Method for producing water treatment agent polyaluminum chloride by using acid pickling aluminum slag

Abstract

The invention relates to the technical field of industrial production waste regeneration water treatment agents, and discloses a method for producing water treatment agent polyaluminum chloride by using acid pickling aluminum slag, which comprises the following steps: S1, acidolysis reaction: mixing raw materials of acid pickling aluminum slag, hydrochloric acid and aluminum hydroxide, heating and acidolysis to generate a basic aluminum salt solution; s2, polymerization reaction: adding the basic aluminum salt solution into water, diluting, adding calcium aluminate powder, and carrying out sealed polymerization reaction to obtain a polymerization reaction solution; and S3, post-treatment: adding water into the polymerization reaction solution, carrying out precipitation separation, taking supernatant, carrying out hydraulic filtration to obtain filtrate and filter residues, and drying the filtrate to obtain a solid polyaluminum chloride product. According to the scheme, in the acid pickling aluminum slag treatment process, the acid pickling aluminum slag can be converted into the solid polyaluminum chloride product by adding conventional reagents (hydrochloric acid, aluminum hydroxide, calcium aluminate powder and the like), the process is simple, the production safety and the product safety are high, and the method is conveniently applied and popularized to treatment of the acid pickling aluminum slag.

Description

Technical Field

[0001] The invention relates to the technical field of utilizing industrial production waste to regenerate water treatment agents, and in particular to a method for producing water treatment agent polyaluminium chloride by utilizing pickled aluminium slag. Background Art

[0002] Acid-washed aluminum slag is mainly composed of undissolved aluminum compounds (such as aluminum oxide, aluminum hydroxide) and other impurities. Common treatment methods include physical treatment (such as filtration, sedimentation, etc.), chemical treatment (such as neutralization, precipitation, etc.), thermal treatment (such as roasting, melting, etc.), biological treatment (such as microbial decomposition and leaching) and comprehensive treatment (used to produce polyaluminum chloride (PAC) solution, aluminum salt, etc.). In order to improve economic benefits, it is selected to be produced as water treatment agent polyaluminum chloride. According to the application field, water treatment agent polyaluminum chloride is divided into drinking water grade national standard "GB 15892-2022 Polyaluminum Chloride for Drinking Water" and industrial grade national standard "GB / T 22627-2022 Water Treatment Agent Polyaluminum Chloride". The former is used for the purification of drinking water, and the latter is used for industrial water supply, wastewater and sewage and sludge treatment.

[0003] Prior art CN105668601A discloses a method for preparing polyaluminium chloride using aluminium-containing waste residue, comprising the following steps: (1) placing 15-20 parts of 31% hydrochloric acid, 8-12 parts of water, and 10-15 parts of aluminium-containing waste residue raw materials in a reaction vessel, heating to 90°C-120°C, and performing acid hydrolysis reaction under normal pressure for 2-3 hours to obtain solution A; (2) adding 4-5 parts of calcium aluminate to the solution A at 70°C-90°C, performing polymerization reaction for 1-2 hours to obtain polymerization reaction solution B; (3) cooling the solution B to 35°C-45°C, adding a polymer coagulant, and keeping the temperature for 1-2 hours to obtain solution C; (4) filtering the solution C to obtain a light yellow polyaluminium chloride solution D. The preparation method of the present invention is simple, low in cost, low in energy consumption, and the addition of a small amount of quaternised polyacrylamide can significantly improve the water purification effect of the prepared polyaluminium chloride.

[0004] However, the prior art still has the following problems: (1) The liquid PAC produced by the prior art contains polyacrylamide, which increases safety hazards; (2) Liquid PAC usually requires dedicated storage tanks and transportation vehicles, which increases the complexity of packaging and transportation; and it requires dedicated storage tanks and sites, which increases costs. The packaging and transportation stages are also more expensive due to their high density. These factors significantly reduce production efficiency; (2) The liquid PAC produced by the prior art may precipitate when left stationary or is easily affected by factors such as temperature and pH value during storage, affecting its stability; and it also needs to be stirred or mixed regularly, which makes storage more troublesome; (3) The liquid PAC produced by the prior art has a relatively short shelf life, and is prone to deterioration, especially in high temperature or high humidity environments, affecting its use effect.

