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

A method for the synergistic recovery of valuable elements from overhaul slag and chromium-aluminum sludge.

[0001] Cross-references to related applications

[0002] 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

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

[0004] The lining of an aluminum electrolytic cell is constantly corroded by electrolytes and high-temperature molten aluminum, making it easy for electrolytes to seep into the lining and cause damage, deformation, or even cracking. Therefore, to prevent further damage, the material in the seeped-in portion of the lining needs to be replaced; this replaced material is called overhaul slag. Currently, the main components of overhaul slag include waste cathode carbon blocks, waste refractory materials, and waste insulation materials. In overhaul slag, the carbon content of waste cathode carbon blocks is 30%–70% by weight, the fluoride content is 30%–50% by weight, and the cyanide content is approximately 0.2% by weight. The main components of waste refractory materials and waste insulation materials include silicon nitride and silicon carbide. In addition, overhaul slag also contains trace amounts of cyanide, which may be formed by the reaction of sodium that seeps into the ends and edges of the aluminum electrolytic cell with nitrogen gas from the air at a high temperature of 800°C.

[0005] Although differences in electrolyte composition, current capacity, operating procedures, and lining replacement frequency in aluminum electrolytic cells can lead to variations in the specific composition of overhaul slag, its main components are currently largely the same, including carbon, fluorides, and small amounts of sodium, aluminum, calcium, iron, silicon, lithium, and cyanides. Due to the high levels of soluble fluorides and cyanides in overhaul slag, it is currently classified as hazardous waste. Direct stockpiling or landfilling of overhaul slag can severely impact the environment 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.

[0006] In the industrial production of sodium dichromate, two main methods are calcium-containing roasting and calcium-free roasting. Compared to 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 a significant amount of sodium silicate and sodium aluminate. These sodium silicates and sodium aluminates enter the alkaline leachate and produce large quantities of chromium-containing aluminum sludge, approximately 5 to 10 times the yield of the calcium-containing roasting method. Chromium-containing aluminum sludge generally contains hexavalent chromium, making it highly toxic. Therefore, chromium-containing aluminum sludge is classified as hazardous waste. Direct dumping or discharge of chromium-containing aluminum sludge can also cause serious environmental damage.

[0007] Currently, the main approach to treating overhaul slag and chromium-containing aluminum sludge is to achieve harmless treatment. However, current technologies are insufficient to effectively and simultaneously recover valuable elements such as chromium, aluminum, and iron. Summary of the Invention

[0008] A method for synergistically recovering valuable elements from overhaul slag and chromium-containing aluminum sludge by utilizing one or more embodiments of the present disclosure solves the problem of how to simultaneously improve the recovery rate of chromium, aluminum, and iron in overhaul slag and chromium-containing aluminum sludge.

[0009] In a first aspect, this disclosure provides a method for the synergistic recovery of valuable elements from overhaul slag and chromium-containing aluminum sludge, wherein the overhaul slag contains fluorides, cyanides, iron, and carbon, and the chromium-containing aluminum sludge contains aluminum, iron, and hexavalent chromium, and the method includes:

[0010] Inorganic acid, the chromium-containing aluminum sludge, and the overhaul slag are mixed to allow hexavalent chromium to undergo a redox reaction with cyanide in an acidic environment, yielding a decyanated material containing fluoride, carbon, aluminum, iron, and chromium. An alkaline component is used to induce a precipitation reaction in the decyanated material, yielding a precipitate containing carbon, aluminum, chromium, iron, and fluorine. First preheated silicon tetrachloride is mixed with the precipitate, and under the influence of carbon in the precipitate, the first preheated silicon tetrachloride undergoes a first chlorination reaction with the iron and fluorine in the precipitate, yielding a first chlorinated flue gas containing iron and fluorine, and a flue gas containing... A first chromium-containing chlorinated slag containing chromium, aluminum, carbon, and fluorine; mixing the first chromium-containing chlorinated slag with second preheated silicon tetrachloride, so that under the action of carbon in the first chromium-containing chlorinated slag, the second preheated silicon tetrachloride undergoes a second chlorination reaction with the chromium, aluminum, and fluorine in the first chromium-containing chlorinated slag, to obtain a second chlorinated flue gas containing aluminum and fluorine and a second chromium-containing chlorinated slag; separating and purifying the first chlorinated flue gas and the second chlorinated flue gas respectively 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 solution containing trivalent chromium. Attached Figure Description

[0011] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0012] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0013] Figure 1 shows a schematic flowchart of a method for the synergistic recovery of valuable elements from overhaul slag and chromium-containing aluminum sludge according to an embodiment of the present disclosure.

