Method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge

Abstract

The present disclosure provides a method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge, comprising: mixing an inorganic acid, chromium-containing aluminum sludge, and overhaul slag to obtain a decyanated material; using an alkaline component to carry out a precipitation reaction on the decyanated material to obtain a precipitate material; mixing first preheated silicon tetrachloride with the precipitate material to obtain first chlorinated flue gas and first chromium-containing chlorinated slag; mixing second preheated silicon tetrachloride with the first chromium-containing chlorinated slag to obtain second chlorinated flue gas and second chromium-containing chlorinated slag; separately carrying out separation and purification on the first chlorinated flue gas and the second chlorinated flue gas to obtain an aluminum-containing solid phase, an iron-containing solid phase, and silicon tetrafluoride; and washing the second chromium-containing chlorinated slag to obtain a trivalent chromium-containing solution.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to Chinese Patent Application No. 202411798740.4, filed on December 9, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present disclosure relates to the technical field of resource utilization of hazardous waste, and in particular, to a method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge. BACKGROUND

[0003] A lining of an aluminum electrolytic cell is eroded over a long period by electrolyte, high-temperature molten aluminum, and the like, so that the electrolyte easily penetrates into the lining of the aluminum electrolytic cell, resulting in damage, deformation, or even cracking of the lining. Therefore, to avoid the lining being further damaged, a material of the penetrated portion of the lining is required to be replaced, and the replaced material is referred to as overhaul slag. At present, main components of the overhaul slag include waste cathode carbon blocks, waste refractory materials, and waste thermal insulation materials, and the like. In the overhaul slag, in waste cathode carbon blocks, mass content of carbon ranges from 30% to 70%, the mass content of fluorides ranges from 30% to 50%, and the mass content of cyanide is about 0.2%. Main components of both the waste refractory materials and waste thermal insulation materials include silicon nitride and silicon carbide. In addition, the overhaul slag also contains trace amounts of cyanides, which may be formed by a reaction of sodium invading from ends and sides of the aluminum electrolytic cell with nitrogen in the air at a high temperature of 800°C.

[0004] Although differences in factors such as an electrolyte composition, a current capacity, operation procedures, and lining replacement schedules of the aluminum electrolytic cell may lead to differences in a specific composition of the overhaul slag, the main components of the overhaul slag are basically the same at the present stage, all including carbon, fluorides, and small amounts of sodium, aluminum, calcium, iron, silicon, lithium, and cyanides. Since the overhaul slag contains a large amount of soluble fluorides and cyanides, it has been classified as hazardous waste at present. Direct stockpiling or landfill disposal of the overhaul slag will seriously affect the environment and even harm human health. Therefore, the realization of the harmless treatment and high-value utilization of the overhaul slag is of great significance for promoting the green and high-quality development of the aluminum industry.

[0005] In addition, a lime-roasting process and a lime-free roasting process are mainly adopted for industrial production of sodium dichromate. Compared with the lime-roasting process, the lime-free roasting process is cleaner and more efficient. However, in the lime-free roasting process, aluminum-silicon compounds will react with soda ash to form substantial amounts of sodium silicate and sodium metaaluminate. These sodium silicate and sodium metaaluminate will enter an alkaline leachate and generate a large amount of chromium-containing aluminum sludge, a yield of which is about 5 to 10 times that of chromium-containing aluminum sludge generated in the lime-roasting process. The chromium-containing aluminum sludge generally contains hexavalent chromium, which makes the chromium-containing aluminum sludge have highly toxic. Therefore, the chromium-containing aluminum sludge is also classified as the hazardous waste. If the chromium-containing aluminum sludge is directly stacked or directly discharged, it will also cause serious harm to the environment.

[0006] At present, treatment of the overhaul slag and the chromium-containing aluminum sludge is dominated by harmless disposal, and existing techniques are difficult to achieve effective and simultaneous recovery of valuable elements such as chromium, aluminum, and iron. SUMMARY

[0007] According to a method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge provided by one or more embodiments of the present disclosure, a problem of how to simultaneously improve recovery rates of chromium, aluminum, and iron from overhaul slag and chromium-containing aluminum sludge is solved.

[0008] In a first aspect, the present disclosure provides a method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge. The overhaul slag contains fluorides, cyanides, iron, and carbon, and the chromium-containing aluminum sludge contains aluminum, iron and hexavalent chromium. The method includes:

[0009] mixing an inorganic acid, the chromium-containing aluminum sludge, and the overhaul slag to make the hexavalent chromium and the cyanide undergo a redox reaction in an acidic environment, to obtain a decyanated material containing fluorides, carbon, aluminum, iron, and chromium; subjecting the decyanated material to a precipitation reaction by using an alkaline component, to obtain a precipitated material containing the carbon, aluminum, chromium, iron, and fluorine; mixing a first preheated silicon tetrachloride with the precipitated material to make the first preheated silicon tetrachloride undergo a first chlorination reaction with the iron and fluorine in the precipitated material under an action of the carbon in the precipitated material, to obtain a first chlorination flue gas containing the iron and fluorine as well as a first chromium-containing chlorination residue containing the chromium, aluminum, carbon, and fluorine; mixing a second preheated silicon tetrachloride with the first chromium-containing chlorination residue to make the second preheated silicon tetrachloride undergo a second chlorination reaction with the chromium, aluminum, and fluorine in the first chromium-containing chlorination residue under an action of the carbon in the first chromium-containing chlorination residue, to obtain a second chlorination flue gas containing the aluminum and fluorine, and a second chromium-containing chlorination residue; separating and purifying the first chlorination flue gas and the second chlorination flue gas respectively, to obtain an aluminum-containing solid phase, an iron-containing solid phase, and silicon tetrafluoride; and washing the second chromium-containing chlorination residue to obtain a solution containing trivalent chromium. BRIEF DESCRIPTION OF DRAWINGS

[0010] The accompanying drawings are incorporated into and constitute a part of the specification, and illustrate embodiments consistent with the present disclosure, which are used together with the specification to explain the principles of the present disclosure.

[0011] To more clearly describe the technical solutions in the embodiments or the related art of the present disclosure, the drawings required for describing the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can derive other drawings based on these drawings without creative labor.

[0012] FIG. 1 shows a schematic flowchart of a method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge according to an embodiment of the present disclosure.

