A method for harmless treatment of industrial aluminum ash, phosphogypsum and carbon dioxide

Abstract

The application discloses a harmless combined treatment method for industrial aluminum ash, phosphogypsum and carbon dioxide, and comprises the following steps: S1, putting secondary aluminum ash into a sodium hydroxide aqueous solution, collecting tail gas and filtering; S2, slowly passing CO2 gas into the filtrate of S1, and performing three times of washing and filtering to obtain filter residue aluminum hydroxide; S3, adding phosphogypsum into the mixed solution of the second and third washing filtrates of S2, stirring and reacting, washing and filtering, and then evaporating and crystallizing the filtrate to obtain sodium sulfate; S4, calcining the filter residue of S3, and passing the generated gas into S2; S5, mixing and reacting the calcined solid with the tail gas collected in S1, collecting the reacted tail gas again and passing it into S4; and S6, reacting the solid in S5 with the first washing filtrate of S2, returning the filtrate to S1 after washing and filtering, and repeating S4 for the filter residue.

Description

Technical Field

[0001] This invention relates to the field of harmless disposal and resource utilization of industrial waste, specifically a method for the combined harmless treatment of industrial aluminum ash, phosphogypsum, and carbon dioxide. Background Technology

[0002] Aluminum, the second most abundant metal after iron, has wide applications in aerospace, construction, automotive, and new materials industries. As aluminum production increases year by year, the problem of disposing of aluminum ash generated during the smelting process is becoming increasingly prominent.

[0003] Based on the number of times aluminum ash is used in the aluminum recycling process and its elemental aluminum content, aluminum ash can be divided into primary aluminum ash and secondary aluminum ash. Secondary aluminum ash exhibits significant chemical reactivity and hazardous characteristics such as leaching of toxic and harmful substances. Currently, aluminum ash is managed as hazardous waste instead of general industrial solid waste. The disposal of hazardous aluminum ash has become a bottleneck problem that urgently needs to be solved in the aluminum industry, restricting its healthy development. Eliminating the hazardous waste attributes of aluminum ash while realizing the resource utilization of its components is of great significance for building a resource-saving society.

[0004] Phosphogypsum is an industrial waste residue discharged from the wet process of phosphoric acid production. Its production volume is enormous, and its main component is calcium sulfate dihydrate. Due to the complex composition of impurities in phosphogypsum, its treatment and comprehensive utilization are considered a global challenge. The large quantities of phosphogypsum not only occupy significant land resources but also pollute the surrounding soil, water resources, and atmosphere, which is one of the major obstacles to the sustainable development of phosphate fertilizer companies.

[0005] Currently, there are no reports on the combined resource utilization of aluminum ash, phosphogypsum, and carbon dioxide. Therefore, researching and exploring synergistic technologies for the harmless disposal and resource utilization of aluminum ash, phosphogypsum, and carbon dioxide can provide a reference for solving the problems caused by these substances. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for the harmless combined treatment of aluminum ash, phosphogypsum and carbon dioxide. Specifically, it is a method for the harmless combined preparation of sodium sulfate and aluminum hydroxide from industrial hazardous waste secondary aluminum ash and solid waste phosphogypsum. This method can simultaneously treat industrial hazardous waste secondary aluminum ash, solid waste phosphogypsum and carbon dioxide gas released from fuel, realize the recycling of intermediate products, and obtain sodium sulfate and aluminum hydroxide products.

[0007] The technical solution of this invention is as follows:

[0008] A method for the combined harmless treatment of aluminum ash, phosphogypsum, and carbon dioxide includes the following steps:

[0009] S1. Slowly add the secondary aluminum ash to a sodium hydroxide aqueous solution with a mass fraction of 30-50%, controlling the reaction temperature to not exceed 90℃ throughout the process, and collect the tail gas generated during the entire reaction. After the addition is completed, continue the reaction for 6-8 hours, and then filter. The sodium hydroxide aqueous solution accounts for 80%-120% of the mass of the secondary aluminum ash.

[0010] S2. Under stirring at 60℃~70℃, CO2 gas is slowly introduced into the filtrate after filtration. After the pressure in the system is constant, the gas introduction is stopped. The filter residue is aluminum hydroxide after washing and filtration three times. The CO2 gas introduction rate should be such that the time from the start of gas introduction to the pressure being constant is ≥120min.