[0014] Figure 2 shows a detailed flowchart of a method for the synergistic recovery of valuable elements from overhaul slag and chromium-containing aluminum sludge according to an embodiment of the present disclosure.

[0015] Figure 3 shows a schematic diagram of the actual process of a method for the synergistic recovery of valuable elements from overhaul slag and chromium-aluminum mud according to an embodiment of the present disclosure. Embodiments of the present invention

[0016] 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.

[0017] 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 specifically discloses all possible subranges and single numerical values ​​within that range; for example, it should be considered that the range description from 1 to 6 specifically discloses subranges 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 said ranges, 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 referred range.

[0018] 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, parameters described by proportion should be understood as the first term of the proportion, following the order of description, while the proportion figures should be understood as the second term. 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 formula according to the order of description; that is, the mass of substance A : the mass of substance B : the mass of substance C = 1:2:3.

[0019] 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.

[0020] Figure 1 shows a schematic flowchart of a method for the synergistic recovery of valuable elements from overhaul slag and chromium-aluminum mud according to an embodiment of the present disclosure.

[0021] As shown in Figure 1, this disclosure provides a method for the synergistic recovery of valuable elements from overhaul slag and chromium-containing aluminum sludge. The overhaul slag contains fluorides, cyanides, iron, and carbon, while the chromium-containing aluminum sludge contains aluminum, iron, and hexavalent chromium. The method includes:

[0022] 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, iron and chromium.

[0023] S2. Use alkaline components to cause a precipitation reaction in the decyanated material to obtain a precipitate containing carbon, aluminum, chromium, iron and fluorine;

[0024] S3. The first preheated silicon tetrachloride is mixed with the precipitate so that, under the action of carbon in the precipitate, the first preheated silicon tetrachloride reacts with iron and fluorine in the precipitate to produce the first chlorination reaction, which yields the first chlorinated flue gas containing iron and fluorine and the first chromium-containing chlorinated slag containing chromium, aluminum, carbon and fluorine.

[0025] S4. The second preheated silicon tetrachloride is mixed with the first chromium-containing chlorinated slag, so that under the action of carbon in the first chromium-containing chlorinated slag, the second preheated silicon tetrachloride reacts with chromium, aluminum and fluorine in the first chromium-containing chlorinated slag to obtain the second chlorinated flue gas containing aluminum and fluorine and the second chromium-containing chlorinated slag.

[0026] S5. The first chlorination flue gas and the second chlorination flue gas are separated and purified to obtain an aluminum-containing solid phase, an iron-containing solid phase, and silicon tetrafluoride; and

[0027] S6. Wash the second chromium-containing chloride residue to obtain a solution containing trivalent chromium.

[0028] It should be noted that carbon in overhaul slag can significantly improve the fluidization quality of chromium-aluminum mud, thereby effectively promoting redox reactions. The carbon in the overhaul slag can exist in either carbon form or silicon carbide form. When the carbon in the overhaul slag exists in carbon form, some carbon is lost during both the first and second chlorination reactions. However, when the carbon in the overhaul slag exists in silicon carbide form, due to the stability of silicon carbide, the loss of silicon carbide during the first and second chlorination reactions is smaller.

[0029] It should be noted that the precipitate needs to be purified before the chlorination reaction to remove moisture and avoid loss of silicon tetrachloride during the first preheating. Purification can be achieved through drying.

[0030] It should be noted that the temperature of the first preheated silicon tetrachloride can be lower than the temperature of the first chlorination reaction. The temperature of the first preheated silicon tetrachloride is determined based on the actual heat exchange conditions. Regardless of the initial temperature of the first preheated silicon tetrachloride, it can be rapidly heated to the temperature of the first chlorination reaction using microwave heating. Similarly, the temperature of the second preheated silicon tetrachloride also needs to be clearly controlled.

