A method for preparing slow-release phosphate fertilizer from monoammonium phosphate by-product ammoniation slag

Abstract

The present invention discloses a method for preparing a slow-release phosphate fertilizer from ammoniated slag produced by monoammonium phosphate, which specifically includes the following steps: step 1: adding phosphoric acid or phosphate-containing salts to the ammonated slag, adjusting the mixture of citric acid-soluble phosphorus: water-soluble phosphorus to 0.5-1.5:1, controlling the ratio of the mass of sulfur, magnesium, iron, and calcium in the mixture to the mass of P2O5 in the mixture to 0.1-0.3:1, controlling the pH of the mixture to 1-4, and then adding urea to adjust the molar ratio of P2O5:N to 2-3:1, and heating to obtain a mixed slurry after the urea is dissolved. The present invention converts part of the orthophosphate in the ammonated slag into ammonium polyphosphate by controlling the polymerization conditions, while ensuring that the proportion of effective phosphorus is as high as 97% to 100%, and the ammonium polyphosphate chelates the medium and trace elements in the ammonated slag during the polymerization process. The polyphosphate in the prepared polymorphic phosphate fertilizer containing medium and trace elements has the characteristics of long-term slow release and high utilization rate, and the chelated medium and trace elements are more easily absorbed by plants, which greatly improves the fertilizer effect of the ammonated slag and realizes the added value of industrial-grade ammonium polyphosphate.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of slow-release phosphate fertilizer, and in particular to a method for preparing slow-release phosphate fertilizer from by-product ammoniation slag of monoammonium phosphate. Background Art

[0002] The ammoniation slag produced as a byproduct of industrial-grade monoammonium phosphate contains a large amount of available phosphorus and trace elements, but due to its poor water solubility, it can only be used as a low-value base fertilizer as a byproduct. The orthophosphate and trace elements in it have a short fertilizer effect during application and are easily fixed by the soil and converted into substances that are difficult to be used by crops.

[0003] The invention patent with publication number: CN 112979386 A discloses a low-polymerization degree ammonium polyphosphate granular multi-component compound fertilizer and a preparation method thereof. It adopts agricultural-grade monoammonium phosphate to prepare an acidic ammonium polyphosphate viscous solution, and generates an ammonium polyphosphate viscous slurry by ammoniation reaction in a tubular reactor. Then, nitrogen, phosphorus, potassium and organic matter are added to granulate in a rotary drum granulator to obtain a low-polymerization degree ammonium polyphosphate granular multi-component compound fertilizer.

[0004] This method has a long process, which increases processing costs. The prepared product has a low polymerization rate and cannot adjust the proportion of various forms of phosphorus. The raw material used is agricultural-grade monoammonium phosphate, which has a high cost. In addition, the low-polymerization degree ammonium polyphosphate granular multi-component fertilizer prepared using agricultural-grade monoammonium phosphate has a low content of trace elements. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a slow-release phosphate fertilizer from by-product ammoniation slag of monoammonium phosphate. The polymorphic phosphate fertilizer obtained by polymerization according to the present invention has an effective phosphorus content of 97% to 100%, a polymerized phosphorus content of 50% to 60%, and phosphorus elements in water-soluble orthophosphate, water-soluble polyphosphate, citrate-soluble orthophosphate and citrate-soluble polyphosphate each accounting for about 1 / 4 by weight. Phosphorus in various forms is beneficial to prolonging the fertilizer effect and improving the utilization rate of nutrients by plants.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A method for preparing slow-release phosphate fertilizer from by-product ammoniation slag of monoammonium phosphate, specifically comprising the following steps:

[0008] Step 1:

[0009] Phosphoric acid or phosphate-containing salts are added to the ammoniation slag to adjust the mixture to have a ratio of citric acid-soluble phosphorus to water-soluble phosphorus of 0.5-1.5:1, the ratio of the mass of sulfur, magnesium, iron, calcium in the mixture to the mass of P2O5 in the mixture is controlled to be 0.1-0.3:1, the pH of the mixture is controlled to be 1-4, urea is added to adjust the molar ratio of P2O5:N to 2-3:1, and the mixture is heated until the urea is dissolved to obtain a mixed slurry;

[0010] Step 2, polymerizing the slurry obtained in step 1 at 130-200° C. for 0.5-2h, controlling the effective phosphorus content of the product to be 97%-100%, the phosphorus polymerization rate to be 40%-60%, controlling the mass proportions of phosphorus in water-soluble orthophosphate, water-soluble polyphosphate, citrate-soluble orthophosphate and citrate-soluble polyphosphate in the polymerized material to be 20%-30%, 20%-30%, 20-30% and 20%-30% respectively, controlling the ratio of the mass of effective sulfur, magnesium, iron and calcium in the polymerized material to the mass of effective P2O5 in the mixture to be 0.1-0.3:1, and crushing and packaging the material after cooling to obtain a powdery multi-form phosphate fertilizer product.