[0013] FIG. 2 shows a detailed schematic flowchart of a method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge according to an embodiment of the present disclosure.

[0014] FIG. 3 shows an actual schematic flowchart of a method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0015] To make the purposes, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are partial embodiments of the present disclosure, rather than all embodiments. All embodiments obtained by those skilled in the art based on the embodiments of the present disclosure without creative labor shall fall within the protection scope of the present disclosure.

[0016] Various embodiments of the present disclosure may be described in the form of numerical ranges. It should be understood that such range descriptions are merely for convenience and conciseness, and shall not be interpreted as rigid limitations on the scope of the present disclosure. Therefore, the described ranges shall be deemed to specifically disclose all sub-ranges and individual values within the ranges. For example, a range description of 1 to 6 shall be regarded as specifically disclosing sub-ranges such as 1 to 3, 1 to 4, 1 to 5, 2 to 4, 2 to 6 and 3 to 6, as well as individual numbers of 1, 2, 3, 4, 5 and 6, and this rule applies to all ranges regardless of types. In addition, every time a numerical range is mentioned herein, it covers any cited numbers (fractions or integers) within the range.

[0017] Terms such as "comprise" used herein mean "including but not limited to". Relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or sequence between such entities or operations. The term "and / or" describes an association relationship of associated objects and indicates three possible relationships. For example, A and / or B may indicate that A exists alone, A and B exist simultaneously, or B exists alone, where A and B may be singular or plural. "At least one" means one or more, and "plural" means two or more. Expressions such as "at least one", "at least one of the following" or the like refer to any combination of the items, including single items or combinations of multiple items. For example, "at least one of a, b or c" or "at least one of a, b and c" may all refer to a, b, c, a-b, a-c, b-c or a-b-c, where a, b and c may each be singular or plural. The "parts-by notation" such as parts by weight, parts by mass, etc., indicates a proportional relationship between components. For proportional relationships mentioned herein, parameters described in sequence shall be interpreted as antecedents of the proportional formulas, and proportional figures shall be interpreted as consequents of the proportional formulas. For example, if a mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one-to-one to the proportional numbers in the ratio in the described order, i.e., mass of substance A : mass of substance B : mass of substance C = 1:2:3.

[0018] Unless otherwise specified, various raw materials, reagents, instruments and equipment mentioned herein are all commercially available or may be prepared by existing methods.

[0019] FIG. 1 shows a schematic flowchart of a method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge according to an embodiment of the present disclosure.

[0020] As shown in FIG. 1, an embodiment of the present disclosure provides a method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge. The overhaul slag contains fluorides, cyanides, iron, and carbon, and the chromium-containing aluminum sludge contains aluminum, iron, and hexavalent chromium. The method includes:

[0021] step S1, mixing an inorganic acid, the chromium-containing aluminum sludge, and the overhaul slag to make the hexavalent chromium and the cyanide undergo a redox reaction in an acidic environment, to obtain a decyanated material containing fluorides, carbon, aluminum, iron, and chromium;

[0022] step S2, subjecting the decyanated material to a precipitation reaction by using an alkaline component, to obtain a precipitated material containing the carbon, aluminum, chromium, iron, and fluorine;

[0023] step S3, mixing a first preheated silicon tetrachloride with the precipitated material to make the first preheated silicon tetrachloride undergo a first chlorination reaction with the iron and fluorine in the precipitated material under an action of the carbon in the precipitated material, to obtain a first chlorination flue gas containing the iron and fluorine as well as a first chromium-containing chlorination residue containing the chromium, aluminum, carbon, and fluorine;

[0024] step S4, mixing a second preheated silicon tetrachloride with the first chromium-containing chlorination residue to make the second preheated silicon tetrachloride undergo a second chlorination reaction with the chromium, aluminum, and fluorine in the first chromium-containing chlorination residue under an action of the carbon in the first chromium-containing chlorination residue, to obtain a second chlorination flue gas containing the aluminum and fluorine as well as a second chromium-containing chlorination residue;

[0025] step S5, separating and purifying the first chlorination flue gas and the second chlorination flue gas respectively, to obtain an aluminum-containing solid phase, an iron-containing solid phase, and silicon tetrafluoride; and

[0026] step S6, washing the second chromium-containing chlorination residue to obtain a solution containing trivalent chromium.

[0027] It should be noted that the carbon in the overhaul slag may significantly improve fluidization quality of the chromium-containing aluminum sludge, and thus progress of the redox reaction is effectively promoted. The carbon in the overhaul slag may be present in the form of carbonaceous material or in the form of silicon carbide. In a case that the carbon in the overhaul slag is present in the form of the carbonaceous material, a portion of the carbonaceous material will be lost during the first chlorination reaction and the second chlorination reaction; while in a case that the carbon in the overhaul slag is present in the form of the silicon carbide, the loss of the silicon carbide during the first chlorination reaction and the second chlorination reaction is relatively small due to stable characteristics of the silicon carbide.

[0028] It should be noted that the precipitated material is required to be subjected to a purification treatment before the chlorination reaction to remove moisture from the precipitated material, and thus loss of the first preheated silicon tetrachloride is avoided. The purification treatment may be a drying treatment.

[0029] It should be noted that a temperature of the first preheated silicon tetrachloride may be lower than a temperature of the first chlorination reaction. The temperature of the first preheated silicon tetrachloride is determined according to actual heat exchange conditions. Regardless of whether an initial temperature of the first preheated silicon tetrachloride is high or low, the first preheated silicon tetrachloride can be rapidly heated to the temperature of the first chlorination reaction by a heating way of microwave heating for the first chlorination reaction. Similarly, a temperature of the second preheated silicon tetrachloride is also required to be clearly controlled.

[0030] It should be noted that both the first chlorination reaction and the second chlorination reaction may be carried out in a gas-solid fluidized bed reactor. The gas-solid fluidized bed reactor can realize efficient mixing and contact between the first preheated silicon tetrachloride and the precipitated material, as well as between the second preheated silicon tetrachloride and the first chromium-containing chlorination residue, and has characteristics of fast mass and heat transfer rates and a high reaction efficiency.

[0031] It should be noted that the inorganic acid may be hydrochloric acid, so that synergistic effects are produced with the first preheated silicon tetrachloride and the second preheated silicon tetrachloride in the subsequent first chlorination reaction and second chlorination reaction respectively, to generate chromium-containing chloride salts, iron-containing chloride salts, and aluminum-containing chloride salts.

