Efficient recovery method of agrochemical byproduct sodium tetrachloroaluminate solid slag

Abstract

The invention relates to the technical field of chemical by-product treatment, in particular to an efficient recycling method for agrochemical by-product sodium tetrachloroaluminate solid residues. The efficient recycling method for the agrochemical byproduct sodium tetrachloroaluminate solid residues comprises the following steps that the sodium tetrachloroaluminate solid residues and a hydrochloric acid solution are mixed, stirred and dissociated, sodium chloride crystals are separated out, and filtrate A is collected; concentrating the filtrate A, and introducing ammonia gas into the concentrated solution; when it is detected that the pH value of the concentrated solution is 2-3, adding a hydrofluoric acid solution into the concentrated solution, continuously introducing ammonia gas to keep the pH value of a concentrated solution system at 3-4, and stopping introducing the ammonia gas after the hydrofluoric acid solution is completely added; stirring the concentrated solution system at room temperature, filtering and washing to obtain an aluminum fluoride filter cake, and collecting filtrate B; drying and grinding the aluminum fluoride filter cake to obtain white aluminum fluoride powder; and continuously introducing ammonia gas into the filtrate B until the pH value is 6-7, and then concentrating the filtrate B to obtain ammonium chloride containing organic phosphorus. The method provided by the invention is efficient and environment-friendly, and comprehensive utilization of waste resources is realized.

Description

Technical Field

[0001] This application relates to the field of chemical by-product treatment technology, and in particular to an efficient method for recovering sodium tetrachloroaluminate solid slag, an agrochemical by-product. Background Technology

[0002] Aluminum fluoride has wide applications in aluminum smelting, ceramic preparation, optical lenses, electronic materials, and catalysts. It is insoluble in water, acids, and alkalis, and is stable at room temperature. When heated to 300-400℃, it can be partially decomposed by water vapor into hydrogen fluoride and aluminum oxide. In recent years, with the increasing awareness of low-carbon, energy-saving, and environmental protection, high-energy-consuming industries such as electrolytic aluminum have been subject to greater regulation, making energy reduction and environmental pollution control key issues. Aluminum fluoride (AlF3) is mainly used as a flux in aluminum electrolysis, lowering the electrolysis temperature, reducing electrolyte evaporation losses, effectively reducing energy consumption during electrolysis, achieving energy conservation and emission reduction, and also adjusting the electrolyte molecular ratio and enhancing conductivity. Currently, nearly 90% of aluminum fluoride in China is used in electrolytic aluminum production, and about 10% is exported. In recent years, due to the continuous increase in downstream automotive and new energy demand, the demand for aluminum products has shown an upward trend, and the demand for aluminum fluoride is expected to increase significantly as well.

[0003] Sodium tetrachloroaluminate is a byproduct of the preparation of methylphosphonic acid, an intermediate in agrochemical processes. During its separation from methylphosphonic acid, in addition to the main component sodium tetrachloroaluminate, a certain amount of organoaluminum and organophosphorus impurities remain. Industrially, sodium tetrachloroaluminate is generally dissolved in water, hydrolyzed, and then directly discharged, which not only causes significant environmental pollution but also wastes resources. Developing a low-cost, low-pollution treatment method is therefore of great significance.

