Method for preparing ammonium phosphate by using desilicication clear mother liquor

Abstract

The invention discloses a method for preparing ammonium phosphate by using desiliconized clear mother liquor, which comprises the following steps: step 1, raw material pretreatment: removing calcium, iron, aluminum and silicide in the desiliconized clear mother liquor to obtain refined mother liquor; step 2, preparing an ammonium phosphate intermediate through a neutralization reaction: adding an ammoniating agent into the refined mother liquor, reacting to obtain an ammonium phosphate reaction solution, carrying out filter pressing on the ammonium phosphate reaction solution, and washing to obtain an ammonium phosphate solution and a white fertilizer; and step 3, preparing a finished product: heating and concentrating the ammonium phosphate solution, naturally cooling and crystallizing after the specific gravity of concentrated slurry reaches 1.38-1.45 to obtain ammonium phosphate crystal slurry, then separating crystals and mother liquor by adopting vacuum filtration to obtain wet ammonium phosphate crystals, and drying the wet ammonium phosphate crystals in a drying box to obtain the agricultural ammonium phosphate finished product with the water content of less than or equal to 2%. According to the method, the desilicication clear mother liquor is used as a raw material to prepare agricultural ammonium phosphate, so that comprehensive utilization of resources is realized, resource waste is avoided, and the production cost of ammonium phosphate is reduced.

Description

Technical Field

[0001] This invention relates to the field of phosphate rock processing technology, and specifically to a method for preparing ammonium phosphate using desilication mother liquor. Background Technology

[0002] In the phosphorus chemical industry (such as phosphoric acid preparation and phosphate rock processing), in order to reduce the silicon content in phosphorus products and improve product purity, a "desiliconization process" (such as adding desiliconizing agents, sedimentation separation, etc.) is usually adopted. This process generates a large amount of "desiliconization mother liquor". According to industry statistics, about 3-5 tons of desiliconization mother liquor are generated for every ton of industrial-grade phosphoric acid produced. This mother liquor contains abundant effective components (such as soluble phosphorus, content 8%-12%; ammonium nitrogen, content 3%-5%), and is accompanied by a small amount of impurities (such as residual silicides, content 0.8%-1.5%; trace heavy metal ions, such as iron and aluminum, total content ≤0.1%).

[0003] Currently, most companies treat desiliconization mother liquor as "wastewater," discharging it after neutralization, precipitation, and filtration. This not only leads to the complete waste of nutrients such as phosphorus and nitrogen in the mother liquor but also incurs high wastewater treatment costs. A few companies attempt to recover phosphorus from the mother liquor, but the "direct evaporation concentration" process is problematic. Impurities (silicides) in the mother liquor easily form scale during evaporation, causing equipment blockage, high maintenance costs, and low purity of the recovered product (ammonium phosphate purity ≤75%), with impurity content exceeding standards (silicon content ≥2%). This fails to meet the requirements of the "Agricultural Monoammonium Phosphate and Diammonium Phosphate" standard (GB / T10205-2009) and can only be used as a low-value industrial-grade auxiliary material.

[0004] In addition, the current preparation of agricultural ammonium phosphate (such as monoammonium phosphate and diammonium phosphate) mainly relies on the direct neutralization process of "high-purity phosphoric acid + industrial ammonia". The raw material cost accounts for 60%-70% of the total product cost, and a large amount of energy is required for phosphoric acid purification, which is not in line with the industrial development direction of "green, low-carbon and resource recycling". Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a method for preparing ammonium phosphate using desilication mother liquor. The method uses desilication mother liquor as a raw material to prepare agricultural ammonium phosphate, thereby solving the problem of resource waste and saving costs.

[0006] The technical solution adopted by this invention to solve its technical problem is: A method for preparing ammonium phosphate using desilication mother liquor includes the following steps: Step 1, Raw material pretreatment: Remove calcium, iron, aluminum and silicides from the desiliconized mother liquor to obtain refined mother liquor; Step 2, Neutralization reaction to prepare ammonium phosphate intermediate: Add an ammoniac to the purified mother liquor, react to obtain ammonium phosphate reaction solution, filter and wash the ammonium phosphate reaction solution to obtain ammonium phosphate solution and white fertilizer; Step 3: Preparation of finished product: The ammonium phosphate solution is heated and concentrated. After the specific gravity of the concentrated slurry reaches 1.38-1.45, it is naturally cooled and crystallized to obtain ammonium phosphate crystal slurry. Then, the crystals and mother liquor are separated by vacuum filtration to obtain wet ammonium phosphate crystals. The wet ammonium phosphate crystals are sent to a drying oven for drying to obtain agricultural ammonium phosphate finished product with a moisture content of ≤2%.

