A method for harmless treatment of secondary aluminum ash by oxygen-enriched roasting and self-denitrification

Abstract

The invention discloses a method for harmless treatment of oxygen-enriched roasting of secondary aluminum ash by self-denitrification, which comprises placing a mixture of secondary aluminum ash and aluminum smelting pipeline ash in an oxygen-containing atmosphere and heating it to an initiation temperature, adding water to initiate a self-heating roasting reaction, and obtaining a high-aluminum material. The method makes full use of the self-heating performance of aluminum smelting pipeline ash, and can continuously roast the secondary aluminum ash at a high temperature without an external heat source. While achieving denitrification and defluorination of the secondary aluminum ash, high-quality aluminum material can be obtained, providing high-quality raw materials for cement auxiliary materials, refractory materials, corundum, calcium aluminate and other products, and having high economic value. The method has a wide source of raw materials, is simple, has low energy consumption, high processing efficiency, and low cost, and can effectively solve the technical problem of environmental pollution caused by secondary aluminum ash and aluminum smelting pipeline ash.

Description

Technical Field

[0001] The invention relates to an aluminum ash treatment method, in particular to a secondary aluminum ash oxygen-enriched roasting self-denitrification harmless treatment method, belonging to the technical field of metal regeneration and comprehensive utilization of solid waste. Background Art

[0002] Secondary aluminum ash is currently a major problem facing all recycled aluminum companies. Since secondary aluminum ash was listed as hazardous waste in 2021, recycled aluminum companies, research institutes and universities have been looking for a technical route suitable for industrialized, large-scale and harmless treatment of secondary aluminum ash. However, to date, secondary aluminum ash has not yet formed a relatively complete industrial application system and is mostly limited to laboratory conditions. At this stage, recycled aluminum companies still need to explore technical routes.

[0003] There are two main reasons why secondary aluminum ash is listed as hazardous waste: the first is that secondary aluminum ash contains a high content of aluminum nitride, which can react with moisture in the air to produce ammonia at room temperature and pressure. Therefore, in the secondary aluminum ash storage plant of the recycled aluminum company, a strong "ammonia smell" can be smelled. The specific reaction equation is: AlN+3H2O=Al(OH)3+NH3; the second reason is mainly inorganic fluoride (excluding calcium fluoride). The leaching toxicity of fluorine exceeds the standard, which is mainly reflected in the electrolytic aluminum industry. A high content of cryolite must be added to the electrolytic cell of electrolytic aluminum to promote the molten electrolysis of alumina. Therefore, the leaching toxicity of fluorine in the secondary aluminum ash produced by the electrolytic aluminum industry often exceeds the standard. In the recycled aluminum industry, only a small number of processing processes will add fluoride salts. Therefore, generally speaking, the leaching toxicity of fluorine in the secondary aluminum ash produced by the recycled aluminum industry will not exceed the standard.

[0004] In order to transform secondary aluminum ash into general solid waste or even into products, most small and medium-sized recycled aluminum enterprises are in urgent need of a technical route with low equipment investment and large-scale continuous production. In order to achieve this goal, recycled aluminum enterprises, scientific research institutes and universities have made a lot of efforts. At present, the research focus of universities and scientific research institutes is on the wet harmless treatment of secondary aluminum ash. In the process of wet detoxification, the process is long, and the leaching time is at least more than 8 hours. In addition, the generation of ammonia is inevitable during the leaching process, and impurity gases such as hydrogen are also generated. The generation of these gases requires the use of equipment such as ammonia absorption towers, and the leachate after leaching needs to be evaporated and crystallized to recover the soluble salts therein. In summary, the wet process has high energy consumption and large equipment investment, and most recycled aluminum enterprises cannot afford the high equipment investment cost. Therefore, it is necessary to explore a technical route with small investment, low cost, simple process, and affordable for small and medium-sized recycled aluminum enterprises. Summary of the invention

[0005] In view of the shortcomings of the existing secondary aluminum ash treatment technology, such as complex process, high cost, low treatment efficiency, and expensive investment equipment, the purpose of the present invention is to provide a method for self-denitrification and harmless treatment of secondary aluminum ash by oxygen-enriched roasting. This method can not only achieve denitrification and defluorination of secondary aluminum ash, but also obtain high-quality aluminum material, provide high-quality raw materials for cement auxiliary materials, refractory materials, corundum, calcium aluminate and other products, and has high economic value. In addition, this method has a wide source of raw materials, is simple, has low energy consumption, high treatment efficiency, and low cost, and can effectively solve the technical problem of environmental pollution caused by secondary aluminum ash and aluminum smelting pipeline ash.