[0032] It should be noted that the alkaline component may be ammonia water or an alkaline metal oxide. In a case that the alkaline metal oxide is calcium oxide, the fluorine in the precipitated material is present in the form of calcium fluoride. At this time, products obtained from the precipitation reaction, in addition to the precipitated material, also include a waste liquid containing calcium and other unreacted impurities. The waste liquid may be further treated to obtain a harmless waste liquid. In a case that the alkaline component is the ammonia water, the fluorine in the precipitate is present in the form of fluorine-containing compounds (e.g., aluminum fluoride). At this time, the products obtained from the precipitation reaction, in addition to the precipitated material, also include a mixed solution formed by a portion of incompletely reacted ammonia water and soluble fluorine-containing compounds. The mixed solution is first required to be treated with a calcium-containing compound (generally calcium oxide) to make the fluorine-containing compounds in the mixed solution form calcium fluoride to precipitate out, and the remaining mixed solution may be further treated to obtain a harmless waste liquid.

[0033] It should be noted that after washing the second chromium-containing chlorination residue, chromium chloride may be removed, so that a high-purity solution containing trivalent chromium is obtained.

[0034] It should be noted that the overhaul slag is also required to be ground before use, to control a particle size of the overhaul slag to be <10 gm. The overhaul slag within this particle size range has a high specific surface area. The overhaul slag with a high specific surface area can increase its contact area with the chromium-containing aluminum sludge, so that the cyanides in the overhaul slag is capable of fully undergoing the redox reaction with the hexavalent chromium in the chromium-containing aluminum sludge.

[0035] It should be noted that sources of the first preheated silicon tetrachloride and the second preheated silicon tetrachloride may be silicon tetrachloride, which is a hazardous waste generated during production of polysilicon.

[0036] It should be noted that a tail residue after washing the second chromium-containing chlorination residue has reached harmless standards, and can be applied to multiple fields such as construction and fillers.

[0037] In summary, the embodiments of the present disclosure provide a method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge. Through the redox reaction, precipitation reaction, and chlorination reactions, toxic elements (such as cyanides and hexavalent chromium) are capable of being effectively removed from the overhaul slag and chromium-containing aluminum sludge, and thus efficient recovery of valuable elements (such as aluminum, iron, and chromium) is achieved. Advantages of the method are mainly reflected in the following aspects:

[0038] (1) Removal of toxic elements: cyanides and hexavalent chromium are converted into harmless or low-toxicity products through redox reaction and precipitation reaction, and thus effective removal of toxic elements is achieved;

[0039] (2) Recovery of valuable elements: fluorine, aluminum, iron, and chromium are respectively converted into corresponding chloride salts through multiple chlorination reactions, and high-purity valuable element products with a relatively high purity are obtained via subsequent purification steps;

[0040] (3) Environmentally friendly: by-products generated in the whole process (such as ammonia, carbon dioxide, silicon tetrafluoride, etc.) are all harmless or low-toxicity substances, and thus environmental protection requirements are satisfied.

[0041] Therefore, according to this method, through a series of chemical reactions, simultaneous recovery and utilization of the valuable elements from the overhaul slag and chromium-containing aluminum sludge is achieved, so that not only a removal effect of toxic elements is improved, but also a recovery rate of valuable elements is effectively improved, and thus efficient resource recovery is achieved. This provides a new idea and method for solving industrial waste problems, and helps to achieve sustainable utilization of resources and environmental protection.

[0042] In some optional embodiments, a temperature of the first chlorination reaction ranges from 500°C to 700°C, and a time of the first chlorination reaction ranges from 0.5 h to 2 h; and / or

[0043] a temperature of the second chlorination reaction ranges from 800°C to 900°C, and a time of the second chlorination reaction ranges from 0.5 h to 2 h.

[0044] In some embodiments, the temperature of the first chlorination reaction may range from 500°C to 700°C, and the time of the first chlorination reaction may range from 0.5 h to 2 h. Under the action of the carbon in the precipitated material, sufficient reaction among the first preheated silicon tetrachloride and iron and fluorine in the precipitated material is promoted by the first chlorination reaction, to obtain iron-containing chlorides and silicon tetrafluoride, thereby facilitating the subsequent second chlorination reaction and separation and purification steps. In addition, the temperature of the second chlorination reaction may range from 800°C to 900°C, and the time of the second chlorination reaction may range from 0.5 h to 2 h. Under the action of the carbon in the first chromium-containing chlorination residue, sufficient reaction among the second preheated silicon tetrachloride and chromium, aluminum, and fluorine in the first chromium-containing chlorination residue is promoted by the second chlorination reaction, to obtain aluminum-containing chloride salts, chromium-containing chloride salts, and silicon tetrafluoride, thereby facilitating subsequent separation, purification, and washing steps.

[0045] The temperature of the first chlorination reaction may be 500°C, 520°C, 540°C, 560°C, 580°C, 600°C, 620°C, 640°C, 660°C, 680°C, or 700°C.

[0046] The time of the first chlorination reaction may be 0.5 h, 1.0 h, 1.5 h, or 2.0 h.

[0047] The temperature of the second chlorination reaction may be 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, or 900°C.

[0048] The time of the second chlorination reaction may be 0.5 h, 1.0 h, 1.5 h, or 2.0 h.

[0049] In some optional embodiments, both the first chlorination reaction and the second chlorination reaction are carried out by a heating way of microwave heating.

[0050] In some embodiments, both the first chlorination reaction and the second chlorination reaction are carried out by a heating way of microwave heating. During the microwave heating, the carbon in the precipitated material and the carbon in the first chromium-containing chlorination residue may serve as a highly efficient microwave-absorbing material, absorbing and storing energy transferred by microwave heating. The carbon that has stored sufficient energy can not only cause the precipitated material and the first chromium-containing chlorination residue to be rapidly heated, so that a temperature of the precipitated material meets the requirements of the first chlorination reaction and a temperature of the first chromium-containing chlorination residue meets the requirements of the second chlorination reaction, but also may make other materials in the precipitate material be uniformly dispersed during the microwave heating. In addition, the carbon in the precipitated material and the carbon in the first chromium-containing chlorination residue can also serve as a carbon sources to enhance the intensity of the first and second chlorination reactions, promoting chromium, iron and aluminum to react, thereby generating chromium-containing chloride salts, iron-containing chloride salts and aluminum-containing chloride salts.

