Preparation process of aluminum hydroxide flame retardant synthesized by two kinds of solid hazardous waste

Abstract

The present application relates to a kind of preparation process of synthesizing aluminium hydroxide flame retardant using two kinds of solid hazardous waste, comprising the following synthesis steps: (1), in water, add hazardous waste aluminum ash, under stirring, add sodium hydroxide solution to react;(2), the material of reaction completion in step (1) is filtered by negative pressure, to obtain filtrate;(3), in the filtrate obtained in step (2), add solid waste sodium tetrachloroaluminate, control pH value, stir and react;(4), the material of reaction completion in step (3) is filtered by negative pressure, the filter solid obtained is washed with water, after washing, the filter solid is dried, to obtain solid aluminium hydroxide.The present application simultaneously disposes two kinds of hazardous waste and synthesizes target product aluminium hydroxide, and the method has economic feasibility.

Description

Technical Field

[0001] This invention belongs to the field of chemical hazardous waste treatment technology, specifically relating to a preparation process for synthesizing aluminum hydroxide flame retardant using two types of solid hazardous waste. Background Technology

[0002] Aluminum hydroxide (ATH, Al(OH)3) is currently the most widely used inorganic halogen-free flame retardant, accounting for approximately 50% of global flame retardant consumption and 75% of the inorganic flame retardant market. Its main application areas include wires and cables (the largest application market), electronics and electrical equipment (printed circuit boards, electronic component packaging, insulation materials, consumer electronics casings), and building materials (PVC flooring, wall panels, pipes, aluminum composite panels, insulation materials), etc. Its core advantages as a flame retardant are: halogen-free and environmentally friendly, producing no toxic or corrosive gases during combustion; excellent smoke suppression performance, with water vapor generated during thermal decomposition significantly reducing smoke density; high cost-effectiveness, abundant raw materials, and mature production processes; dual function, combining flame retardant and filler functions to improve product rigidity; and good electrical insulation, making it suitable for electrical applications. However, it also has limitations, mainly in its high addition amount, typically requiring 40-70% to achieve the ideal flame retardant rating, which may affect the material's mechanical properties and processing flowability.

[0003] Aluminum ash, also known as primary aluminum ash, is a solid waste generated during the electrolytic aluminum industry, recycled aluminum industry, and aluminum product processing industry. Aluminum ash mainly consists of metallic and non-metallic aluminum oxides, with aluminum oxide typically accounting for over 70%. It also contains a certain amount of electrolytic electrode residue, especially aluminum nitride, which is corrosive and toxic. Currently, the treatment of hazardous aluminum ash typically involves chemical reactions to remove corrosive and toxic aluminum nitride and fluorides, transforming it into non-hazardous solid waste, which can then be used as aggregate or filler in cement products. There are also processes to extract aluminum hydroxide from it to maximize the utilization of aluminum resources. The technical route mainly involves adding sodium hydroxide to the aluminum ash, reacting to produce sodium aluminate, and then adding an acid (such as carbon dioxide or hydrochloric acid) to neutralize it and produce aluminum hydroxide. The reaction equation is as follows: Step 1: Al₂O₃ + 2NaOH = 2NaAlO₂ + H₂O Step 2: 2NaAlO2 + 2HCl + 2H2O = 2Al(OH)3↓ + 2NaCl Based on the above reaction equation, theoretically, the mass ratio of sodium hydroxide used to aluminum hydroxide produced in this reaction should be 1:1.95. However, in actual preparation, this theoretical design value cannot be achieved at all. This method consumes a large amount of sodium hydroxide and acid, and the value of the recovered aluminum hydroxide is disproportionate to the input costs. Therefore, it is not economically feasible, and there are no reports to date of large-scale production using this method.

