A method and system for preparing compound fertilizer from acid sludge and ammoniated sludge

Abstract

The present application relates to the field of fertilizer, especially to a method and system for preparing compound fertilizer from acid residue and ammoniated residue, which comprises: uniformly mixing acid residue, ammoniated residue and concentrated strong acid, and obtaining reslurry material after sufficient acid leaching; continuously conveying the obtained reslurry material to a reactor, and introducing neutralization raw material into the reactor to carry out neutralization reaction, thereby obtaining wet material; rapidly drying the obtained wet material to obtain powdery dry crude product, and then granulating to obtain granular multi-element compound fertilizer. The scheme can realize synchronous recycling of acid residue and ammoniated residue, significantly improve the utilization rate of phosphorus resources and the added value of products, and has a compact process flow. Meanwhile, the scheme effectively overcomes the problems of uneven mixing of materials, low reaction efficiency and the like in the prior art, and the product has high nutrients, and has practical application value and promotion prospect.

Description

Technical Field

[0001] This invention relates to the field of fertilizers, and in particular to a method and system for preparing compound fertilizer from acid residue and ammoniation residue. Background Technology

[0002] The production of wet-process phosphoric acid and industrial-grade ammonium phosphate products typically generates numerous byproducts, such as acid slag and ammoniation slag. These byproducts are abundant and complex in composition. Failure to efficiently utilize these byproducts not only wastes phosphorus resources in practical applications but also leads to serious environmental pollution problems.

[0003] Specifically, acid sludge from acid pressure filtration (hereinafter referred to as acid sludge) is a slurry formed during the wet-process phosphoric acid production process (such as extraction, concentration, impurity removal, or storage). This slurry is composed of phosphoric acid and various complex inorganic compounds (including salts of calcium, magnesium, aluminum, iron, silicon, and fluorine). Due to the uneven grade of phosphate rock resources in my country, the composition of acid sludge varies from place to place, and the annual output is relatively large.

[0004] On the other hand, in the production of industrial monoammonium phosphate / water-soluble monoammonium phosphate using the wet-process phosphoric acid method, the high concentration of metal ion impurities in the wet-process phosphoric acid reacts with ammonia gas during the ammonia reaction to form a large amount of poorly water-soluble ammonium sludge, also known as ammonium slag. Due to its low nutrient content and poor water solubility, the ammonium slag has limited disposal pathways and is typically only used as a raw material for low-end compound fertilizers, resulting in poor economic viability. Furthermore, the composition of ammonium slag varies depending on the type and content of impurities in phosphate rock from different regions, further complicating its processing.

[0005] In recent years, with the gradual depletion of phosphate rock resources and the government's increasing demands for green and environmentally friendly development, how to achieve efficient reuse of industrial by-products such as acid slag and ammoniation slag has become a key research focus and an urgent issue that needs to be addressed.

[0006] However, current methods for treating acid slag and ammoniation slag still have many drawbacks, such as long process flows, high energy consumption, low added value of the final product, limited economic benefits, and the potential for secondary environmental pollution during processing and storage. More importantly, existing research focuses only on the utilization of single byproducts and has not yet discovered a complete method for the simultaneous and efficient recycling of acid slag and ammoniation slag. How to simultaneously explore the synergistic advantages of acid slag and ammoniation slag is worthy of further research. Summary of the Invention

[0007] The purpose of this invention is to provide a method and system for preparing compound fertilizer from acid slag and ammoniation slag. This method can realize the simultaneous recycling and utilization of acid slag and ammoniation slag, significantly improve the utilization rate of phosphorus resources and the added value of products, has a compact process flow, and effectively overcomes the problems of uneven material mixing and low reaction efficiency in the prior art. The product has high nutrient content and has practical application value and promotion prospects.

[0008] The specific technical solution of this invention is as follows: In a first aspect, the present invention provides a method for preparing compound fertilizer from acid slag and ammoniation slag, comprising the following steps: Step (1) Mix the acid residue, ammonification residue and concentrated strong acid evenly, and obtain the re-pulping material after sufficient acid leaching; Step (2) The re-slurry material obtained in step (1) is continuously fed into the reactor, and neutralization raw materials are introduced into the reactor for neutralization reaction to obtain wet material; Step (3) The wet material obtained in step (2) is dried quickly to obtain a powdery dry crude product, which is then granulated to obtain a granular compound fertilizer.

[0009] As a preferred option, in step (1), the P2O5 content of the acid slag is 25%~35%, and the P2O5 content of the ammoniation slag is 30%~40%; the mass ratio of acid slag to ammoniation slag is 1:1~1.5.

[0010] The concentrated strong acid is one or both of concentrated sulfuric acid and concentrated nitric acid. When combined, the mass ratio of concentrated sulfuric acid to concentrated nitric acid is 1:1.2~1.6, the mass fraction of concentrated sulfuric acid is 70%~90%, and the mass fraction of concentrated nitric acid is 50%~70%.