[0051] In some optional embodiments, a pH value of the redox reaction ranges from 4 to 6, and a time of the redox reaction ranges from 0.5 h to 2 h.

[0052] In some embodiments, the pH value of the redox reaction may range from 4 to 6, and the time of the redox reaction may range from 0.5 h to 2 h. Under an acidic environment provided by the inorganic acid, the pH value of the redox reaction may reach 4 to 6, so that the hexavalent chromium in chromium-containing aluminum sludge and cyanides in spent potlining can fully react, so that cyanides are oxidized to harmless carbon dioxide and nitrogen and the hexavalent chromium is reduced into harmless trivalent chromium, and thus toxic elements are effectively removed from the chromium-containing aluminum sludge and the overhaul slag.

[0053] The pH value of the redox reaction may 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.

[0054] The time of the redox reaction may be 0.5 h, 1 h, 1.5 h, or 2 h.

[0055] In some optional embodiments, a weight of the cyanides in the decyanated material is less than or equal to 0.05% of a weight of the decyanated material, and a weight of the hexavalent chromium in the decyanated material is less than or equal to 0.05% of the weight of the decyanated material.

[0056] In some embodiments, the weight of the cyanides in the decyanated material may be less than or equal to 0.05% of the weight of the decyanated material, and the weight of the hexavalent chromium in the decyanated material may be less than or equal to 0.05% of the weight of the decyanated material, which indicates that the hexavalent chromium in the chromium-containing aluminum sludge and the cyanides in the overhaul slag have already undergone sufficient reaction during the redox reaction.

[0057] In some optional embodiments, a pH value of the precipitation reaction ranges from 8 to 11.

[0058] In some embodiments, the pH value of the precipitation reaction may range from 8 to 11, which indicates that the precipitation reaction is carried out in an alkaline environment, and the alkaline environment may promote the conversion of aluminum, iron, and chromium into hydroxide precipitates, and thus promoting the conversion of aluminum, iron, and chromium in the decyanated material into the precipitated material. In addition, in a case that the alkaline component is calcium oxide, in an alkaline environment, the calcium in the calcium oxide can undergo a precipitation reaction with fluorine in the decyanated material to obtain a calcium fluoride precipitate, and thus facilitating subsequent recovery and treatment.

[0059] The pH value of the precipitation reaction may be 8, 8.5, 9.0, 9.5, 10.0, 10.5, or 11.0.

[0060] FIG. 2 shows a detailed schematic flowchart of a method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge according to an embodiment of the present disclosure.

[0061] FIG. 3 shows an actual schematic flowchart of a method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge according to an embodiment of the present disclosure.

[0062] In some optional embodiments, as shown in FIG. 2 and FIG. 3, the separating and purifying the first chlorination flue gas and the second chlorination flue gas respectively, to obtain the aluminum-containing solid phase, the iron-containing solid phase, and the silicon tetrafluoride include the following steps:

[0063] step S501, subjecting the first chlorination flue gas to a first multi-stage condensation to obtain the iron-containing solid phase, a first circulating liquid-phase silicon tetrachloride, and a first gaseous-phase silicon tetrafluoride;

[0064] step S502, subjecting the second chlorination flue gas to a second multi-stage condensation to obtain the aluminum-containing solid phase, a second circulating liquid-phase silicon tetrachloride, and a second gaseous-phase silicon tetrafluoride;

[0065] step S503, combining the first gaseous-phase silicon tetrafluoride and the second gaseous-phase silicon tetrafluoride to obtain the silicon tetrafluoride; and

[0066] step S504, vaporizing the first circulating liquid-phase silicon tetrachloride and the second circulating liquid-phase silicon tetrachloride respectively to obtain a first circulating gaseous-phase silicon tetrachloride and a second circulating gaseous-phase silicon tetrachloride.

[0067] In some embodiments, different multi-stage condensation separation and vaporization modes are used for separating and purifying different chlorination flue gases. For the first chlorination flue gas, separation is realized through first multi-stage condensation, and based on a difference in boiling points between the iron-containing solid phase and silicon tetrafluoride in the first chlorination flue gas containing the iron and fluorine, the iron and fluorine are respectively condensed and precipitated out, thereby achieving recovery of the iron and fluorine. For the second chlorination flue gas, separation is realized through second multi-stage condensation, and based on a difference in boiling points between the aluminum-containing solid phase and the silicon tetrafluoride in the second chlorination flue gas containing the aluminum and fluorine, the aluminum and fluorine are respectively condensed and precipitated out, and thus recovery of the aluminum and fluorine is achieved. In addition, vaporization of separated liquid-phase silicon tetrachloride can realize regeneration of silicon tetrachloride.

[0068] It should be noted that a temperature for vaporizing the precipitated first circulating liquid-phase silicon tetrachloride and second circulating liquid-phase silicon tetrachloride may range from 70°C to 100°C.

[0069] In some optional embodiments, the first multi-stage condensation includes a first cooling section and a second cooling section. The first cooling section is configured to condense the first chlorination flue gas containing the iron and fluorine to obtain the iron-containing solid phase, and the second cooling section is configured to condense the first chlorination flue gas containing the iron and fluorine to respectively obtain the first gaseous-phase silicon tetrafluoride and the first circulating liquid-phase silicon tetrachloride. A temperature of the first cooling section ranges from 70°C to 290°C, and a temperature of the second cooling section ranges from 20°C to 50°C.

[0070] In some embodiments, the first multi-stage condensation may include a first cooling section. The first cooling section may be configured to condense the first chlorination flue gas containing the iron and fluorine to obtain an iron-containing solid phase. The temperature of the first cooling section may range from 70°C to 290°C. Based on a difference in boiling points between the iron chloride component and other components in the first chlorination flue gas, the iron chloride component may be condensed into an iron-containing solid phase to achieve recovery of the iron. In addition, the first multi-stage condensation may include a second cooling section. The second cooling section is configured to condense the first chlorination flue gas containing the iron and fluorine to respectively obtain a first gaseous-phase silicon tetrafluoride and a first circulating liquid-phase silicon tetrachloride. The temperature of the second cooling section may range from 20°C to 50°C. Based on a difference in boiling points between the silicon tetrafluoride and the silicon tetrachloride in the first chlorination flue gas, the silicon tetrachloride component can be condensed into a first circulating liquid-phase silicon tetrachloride, so that separation of the silicon tetrafluoride and silicon tetrachloride is achieved, thereby facilitating subsequent regeneration of the silicon tetrachloride by vaporization, and thus facilitating the recycling use of the silicon tetrachloride.