[0004] Sodium tetrachloroaluminate, a solid waste, is generated during the preparation of methyldichlorophosphine, a core intermediate involved in the production of the agricultural herbicide glufosinate. The preparation of methyldichlorophosphine mainly employs the ternary complex method and the alkylaluminum method. Both methods generate large quantities of sodium tetrachloroaluminate during the preparation process. This sodium tetrachloroaluminate also contains small amounts of organic phosphine and inorganic phosphorus impurities (hereinafter referred to as total phosphorus impurities). During storage, this solid waste absorbs moisture from the air, releases a large amount of heat and hydrogen chloride gas, and is highly acidic, making it hazardous and difficult to handle. Since the advent of methyldichlorophosphine synthesis technology, sodium tetrachloroaluminate waste salt has been a persistent and insurmountable challenge for related industries. There are also processes to maximize the utilization of its aluminum resources by extracting aluminum hydroxide. The main technical route involves adding sodium hydroxide to the solid waste sodium tetrachloroaluminate to react and directly obtain aluminum hydroxide. The reaction equation is as follows: NaAlCl4+ 3NaOH + H2O = Al(OH)3↓ + 4NaCl + H2O Based on the above reaction equation, theoretically, the mass ratio of sodium hydroxide input to aluminum hydroxide output should be 1:0.65. According to the calculations regarding aluminum ash, this method is even less economically feasible.

[0005] In summary, both types of solid waste can be refined to produce aluminum hydroxide, but both suffer from uneconomical processing methods. Summary of the Invention

[0006] To address the above problems, this invention provides a preparation process for synthesizing aluminum hydroxide flame retardant using two types of solid hazardous waste. Specifically, it uses hazardous waste aluminum ash and solid waste sodium tetrachloroaluminate as reaction raw materials, and simultaneously treats the two types of hazardous waste in a single preparation process to synthesize the target product aluminum hydroxide. This method is economically feasible.

[0007] The technical solution of the present invention: A process for synthesizing aluminum hydroxide flame retardant using two types of solid hazardous waste includes the following synthesis steps: (1) Add hazardous waste aluminum ash to water, and add sodium hydroxide solution while stirring to carry out the reaction; The main reaction in step (1) is the reaction of the abundant alumina in the aluminum ash to form sodium aluminate, thus completing the reuse of aluminum resources in the hazardous waste aluminum ash. The secondary reaction is the reaction of the hazardous compound aluminum nitride to form sodium aluminate, thus completing the harmless treatment of the hazardous waste aluminum ash. The chemical reaction equations are as follows: Main reaction: Al₂O₃ + 2NaOH = 2NaAlO₂ + H₂O Secondary reaction: AlN + 3H2O = Al(OH)3↓ + NH3↑ NaOH + Al(OH)3 = NaAlO2 + H2O (2) The material that has completed the reaction in step (1) is filtered under negative pressure to obtain the filtrate; The material from the reaction in step (1) is filtered under negative pressure. The resulting filter solid is then dried to obtain harmless aluminum ash solid powder, which can be used as aggregate or filler in cement products. The resulting filtrate is used in the next reaction step.

[0008] (3) Add sodium tetrachloroaluminate (SCA) to the filtrate obtained in step (2), control the pH value, and stir the reaction. The main chemical reaction occurring in step (3) is the reaction between the solid waste sodium tetrachloroaluminate and the sodium aluminate in the filtrate to generate a large amount of the target product, aluminum hydroxide, as a precipitate. The secondary chemical reaction occurring in this process is the reaction between the total phosphorus impurities in the solid waste sodium tetrachloroaluminate and the sodium aluminate in the filtrate to generate methyl aluminum hypophosphite and aluminum hypophosphite precipitates. Therefore, not only is the aluminum resource in the solid waste sodium tetrachloroaluminate utilized, but the total phosphorus impurities are also utilized to generate effective components, thus completing the harmless treatment of the solid waste sodium tetrachloroaluminate. The chemical reaction equations are as follows: Main reaction: 3NaAlO2 + NaAlCl4 + 6H2O = 4Al(OH)3↓ + 4NaCl Secondary reaction: CH3Cl2P + 2H2O → CH3P(O)OH2 + 2HCl PCl3 + 3H2O → H3PO3 + 3HCl CH3P(O)OH2+ Al(OH)3→Al(CH3P(O)OH)3↓ + H2O H3PO3+ Al(OH)3→Al2(HPO3)3↓+ H2O (4) The material that has completed the reaction in step (3) is filtered by negative pressure filtration. The resulting filter solid is washed with water and then dried to obtain solid aluminum hydroxide.