[0005] In view of this, developing a more economical method for producing polyaluminium chloride as a water treatment agent using pickled aluminium slag not only effectively makes up for the deficiencies of the existing technology, but is also very important for the resource recycling of pickled aluminium slag. Summary of the invention

[0006] The present invention aims to provide a method for producing polyaluminium chloride, a water treatment agent, by using pickled aluminium slag, so as to solve the technical problem that the water treatment agent obtained by treating the pickled aluminium slag in the prior art contains polyacrylamide and has potential safety hazards.

[0007] To achieve the above object, the present invention adopts the following technical scheme: a method for producing polyaluminium chloride as a water treatment agent by using pickled aluminium slag, comprising the following steps:

[0008] S1, acid hydrolysis reaction: mix the raw materials of pickled aluminum slag, hydrochloric acid and aluminum hydroxide, heat and acid hydrolyze to generate basic aluminum salt solution;

[0009] S2, polymerization reaction: adding the above basic aluminum salt solution into water, adding calcium aluminate powder after dilution, sealing the polymerization reaction, and obtaining a polymerization reaction solution;

[0010] S3, post-treatment: adding water to the above polymerization reaction solution, taking the supernatant after precipitation separation and filtering to obtain a filtrate and a filter residue, and drying the filtrate to obtain a solid polyaluminium chloride product.

[0011] The principles and advantages of this solution are:

[0012] First, hydrochloric acid is used to dissolve the aluminum oxide and other metal oxides in the aluminum slag to form chlorides; and the addition of aluminum hydroxide can ensure that the basic aluminum salt (such as Al(OH)Cl2 or Al(OH)2Cl) is generated by adjusting the pH value of the solution, rather than pure aluminum chloride (AlCl3). 3+ ) will undergo hydrolysis and polymerization under alkaline conditions (achieved by adding calcium aluminate powder) to form multinuclear hydroxyl complexes (such as [Al13 O4(OH) 24 (H2O) 12 ] 7+ ), these polynuclear hydroxyl complexes have good flocculation properties. Finally, the polymerization reaction solution will be further diluted by water, and because the polynuclear hydroxyl complexes have a large molecular weight and a high charge density, they will gradually condense and settle in the solution to form a solid precipitate. The solid polyaluminium chloride product can be obtained by precipitation separation and filter pressing. The supernatant after filter pressing can be dried to obtain the solid polyaluminium chloride product.

[0013] 1. Compared with the existing technology, the liquid PAC produced contains polyacrylamide, which increases safety hazards. In the process of treating pickled aluminum slag, the present solution can convert the pickled aluminum slag into a solid polyaluminum chloride product by adding conventional reagents. Not only is the process simple, but the production and product safety are also high, which is easy to promote and apply to the treatment of pickled aluminum slag.

[0014] 2. This solution not only effectively realizes the resource recycling of pickled aluminum slag by regenerating the pickled aluminum slag into solid polyaluminium chloride products. In addition, the solid polyaluminium chloride products obtained by treating the pickled aluminum slag in this solution are small in size and highly stable, which is not only convenient for storage and transportation, but also reduces costs; it can also extend the product application validity period and improve the product application effect.

[0015] Preferably, as an improvement, in S1, the mixing mass ratio of the raw materials of pickled aluminum slag, hydrochloric acid and aluminum hydroxide is 2-3:18-20:1-1.5.

