A method for the combined treatment of secondary aluminum ash by ball milling separation, low-temperature roasting and water washing and leaching

Abstract

The present invention discloses a method for the combined treatment of secondary aluminum ash by ball milling, sorting, low-temperature roasting and water washing and leaching, which belongs to the technical field of aluminum ash treatment. This technology uses screening to perform step-by-step screening on the secondary aluminum ash after ball milling to obtain secondary aluminum ash with three particle sizes: coarse, medium and fine. The medium-sized secondary aluminum ash is treated by low-temperature roasting, and the fine-sized secondary aluminum ash is treated by low-temperature roasting with a doped electrolytic aluminum electrolyte. After treatment, the medium-sized and fine-sized secondary aluminum ashes are washed and leached together with the coarse-sized secondary aluminum ashes to obtain harmless secondary aluminum ash and inorganic salts. The present invention fundamentally solves the safety risks brought by active substances such as aluminum nitride, aluminum carbide and inorganic salts in the secondary aluminum ash, and at the same time realizes the resource utilization of the secondary aluminum ash.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum ash treatment and relates to a method for the combined treatment of secondary aluminum ash by ball milling separation, low-temperature roasting and water washing and leaching. Background Art

[0002] Secondary aluminum ash is a hazardous waste with extremely high recycling value. However, due to the lack of low-cost, scalable, and relatively mature treatment processes, on-site landfill and accumulation remain the primary disposal methods for secondary aluminum ash. These practices not only waste the aluminum resources contained in the ash but also cause serious environmental pollution. Therefore, the harmlessness, reduction, and resource utilization of secondary aluminum ash are urgently needed. The removal and conversion of active substances in secondary aluminum ash have become crucial issues in its harmless treatment.

[0003] A Chinese patent (application number: 202210492536.4) discloses a method for harmless treatment of secondary aluminum ash by weak alkaline water washing, which adds a carbonate catalyst and boils it with water and secondary aluminum ash to significantly remove aluminum nitride from the secondary aluminum ash. However, this method requires additional collection and treatment of ammonia, and cannot guarantee the removal of fluoride, and there is still an environmental risk. A Chinese patent (application number: 202111623065.8) discloses a method for denitrification and defluorination of secondary aluminum ash, which utilizes water immersion high-pressure denitrification and adds a defluorinating agent for denitrification and defluorination. However, this method requires repeated pressurization and depressurization, and the operation is complicated and difficult to control. A Chinese patent (application number: 202010970221.7) discloses a method for harmless comprehensive utilization of secondary aluminum ash and its preparation method, which includes the steps of grinding secondary aluminum ash, water immersion deamination, filter residue roasting, water washing and desalting, adding a defluorinating agent for combined defluorination, evaporation and crystallization, etc., to achieve efficient separation and recycling of each component. However, this method is complex and costly, making it unsuitable for large-scale application. A Chinese patent (application number: 202010970221.7) discloses a method for the harmless comprehensive utilization of secondary aluminum ash, which includes grinding and screening the secondary aluminum ash, water leaching for deammonification, and roasting the secondary aluminum ash, achieving efficient separation of the components. However, this method requires high-temperature roasting, which causes the volatilization of inorganic salts, easily causing equipment corrosion and increasing costs.

[0004] Existing wet processes for treating secondary aluminum ash, mostly through acid leaching and alkaline fusion, remain largely laboratory-based. Due to difficulties in separation, high costs, and the generation of secondary hazardous waste, these methods are unsuitable for large-scale harmless treatment. Furthermore, existing pyrometallurgical harmless treatment technologies primarily aim to convert active substances in secondary aluminum ash. However, achieving complete conversion of active substances such as AlN, Al, and Al3C4 requires high temperatures, accompanied by the volatilization of inorganic salts, which can cause equipment corrosion and increase costs. Summary of the Invention

[0005] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a method for the combined treatment of secondary aluminum ash by ball milling and sorting, low-temperature roasting, and water washing and leaching.

[0006] In order to achieve the above technical objectives, the technical solution of the present invention is:

[0007] A method for the combined treatment of secondary aluminum ash by ball milling separation, low-temperature roasting, and water washing and leaching comprises the following steps:

[0008] Step 1, the secondary aluminum ash is subjected to dry ball milling and screening to obtain three types of secondary aluminum ash: coarse, medium and fine;

[0009] Step 2: low-temperature roasting the medium-sized secondary aluminum ash obtained in step 1, and low-temperature roasting the fine-sized secondary aluminum ash mixed with electrolytic aluminum electrolyte;

[0010] Step 3: The medium-sized and fine-sized secondary aluminum ash after treatment in step 2 and the coarse-sized secondary aluminum ash in step 1 are washed, filtered, and dried together to obtain inorganic salts and harmless secondary aluminum ash.