[0071] The temperature of the first cooling section may be 70°C, 90°C, 110°C, 130°C, 150°C, 170°C, 190°C, 210°C, 230°C, 250°C, 270°C, or 290°C.

[0072] The temperature of the second cooling section may be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, or 50°C.

[0073] In some optional embodiments, the second multi-stage condensation includes a third cooling section and a fourth cooling section. The third cooling section is configured to condense the second chlorination flue gas containing the aluminum and fluorine to obtain the aluminum-containing solid phase. The fourth cooling section is configured to condense the second chlorination flue gas containing the aluminum and fluorine to respectively obtain the second gaseous-phase silicon tetrafluoride and the second circulating liquid-phase silicon tetrachloride. A temperature of the third cooling section ranges from 70°C to 170°C, and a temperature of the fourth cooling section ranges from 20°C to 50°C.

[0074] In some embodiments, the second multi-stage condensation may include a third cooling section. The third cooling section may be configured to condense the second chlorination flue gas containing the aluminum and fluorine to obtain the aluminum-containing solid phase. The temperature of the third cooling stage may range from 70°C to 170°C. Based on a difference in boiling points between the aluminum chloride component and other components in the second chlorination flue gas, the aluminum chloride component may be condensed into an aluminum-containing solid phase to recover aluminum. In addition, the second multi-stage condensation may include a fourth cooling section. The fourth cooling section may be configured to condense the second chlorination flue gas containing the aluminum and fluorine to respectively obtain the second gaseous-phase silicon tetrafluoride and the second circulating liquid-phase silicon tetrachloride. The temperature of the fourth cooling section may range from 20°C to 50°C. Based on a difference in boiling points between the silicon tetrafluoride and the silicon tetrachloride in the second chlorination flue gas, the silicon tetrachloride component may be condensed into a second circulating liquid-phase silicon tetrachloride, so that separation of the silicon tetrafluoride and the silicon tetrachloride is achieved, thereby facilitating subsequent regeneration of the silicon tetrachloride by vaporization, and thus facilitating the recycling use of the silicon tetrachloride.

[0075] The temperature of the third cooling section may be 70°C, 90°C, 110°C, 130°C, 150°C, or 170°C.

[0076] The temperature of the fourth cooling section may be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, or 50°C.

[0077] In some optional embodiments, before the washing the second chromium-containing chlorination residue to obtain the solution containing trivalent chromium, and after the vaporizing the first circulating liquid-phase silicon tetrachloride and the second circulating liquid-phase silicon tetrachloride respectively to obtain the first circulating gaseous-phase silicon tetrachloride and the second circulating gaseous-phase silicon tetrachloride, the above method further includes the following steps:

[0078] step S601, vaporizing and classifying the silicon tetrachloride to obtain the first gaseous-phase silicon tetrachloride and the second gaseous-phase silicon tetrachloride respectively;

[0079] step S602, respectively introducing the first gaseous-phase silicon tetrachloride and the first circulating gaseous-phase silicon tetrachloride into the first chromium-containing chlorination residue for heat exchange, to obtain the first preheated silicon tetrachloride; and

[0080] step S603, respectively introducing the second gaseous-phase silicon tetrachloride and the second circulating   gaseous-phase   silicon tetrachloride into the second chromium-containing chlorination residue for heat exchange, to obtain the second preheated silicon tetrachloride.

[0081] In some embodiments, the silicon tetrachloride can be vaporized and classified. Supplementation of the first gas-phase circulating silicon tetrachloride and the second gas-phase circulating silicon tetrachloride is carried out according to the actual consumption of silicon tetrachloride in the first and second chlorination reactions. In addition, through heat exchange of the first gaseous-phase silicon tetrachloride and the first circulating gaseous-phase silicon tetrachloride with the first chromium-containing chlorination residue, heat of the first chromium-containing chlorination residue may be recovered; and through heat exchange of the second gaseous-phase silicon tetrachloride and the second circulating gaseous-phase silicon tetrachloride with the second chromium-containing chlorination residue, heat of the second chromium-containing chlorination residue may be recovered. That is to say, the heat of the first chromium-containing chlorination residue can be utilized to preheat the first gaseous-phase silicon tetrachloride and the first circulating gaseous-phase silicon tetrachloride to obtain the first preheated silicon tetrachloride, and the heat of the second chromium-containing chlorination can be utilized to preheat the second gaseous-phase silicon tetrachloride and the second circulating gaseous-phase silicon tetrachloride to obtain the second preheated silicon tetrachloride, so as to recover the heat of the first chlorination reaction and the second chlorination reaction, and thus the overall energy consumption of the method of the present disclosure is reduced, and a thermal efficiency of the method of the present disclosure is improved.

[0082] The present disclosure will be further described below in conjunction with specific examples. For experimental methods without specified conditions in the following examples, tests are carried out in accordance with Chinese national standards / industrial standards. If there is no corresponding Chinese national / industrial standards, tests are carried out in accordance with general international standards, conventional conditions or conditions recommended by manufacturers.

