Method for preparing slow-release compound fertilizer from ammonium slag

Abstract

The invention belongs to the field of environmental protection, and particularly relates to a method for preparing a slow-release compound fertilizer by using ammoniation slag, which comprises the following steps: mixing ammoniation slag and urea, heating, and carrying out polymerization reaction to obtain the slow-release compound fertilizer, the ammonium slags are filter slags generated in a neutralization procedure in a process of producing monoammonium phosphate from wet-process phosphoric acid; on a dry basis, the total Mg content of the ammonium slag is 65000 to 110000 ppm. According to the method, the ammonium slag and the urea are mixed and then directly subjected to the high-temperature polymerization reaction, the efficient compound fertilizer containing ammonium polyphosphate, calcium ammonium polyphosphate and magnesium ammonium phosphate is obtained, the method is short in preparation process and low in cost, the total nutrient content and the slow release effect of the product are greatly improved, and comprehensive and efficient utilization of ammonium slag resources is achieved.

Description

Technical Field

[0001] The invention belongs to the field of environmental protection, and in particular relates to a method for preparing a slow-release compound fertilizer by utilizing ammonium slag. Background Art

[0002] Ammonium slag, i.e. monoammonium phosphate filter residue, is a by-product of the production of monoammonium phosphate from wet-process phosphoric acid. The comprehensive utilization of this filter residue is one of the difficult problems faced by phosphorus chemical companies.

[0003] Ammonium slag has the characteristics of complex composition, high content of trace elements such as magnesium and calcium, high proportion of effective P, and high yield. However, due to its poor water solubility, it can only be used as a low-value base fertilizer as a by-product. The orthophosphate and trace elements in it have short fertilizer effects during application and are easily fixed by the soil and converted into substances that are difficult to be used by crops.

[0004] At present, one of the main uses of ammonium slag is to regulate the nutrients of powdered monoammonium phosphate and diammonium phosphate. This not only consumes a certain amount of high-quality phosphoric acid, but also the ammonium phosphate products produced by filter residue regulation are low-concentration phosphate fertilizers. As the production capacity of phosphate compound fertilizer products continues to increase, the selling price of such low-concentration products is often lower than the cost, and there is no competitive advantage at all. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for preparing a slow-release compound fertilizer using ammonium slag, which has a short process and low cost, and the prepared compound fertilizer has a high nutrient content and good slow-release properties.

[0006] The present invention provides a method for preparing a slow-release compound fertilizer by utilizing ammonium slag, comprising the following steps:

[0007] After the ammonium slag is mixed with urea, the mixture is heated to undergo a polymerization reaction to obtain a slow-release compound fertilizer;

[0008] The ammonium slag is the filter residue produced in the neutralization process during the production of monoammonium phosphate by wet-process phosphoric acid; the total Mg content of the ammonium slag is 65,000 to 110,000 ppm on a dry basis.

[0009] Preferably, the neutralization step specifically includes:

[0010] Using ammonia to remove SO4 2- The wet-process phosphoric acid is subjected to the first stage of neutralization and filtration to obtain a filtrate and a filter residue;

[0011] The first stage filtrate is subjected to a second stage neutralization with aqueous ammonia, and filtered to obtain a second stage filtrate and a second stage filter residue;

[0012] The ammonium slag is the second-stage filter residue produced in the neutralization process.

[0013] Preferably, on a dry basis, the total P2O5 content of the ammonium slag is 40 to 60 wt%, the effective P2O5 content of the ammonium slag accounts for 90 to 99.6 wt% of the total P2O5 content, and the water-soluble P2O5 content of the ammonium slag accounts for 40 to 50 wt% of the total P2O5 content.

[0014] Preferably, on a dry basis, the effective Mg content of the ammonium slag accounts for 90-99.5wt% of the total Mg content, and the water-soluble Mg content of the ammonium slag accounts for 15-30wt% of the total Mg content.

[0015] Preferably, on a dry basis, the total Ca content of the ammonium slag is 30,000 to 50,000 ppm, the effective Ca content of the ammonium slag accounts for 90 to 99 wt % of the total Ca content, and the water-soluble Ca content of the ammonium slag accounts for 5 to 10 wt % of the total Ca content.

[0016] Preferably, the ammonia nitrogen content of the ammonium slag is 5 to 10 wt % on a dry basis.

[0017] Preferably, on a dry basis, the total F content of the ammonium slag is ≤ 1 wt%.

