Method for recycling overhaul slag and chromium-containing aluminum sludge

Abstract

A method for recycling overhaul slag and chromium-containing aluminum sludge. The overhaul slag contains a fluoride, a cyanide and carbon, and the chromium-containing aluminum sludge contains aluminum and hexavalent chromium. The method comprises: performing a redox reaction on an inorganic acid, chromium-containing aluminum sludge and overhaul slag to obtain a decyanated material containing a fluoride, carbon, aluminum and chromium; using a calcium-containing basic oxide to perform a precipitation reaction on the decyanated material so as to obtain a precipitated material containing chromium, aluminum, carbon and fluorine; using preheated chlorine gas to perform a chlorination reaction on the precipitated material so as to obtain aluminum-containing chlorinated flue gas and chromium-containing chlorinated slag; separating and purifying the aluminum-containing chlorinated flue gas to obtain an aluminum-containing solid phase; and washing the chromium-containing chlorinated slag to obtain a trivalent chromium-containing solution.

Description

A method for recycling overhaul slag and chromium-containing aluminum sludge

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese patent application No. 202411798634.6, filed on December 9, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of hazardous waste resource utilization technology, and in particular to a method for recycling overhaul slag and chromium-containing aluminum sludge. Background Technology

[0004] In the process of aluminum electrolysis, 30-50 kg of overhaul slag is generated for every ton of primary aluminum produced. The specific composition of the overhaul slag varies depending on factors such as the electrolyte composition, current capacity, operating procedures, and lining replacement frequency during aluminum electrolysis. However, the main components of the overhaul slag are basically the same, including carbon, fluorides, and small amounts of sodium, aluminum, calcium, iron, silicon, and cyanides. Because overhaul slag contains a large amount of soluble fluorides and a small amount of cyanides, it is currently classified as hazardous waste. Directly stockpiling or landfilling overhaul slag would have serious environmental impacts and even endanger human health. Therefore, achieving the harmless treatment and high-value utilization of overhaul slag is of great significance for promoting the green and high-quality development of the aluminum industry. In addition, in the industrial production of sodium dichromate, two main methods are used: calcium-containing roasting and calcium-free roasting. Compared with calcium-containing roasting, calcium-free roasting is cleaner and more efficient. However, in calcium-free roasting, aluminum-silicon compounds react with soda ash to form significant amounts of sodium silicate and sodium aluminate. These sodium silicates and aluminates enter the alkaline leachate, generating large quantities of chromium-containing aluminum sludge, approximately 5 to 10 times the yield of the calcium-roasting method. Chromium-containing aluminum sludge typically contains hexavalent chromium, making it highly toxic. Therefore, it is also classified as hazardous waste. Direct dumping or discharge of chromium-containing aluminum sludge will also cause serious environmental damage.

[0005] Chromium-containing aluminum sludge contains abundant chromium and aluminum resources. Comprehensive utilization of chromium-containing aluminum sludge through appropriate methods can not only eliminate its environmental pollution but also effectively promote the green and sustainable development of the chromium salt industry. Currently, the co-utilization of overhaul slag and chromium-containing aluminum sludge mostly remains at the level of physical mixing or simple treatment, making it difficult to effectively remove toxic elements and recover valuable elements such as aluminum and chromium. Summary of the Invention

[0006] This disclosure provides a method for recycling overhaul slag and chromium-containing aluminum sludge, solving the problem of how to simultaneously improve the removal efficiency of toxic elements and the recovery rate of valuable elements in overhaul slag and chromium-containing aluminum sludge.