[0016] Technical effect: This scheme adopts the above-mentioned setting, which is convenient for acid hydrolysis of aluminum oxide to form basic aluminum salt, improves the aluminum ion fixation effect, and by optimizing the raw material ratio, it can also reduce the amount of raw material calcium aluminate powder, reduce the amount of heavy metals brought into the product by the raw materials, and reduce the amount of reaction residues, thereby improving the environmental benefits of production. The applicant has found through long-term experiments that if the amount of hydrochloric acid added is too little, the aluminum hydroxide will not be completely dissolved, resulting in incomplete acid hydrolysis reaction, reduced chloride ion fixation effect and stability, and reduced product yield, and may also lead to unstable product quality. If the amount of hydrochloric acid added is too much, the pH value is too low, which will not only easily corrode the equipment, but also increase the equipment maintenance cost; and many subsequent water treatment or chemical reaction steps (such as flocculation, precipitation, adsorption, etc.) are very sensitive to pH value. Too low pH value may make these steps unable to proceed normally, resulting in reduced product quality or poor treatment effect. In addition, too much hydrochloric acid will also increase side reactions, generate harmful substances such as chlorides and chlorine, increase the difficulty of treatment and bring safety hazards. If too little aluminum hydroxide is added, it will not be able to react with enough hydrochloric acid, resulting in incomplete acid hydrolysis reaction, which will not only reduce the product yield and production efficiency; incomplete acid hydrolysis will also cause unreacted hydrochloric acid to remain in the solution, resulting in the pH value of the solution being too low, affecting subsequent processing steps and product quality; if too much aluminum hydroxide is added, it will react with other impurities to reduce product purity and increase the difficulty of purification; and the weak alkalinity of aluminum hydroxide can also adjust the pH value of the solution to increase and interfere with subsequent acid treatment steps, affecting the quality and stability of the product.

[0017] Preferably, as an improvement, in S1, the raw material pickled aluminum slag is obtained by washing aluminum oxide in aluminum material with hydrochloric acid to generate aluminum chloride solution which is filtered, and the pickled aluminum slag has a solid content of 50-70%, contains 53-65% aluminum chloride, and has a pH of 6.7-7.3.

[0018] Preferably, as an improvement, in S1, the acid hydrolysis reaction is carried out by heating the temperature to 90-100° C. for 2-3 hours.

[0019] Technical effect: This scheme adopts the above-mentioned setting, which is convenient for hydrochloric acid and aluminum hydroxide to fully and quickly acidolyze aluminum oxide in the raw material, increase the content of effective ingredients in the solution, reduce the content of insoluble matter, and effectively improve the efficiency of acidolysis. And the reaction temperature range of this scheme can ensure that the temperature distribution in the reaction system is relatively uniform, avoid local overheating or overcooling, thereby ensuring the uniformity and consistency of the reaction, and the quality of the final product is more stable. And the reaction conditions are relatively mild in this temperature range, which can effectively reduce unnecessary side reactions and avoid the generation of impurities, thereby effectively improving the purity of the product.

[0020] The applicant has found through long-term experiments that if the reaction temperature is too high, not only will the energy consumption be high, but the reaction will be too violent, and it will be more likely to trigger other side reactions, generate complex by-products and reduce the purity of the product; and hydrochloric acid may decompose to generate chlorine (Cl2) at high temperatures, which is a toxic gas that will not only threaten the health of operators, but also corrode equipment. The high temperature of the acidolysis process will also increase equipment corrosion and accelerate the risk of seal aging, thereby increasing safety risks. If the reaction temperature is too low, the production efficiency will be reduced due to a significant decrease in the reaction rate; and under low temperature conditions, the solubility of aluminum hydroxide is low, which may cause some aluminum hydroxide to be unable to be completely dissolved, and the acidolysis reaction is incomplete, affecting the yield and purity of the product. If the reaction time is too long, the by-product content will increase significantly and reduce the purity of the product. If the reaction time is too short, the product yield and stability will be reduced due to incomplete reaction.

[0021] Preferably, as an improvement, in S2, the amount of calcium aluminate powder added is 1.8 to 2.2 times the amount of acid-hydrolyzed aluminum slag.

[0022] Technical effect: This scheme adopts the above-mentioned setting, which is convenient for producing high-purity solid polyaluminum chloride products. The applicant has found through long-term experiments that if too much calcium aluminate powder is added, because the main components of calcium aluminate powder are calcium oxide (CaO) and aluminum oxide (Al2O3), excessive addition will cause these components to fail to fully participate in the reaction and remain in the final product, reducing the purity of the product; in addition, it can also adjust the solution pH too high and affect the subsequent steps to be unable to proceed normally, resulting in a decline in product quality or poor treatment effect. If too little calcium aluminate powder is added, the insufficient amount will lead to incomplete reaction and fail to provide sufficient calcium ions and aluminum ions to participate in the polymerization reaction. This will affect the molecular weight and cross-linking degree of the product and reduce the mechanical strength and stability of the product.