[0018] Preferably, on a dry basis, the moisture content of the ammonium slag is ≥ 20 wt %.

[0019] Preferably, the N / P molar ratio of the ammonium slag after mixing with urea is 1 to 2.2.

[0020] Preferably, the polymerization reaction temperature is 180-260° C.; the polymerization reaction time is 1-4 hours.

[0021] Compared with the prior art, the present invention provides a method for preparing a slow-release compound fertilizer using ammonium slag, comprising the following steps: mixing the ammonium slag with urea, heating and performing a polymerization reaction to obtain a slow-release compound fertilizer; the ammonium slag is a filter residue produced by a neutralization process in the production of monoammonium phosphate by wet-process phosphoric acid; the total Mg content of the ammonium slag is 65,000 to 110,000 ppm on a dry basis. The present invention obtains a high-efficiency compound fertilizer containing ammonium polyphosphate, calcium ammonium polyphosphate and magnesium ammonium phosphate by directly performing a high-temperature polymerization reaction after mixing the ammonium slag with urea. The preparation process of the method is short and the cost is low, and the total nutrient content and slow-release effect of the product are greatly improved, thereby realizing the comprehensive and efficient utilization of ammonium slag resources. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The present invention provides a method for preparing a slow-release compound fertilizer by utilizing ammonium slag, comprising the following steps:

[0024] After the ammonium slag is mixed with urea, the mixture is heated to undergo a polymerization reaction to obtain a slow-release compound fertilizer;

[0025] The ammonium slag is the filter residue produced in the neutralization process during the production of monoammonium phosphate by wet-process phosphoric acid; the total Mg content of the ammonium slag is 65,000 to 110,000 ppm on a dry basis.

[0026] In the method provided by the present invention, the neutralization process in the process of producing monoammonium phosphate from wet-process phosphoric acid includes two stages of neutralization, and the specific process includes:

[0027] Using ammonia to remove SO4 2- The wet-process phosphoric acid is subjected to the first stage of neutralization and filtration to obtain a filtrate and a filter residue;

[0028] The first stage filtrate is subjected to second stage neutralization with aqueous ammonia, and filtered to obtain a second stage filtrate and a second stage filter residue.

[0029] In the method provided by the present invention, since the first-stage filter residue generally contains a high level of F which is harmful to plants, the second-stage filter residue is preferably used as the ammonium residue used in the production of the present invention.

[0030] In the method provided by the present invention, on a dry basis, the total P2O5 content of the ammonium slag is preferably 40-60wt%, more preferably 45-55wt%, and specifically 48.26wt%; the effective P2O5 content of the ammonium slag preferably accounts for 90-99.6wt% of the total P2O5 content, more preferably 99-99.5wt%, and specifically 99.44wt%; the water-soluble P2O5 content of the ammonium slag preferably accounts for 40-50wt% of the total P2O5 content, more preferably 42-46wt%, and specifically 44.14wt%.

[0031] In the method provided by the present invention, the ammonia nitrogen content of the ammonium slag is preferably 5-10wt%, more preferably 7-9wt%, and specifically 8.78wt%, calculated on a dry basis.

[0032] In the method provided by the present invention, the total Mg content of the ammonium slag is 65000-110000 ppm, preferably 90000-100000 ppm, and specifically 94100 ppm, on a dry basis; the effective Mg content of the ammonium slag preferably accounts for 90-99.5wt% of the total Mg content, more preferably 98-99wt%, and specifically 98.72wt%; the water-soluble Mg content of the ammonium slag preferably accounts for 15-30wt% of the total Mg content, more preferably 18-25wt%, and specifically 20.09wt%.

[0033] In the method provided by the present invention, on a dry basis, the total Ca content of the ammonium slag is preferably 30,000 to 50,000 ppm, more preferably 35,000 to 45,000 ppm, and specifically 39,200 ppm; the effective Ca content of the ammonium slag preferably accounts for 90 to 99 wt% of the total Ca content, more preferably 96 to 98 wt%, and specifically 97.19 wt%; the water-soluble Ca content of the ammonium slag accounts for 5 to 10 wt% of the total Ca content, more preferably 7 to 9 wt%, and specifically 8.42 wt%.

[0034] In the method provided by the present invention, the total F content of the ammonium slag is preferably ≤1 wt %, more preferably 0.6-0.9 wt %, and specifically 0.827 wt %, calculated on a dry basis.

[0035] In the method provided by the present invention, the moisture content of the ammonium slag is preferably ≥20wt%, more preferably 25-35wt%, specifically 31.27wt%, calculated on a dry basis.