[0006] In order to achieve the above technical objectives, the present invention provides a method for self-denitrification and harmless treatment of secondary aluminum ash by oxygen-enriched roasting, which comprises placing a mixture of secondary aluminum ash and aluminum smelting pipeline ash in an oxygen-containing atmosphere and heating it to an initiation temperature, adding water to initiate a self-heating roasting reaction to obtain a high-aluminum material.

[0007] In the present invention, secondary aluminum ash is synergistically treated with aluminum smelting pipeline ash (pipeline dust removal ash), and the iron oxide, ferroferric oxide, manganese oxide, etc. contained in the pipeline ash and the metal aluminum in the secondary aluminum ash are used to generate an aluminothermic reaction at high temperature (2Al+Fe2O3=2Fe+Al2O3; 8Al+3Fe3O4=9Fe+4Al2O3; 4Al+3MnO2=3Mn+2Al2O3), resulting in a "spontaneous combustion" phenomenon and releasing a large amount of heat. By utilizing the self-heating property, the mixed system can continuously perform high-temperature roasting on the secondary aluminum ash without an external heat source. Although the aluminum nitride in the aluminum ash is more likely to generate nitrogen during the roasting process, it is inevitable to generate nitrogen oxides. The water additive added during the roasting process can react with the aluminum nitride in the aluminum ash to generate ammonia (3AlN+ 3H2O = NH3+ Al(OH)3), ammonia can react with nitrogen oxides to generate nitrogen and water, and part of the generated water can react with aluminum nitride to generate ammonia, promoting the conversion of nitrogen oxides, thereby removing nitrogen oxides generated during the secondary aluminum ash roasting process, and finally obtaining a high-aluminum product. Moreover, this reaction is an exothermic reaction, which can further increase the roasting temperature.

[0008] The aluminum smelting pipeline ash of the present invention is obtained by adding additives such as magnesium removal agent during the aluminum smelting process, and the dust removal ash obtained from the flue gas pipeline system during the aluminum smelting process is also called environmental protection ash, black ash, etc.

[0009] As a preferred solution, the particle size of the secondary aluminum ash is -120 mesh.

[0010] Using secondary aluminum ash in this particle size range can make the roasting reaction more complete. However, if the particle size is too large, on the one hand, the metallic aluminum content in the high-particle secondary aluminum ash will be relatively high, resulting in waste of metallic aluminum. On the other hand, the high-particle secondary aluminum ash will make it difficult to "burn through" the secondary aluminum ash during the roasting process, that is, the roasting is insufficient, and the harmful elements in the secondary aluminum ash are difficult to effectively remove.

[0011] As a preferred solution, the content of metallic aluminum in the secondary aluminum ash is 3-5wt%, the content of aluminum nitride is 15-25wt%, and the salt component in the secondary aluminum ash does not exceed 10%.

[0012] During the roasting process, the salt-containing components in the secondary aluminum ash will volatilize and be collected and reused by the dust removal system, while the metallic aluminum and aluminum nitride therein will undergo an exothermic reaction during the oxidation process. Therefore, the presence of aluminum nitride and metallic aluminum is conducive to the heating of the secondary aluminum ash.

[0013] As a preferred solution, the aluminum smelting pipeline ash contains main components including iron oxide, manganese oxide, sodium chloride, hexafluoroaluminate, sulfate, aluminum oxide and silicon dioxide. Hexafluoroaluminate is potassium hexafluoroaluminate, sodium hexafluoroaluminate, etc. Sulfate is sodium sulfate, potassium sulfate, etc. Iron oxide is ferric oxide, etc., and manganese oxide is manganese oxide, etc.

[0014] As a preferred solution, the mass ratio of the secondary aluminum ash to the aluminum smelting pipeline ash is 1:0.1-0.2.

[0015] Since the secondary aluminum ash and the pipeline ash can "self-ignite" during the roasting process, energy consumption can be saved. Controlling the amount of pipeline ash added within an appropriate range can ensure that the secondary aluminum ash is heated to the set temperature. When the amount of pipeline ash added is too low, it is difficult to ensure that the secondary aluminum ash is heated to the predetermined temperature without an external heat source, and the temperature rise rate is extremely slow, which is difficult to meet the requirements of industrial continuous operation; when the amount of pipeline ash added is too high, although the secondary aluminum ash can be quickly heated to the set temperature, the secondary aluminum ash still contains a high content of salt-containing components. Even if the salt-containing components can be collected by environmental protection equipment, they will cause corrosion of environmental protection equipment in the long run, reduce the service life of the equipment, and the salt-containing components are difficult to be completely recovered by environmental protection equipment during the actual roasting process at the set temperature. There are still a small amount of salt-containing components left in the secondary aluminum ash. Therefore, if the amount of pipeline ash added is too high, the salt-containing component content in the mixture will be too high, which will cause the salt component content of the high-aluminum material to exceed the standard after roasting, affecting the direct value of the high-aluminum material and the subsequent resource utilization field.