[0083] Example 1

[0084] As shown in FIG. 2, a method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge. The overhaul slag contains fluorides, cyanides, iron, and carbon, and the chromium-containing aluminum sludge contains aluminum, iron, and hexavalent chromium. The method includes:

[0085] step S1, mixing an inorganic acid, the chromium-containing aluminum sludge, and the overhaul slag (with a particle size of less than 10 um) to make the hexavalent chromium and the cyanide undergo a redox reaction in an acidic environment, to obtain a decyanated material containing fluorides, carbon, aluminum, iron, and chromium;

[0086] step S2, subjecting the decyanated material to a precipitation reaction by using calcium oxide, to obtain a precipitated material containing the carbon, aluminum, chromium, iron, and fluorine;

[0087] step S3, mixing a first preheated silicon tetrachloride with the precipitated material to make the first preheated silicon tetrachloride undergo a first chlorination reaction with the iron and fluorine in the precipitated material under an action of the carbon in the precipitated material, to obtain a first chlorination flue gas containing the iron and fluorine as well as a first chromium-containing chlorination residue containing the chromium, aluminum, carbon, and fluorine;

[0088] step S4, mixing a second preheated silicon tetrachloride with the first chromium-containing chlorination residue to make the second preheated silicon tetrachloride undergo a second chlorination reaction with the chromium, aluminum, and fluorine in the first chromium-containing chlorination residue under an action of the carbon in the first chromium-containing chlorination residue, to obtain a second chlorination flue gas containing the aluminum and fluorine as well as a second chromium-containing chlorination residue;

[0089] step S501, subjecting the first chlorination flue gas containing the iron and fluorine to a first multi-stage condensation to obtain the iron-containing solid phase, a first circulating liquid-phase silicon tetrachloride, and a first gaseous-phase silicon tetrafluoride;

[0090] step S502, subjecting the second chlorination flue gas containing the aluminum and fluorine to a second multi-stage condensation to obtain the aluminum-containing solid phase, a second circulating liquid-phase silicon tetrachloride, and a second gaseous-phase silicon tetrafluoride;

[0091] step S503. combining the first gaseous-phase silicon tetrafluoride and the second gaseous-phase silicon tetrafluoride to obtain the silicon tetrafluoride;

[0092] step S504, vaporizing the first circulating liquid-phase silicon tetrachloride and the second circulating liquid-phase silicon tetrachloride respectively to obtain a first circulating gaseous-phase silicon tetrachloride and a second circulating gaseous-phase silicon tetrachloride;

[0093] step S601, vaporizing and classifying the silicon tetrachloride to obtain the first gaseous-phase silicon tetrachloride and the second gaseous-phase silicon tetrachloride respectively;

[0094] step S602, respectively introducing the first gaseous-phase silicon tetrachloride and the first circulating gaseous-phase silicon tetrachloride into the first chromium-containing chlorination residue for heat exchange, to obtain the first preheated silicon tetrachloride;

[0095] step S603, respectively introducing the second gaseous-phase silicon tetrachloride and the second circulating gaseous-phase silicon tetrachloride into the second chromium-containing chlorination residue for heat exchange, to obtain the second preheated silicon tetrachloride; and

[0096] step S6, washing the second chromium-containing chlorination residue to obtain a solution containing trivalent chromium.

[0097] A temperature of the first chlorination reaction is 500°C, and a time of the first chlorination reaction is 2 h.

[0098] A temperature of the second chlorination reaction is 800°C, and a time of the second chlorination reaction is 2 h.

[0099] Both the first chlorination reaction and the second chlorination reaction are carried out by a heating way of microwave heating.

[0100] A pH value of the redox reaction is 4, and a time of the redox reaction is 0.5 h.

[0101] A weight of the cyanides in the decyanated material is less than or equal to 0.05% of a weight of the decyanated material, and a weight of the hexavalent chromium in the decyanated material is less than or equal to 0.05% of the weight of the decyanated material.

[0102] A pH value of the precipitation reaction is 8.

[0103] The first multi-stage condensation includes a first cooling section and a second cooling section. The first cooling section is configured to condense the first chlorination flue gas containing the iron and fluorine to obtain an iron-containing solid phase. The second cooling section is configured to condense the first chlorination flue gas containing the iron and fluorine to respectively obtain the first gaseous-phase silicon tetrafluoride and the first circulating liquid-phase silicon tetrachloride. A temperature of the first cooling section is 70°C, and a temperature of the second cooling section is 20°C.

[0104] The second multi-stage condensation includes a third cooling section and a fourth cooling section. The third cooling section is configured to condense the second chlorination flue gas containing the aluminum and fluorine to obtain the aluminum-containing solid phase. The fourth cooling section is configured to condense the second chlorination flue gas containing the aluminum and fluorine to respectively obtain the second gaseous-phase silicon tetrafluoride and the second circulating liquid-phase silicon tetrachloride. A temperature of the third cooling section is 70°C, and a temperature of the fourth cooling section is 20°C.

[0105] A temperature of vaporization is 70°C.

[0106] Example 2

[0107] On the basis of the content disclosed in Example 1, the reaction conditions are further adjusted as follows:

[0108] The temperature of the first chlorination reaction is 700°C, and the time of the first chlorination reaction is 0.5 h.

[0109] The temperature of the second chlorination reaction is 900°C, and the time of the second chlorination reaction is 0.5 h.

[0110] The pH value of the redox reaction is 6, and the time of the redox reaction is 2 h.

[0111] The pH value of the precipitation reaction is 10.

[0112] The first multi-stage condensation includes a first cooling section and a second cooling section. The first cooling section is configured to condense the first chlorination flue gas containing the iron and fluorine to obtain the iron-containing solid phase. The second cooling section is configured to condense the first chlorination flue gas containing the iron and fluorine to respectively obtain the first gaseous-phase silicon tetrafluoride and the first circulating liquid-phase silicon tetrachloride. The temperature of the first cooling section is 290°C. The temperature of the second cooling section is 50°C.

[0113] The second multi-stage condensation includes a third cooling section and a fourth cooling section. The third cooling section is configured to condense the second chlorination flue gas containing the aluminum and fluorine to obtain the aluminum-containing solid phase. The fourth cooling section is configured to condense the second chlorination flue gas containing the aluminum and fluorine to respectively obtain the second gaseous-phase silicon tetrafluoride and the second circulating liquid-phase silicon tetrachloride. The temperature of the third cooling section is 170°C, and the temperature of the fourth cooling section is 50°C.

[0114] The temperature of vaporization is 100°C.

[0115] Example 3

[0116] On the basis of the content disclosed in Example 1, the reaction conditions are further adjusted as follows:

[0117] The temperature of the first chlorination reaction is 600°C, and the time of the first chlorination reaction is 1 h.

[0118] The temperature of the second chlorination reaction is 850°C, and the time of the second chlorination reaction is 1 h.

[0119] The pH value of the redox reaction is 5, and the time of the redox reaction is 1 h.

[0120] The pH value of the precipitation reaction is 9.