[0011] As a preferred option, in step (1), the liquid-to-solid mass ratio of the acid leaching reaction is 1:1~5, the reaction temperature is 60℃~90℃, and the reaction time is 0.5h~1h.

[0012] As a preferred option, in step (2), the pH value of the neutralization reaction slurry is controlled between 7.5 and 8.0, the neutralization reaction temperature is 60℃ to 90℃, the reaction time is 2 h to 3 h, and the neutralization raw materials are one or more of ammonia, potassium hydroxide, potassium carbonate, potassium chloride, potassium sulfate and urea.

[0013] Secondly, the present invention provides a compound fertilizer prepared from acid slag and ammoniation slag, wherein the total nutrient content of the compound fertilizer is ≥30%.

[0014] Thirdly, the present invention provides a system for preparing compound fertilizer from acid slag and ammoniation slag, including a double-blade mixer, a twin-screw gas-liquid-solid reactor and a drying system. The dual-blade mixer includes a tube body, two mixing blades inside the tube body, the two mixing blades being driven by a motor, and several extrusion balls distributed around the tube body near the mixing blades. Acid sludge, ammonification sludge and concentrated strong acid are uniformly mixed in a double-blade mixer, and after thorough acid leaching, a re-slurry is obtained. The re-slurry material is continuously fed into a twin-screw gas-liquid-solid reactor, and ammonia or potassium hydroxide is introduced into the reactor for neutralization reaction to obtain wet material; The obtained wet material is subjected to rotary flash evaporation in a drying equipment to obtain a powdery dry crude product, which is then granulated to obtain granular multi-element compound fertilizer.

[0015] As a preferred embodiment, the dual-blade mixer includes a feed inlet on the tube body, and a pair of rotating blades on the feed inlet.

[0016] As a preferred embodiment, the twin-screw gas-liquid-solid reactor includes a twin screw disposed within a tube body, a feed inlet disposed above one side of the tube body, an air inlet disposed next to the feed inlet, and a discharge outlet disposed below the other side of the tube body.

[0017] As a preferred option, a pair of vertically arranged rotating blades are provided inside the feed inlet.

[0018] As a preferred option, the drying equipment is a rotary flash dryer. The rotary flash dryer has a feeding device on one side and a blower heating device at the bottom. It is equipped with a stirring motor with a stirring paddle inside. The upper discharge port is connected to a cyclone separator. A rotary pulverizer is installed at the lower end of the cyclone separator. The rotary pulverizer has a discharge port at the lower end. A dust collector is connected to the upper end of the cyclone separator. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of one embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the dual-blade mixer according to an embodiment of the present invention; Among them: 1-Double blade mixer, 1.1-Feed inlet, 1.2-Rotating blade, 1.3-Liquid inlet, 1.4-Nozzle, 1.5-Extrusion ball, 1.6-Blade, 1.7-Motor, 1.8-Discharge outlet, 1.9-Carrying tray, 1.10-Shelf; Figure 3 This is a schematic diagram of the structure of a twin-screw gas-liquid-solid reactor according to an embodiment of the present invention; Wherein: 2-Twin-screw gas-liquid-solid reactor, 2.1-Stirring motor, 2.2-Feed inlet, 2.3-Rotating blades, 2.4-Air inlet, 2.5-Screw motor, 2.6-Screw, 2.7-Discharge outlet; Figure 4 This is a schematic diagram of the rotary flash drying system according to an embodiment of the present invention; Among them: 3-rotary flash drying system, 3.1-blower, 3.2-air heater, 3.3-screw motor, 3.4-first stirring motor, 3.5-feed inlet, 3.6-stirring paddle, 3.7-screw, 3.8-rotary flash dryer body, 3.9-second stirring motor, 3.10-cyclone separator, 3.11-rotary pulverizer, 3.12-discharge port, 3.13-dust collector, 3.14-bag filter, 3.15-dust collector discharge port, 3.16-induced draft fan. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased.

[0021] Unless otherwise stated, all percentages in this invention represent mass fractions. Ratios are mass percentages, and concentrations are mass concentrations.

[0022] Unless otherwise specified, all materials, instruments, and equipment used below are conventional materials, instruments, and equipment or obtained through commercial channels; all testing methods used are existing methods unless otherwise specified.

[0023] In existing technologies, acid residue is commonly used to prepare products such as polyphosphates, superphosphate, compound phosphate fertilizers, and phosphate rock flotation modifiers. For example, one existing method for the resource utilization of phosphate residue involves acidolysis of phosphate residue and a substance containing metal elements to obtain a mixed slurry, which is then further calcined at high temperature to obtain a slow-release polyphosphate fertilizer. Its disadvantage is that it requires high-temperature calcination, resulting in high energy consumption.