[0007] In a first aspect, this disclosure provides a method for recycling overhaul slag and chromium-containing aluminum sludge, wherein the overhaul slag contains fluoride, cyanide, and carbon, and the chromium-containing aluminum sludge contains aluminum and hexavalent chromium. The method includes: mixing an inorganic acid, the chromium-containing aluminum sludge, and the overhaul slag to allow the hexavalent chromium to undergo a redox reaction with the cyanide in an acidic environment to obtain a decyanated material containing fluoride, carbon, aluminum, and chromium; using a calcium-containing alkaline oxide to precipitate the decyanated material to obtain a precipitate containing chromium, aluminum, carbon, and fluorine; mixing preheated chlorine gas with the precipitate to allow the preheated chlorine gas to react with the chromium and aluminum in the precipitate under the action of carbon in the precipitate to obtain aluminum-containing chlorinated flue gas and chromium-containing chlorinated slag; separating and purifying the aluminum-containing chlorinated flue gas to obtain an aluminum-containing solid phase; and washing the chromium-containing chlorinated slag to obtain a solution containing trivalent chromium. Attached Figure Description

[0008] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0009] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 shows a schematic flowchart of a method for recycling overhaul slag and chromium-containing aluminum sludge according to an embodiment of the present disclosure.

[0011] Figure 2 shows a detailed process diagram of a method for recycling overhaul slag and chromium-containing aluminum sludge according to an embodiment of the present disclosure.

[0012] Figure 3 shows a schematic diagram of the actual process of a method for recycling overhaul slag and chromium-containing aluminum sludge according to an embodiment of the present disclosure. Embodiments of the present invention

[0013] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0014] Various embodiments of this disclosure may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this disclosure; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range such as 1, 2, 3, 4, 5, and 6, regardless of the range; furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0015] In this document, terms such as “comprising” mean “including but not limited to”. Relational terms such as “first” and “second” are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. “And / or” describes the relationship between related objects, indicating that there can be three relationships, for example, A and / or B can mean: A alone, A and B simultaneously, or B alone; where A and B can be singular or plural. “At least one” means one or more, “more” means two or more; “at least one,” “at least one of the following,” or similar expressions refer to any combination of these items, including any combination of single or plural items; for example, “at least one of a, b, or c,” or “at least one of a, b, and c,” can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. "Parts representation" such as parts by weight or parts by mass indicates the proportional relationship between components. In the proportional relationships discussed in this article, the parameters that need to be described by proportion should be understood as the first term of the proportion in the order of description, and the proportion figures should be understood as the second term of the proportion. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substances A, B, and C should correspond one-to-one with the proportion figures in the proportion in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0016] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this article can be purchased from the market or prepared by existing methods.

[0017] Figure 1 illustrates, by way of example, a process flow diagram of a method for recycling overhaul slag and chromium-containing aluminum sludge according to an embodiment of the present disclosure.

[0018] As shown in Figure 1, embodiments of this disclosure provide a method for recycling overhaul slag and chromium-containing aluminum sludge. The overhaul slag contains fluorides, cyanides, and carbon, while the chromium-containing aluminum sludge contains aluminum and hexavalent chromium. The method includes:

[0019] S1. Inorganic acid, chromium-containing aluminum sludge and overhaul slag are mixed to allow hexavalent chromium to undergo an oxidation-reduction reaction with cyanide in an acidic environment, resulting in a decyanated material containing fluoride, carbon, aluminum and chromium.

[0020] S2. The decyanated material is subjected to a precipitation reaction using a calcium-containing alkaline oxide to obtain a precipitate containing chromium, aluminum, carbon and fluorine;

[0021] S3. Preheated chlorine gas is mixed with precipitate so that, under the action of carbon in the precipitate, the preheated chlorine gas reacts with chromium and aluminum in the precipitate to obtain aluminum-containing chlorinated flue gas and chromium-containing chlorinated slag.

[0022] S4. The aluminum-containing chlorinated flue gas is separated and purified to obtain an aluminum-containing solid phase; and

[0023] S5. Wash the chromium-containing chloride residue to obtain a solution containing trivalent chromium.

[0024] It should be noted that the carbon in the overhaul slag can significantly improve the fluidization quality of chromium-containing aluminum sludge, thereby effectively promoting the redox reaction.

[0025] It should be noted that the precipitate needs to be purified before the chlorination reaction to remove moisture and avoid loss of chlorine gas during preheating. Purification can be achieved through drying.

[0026] It should be noted that the preheating temperature of the chlorine gas can be lower than the operating temperature of the chlorination reaction, and the preheating temperature is determined based on the actual heat exchange conditions. Regardless of the preheating temperature, the chlorine gas can be rapidly heated to the operating temperature of the chlorination reaction using heating methods such as microwave heating.