[0036] In the method provided by the present invention, the phosphorus polymerization rate in the ammonium slag is preferably ≤3%, more preferably 1-2%, and specifically 1.62%, based on dry basis. In the present invention, the phosphorus polymerization rate means the ratio of the number of phosphorus molecules that have been polymerized in the polymerization reaction to the total number of P molecules of the reactant; that is, φ=(AB) / A×100%, A is the total P content, and B is the positive P content.

[0037] In the method provided by the present invention, the water-insoluble matter G1 content of the ammonium slag is preferably 40-60wt%, more preferably 45-50wt%, and specifically 47.09wt%, calculated on a dry basis. In the present invention, G1 represents the model of a glass sand core crucible filter, and the pore size of G1 is 80-120μm, which is mainly used to filter out coarse particle precipitation.

[0038] In the method provided by the present invention, the total Fe content of the ammonium slag is preferably 2500-5000 ppm, more preferably 3000-4000 ppm, and specifically 3500 ppm, calculated on a dry basis.

[0039] In the method provided by the present invention, the total SO4 2- The content is preferably 3000-6000ppm, more preferably 4000-5000ppm, and specifically 4300ppm; the effective SO4 2- The content preferably accounts for the total SO4 2- The content is 75-95wt%, more preferably 80-90wt%, and specifically 86.05wt%; the water-soluble SO4 2- Content accounts for total SO4 2- The content is 70-90wt%, more preferably 75-85wt%, specifically 79.07wt%.

[0040] In the method provided by the present invention, the total SiO2 content of the ammonium slag is preferably 1000-2000 ppm, more preferably 1200-1800 ppm, and specifically 1595 ppm, calculated on a dry basis.

[0041] In the method provided by the present invention, the total K content of the ammonium slag is preferably 400 to 800 ppm, more preferably 500 to 700 ppm, and specifically 600 ppm, calculated on a dry basis.

[0042] In the method provided by the present invention, the total Al content of the ammonium slag is preferably 500 to 2000 ppm, more preferably 1000 to 1500 ppm, and specifically 1300 ppm, calculated on a dry basis.

[0043] In the method provided by the present invention, the N / P molar ratio after the ammonium slag and urea are mixed is preferably 1 to 2.2, specifically 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1 or 2.2.

[0044] In the method provided by the present invention, during the heating reaction, monoammonium phosphate in the ammonium slag polymerizes with urea to form ammonium polyphosphate, and calcium ammonium phosphate in the ammonium slag is dehydrated at high temperature to form calcium ammonium polyphosphate.

[0045] In the method provided by the present invention, the temperature of the polymerization reaction is preferably 180-260°C, specifically 180°C, 185°C, 190°C, 195°C, 200°C, 210°C, 215°C, 220°C, 225°C, 230°C, 235°C, 240°C, 245°C, 250°C, 255°C or 260°C; the time of the polymerization reaction is preferably 1-4h, specifically 1h, 1.5h, 2h, 2.5h, 3h, 3.5h or 4h.

[0046] In the method provided by the present invention, after the polymerization reaction is completed, the obtained reaction product is preferably crushed.

[0047] The technical solution provided by the present invention directly performs a high-temperature polymerization reaction after mixing ammonium slag with urea to obtain a high-efficiency compound fertilizer containing ammonium polyphosphate, calcium ammonium polyphosphate and magnesium ammonium phosphate. The preparation process of this method is short and the cost is low. The total nutrient content and slow-release effect of the product are greatly improved, and the comprehensive and efficient utilization of ammonium slag resources is achieved. More specifically, the technical solution provided by the present invention has at least the following advantages:

[0048] 1) The calcium ammonium polyphosphate in the prepared compound fertilizer helps to improve the texture and structure of the soil;

[0049] 2) Calcium ammonium polyphosphate and magnesium ammonium phosphate in the prepared compound fertilizer can reduce the acidity of the soil, thereby improving the soil environment and facilitating the growth of crops;

[0050] 3) The calcium ammonium pyrophosphate and magnesium ammonium phosphate in the prepared compound fertilizer have a lower risk of environmental pollution. They release phosphorus slowly in the soil, which can prevent excessive phosphorus from being lost to groundwater or water bodies, and their poor solubility in water will not cause eutrophication of water bodies;

[0051] 4) The polyphosphate contained in the prepared compound fertilizer has the characteristics of long-term slow release and high utilization rate. The trace elements chelated by the polyphosphate in the compound fertilizer are more easily absorbed by plants, which greatly improves the fertilizer efficiency and realizes the added value of ammonium slag.

