilizer slurry; S2. Add sulfuric acid to the white phosphorus fertilizer slurry, stir and heat to 60-100° C., react for 60-120 minutes, and obtain white phosphorus fertilizer acidolysis slurry; S3, filtering the white phosphate fertilizer acidolysis slurry while hot to obtain white phosphate fertilizer acidolysis filtrate and acidolysis filter cake, and washing the acidolysis filter cake with hot water to obtain phosphogypsum and washing water; S4, adding a neutralizing agent to the obtained white phosphate fertilizer acid hydrolysis filtrate, maintaining the temperature at the acid hydrolysis temperature, stirring the reaction for 10 to 60 minutes, and obtaining a neutralization adjustment slurry; S5. Concentrate the obtained neutralized and adjusted slurry to 30% water content, transfer it to a polymerization reaction device, add a condensation agent, raise the temperature to 110-250° C., react for 45-180 minutes, and obtain polyphosphate.

2. The method for preparing polyphosphate using white phosphate fertilizer according to claim 1, characterized in that: The white phosphate fertilizer described in step S1 is a neutralization byproduct of feed-grade calcium hydrogen phosphate production, wherein the dry basis P2O5 content is 25-35wt%, and the water-soluble P2O5 accounts for 0%-15% of the effective P2O5 content.

3. The method for preparing polyphosphate using white phosphate fertilizer according to claim 1, characterized in that: The concentration of sulfuric acid added in step S2 is 60% to 98%, and the ratio of the amount of S in sulfuric acid to the amount of P in white phosphate fertilizer is 0.8 to 2.

0.

4. The method for preparing polyphosphate using white phosphate fertilizer according to claim 1, characterized in that: The neutralizing adjusting agent in step S4 is at least one of liquid ammonia, urea, sulfuric acid, ammonium sulfate, urea sulfate, urea phosphate, and ammonium phosphate, so as to maintain the mass ratio of nitrogen to phosphorus in the neutralizing adjusting slurry at 0.2-0.5 and the mass ratio of sulfur to phosphorus at 0.5-1.

0.

5. The method for preparing polyphosphate using white phosphate fertilizer according to claim 1, characterized in that: The pH value of the neutralized slurry obtained in step S4 is 2.0 to 2.

5.

6. The method for preparing polyphosphate using white phosphate fertilizer according to claim 1, characterized in that: The condensing agent in step S5 is at least one of ammonium sulfate, melamine, urea and dicyandiamide.

7. The method for preparing polyphosphate using white phosphate fertilizer according to claim 6, characterized in that: The amount of the condensing agent added is 0.05-1wt% of the neutralized adjustment slurry.

8. The method for preparing polyphosphate using white phosphate fertilizer according to claim 1, characterized in that: The polyphosphate obtained in step S5 has a water-soluble phosphorus content of 50%-95% of the available phosphorus, a phosphorus polymerization rate of 20%-95%, a product pH value of 2-5, and a polymerization degree of 2-5.

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