Product for preparing fertilizer containing ammonium calcium magnesium iron polyphosphate based on phosphate tailings extracted after activation of ammonium phosphate slag slurry and preparation method

Abstract

The invention discloses a product for preparing a fertilizer containing ammonium polyphosphate calcium magnesium iron on the basis of extracting phosphate tailings after activating ammonium phosphate slag slurry and a preparation method, and belongs to the technical field of chemical fertilizer production. The preparation method comprises the following steps: with sulfuric acid, ammonium phosphate slurry and phosphate tailings as core raw materials, carrying out two-phase pretreatment on the ammonium phosphate slurry and the phosphate tailings, carrying out three-step gradient activation coupling by sulfuric acid, and finally, carrying out high-temperature polymerization and grinding to obtain the target fertilizer. The effective P2O5 content of the product reaches 30%-35%, the N content reaches 3.0%-4.5%, the CaO content reaches 10.0%-11.0%, the MgO content reaches 4.8%-6.0%, the Fe content reaches 3.0%-4.0%, the P2O5 polymerization rate reaches 65%-75%, and the water solubility reaches 67%-75%. Compared with the prior art, the water solubility of the product is remarkably improved, the polymerization rate at the same temperature is improved by 10% or above compared with the prior art, beneficial elements can be chelated, loss is reduced, and the absorption rate is improved; in addition, the polymerization temperature is reduced through the synergistic effect of the steps, and the unit energy consumption is reduced by 23% or above compared with the prior art; high-value utilization of the ammonium phosphate slag slurry and the phosphate tailings is achieved, 0.8-1.2 tons of solid waste is consumed per ton, and the environmental problems and the treatment cost are reduced.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer production technology, specifically relating to a product and preparation method for preparing ammonium polyphosphate calcium magnesium iron fertilizer based on the extraction of phosphorus tailings after activating ammonium phosphate slurry. Background Technology

[0002] In the process of coordinated development of modern agriculture and industry, the efficient utilization of phosphorus resources and the resource-based treatment of industrial solid waste have become key issues. Phosphate slurry, a byproduct of the wet-process phosphoric acid production of monoammonium phosphate, contains certain amounts of nitrogen, phosphorus, calcium, magnesium, iron, and other elements. However, it is currently mostly recovered inefficiently or directly stockpiled, which not only wastes resources but may also cause environmental problems. Phosphate slurry contains small amounts of water-soluble (NH4)2HPO4 and NH4H2PO4, as well as large amounts of water-insoluble MgHPO4 and FeMg(NH4)2(HPO4)2F3, with considerable nitrogen and phosphorus content. Failure to utilize it rationally will result in a significant loss of resources.

[0003] The treatment of phosphorus tailings also faces numerous challenges. With the continuous increase in mining volume, the stockpile of phosphorus tailings is growing increasingly large. These tailings not only occupy vast amounts of land but also pose environmental risks such as groundwater pollution, soil desertification, and secondary dust pollution. Although current resource utilization pathways for phosphorus tailings cover multiple fields, including building material production, element recovery, agricultural applications, and environmental protection materials, existing methods generally suffer from high costs and small utilization volumes, making large-scale resource utilization difficult.