[0011] The secondary aluminum ash in step 1 includes secondary aluminum ash generated by any one of the industries of aluminum electrolysis, aluminum recycling or aluminum processing.

[0012] The dry ball milling time in step 1 is controlled to be 0.5-2h, and the ball mill speed is controlled to be 200-400r / min.

[0013] In step 1, a vibrating screen is used to separate the secondary aluminum ash into three particle sizes: coarse particle size, medium particle size, and fine particle size. The particle sizes are greater than 0.5 mm, 0.2 mm-0.5 mm, and less than 0.2 mm.

[0014] Among them, Al mainly exists in coarse-grained secondary aluminum ash, fluoride mainly exists in medium-grained secondary aluminum ash, and AlN, Al3C4 and inorganic salts mainly exist in fine-grained secondary aluminum ash.

[0015] The aluminum electrolysis electrolyte in step 2 is composed of one or more of cryolite, fluorosilicate, and fluoride salts.

[0016] The aluminum electrolytic electrolyte in step 2 is composed of one or more of cryolite (Na3AlF6) and other salt additives (such as AlF3, CaF2, MgF2 and LiF).

[0017] The calcination conditions in step 2 are as follows: the calcination temperature is 500-900° C., preferably 800-900° C., the calcination time is 30-150 min, and the amount of electrolytic aluminum electrolyte added does not exceed 10%.

[0018] The roasting temperature in step 2 is relatively important. A temperature between 800-900°C can achieve a denitrification rate and a salt recovery rate of more than 90%.

[0019] The heating rate in the calcination conditions in step 2 is controlled at 10°C / min-20°C / min.

[0020] In the step 3, the roasted slag is added to washing water at room temperature with a pH of 6.5-8.5 to wash away the soluble salt in the secondary aluminum ash, and the mixture is fully stirred, filtered and dried to obtain inorganic salt and harmless secondary aluminum ash.

[0021] In step 3, the washing liquid-solid ratio is controlled within the range of 3:1-10:1, the washing temperature is controlled within the range of 55-95° C., the rotation speed is controlled within the range of 100-400 r / min, and the washing time is controlled within the range of 60-180 min.

[0022] The filtrate obtained in step 3 is dried at a constant temperature of 90° C. for 12 h to obtain an inorganic salt.

[0023] This invention achieves the complete low-temperature conversion and batch disposal of active substances such as AlN, Al, and Al3C4 in secondary aluminum ash, while also recovering inorganic salts. This fundamentally addresses the safety risks posed by active substances such as aluminum nitride, aluminum carbide, and inorganic salts in secondary aluminum ash, while also realizing the resource utilization of secondary aluminum ash. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a process flow chart of the combined treatment of secondary aluminum ash including ball milling and separation, low-temperature roasting, and water washing and leaching according to the present invention.

[0025] Figure 2 This is the XRD diagram of the secondary aluminum ash of the present invention.

[0026] Figure 3 This is a risk diagram of secondary aluminum ash with different particle sizes according to the present invention ((a) AlN content at different particle sizes; (b) corrosiveness identification of secondary aluminum ash; (c) leaching toxicity identification of secondary aluminum ash; (d) reactivity identification of secondary aluminum ash).

[0027] Figure 4 This is a comparison diagram of the actual objects before and after the secondary aluminum ash treatment of the present invention, where the left side is before treatment and the right side is after treatment.

[0028] Figure 5 This is a schematic diagram of the principle of the reaction of adding fine particles of secondary aluminum ash to electrolytic aluminum electrolyte in the present invention. DETAILED DESCRIPTION

[0029] Take the secondary aluminum ash produced by a renewable resource recycling enterprise in my country as an example.

[0030] Example 1

[0031] Secondary aluminum ash was sieved using 0.2mm and 0.5mm sieves to obtain three particle sizes of secondary aluminum ash: less than 0.2mm, 0.2-0.5mm, and greater than 0.5mm. The medium-sized secondary aluminum ash was directly calcined at 700°C for 100 minutes, while the fine-sized secondary aluminum ash was co-calcined with 3% electrolytic aluminum electrolyte (Na3AlF6:NaF:CaF2 in a ratio of 1:1:4). After calcination, the three particle sizes of secondary aluminum ash were washed and leached at 85°C, a liquid-to-solid ratio of 7:1, and 300rpm for 150 minutes. The filtrate was then filtered and dried at a constant temperature of 90°C for 12 hours to obtain inorganic salts. The denitrification rate of the secondary aluminum ash was 63.54%, and the salt recovery rate was 93.78%.