[0027] It should be noted that the chlorination reaction can be carried out in a gas-solid fluidized bed reactor. The gas-solid fluidized bed reactor can achieve efficient mixing and contact between preheated chlorine gas and precipitate, and has the characteristics of fast mass and heat transfer rate and high reaction efficiency.

[0028] It should be noted that the inorganic acid can be hydrochloric acid, so that it can work synergistically with preheated chlorine gas in the subsequent chlorination reaction to produce chromium-containing chloride salts and aluminum-containing chloride salts.

[0029] It should be noted that the products obtained from the precipitation reaction include not only the precipitate but also a mixed solution of calcium chloride and sodium chloride. The mixed solution can be treated to obtain harmless waste liquid.

[0030] It should be noted that after washing, chromium chloride and calcium fluoride can be separated from chromium chloride residue. The resulting product contains not only trivalent chromium solution but also calcium fluoride.

[0031] It should be noted that the overhaul residue needs to be ground before use in order to control the particle size of the overhaul residue to <10μm.

[0032] In summary, the method for recycling overhaul slag and chromium-containing aluminum sludge according to the embodiments of this application has the following advantages:

[0033] 1. Improve the removal efficiency of toxic elements

[0034] The removal of cyanide through redox reactions reduces the content of toxic substances; subsequent precipitation and chlorination reactions further remove elements such as fluoride, aluminum, and chromium that may be harmful to the environment.

[0035] 2. Improve the recovery rate of valuable elements

[0036] In the chlorination reaction, the carbon in the precipitate is used as a heating medium, which effectively promotes the conversion of chromium and aluminum, thereby improving the recovery rate of valuable elements. In addition, aluminum-containing chlorination flue gas can be purified to obtain an aluminum-containing solid phase, realizing the recovery of aluminum. Meanwhile, chromium-containing chlorination slag can be washed to obtain a trivalent chromium solution, creating conditions for the further utilization of chromium.

[0037] This method achieves the simultaneous recycling of overhaul slag and chromium-aluminum sludge through a series of chemical reactions, which not only improves the removal efficiency of toxic elements but also effectively increases the recovery rate of valuable elements. This provides a new approach and method for solving the problem of industrial waste treatment, contributing to the sustainable use of resources and environmental protection.

[0038] In some optional embodiments, the chlorination reaction temperature is 500℃~900℃, and the chlorination reaction time is 0.5h~3h;

[0039] In some embodiments, the chlorination reaction temperature can be 500℃~900℃, and the chlorination reaction time can be 0.5h~3h. Under these conditions, the carbon in the precipitate can promote a full reaction between the preheated chlorine gas and the chromium and aluminum in the precipitate to generate chromium-containing chloride salts and aluminum-containing chloride salts, which is beneficial for subsequent separation, purification, and washing.

[0040] The chlorination reaction temperature can be 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃ or 900℃.

[0041] The chlorination reaction can take 0.5h, 1.5h, 2.0h, 2.5h or 3.0h.

[0042] In some alternative implementations, the chlorination reaction is carried out using microwave heating.

[0043] It should be noted that the chlorination reaction can be carried out using microwave heating. During microwave heating, the carbon in the precipitate can act as a highly efficient microwave absorbing material, absorbing and storing the energy transferred by the microwave heating. The carbon storing sufficient energy not only promotes rapid heating of the precipitate, ensuring its temperature meets the requirements of the chlorination reaction, but also helps to uniformly disperse other materials in the precipitate during microwave heating. Furthermore, the carbon in the precipitate can also act as a carbon source, increasing the intensity of the chlorination reaction and promoting the reaction of chromium and aluminum to form chromium chloride and aluminum chloride salts.