[0004] In the field of phosphate fertilizer production, traditional fertilizer preparation methods struggle to fully utilize the nutrients in ammonium phosphate slurry and phosphate tailings, leading to resource waste and the limited nutrient content of fertilizer products. Existing technologies include the following: Chinese Patent Publication No. CN101367673A discloses a "Method for Directly Preparing Phosphorus Magnesium Fertilizer from Phosphorus Rock Flotation By-product Tailings," specifically using a sulfuric-phosphoric mixed acid to decompose the flotation tailings at 60-90℃, followed by drying to prepare powdered or granular compound fertilizer. This patent only uses acid to decompose phosphate tailings, resulting mainly in calcium sulfate and calcium phosphate salts, which are insoluble salts with low utilization rates. Chinese Patent Publication No. CN118479939A discloses a "Method for Preparing Polyphosphate Calcium Magnesium Slow-Release Fertilizer from Racking Residue Acid and Flotation Phosphorus Tailings," specifically mixing and reacting racking residue acid with phosphate tailings, allowing it to stand at 70℃ for 2 days, drying the slurry to constant weight at 100℃, and then polymerizing at 340℃ for 60 minutes. This patent utilizes residual acid as a phosphorus source for activation, but it fails to adequately consider the large amount of heavy metals contained in the residual acid, which may lead to excessive heavy metal content in the fertilizer. Because the reaction slurry is acidic, phosphorus-containing, and viscous, drying it at 100℃ requires a long time, approximately two days as verified by the laboratory. Simultaneously, its storage time at 70℃ is two days, resulting in significant energy consumption and making industrialization difficult. Chinese Patent Publication No. CN108456007A discloses "A calcium magnesium polyphosphate fertilizer prepared from phosphoric acid and phosphate tailings as raw materials and its preparation method," specifically involving the decomposition of phosphate tailings with phosphoric acid, followed by constant-temperature low-pressure concentration of the slurry to 35%-45% moisture, and high-temperature calcination at 350-450℃ to obtain the calcium magnesium polyphosphate product. This patent uses phosphoric acid from wet-process phosphoric acid, resulting in higher costs. The product does not contain ammonium polyphosphate, leading to a higher polymerization temperature and longer polymerization time required to achieve the specified polymerization rate, resulting in higher energy consumption. It also results in poor water solubility and low chelation performance for metal ions, leading to poor absorption and utilization rates. The market demand for new types of fertilizers that can simultaneously provide multiple nutrients, improve fertilizer utilization, have relatively low energy consumption, and reduce environmental pollution is growing. Therefore, developing a method for efficiently preparing calcium-magnesium-iron fertilizer containing ammonium polyphosphate by extracting phosphate tailings after sulfuric acid activation of ammonium phosphate slurry has significant practical implications and broad market prospects. Summary of the Invention

[0005] This invention aims to solve the problems of low resource utilization rate and high processing cost of ammonium phosphate slurry and phosphate tailings in the prior art, as well as the single nutrient content and low utilization rate of related fertilizer products. It provides a method for preparing calcium magnesium iron fertilizer containing ammonium polyphosphate by activating ammonium phosphate slurry with sulfuric acid and then extracting phosphate tailings.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: A method for preparing ammonium polyphosphate-containing calcium magnesium iron fertilizer based on the extraction of phosphate tailings after activation of ammonium phosphate slurry includes the following steps: S1 two-phase pretreatment: (1) Pretreatment of ammonium phosphate slurry: The ammonium phosphate slurry is separated into solid phase slag and liquid phase ammonium phosphate according to the solid-liquid separation. The liquid phase ammonium phosphate is introduced into a microchannel reactor and reacted with industrial waste gas to generate nano-sized ammonium-containing precursors. The pH is adjusted to 4.0 to obtain ammonium-containing activated liquid A. (2) Mechanical and chemical modification of phosphorus tailings: Phosphorus tailings are pretreated by low-temperature plasma (120°C) under an argon atmosphere to introduce hydroxyl / carboxyl active sites on the surface. Citric acid of 5% of the phosphorus tailings mass is added and the mixture is ball-milled at 500 r / min for 30 min to obtain modified phosphorus tailings B.