[0121] The first multi-stage condensation includes a first cooling section and a second cooling section. The first cooling section is configured to condense the first chlorination flue gas containing the iron and fluorine to obtain the iron-containing solid phase. The second cooling section is configured to condense the first chlorination flue gas containing the iron and fluorine to respectively obtain the first gaseous-phase silicon tetrafluoride and the first circulating liquid-phase silicon tetrachloride. The temperature of the first cooling section is 150°C, and the temperature of the second cooling section is 30°C.

[0122] The second multi-stage condensation includes a third cooling section and a fourth cooling section. The third cooling section is configured to condense the second chlorination flue gas containing the aluminum and fluorine to obtain the aluminum-containing solid phase. The fourth cooling section is configured to condense the second chlorination flue gas containing the aluminum and fluorine to respectively obtain the second gaseous-phase silicon tetrafluoride and the second circulating liquid-phase silicon tetrachloride. The temperature of the third cooling section is 120°C, and the temperature of the fourth cooling section is 35°C.

[0123] The temperature of vaporization is 85°C.

[0124] Related experimental and effect data are as follows.

[0125] The yields of an aluminum element in the obtained aluminum-containing solid phase, an iron element in the iron-containing solid phase, and a chromium element in the solution containing trivalent chromium of each example are counted, and the recovery rates of the valuable elements such as aluminum, iron, and chromium are calculated. In addition, the weight content of the cyanides and the weight content of the hexavalent chromium in the decyanated material are counted. The results are shown in Table 1.

[0126] Table 1 Recovery rates of valuable elements and weight contents of cyanides and hexavalent chromium in the decyanated material for each example \ Item Group Recovery rate of Al (%) Recovery rate of Cr (%) Recovery rate ofFe(%) Weight content of cyanides in decyanated material (%) Weight content of hexavalent Cr in decyanated material (%) Example 1 95.16 96.23 96.54 0.03 0.04 Example 2 95.67 95.73 96.42 0.02 0.03 Example 3 96.23 97.14 95.85 0.02 0.03

[0127] It can be seen from Table 1, according to the method for synergistically recovering the valuable elements from the overhaul slag and chromium-containing aluminum sludge provided by the embodiments of the present disclosure, the chromium-containing aluminum sludge and overhaul slag are adopted as raw materials. Through redox reaction, precipitation reaction and multiple chlorination reactions, the removal rate of toxic elements in the overhaul slag and chromium-containing aluminum sludge can be simultaneously increased to above 99.95%, and the recovery rates of valuable elements such as aluminum, iron and chromium can be increased to over 95%.

[0128] In summary, the embodiments of the present disclosure provide a method for synergistically recovering valuable elements from spent potlining and chromium-containing aluminum sludge. The aluminum sludge provided by the embodiments of the present disclosure utilizes redox characteristics of the chromium-containing aluminum sludge and the overhaul slag to realize collaborative detoxification. In addition, valuable elements such as aluminum, chromium and iron are recovered via multiple chlorination reactions. Therefore, through the method, not only harmless treatment of the overhaul slag and the chromium-containing aluminum sludge is achieved, but also the valuable elements such as chromium, aluminum, and iron therein are effectively recovered.

[0129] In addition, in the method for synergistically recovering the valuable elements from the overhaul slag and the chromium-containing aluminum sludge provided by the embodiments of the present disclosure, based on the characteristics of a rapid heating rate and uniform heating of the carbon in the overhaul slag and the first chromium-containing chlorination residue, the reaction rates and degrees of the first chlorination reaction and the second chlorination reaction can be increased, and thus promoting the sufficient conversion of the valuable elements such as aluminum, chromium, iron, and fluorine in the precipitated material into aluminum-containing chloride salts, iron-containing chloride salts and chromium-containing chloride salts, and silicon tetrafluoride.

[0130] Furthermore, according to the method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge provided by the embodiments of the present disclosure, the heat of the chromium-containing chlorination residues obtained from each stage of chlorination reaction may be also recovered, and the recovered heat is used for preheating the silicon tetrachloride, thereby recycling use of the heat is achieved, and thus an energy utilization efficiency is improved. In addition, the method may also achieve regeneration of the silicon tetrachloride through separation and purification steps, and thus having good economic and social benefits.

[0131] The technical solutions provided by the embodiments of the present disclosure have the following advantages compared with the related art:

[0132] The embodiments of the present disclosure provide a method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge, which aims to simultaneously treat the overhaul slag (containing fluorides, cyanides, iron, and carbon) and the chromium-containing aluminum sludge (containing aluminum, iron, and hexavalent chromium). A series of chemical reactions are adopted to realize removal of toxic elements and recovery of valuable elements. The method includes the following steps.

[0133] Redox reaction step: an inorganic acid, chromium-containing aluminum sludge and the overhaul slag are mixed. The acidic environment provided by the inorganic acid promotes redox reaction between hexavalent chromium and cyanides to remove cyanides. In this step, hexavalent chromium, as an oxidant, undergoes a redox reaction with cyanides to generate harmless or low-toxicity products, and to obtain a decyanated material containing fluorides, carbon, aluminum, iron, and chromium.

[0134] Precipitation reaction step: an alkaline component (e.g., ammonia water or calcium oxide) is used for making the decyanated material undergo a precipitation reaction, to remove chromium, aluminum, iron, and fluorides therefrom. In addition, the precipitation reaction forms precipitates such as calcium fluoride, aluminum hydroxide and iron hydroxide to realize separation of the above elements, and thus a precipitated material containing carbon, aluminum, chromium, iron, and fluorine (partially unprecipitated) is obtained.

[0135] Chlorination reaction step: the precipitate material is subjected to the first chlorination reaction by using the first preheated silicon tetrachloride, and the carbon in the precipitated material is used as a heating medium to promote the reaction of chromium, iron, and aluminum to form iron-containing chloride salts, chromium-containing chloride salts and aluminum-containing chloride salts. The first chlorination reaction produces a first chlorination flue gas containing iron and fluorine, and a first chromium-containing chlorination residue containing chromium, aluminum, carbon, and fluorine. The first chlorination flue gas can be further purified in subsequent steps to obtain an iron-containing solid phase and silicon tetrafluoride. In addition, a second chlorination reaction is performed on the first chromium-containing chlorination residue, and the carbon in the first chromium-containing chlorination residue is used as a heating medium to promote the reaction of chromium and aluminum to generate chromium chloride salts and aluminum chloride salts. The second chlorination reaction produces a second chlorination flue gas containing aluminum and fluorine, and a second chromium-containing chlorination residue containing chromium. The second chlorination flue gas can be further purified in subsequent steps to obtain an aluminum-containing solid phase and silicon tetrafluoride. The second chromium-containing chlorination residue can be washed to obtain a solution containing trivalent chromium, and thus recovery of chromium is achieved.