[0011] S3. Under normal temperature stirring, add phosphogypsum to the mixture of the second and third washing filtrates from step S2, stir and react for 24–72 hours. After 2–3 washings and filtrations, the filtrate is evaporated and crystallized to obtain sodium sulfate. The amount of phosphogypsum used is 40%–50% of the mass of aluminum hydroxide in step S2.

[0012] S4. The filter residue after step S3 is calcined at a temperature of 700℃-900℃, and the gas generated by calcination is recycled into step S2.

[0013] Step S5: Mix the powdered solid formed after calcination with the tail gas collected in step S1 and react. The tail gas produced by the reaction is collected again and recycled in step S4.

[0014] S6. The solids reacted in step S5 and the first washing filtrate from step S2 are reacted together under stirring for 24-72 hours. After the reaction is completed, the solids are washed and filtered 1-2 times. The filtrate is returned to step S1 for continued recycling, and the filter residue is processed in step S4.

[0015] The mechanism of this invention includes:

[0016] Secondary aluminum ash contains elemental aluminum, aluminum nitride, aluminum oxide, aluminum carbonate, etc., which react with excess sodium hydroxide to produce aluminates and flammable gases such as hydrogen, ammonia, and methane. The aluminates react with a small amount of carbon dioxide to produce aluminum hydroxide and sodium carbonate. Filtration and washing yield crude aluminum hydroxide and a sodium carbonate solution. The filtrate from the first washing and filtration has a high sodium carbonate content and can react with calcium hydroxide to produce sodium hydroxide and calcium carbonate. The resulting sodium hydroxide solution can be reused in the reaction with secondary aluminum ash, achieving product recycling in the process. The main reaction formula is:

[0017] AlN + 3H₂O = Al(OH)₃↓ + NH₃↑

[0018] Al4C3+12H2O=4Al(OH)3↓+3CH4↑

[0019] Al(OH)3 + NaOH = NaAlO2 + 2H2O

[0020] 4AlN+4NaOH+3O2=4NaAlO2+2H2O+2N2↑

[0021] 2Al+2H2O+2NaOH=2NaAlO2+3H2↑

[0022] Al₂O₃ + 2NaOH = 2NaAlO₂ + H₂O

[0023] 2NaAlO2+CO2+3H2O==2Al(OH)3↓+Na2CO3

[0024] The CaSO4·2H2O content in phosphogypsum is as high as 82% or more. The sodium carbonate content in the filtrate from the second and third washing and filtration is relatively low, which is conducive to the reaction between phosphogypsum and sodium carbonate to form calcium carbonate and sodium sulfate. Crude calcium carbonate and sodium sulfate products can be obtained by filtration, washing, evaporation and crystallization. The reaction formula is as follows:

[0025] Na2CO3+CaSO4·2H2O=CaCO3↓+Na2SO4+2H2O

[0026] Calcium carbonate, after high-temperature calcination, forms calcium oxide and releases carbon dioxide gas. This released carbon dioxide gas can be recycled and reused to react with aluminates. The calcium oxide produced during calcination can be used to dry the flammable gases such as hydrogen, ammonia, and methane generated in the reaction (the high-temperature reaction of secondary aluminum ash with sodium hydroxide causes the gases to carry some water vapor), thus forming calcium hydroxide. This calcium hydroxide then reacts with the filtrate from the first washing and filtration process, containing sodium carbonate, and is recycled again. The flammable gases such as hydrogen, ammonia, and methane after drying can then be used for the calcination of calcium carbonate. The heat released from the reaction of secondary aluminum ash with sodium hydroxide can also provide a heat source for the calcination of calcium carbonate. The reaction equation is as follows:

[0027] CaCO3 high temperature CaO + CO2↑

[0028] CaO + H₂O = Ca(OH)₂

[0029] Ca(OH)2+Na2CO3=CaCO3↓+2NaOH

[0030] The beneficial effects of this invention include:

[0031] (1) The method for the combined harmless treatment of aluminum ash, phosphogypsum and carbon dioxide provided by the present invention realizes the combined harmless treatment and resource recycling of hazardous waste aluminum ash, solid waste phosphogypsum and greenhouse gas carbon dioxide.