[0032] Example 2

[0033] Secondary aluminum ash was sieved using 0.2mm and 0.5mm sieves to obtain three particle sizes: less than 0.2mm, 0.2-0.5mm, and greater than 0.5mm. The medium-sized secondary aluminum ash was directly calcined at 900°C for 120 minutes, while the fine-sized secondary aluminum ash was co-calcined with a 6% electrolytic aluminum electrolyte (Na3AlF6:NaF:AlF3 in a ratio of 2:1:3). After calcination, the three particle sizes of secondary aluminum ash were washed and leached at 75°C, a liquid-to-solid ratio of 6:1, and 300 rpm for 120 minutes. The filtrate was then filtered and dried at a constant temperature of 90°C for 12 hours to obtain inorganic salts. The denitrification rate was 95.67%, and the salt recovery rate was 91.18%.

[0034] Example 3

[0035] Secondary aluminum ash was sieved using 0.2mm and 0.5mm sieves to obtain three particle sizes: less than 0.2mm, 0.2-0.5mm, and greater than 0.5mm. The medium-sized secondary aluminum ash was directly calcined at 500°C for 120 minutes, while the fine-sized secondary aluminum ash was co-calcined with a 9% electrolytic aluminum electrolyte (Na3AlF6:NaF at a ratio of 2:3). After calcination, the three particle sizes of secondary aluminum ash were washed and leached at 85°C, a liquid-to-solid ratio of 5:1, and 200 rpm for 90 minutes. The filtrate was then filtered and dried at a constant temperature of 90°C for 12 hours to obtain inorganic salts. The denitrification rate was 46.19%, and the salt recovery rate was 85.43%.

[0036] Example 4

[0037] Secondary aluminum ash was sieved using 0.2mm and 0.5mm sieves to obtain three particle sizes: less than 0.2mm, 0.2-0.5mm, and greater than 0.5mm. The medium-sized secondary aluminum ash was directly calcined at 600°C for 90 minutes, while the fine-sized secondary aluminum ash was co-calcined with 5% electrolytic aluminum electrolyte (Na3AlF6:AlF3 at a ratio of 1:2). After calcination, the three particle sizes of secondary aluminum ash were washed and leached at 55°C, a liquid-to-solid ratio of 6:1, and 300rpm for 120 minutes. The filtrate was then filtered and dried at a constant temperature of 90°C for 12 hours to obtain inorganic salts. The denitrification rate was 58.26%, and the salt recovery rate was 89.32%.

[0038] Comparative Example 1

[0039] This comparative example provides a method for secondary aluminum ash denitrification and defluorination. In the method, only 6% cryolite is added for calcination, and the remaining steps are the same as those in Example 2. The denitrification rate is 79.32% and the salt recovery rate is 81.25%.

[0040] Comparative Example 2

[0041] This comparative example provides a method for secondary aluminum ash denitrification and defluorination. In the method, only 20% cryolite is added for calcination, and the remaining steps are the same as those in Example 2. The denitrification rate is 93.95% and the salt recovery rate is 88.23%.

[0042] Comparative Example 3

[0043] This comparative example provides a method for denitrification and defluorination of secondary aluminum ash. In the method steps, the secondary aluminum ash is sieved using sieves with pore sizes of 0.5 mm and 1 mm to obtain secondary aluminum ash with three particle sizes of less than 0.5 mm, 0.5-1 mm and greater than 1 mm. The remaining steps are the same as those in Example 2. The denitrification rate is 86.95% and the salt recovery rate is 90.23%.

[0044] After particle size sorting in the present invention, inorganic salts, AlN, and Al4C3 particles are concentrated in fine particles. After the electrolytic aluminum electrolyte is introduced, they jointly promote the oxidation reaction of AlN and Al4C3 particles with the inorganic salts. Combining Example 2 and Comparative Example 1, it can be seen that Example 2 achieves a higher denitrification rate and salt recovery rate after using a combination of cryolite, NaF, and AlF3. Comparative Example 2 performs a roasting reaction with an increased amount of pure cryolite. Both Example 2 and Comparative Example 2 achieve a higher denitrification rate. However, Comparative Example 2 requires nearly three times the amount of electrolytic aluminum electrolyte added, which on the one hand leads to resource consumption. On the other hand, the excess cryolite reacts with the calcium oxide in the secondary aluminum ash to form water-insoluble calcium fluoride, causing fluoride pollution. The denitrification rate obtained in Comparative Example 3 is also lower than that in Example 2. This is attributed to the different components of secondary aluminum ash of different particle sizes. Comparative Example 3 may be mixed with a small amount of elemental aluminum, which easily causes aluminum combustion during the roasting process, which is not conducive to the oxidation reaction of AlN and Al4C3 particles. This shows that the method of the present invention for the combined treatment of secondary aluminum ash by ball milling and sorting - low-temperature roasting - water washing and leaching has obvious advantages in the process of harmlessness and resource utilization of secondary aluminum ash.