[0023] Preferably, as an improvement, in S2, the polymerization reaction is carried out by heating the temperature to 90-100° C. for 2-3 hours.

[0024] Technical effect: This scheme adopts the above setting, which is convenient for full reaction. The applicant has found through long-term experiments that the polymerization reaction is carried out under normal pressure, and the requirements for reaction equipment are not high. According to the above setting conditions, batch production can be effectively carried out.

[0025] Preferably, as an improvement, in S3, the amount of water added is to dilute the polymerization reaction solution until the specific gravity of liquid polyaluminium chloride is 1.18 to 1.23.

[0026] Technical effect: This solution adopts the above-mentioned setting, which facilitates the precipitation and separation of impurities after dilution, and helps to improve the purity and quality of the product. The applicant has found through long-term experiments that if the amount of water added is too little, the liquid will be too thick and it will be difficult to roll and dry; if too much water is added, the drying cost will be too high due to insufficient product content.

[0027] Preferably, as an improvement, in S3, the precipitation is allowed to stand at room temperature for 18 to 20 hours.

[0028] Technical effect: This scheme adopts the above-mentioned setting, which is convenient for the impurities to be fully settled and separated, and pays attention to reducing the impurity content in the product and improving the quality. The applicant has found through long-term experiments that if the precipitation time is too short, the product purity will be reduced due to poor separation of coarse particles and unreacted impurities (other solid substances contained in calcium aluminate powder); if the precipitation time is too long, the production efficiency will be reduced due to wasted time.

[0029] Preferably, as an improvement, in S3, the particle size of the solid polyaluminium chloride is 180-250 μm, and the water content is 3-8%.

[0030] Technical effect: This solution adopts the above-mentioned settings to effectively improve the storage stability of the product, so that its stability remains high after long-term storage.

[0031] Preferably, as an improvement, the drying is to place the filtrate in a drum, control the steam temperature to 170°C, and rotate and dry at 2-4 rpm for one week, and the material scraped off by the scraper is the solid polyaluminium chloride product.

[0032] Technical effect: This scheme adopts the above settings to facilitate it to meet the quality requirements of polyaluminum chloride products in the industrial-grade national standard "GB / T 22627-2022 Water Treatment Agent Polyaluminum Chloride". DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following examples and experimental examples are conventional means well known to those skilled in the art, and the materials, reagents, etc. used can be obtained from commercial sources.

[0034] Example 1

[0035] This scheme provides a method for producing polyaluminium chloride, a water treatment agent, by using pickled aluminium slag, comprising the following steps:

[0036] S1, acid hydrolysis reaction: mix the raw materials of pickled aluminum slag, hydrochloric acid and aluminum hydroxide, heat and acid hydrolyze to generate basic aluminum salt solution;

[0037] As a reference, the raw material pickled aluminum slag is obtained by washing aluminum oxide in aluminum with hydrochloric acid to generate aluminum trichloride solution, which is filtered by pressure. The solid content of the pickled aluminum slag is 50-70%, containing 53-65% aluminum trichloride, and the pH is 6.7-7.3. The mixed mass ratio of the raw material pickled aluminum slag, hydrochloric acid and aluminum hydroxide is 2-3:18-20:1-1.5. The acidolysis reaction is heated to 90-100℃ and reacted for 2-3h.

[0038] In the acid hydrolysis reaction, hydrochloric acid reacts with the aluminum oxide in the pickled aluminum slag to produce soluble aluminum chloride (AlCl3). At the same time, the presence of aluminum hydroxide can adjust the pH value of the reaction to ensure that basic aluminum salts (such as Al(OH)Cl2 or Al(OH)2Cl) are produced instead of pure aluminum chloride. The reaction equation is as follows:

[0039] Al2O3+6HC1→2AlCl3+3H2O

[0040] Al(OH)3+3HC1→AlCl3+3H2O

[0041] To form basic aluminum salts, some aluminum chloride combines with hydroxide ions (OH-) in water to form basic aluminum chloride (such as Al(OH)Cl2 or Al(OH)2Cl):