[0004] Currently, most manufacturers of methylphosphonic acid generally hydrolyze sodium tetrachloroaluminate after dissolving it in water, then adjust the pH of the reaction solution by adding alkali or other alkaline substances, and finally concentrate it to a certain extent to obtain polyaluminum chloride. Patent CN108238621B discloses a method for producing polyaluminum chloride using a byproduct of diethyl methylphosphonate production. Specifically, it discloses dissolving and dissociating the byproduct sodium tetrachloroaluminate in a dissolving tank, then separating the sodium chloride crystals, collecting the filtrate, and then adding a certain amount of ferric chloride, hydrochloric acid, aluminum hydroxide, and calcium aluminate to the filtrate to carry out a polymerization reaction. The resulting polyaluminum chloride is then concentrated and evaporated to dryness. This method has high recovery costs, and the prepared polyaluminum chloride contains a certain amount of organophosphorus compounds, which can easily cause cross-contamination of the product and is not environmentally friendly. Patent CN111804704B discloses a method for treating sodium tetrachloroaluminate solid slag. Specifically, it involves mixing the sodium tetrachloroaluminate solid slag with water for dissociation, then adding alkali to initiate a polymerization reaction, followed by concentration and crystallization, and solid-liquid separation to obtain sodium chloride solid and concentrated mother liquor. The concentrated mother liquor is then matured to obtain polyaluminum chloride liquid product. This recycling method is low-cost and has minimal environmental pollution, but it still presents the problem of cross-contamination between products, and the organophosphorus compounds in the polyaluminum chloride are not eliminated, making it less environmentally friendly. Summary of the Invention

[0005] This application provides an efficient method for recovering sodium tetrachloroaluminate solid residue, an agrochemical byproduct, to solve the problems of cross-contamination of products and the failure to eliminate organophosphorus compounds in polyaluminum chloride during the treatment of sodium tetrachloroaluminate solid residue in related technologies.

[0006] In a first aspect, this application provides a method for the efficient recovery of sodium tetrachloroaluminate solid slag, an agrochemical byproduct, comprising the following steps: S101, mix sodium tetrachloroaluminate solid residue with hydrochloric acid solution at a mass ratio of 1:3-1:5, stir to dissociate, precipitate sodium chloride crystals, and collect filtrate A; S102, concentrate filtrate A until the alumina mass content in the system is 10%-18%, stop concentration, and introduce ammonia gas into the concentrate; S103, when the pH value of the concentrate is detected to be 2-3, add hydrofluoric acid solution to the concentrate and continuously introduce ammonia gas to keep the pH value of the concentrate system at 3-4. After the hydrofluoric acid solution is added, stop introducing ammonia gas. S104, stir the concentrated liquid system at room temperature, filter and wash to obtain aluminum fluoride filter cake, and collect filtrate B; S105, dry and grind aluminum fluoride filter cake at 80-120℃ to obtain white aluminum fluoride powder; S106. Ammonia gas is continuously introduced into filtrate B until the pH value is 6-7. Then, filtrate B is concentrated to obtain ammonium chloride containing organic phosphorus.

[0007] In some embodiments, in step S101, the mass concentration of the hydrochloric acid solution is 18%-25%.

[0008] In some embodiments, the composition of the sodium tetrachloroaluminate solid slag, by mass percentage, is: 96% sodium tetrachloroaluminate and 4% phosphorus impurities.

[0009] In some embodiments, the stirring time in step S101 is 1-2 hours.

[0010] In some embodiments, in step S102, the distillate produced during the concentration process is used to dissolve the hydrochloric acid solution.

[0011] In some embodiments, in step S103, the molar ratio of hydrofluoric acid added to aluminum ions in filtrate A is 3:1 to ensure that hydrofluoric acid and aluminum ions react fully and avoid cross-contamination of the product.

[0012] In some embodiments, in step S103, the mass concentration of the hydrofluoric acid solution is 35%-45%.

[0013] In some embodiments, the stirring time in step S104 is 2-4 hours.