[0044] In some optional embodiments, the pH of the redox reaction is 4 to 6, and the reaction time is 0.5 h to 2 h;

[0045] In some embodiments, the pH of the redox reaction can be 4-6, and the reaction time can be 0.5-2 hours. Under an acidic inorganic acid environment, the pH of the redox reaction can reach 4-6, allowing the hexavalent chromium in the chromium-containing aluminum sludge and the cyanide in the overhaul slag to react fully. This oxidizes the cyanide into harmless carbon dioxide and nitrogen, and reduces the hexavalent chromium to harmless trivalent chromium, thereby effectively removing toxic elements from the chromium-containing aluminum sludge and overhaul slag.

[0046] The pH of a redox reaction can be 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9 or 6.0.

[0047] The redox reaction can take 0.5h, 1h, 1.5h or 2h.

[0048] In some optional embodiments, the weight of cyanide in the decyanating feed is less than or equal to 0.05% of the weight of the decyanating feed, and the weight of hexavalent chromium in the decyanating feed is less than or equal to 0.05% of the weight of the decyanating feed.

[0049] In some embodiments, the weight of cyanide in the decyanating material can be less than or equal to 0.05% of the weight of the decyanating material, and the weight of hexavalent chromium in the decyanating material can be less than or equal to 0.05% of the weight of the decyanating material, indicating that the hexavalent chromium in the chromium-containing aluminum sludge and the cyanide in the overhaul slag have undergone sufficient reaction in the redox reaction process.

[0050] In some alternative implementations, the pH of the precipitation reaction is 8 to 11;

[0051] In some embodiments, the pH of the precipitation reaction can be 8 to 11, indicating that the precipitation reaction is carried out in an alkaline environment. The alkaline environment can promote the conversion of aluminum and chromium into hydroxide precipitates, thereby promoting the conversion of aluminum and chromium in the decyanation material into precipitates. In addition, in an alkaline environment, calcium in calcium oxide can react with fluorine in the decyanation material to obtain calcium fluoride precipitate, which is convenient for subsequent recycling.

[0052] The pH of the precipitation reaction can be 8, 8.5, 9.0, 9.5, 10.0, 10.5, or 11.0.

[0053] Figure 2 illustrates, by way of example, a detailed process diagram of a method for recycling overhaul slag and chromium-containing aluminum sludge according to an embodiment of the present disclosure.

[0054] Figure 3 illustrates, by way of example, a process flow diagram of a method for recycling overhaul slag and chromium-containing aluminum sludge according to an embodiment of the present disclosure.

[0055] In some optional embodiments, as shown in Figures 2 and 3, the aluminum-containing chlorinated flue gas is separated and purified to obtain an aluminum-containing solid phase, including the following steps:

[0056] S401. Aluminum-containing chlorinated flue gas is subjected to multi-stage condensation and separation to obtain an aluminum-containing solid phase and liquid chlorine; and

[0057] S402. Liquid chlorine is vaporized to obtain chlorine gas.

[0058] In some implementations, separation and purification can be achieved through multi-stage condensation separation and gasification. Multi-stage condensation separation allows for the separate condensation and precipitation of the aluminum-containing solid phase and liquid chlorine in the aluminum-containing chlorination flue gas, based on the difference in boiling points, thereby enabling aluminum recovery. Furthermore, the precipitated liquid chlorine can be gasified to regenerate the chlorine gas.

[0059] In some optional embodiments, the multi-stage condensation separation includes a first cooling section and a second cooling section. The first cooling section is used to condense aluminum-containing chlorinated flue gas to obtain an aluminum-containing solid phase, and the second cooling section is used to condense the aluminum-containing chlorinated flue gas to obtain liquid chlorine. The temperature of the first cooling section is 70°C to 170°C, and the temperature of the second cooling section is -70°C to -40°C.

[0060] In some embodiments, multi-stage condensation separation may include a first cooling section. The first cooling section is used to condense aluminum-containing chlorinated flue gas to obtain an aluminum-containing solid phase. The temperature of the first cooling section can be 70°C to 170°C, thereby condensing the aluminum chloride component in the aluminum-containing chlorinated flue gas into an aluminum-containing solid phase based on the boiling point difference between the aluminum chloride component and other components, thus achieving aluminum recovery. Multi-stage condensation separation may also include a second cooling section. The second cooling section is used to condense the aluminum-containing chlorinated flue gas to obtain liquid chlorine. The temperature of the second cooling section can be -70°C to -40°C, thereby condensing the chlorine component in the aluminum-containing chlorinated flue gas into liquid chlorine based on the boiling point difference between the chlorine gas and other components, facilitating subsequent regeneration of chlorine through gasification, thus promoting the recycling of chlorine.