[0042]

[0043] In the process, the main function of hydrochloric acid is to dissolve the aluminum oxide in the aluminum slag to generate soluble aluminum chloride. By controlling the concentration and dosage of hydrochloric acid, the reaction speed and product composition can be adjusted. The addition of aluminum hydroxide helps to adjust the pH value of the reaction system to ensure that basic aluminum salts are generated instead of simple aluminum chloride. Basic aluminum salts have better flocculation properties and can be better used in water treatment. Heating during the acidolysis process effectively accelerates the reaction rate and promotes the dissolution of aluminum oxide and the formation of basic aluminum salts.

[0044] S2, polymerization reaction: add the above basic aluminum salt solution into water, dilute and add calcium aluminate powder (the amount of calcium aluminate powder added is 1.8 to 2.2 times the amount of acid hydrolyzed aluminum slag), seal and heat to 90 to 100° C. for polymerization reaction for 2 to 3 hours to obtain a polymerization reaction solution;

[0045] In the polymerization reaction, the aluminum ions (Al 3+ ) will undergo hydrolysis and polymerization under alkaline conditions to generate polynuclear hydroxyl complexes (such as [Al 13 O4(OH) 24 (H2O) 12 ] 7+), these multinuclear hydroxyl complexes have good flocculation properties. The addition of calcium aluminate powder can increase the alkalinity of the solution and promote the hydrolysis and polymerization of aluminum salts. The reaction equation is as follows:

[0046] Al(OH)Cl2+H2O→Al(OH)2Cl+H +

[0047] Al(OH)2Cl+H2O→Al(OH)3+H + +Cl -

[0048] As the reaction proceeds, multiple aluminum ions can form polynuclear hydroxyl complexes through hydroxyl bridging:

[0049] nAl(OH)2Cl→[Al n (OH) (3n-2) Cl2] (6-n)+ +(n-2)H2O

[0050] mAl2(OH) n Cl 6-n +m H2O→[Al2(OH) n Cl 6-n· xH2O] m (n: 3-5, m<10)

[0051] Wherein, n is the number of aluminum ions. The applicant has found through long-term experiments that the multi-nuclear hydroxyl complex formed when n=3-5 has the best flocculation effect.

[0052] In the process, the basic aluminum salt solution is the basis of the polymerization reaction and provides a source of aluminum ions. Through hydrolysis and polymerization reactions, aluminum ions will form multi-nuclear hydroxyl complexes. These complexes have good flocculation properties and can effectively remove suspended particles and colloids in water. This solution can effectively increase the alkalinity of the solution by adding calcium aluminate powder, promoting the hydrolysis and polymerization of aluminum salts. It can also help adjust the pH value of the solution to ensure that the reaction is carried out within an appropriate pH range (usually 3.5-4.5). In addition, the calcium ions (Ca 2 +) forms a complex with aluminum ions, which can further enhance the flocculation effect. Water effectively dilutes the basic aluminum salt solution and provides a suitable reaction environment for the overall reaction. However, the applicant has found through long-term experiments that the amount of water needs to be properly controlled to ensure that the reaction can be carried out at a suitable concentration to avoid being too diluted or too concentrated to affect the polymerization effect.

[0053] S3, post-treatment: add water to the above polymerization reaction solution to dilute the polymerization reaction solution to a specific gravity of 1.18-1.23. Let it stand at room temperature for 18-20 hours; after precipitation separation, take the supernatant and filter it to obtain the filtrate and filter residue, and dry the filter residue to constant weight to obtain solid polyaluminum chloride; place the filtrate in a drum, steam temperature control 170°C, 2-4rpm rotary drying for one week, and the scraped material is the solid polyaluminum chloride product. The particle size of solid polyaluminum chloride is 180-250μm, and the water content is 3-8%.

[0054] In the post-treatment step, the polymerization reaction solution will be further diluted, and because the polynuclear hydroxy complexes have a large molecular weight and a high charge density, they will gradually condense and settle in the solution to form a solid precipitate. The solid polyaluminum chloride product can be obtained by precipitation separation and filter pressing. The supernatant after filter pressing can be dried to obtain the solid polyaluminum chloride product.