[0014] The beneficial effects of the technical solution provided in this application include: 1. This application utilizes hydrochloric acid with a mass concentration of 18%-25% to dissociate sodium tetrachloroaluminate solid residue, and separates the sodium chloride dissociated from sodium tetrachloroaluminate from the filtrate as much as possible to avoid the occurrence of other by-products in the preparation of aluminum fluoride; 2. The amount of hydrofluoric acid added should be in a 3:1 molar ratio with the aluminum ions in the filtrate. The two should react fully to avoid cross-contamination of the products. The pH value of the system needs to be strictly controlled during the reaction of hydrofluoric acid and aluminum ions. Aluminum fluoride has a certain solubility in a certain concentration of hydrogen fluoride solution. When the pH value of the solution is 4, aluminum fluoride is basically insoluble in the system and can be completely removed from the system. Even if a small amount of hydrogen fluoride does not participate in the reaction, it will be evaporated with the water during the evaporation of the filtrate. It can be reused without causing pollution to the environment. 3. The method provided in this application processes the by-product double salt in the production of methyl dichlorophosphorus into aluminum fluoride and phosphorus-containing ammonium chloride nitrogen-phosphate fertilizer with certain economic value, thereby reducing the treatment cost of the by-product double salt. The entire recycling process generates no waste gas or solid waste, is highly efficient and environmentally friendly, and realizes the comprehensive utilization of waste resources. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a flowchart illustrating an efficient method for recovering sodium tetrachloroaluminate solid slag, an agrochemical byproduct, provided in this application. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] This application provides an efficient method for recovering sodium tetrachloroaluminate solid residue, an agricultural byproduct, which can solve the problems of cross-contamination of products and failure to eliminate organophosphorus compounds in polyaluminum chloride during the treatment of sodium tetrachloroaluminate solid residue in the prior art.

[0019] refer to Figure 1 This application provides a method for the efficient recovery of sodium tetrachloroaluminate solid slag, an agricultural byproduct, comprising the following steps: Step S101: Mix sodium tetrachloroaluminate solid residue with hydrochloric acid solution with a mass concentration of 18%-25% at a mass ratio of 1:3-1:5, stir for 1-2 hours to dissociate, precipitate sodium chloride crystals, and collect filtrate A; In step S102, concentrate filtrate A until the alumina content in the system is 10%-18% by mass, stop the concentration, and introduce ammonia gas into the concentrate; the distillate produced during the concentration process is used to dissolve the hydrochloric acid solution to be used in step S101. In step S103, when the pH value of the concentrate is detected to be 2-3, hydrofluoric acid solution is added to the concentrate, and ammonia gas is continuously introduced to maintain the pH value of the concentrate system at 3-4. After the hydrofluoric acid solution is added, the ammonia gas is stopped. The molar ratio of the amount of hydrofluoric acid added to the amount of aluminum ions in filtrate A is 3:1. Step S104: Stir the concentrated liquid system at room temperature for 2-4 hours, filter and wash to obtain aluminum fluoride filter cake, and collect filtrate B; Step S105: Dry and grind the aluminum fluoride filter cake at 80-120℃ to obtain white aluminum fluoride powder. Step S106: Ammonia gas is continuously introduced into filtrate B until the pH value is 6-7, and then filtrate B is concentrated to obtain ammonium chloride containing organic phosphorus.

[0020] The following describes in detail the efficient recovery method for sodium tetrachloroaluminate solid slag, a byproduct of agrochemicals, provided in this application, with reference to embodiments and comparative examples.

[0021] Example 1: (1) Dissolve 100g of sodium tetrachloroaluminate solid residue (including 96% sodium tetrachloroaluminate and 4% phosphorus impurities by mass percentage) generated during the preparation of methylphosphine dichloride in 300g of 21% hydrochloric acid solution, stir for 1h to dissociate and precipitate sodium chloride crystals, filter the solution to remove 29.5g of sodium chloride, and collect filtrate A; (2) Concentrate filtrate A until the mass content of alumina in the system is 12%, stop the concentration, and introduce ammonia into the concentrate; (3) When the pH value of the concentrate is detected to be 2, 75g of hydrofluoric acid solution with a mass concentration of 40% is slowly added to the concentrate at the same time, and ammonia gas is continuously introduced to keep the pH value of the concentrate system at 3. After the hydrofluoric acid solution is added, the ammonia gas is stopped. (4) Stir the concentrated liquid system at room temperature for 4 hours, then filter and wash to obtain aluminum fluoride filter cake, and collect filtrate B; (5) The aluminum fluoride filter cake was dried and ground at 80°C to obtain 69.8g of white aluminum fluoride powder; (6) Continue to pass ammonia gas into filtrate B until the pH value is 7, then evaporate filtrate B to obtain 84g of ammonium chloride containing organic phosphorus, which can be used as nitrogen and phosphorus fertilizer.