[0009] The filtrate produced after filtration in step (4) mainly consists of sodium chloride, and also contains trace amounts of soluble fluoride salts. Existing technologies can be used for defluorination treatment. The remaining filtrate, after concentration and crystallization, meets the requirements for caustic soda salt using ion-exchange membranes as specified in the national standard QB / T5270-2018, and can be circulated as a by-product. This part of the process falls within the scope of existing technology and is not within the scope of the claims of this invention.

[0010] The purity and impurity content of the target product, aluminum hydroxide, obtained in step (4) were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The measured indicators were: aluminum hydroxide content: 96.5%~98.5%; total content of aluminum methylphosphite and aluminum hypophosphite: 1%~3%; total content of other impurities <0.5%.

[0011] Preferably, the hazardous aluminum ash mentioned in step (1) is the residue after refining and recovering metallic aluminum. The hazardous aluminum ash includes the following components by mass percentage: aluminum: <2%, alumina: 60%~70%, aluminum nitride: 10%~40%, and the balance being oxides of Si, Fe, Ca, and Mg.

[0012] Preferably, the mass ratio of hazardous waste aluminum ash to water in step (1) is 1:0.8~1.5; The sodium hydroxide solution in step (1) has a mass concentration of 32%, and the amount of sodium hydroxide solution added is 80% to 120% of the mass of hazardous waste aluminum ash. In step (1), the reaction time is 1-4 hours, the reaction temperature is 10-60℃, and the stirring speed is 200-600 RPM.

[0013] Preferably, the amount of sodium hydroxide solution added in step (1) is 95% to 105% of the mass of hazardous waste aluminum ash; the reaction time in step (1) is 1.5 to 3 hours, and the reaction temperature is 25-50℃.

[0014] Preferably, the pressure of the negative pressure filtration in step (2) is 0.08~0.09 MPa.

[0015] Preferably, the solid waste sodium tetrachloroaluminate mentioned in step (3) is a solid waste salt generated during the preparation of methyldichlorophosphine by the ternary complex method or the alkylaluminum method.

[0016] Preferably, the solid waste sodium tetrachloroaluminate in step (3) comprises the following components in mass percentage: 65%~70% sodium tetrachloroaluminate, 25%~30% sodium chloride, and 3%~5% total phosphorus; the total phosphorus is residual methyl dichloride and phosphorus trichloride.

[0017] Preferably, the mass of sodium tetrachloroaluminate added in step (3) is determined by the pH value of the filtrate, and the pH value is controlled between 6 and 8 in step (3). In step (3), the stirring speed is 200-600 RPM, and the reaction time is 1-5 hours.

[0018] Preferably, the pH value is controlled between 7 and 7.5.

[0019] Preferably, the filter solid obtained in step (4) is washed with deionized water until the sodium chloride content in the filter solid is ≤0.05%, and the drying in step (4) is spray drying, with the spray drying temperature being 100~110℃.

[0020] The present invention has the following beneficial effects: 1. This invention not only renders hazardous aluminum ash harmless, but also makes full use of its aluminum resources, enabling it to be recycled and turned from waste into treasure, thus demonstrating atom economy.

[0021] 2. This invention not only renders solid waste sodium tetrachloroaluminate harmless, but also makes full use of the aluminum resources in the solid waste sodium tetrachloroaluminate. At the same time, the total phosphorus impurities in the solid waste sodium tetrachloroaluminate are also utilized to generate effective components, maximizing the utilization of aluminum and phosphorus elements, realizing the efficient and high-value recycling of process raw materials, turning waste into treasure, and reflecting atom economy.

[0022] 3. This invention utilizes two types of solid waste as raw materials, and a single preparation process synthesizes the target product aluminum hydroxide. According to the chemical reaction method in the invention, the mass ratio of the input sodium hydroxide raw material to the recovered target product aluminum hydroxide is 1:2.6, resulting in considerable economic benefits.