[0032] (2) The method for harmlessly treating aluminum ash, phosphogypsum and carbon dioxide provided by the present invention not only solves the problem of industrial waste residue and waste gas disposal, but also prepares commercially valuable aluminum hydroxide and sodium sulfate products, which have good social and economic benefits.

[0033] (3) This invention makes full use of raw materials, intermediate products, heat and other materials in the process, realizes a closed loop mode, maximizes resource utilization and minimizes waste emissions. Its harmless treatment and resource recycling costs are low, the process is simple and it is easy to implement on a large scale. It has significant economic benefits and is of great significance for building a resource-saving society. Attached Figure Description

[0034] Figure 1 This is a flowchart of the method for the combined harmless treatment of aluminum ash, phosphogypsum, and carbon dioxide according to the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] Example 1

[0037] This embodiment provides a method for the combined harmless treatment of aluminum ash, phosphogypsum, and carbon dioxide, including:

[0038] S1. Add 50 kg of water and 50 kg of sodium hydroxide to the reactor and stir for 1 hour to dissolve. Then slowly add 100 kg of secondary aluminum ash. The addition is completed in 76 minutes. The maximum temperature is 90℃. After the addition is completed, the reaction continues for 6 hours. After the reaction is completed, filter the solution to obtain the filtrate. The tail gas is collected through a recovery device during the reaction.

[0039] S2. Under stirring at 65℃, CO2 gas was slowly introduced into the filtrate after filtration for 142 minutes. The pressure in the system remained basically constant. After washing and filtration three times, aluminum hydroxide residue was obtained. After drying, it was weighed to obtain 51.30 kg.

[0040] S3. Under normal temperature stirring, add 21.24 kg of phosphogypsum to the mixture of the second and third washing filtrates in step S2, stir and react for 28 h, wash and filter 2-3 times, and then evaporate and crystallize the filtrate to obtain sodium sulfate. After drying, weigh to obtain 12.09 kg.

[0041] S4. The filter residue after step S3 is calcined at 720°C for 8 hours, and the gas generated during calcination is recycled into step S2.

[0042] S5. The powdered solid formed after calcination is mixed with the tail gas collected in step S1 and reacted. The tail gas produced by the reaction is collected again and recycled in step S4.

[0043] S6. The solids reacted in step S5 and the first washing filtrate from step S2 are reacted together for 48 hours under stirring. After the reaction is completed, the solids are washed and filtered 1-2 times. The filtrate is returned to step S1 for continued recycling, and the filter residue is processed in step S4.

[0044] Cost calculation:

[0045] Secondary aluminum ash cost: -500 to -1200 yuan (subsidy);

[0046] Cost of phosphogypsum: -200 to -500 yuan (paid by the phosphating plant company);

[0047] Sodium hydroxide, latest price quoted by Henan Livit Chemical Technology Co., Ltd. on April 18, 2023, is 3100 yuan / ton excluding tax and freight;

[0048] Shandong Zhenkun New Materials Co., Ltd.'s latest price quote for Luxi Chemical in Liaocheng City, Shandong Province, on November 21, 2023: 99.9% liquid carbon dioxide, excluding tax and freight, is 260 yuan / ton.

[0049] In Example 1, after the first reaction, 18.40 kg of sodium hydroxide was recovered (calculated from the product concentration in step S4); 13.47 kg of carbon dioxide was recovered.

[0050]

[0051] Example 2

[0052] This embodiment provides a method for the combined harmless treatment of aluminum ash, phosphogypsum, and carbon dioxide, including:

[0053] S1. Add 98 kg of water and 46 kg of sodium hydroxide to the reactor and stir for 1 hour to dissolve. Then slowly add 120 kg of secondary aluminum ash over 80 minutes. The maximum temperature is 90°C. After the addition is complete, continue the reaction for 8 hours. After the reaction is complete, filter the solution to obtain the filtrate. The tail gas is collected by a recovery device during the reaction.