[0031] It should be noted that both the first chlorination reaction and the second 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 the first preheated silicon tetrachloride and the precipitate, and the second preheated silicon tetrachloride and the first chromium-containing chlorinated slag, and has the characteristics of fast mass and heat transfer rate and high reaction efficiency.

[0032] It should be noted that the inorganic acid can be hydrochloric acid, so that it can synergistically react with the first and second preheated silicon tetrachloride in the subsequent first and second chlorination reactions to generate chromium-containing chloride salts, iron-containing chloride salts, and aluminum-containing chloride salts, respectively.

[0033] It should be noted that the alkaline component can be ammonia or an alkaline metal oxide. When the alkaline metal oxide is calcium oxide, the fluorine in the precipitate exists as calcium fluoride. In this case, the product of the precipitation reaction includes not only the precipitate but also waste liquid containing calcium and other unreacted impurities. This waste liquid can be further treated to obtain a harmless waste liquid. When the alkaline component is ammonia, the fluorine in the precipitate exists as a fluorine-containing compound (e.g., aluminum fluoride). In this case, the product of the precipitation reaction includes not only the precipitate but also a mixed solution formed by some unreacted ammonia and soluble fluorine-containing compounds. This mixed solution needs to be treated with a calcium-containing compound (usually calcium oxide) to cause the fluorine-containing compounds in the mixed solution to precipitate as calcium fluoride. The remaining mixed solution then needs further treatment to obtain a harmless waste liquid.

[0034] It should be noted that the second chromium-containing chloride residue can be washed to remove chromium chloride, thereby obtaining a high-purity trivalent chromium solution.

[0035] It should be noted that the overhaul slag needs to be ground before use to control the particle size to <10μm; overhaul slag within this particle size range has a high specific surface area. The high specific surface area of ​​the overhaul slag can increase its contact area with the chromium-containing aluminum mud, allowing the cyanide in the overhaul slag to fully undergo a redox reaction with the hexavalent chromium in the chromium-containing aluminum mud.

[0036] It should be noted that the first and second preheated silicon tetrachloride can be sourced from silicon tetrachloride, a hazardous waste generated during the polysilicon production process.

[0037] It should be noted that the tailings of the second chromium-containing chlorinated slag, after washing, have reached the harmless standard and can be used in multiple fields such as construction and filler.

[0038] In summary, the embodiments of this disclosure provide a method for the synergistic recovery of valuable elements from overhaul slag and chromium-containing aluminum sludge. This method, through redox reactions, precipitation reactions, and chlorination reactions, can effectively remove toxic elements (such as cyanide and hexavalent chromium) from overhaul slag and chromium-containing aluminum sludge, thereby achieving efficient recovery of valuable elements (such as aluminum, iron, and chromium). The advantages of this method are mainly reflected in the following aspects:

[0039] (1) Removal of toxic elements: Through oxidation-reduction reaction and precipitation reaction, cyanide and hexavalent chromium are converted into harmless or low-toxicity products, thus achieving effective removal of toxic elements;

[0040] (2) Recovery of valuable elements: Through multiple chlorination reactions, fluorine, aluminum, iron and chromium are converted into corresponding chloride salts, and then high-purity valuable element products are obtained through subsequent purification steps.

[0041] (3) Environmentally friendly: The by-products generated throughout the process (such as ammonia, carbon dioxide, silicon tetrafluoride, etc.) are all harmless or low-toxic substances, which meet the environmental protection requirements.

[0042] Therefore, this method, through a series of chemical reactions, achieves the simultaneous recovery and utilization of valuable elements from overhaul slag and chromium-aluminum sludge. This not only improves the removal efficiency of toxic elements but also effectively increases the recovery rate of valuable elements, achieving efficient resource recycling. This provides a new approach and method for solving industrial waste problems, contributing to the sustainable use of resources and environmental protection.