[0052] For the purpose of greater clarity, the present invention is described in detail with reference to the following examples and comparative examples.

[0053] In the following embodiments and comparative examples of the present invention, the main components of the second-stage ammoniation slag used are as follows, on a dry basis: total P2O5 content 48.26wt%, effective P2O5 content 47.99wt%, water-soluble P2O5 content 21.3wt%, phosphorus polymerization rate 1.62%, ammonia nitrogen content 8.78wt%, water-insoluble G1 content 47.09wt%, moisture content 31.27wt%, F content 0.827wt%, Fe content 3500ppm, total SO4 2- Content 4300ppm, effective SO4 2- Content 3700ppm, water-soluble SO4 2- Content 3400ppm, total Ca content 39200ppm, effective Ca content 38100ppm, water-soluble Ca content 3300ppm, total Mg content 94100ppm, effective Mg content 92900ppm, water-soluble Mg content 18900ppm, SiO2 content 1595ppm, K content 600ppm, Al content 1300ppm.

[0054] Example 1

[0055] Add urea to the second-stage ammoniation slag (wet slag), control the N / P molar ratio of the mixed system to be 1.2, and stir evenly; carry out polymerization reaction at 220° C. for 2 hours, and then crush the reaction product to obtain a compound fertilizer containing ammonium polyphosphate, calcium ammonium polyphosphate and magnesium ammonium phosphate (6-55-0, 6 corresponds to ammonia nitrogen content, 55 corresponds to effective P2O5 content, 0 corresponds to potassium content, the same below).

[0056] The composition of the compound fertilizer was tested, and the results were as follows: the phosphorus polymerization rate in the compound fertilizer reached 58.95%, the ammonia nitrogen content was 6.59wt%, the effective P2O5 content was 55.30wt%, and the water-soluble P2O5 content was 5.26wt%.

[0057] The slow-release effect of the above compound fertilizer was evaluated: the compound fertilizer was prepared into an aqueous solution at a ratio of 5wt%, the pH value was 6.42, and it was placed at a constant temperature of 25°C for 35 days. The positive P content in the aqueous solution increased from 0.15wt% to 0.89wt%, and the polymerization rate of phosphorus decreased from 43% to 23%. This shows that during the hydrolysis process of the compound fertilizer, the polymerized P gradually hydrolyzed into positive P that can be absorbed by plants, and the compound fertilizer has a good slow-release effect.

[0058] Example 2

[0059] Add urea to the second-stage ammoniation slag (wet slag), control the N / P molar ratio of the mixed system to be 2.0, and stir evenly; carry out polymerization reaction at 220° C. for 2 hours, and then crush the reaction product to obtain a compound fertilizer (8-52-0) containing ammonium polyphosphate, calcium ammonium polyphosphate and magnesium ammonium phosphate.

[0060] The composition of the above-mentioned compound fertilizer was tested, and the results were as follows: the phosphorus polymerization rate in the compound fertilizer reached 58.88%, the ammonia nitrogen content was 8.18wt%, the effective P2O5 content was 51.92wt%, and the water-soluble P2O5 content was 11.08wt%.

[0061] The slow-release effect of the above compound fertilizer was evaluated: the compound fertilizer was prepared into an aqueous solution at a ratio of 5wt%, the pH value was 6.85, and it was placed at a constant temperature of 25°C for 35 days. The positive P content in the aqueous solution increased from 0.15wt% to 0.84wt%, and the polymerization rate of phosphorus decreased from 52.58% to 28.90%. This shows that during the hydrolysis process of the compound fertilizer, the polymerized P gradually hydrolyzed into positive P that can be absorbed by plants, and the compound fertilizer has a good slow-release effect.

[0062] Example 3

[0063] Add urea to the second-stage ammoniation slag (wet slag), control the N / P molar ratio of the mixed system to be 2.0, and stir evenly; carry out polymerization reaction at 220° C. for 3 hours, and then crush the reaction product to obtain a compound fertilizer (8-51-0) containing ammonium polyphosphate, calcium ammonium polyphosphate and magnesium ammonium phosphate.

[0064] The composition of the above-mentioned compound fertilizer was tested, and the results were as follows: the phosphorus polymerization rate in the compound fertilizer reached 53.95%, the ammonia nitrogen content was 8.45wt%, the effective P2O5 content was 51.42wt%, and the water-soluble P2O5 content was 11.31wt%.