[0061] It should be noted that the second cooling section can separate gaseous carbon dioxide and liquid chlorine to achieve the recovery of liquid chlorine.

[0062] The temperature of the first cooling section can be 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃ or 170℃.

[0063] The temperature of the second cooling section can be -70℃, -65℃, -60℃, -55℃, -50℃, -45℃, or -40℃.

[0064] In some alternative embodiments, where the overhaul slag also includes iron and silicon, the multi-stage condensation separation further includes a third cooling section and a fourth cooling section. The third cooling section is used to condense the aluminum-containing chlorinated flue gas to obtain an iron-containing solid phase, and the fourth cooling section is used to condense the aluminum-containing chlorinated flue gas to obtain a silicon-containing liquid phase. The temperature of the third cooling section is 190°C to 290°C, and the temperature of the fourth cooling section is 20°C to 50°C.

[0065] In some embodiments, where the overhaul slag also includes iron and silicon, the multi-stage condensation separation may further include a third cooling section and a fourth cooling section. The third cooling section is used to condense the aluminum-containing chlorinated flue gas to obtain an iron-containing solid phase, and the fourth cooling section is used to condense the aluminum-containing chlorinated flue gas to obtain a silicon-containing liquid phase. The temperature of the third cooling section can be 190°C to 290°C, and the temperature of the fourth cooling section can be 20°C to 50°C. Based on the boiling point differences between ferric chloride, silicon tetrachloride, and other components in the overhaul slag, ferric chloride can be condensed into a ferric chloride solid phase, and silicon tetrachloride can be condensed into a silicon tetrachloride liquid phase, thereby achieving the recovery of iron and silicon from the overhaul slag.

[0066] The temperature of the third cooling section can be 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃, 240℃, 245℃, 250℃, 255℃, 260℃, 265℃, 270℃, 275℃, 280℃, 285℃, or 290℃.

[0067] The temperature of the fourth cooling section can be 20℃, 25℃, 30℃, 35℃, 40℃, 45℃ or 50℃.

[0068] It should be noted that the first, second, third, and fourth cooling sections are arranged in descending order of temperature.

[0069] In some alternative embodiments, before washing the chromium-containing chloride residue to obtain a trivalent chromium-containing solution, and after vaporizing the liquid chlorine to obtain chlorine gas, the above method further includes the following steps:

[0070] S501. Chlorine gas is exchanged with chromium-containing chlorine slag to preheat the chlorine gas and obtain preheated chlorine gas.

[0071] In some embodiments, heat exchange is performed between chlorine gas and chromium-containing chlorination slag. The heat from the chromium-containing chlorination slag can be used to preheat the chlorine gas to recover the heat from the chlorination reaction, thereby reducing the energy consumption of the method disclosed herein and improving the thermal efficiency of the method disclosed herein.

[0072] Through the heat exchange operation of S501, preheated chlorine gas is provided for the chlorination reaction, realizing energy recovery. On the other hand, the temperature of the chromium-containing chlorination slag is reduced, making it easier to safely and efficiently carry out the washing operation in the subsequent step S5, thereby obtaining a solution containing trivalent chromium.

[0073] The present disclosure is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards. If no corresponding national / industry standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0074] Example 1

[0075] As shown in Figure 2, a method for recycling overhaul slag and chromium-containing aluminum sludge is described. The overhaul slag contains fluorides, iron, silicon, cyanide, and carbon, while the chromium-containing aluminum sludge contains aluminum and hexavalent chromium.

[0076] S1. Inorganic acid, chromium-containing aluminum sludge and overhaul slag with a particle size of less than 10 μm are mixed to allow hexavalent chromium to undergo an oxidation-reduction reaction with cyanide in an acidic environment, resulting in a decyanated material containing fluoride, carbon, aluminum and chromium.