[0016] As a preferred solution, the oxygen-containing atmosphere is an oxygen-rich atmosphere with an oxygen volume percentage concentration in the range of 21 to 30%; the oxygen-rich atmosphere is maintained for no less than 10 minutes, and more preferably for 20 to 30 minutes.

[0017] During the roasting reaction, in the absence of an external heat source, although only adding pipeline ash can raise the temperature to the predetermined temperature, the efficiency is slow. During the heating process of secondary aluminum ash and pipeline ash, the heat release of metal aluminum is mainly due to oxidation. In order to make the oxidation heat release more intense during the reaction, oxygen needs to be introduced during the heating process of secondary aluminum ash and pipeline ash. If oxygen is not introduced during the roasting process, the oxidation exothermic reaction of metal aluminum will slow down due to the decrease in oxygen concentration in the furnace, which will result in a longer time to heat the secondary aluminum ash to the predetermined temperature, which will reduce production efficiency and is not conducive to industrial continuous production. Oxygen is introduced into the furnace until its oxygen volume concentration reaches an oxygen-rich atmosphere of 21%~30%, and the oxygen-rich atmosphere is maintained for more than 10 minutes. Under this control condition, it can be ensured that most of the metallic aluminum in the secondary aluminum ash and pipeline ash has undergone an exothermic oxidation reaction. If the oxygen ventilation time is too short, it will take a longer time to heat to the predetermined temperature; if the oxygen ventilation time is too long, it will lead to oxygen waste and excessive furnace temperature. Excessive furnace temperature will cause serious kiln stagnation of secondary aluminum ash, which is not conducive to the continuous preparation of high-aluminum materials.

[0018] As a preferred solution, the initiation temperature is 900-1000°C. When the initiation temperature reaches 900-1000°C, it is conducive to the reaction of aluminum nitride with water to produce ammonia, which can react with nitrogen oxides to generate nitrogen and water, and part of the generated water can react with aluminum nitride to generate ammonia, promoting the conversion of nitrogen oxides. In the actual continuous production process, part of the high-temperature high-aluminum material can be retained in the furnace as a heat source to preheat the newly added secondary aluminum ash and aluminum smelting pipeline ash.

[0019] As a preferred solution, the amount of water added is 0.5-1.5wt% of the total mass of the secondary aluminum ash and the aluminum smelting pipeline ash. If the amount of water added is too low, the amount of ammonia generated will be reduced, thereby reducing the removal rate of nitrogen oxides; if the amount of water added is too high, on the one hand, the furnace temperature will drop and it will be difficult to rise to the target temperature, and on the other hand, the ammonia content generated will be too high, resulting in a large amount of ammonia escaping and polluting the test environment.

[0020] As a preferred solution, the calcination reaction conditions are: temperature of 1300-1400° C. and time of 30-60 min.

[0021] The harmless treatment of secondary aluminum ash mainly involves converting aluminum nitride and removing salt-containing components, controlling the roasting temperature and time within a reasonable range, so that the content of harmful elements such as N, Na, Cl, and K in the high-aluminum material after roasting can be reduced to below 0.2%, thereby meeting the requirements of subsequent resource utilization. If the roasting time is too short or the roasting temperature is too low, the content of harmful elements in the obtained high-aluminum material will be too high, affecting the subsequent resource utilization; if the roasting time is too long or the roasting temperature is too high, on the one hand, it will cause the high-aluminum material to stagnate in the kiln, and on the other hand, it will also affect the subsequent continuous production, both of which will reduce the treatment efficiency of secondary aluminum ash.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) Using secondary aluminum ash and pipeline ash from industrial hazardous waste as raw materials, they are harmlessly disposed of by high-temperature roasting. The method is simple, efficient and low-cost. The high-aluminum material prepared can be used as a high-quality raw material for refractory materials, water purifiers, cement auxiliary materials, calcium aluminate and other products, and can even be used as a substitute for some bauxite, with high potential economic value;

[0024] (2) By adding pipeline ash and introducing oxygen, the harmless utilization of secondary aluminum ash is achieved without external heat source;

[0025] (3) Adding water-containing additives during the high-temperature process to remove nitrogen oxides produced during the oxidation of aluminum nitride in the secondary aluminum ash not only saves energy and is environmentally friendly, but also reduces production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a qualitative (semi-quantitative) analysis chart of X-ray fluorescence of aluminum smelting pipe ash.