[0043] In some optional embodiments, the temperature of the first chlorination reaction is 500°C to 700°C, and the time of the first chlorination reaction is 0.5 h to 2 h; and / or

[0044] The temperature of the second chlorination reaction is 800℃~900℃, and the reaction time is 0.5h~2h.

[0045] In some embodiments, the temperature of the first chlorination reaction can be 500℃~700℃, and the reaction time can be 0.5h~2h. Under the influence of carbon in the precipitate, the first chlorination reaction promotes a full reaction between the first preheated silicon tetrachloride and the iron and fluorine in the precipitate to obtain iron-containing chlorides and silicon tetrafluoride, thus facilitating the subsequent second chlorination reaction and separation and purification. Alternatively, the temperature of the second chlorination reaction can be 800℃~900℃, and the reaction time can be 0.5h~2h. Under the influence of carbon in the first chromium-containing chlorination slag, the second chlorination reaction promotes a full reaction between the second preheated silicon tetrachloride and the chromium, aluminum, and fluorine in the first chromium-containing chlorination slag to obtain aluminum-containing chlorides, chromium-containing chlorides, and silicon tetrafluoride, thus facilitating subsequent separation, purification, and washing.

[0046] The temperature for the first chlorination reaction can be 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, 620℃, 640℃, 660℃, 680℃, or 700℃.

[0047] The time for the first chlorination reaction can be 0.5h, 1.0h, 1.5h or 2.0h.

[0048] The temperature for the second chlorination reaction can be 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, or 900℃.

[0049] The second chlorination reaction can take 0.5 h, 1.0 h, 1.5 h, or 2.0 h.

[0050] In some alternative implementations, both the first and second chlorination reactions are carried out by microwave heating.

[0051] In some embodiments, both the first and second chlorination reactions are carried out by microwave heating. During microwave heating, the carbon in the precipitate and the carbon in the first chromium-containing chlorination slag can act as highly efficient microwave absorbing materials, absorbing and storing the energy transferred by microwave heating. The carbon storing sufficient energy not only promotes rapid heating of the precipitate and the first chromium-containing chlorination slag, ensuring the temperature of the precipitate meets the requirements of the first chlorination reaction and the temperature of the first chromium-containing chlorination slag meets the requirements of the second chlorination reaction, but also ensures uniform dispersion of other materials in the precipitate during microwave heating. Furthermore, the carbon in the precipitate and the carbon in the first chromium-containing chlorination slag can also act as a carbon source, increasing the intensity of the first and second chlorination reactions and promoting the reaction of chromium, iron, aluminum, and fluorine to form chromium-containing chlorides, aluminum-containing chlorides, iron-containing chlorides, and silicon tetrafluoride.

[0052] In some alternative embodiments, the pH of the redox reaction is 4 to 6, and the reaction time is 0.5 h to 2 h.

[0053] 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 to harmless carbon dioxide and nitrogen, and reduces the hexavalent chromium to harmless trivalent chromium, effectively removing toxic elements from the chromium-containing aluminum sludge and overhaul slag.

[0054] 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.

[0055] The redox reaction can take 0.5h, 1h, 1.5h or 2h.

[0056] In some optional embodiments, 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.

[0057] In some embodiments, the weight of cyanide in the decyanation material can be less than or equal to 0.05% of the weight of the decyanation material, and the weight of hexavalent chromium in the decyanation material can be less than or equal to 0.05% of the weight of the decyanation material. This indicates that the hexavalent chromium in the chromium-containing aluminum sludge and the cyanide in the overhaul slag have undergone sufficient reaction during the redox reaction process.

[0058] In some alternative implementations, the pH of the precipitation reaction is 8 to 11;

[0059] 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. An alkaline environment can promote the conversion of aluminum, iron, and chromium into hydroxide precipitates, thereby promoting the conversion of aluminum, iron, and chromium in the decyanation material into precipitates. In addition, when the alkaline component is calcium oxide, the calcium in the calcium oxide can react with the fluorine in the decyanation material to obtain calcium fluoride precipitate in an alkaline environment, which is convenient for subsequent recycling.

[0060] The pH of the precipitation reaction can be 8, 8.5, 9.0, 9.5, 10.0, 10.5, or 11.0.