[0022] Example 2: (1) Dissolve 100g of sodium tetrachloroaluminate solid residue (including 96% sodium tetrachloroaluminate and 4% phosphorus impurities by mass percentage) generated during the preparation of methylphosphine dichloride in 300g of 22% hydrochloric acid solution, stir for 1h to dissociate and precipitate sodium chloride crystals, filter the solution to remove 30.1g of sodium chloride, and collect filtrate A; (2) Concentrate filtrate A until the mass content of alumina in the system is 13%, stop the concentration, and introduce ammonia into the concentrate; (3) When the pH value of the concentrate is detected to be 3, 75g of hydrofluoric acid solution with a mass concentration of 40% is slowly added to the concentrate at the same time. Ammonia gas is continuously introduced to keep the pH value of the concentrate system at 4. After the hydrofluoric acid solution is added, the ammonia gas is stopped. (4) Stir the concentrated liquid system at room temperature for 2 hours, then filter and wash to obtain aluminum fluoride filter cake, and collect filtrate B; (5) The aluminum fluoride filter cake was dried and ground at 100℃ to obtain 69.2g of white aluminum fluoride powder; (6) Continue to pass ammonia gas into filtrate B until the pH value is 6, then evaporate filtrate B to obtain 87g of ammonium chloride containing organic phosphorus, which can be used as nitrogen and phosphorus fertilizer.

[0023] Comparative Example 1: (1) Dissolve 100g of sodium tetrachloroaluminate solid residue (including 96% sodium tetrachloroaluminate and 4% phosphorus impurities by mass percentage) generated during the preparation of methylphosphine dichloride in 300g of water, stir for 1h to dissociate it, and no sodium chloride crystals precipitate out. Collect filtrate A. (2) Next, concentrate the filtrate A until the mass content of alumina in the system is 10%, stop the concentration, and introduce ammonia into the concentrate. (3) When the pH value of the concentrate is detected to be 2, 25g of hydrofluoric acid solution with a mass concentration of 40% is slowly added to the concentrate at the same time, and ammonia gas is continuously introduced to keep the pH value of the concentrate system at 3. After the hydrofluoric acid solution is added, the ammonia gas is stopped. (4) Stir the concentrated liquid system at room temperature for 4 hours, then filter and wash to obtain aluminum fluoride filter cake, and collect filtrate B; (5) The aluminum fluoride filter cake was dried and ground at 80°C to obtain 88.5g of a white powdery solid mixture of sodium chloride, aluminum fluoride and sodium hexafluoroaluminate; (6) Ammonia gas was continued to be introduced into filtrate B until the pH value was 7, and then filtrate B was evaporated to dryness to obtain 83g of ammonium chloride containing organophosphorus compounds.

[0024] In Comparative Example 1, water was used instead of hydrochloric acid for the dissociation process. After dissociation, no sodium chloride crystals were precipitated. The final product was a mixture of sodium chloride, aluminum fluoride, and sodium hexafluoroaluminate, instead of pure aluminum fluoride.