[0054] S2. Under stirring at 60℃, CO2 gas was slowly introduced into the filtrate after filtration for 126 minutes. The pressure in the system remained basically constant. After washing and filtration three times, aluminum hydroxide residue was obtained. After drying, it was weighed to obtain 56.52 kg.

[0055] S3. Under normal temperature stirring, add 24.66 kg of phosphogypsum to the mixture of the second and third washing filtrates in step S2, stir and react for 48 h, wash and filter 2-3 times, and then evaporate and crystallize the filtrate to obtain sodium sulfate. After drying, weigh to obtain 14.47 kg.

[0056] S4. The filter residue after step S3 is calcined at 840℃ for 6 hours, and the gas generated during calcination is recycled into step S2.

[0057] S5. The powdered solid formed after calcination is mixed with the tail gas collected in step S1 and reacted. The tail gas produced by the reaction is collected again and recycled in step S4.

[0058] S6. The solids reacted in step S5 and the first washing filtrate from step S2 are reacted together for 24 hours under stirring. After the reaction is completed, the solids are washed and filtered 1-2 times. The filtrate is returned to step S1 for continued recycling, and the filter residue is processed in step S4.

[0059] Example 3

[0060] This embodiment provides a method for the combined harmless treatment of aluminum ash, phosphogypsum, and carbon dioxide, including:

[0061] S1. Add 54 kg of water and 36 kg of sodium hydroxide to the reactor and stir for 1 hour to dissolve. Then slowly add 100 kg of secondary aluminum ash, which is added in 64 minutes. The maximum temperature is 89°C. After the addition is completed, the reaction continues for 7 hours. After the reaction is completed, filter the solution to obtain the filtrate. The tail gas is collected by a recovery device during the reaction.

[0062] S2. Under stirring at 70℃, CO2 gas was slowly introduced into the filtrate after filtration for 150 minutes. The pressure in the system remained basically constant. After washing and filtration three times, aluminum hydroxide residue was obtained. After drying, it was weighed to obtain 48.24 kg.

[0063] S3. Under normal temperature stirring, add 20.16 kg of phosphogypsum to the mixture of the second and third washing filtrates in step S2, stir and react for 72 h, wash and filter 2-3 times, and then evaporate and crystallize the filtrate to obtain sodium sulfate. After drying, weigh to obtain 12.05 kg.

[0064] S4. The filter residue after step S3 is calcined at 900℃ for 5 hours, and the gas generated during calcination is recycled into step S2.

[0065] S5. The powdered solid formed after calcination is mixed with the tail gas collected in step S1 and reacted. The tail gas produced by the reaction is collected again and recycled in step S4.

[0066] S6. The solids reacted in step S5 and the first washing filtrate from step S2 are reacted together for 56 hours under stirring. After the reaction is completed, the solids are washed and filtered 1-2 times. The filtrate is returned to step S1 for continued recycling, and the filter residue is processed in step S4.

[0067] Example 4

[0068] This embodiment provides a method for the combined harmless treatment of aluminum ash, phosphogypsum, and carbon dioxide, including:

[0069] S1. Add 42kg of water and 48kg of sodium hydroxide to the reactor and stir for 1 hour to dissolve. Then slowly add 116kg of secondary aluminum ash, and the addition is completed in 90 minutes. The maximum temperature is 90℃. After the addition is completed, the reaction continues for 8 hours. After the reaction is completed, filter the solution to obtain the filtrate. The tail gas is collected through a recovery device during the reaction.

[0070] Under stirring at 63℃, CO2 gas was slowly introduced into the filtrate after filtration for 127 minutes. The pressure in the system remained basically constant. After washing and filtration three times, aluminum hydroxide residue was obtained. After drying, it was weighed to obtain 56.26 kg.

[0071] S3. Under normal temperature stirring, add 24.34 kg of phosphogypsum to the mixture of the second and third washing filtrates in step S2, stir and react for 34 h, wash and filter 2-3 times, and then evaporate and crystallize the filtrate to obtain sodium sulfate. After drying, weigh to obtain 14.57 kg.

[0072] S4. The filter residue after step S3 is calcined at 780℃ for 8 hours, and the gas generated during calcination is recycled into step S2.