[0007] As a further improvement to the above technical solution, the specific steps for removing calcium, iron, aluminum and silicides from the desilication mother liquor in step 1 are as follows: add concentrated sulfuric acid to the desilication mother liquor, the amount of concentrated sulfuric acid added is 0.05%-1.0% of the mass of the desilication mother liquor, and filter the reaction solution of the desilication mother liquor and concentrated sulfuric acid to obtain the refined mother liquor.

[0008] As a further improvement to the above technical solution, in step 1, the desilication mother liquor is first pumped into the pretreatment reactor, the stirring mechanism of the pretreatment reactor is turned on, and then concentrated sulfuric acid is added to the pretreatment reactor while continuously stirring.

[0009] As a further improvement to the above technical solution, the stirring speed of the stirring mechanism of the pretreatment reactor is 200-250 r / min.

[0010] As a further improvement to the above technical solution, the internal temperature of the pretreatment reactor is 40-45℃.

[0011] As a further improvement to the above technical solution, the reaction time of the desilication mother liquor and concentrated sulfuric acid in the pretreatment reactor is 30-40 minutes.

[0012] As a further improvement to the above technical solution, the ammoniaating agent is ammonia water with a concentration of 24%-28%.

[0013] As a further improvement to the above technical solution, in step 2, the refined mother liquor obtained in step 1 is first pumped into the neutralization reactor. The temperature inside the neutralization reactor is at room temperature. The stirring mechanism of the neutralization reactor is turned on to stir the refined mother liquor. While stirring, the ammonia agent is added. When the pH value of the slurry in the neutralization reactor stabilizes at 4.0-4.5 and remains unchanged for 10 minutes, the addition of the ammonia agent is stopped. Then, the temperature inside the neutralization reactor is raised to 75-80℃ and the stirring reaction continues for 30-40 minutes to obtain the ammonium phosphate reaction solution.

[0014] As a further improvement to the above technical solution, the stirring speed of the stirring mechanism of the neutralization reactor is 150-180 r / min.

[0015] As a further improvement to the above technical solution, in step 3, the ammonium phosphate solution obtained in step 2 is first pumped into a concentration reactor, and then the temperature inside the concentration reactor is raised to 120-130℃ for concentration. After the specific gravity of the concentrated slurry reaches 1.38-1.45, it is naturally cooled and crystallized. When the temperature drops to 50-55℃, cooling and crystallization are started. When the temperature inside the reactor drops to 30-35℃, cooling is stopped, and the crystallization is allowed to stand for 30-40 minutes to form the ammonium phosphate crystal slurry.

[0016] The beneficial effects of this invention are as follows: using desilication mother liquor as raw material, after pretreatment to remove impurities such as calcium, iron, aluminum, and silicides, an ammonia-forming agent is added for neutralization to obtain ammonium phosphate solution and white fertilizer. Then, the ammonium phosphate solution is concentrated and crystallized to obtain ammonium phosphate. This method achieves comprehensive resource utilization, avoids resource waste, and reduces the production cost of ammonium phosphate. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] Figure 1 This is a flowchart of a method for preparing ammonium phosphate using desilication mother liquor according to the present invention. Detailed Implementation

[0019] The following will clearly and completely describe the concept, specific structure, and technical effects of the present invention in conjunction with embodiments and accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. The various technical features in the present invention can be combined interactively without contradicting each other.

[0020] Reference Figure 1 The present invention provides a method for preparing ammonium phosphate using desilication mother liquor, comprising the following steps: Step 1: Raw Material Pretreatment: Concentrated sulfuric acid is added to the desiliconized mother liquor for decalcification. The amount of concentrated sulfuric acid added is 0.05%-1.0% of the mass of the desiliconized mother liquor. Decalcification simultaneously removes iron, aluminum, and silicides. After filtration, a refined mother liquor is obtained. Specifically, the desiliconized mother liquor is first pumped into a pretreatment reactor. The temperature inside the pretreatment reactor is 40-45℃. The stirring mechanism of the pretreatment reactor is turned on, and the stirring speed is 200-250 r / min. Then, concentrated sulfuric acid is added to the pretreatment reactor, and the reaction is carried out gradually while continuously stirring. The reaction time is 30-40 min, resulting in a precipitate. The precipitate is then filtered through a plate and frame filter press to obtain the refined mother liquor.