[0024] Another existing technology discloses a method for producing superphosphate using phosphate rock tailings and phosphate residue acid. This method involves thoroughly mixing four raw materials: phosphate rock tailings, phosphate residue acid, phosphate rock powder, and concentrated sulfuric acid. Quicklime is then added to neutralize the free acid, followed by composting and maturation to ultimately produce ordinary superphosphate fertilizer. Its drawback is that the resulting superphosphate has a low nutrient content.

[0025] Ammoniation slag is typically dried, dust-removed, and packaged before being resold or used as a raw material for NPK compound fertilizer production. For example, one existing method for recycling ammoniation slag involves mixing it with concentrated phosphoric acid to obtain a re-slurry, which is then used to produce phosphate fertilizer. However, this method has limitations in utilizing the effectiveness of concentrated phosphoric acid leaching. Therefore, exploring the synergistic advantages of both acid slag and ammoniation slag is worthwhile research.

[0026] Furthermore, in the first aspect, such as Figure 1 As shown in the figure, this invention provides a method for preparing compound fertilizer from acid slag and ammoniation slag, comprising the following steps: Step (1) Mix the acid residue, ammonification residue and concentrated strong acid evenly, and obtain the re-pulping material after sufficient acid leaching; Step (2) The re-slurry material obtained in step (1) is continuously fed into the reactor, and neutralization raw materials are introduced into the reactor for neutralization reaction to obtain wet material; Step (3) The wet material obtained in step (2) is dried quickly to obtain a powdery dry crude product, which is then granulated to obtain a granular compound fertilizer.

[0027] Traditional processes treat acid slag and ammoniation slag separately, resulting in high costs and low efficiency. This invention innovatively achieves continuous and synergistic utilization of these two low-value waste residues, as well as flexible production of various high-value-added products. Specifically, the acid slag and ammoniation slag are first thoroughly and uniformly mixed, then concentrated strong acid is added. In a twin-paddle mixer, the available phosphorus and nitrogen in the byproducts are dissolved as much as possible into the re-slurry (converting into water-soluble phosphorus). Neutralization is then carried out in a twin-screw gas-liquid-solid reactor by adding neutralizing raw materials, followed by thorough drying in a rotary flash dryer, ultimately producing a multi-element compound fertilizer.

[0028] This invention, for the first time, utilizes the chemical complementarity between the two. The acid slag provides an acidic environment and some phosphate ions, while the ammoniation slag provides a nitrogen source and ammonium metal phosphate salts, both dissolving under strong acid to achieve activation. This process is significantly different from the traditional method of separately treating phosphate fertilizer industry byproducts (acid slag and ammoniation slag), creatively co-processing these two industrial wastes within the same continuous production system, ultimately achieving an upgrade from intermittent, multi-unit processing to integrated, continuous production.

[0029] This invention transforms two low-end byproducts (acid slag and ammonification slag) that are difficult to utilize in a high-value and efficient manner into high-value compound fertilizer products, realizing the resource utilization and high-value utilization of low-quality phosphorus resources, solving the environmental pressure and phosphorus resource waste caused by their stockpiling, and meeting the requirements of green circular economy.

[0030] This invention, through acid leaching, significantly increases the proportion of water-soluble phosphorus and the total nutrient content, and activates the micronutrients in the ammoniation slag, resulting in a more efficient and faster-acting compound fertilizer product. Transforming low-value waste into high-value compound fertilizer significantly reduces production costs. Furthermore, different formulations of compound fertilizers can be flexibly produced based on soil conditions and crop nutrient requirements in different regions, enabling companies to quickly respond to market demands, tailor fertilizer production to local conditions, and enhance market competitiveness.

[0031] The process flow of this invention is compact, including continuous process steps of mixing reaction, neutralization and drying. The compact flow is conducive to realizing automated and continuous control, and improving the production efficiency and stability of the entire process.

[0032] In one embodiment, in step (1), the P2O5 content of the acid slag is 25%~35%, and the P2O5 content of the ammoniation slag is 30%~40%; the mass ratio of acid slag to ammoniation slag is 1:1~1.5.

[0033] The concentrated strong acid is one or both of concentrated sulfuric acid and concentrated nitric acid. When combined, the mass ratio of concentrated sulfuric acid to concentrated nitric acid is 1:1.2~1.6, the mass fraction of concentrated sulfuric acid is 70%~90%, and the mass fraction of concentrated nitric acid is 50%~70%.

[0034] The phosphoric acid in the slag acid and the added concentrated strong acid are used to convert the citrate-soluble phosphorus in the acid slag and ammonification slag into water-soluble phosphorus, thereby further increasing the content of available phosphorus and nitrogen in the re-slurry material.