[0027] Figure 2 This is the XRD pattern of aluminum smelting pipe ash. DETAILED DESCRIPTION

[0028] The following examples are intended to further illustrate the present invention, rather than to limit the scope of protection of the claims of the present invention.

[0029] In order to further illustrate the method for harmless treatment of secondary aluminum ash by oxygen-enriched roasting and self-denitrification according to the present invention and achieve the intended purpose of the invention, the specific implementation method, structure, characteristics and efficacy of the method for harmless treatment of secondary aluminum ash by oxygen-enriched roasting and self-denitrification according to the present invention are described in detail below in combination with preferred embodiments. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics of one or more embodiments may be combined in any form.

[0030] The following will further introduce in detail the method for self-denitrification and harmless treatment of secondary aluminum ash by oxygen-enriched roasting of the present invention in conjunction with specific embodiments. Example 1

[0031] The secondary aluminum ash (metal aluminum content 4.23%, AlN content 19.97%, chlorine content 1.64%) produced by a recycled aluminum plant of -120 mesh was used as raw material. The secondary aluminum ash and pipeline ash were mixed in a rotary kiln (the ratio of secondary aluminum ash to pipeline ash was secondary aluminum ash: pipeline ash = 1:0.15). At the same time, oxygen was introduced to control the oxygen volume percentage concentration in the furnace to about 23% and maintained for 25 minutes. When the roasting temperature rose to 950℃, 1.0% of water was added. The target temperature could be reached after 40 minutes. The roasting temperature was controlled to be 1400℃, and the roasting time was 45 minutes. After cooling, the high aluminum material and the flue gas discharged were tested. The test results showed that the content of aluminum oxide in the high aluminum material was 92.73%, the content of aluminum nitride was less than 0.01%, the content of NOx in the flue gas was 35ppm, and the content of chlorine was 0.08%, which met the requirements of industrialization and subsequent resource utilization. The high aluminum material can be used as a partial substitute for high aluminum bauxite. In the present invention, the aluminum oxide content is determined by EDTA titration, the aluminum nitride content is determined by oxygen, nitrogen and hydrogen analyzer, the NOx content in the flue gas is detected by a flue gas analyzer, and the chlorine content is determined by potentiometric titration. Example 2

[0032] The secondary aluminum ash (metal aluminum content 4.23%, AlN content 19.97%, chlorine content 1.64%) produced by a recycled aluminum plant of -120 mesh was used as raw material. The secondary aluminum ash and pipeline ash were mixed in a rotary kiln (the mass ratio of secondary aluminum ash to pipeline ash was secondary aluminum ash: pipeline ash = 1:0.15). At the same time, oxygen was introduced to control the oxygen volume percentage concentration in the furnace to about 21% and maintained for 25 minutes. When the roasting temperature rose to 950℃, 1.0wt% of water was added to the mixed ingredients. The target temperature could be reached after 30 minutes. The roasting temperature was controlled to 1300℃ and the roasting time was 30 minutes. After cooling, the high aluminum material and the flue gas discharged were tested. The test results showed that the content of alumina in the high aluminum material was 90.82%, the content of aluminum nitride was less than 0.01%, the content of NOx in the flue gas was 42ppm, and the content of chlorine was 0.17%, which met the requirements of industrialization and subsequent resource utilization. The high aluminum material can be used as a partial substitute for high aluminum bauxite. Comparative Example 1

[0033] The method of Example 1 is used to treat secondary aluminum ash, except that the mass ratio of secondary aluminum ash to pipeline ash is secondary aluminum ash: pipeline ash = 1:0.35, and 1.0wt% of moisture is added to the mixed ingredients. The target temperature can be reached after 30 minutes.

[0034] The high-aluminum material obtained under the comparative example has an aluminum oxide content of 83.79%, an aluminum nitride content of less than 0.01%, a NOx content of 70 ppm in the flue gas, and a chlorine content of 2.47%. The salt component content in the high-aluminum material is too high, making it difficult to perform subsequent resource utilization, and further desalination is still required for subsequent utilization. Comparative Example 2

[0035] Taking -120 mesh secondary aluminum ash (metal aluminum content 4.23%, AlN content 19.97%, chlorine content 1.64%) produced by a recycled aluminum plant as raw material, the secondary aluminum ash and pipeline ash were mixed in a rotary kiln (the mass ratio of secondary aluminum ash to pipeline ash was secondary aluminum ash: pipeline ash = 1:0.05), and the pipeline ash was heated by utilizing its self-heating property, and oxygen was introduced for 25 minutes at the same time to control the oxygen volume concentration in the furnace at about 23%. When the roasting temperature was raised to 950°C, 1.0wt% of moisture was added to the mixed ingredients, and it was difficult to reach the roasting temperature of 1400°C, and it was difficult to complete the harmlessness. Comparative Example 3

[0036] The method of Example 1 is used to treat secondary aluminum ash, except that oxygen is introduced to control the oxygen volume percentage concentration in the furnace to about 21% and maintained for 5 minutes, and the target temperature can be reached after 240 minutes.