[0007] S2 gradient activation coupling: (1) Mix the activation solution A and the modified phosphate tailings B, add chitosan for pre-dispersion, and stir for 30 min to obtain the mixture C; (2) Add 40% of the mass of the solid residue obtained in step S1 (1) to the mixed liquid C, and at the same time add 40% of the total mass of sulfuric acid required and react for 20 min. Then add 40% of the total mass of sulfuric acid and 40% of the solid residue and react for 20 min. Finally add the remaining solid residue and the remaining sulfuric acid and continue to react for 40 min to obtain extract D. S3 Directed-Guided Aggregation: (1) Add polyphosphoric acid to extract D and continue stirring for 10 min until well mixed to obtain a mixture E containing polyphosphoric acid precursor; (2) The mixture E is introduced into the polymerization reactor and processed by the following procedure: first, it is dried at 120-150℃ for 20-30 min, then polymerized at 230-250℃ under nitrogen atmosphere for 60-120 min, and finally the particles with a particle size of 0.5-2 mm are pulverized by airflow to obtain ammonium calcium magnesium iron polyphosphate fertilizer.

[0008] Furthermore, in step S1 (1), the industrial waste gas contains CO2 / SO2 / NO. X .

[0009] Furthermore, in step S1 (2), the phosphorus tailings are ground to 60-100 mesh.

[0010] Furthermore, the amount of chitosan added in step S2(1) is 0.5% of the mass of the phosphorus tailings in S1(2).

[0011] Furthermore, the mass ratio of the ammonium phosphate slurry in step S1 (1) to the total amount of sulfuric acid in step S2 (2) is 1:0.25-0.5; the sulfuric acid is industrial sulfuric acid with a mass concentration of 98%.

[0012] Furthermore, the mass ratio of ammonium phosphate slurry to phosphorus tailings in step S1(1) is 2-4:1.

[0013] Furthermore, in step S3 (1), the amount of polyphosphoric acid added is 0.05% of the mass of extract D.

[0014] Furthermore, the phosphate slurry in step S1 (1) is a byproduct generated during the wet process of producing monoammonium phosphate by passing ammonia through phosphate. The phosphate slurry is wet-based and, by weight percentage, contains: N 4.0%-5.5%, P2O5 25.0%-30.0%, CaO 2%-2.5%, MgO 2%-2.5%, Fe 1.5%-3.5%, and moisture 40%-50%.

[0015] Furthermore, the phosphorus tailings in step S1 (2) are low-grade phosphorus ore that is eliminated after flotation during the wet phosphoric acid production process. The phosphorus tailings are: P2O 57.04%, CaO 30.76%, MgO 11.29%, Fe 2.12% by weight percentage.

[0016] A product prepared by a method for extracting phosphate tailings from activated ammonium phosphate slurry to prepare calcium, magnesium, and iron fertilizer containing ammonium polyphosphate is characterized by the following composition by weight percentage: 30%-35% effective P2O5, 3.0%-4.5% N, 10.0%-11.0% effective CaO, 4.8%-6.0% effective MgO, 3.0%-4.0% effective Fe, pH 2.5-2.8, P2O5 polymerization rate 67%-75%, and water solubility 65%-75%.

[0017] According to the preparation method of the present invention, the amount of phosphorus tailings added must be in the mass ratio of ammonium phosphate slurry to phosphorus tailings of 2-4:1. When the amount of phosphorus tailings added is too low, that is, when the mass ratio of ammonium phosphate slurry to phosphorus tailings is less than 4:1, the pH of the product slurry is low, and there is excessive acid, which makes the product difficult to dry and has a low pH, increases energy consumption and reduces marketability. When the amount of phosphorus tailings added is too high, that is, when the mass ratio of ammonium phosphate slurry to phosphorus tailings is less than 2:1, there is too much calcium and magnesium in the product, the slurry fluidity is reduced, stirring is difficult, the reaction is insufficient, resulting in a decrease in polymerization rate and a decrease in available phosphorus, making production operation difficult.

[0018] This invention controls the calcination temperature in two stages to ensure that the polymerization rate of the product is between 65-75% and that it has good water solubility.