[0035] The principle is as follows: Taking one of the main components in ammoniation slag, (Fe, Al)NH4HPO4F2, as an example:

[0036] Taking one of the main components in acid residue (Na, K, Fe, Al, Mg, Si, F)(PO4) as an example: In one embodiment, in step (1), the liquid-to-solid ratio of the acid leaching reaction is 1:1 to 5, the reaction temperature is 60°C to 90°C, and the reaction time is 0.5 h to 1 h. The above-mentioned temperature and time limits ensure that the reaction is complete.

[0037] In one implementation method, in step (2), the pH value of the neutralization reaction slurry is controlled between 7.5 and 8.0, the neutralization reaction temperature is 60℃ to 90℃, the reaction time is 2 h to 3 h, and the neutralization raw materials are one or more of ammonia, potassium hydroxide, potassium carbonate, potassium chloride, potassium sulfate, and urea. The above parameters limit the reaction to ensure a complete reaction, using alkaline substances such as ammonia or potassium hydroxide to neutralize the free acid in the re-slurry material obtained after acid leaching, and generating compounds containing multiple nutrients through chemical reaction, thereby increasing the fertilizer nutrient content and forming compound fertilizer.

[0038] The main reaction equations involved in this step are:

[0039] Secondly, embodiments of the present invention also provide a compound fertilizer prepared from acid slag and ammoniation slag, wherein the total nutrient content of the compound fertilizer is ≥30%.

[0040] The embodiments of the present invention can also flexibly adjust the type of acid (H2SO4 or HNO3) in the acid leaching reaction and the type of alkali (NH3 / KOH) in the neutralization stage. This allows for rapid switching of product types without changing major equipment or interrupting the production process, accurately responding to the personalized fertilization needs of different regions and crops. It enables the production of compound fertilizers with different formulations based on nitrogen and phosphorus (NP), nitrogen, phosphorus and potassium (NPK), nitrogen, phosphorus and sulfur (NPS), and nitrogen, phosphorus and sulfur and potassium (NPSK), achieving on-demand production and multi-purpose use on a single line.

[0041] Thirdly, embodiments of the present invention also provide a system for preparing compound fertilizer from acid slag and ammoniation slag, including a double-bladed mixer, a twin-screw gas-liquid-solid reactor and a drying system; The dual-blade mixer includes a tube body, two mixing blades inside the tube body, the two mixing blades being driven by a motor, and several extrusion balls distributed around the tube body near the mixing blades. Acid sludge, ammonification sludge and concentrated strong acid are uniformly mixed in a double-blade mixer, and after thorough acid leaching, a re-slurry is obtained. The re-slurry material is continuously fed into a twin-screw gas-liquid-solid reactor, and ammonia or potassium hydroxide is introduced into the reactor for neutralization reaction to obtain wet material; The obtained wet material is subjected to rotary flash evaporation in a drying equipment to obtain a powdery dry crude product, which is then granulated to obtain granular multi-element compound fertilizer.

[0042] Currently used chemical equipment has many problems. For example, the structure of traditional mixers is relatively simple, and the mixing effect of materials is not ideal. In traditional batch or tubular reactors, the contact between reactants is insufficient, resulting in low reaction efficiency.

[0043] Furthermore, the system of this invention includes core units such as a twin-paddle mixer, a twin-screw reactor, and a rotary flash dryer. First, the acid sludge and ammoniation sludge are uniformly mixed in the twin-paddle mixer to form a re-slurry, allowing the available phosphorus and nitrogen elements contained in the byproducts to be fully dissolved and initially homogenized. Subsequently, the re-slurry is continuously conveyed to the twin-screw reactor, where it reacts fully with the introduced alkaline material under high-efficiency shearing and extrusion conditions to generate a wet material containing a complex of multiple elements. Finally, the resulting wet material is rapidly dried using a rotary flash dryer to obtain the target multi-element compound fertilizer product.

[0044] The dual-blade mixer of this invention utilizes the synergistic shearing action of the blades and multiple extrusion balls to enhance mixing and reaction efficiency, resulting in a stable re-slurry. Compared with traditional single-stirring devices with simpler structures, this device has advantages such as thorough mixing and high reaction efficiency. It is particularly suitable for the synergistic treatment of solid by-products and liquids, and is beneficial for the thorough contact and mixing of ammonification slag, acid slag, and strong acid.

[0045] Compared with existing technologies, this system achieves the synergistic utilization of acid slag and ammoniation slag through a continuous and integrated process, significantly improving the recovery rate of nitrogen and phosphorus resources in by-products, shortening the production cycle, and reducing energy consumption and processing costs. This system provides a novel and feasible technical approach for the resource utilization of low-value by-products in phosphorus chemical production.

[0046] In one embodiment, the dual-blade mixer includes a feed inlet on a tube body, and a pair of rotating blades are mounted on the feed inlet. By adding multiple rotating blades at the feed inlet of the dual-blade mixer, the solid material is pre-treated, achieving thorough pulverization of the solid material.