[0023] 4. Although the chemical reactions involved in this invention are relatively complex, the core operation only requires controlling the pH value, thus the process is simple and has the conditions for large-scale production.

[0024] 5. Although the aluminum hydroxide obtained by this invention has low purity and contains a small amount of methyl aluminum hypophosphite and aluminum hypophosphite, when applied to flame retardants, the methyl aluminum hypophosphite and aluminum hypophosphite it contains have the function of rapidly catalyzing the carbonization of plastic resin during flame combustion. This makes its flame retardant efficiency significantly better than that of traditional inorganic aluminum hydroxide flame retardants. Therefore, it can achieve the flame retardant effect of traditional inorganic aluminum hydroxide with a small amount of addition, thus solving the limitations of existing inorganic aluminum hydroxide applications. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative design and practice are within the scope of protection of the present invention.

[0026] Example 1

[0027] Add 1000g of hazardous aluminum ash to 1000g of water and stir well. Dissolve 320g of sodium hydroxide in 680g of water to prepare a 32% sodium hydroxide solution, and slowly add it to the above materials. Collect the generated gas, which is then absorbed by water to form ammonia water as a byproduct. Control the reaction temperature at 50℃ and the stirring speed at 400 RPM, and react for 2 hours. Filter the above materials under negative pressure, controlling the pressure between 0.08 and 0.09 MPa. Wash the obtained filter solid with 500g of water, and then filter it again under negative pressure. After drying the obtained filter solid at 100℃, it becomes a non-hazardous solid byproduct, which can be used as aggregate or filler in cement products. The combined weight of the primary and secondary filtrates is 2620g.

[0028] In the above filtrate, sodium tetrachloroaluminate was slowly added to dissolve under mechanical stirring at a speed of 400 RPM, and the pH value of the solution was measured continuously. When 585 grams of sodium tetrachloroaluminate were added, the pH value was measured to be 7.5, which was deemed acceptable. The reaction was continued for 4 hours until a large amount of white precipitate was produced in the material. The above material was then filtered under negative pressure at a pressure of 0.08~0.09 MPa. The filtered solid was washed with 1200 grams of deionized water and then filtered under negative pressure. This washing process was repeated 3 times. The sodium chloride content of the obtained filter solid was measured to be 0.05%, which was deemed acceptable. The obtained filter solid was spray-dried at a temperature of 110℃ to obtain 802 grams of final product aluminum hydroxide. The mass ratio of the added raw material sodium hydroxide to the obtained finished aluminum hydroxide was 1:2.506. The purity and impurity percentage of the obtained product were determined by inductively coupled plasma optical emission spectrometry (ICP-OES): aluminum hydroxide 96.80%; impurities methyl aluminum hypophosphite and total aluminum hypophosphite content 2.19%.

[0029] Example 2

[0030] Add 800g of hazardous aluminum ash to 1000g of water and stir well. Dissolve 204g of sodium hydroxide in 434g of water to prepare a 32% sodium hydroxide solution, and slowly add it to the above materials. Collect the generated gas, which is then absorbed by water to form ammonia water as a byproduct. Control the reaction temperature at 35℃ and the stirring speed at 300 RPM, and react for 3 hours. Filter the above materials under negative pressure, controlling the pressure between 0.08 and 0.09 MPa. Wash the obtained filter solid with 500g of water, and then filter it again under negative pressure. After drying the obtained filter solid at 100℃, it becomes a non-hazardous solid byproduct, which can be used as aggregate or filler in cement products. The combined weight of the primary and secondary filtrates is 2338g.