[0019] Beneficial effects 1. Rich in nutrients: Contains abundant nitrogen, phosphorus, calcium, magnesium, iron, and other nutrients to meet the diverse nutritional needs of crops. The product has an effective P2O5 content of up to 30%-35% and a polymerization rate of 65%-75%, exhibiting slow-release properties that improve phosphorus utilization. 2. Contains ammonium polyphosphate, enhancing performance: (1) Water solubility: The product fully utilizes the nitrogen element in the ammonium phosphate slurry, and generates ammonium polyphosphate through polymerization to improve the water solubility of the product; (2) Two-phase pretreatment effectively enhances the leaching activity of calcium, magnesium and iron; (3) Improved utilization rate: Sulfuric acid is added in steps to prevent the generation of insoluble substances by adding it all at once from adhering to the surface of phosphorus tailings and ammonium phosphate slag, affecting its activation efficiency. 3. Low product cost: (1) Raw materials: Low-cost sulfuric acid is used as an activator, making full use of low-cost slurry and slag resources, resulting in the lowest raw material cost; (2) Energy consumption: Activation and extraction are carried out at room temperature without additional energy. At the same time, due to the presence of ammonium polyphosphate, its synergistic effect with calcium, magnesium and iron makes the temperature required to achieve the same polymerization rate lower. Compared with other patented processes, the total energy consumption is reduced by more than 23%, saving a lot of energy. 4. High-value utilization of solid waste: It realizes the resource utilization of phosphate slag slurry and phosphate tailings, reduces the environmental problems caused by solid waste stockpiling, and can dispose of 0.8-1.2 tons of solid waste per ton of product, thereby reducing the cost of solid waste treatment; 5. Technological Innovation: By using a two-phase pretreatment process of low-temperature plasma and citric acid, followed by a three-step addition of sulfuric acid, the effective components in the two types of solid waste are synergistically utilized. This low-cost approach provides a new path for phosphorus resource recycling and green fertilizer research and development. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0021] The contents of P2O5, CaO, MgO, and Fe below are all effective contents, and "%" represents the mass percentage. All sulfuric acid used is 98% sulfuric acid from the Shikefeng workshop. The composition of the phosphate tailings used in the examples, expressed as a percentage by mass, is as follows: P2O5 7.04%, CaO 30.76%, MgO 11.29%, and Fe 2.12%. The main components of the phosphate ammonium slurry residue used in the examples are shown in Table 1. Table 1. Main Components of Phosphate Fertilizer Slurry

[0022] Example 1 A method for preparing ammonium polyphosphate-containing calcium magnesium iron fertilizer based on the extraction of phosphate tailings after activation of ammonium phosphate slurry includes the following steps: S1 two-phase pretreatment: (1) Pretreatment of ammonium phosphate slurry: 60 kg of ammonium phosphate slurry was separated into 42 kg of solid phase slurry and 18 kg of liquid phase ammonium phosphate according to the solid-liquid separation method. The liquid phase ammonium phosphate was introduced into a microchannel reactor and reacted with industrial waste gas to generate nano-sized ammonium-containing precursors. The pH was adjusted to 4.0 to obtain ammonium-containing activated liquid A. (2) Mechanical and chemical modification of phosphorus tailings: 15 kg of phosphorus tailings were pretreated by low-temperature plasma (120 °C) under an argon atmosphere, and 5% of the phosphorus tailings mass of citric acid was added. The mixture was ball-milled for 30 min at a speed of 500 r / min to obtain modified phosphorus tailings B.

[0023] S2 gradient activation coupling: (1) Mix the activation solution A and the modified phosphate tailings B, add 75g of chitosan for pre-dispersion, and stir for 30min to obtain the mixture C; (2) Add 16.8 kg of solid residue obtained in step S1 (1) to the mixed liquid C, and add 6 kg of sulfuric acid to react for 20 min. Then add 6 kg of sulfuric acid and 16.8 kg of solid residue to react for 20 min. Finally add 8.4 kg of solid residue and 3 kg of sulfuric acid to continue the reaction for 40 min to obtain extract D. S3 Directed-Guided Aggregation: (1) Add polyphosphoric acid to extract D and continue stirring for 10 min until well mixed to obtain a mixture E containing polyphosphoric acid precursor; (2) The mixture E is introduced into the polymerization reactor and processed by the following procedure: first, it is dried at 120°C for 20 min, then polymerized at 230°C under a nitrogen atmosphere for 120 min, and finally the particles with a particle size of 0.5-2 mm are pulverized by airflow to obtain ammonium calcium magnesium iron polyphosphate fertilizer.