[0077] S2. Use calcium oxide to precipitate the decyanated material to obtain a precipitate containing chromium, aluminum, carbon and fluorine;

[0078] S3. Preheated chlorine gas is mixed with precipitate so that, under the action of carbon in the precipitate, the preheated chlorine gas reacts with chromium and aluminum in the precipitate to obtain aluminum-containing chlorinated flue gas and chromium-containing chlorinated slag.

[0079] S401. Aluminum-containing chlorinated flue gas is subjected to multi-stage condensation and separation to obtain aluminum-containing solid phase and liquid chlorine;

[0080] S402. Liquid chlorine is vaporized to obtain chlorine gas;

[0081] S501. The chlorine gas is preheated by exchanging heat with chromium-containing chlorination slag to obtain preheated chlorine gas;

[0082] S5. Wash the chromium-containing chloride residue to obtain a solution containing trivalent chromium.

[0083] The chlorination reaction was carried out at a temperature of 500℃ for 3 hours.

[0084] The chlorination reaction is carried out using microwave heating.

[0085] The pH of the redox reaction is 4, and the reaction time is 0.5 h.

[0086] The weight of cyanide in the decyanation feed is less than or equal to 0.05% of the weight of the decyanation feed, and the weight of hexavalent chromium in the decyanation feed is less than or equal to 0.05% of the weight of the decyanation feed.

[0087] The pH of the precipitation reaction is 8.

[0088] The multi-stage condensation separation includes a first cooling section and a second cooling section. The first cooling section is used to condense aluminum-containing chlorinated flue gas to obtain an aluminum-containing solid phase, and the second cooling section is used to condense the aluminum-containing chlorinated flue gas to obtain liquid chlorine. The temperature of the first cooling section is 70℃, and the temperature of the second cooling section is -70℃.

[0089] The multi-stage condensation separation also includes a third cooling section and a fourth cooling section. The third cooling section is used to condense aluminum-containing chlorinated flue gas to obtain an iron-containing solid phase, and the fourth cooling section is used to condense aluminum-containing chlorinated flue gas to obtain a silicon-containing liquid phase. The temperature of the third cooling section is 190℃, and the temperature of the fourth cooling section is 20℃.

[0090] Example 2

[0091] Based on the content disclosed in Example 1, the following changes were made to the reaction conditions:

[0092] The chlorination reaction was carried out at a temperature of 900℃ for 0.5 hours.

[0093] The pH of the redox reaction is 6, and the reaction time is 2 hours.

[0094] The pH of the precipitation reaction is 11.

[0095] The multi-stage condensation separation includes a first cooling section and a second cooling section. The first cooling section is used to condense aluminum-containing chlorinated flue gas to obtain an aluminum-containing solid phase, and the second cooling section is used to condense aluminum-containing chlorinated flue gas to obtain liquid chlorine. The temperature of the first cooling section is 170℃, and the temperature of the second cooling section is -40℃.

[0096] The multi-stage condensation separation also includes a third cooling section and a fourth cooling section. The third cooling section is used to condense aluminum-containing chlorinated flue gas to obtain an iron-containing solid phase, and the fourth cooling section is used to condense aluminum-containing chlorinated flue gas to obtain a silicon-containing liquid phase. The temperature of the third cooling section is 290℃, and the temperature of the fourth cooling section is 50℃.

[0097] Example 3

[0098] Based on the content disclosed in Example 1, the following changes were made to the reaction conditions:

[0099] The chlorination reaction was carried out at a temperature of 800℃ for 1.5 hours.

[0100] The pH of the redox reaction is 5, and the reaction time is 1 hour.

[0101] The pH of the precipitation reaction is 10.

[0102] The multi-stage condensation separation includes a first cooling section and a second cooling section. The first cooling section is used to condense aluminum-containing chlorinated flue gas to obtain an aluminum-containing solid phase, and the second cooling section is used to condense aluminum-containing chlorinated flue gas to obtain liquid chlorine. The temperature of the first cooling section is 120℃, and the temperature of the second cooling section is -60℃.