[0055] In actual production, the conventional ratio of raw materials pickled aluminum slag, hydrochloric acid and aluminum hydroxide, and calcium aluminate powder is 2:19:1:4. Specifically, the applicant currently consumes 900t of pickled aluminum slag, 1350t of hydrochloric acid (HCl≥31%), 450t of aluminum hydroxide, and 1800t of calcium aluminate powder each year, with an annual output of 1500t of solid polyaluminum chloride, and the aluminum oxide content in the polyaluminum chloride obtained from different batches is 39.7-45.2%, which meets the quality requirements of "GB / T 22627-2022 Water Treatment Agent Polyaluminum Chloride".

[0056] In summary, this scheme effectively improves the yield and production efficiency of the water treatment agent polyaluminium chloride by limiting the proportion of each raw material addition, the process parameters of the acid hydrolysis stage and the polymerization stage, and the safety of production and products is relatively high, which is convenient for promotion and application to the treatment of pickled aluminium slag.

[0057] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for producing polyaluminium chloride as a water treatment agent using pickled aluminium slag, characterized in that: The steps include: S1, acid hydrolysis reaction: mix the raw materials of pickled aluminum slag, hydrochloric acid and aluminum hydroxide, heat and acid hydrolyze to generate basic aluminum salt solution; S2, polymerization reaction: adding the above basic aluminum salt solution into water, adding calcium aluminate powder after dilution, sealing the polymerization reaction, and obtaining a polymerization reaction solution; S3, post-treatment: adding water to the above polymerization reaction solution, taking the supernatant after precipitation separation and filtering to obtain a filtrate and a filter residue, and drying the filtrate to obtain a solid polyaluminium chloride product.

2. The method for producing polyaluminium chloride as a water treatment agent by using pickled aluminium slag according to claim 1, characterized in that: In S1, the mixing mass ratio of the raw materials of pickled aluminum slag, hydrochloric acid and aluminum hydroxide is 2-3:18-20:1-1.

5.

3. The method for producing polyaluminium chloride as a water treatment agent by using pickled aluminium slag according to claim 1, characterized in that: In S1, the raw material pickled aluminum slag is obtained by washing aluminum oxide in aluminum material with hydrochloric acid to generate aluminum chloride solution which is filtered by pressure. The pickled aluminum slag has a solid content of 50-70%, contains 53-65% aluminum chloride, and has a pH of 6.7-7.

3.

4. The method for producing polyaluminium chloride as a water treatment agent by using pickled aluminium slag according to claim 2, characterized in that: In S1, the acid hydrolysis reaction is carried out by heating the temperature to 90-100°C for 2-3h.

5. The method for producing polyaluminium chloride as a water treatment agent by using pickled aluminium slag according to claim 1, characterized in that: In S2, the amount of calcium aluminate powder added is 1.8 to 2.2 times the amount of acid-decomposed aluminum slag.

6. The method for producing polyaluminium chloride as a water treatment agent by using pickled aluminium slag according to claim 5, characterized in that: In S2, the polymerization reaction is carried out by heating the temperature to 90-100°C for 2-3h.

7. The method for producing polyaluminium chloride as a water treatment agent by using pickled aluminium slag according to claim 1, characterized in that: In S3, the amount of water added is to dilute the polymerization reaction solution until the specific gravity of liquid polyaluminium chloride is 1.18 to 1.

23.

8. The method for producing polyaluminium chloride as a water treatment agent by using pickled aluminium slag according to claim 1, characterized in that: In S3, the precipitation is allowed to stand at room temperature for 18 to 20 hours.

9. The method for producing polyaluminium chloride as a water treatment agent by using pickled aluminium slag according to claim 1, characterized in that: In S3, the particle size of the solid polyaluminium chloride is 180-250 μm, and the water content is 3-8%.

10. The method for producing polyaluminium chloride as a water treatment agent by using pickled aluminium slag according to claim 1, characterized in that: The drying step is to place the filtrate in a drum, control the temperature with steam at 170°C, and rotate at 2-4 rpm for one cycle, and the solid polyaluminium chloride product is scraped off by a scraper.

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