[0024] In step S1 (1), the industrial waste gas contains CO2 / SO2 / NO X .

[0025] In step S1 (2), the phosphorus tailings are ground to 60-100 mesh.

[0026] In step S3 (1), the amount of polyphosphoric acid added is 0.05% of the mass of extract D.

[0027] In step S1 (1), the ammonium phosphate slurry is a byproduct generated during the wet process of producing monoammonium phosphate by passing ammonia through phosphoric acid, and the ammonium phosphate slurry with a sampling batch of 1 is used.

[0028] Example 2 Compared with Example 1, this embodiment is identical to Example 1 except that the total mass of sulfuric acid is changed to 30 kg, and 12 kg is added for the first reaction and reacted for 20 min, 12 kg is added for the second reaction and reacted for 20 min, and the remaining 6 kg is added for the third reaction and reacted for 40 min.

[0029] Example 3 Compared with Example 1, this embodiment is identical to Example 1 except that the total amount of phosphorus tailings is changed to 30 kg.

[0030] Example 4 Compared with Example 1, this embodiment is the same as Example 1 except that the drying temperature in step S3 (2) is changed to 150°C and the polymerization temperature is changed to 250°C.

[0031] Example 5 Compared with Example 1, this embodiment is the same as Example 1 except that the polymerization time in step S3 (2) is 60 min.

[0032] Example 6 Compared with Example 1, this embodiment uses the same raw materials and steps as Example 1, except that it uses phosphate slag slurry from sampling batch 2.

[0033] Example 7 Compared with Example 1, this embodiment uses the same raw materials and steps as Example 1, except that it uses phosphate slag slurry from sampling batch 3.

[0034] Comparative Example 1 Compared with Example 1, this comparative example was identical to Example 1 except for the total amount of sulfuric acid used, which was changed to 10 kg. Experimental results: The water content in the sulfuric acid and ammonium phosphate slurry was insufficient for mixing, making it impossible to add more phosphorus tailings subsequently; the experiment failed.

[0035] Comparative Example 2 Compared with Example 1, this comparative example is identical to Example 1 except that the total amount of sulfuric acid used is changed to 40 kg.

[0036] Comparative Example 3 Compared with Example 1, this comparative example is identical to Example 1 except that the amount of phosphorus tailings used is changed to 5 kg.

[0037] Comparative Example 4 Compared with Example 1, this comparative example was identical to Example 1 except for the amount of phosphate tailings, which was changed to 25 kg. Experimental results: During the later stages of the slow addition of the phosphate tailings, the system became quite viscous, and the experiment ended when the stirring motor became hot, indicating a failure.

[0038] Comparative Example 5 Compared with Example 1, this comparative example is identical to Example 1 except that the biphasic pretreatment in the S1 process is omitted.

[0039] Comparative Example 6 Compared with Example 1, this comparative example is identical to Example 1 except that sulfuric acid and solid residue are mixed all at once in step S2.

[0040] Test The products prepared in Examples 1-7 and Comparative Examples 1-6 were tested for results.

[0041] N, effective P2O5, and P2O5 polymerization rate: determined according to HG / T 5939-2021 "Fertilizer Grade Ammonium Polyphosphate" standard; Available CaO, available MgO, and available Fe: extracted according to HG / T 5939-2021 "Fertilizer Grade Ammonium Polyphosphate" standard, and determined by ICP.