[0047] As one embodiment, the twin-screw gas-liquid-solid reactor includes a twin screw disposed within a tube body, a feed inlet disposed above one side of the tube body, an air inlet disposed next to the feed inlet, and a discharge outlet disposed below the other side of the tube body.

[0048] Existing twin-screw extruders only have heating and pulverizing functions, resulting in poor process adaptability. This invention adds an air inlet to a traditional twin-screw extruder, enabling highly efficient reactions of multiphase raw materials such as gas-solid, liquid-solid, and gas-liquid-solid mixtures. This ensures more thorough contact between raw materials, significantly improving reaction rate and conversion rate. Compared to traditional batch reactors or single-screw extruders, this device offers advantages in high mixing efficiency and good reaction uniformity, which is beneficial for the complete ammoniaation of re-slurry materials.

[0049] In one embodiment, a pair of vertically arranged rotating blades are provided in the feed inlet to further pulverize the material.

[0050] In one embodiment, the drying equipment is a rotary flash dryer. The rotary flash dryer has a feeding device on one side and a blower heating device at the bottom. It is equipped with a stirring motor with a stirring paddle inside. The upper discharge port is connected to a cyclone separator. A rotary pulverizer is installed at the lower end of the cyclone separator. The lower end of the rotary pulverizer has a discharge port. The upper end of the cyclone separator is connected to a dust collector. The wet material is dried efficiently and quickly to remove moisture from the reaction slurry and obtain a binary or ternary compound fertilizer product based on nitrogen and phosphorus, or further containing elements such as potassium and sulfur, with a total nutrient content ≥30%.

[0051] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a method and system for preparing compound fertilizer from acid slag and ammoniation slag provided by the present invention.

[0052] like Figure 2 , 3 As shown in Figure 4, the system for preparing compound fertilizer from acid residue and ammoniation residue in this embodiment includes a double-blade mixer 1, a twin-screw gas-liquid-solid reactor 2, and a rotary flash drying system 3.

[0053] The dual-blade mixer 1 includes two intersecting annular tubes. One side of the annular tube is provided with a feed inlet 1.1. A pair of horizontally arranged rotating blades 1.2 are provided on the feed inlet 1.1. Liquid inlets 1.3 are provided on both sides of the feed inlet 1.1. A nozzle 1.4 is provided at the lower end of the liquid inlet.

[0054] The annular tube is equipped with two mixing paddles with blades 1.6, which are driven by a motor 1.7. Several extrusion balls 1.5 are distributed around the tube near the blades 1.6. A discharge port 1.8 is also provided below the annular tube, and a valve is provided on the discharge port 1.8. After the reaction is completed, the valve is opened to discharge the re-slurry material. A carrying tray 1.9 is provided below the discharge port 1.8. The motor 1.7 is placed next to the annular tube and supported by a shelf 1.10.

[0055] The re-slurry material is continuously fed into the twin-screw gas-liquid-solid reactor 2. The twin-screw gas-liquid-solid reactor 2 includes a feed inlet 2.2 located above one side of the tube body. Inside the feed inlet 2.2, there is a pair of vertically arranged rotating blades 2.3. The re-slurry material can be fed from the side. The rotating blades 2.3 are driven by a stirring motor 2.1 located above the feed inlet. An air inlet 2.4 is located next to the feed inlet 2.2. Inside the tube body, there are two vertically arranged screws 2.6, which are driven by screw motors 2.5 respectively. There is a discharge outlet 2.7 located below the other side of the tube body.

[0056] The obtained wet material is conveyed to the rotary flash drying system 3. The main body 3.8 of the rotary flash dryer is connected to a feeding device on one side. The feeding device is a screw feeder, which includes a feed pipe with a feed inlet 3.5. A stirring paddle 3.6 is installed in the feed inlet 3.5 and is driven by a first stirring motor 3.4. A screw 3.7 is installed in the feed pipe and is driven by a screw motor 3.3.

[0057] The rotary flash dryer body 3.8 has an air heater 3.2 connected to its bottom. A blower 3.1 is located on one side of the air heater 3.2. The rotary flash dryer body 3.8 has a second stirring motor 3.9 with a stirring paddle 3.6 inside. The upper discharge port of the rotary flash dryer body 3.8 is connected to a cyclone separator 3.10. A rotary pulverizer 3.11 is located at the lower end of the cyclone separator 3.10. The lower end of the rotary pulverizer 3.11 has a discharge port 3.12. The upper end of the cyclone separator 3.10 is connected to a dust collector 3.13. The lower end of the dust collector 3.13 has a bag filter 3.14. The lower part of the bag filter 3.14 has a dust collector discharge port 3.15. An induced draft fan 3.16 is located on one side of the dust collector 3.13.