[0021] Step 2: Neutralization reaction to prepare ammonium phosphate intermediate: The refined mother liquor obtained in Step 1 is pumped into a neutralization reactor. The temperature inside the neutralization reactor is at room temperature (20-25℃). The stirring mechanism of the neutralization reactor is turned on to stir the refined mother liquor at a stirring speed of 150-180 r / min. While stirring, an ammonia agent with a concentration of 24%-28% ammonia water is added. When the pH value of the slurry in the neutralization reactor stabilizes at 4.0-4.5 and remains unchanged for 10 minutes, the addition of the ammonia agent is stopped. Then, the temperature inside the neutralization reactor is raised to 75-80℃ and the reaction is continued for 30-40 minutes to obtain the ammonium phosphate reaction solution. After pressure filtration and washing of the ammonium phosphate reaction solution, ammonium phosphate liquid and white fertilizer are obtained. The white fertilizer contains nitrogen, phosphorus, calcium, magnesium, iron, and aluminum, of which phosphorus pentoxide > 25% and nitrogen content > 18%.

[0022] Step 3: Preparation of the finished product: The ammonium phosphate solution obtained in Step 2 is pumped into a concentration reactor. The temperature inside the concentration reactor is then raised to 120-130℃ for concentration. After the specific gravity of the concentrated slurry reaches 1.38-1.45, it is allowed to cool and crystallize naturally. When the temperature drops to 50-55℃, cooling crystallization is started. When the temperature inside the reactor drops to 30-35℃, cooling is stopped, and the crystallization is allowed to stand for 30-40 minutes to form the ammonium phosphate crystal slurry. Then, the crystallization and the mother liquor are separated by vacuum filtration to obtain wet ammonium phosphate crystals with a moisture content of 15-20%. The wet ammonium phosphate crystals are sent to a drying oven for drying at a temperature of 80-100℃ for 1-2 hours until an agricultural ammonium phosphate product with a moisture content ≤2% is obtained.

[0023] It can be understood that in step 1, the desilication mother liquor is strongly acidic, with a phosphorus content of 6%-18% and a nitrogen content of 3%-10%; the concentrated sulfuric acid is 98% industrial concentrated sulfuric acid. Adding 98% concentrated sulfuric acid to the desilication mother liquor utilizes the strong acidity of the concentrated sulfuric acid to disrupt the crystal structure of silicon-containing minerals (such as silicates), causing the silicates to depolymerize and the silicon element to be converted into filterable silicon dioxide (or silicic acid dehydrates to generate SiO2), ultimately accumulating in the residue in solid form. Silicon removal is achieved through solid-liquid separation. Utilizing the chemical reaction between sulfuric acid and calcium-containing compounds, calcium sulfate (CaSO4) is generated. Since calcium sulfate is slightly soluble, it precipitates out of the system, and calcium removal is achieved through solid-liquid separation methods such as filtration.

[0024] It can be understood that the iron and aluminum in the desilication mother liquor are not free ions, but rather form stable aluminosilicate and ferrosilicate complex systems with silicides. The core of iron and aluminum removal is to first break bonds to release ions, then convert them into low-soluble polymeric salts, and finally co-precipitate and retain them with other precipitates, rather than relying on simple sulfate precipitation. Specifically, the strong acidity of 98% concentrated sulfuric acid combined with a reaction temperature of 40-45℃ will destroy the crystal structure of aluminosilicates and ferrosilicates, releasing iron and aluminum ions into the system. At the same time, excess sulfate ions combine with the released iron and aluminum ions to form polymeric basic ferric sulfate and basic aluminum sulfate. These polymeric salts have extremely low solubility under the temperature and acidity conditions and will spontaneously aggregate to form fine particles. The polymeric iron and aluminum precipitates will mutually adsorb and agglomerate with the simultaneously generated calcium sulfate (CaSO2) precipitate and silica (SiO2) residue to form large-particle filter cakes, which are finally separated from the purified mother liquor by plate and frame filtration, achieving deep removal of iron and aluminum ions.

[0025] In step 2, 24%-28% ammonia water is added to the purified mother liquor, and the reaction formula is: H3PO4+NH3·H2O=NH4H2PO4+H2O, which yields ammonium phosphate solution.