[0042] pH value: determined according to NY / T 1973-2010 "Determination of water-insoluble matter content and pH of water-soluble fertilizers" standard; Water solubility: The determination of water insoluble matter was carried out according to the improved method in NY / T1973-2010 "Determination of water insoluble matter content and pH of water-soluble fertilizers". The improved method involves changing the standard method of stirring thoroughly for 3 minutes to shaking at 180 r / min in a 25℃ constant temperature water bath for 10 days. Other steps are the same as in NY / T1973-2010 "Determination of water insoluble matter content and pH of water-soluble fertilizers". The results of the above data testing are shown in Tables 2 and 3.

[0043] Table 2. Product Analysis Results of Examples 1-7

[0044] Table 3 shows the analysis results of products in Comparative Examples 1-6.

[0045] As shown in Tables 2 and 3, the polymerization rate of Comparative Example 2 decreased significantly compared to Example 1, mainly due to the excess sulfuric acid limiting P2O5 polymerization. The product's pH was 1.29, which is relatively low and makes application difficult. The polymerization rate of Comparative Example 3 decreased from 71.88% to 50.37% compared to Example 1, mainly because the amount of phosphate tailings added was too low, resulting in an excess of phosphoric acid in the solution. This increased viscosity during drying, making the product softer than that of Example 1, causing adhesion during crushing. The product's pH was 1.31, which is relatively low and makes application difficult. The effective P2O5 and CaO / MgO content of Comparative Example 5 decreased significantly compared to Example 1, mainly because no two-way pretreatment was performed, and the calcium, magnesium, and iron elements in the phosphate tailings were not effectively extracted, limiting the dissolution rate. Compared to Example 1, the effective P2O5 and CaO / MgO content of Comparative Example 6 decreased significantly, mainly because the ammonium phosphate filter residue and sulfuric acid were not added in steps, leading to calcium sulfate adhering to the surface of unreacted particles during the reaction, resulting in uneven reaction and affecting product quality.

[0046] According to the product water solubility test method of this patent, the water solubility and polymerization rate of the product at the same temperature were compared with those of the product published by three patent publication numbers CN101367673A, CN118479939A, and CN108456007A.

[0047] The synthesis process of the three patented products was carried out in the laboratory according to their patent specifications. The tailings, phosphoric acid, raffinate, and sulfuric acid were all from the same batch as those from Shikefeng. The synthesis steps are as follows: (a) The synthesis steps of patent publication number CN101367673A are carried out according to the patent specification, and the dosage and steps are as follows: Add 1.3 kg of water to 3.34 kg of phosphate tailings, then add 2 kg of concentrated sulfuric acid and 1 kg of concentrated phosphoric acid with a 45% P2O5 content. Stir at 400 r / min for 45 min, then process at 80℃ for 50 min. After solidification, store and mature for 5 days. The product is still in an adhesive state and cannot be crushed. Dry at a low temperature of 80 degrees Celsius and then crush to obtain the product.

[0048] (II) The synthesis steps of patent publication number CN118479939A are carried out according to the patent specification, and the dosage and steps are as follows: 60g of phosphate tailings and 200g of raffinate were stirred at 70℃ for 20min, then kept at 70℃ for 5h, stored at room temperature for 2 days, and then dried at 100℃ to constant weight. 50g of the mixture was polymerized at 220℃ for 60min, and the product was then ground to obtain the polymerization rate. 50g of the mixture was polymerized at 340℃ for 60min, and the product was then ground to obtain the water solubility.

[0049] (III) The synthesis steps of patent publication number CN108456007A are carried out in accordance with the patent specification, and the dosage and steps are as follows: 100g of phosphate tailings was reacted with 500g of phosphoric acid with a w(P2O5) content of 22.39% at room temperature for 1 hour. The mixture was then concentrated to 35%-36% moisture content under vacuum at 90°C and 30kPa. 50g of the concentrated solution was polymerized at 220°C for 4 hours. The resulting product was then ground and used to test the polymerization rate. 50g of the product was polymerized at the patent-recommended polymerization temperature of 400°C for 60 minutes, then ground and tested for water solubility.