[0073] S5. The powdered solid formed after calcination is mixed with the tail gas collected in step S1 and reacted. The tail gas produced by the reaction is collected again and recycled in step S4.

[0074] S6. The solids reacted in step S5 and the first washing filtrate from step S2 are reacted together for 38 hours under stirring. After the reaction is completed, the solids are washed and filtered 1-2 times. The filtrate is returned to step S1 for continued recycling, and the filter residue is processed in step S4.

[0075] Sodium sulfate content was determined according to GB / T 6009-2014 Industrial Anhydrous Sodium Sulfate 6.3 Gravimetric Method, and aluminum oxide content was determined according to GB / T4294-2010 Aluminum Hydroxide.

[0076] Table 1. Contents of sodium sulfate and aluminum oxide in the products of Examples 1-4

[0077] Sodium sulfate content, % Alumina content, % Example 1 92.1 63.7 Example 2 91.7 62.5 Example 3 92.3 63.1 Example 4 92.0 62.8

[0078] Comparative Example 1

[0079] S1. Add 50 kg of water and 50 kg of sodium hydroxide to the reactor and stir for 1 hour to dissolve them. Then slowly add 100 kg of aluminum ash, which is added in 76 minutes. The maximum temperature is 90°C. After the addition is completed, continue the reaction for 6 hours. After the reaction is completed, filter the solution with a filter to obtain the filtrate. The tail gas is collected by a recovery device during the reaction.

[0080] S2. Under stirring at 65℃, CO2 gas was introduced into the filtrate after filtration for 4 minutes. The pressure in the system remained basically constant. After washing and filtration three times, aluminum hydroxide residue was obtained. After drying, it was weighed to obtain 51.76 kg.

[0081] S3. Under normal temperature stirring, add 11.8 kg of phosphogypsum to the mixture of the second and third washing filtrates in step S2, stir and react for 28 h, wash and filter 2-3 times, and then evaporate and crystallize the filtrate to obtain sodium sulfate. After drying, weigh to obtain 0.92 kg.

[0082] Comparative Example 2

[0083] 50 kg of water and 50 kg of sodium hydroxide were added to the reactor and stirred for 1 hour to dissolve them. Then, 100 kg of aluminum ash was slowly added, and the addition was completed in 76 minutes. The maximum temperature was 90°C. After the addition was completed, the reaction continued for 6 hours. After the reaction was completed, the filtrate was obtained by filtering with a filter. The tail gas was collected by a recovery device during the reaction.

[0084] Comparative Example 3

[0085] CO2 gas was slowly introduced into a 296 kg sodium aluminate solution with a mass fraction of 30% for 142 minutes under stirring at 65℃. The pressure in the system remained basically constant. After washing and filtering three times, aluminum hydroxide residue was obtained. After drying, it was weighed to obtain 52.10 kg.

[0086] Comparative Example 4

[0087] Under stirring at room temperature, 28.33 kg of phosphogypsum was added to 33.8 kg of sodium carbonate solution with a mass fraction of 30%, and the mixture was stirred and reacted for 28 hours. After washing and filtering 2-3 times, the filtrate was evaporated and crystallized to obtain sodium sulfate, which was dried and weighed to obtain 11.76 kg.

[0088] Analysis of the data from Example 1 and Comparative Examples 1-4 shows that:

[0089] (1) In Comparative Example 1, rapid introduction of carbon dioxide gas resulted in an excess of carbon dioxide, and most of the product was converted into sodium bicarbonate. Since the solubility of calcium carbonate is similar to that of calcium sulfate, under slightly alkaline conditions, the small amount of calcium carbonate and sodium bicarbonate reacted with phosphogypsum to produce very little product. The reaction formula is as follows:

[0090] NaAlO2+CO2+2H2O=Al(OH)3↓+NaHCO3

[0091] (2) In Comparative Example 2, sodium aluminate was prepared by reacting aluminum ash with an aqueous solution of sodium hydroxide, generating a large amount of flammable gases such as hydrogen, ammonia, and methane. Due to the complexity of the aluminum ash composition, the purity of the sodium aluminate solution was affected, making it unusable directly. Furthermore, the large amounts of flammable gases generated, such as hydrogen, ammonia, and methane, failed to meet emission standards. The process in Comparative Example 2 generated industrial waste liquid and waste gas while treating hazardous aluminum ash, causing secondary pollution.