[0103] The multi-stage condensation separation also includes a third cooling section and a fourth cooling section. The third cooling section is used to condense aluminum-containing chlorinated flue gas to obtain an iron-containing solid phase, and the fourth cooling section is used to condense aluminum-containing chlorinated flue gas to obtain a silicon-containing liquid phase. The temperature of the third cooling section is 250℃, and the temperature of the fourth cooling section is 35℃.

[0104] The relevant experimental data and results are as follows:

[0105] The yields of aluminum in the aluminum-containing solid phase and chromium in the trivalent chromium solution obtained from each embodiment and comparative example were statistically analyzed, and the recovery rates of valuable elements such as aluminum and chromium were calculated. In addition, the weight content of cyanide and hexavalent chromium in the decyanation material were statistically analyzed, and the results are shown in Table 1.

[0106] Table 1. Recovery rates of valuable elements and weight contents of cyanide and hexavalent chromium in the decyanated feedstocks for each embodiment and comparative example.

[0107]

[0108] As shown in Table 1, the method for recycling overhaul slag and chromium-containing aluminum sludge provided in the embodiments of this disclosure uses chromium-containing aluminum sludge and overhaul slag as raw materials. Through oxidation-reduction reaction, precipitation reaction and chlorination reaction, the removal rate of toxic elements in overhaul slag and chromium-containing aluminum sludge can be simultaneously increased to over 99.95%, and the recovery rate of valuable elements such as aluminum and chromium can be increased to over 95%.

[0109] In summary, the method for recycling overhaul slag and chromium-containing aluminum sludge provided in the embodiments of this disclosure utilizes the redox properties of chromium-containing aluminum sludge and overhaul slag to achieve synergistic "detoxification." Furthermore, this method recovers valuable elements such as aluminum and chromium through a chlorination reaction. Therefore, this method not only achieves the harmless treatment of overhaul slag and chromium-containing aluminum sludge but also effectively recovers valuable elements such as chromium and aluminum.

[0110] In addition, in the method for recycling overhaul slag and chromium-containing aluminum sludge provided in the embodiments of this disclosure, the carbon in the overhaul slag has the characteristics of fast heating rate and uniform heating, which can improve the reaction rate and degree of chlorination reaction, thereby promoting the full conversion of aluminum and chromium in the precipitate into aluminum chloride salts and chromium chloride salts.

[0111] In addition, the method for recycling overhaul slag and chromium-containing aluminum sludge provided in the embodiments of this disclosure can also recover the heat of the chromium-containing chlorinated slag obtained from the chlorination reaction and use the recovered heat to preheat chlorine gas, thereby realizing the recycling of heat and improving energy utilization efficiency. Furthermore, this method can also regenerate chlorine gas through separation and purification, thus having good economic and social benefits.

[0112] Compared with related technologies, the technical solutions provided by the embodiments of this disclosure have the following advantages:

[0113] The embodiments of this disclosure provide a method for recycling overhaul slag and chromium-containing aluminum sludge. This method aims to simultaneously process overhaul slag (containing fluorides, cyanides, and carbon) and chromium-containing aluminum sludge (containing aluminum and hexavalent chromium) through a series of chemical reactions to achieve the removal of toxic elements and the recovery of valuable elements. The method includes the following steps.

[0114] Redox reaction step: Inorganic acid, chromium-containing aluminum sludge, and overhaul slag are mixed. The acidic environment of the inorganic acid promotes the reaction between hexavalent chromium and cyanide, thereby removing the cyanide. In this step, hexavalent chromium acts as an oxidant, undergoing a redox reaction with cyanide to generate harmless or low-toxicity products, and yielding a decyanated material containing fluoride, carbon, aluminum, and chromium.

[0115] Precipitation reaction step: A calcium-containing basic oxide (e.g., calcium oxide) is used to precipitate the cyanide-removing material to remove chromium, aluminum, and fluorides. The precipitation reaction forms precipitates such as calcium fluoride and aluminum hydroxide, thereby achieving the separation of these elements and obtaining a precipitate containing chromium, aluminum, carbon, and fluorine (which may be partially unprecipitated).