[0058] Example 1

[0059] The method for preparing compound fertilizer from acid residue and ammoniation residue in this embodiment includes the following steps: Step (1) Add acid slag with a P2O5 content of 32% and ammonification slag with a P2O5 content of 35% to the double-blade mixer at a mass ratio of 1:1.2. The specific composition of the raw materials is shown in Table 1 below: Table 1

[0060] Concentrated nitric acid with a mass fraction of 60% (liquid-to-solid ratio of 1:2) was then added to the device. The three materials were mixed evenly and thoroughly acid-leached at a reaction temperature of 70°C to obtain the re-slurry material. The reaction time was 0.5 h.

[0061] Step (2) involves continuously feeding the re-slurry obtained in step (1) into a twin-screw reactor, and introducing ammonia gas into the reactor for neutralization to obtain a slurry. In this step, the pH of the neutralized slurry is controlled at approximately 7.6. The neutralization reaction temperature is 65℃. The reaction time is 2 hours.

[0062] Step (3) The wet material obtained in step (2) is rapidly dried using a rotary flash dryer to obtain a powdered binary compound fertilizer with nitrogen and phosphorus as the basic nutrients. The total nutrient content is 36%, the nitrate nitrogen content is 6%, and the ammonium nitrogen content is 10%. The composition is shown in Table 2 below: Table 2 .

[0064] Example 2

[0065] The method for preparing compound fertilizer from acid residue and ammoniation residue in this embodiment includes the following steps: Step (1) Add acid slag with a P2O5 content of 33% and ammonification slag with a P2O5 content of 36% to the double-blade mixer at a mass ratio of 1:1.1. The specific composition of the raw materials is shown in Table 3 below: Table 3

[0066] Concentrated nitric acid with a mass fraction of 60% (liquid-to-solid ratio of 1:1.7) was then added to the apparatus. The three materials were mixed evenly and thoroughly acid-leached at a reaction temperature of 70°C to obtain the re-slurry material. The reaction time was 0.5 h.

[0067] Step (2) involves continuously feeding the re-slurry obtained in step (1) into a twin-screw reactor, and adding potassium hydroxide to the reactor for neutralization to obtain a slurry. In this step, the pH of the neutralized slurry is controlled at approximately 7.5. The neutralization reaction temperature is 65℃, and the reaction time is 2 hours. Neutralization using a potassium-containing alkali is an important step in the preparation of potassium-containing compound fertilizer.

[0068] Step (3) The wet material obtained in step (2) is rapidly dried using a rotary flash dryer. The powdered dried crude product is then granulated to obtain granular ternary compound fertilizer with nitrogen, phosphorus, and potassium as the basic nutrients. The total nutrient content is 35%, the nitrate nitrogen content is 3%, and the ammonium nitrogen content is 7%. The composition is shown in Table 4 below: Table 4 .

[0070] Example 3

[0071] The method for preparing compound fertilizer from acid residue and ammoniation residue in this embodiment includes the following steps: Step (1) Add acid slag with a P2O5 content of 35% and ammonification slag with a P2O5 content of 35% to the double-blade mixer at a mass ratio of 1:1.2. The specific composition of the raw materials is shown in Table 5 below: Table 5

[0072] Concentrated sulfuric acid with a mass fraction of 80% (liquid-to-solid ratio of 1:3) was then added to the apparatus. The three materials were mixed evenly and thoroughly acid-leached at a reaction temperature of 70°C to obtain the re-slurry material. The reaction time was 0.5 h.

[0073] Step (2) involves continuously feeding the re-slurry obtained in step (1) into a twin-screw reactor, and introducing ammonia gas into the reactor for neutralization to obtain a slurry. In this step, the pH of the neutralized slurry is controlled at approximately 7.7. The neutralization reaction temperature is 65℃. The reaction time is 2 hours.

[0074] Step (3) The wet material obtained in step (2) is rapidly dried using a rotary flash dryer. The powdered dried crude product is then granulated to obtain granular ternary compound fertilizer (sulfur-containing ammonium phosphate) with nitrogen, phosphorus, and sulfur as the basic nutrients. The total nutrient content is 38%, and the sulfur content is 5%. The composition is shown in Table 6 below: Table 6 .

[0076] Example 4

[0077] The method for preparing compound fertilizer from acid residue and ammoniation residue in this embodiment includes the following steps: Step (1) Add acid slag with a P2O5 content of 34% and ammoniation slag with a P2O5 content of 36% to the double-blade mixer at a mass ratio of 1:1.1. The specific composition of the raw materials is shown in Table 7 below: Table 7

[0078] Concentrated sulfuric acid with a mass fraction of 80% (liquid-to-solid ratio of 1:3.75) was then added to the device. The three materials were mixed evenly and thoroughly acid-leached at a reaction temperature of 70°C to obtain the re-slurry material. The reaction time was 0.5 hours.