[0031] In the above filtrate, sodium tetrachloroaluminate was slowly added and dissolved under mechanical stirring at 400 RPM, with the pH value of the solution being measured continuously. When 472 g of sodium tetrachloroaluminate was added, the pH value was measured to be 7.5, which was deemed acceptable. The reaction was continued for 5 hours until a large amount of white precipitate was produced in the material. The above material was then filtered under negative pressure at a pressure of 0.08~0.09 MPa. The filtered solid was washed with 800 g of deionized water and then filtered under negative pressure again. This washing process was repeated 3 times. The sodium chloride content of the obtained filter solid was measured to be 0.05%, which was deemed acceptable. The obtained filter solid was then spray-dried at a temperature of 110℃ to obtain 416 g of the final product, aluminum hydroxide. The mass ratio of the added sodium hydroxide to the obtained aluminum hydroxide was 1:2.039. The purity and impurity percentage of the obtained product were determined by inductively coupled plasma optical emission spectrometry (ICP-OES): aluminum hydroxide 97.02%; total content of impurities methyl aluminum hypophosphite and aluminum hypophosphite 1.87%.

[0032] Example 3

[0033] Add 1500g of hazardous aluminum ash to 1000g of water and stir well. Dissolve 400g of sodium hydroxide in 850g of water to prepare a 32% sodium hydroxide solution, and slowly add it to the above materials. Collect the generated gas, which is then absorbed by water to form ammonia water as a byproduct. Control the reaction temperature at 50℃ and the stirring speed at 400 RPM, and react for 2 hours. Filter the above materials under negative pressure, controlling the pressure between 0.08 and 0.09 MPa. Wash the obtained filter solid with 500g of water, and then filter it again under negative pressure. After drying the obtained filter solid at 100℃, it becomes a non-hazardous solid byproduct, which can be used as aggregate or filler in cement products. The combined weight of the primary and secondary filtrates is 2840g.

[0034] In the above filtrate, sodium tetrachloroaluminate was slowly added and dissolved under mechanical stirring at 400 RPM, with the pH value of the solution being measured continuously. When 716 g of sodium tetrachloroaluminate was added, the pH value was measured to be 7.5, which was deemed acceptable. The reaction was continued for 2 hours until a large amount of white precipitate was produced in the material. The above material was then filtered under negative pressure at a pressure of 0.08~0.09 MPa. The filtered solid was washed with 1800 g of deionized water and then filtered under negative pressure again. This washing process was repeated 3 times. The sodium chloride content of the obtained filter solid was measured to be 0.05%, which was deemed acceptable. The obtained filter solid was then spray-dried at a temperature of 110℃ to obtain 940 g of final product aluminum hydroxide. The mass ratio of the added raw material sodium hydroxide to the obtained finished aluminum hydroxide was 1:2.350. The purity and impurity percentage of the obtained product were determined by inductively coupled plasma optical emission spectrometry (ICP-OES): aluminum hydroxide 96.52%; impurities methyl aluminum hypophosphite and total aluminum hypophosphite content 2.41%.

[0035] Application examples Solid aluminum hydroxide prepared in Examples 1-3 of this invention and commercially available aluminum hydroxide in comparative proportions were mixed with PVC resin, terephthalic acid plasticizer, calcium-zinc heat stabilizer, and Sb2O3 flame retardant in specific ratios and extruded to produce PVC plastic. Since the aluminum hydroxide flame retardant decomposes and releases moisture above 180°C, the temperature of the plasticizing section was controlled at 165±2°C and the screw speed at 30 rpm during the extrusion process.

[0036] Table 1: Comparison of flame retardant properties of Examples 1-3 and commercially available aluminum hydroxide in flexible PVC plastics Note: Comparative example: Inorganic aluminum hydroxide (CAS 21645-51-2), purity 99.5%.

[0037] As can be seen from Table 1, when the addition amount is low (①), the flexible PVC plastic of Application Examples 1-3① of this invention exhibits a high flame retardant oxygen index and vertical combustion performance, and also has a good smoke suppression effect. The flexible PVC plastic of Comparative Example ① exhibits a low flame retardant oxygen index and vertical combustion performance.

[0038] When the addition amount is high (②), the solid aluminum hydroxide in Examples 1-3 of the present invention and the traditional inorganic aluminum hydroxide (comparative example) flame retardant both seriously affect the mechanical properties of PVC materials.