[0011] Among them, in step 1, the ammoniated slag is a by-product slag produced in the ammoniated impurity removal step in the process of preparing industrial-grade monoammonium phosphate with wet phosphoric acid, and the ratio of the mass of sulfur, magnesium, iron and calcium in the ammoniated slag to the mass of P2O5 in the ammoniated slag is 0.1-0.3:1.

[0012] Further optimized, in step 1, the phosphoric acid is one or more of industrial grade phosphoric acid, fertilizer grade phosphoric acid and raffinate phosphoric acid, and raffinate phosphoric acid refers to the raffinate phosphoric acid produced as a by-product when industrial grade phosphoric acid is purified by wet phosphoric acid solvent extraction.

[0013] Wherein, in step 1, the phosphate-containing salt is one or more of monoammonium phosphate, diammonium phosphate, and urea phosphate.

[0014] It is further defined that in step 1, the ratio of citrate-soluble phosphorus to water-soluble phosphorus is adjusted to 0.5-1.5:1 by adding phosphoric acid or phosphate, and the pH of the mixture is controlled to 3.

[0015] Wherein, before polymerization, the pH of the slurry is controlled to be 1-4 and the molar ratio of P2O5:N is 1.5-3:1.

[0016] Further optimization, the multi-morphological phosphate fertilizer product prepared in step 2 is granulated into a granular multi-morphological phosphate fertilizer product.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention adjusts the ratio of water-soluble and citrate-soluble phosphorus in the slurry before polymerization and the pH value of the mixed slurry by adding phosphoric acid or phosphate-containing salts, and controls the ratio of P2O5 and N at the same time, so as to prevent the pH of the system from being too high during the polymerization process, resulting in the conversion of effective phosphorus into ineffective phosphorus. The polymorphic phosphate fertilizer obtained after polymerization has an effective phosphorus ratio of 97% to 100%, a polymerized phosphorus ratio of 50% to 60%, and phosphorus elements in water-soluble orthophosphate, water-soluble polyphosphate, citrate-soluble orthophosphate and citrate-soluble polyphosphate each accounting for about 1 / 4 in mass. Various forms of phosphorus are conducive to prolonging the fertilizer effect and improving the utilization rate of nutrients by plants.

[0019] In addition, the present invention controls the polymerization conditions to convert part of the orthophosphate in the ammoniation slag into ammonium polyphosphate while ensuring that the proportion of effective phosphorus is as high as 97% to 100%. During the polymerization process, the ammonium polyphosphate chelates the trace elements in the ammoniation slag. The polyphosphate in the prepared multi-form phosphate fertilizer containing trace elements has the characteristics of long-term slow release and high utilization rate. The chelated trace elements are more easily absorbed by plants, which greatly improves the fertilizer effect of the ammoniation slag and realizes the added value of the industrial-grade monoammonium phosphate by-product ammoniation slag. DETAILED DESCRIPTION

[0020] In the following, only some exemplary embodiments are briefly described. As those skilled in the art can realize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the embodiments of the present invention.

[0021] Embodiment 1

[0022] This embodiment discloses a method for preparing a slow-release phosphate fertilizer from monoammonium phosphate by-product ammoniation slag, which specifically comprises the following steps:

[0023] Step 1:

[0024] Phosphoric acid or phosphate-containing salts are added to the ammoniation slag to adjust the mixture to have a ratio of citric acid-soluble phosphorus to water-soluble phosphorus of 0.5-1.5:1, the ratio of the mass of sulfur, magnesium, iron, calcium in the mixture to the mass of P2O5 in the mixture is controlled to be 0.1-0.3:1, the pH of the mixture is controlled to be 1-4, urea is added to adjust the molar ratio of P2O5:N to 2-3:1, and the mixture is heated until the urea is dissolved to obtain a mixed slurry;

[0025] In this embodiment, the water-soluble phosphorus is 0.7:1, the ratio of the mass of sulfur, magnesium, iron, and calcium in the mixture to the mass of P2O5 in the mixture is controlled to be 0.2:1, the pH of the mixture is controlled to be 3, and urea is added to adjust the molar ratio of P2O5:N to 2.5:1