[0026] In addition, this embodiment achieves targeted removal of impurities during the raw material pretreatment stage, and improves removal efficiency and accuracy through process parameters. Parameter synergy enhances the targeted reaction of concentrated sulfuric acid with calcium and silicon impurities, avoiding incomplete reactions or excessive reagent consumption. Specifically, the temperature of the pretreatment reactor is controlled at 40-45℃. This temperature range increases the reaction rate of concentrated sulfuric acid with calcium and magnesium ions by 40%-50% compared to room temperature (20-25℃); simultaneously, it reduces sulfuric acid volatilization compared to temperatures above 50℃. The stirring speed is controlled at 200-250 r / min, and the high-speed stirring creates a strong turbulent flow field, allowing concentrated sulfuric acid to quickly disperse into the desilication mother liquor, avoiding excessively high local acid concentrations. The amount of concentrated sulfuric acid added is precisely matched to the calcium content in the desilication mother liquor, achieving maximum calcium removal while avoiding excessive sulfuric acid leading to increased consumption of ammonia-removing agents in the subsequent neutralization reaction.

[0027] In this embodiment, by setting the pretreatment temperature and stirring parameters, the impurity content of the refined mother liquor can be ≤0.1%, thereby reducing interference to the neutralization reaction.

[0028] During the neutralization reaction stage, the reaction rate and product purity are balanced through stepwise control of temperature, stirring, and pH, ensuring the quality of the ammonium phosphate intermediate and achieving efficient separation of ammonium phosphate and white fertilizer. Specifically, the temperature inside the neutralization reactor is controlled at room temperature. Ammonia evaporates at room temperature (evaporation loss ≤0.5%). If the initial temperature is too high, it will increase the amount of ammonia volatilized, leading to waste of the ammoniaizing agent. If the initial temperature is too low, the viscosity of the ammonia will increase, reducing the uniformity of mixing with the refined mother liquor. The stirring speed is controlled at 150-180 r / min, which ensures thorough mixing of ammonia and refined mother liquor while avoiding excessive foaming caused by vigorous stirring. Foam can carry ammonium phosphate particles into the white fertilizer filter residue. The pH is maintained at 4.0-4.5 for 10 minutes. pH 4.0-4.5 is the stable formation range of monoammonium phosphate (MAP), at which ammonium phosphate solubility is lowest. Maintaining stability for 10 minutes ensures complete reaction and avoids batch-to-batch quality fluctuations. Then, by raising the temperature to 75-80℃, the equilibrium of the ammoniation reaction can be shifted to the right, thereby increasing the conversion rate of residual ammonium nitrogen. A reaction time of 30-40 minutes can ensure complete crystal growth and avoid crystal agglomeration, which would increase the difficulty of washing.

[0029] During the finished product preparation stage, precise control of temperature, specific gravity, and cooling rate ensures that crystal precipitation efficiency and finished product moisture content meet standards, while reducing drying energy consumption. Specifically, the concentration temperature is controlled at 120-130℃ to improve concentration efficiency while avoiding the decomposition rate of ammonium phosphate. When the specific gravity of the concentrated slurry is 1.38-1.45, the ammonium phosphate content in the slurry reaches 45%-50%, resulting in a high crystallization yield. If the specific gravity of the concentrated slurry is too low, the crystallization yield decreases, the mother liquor circulation volume increases, leading to increased energy consumption. If the specific gravity of the concentrated slurry is too high, the slurry viscosity increases, easily clogging pipes and increasing the risk of scaling in the concentration reactor. Then, a stepped cooling process is used: first, the mixture is allowed to cool naturally to 50-55℃, then the concentration reactor is cooled to 30-35℃ and allowed to stand for 30-40 minutes. Natural cooling to 50-55℃ avoids crystal breakage caused by excessive temperature differences, as broken crystals increase filtration difficulty. The mixture is then cooled further to 30-35℃ to increase the crystal precipitation rate, and allowed to stand for 30-40 minutes to ensure complete crystal settling. Drying parameters are controlled at 80-100℃ for 1-2 hours, with a moisture content ≤2%, achieving a balance between drying rate and energy consumption, ensuring drying effectiveness while reducing energy consumption.

[0030] In this embodiment, desilication mother liquor (phosphorus content 15.58%, nitrogen content 6.12%, silicon content 0.6%, total metal content 0.99%) was used as raw material for a small-scale test. The test data are shown in the table below:

[0031] The phosphate fertilizer samples obtained from the small-scale test were tested, and the results are shown in the table below:

[0032] Based on the above experimental data, the total nutrient content (N+P2O5) of the ammonium phosphate obtained in this embodiment is greater than 67%, which meets the requirement of ≥55.0% for total nutrient content (N+P2O5) as specified in the standard GB / T 10205-2009 "Agricultural Monoammonium Phosphate and Diammonium Phosphate".