[0136] Therefore, the method removes toxic elements from the overhaul slag and 5   chromium-containing aluminum sludge through redox reaction, and recovers aluminum, iron and chromium efficiently via multiple chlorination reactions.

[0137] The above are only specific embodiments of the present disclosure, enabling those skilled in the art to understand or implement the present disclosure. Various modifications to these embodiments will be apparent to those skilled in the art. The general principles defined 10 herein can be implemented in other embodiments without departing from the spirit and scope of the present disclosure. Therefore, the present disclosure will not be limited to the embodiments shown herein, but will conform to the broadest scope consistent with the principles and novel features claimed by the present disclosure.

Claims

1. A method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge, the overhaul slag containing fluorides, cyanides, iron and carbon, the chromium-containing aluminum sludge containing aluminum, iron and hexavalent chromium, the method comprising:mixing an inorganic acid, the chromium-containing aluminum sludge, and the overhaul slag to make the hexavalent chromium and the cyanide to undergo a redox reaction in an acidic environment, to obtain a decyanated material containing fluorides, carbon, aluminum, iron, and chromium;subjecting the decyanated material to a precipitation reaction by using an alkaline component, to obtain a precipitated material containing the carbon, aluminum, chromium, iron, and fluorine;mixing a first preheated silicon tetrachloride with the precipitated material to make the first preheated silicon tetrachloride to undergo a first chlorination reaction with the iron and fluorine in the precipitated material under an action of the carbon in the precipitated material, to obtain a first chlorination flue gas containing the iron and fluorine as well as a first chromium-containing chlorination residue containing the chromium, aluminum, carbon, and fluorine;mixing a second preheated silicon tetrachloride with the first chromium-containing chlorination residue to make the second preheated silicon tetrachloride to undergo a second chlorination reaction with the chromium, aluminum, and fluorine in the first chromium-containing chlorination residue under an action of the carbon in the first chromium-containing chlorination residue, to obtain a second chlorination flue gas containing the aluminum and fluorine as well as a second chromium-containing chlorination residue;separating and purifying the first chlorination flue gas and the second chlorination flue gas, respectively, to obtain an aluminum-containing solid phase, an iron-containing solid phase, and silicon tetrafluoride; andwashing the second chromium-containing chlorination residue to obtain a solution containing trivalent chromium.

2. The method according to claim 1, wherein a temperature of the first chlorination reaction ranges from 500°C to 700°C, and a time of the first chlorination reaction ranges from 0.5 h to 2 h; and / ora temperature of the second chlorination reaction ranges from 800°C to 900°C, and a time of the second chlorination reaction ranges from 0.5 h to 2 h.

3. The method according to claim 1, wherein both the first chlorination reaction and the second chlorination reaction are carried out by a heating way of microwave heating.

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

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

6. The method according to claim 1, wherein a pH value of the precipitation reaction ranges from 8 to 11.

7. The method according to claim 1, wherein the separating and purifying the first chlorination flue gas and the second chlorination flue gas respectively, to obtain the aluminum-containing solid phase, the iron-containing solid phase, and the silicon tetrafluoride, comprises:subjecting the first chlorination flue gas to a first multi-stage condensation, to obtain the iron-containing solid phase, a first circulating liquid-phase silicon tetrachloride, and a first gaseous-phase silicon tetrafluoride;subjecting the second chlorination flue gas to a second multi-stage condensation, to obtain the aluminum-containing solid phase, a second circulating liquid-phase silicon tetrachloride, and a second gaseous-phase silicon tetrafluoride;combining the first gaseous-phase silicon tetrafluoride and the second gaseous-phase silicon tetrafluoride to obtain the silicon tetrafluoride; andvaporizing the first circulating liquid-phase silicon tetrachloride and the second circulating liquid-phase silicon tetrachloride, respectively, to obtain a first circulating gaseous-phase silicon tetrachloride and a second circulating gaseous-phase silicon tetrachloride.

8. The method according to claim 7, wherein the first multi-stage condensation comprises a first cooling section and a second cooling section;the first cooling section is configured to condense the first chlorination flue gas containing the iron and fluorine to obtain the iron-containing solid phase;the second cooling section is configured to condense the first chlorination flue gas containing the iron and fluorine to respectively obtain the first gaseous-phase silicon tetrafluoride and the first circulating liquid-phase silicon tetrachloride; anda temperature of the first cooling section ranges from 70°C to 290°C, and a temperature of the second cooling section ranges from 20°C to 50°C.

9. The method according to claim 7, wherein the second multi-stage condensationcomprises a third cooling section and a fourth cooling section;the third cooling section is configured to condense the second chlorination flue gas containing the aluminum and fluorine to obtain the aluminum-containing solid phase;the fourth cooling section is configured to condense the second chlorination flue gas containing the aluminum and fluorine to respectively obtain the second gaseous-phase silicon tetrafluoride and the second circulating liquid-phase silicon tetrachloride;a temperature of the third cooling section ranges from 70°C to 170°C; anda temperature of the fourth cooling section ranges from 20°C to 50°C.

10. The method according to any one of claims 7 to 9, wherein, before the washing the second chromium-containing chlorination residue to obtain the solution containing trivalent chromium, and after the vaporizing the first circulating liquid-phase silicon tetrachloride and the second circulating liquid-phase silicon tetrachloride respectively to obtain the first circulating gaseous-phase silicon tetrachloride and the second circulating gaseous-phase silicon tetrachloride, the method further comprises:vaporizing and classifying silicon tetrachloride to obtain a first gaseous-phase silicon tetrachloride and a second gaseous-phase silicon tetrachloride respectively;respectively introducing the first gaseous-phase silicon tetrachloride and the first circulating gaseous-phase silicon tetrachloride into the first chromium-containing chlorination residue for heat exchange, to obtain the first preheated silicon tetrachloride; andrespectively introducing the second gaseous-phase silicon tetrachloride and the second circulating gaseous-phase silicon tetrachloride into the second chromium-containing chlorination residue for heat exchange, to obtain the second preheated silicon tetrachloride.

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