[0026] Step 2, polymerizing the slurry obtained in step 1 at 130-200° C. for 0.5-2h, controlling the effective phosphorus content of the product to be 97%-100%, the phosphorus polymerization rate to be 40%-60%, controlling the mass proportions of phosphorus in water-soluble orthophosphate, water-soluble polyphosphate, citrate-soluble orthophosphate and citrate-soluble polyphosphate in the polymerized material to be 20%-30%, 20%-30%, 20-30% and 20%-30% respectively, controlling the ratio of the mass of effective sulfur, magnesium, iron and calcium in the polymerized material to the mass of effective P2O5 in the mixture to be 0.1-0.3:1, and crushing and packaging the material after cooling to obtain a powdery multi-form phosphate fertilizer product.

[0027] In this embodiment, the slurry is polymerized at 180° C. for 1 hour, the effective phosphorus content of the product is controlled to be 980%, the phosphorus polymerization rate is 50%, the mass proportions of phosphorus in water-soluble orthophosphate, water-soluble polyphosphate, citrate-soluble orthophosphate and citrate-soluble polyphosphate in the polymerized material are controlled to be 25%, 25%, 25% and 25% respectively, and the ratio of the effective sulfur, magnesium, iron and calcium mass in the polymerized material to the effective P2O5 mass in the mixture is controlled to be 0.2:1.

[0028] Among them, in step 1, the ammoniated slag is a by-product slag produced in the ammoniated impurity removal step in the process of preparing industrial-grade monoammonium phosphate with wet phosphoric acid, and the ratio of the mass of sulfur, magnesium, iron and calcium in the ammoniated slag to the mass of P2O5 in the ammoniated slag is 0.1-0.3:1; preferably 0.2:1.

[0029] Further optimized, in step 1, the phosphoric acid is one or more of industrial grade phosphoric acid, fertilizer grade phosphoric acid and raffinate phosphoric acid, and raffinate phosphoric acid refers to the raffinate phosphoric acid produced as a by-product when industrial grade phosphoric acid is purified by wet phosphoric acid solvent extraction.

[0030] In this embodiment, fertilizer-grade phosphoric acid and raffinate phosphoric acid are preferably used in a mass ratio of 1:1.

[0031] Wherein, in step 1, the phosphate-containing salt is one or more of monoammonium phosphate, diammonium phosphate, and urea phosphate, and monoammonium phosphate is preferred in this embodiment.

[0032] Wherein, in step 1, phosphoric acid or phosphate is added to adjust the ratio of citrate-soluble phosphorus to water-soluble phosphorus to 0.5-1.5, preferably 1:1, and the pH of the mixture is controlled to 3.

[0033] Further optimization is carried out to control the slurry pH to 1-4 and the P2O5:N molar ratio to 1.5-3:1 before polymerization, preferably the pH to 3 and the P2O5:N molar ratio to 2:1.

[0034] In this embodiment,

[0035] The multi-form slow-release phosphate fertilizer containing medium and trace elements prepared by using ammoniation slag and urea, after testing, the raw material ammoniation slag (dry basis) N content: 8.25%, total P2O5 content: 45.43%; effective P2O5 content: 44.15%;

[0036] Total phosphorus: 43.1%, available phosphorus 42%; N: 12.59%, water-soluble orthophosphate 21%;

[0037] Water-soluble polyphosphate 10%;

[0038] Water-soluble orthophosphate 11%;

[0039] Citrate-soluble orthophosphate 11%;

[0040] Citrate soluble polyphosphate 10%, Mg: 2.3%; Fe: 0.42%; Ca: 0.23%; K: 0.31%, SO4 2- :1.1%.

[0041] The present invention adjusts the ratio of water-soluble and citrate-soluble phosphorus in the slurry before polymerization and the pH value of the mixed slurry by adding phosphoric acid or phosphate-containing salts, and controls the ratio of P2O5 and N at the same time, so as to prevent the pH of the system from being too high during the polymerization process, resulting in the conversion of effective phosphorus into ineffective phosphorus. The polymorphic phosphate fertilizer obtained after polymerization has an effective phosphorus ratio of 97% to 100%, a polymerized phosphorus ratio of 50% to 60%, and phosphorus elements in water-soluble orthophosphate, water-soluble polyphosphate, citrate-soluble orthophosphate and citrate-soluble polyphosphate each accounting for about 1 / 4 in mass. Various forms of phosphorus are conducive to prolonging the fertilizer effect and improving the utilization rate of nutrients by plants.