[0033] Therefore, the method of the present invention, through the comprehensive optimization of impurity-oriented removal, neutralization process and crystallization process, can efficiently convert desiliconized mother liquor into agricultural phosphate fertilizer products that meet the GB / T 10205-2009 standard. The resulting product has low impurity content and no obvious agglomeration. It achieves the dual goals of "resource utilization of phosphate chemical by-products" and "low-cost preparation of agricultural fertilizers", and has the potential for industrial promotion.

[0034] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A method for preparing ammonium phosphate using desilication mother liquor, characterized in that: Includes the following steps: Step 1, Raw material pretreatment: Remove calcium, iron, aluminum and silicides from the desiliconized mother liquor to obtain refined mother liquor; Step 2, Neutralization reaction to prepare ammonium phosphate intermediate: Add an ammoniac to the purified mother liquor, react to obtain ammonium phosphate reaction solution, filter and wash the ammonium phosphate reaction solution to obtain ammonium phosphate solution and white fertilizer; Step 3: Preparation of finished product: The ammonium phosphate solution is heated and concentrated. After the specific gravity of the concentrated slurry reaches 1.38-1.45, it is naturally cooled and crystallized to obtain ammonium phosphate crystal slurry. Then, the crystals and mother liquor are separated by vacuum filtration to obtain wet ammonium phosphate crystals. The wet ammonium phosphate crystals are sent to a drying oven for drying to obtain agricultural ammonium phosphate finished product with a moisture content of ≤2%.

2. The method for preparing ammonium phosphate using desilication mother liquor according to claim 1, characterized in that: The specific steps for removing calcium, iron, aluminum and silicides from the desilication mother liquor in step 1 are as follows: add concentrated sulfuric acid to the desilication mother liquor, the amount of concentrated sulfuric acid added is 0.05%-1.0% of the mass of the desilication mother liquor, and filter the reaction solution of the desilication mother liquor and concentrated sulfuric acid to obtain the refined mother liquor.

3. The method for preparing ammonium phosphate using desilication mother liquor according to claim 2, characterized in that: In step 1, the desilication mother liquor is first pumped into the pretreatment reactor, the stirring mechanism of the pretreatment reactor is turned on, and then concentrated sulfuric acid is added to the pretreatment reactor while continuously stirring.

4. The method for preparing ammonium phosphate using desilication mother liquor according to claim 3, characterized in that: The stirring speed of the stirring mechanism in the pretreatment reactor is 200-250 r / min.

5. The method for preparing ammonium phosphate using desilication mother liquor according to claim 3, characterized in that: The temperature inside the pretreatment reactor is 40-45℃.

6. The method for preparing ammonium phosphate using desilication mother liquor according to claim 3, characterized in that: The reaction time of the desilication mother liquor and concentrated sulfuric acid in the pretreatment reactor is 30-40 minutes.

7. The method for preparing ammonium phosphate using desilication mother liquor according to claim 1, characterized in that: The ammoniating agent is ammonia water with a concentration of 24%-28%.

8. The method for preparing ammonium phosphate using desilication mother liquor according to claim 7, characterized in that: In step 2, the refined mother liquor obtained in step 1 is first pumped into a neutralization reactor. The temperature inside the neutralization reactor is at room temperature. The stirring mechanism of the neutralization reactor is turned on to stir the refined mother liquor. While stirring, an ammonia agent is added. When the pH value of the slurry in the neutralization reactor stabilizes at 4.0-4.5 and remains unchanged for 10 minutes, the addition of the ammonia agent is stopped. Then, the temperature inside the neutralization reactor is raised to 75-80℃ and the reaction is continued to be stirred for 30-40 minutes to obtain the ammonium phosphate reaction solution.

9. A method for preparing ammonium phosphate using desilication mother liquor according to claim 8, characterized in that: The stirring speed of the stirring mechanism in the neutralization reactor is 150-180 r / min.

10. The method for preparing ammonium phosphate using desilication mother liquor according to claim 1, characterized in that: In step 3, the ammonium phosphate solution obtained in step 2 is first pumped into a concentration reactor. Then, the temperature inside the concentration reactor is raised to 120-130℃ for concentration. After the specific gravity of the concentrated slurry reaches 1.38-1.45, it is allowed to cool and crystallize naturally. When the temperature drops to 50-55℃, cooling and crystallization are started. When the temperature inside the reactor drops to 30-35℃, cooling is stopped, and the crystallization is allowed to stand for 30-40 minutes to form the ammonium phosphate crystal slurry.

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