[0079] Step (2) involves continuously feeding the re-slurry obtained in step (1) into a twin-screw reactor, and adding potassium hydroxide to the reactor for neutralization to obtain a slurry. In this step, the pH of the neutralized slurry is controlled at approximately 7.5. The neutralization reaction temperature is 65℃, and the reaction time is 2 hours. Neutralization using a potassium-containing alkali is an important step in the preparation of potassium-containing compound fertilizer.

[0080] Step (3) The wet material obtained in step (2) is rapidly dried using a rotary flash dryer. The powdered dried crude product is then granulated to obtain granular quaternary compound fertilizer (sulfur-containing ammonium phosphate) with nitrogen, phosphorus, sulfur, and potassium as the basic nutrients. The total nutrient content is 35%, and the sulfur content is 5%. The composition is shown in Table 8 below: Table 8 .

[0082] Example 5

[0083] The method for preparing compound fertilizer from acid residue and ammoniation residue in this embodiment includes the following steps: Step (1) Add acid slag with a P2O5 content of 36% and ammonification slag with a P2O5 content of 35% to the double-paddle mixer at a mass ratio of 1:1.2. The specific composition of the raw materials is shown in Table 9 below: Table 9

[0084] A mixture of 60% concentrated nitric acid and 80% concentrated sulfuric acid (mass ratio of concentrated sulfuric acid to concentrated nitric acid was 1:1.5, liquid-solid ratio was 1:2.4) was then added to the apparatus. The four materials were mixed evenly and thoroughly acid-leached at a reaction temperature of 70°C to obtain the re-slurry. The reaction time was 0.5 h.

[0085] Step (2) involves continuously feeding the re-slurry obtained in step (1) into a twin-screw reactor, and introducing ammonia gas into the reactor for neutralization to obtain a slurry. In this step, the pH of the neutralized slurry is controlled at approximately 7.6. The neutralization reaction temperature is 65℃. The reaction time is 2 hours.

[0086] Step (3) The wet material obtained in step (2) is rapidly dried using a rotary flash dryer. The powdered dried crude product is then granulated to obtain granular ternary compound fertilizer (sulfur-containing ammonium phosphate) with nitrogen, phosphorus, and sulfur as the basic nutrients. The total nutrient content is 35%, the sulfur content is 4%, the nitrate nitrogen content is 5%, and the ammonium nitrogen content is 9%. The composition is shown in Table 10 below: Table 10 .

[0088] Example 6

[0089] The method for preparing compound fertilizer from acid residue and ammoniation residue in this embodiment includes the following steps: Step (1) Add acid slag with a P2O5 content of 32% and ammonification slag with a P2O5 content of 36% to the double-blade mixer at a mass ratio of 1:1.1. The specific composition of the raw materials is shown in Table 11 below: Table 11

[0090] A mixture of 60% concentrated nitric acid and 80% concentrated sulfuric acid (mass ratio of concentrated sulfuric acid to concentrated nitric acid was 1:1.3, liquid-solid ratio was 1:1.7) was then added to the apparatus. The four materials were mixed evenly and thoroughly acid-leached at a reaction temperature of 70°C to obtain the re-slurry. The reaction time was 0.5 h.

[0091] Step (2) involves continuously feeding the re-slurry obtained in step (1) into a twin-screw reactor, and adding potassium hydroxide to the reactor for neutralization to obtain a slurry. In this step, the pH of the neutralized slurry is controlled at approximately 7.9. The neutralization reaction temperature is 65℃, and the reaction time is 2 hours. Neutralization using a potassium-containing alkali is an important step in the preparation of potassium-containing multi-element compound fertilizer.

[0092] Step (3) The wet material obtained in step (2) is rapidly dried using a rotary flash dryer. The powdered dried crude product is then granulated to obtain granular quaternary compound fertilizer (containing sulfur-containing ammonium phosphate) with nitrogen, phosphorus, sulfur, and potassium as the basic nutrients. The total nutrient content is 35%, the sulfur content is 4%, the nitrate nitrogen content is 3%, and the ammonium nitrogen content is 7%. The composition is shown in Table 12 below: Table 12 .

[0094] Comparative Example 1 The liquid-to-solid ratio is less than 1:2, and the rest is the same as in Example 1.

[0095] The total nutrient content is less than 35%, acid hydrolysis is incomplete, and the water content is less than 50%, failing to meet the standards for medium-concentration compound fertilizers. Concentrated strong acids not only have high acidity but also excellent liquid fluidity. This invention utilizes this characteristic by adding concentrated strong acids to ammoniation slag and acid slag for re-slurry dissolution, ensuring that the available phosphorus and nitrogen in the slag are fully dissolved in the re-slurry material, thereby ensuring that it meets the standards for fertilizer raw materials. Therefore, the addition of concentrated strong acids is a key and necessary condition for realizing the resource utilization of slag and improving the quality of the re-slurry material. Furthermore, the introduction of concentrated nitric acid replenishes nitrate nitrogen, and the introduction of concentrated sulfuric acid replenishes sulfur; different choices are beneficial for the preparation of different types of multi-element compound fertilizers.