[0116] Chlorination reaction steps: Preheated chlorine gas is used to chlorinate the precipitate, with carbon in the precipitate serving as the heating medium to promote the reaction of chromium and aluminum to form chromium chloride and aluminum chloride. The chlorination reaction produces aluminum-containing chlorinated flue gas and chromium-containing chlorinated slag. The aluminum-containing chlorinated flue gas can be further purified in subsequent steps to obtain an aluminum-containing solid phase, and the chromium-containing chlorinated slag can be washed to obtain a trivalent chromium solution, thereby achieving chromium recovery.

[0117] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined in this disclosure may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this disclosure.

Claims

1. A method for recycling overhaul slag and chromium-containing aluminum sludge, wherein the overhaul slag contains fluoride, cyanide and carbon, and the chromium-containing aluminum sludge contains aluminum and hexavalent chromium, the method comprising: Inorganic acid, the chromium-containing aluminum sludge, and the overhaul slag are mixed to allow the hexavalent chromium to undergo a redox reaction with the cyanide in an acidic environment, resulting in a decyanated material containing fluoride, carbon, aluminum, and chromium. The decyanated material is subjected to a precipitation reaction using a calcium-containing alkaline oxide to obtain a precipitate containing chromium, aluminum, carbon, and fluorine. Preheated chlorine gas is mixed with the precipitate, so that under the action of carbon in the precipitate, the preheated chlorine gas reacts with chromium and aluminum in the precipitate to obtain aluminum-containing chlorinated flue gas and chromium-containing chlorinated slag. The aluminum-containing chlorinated flue gas was separated and purified to obtain an aluminum-containing solid phase; as well as The chromium-containing chloride residue was washed to obtain a solution containing trivalent chromium.

2. The method according to claim 1, wherein, The chlorination reaction is carried out at a temperature of 500℃ to 900℃ for a duration of 0.5h to 3h.

3. The method according to claim 1, wherein, The chlorination reaction is carried out using microwave heating.

4. The method according to claim 1, wherein, The pH of the redox reaction is 4 to 6, and the reaction time is 0.5 h to 2 h.

5. The method according to claim 1, wherein, The weight of cyanide in the decyanation material is less than or equal to 0.05% of the weight of the decyanation material, and the weight of hexavalent chromium in the decyanation material is less than or equal to 0.05% of the weight of the decyanation material.

6. The method according to claim 1, wherein, The pH of the precipitation reaction is 8-11.

7. The method according to claim 1, wherein, The step of separating and purifying the aluminum-containing chlorinated flue gas to obtain an aluminum-containing solid phase includes: The aluminum-containing chlorinated flue gas is subjected to multi-stage condensation and separation to obtain an aluminum-containing solid phase and liquid chlorine; and The liquid chlorine is vaporized to obtain chlorine gas.

8. The method according to claim 7, wherein, The multi-stage condensation separation includes a first cooling section and a second cooling section. The first cooling section is used to condense the aluminum-containing chlorinated flue gas to obtain an aluminum-containing solid phase, and the second cooling section is used to condense the aluminum-containing chlorinated flue gas to obtain liquid chlorine. The temperature of the first cooling section is 70℃~170℃, and the temperature of the second cooling section is -70℃~-40℃.

9. The method according to claim 8, wherein, In the case that the overhaul slag also includes iron and silicon, the multi-stage condensation separation further includes a third cooling section and a fourth cooling section. The third cooling section is used to condense the aluminum-containing chlorinated flue gas to obtain an iron-containing solid phase, and the fourth cooling section is used to condense the aluminum-containing chlorinated flue gas to obtain a silicon-containing liquid phase. The temperature of the third cooling section is 190℃~290℃, and the temperature of the fourth cooling section is 20℃~50℃.

10. The method according to any one of claims 7 to 9, wherein, Before washing the chromium-containing chloride residue to obtain a trivalent chromium solution, and after vaporizing the liquid chlorine to obtain chlorine gas, the method further includes: The chlorine gas is exchanged with the chromium-containing chlorinated slag to obtain preheated chlorine gas.

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