[0025] Comparative Example 2: (1) Dissolve 100g of sodium tetrachloroaluminate solid residue (including 96% sodium tetrachloroaluminate and 4% phosphorus impurities by mass percentage) generated during the preparation of methylphosphine dichloride in 300g of 21% hydrochloric acid solution, stir for 1h to dissociate, precipitate sodium chloride crystals, filter to remove 29.5g of sodium chloride, and collect filtrate A; (2) Concentrate filtrate A until the mass content of alumina in the system is 11%, stop the concentration, and introduce ammonia into the concentrate; (3) When the pH value of the concentrate is detected to be 2, start to slowly add 50g of hydrofluoric acid solution with a mass concentration of 40% to the concentrate at the same time, and continuously pass ammonia gas to keep the pH value of the concentrate system at 3. Stop passing ammonia gas after the hydrofluoric acid solution is added. (4) Stir the concentrated liquid system at room temperature for 4 hours, then filter and wash to obtain aluminum fluoride filter cake, and collect filtrate B; (5) The aluminum fluoride filter cake was dried and ground at 80°C to obtain 46.6g of white aluminum fluoride powder; (6) Ammonia gas was continued to be introduced into filtrate B until the pH value was 7, and a large amount of precipitate appeared in the system.

[0026] In Comparative Example 2, the amount of hydrofluoric acid added was relatively small. After the hydrofluoric acid solution was added, the hydrofluoric acid could not react fully with the aluminum ions, resulting in cross-contamination of the products. A large amount of precipitate appeared in the filtrate B system.

[0027] In the description of this specification, the references to terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example is included in at least one embodiment / mode or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0028] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this application, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly specified.

[0029] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A highly efficient method for recovering sodium tetrachloroaluminate solid slag, an agricultural chemical byproduct, characterized in that, Includes the following steps: S101, mix sodium tetrachloroaluminate solid residue with hydrochloric acid solution at a mass ratio of 1:3-1:5, stir to dissociate, precipitate sodium chloride crystals, and collect filtrate A; S102, concentrate filtrate A until the alumina mass content in the system is 10%-18%, stop concentration, and introduce ammonia gas into the concentrate; S103, when the pH value of the concentrate is detected to be 2-3, add hydrofluoric acid solution to the concentrate and continuously introduce ammonia gas to keep the pH value of the concentrate system at 3-4. After the hydrofluoric acid solution is added, stop introducing ammonia gas. S104, stir the concentrated liquid system at room temperature, filter and wash to obtain aluminum fluoride filter cake, and collect filtrate B; S105, dry and grind aluminum fluoride filter cake at 80-120℃ to obtain white aluminum fluoride powder; S106. Ammonia gas is continuously introduced into filtrate B until the pH value is 6-7. Then, filtrate B is concentrated to obtain ammonium chloride containing organic phosphorus.

2. The efficient recovery method for sodium tetrachloroaluminate solid slag, a by-product of agrochemicals, according to claim 1, is characterized in that, In step S101, the mass concentration of the hydrochloric acid solution is 18%-25%.

3. The efficient recovery method for sodium tetrachloroaluminate solid slag, a by-product of agrochemicals, according to claim 1, is characterized in that... The composition of sodium tetrachloroaluminate solid slag by mass percentage is: 96% sodium tetrachloroaluminate and 4% phosphorus impurities.

4. The efficient recovery method for sodium tetrachloroaluminate solid slag, a by-product of agrochemicals, according to claim 1, is characterized in that... In step S101, the stirring time is 1-2 hours.

5. The efficient recovery method for sodium tetrachloroaluminate solid slag, an agrochemical byproduct, according to claim 1, is characterized in that... In step S102, the distillate produced during the concentration process is used to dissolve the hydrochloric acid solution.

6. The efficient recovery method for sodium tetrachloroaluminate solid slag, an agrochemical byproduct, according to claim 1, is characterized in that, In step S103, the molar ratio of hydrofluoric acid added to aluminum ions in filtrate A is 3:

1.

7. The efficient recovery method for sodium tetrachloroaluminate solid slag, an agrochemical byproduct, according to claim 1, is characterized in that, In step S103, the mass concentration of the hydrofluoric acid solution is 35%-45%.

8. The efficient recovery method for sodium tetrachloroaluminate solid slag, a by-product of agrochemicals, according to claim 1, is characterized in that, In step S104, the stirring time is 2-4 hours.

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