[0037] The high-aluminum material obtained under the conditions of this comparative example has an aluminum oxide content of 92.65%, an aluminum nitride content of less than 0.01%, a NOx content of 50 ppm in the flue gas, and a chlorine content of 0.07%. Although the product can meet the requirements of subsequent resource utilization, the heating time is too long and it is difficult to meet the requirements of large-scale utilization. Comparative Example 4

[0038] The secondary aluminum ash is treated by the method of Example 1, except that: when the roasting temperature is increased to 500°C, 1.0wt% of water is added to the mixed ingredients.

[0039] The high-aluminum material obtained under the conditions of this comparative example has an aluminum oxide content of 92.45%, an aluminum nitride content of less than 0.01%, a NOx content of 390 ppm, a chlorine content of 0.08%, and a nitrogen oxide content that does not meet the emission standards and cannot be used industrially. Comparative Example 5

[0040] The method of Example 1 is adopted to treat the secondary aluminum ash, except that 0.2 wt % of water is added to the mixed ingredients.

[0041] The high-aluminum material obtained under the conditions of this comparative example has an aluminum oxide content of 92.69%, an aluminum nitride content of less than 0.01%, a NOx content of 260 ppm, a chlorine content of 0.09%, and a nitrogen oxide content that does not meet the emission standards and cannot be used industrially. Comparative Example 6

[0042] The method of Example 2 is adopted to treat the secondary aluminum ash, except that the roasting temperature is controlled to be 1100°C.

[0043] The high-aluminum material obtained under the comparative example has an aluminum oxide content of 85.27%, an aluminum nitride content of 0.62%, a NOx content of 92 ppm in the flue gas, and a chlorine content of 0.91%. All indicators cannot meet the requirements of subsequent industrialization and resource utilization. Comparative Example 7

[0044] The secondary aluminum ash is treated by the method of Example 2, except that the roasting time is 10 minutes.

[0045] The high-aluminum material obtained under the comparative example has an aluminum oxide content of 90.82%, an aluminum nitride content of 0.04%, a NOx content of 48 ppm in the flue gas, and a chlorine content of 0.72%. Many indicators cannot meet the requirements of subsequent industrialization and resource utilization.

Claims

1. A method for harmless treatment of secondary aluminum ash by oxygen-enriched roasting and self-denitrification, characterized in that: When the mixture of secondary aluminum ash and aluminum smelting pipeline ash is placed in an oxygen-containing atmosphere and heated to 900-1000°C, water is added to initiate a self-heating roasting reaction to obtain a high-aluminum material; The secondary aluminum ash contains 3-5wt% of metallic aluminum, 15-25wt% of aluminum nitride, and no more than 10% of salt components; The mass ratio of the secondary aluminum ash to the aluminum smelting pipeline ash is 1:0.1-0.2; The amount of water added is 0.5-1.5wt% of the total mass of secondary aluminum ash and aluminum smelting pipeline ash.

2. The method for self-denitrification of secondary aluminum ash by oxygen-enriched roasting according to claim 1 is characterized in that: The particle size of the secondary aluminum ash is -120 mesh.

3. The method for self-denitrification of secondary aluminum ash by oxygen-enriched roasting according to claim 1 is characterized in that: The aluminum smelting pipeline ash contains main components including iron oxide, manganese oxide, sodium chloride, hexafluoroaluminate, sulfate, aluminum oxide and silicon dioxide.

4. The method for self-denitrification of secondary aluminum ash by oxygen-enriched roasting according to claim 1 is characterized in that: The oxygen-containing atmosphere is an oxygen-rich atmosphere with an oxygen volume percentage concentration in the range of 21 to 30%; the oxygen-rich atmosphere is maintained for no less than 10 minutes.

5. The method for self-denitrification of secondary aluminum ash by oxygen-enriched roasting according to claim 1, characterized in that: The conditions of the calcination reaction are: temperature of 1300-1400° C. and time of 30-60 min.

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