[0092] (3) In Comparative Example 3, aluminum hydroxide and sodium carbonate were prepared using sodium aluminate solution and CO2 gas. Although aluminum hydroxide was obtained, the sodium carbonate solution still posed an emission problem. This process generates industrial waste liquid while utilizing carbon dioxide resources.

[0093] (4) In Comparative Example 4, calcium carbonate and sodium sulfate were prepared using sodium carbonate solution and phosphogypsum. A large amount of insoluble matter contained in phosphogypsum will mix with calcium carbonate, which will affect the purity of calcium carbonate and make it unusable. Direct discharge will also have an impact on the environment.

Claims

1. A method for harmless treatment of industrial aluminum ash, phosphogypsum and carbon dioxide, characterized in that, The method comprises the following steps: Step S1, slowly add secondary aluminum ash into sodium hydroxide aqueous solution, control the whole reaction temperature not to exceed 90℃, collect the tail gas generated in the whole reaction, continue to react after the addition is completed, and filter; Step S2, slowly pass CO2 gas into the filtrate after filtering in step S1 under stirring, stop passing after the pressure in the system is constant, and perform 3 times of washing and filtering to obtain filter residue aluminum hydroxide; Step S3, under stirring at room temperature, add phosphogypsum into the mixed solution of the second and third washing filtrate in step S2, stir and react, after washing and filtering, the filtrate is evaporated and crystallized to obtain sodium sulfate; Step S4, calcine the filter residue after filtering in step S3, and pass the gas generated in the calcination into step S2 for recycling; Step S5, mix the powdery solid formed after calcination with the tail gas collected in step S1 to react, collect the tail gas generated in the reaction again and pass it into step S4 for recycling; Step S6, continue to react the solid reacted in step S5 with the first washing filtrate in step S2 under stirring, after the reaction is completed, perform washing and filtering, the filtrate returns to step S1 for recycling, and the filter residue repeats step S4.

2. The method for harmless joint treatment of industrial aluminum ash, phosphogypsum and carbon dioxide according to claim 1, characterized in that: In step S1, the mass fraction of the sodium hydroxide aqueous solution is 30-50%.

3. The method for harmless joint treatment of industrial aluminum ash, phosphogypsum and carbon dioxide according to claim 1, characterized in that: In step S1, continue to react for 6-8 hours after the addition is completed.

4. The method for harmless joint treatment of industrial aluminum ash, phosphogypsum and carbon dioxide according to claim 1, characterized in that: In step S1, the sodium hydroxide aqueous solution accounts for 80%-120% of the mass of the secondary aluminum ash.

5. The method for harmless joint treatment of industrial aluminum ash, phosphogypsum and carbon dioxide according to claim 1, characterized in that: In step S2, the stirring state is performed at 60-70℃.

6. The method for harmless joint treatment of industrial aluminum ash, phosphogypsum and carbon dioxide according to claim 1, characterized in that: In step S2, the slow passing of CO2 gas refers to that the passing speed of the CO2 gas satisfies that the time from the beginning of the passing to the constant pressure is ≥120 minutes.

7. The method of harmless treatment of industrial aluminum ash, phosphogypsum and carbon dioxide according to claim 1, characterized in that, In step S3: The stirring reaction time is 24-72 hours; The washing is performed for 2-3 times.

8. The method for harmless joint treatment of industrial aluminum ash, phosphogypsum and carbon dioxide according to claim 1, characterized in that: In step S3, the amount of the phosphogypsum added accounts for 40%-50% of the mass of the aluminum hydroxide in step S2.

9. The method for harmless joint treatment of industrial aluminum ash, phosphogypsum and carbon dioxide according to claim 1, characterized in that: In step S4, the filter residue is calcined at a temperature of 700-900℃.

10. The method for harmless joint treatment of industrial aluminum ash, phosphogypsum and carbon dioxide according to claim 1, characterized in that: In step S6, the reaction is continued under stirring for 24-72 h, and after the reaction is completed, 1-2 times of washing and filtration are performed.

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