[0045] During the fine particle size and electrolyte roasting process, O2 undergoes oxidation reaction with AlN and Al4C3 particles to produce N2, CO2 and Al2O3. The generated N2 and CO2 are desorbed from the solid surface, while an α-Al2O3 layer is formed and covers the solid surface. As the reaction proceeds, an oxide layer gradually forms around the reaction core, completely wrapping it up to prevent further contact with O2, thereby preventing the reaction from proceeding. The presence of SO2 and SiO2 promotes the low-temperature decomposition of some inorganic salts. The formation of HCl(g) limits the formation of aluminum oxide film on the one hand, and on the other hand reacts with the electrolytic aluminum electrolyte to produce HF(g), which destroys the aluminum oxide film and promotes the oxidation of AlN. At the same time, the electrolytic aluminum electrolyte reacts with α-Al2O3 at high temperature to generate NaAl 11 O 17 This reaction destroys the dense structure of α-Al2O3, causing it to transform into β-Al2O3 and promoting the exchange of oxygen with AlN. Figure 5 This is the fine particle size reaction mechanism diagram of the present invention.

[0046] Finally, a combined treatment method system of ball milling separation-low temperature roasting-water washing and leaching for secondary aluminum ash was established, realizing the batch harmless disposal of secondary aluminum ash.

[0047] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Various improvements and modifications can be made within the scope of knowledge possessed by ordinary technicians in this field without departing from the scope of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for the combined treatment of secondary aluminum ash by ball milling separation, low temperature roasting and water washing and leaching, characterized in that: The following steps are involved: Step 1, the secondary aluminum ash is subjected to dry ball milling and screening to obtain three types of secondary aluminum ash: coarse, medium and fine; Step 2: low-temperature roasting the medium-sized secondary aluminum ash obtained in step 1, and low-temperature roasting the fine-sized secondary aluminum ash mixed with electrolytic aluminum electrolyte; Step 3: The medium-sized and fine-sized secondary aluminum ash after treatment in step 2 and the coarse-sized secondary aluminum ash in step 1 are washed, filtered, and dried together to obtain inorganic salts and harmless secondary aluminum ash.

2. The method for combined treatment of secondary aluminum ash by ball milling separation, low temperature roasting and water washing and leaching according to claim 1, characterized in that: The secondary aluminum ash in step 1 includes secondary aluminum ash generated by any one of the industries of aluminum electrolysis, aluminum recycling or aluminum processing.

3. The method for combined treatment of secondary aluminum ash by ball milling separation, low temperature roasting and water washing and leaching according to claim 1, characterized in that: The dry ball milling time in step 1 is controlled to be 0.5-2h, and the ball mill speed is controlled to be 200-400r / min.

4. The method for combined treatment of secondary aluminum ash by ball milling separation, low temperature roasting and water washing and leaching according to claim 1, 2 or 3, characterized in that: In step 1, a vibrating screen is used to separate the secondary aluminum ash into three particle sizes: coarse particle size, medium particle size, and fine particle size. The particle sizes are greater than 0.5 mm, 0.2 mm-0.5 mm, and less than 0.2 mm.

5. The method for combined treatment of secondary aluminum ash by ball milling separation, low temperature roasting and water washing and leaching according to claim 1, characterized in that: The aluminum electrolysis electrolyte in step 2 is composed of one or more of cryolite and other salt additives.

6. The method for combined treatment of secondary aluminum ash by ball milling separation, low temperature roasting and water washing and leaching according to claim 1 or 5, characterized in that: The calcination conditions in step 2 are a calcination temperature of 500-900° C., a calcination time of 30-150 min, and an addition amount of electrolytic aluminum electrolyte not exceeding 10%.

7. The method for combined treatment of secondary aluminum ash by ball milling separation, low temperature roasting and water washing and leaching according to claim 1, characterized in that: The heating rate in the calcination conditions in step 2 is controlled at 10°C / min-20°C / min.

8. The method for combined treatment of secondary aluminum ash by ball milling separation, low temperature roasting and water washing and leaching according to claim 1, characterized in that: In the step 3, the calcined slag is added into water with a pH of 6.5-8.5, soluble salts in the secondary aluminum ash are washed away, the mixture is fully stirred, filtered and dried to obtain inorganic salts and harmless secondary aluminum ash.

9. The method for combined treatment of secondary aluminum ash by ball milling separation, low temperature roasting and water washing and leaching according to claim 1 or 8, characterized in that: In step 3, the washing liquid-solid ratio is controlled within the range of 3:1-10:1, the washing temperature is controlled within the range of 55-95° C., the rotation speed is controlled within the range of 100-400 r / min, and the washing time is controlled within the range of 60-180 min.

10. The method for combined treatment of secondary aluminum ash by ball milling separation, low temperature roasting and water washing and leaching according to claim 1, characterized in that: The filtrate obtained in step 3 is dried at a constant temperature of 90° C. for 12 h to obtain an inorganic salt.

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