[0042] In addition, the present invention controls the polymerization conditions to convert part of the orthophosphate in the ammoniation slag into ammonium polyphosphate while ensuring that the proportion of effective phosphorus is as high as 97% to 100%. During the polymerization process, the ammonium polyphosphate chelates the trace elements in the ammoniation slag. The polyphosphate in the prepared multi-form phosphate fertilizer containing trace elements has the characteristics of long-term slow release and high utilization rate. The chelated trace elements are more easily absorbed by plants, which greatly improves the fertilizer effect of the ammoniation slag and realizes the added value of the industrial-grade monoammonium phosphate by-product ammoniation slag.

[0043] Embodiment 2

[0044] This embodiment is further optimized on the basis of the first embodiment. In this embodiment, the multi-morphological phosphate fertilizer product prepared in step 2 is granulated into a granular multi-morphological phosphate fertilizer product.

[0045] In order to facilitate those skilled in the art to further understand the present invention, the present invention is further described below in conjunction with specific preparation cases.

[0046] Step 1: Take 18.75g of wet-based ammoniation slag, 5g of raffinate and 4g of urea and stir them evenly to obtain a mixed slurry. The pH of the mixed slurry is 2.5, the ratio of citric acid-soluble phosphorus to water-soluble phosphorus is 0.9:1, the ratio of the mass of sulfur, magnesium, iron and calcium to the mass of P2O5 in the mixture is 0.11; the molar ratio of P2O5:N is 2.4.

[0047] Step 2, placing the mixed slurry obtained in step 1 into a 175° C. forced air drying oven and polymerizing it at high temperature for 1.5 hours. After polymerization, the effective phosphorus accounts for 98.3%, the polymerization rate is 48.7%, and the mass proportions of phosphorus in the water-soluble orthophosphate, water-soluble polyphosphate, citrate-soluble orthophosphate and citrate-soluble polyphosphate in the polymer are 23.2%, 25.4%, 28.1% and 23.3%, respectively. Cool to room temperature, and obtain slow-release phosphate fertilizer after crushing.

[0048] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing slow-release phosphate fertilizer from by-product ammoniation slag of monoammonium phosphate, characterized in that: The specific steps include: Step 1: Phosphoric acid or phosphate-containing salts are added to the ammoniation slag to adjust the mixture to have a ratio of citric acid-soluble phosphorus to water-soluble phosphorus of 0.5-1.5:1, the ratio of the mass of sulfur, magnesium, iron, calcium in the mixture to the mass of P2O5 in the mixture is controlled to be 0.1-0.3:1, the pH of the mixture is controlled to be 1-4, urea is added to adjust the molar ratio of P2O5:N to 2-3, and the mixture is heated until the urea is dissolved to obtain a mixed slurry; Step 2, polymerizing the slurry obtained in step 1 at 130-200° C. for 0.5-2h, controlling the effective phosphorus content of the product to be 97%-100%, the phosphorus polymerization rate to be 40%-60%, controlling the mass proportions of phosphorus in water-soluble orthophosphate, water-soluble polyphosphate, citrate-soluble orthophosphate and citrate-soluble polyphosphate in the polymerized material to be 20%-30%, 20%-30%, 20-30% and 20%-30% respectively, controlling the ratio of the mass of effective sulfur, magnesium, iron and calcium in the polymerized material to the mass of effective P2O5 in the mixture to be 0.1-0.3, and crushing and packaging the material after cooling to obtain a powdery multi-form phosphate fertilizer product.

2. The method for preparing slow-release phosphate fertilizer from by-product ammoniation slag of monoammonium phosphate according to claim 1, characterized in that: In step 1, the phosphoric acid is one or more of industrial-grade phosphoric acid, fertilizer-grade phosphoric acid and raffinate phosphoric acid, and raffinate phosphoric acid refers to the raffinate phosphoric acid produced as a by-product when industrial-grade phosphoric acid is purified by a wet phosphoric acid solvent extraction method.

3. The method for preparing slow-release phosphate fertilizer from by-product ammoniation slag of monoammonium phosphate according to claim 1, characterized in that: In step 1, the phosphate-containing salt is one or more of monoammonium phosphate, diammonium phosphate, and urea phosphate.

4. The method for preparing slow-release phosphate fertilizer from by-product ammoniation slag of monoammonium phosphate according to claim 1, characterized in that: The multi-morphological phosphate fertilizer product prepared in step 2 is granulated into a granular multi-morphological phosphate fertilizer product.