[0065] The slow-release effect of the above compound fertilizer was evaluated: the compound fertilizer was prepared into an aqueous solution at a ratio of 5wt%, the pH value was 6.55, and it was placed at a constant temperature of 25°C for 35 days. The positive P content in the aqueous solution increased from 0.16wt% to 0.83wt%, and the polymerization rate of phosphorus decreased from 42.00% to 33.31%. This shows that during the hydrolysis process of the compound fertilizer, the polymerized P gradually hydrolyzed into positive P that can be absorbed by plants, and the compound fertilizer has a good slow-release effect.

[0066] Comparative Example 1

[0067] Take 500g of a section of ammonium slag (dry slag), add 250g of water to prepare a uniform slurry, add 200g of concentrated sulfuric acid at the same time, stir evenly, add 100g of urea after the reaction time of 1h at 90℃, continue stirring, concentrate to a viscous state under negative pressure, add 500g of urea, foam and cure at 170℃ for 1.5h, and obtain a binary fertilizer (11-21-0) containing ammonium polyphosphate.

[0068] The composition of the above binary fertilizer was tested, and the results showed that the phosphorus polymerization rate in the compound fertilizer reached 30.6%, the ammonia nitrogen content was 10.9wt%, the total P2O5 content was 20.8wt%, and the water-soluble P2O5 content was 18.4wt%.

[0069] The slow-release effect of the above binary fertilizer was evaluated: the compound fertilizer was prepared into an aqueous solution at a ratio of 5wt%, the pH value was 4.13, and it was placed at a constant temperature of 25°C for 24 days. The ortho-P content in the aqueous solution increased from 0.32wt% to 1.04wt%, and all polymeric phosphorus was hydrolyzed into ortho-P. This shows that during the hydrolysis of the compound fertilizer, polymeric P was hydrolyzed faster and the slow-release effect was poor. Fertilizers with short slow-release time often lead to nutrient deficiency and frequent application during the plant growth cycle.

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a slow-release compound fertilizer using ammonium slag, characterized in that: The following steps are involved: After the ammonium slag is mixed with urea, the mixture is heated to undergo a polymerization reaction to obtain a slow-release compound fertilizer; The ammonium slag is the filter residue produced in the neutralization process during the production of monoammonium phosphate by wet phosphoric acid; The total Mg content of the ammonium slag is 65000-110000 ppm on a dry basis.

2. The method according to claim 1, characterized in that The neutralization process specifically includes: Using ammonia to remove SO4 2- The wet-process phosphoric acid is subjected to the first stage of neutralization and filtration to obtain a filtrate and a filter residue; The first stage filtrate is subjected to a second stage neutralization with aqueous ammonia, and filtered to obtain a second stage filtrate and a second stage filter residue; The ammonium slag is the second-stage filter residue produced in the neutralization process.

3. The method according to claim 1, characterized in that Calculated on a dry basis, the total P2O5 content of the ammonium slag is 40-60wt%, the effective P2O5 content of the ammonium slag accounts for 90-99.6wt% of the total P2O5 content, and the water-soluble P2O5 content of the ammonium slag accounts for 40-50wt% of the total P2O5 content.

4. The method according to claim 1, characterized in that Calculated on a dry basis, the effective Mg content of the ammonium slag accounts for 90-99.5wt% of the total Mg content, and the water-soluble Mg content of the ammonium slag accounts for 15-30wt% of the total Mg content.

5. The method according to claim 1, characterized in that: On a dry basis, the total Ca content of the ammonium slag is 30000-50000 ppm, the effective Ca content of the ammonium slag accounts for 90-99wt% of the total Ca content, and the water-soluble Ca content of the ammonium slag accounts for 5-10wt% of the total Ca content.

6. The method according to claim 1, characterized in that The ammonia nitrogen content of the ammonium slag is 5-10wt% on a dry basis.

7. The method according to claim 1, characterized in that The total F content of the ammonium slag is ≤1 wt % on a dry basis.

8. The method according to claim 1, characterized in that On a dry basis, the moisture content of the ammonium slag is ≥20wt%.

9. The method according to claim 1, characterized in that: The N / P molar ratio of the ammonium slag after mixing with urea is 1 to 2.

2.

10. The method according to claim 1, characterized in that The polymerization reaction temperature is 180-260° C.; the polymerization reaction time is 1-4 hours.