[0050] Table 4 Results of water solubility and polymerization rate for each product

[0051] Based on the above results, the product of patent publication number CN101367673A has a water solubility of 10.29%, which is consistent with its characteristics as a citrate-soluble salt such as calcium sulfate and calcium phosphate. The products of patent publication numbers CN118479939A and CN108456007A are similar products. When containing only phosphorus, calcium, and magnesium, their recommended commercial water solubility is 45.42% and 39.77%, respectively, far lower than the 71.38% of this invention. The specific reason for this can be analyzed as follows: this patented product contains ammonium polyphosphate, whose water solubility and chelating properties with metal elements promote the product's water solubility.

[0052] Furthermore, the product with patent number CN101367673A is only acid-hydrolyzed and dried, and does not possess polymerization properties. The products with patent publication numbers CN118479939A and CN108456007A, both using the phosphoric acid hydrolysis of phosphate tailings process, have comparable polymerization rates, approximately 10% lower than the product in this patent. This demonstrates that the presence of nitrogen in the ammonium phosphate slurry results in the product containing ammonium polyphosphate. The synergistic effect of ammonium polyphosphate with calcium, magnesium, and iron lowers the temperature required for polymerization, thus reducing energy consumption.

[0053] Regarding the comparison of energy consumption, the data is based on 100kg slurry, with a specific heat capacity of 4.0KJ / (kg.℃), a thermal efficiency of 80%, and a vacuum pump power of 30kW.

[0054] The total energy consumption, Etotal, consists of sensible heat energy consumption (Eheat, heating, calcination), phase change energy consumption (Ephase, evaporation, drying), and electrical energy consumption (Eelec, vacuum concentration). The calculation formula is as follows:

[0055]

[0056]

[0057]

[0058] The value of m above represents mass (kg). Specific heat capacity ( )), t represents the temperature difference (°C) and t represents the time (h). For thermal efficiency, Latent heat of vaporization , Rated power of the equipment (kW). The unit conversion factor is (J / kWh).

[0059] The energy consumption comparison results between the products of patent publication numbers CN118479939A and CN108456007A and the product of this patent are shown in Table 5 below: Table 5 Energy Consumption Results for Each Product

[0060] As can be seen from the above data, by eliminating the drying and concentration steps and directly adopting medium-temperature short-time calcination, the energy consumption per unit of calcination in this invention is reduced by 35% compared to CN118479939A. This reduces the cumulative energy consumption of stepped heating. Compared to other processes, the total energy consumption of this solution is reduced by 23% compared to CN118479939A, while shortening the processing time by 90%. Furthermore, it eliminates the need for vacuum pumps and drying equipment, reducing equipment investment and maintenance costs.

[0061] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A method for preparing ammonium polyphosphate-containing calcium, magnesium, and iron fertilizer based on the extraction of phosphate tailings after activation of ammonium phosphate slurry, characterized in that, Includes the following steps: S1 two-phase pretreatment: (1) Pretreatment of ammonium phosphate slurry: The ammonium phosphate slurry is separated into solid phase slag and liquid phase ammonium phosphate according to the solid-liquid separation. The liquid phase ammonium phosphate is introduced into a microchannel reactor and reacted with industrial waste gas to generate nano-sized ammonium-containing precursors. The pH is adjusted to 4.0 to obtain ammonium-containing activated liquid A. (2) Mechanical and chemical modification of phosphorus tailings: Phosphorus tailings are pretreated by low-temperature plasma (120°C) under an argon atmosphere to introduce hydroxyl / carboxyl active sites on the surface. Citric acid of 5% by weight of phosphorus tailings is added and the mixture is ball-milled at 500 r / min for 30 min to obtain modified phosphorus tailings B. S2 gradient activation coupling: (1) Mix the activation solution A and the modified phosphate tailings B, add chitosan for pre-dispersion, and stir for 30 min to obtain the mixture C; (2) Add 40% of the mass of the solid residue obtained in step S1 (1) to the mixed liquid C, and at the same time add 40% of the total mass of sulfuric acid required and react for 20 min. Then add 40% of the total mass of sulfuric acid and 40% of the solid residue and react for 20 min. Finally add the remaining solid residue and the remaining sulfuric acid and continue to react for 40 min to obtain extract D. S3 Directed-Guided Aggregation: (1) Add polyphosphoric acid to extract D and continue stirring for 10 min until well mixed to obtain a mixture E containing polyphosphoric acid precursor; (2) The mixture E is introduced into the polymerization reactor and processed by the following procedure: first, it is dried at 120-150℃ for 20-30 min, then polymerized at 230-250℃ under nitrogen atmosphere for 60-120 min, and finally the particles with a particle size of 0.5-2 mm are pulverized by airflow to obtain ammonium calcium magnesium iron polyphosphate fertilizer.