[0039] The solid aluminum hydroxide prepared in Examples 1-3 of this invention can achieve a high flame retardant effect in PVC plastic with a low addition amount, thereby avoiding the problem of decreased mechanical properties of PVC plastic under high aluminum hydroxide addition conditions.

[0040] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A preparation process for synthesizing aluminum hydroxide flame retardant using two types of solid hazardous waste, characterized in that, The synthesis steps include the following: (1) Add hazardous waste aluminum ash to water, and add sodium hydroxide solution while stirring to carry out the reaction; (2) The material that has completed the reaction in step (1) is filtered under negative pressure to obtain the filtrate; (3) Add sodium tetrachloroaluminate (SCA) to the filtrate obtained in step (2), control the pH value, and stir the reaction. (4) The material that has completed the reaction in step (3) is filtered by negative pressure filtration. The resulting filter solid is washed with water and then dried to obtain solid aluminum hydroxide.

2. The preparation process for synthesizing aluminum hydroxide flame retardant using two types of solid hazardous waste according to claim 1, characterized in that, The hazardous aluminum ash mentioned in step (1) is the residue after refining and recovering metallic aluminum. The hazardous aluminum ash includes the following components by mass percentage: aluminum: <2%, alumina: 60%~70%, aluminum nitride: 10%~40%, and the balance being oxides of Si, Fe, Ca, and Mg.

3. The preparation process for synthesizing aluminum hydroxide flame retardant using two types of solid hazardous waste according to claim 1, characterized in that, In step (1), the mass ratio of hazardous waste aluminum ash to water is 1:0.8~1.5; The sodium hydroxide solution in step (1) has a mass concentration of 32%, and the amount of sodium hydroxide solution added is 80% to 120% of the mass of hazardous waste aluminum ash. In step (1), the reaction time is 1-4 hours, the reaction temperature is 10-60℃, and the stirring speed is 200-600 RPM.

4. The preparation process for synthesizing aluminum hydroxide flame retardant using two types of solid hazardous waste according to claim 3, characterized in that, The amount of sodium hydroxide solution added in step (1) is 95% to 105% of the mass of hazardous waste aluminum ash; the reaction time in step (1) is 1.5 to 3 hours, and the reaction temperature is 25-50℃.

5. The preparation process for synthesizing aluminum hydroxide flame retardant using two types of solid hazardous waste according to claim 1, characterized in that, The pressure for negative pressure filtration in step (2) is 0.08~0.09 MPa.

6. The preparation process for synthesizing aluminum hydroxide flame retardant using two types of solid hazardous waste according to claim 1, characterized in that, The solid waste sodium tetrachloroaluminate mentioned in step (3) is a solid waste salt generated during the preparation of methyldichlorophosphine by the ternary complex method or the alkylaluminum method.

7. The preparation process for synthesizing aluminum hydroxide flame retardant using two types of solid hazardous waste according to claim 6, characterized in that, The solid waste sodium tetrachloroaluminate mentioned in step (3) includes the following components by mass percentage: 65%~70% sodium tetrachloroaluminate, 25%~30% sodium chloride, and 3%~5% total phosphorus; the total phosphorus is residual methyl dichloride and phosphorus trichloride.

8. The preparation process for synthesizing aluminum hydroxide flame retardant using two types of solid hazardous waste according to claim 1, characterized in that, The amount of sodium tetrachloroaluminate added in step (3) is determined by the pH value of the material. In step (3), the pH value is controlled between 6 and 8. The stirring speed in step (3) is 200-600 RPM, and the reaction time is 1-5 hours.

9. The preparation process for synthesizing aluminum hydroxide flame retardant using two types of solid hazardous waste according to claim 8, characterized in that, Control the pH value between 7 and 7.

5.

10. The preparation process for synthesizing aluminum hydroxide flame retardant using two types of solid hazardous waste according to claim 1, characterized in that, The filter solid obtained in step (4) is washed with deionized water until the sodium chloride content in the filter solid is ≤0.05%. The drying in step (4) is spray drying, and the spray drying temperature is 100~110℃.

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