[0096] In Example 2, if the liquid-to-solid ratio is less than 1:1.7, the total nutrient content is less than 35%, and the acid hydrolysis is insufficient, and the water-to-solid ratio is less than 50%, it does not meet the standard for medium-concentration compound fertilizer.

[0097] Comparative Example 2 The mass ratio of acid residue to ammoniation residue is less than 1:1, and the rest is the same as in Example 1.

[0098] Acid slag provides an acidic environment and some phosphate ions; its deficiency leads to a decrease in effective phosphorus dissolution rate and a water content of less than 50%. A high proportion of ammoniation slag results in high material viscosity, uneven mixing, and a tendency to cause blockages in subsequent conveying and reaction processes. Ultimately, the unreacted slag forms inert packing material, leading to low particle strength and easy pulverization.

[0099] A mass ratio of acid residue to ammoniation residue higher than 1:1.5 will directly lead to a lower total nitrogen content and a total nutrient content of less than 35% in the product. In addition, excessive acid residue will result in overly acidic re-pulping materials, increasing the amount of alkaline raw materials required for subsequent neutralization, thereby increasing costs.

[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing compound fertilizer from acid slag and ammoniation slag, characterized in that: Includes the following steps: Step (1) Mix the acid residue, ammonification residue and concentrated strong acid evenly, and obtain the re-pulping material after sufficient acid leaching; Step (2) The re-slurry material obtained in step (1) is continuously fed into the reactor, and neutralization raw materials are introduced into the reactor for neutralization reaction to obtain wet material; Step (3) The wet material obtained in step (2) is dried quickly to obtain a powdery dry crude product, which is then granulated to obtain a granular compound fertilizer.

2. The method according to claim 1, characterized in that: In step (1), the P2O5 content of the acid residue is 25%~35%, and the P2O5 content of the ammoniation residue is 30%~40%; the mass ratio of acid residue to ammoniation residue is 1:1~1.

5. The concentrated strong acid is one or both of concentrated sulfuric acid and concentrated nitric acid. When combined, the mass ratio of concentrated sulfuric acid to concentrated nitric acid is 1:1.2~1.6, the mass fraction of concentrated sulfuric acid is 70%~90%, and the mass fraction of concentrated nitric acid is 50%~70%.

3. The method according to claim 1, characterized in that: In step (1), the liquid-solid mass ratio of the acid leaching reaction is 1:1~5, the reaction temperature is 60℃~90℃, and the reaction time is 0.5h~1h.

4. The method according to claim 1, characterized in that: In step (2), the pH value of the neutralization reaction slurry is controlled between 7.5 and 8.0, the neutralization reaction temperature is 60℃ to 90℃, the reaction time is 2 h to 3 h, and the neutralization raw materials are one or more of ammonia, potassium hydroxide, potassium carbonate, potassium chloride, potassium sulfate and urea.

5. A compound fertilizer, characterized in that: Prepared from acid residue and ammonification residue, the compound fertilizer has a total nutrient content of ≥30%.

6. A system for preparing compound fertilizer from acid slag and ammoniation slag, characterized in that: Includes a twin-blade mixer, a twin-screw gas-liquid-solid reactor, and a drying system; The dual-blade mixer includes a tube body, two mixing blades inside the tube body, the two mixing blades being driven by a motor, and several extrusion balls distributed around the tube body near the mixing blades. Acid sludge, ammonification sludge and concentrated strong acid are uniformly mixed in a double-blade mixer, and after thorough acid leaching, a re-slurry is obtained. The re-slurry material is continuously fed into a twin-screw gas-liquid-solid reactor, and ammonia or potassium hydroxide is introduced into the reactor for neutralization reaction to obtain wet material; The obtained wet material is subjected to rotary flash evaporation in a drying device to obtain a powdery dry crude product, which is then granulated to obtain granular multi-element compound fertilizer.

7. The system according to claim 6, characterized in that: The dual-blade mixer includes a feed inlet on the tube body, and a pair of rotating blades on the feed inlet.

8. The system according to claim 6, characterized in that: The twin-screw gas-liquid-solid reactor includes twin screws inside the tube, a feed inlet located above one side of the tube, an air inlet located next to the feed inlet, and a discharge outlet located below the other side of the tube.

9. The system according to claim 8, characterized in that: A pair of vertically arranged rotating blades are installed inside the feed inlet.

10. The system according to claim 6, characterized in that: The drying equipment is a rotary flash dryer. The rotary flash dryer has a feeding device on one side and a blower heating device at the bottom. It is equipped with a stirring motor with a stirring paddle inside. The upper discharge port is connected to a cyclone separator. A rotary pulverizer is installed at the lower end of the cyclone separator. The rotary pulverizer has a discharge port at the lower end. A dust collector is connected to the upper end of the cyclone separator.

Images