2. The preparation method for preparing ammonium polyphosphate-containing calcium magnesium iron fertilizer based on the extraction of phosphate tailings after activation of ammonium phosphate slurry according to claim 1, characterized in that, In step S1 (1), the industrial waste gas contains CO2 / SO2 / NO X .

3. The preparation method for preparing ammonium polyphosphate-containing calcium magnesium iron fertilizer based on the extraction of phosphate tailings after activation of ammonium phosphate slurry according to claim 1, characterized in that, The amount of chitosan added in step S2(1) is 0.5% of the mass of the phosphorus tailings in S1(2).

4. The preparation method for preparing ammonium polyphosphate-containing calcium magnesium iron fertilizer based on the extraction of phosphate tailings after activation of ammonium phosphate slurry according to claim 1, characterized in that, In step S1(1), the mass ratio of ammonium phosphate slurry residue to the total amount of sulfuric acid in S2(2) is 1:0.25-0.5; the sulfuric acid is industrial sulfuric acid with a mass concentration of 98%.

5. The preparation method for preparing ammonium polyphosphate-containing calcium magnesium iron fertilizer based on the extraction of phosphate tailings after activation of ammonium phosphate slurry according to claim 1, characterized in that, In step S1(1), the mass ratio of ammonium phosphate slurry residue to phosphorus tailings in step S1(2) is 2-4:

1.

6. The preparation method for preparing ammonium polyphosphate-containing calcium magnesium iron fertilizer based on the extraction of phosphate tailings after activation of ammonium phosphate slurry according to claim 1, characterized in that, In step S3 (1), the amount of polyphosphoric acid added is 0.05% of the mass of extract D.

7. The preparation method for preparing ammonium polyphosphate-containing calcium magnesium iron fertilizer based on the extraction of phosphate tailings after activation of ammonium phosphate slurry according to claim 1, characterized in that, The phosphate slurry in step S1 (1) is a byproduct of the production of monoammonium phosphate by wet-process phosphoric acid with ammonia. The phosphate slurry is wet-based and has the following weight percentages: N 4.0%-5.5%, P2O5 25.0%-30.0%, CaO 2%-2.5%, MgO 2%-2.5%, Fe 1.5%-3.5%, and moisture 40%-50%.

8. The preparation method for preparing ammonium polyphosphate-containing calcium magnesium iron fertilizer based on the extraction of phosphate tailings after activation of ammonium phosphate slurry according to claim 1, characterized in that, The phosphorus tailings in step S1 (2) are low-grade phosphorus ore that is eliminated after flotation during the wet phosphoric acid production process. The phosphorus tailings are: P2O5 7.04%, CaO 30.76%, MgO 11.29%, Fe 2.12% by weight percentage.

9. A product prepared by the method of claim 1, which involves extracting phosphorus tailings from activated ammonium phosphate slurry to prepare calcium, magnesium, and iron fertilizer containing ammonium polyphosphate, characterized in that... By weight percentage: available P2O5 30%-35%, N 3.0%-4.5%, available CaO 10.0%-11.0%, available MgO 4.8%-6.0%, available Fe 3.0%-4.0%, pH 2.5-2.8, P2O5 polymerization rate 65%-75%, water solubility 67%-75%.

Images