[0061] Figure 2 shows a detailed flowchart of a method for the synergistic recovery of valuable elements from overhaul slag and chromium-aluminum mud according to an embodiment of the present disclosure.

[0062] Figure 3 shows a schematic diagram of the actual process of a method for the synergistic recovery of valuable elements from overhaul slag and chromium-aluminum mud according to an embodiment of the present disclosure.

[0063] In some optional embodiments, as shown in Figures 2 and 3, the first chlorinated flue gas and the second chlorinated flue gas are separated and purified to obtain an aluminum-containing solid phase, an iron-containing solid phase, and silicon tetrafluoride, including the following steps:

[0064] S501. The first chlorinated flue gas is subjected to first multi-stage condensation to obtain an iron-containing solid phase, a first circulating liquid phase silicon tetrachloride, and a first gas phase silicon tetrafluoride.

[0065] S502. The second chlorinated flue gas is subjected to a second multi-stage condensation to obtain an aluminum-containing solid phase, a second circulating liquid phase silicon tetrachloride, and a second gas phase silicon tetrafluoride.

[0066] S503. Combine the first fumed silicon tetrafluoride and the second fumed silicon tetrafluoride to obtain silicon tetrafluoride; and

[0067] S504. The first circulating liquid-phase silicon tetrachloride and the second circulating liquid-phase silicon tetrachloride are vaporized to obtain the first circulating gaseous-phase silicon tetrachloride and the second circulating gaseous-phase silicon tetrachloride.

[0068] In some embodiments, the separation and purification employs different multi-stage condensation separation and gasification methods for different chlorinated flue gases. For the first chlorinated flue gas, through the first multi-stage condensation separation, based on the boiling point difference between the iron-containing solid phase and silicon tetrafluoride in the iron- and fluorine-containing first chlorinated flue gas, the two are condensed and precipitated separately, thereby achieving the recovery of iron and fluorine. For the second chlorinated flue gas, through the second multi-stage condensation separation, based on the boiling point difference between the aluminum-containing solid phase and silicon tetrafluoride in the aluminum- and fluorine-containing second chlorinated flue gas, the two are condensed and precipitated separately, thereby achieving the recovery of aluminum and fluorine. In addition, the precipitated first and second circulating liquid silicon tetrachloride are gasified to achieve the regeneration of silicon tetrachloride.

[0069] It should be noted that the temperature at which the precipitated first and second circulating liquid silicon tetrachloride is vaporized can be 70℃~100℃.

[0070] In some optional embodiments, the first multi-stage condensation includes a first cooling section and a second cooling section. The first cooling section is used to condense the first chlorinated flue gas containing iron and fluorine to obtain an iron-containing solid phase, and the second cooling section is used to condense the first chlorinated flue gas containing iron and fluorine to obtain a first gaseous silicon tetrafluoride and a first circulating liquid silicon tetrachloride, respectively. The temperature of the first cooling section is 70°C to 290°C, and the temperature of the second cooling section is 20°C to 50°C.

[0071] In some embodiments, the first multi-stage condensation may include a first cooling section. The first cooling section can be used to condense the first chlorinated flue gas containing iron and fluorine to obtain an iron-containing solid phase. The temperature of the first cooling section can be 70°C to 290°C. Based on the boiling point difference between the ferric chloride component and other components in the first chlorinated flue gas, the ferric chloride component can be condensed into an iron-containing solid phase to achieve iron recovery. Alternatively, the first multi-stage condensation may include a second cooling section. The second cooling section is used to condense the first chlorinated flue gas containing iron and fluorine to obtain a first gaseous silicon tetrafluoride and a first circulating liquid silicon tetrachloride, respectively. The temperature of the second cooling section can be 20°C to 50°C. Based on the boiling point difference between silicon tetrafluoride and silicon tetrachloride in the first chlorinated flue gas, the silicon tetrachloride component can be condensed into a first circulating liquid silicon tetrachloride, achieving separation of silicon tetrafluoride and silicon tetrachloride, facilitating subsequent regeneration of silicon tetrachloride through gasification, thereby promoting the recycling of silicon tetrachloride.

[0072] The temperature of the first cooling section can be 70℃, 90℃, 110℃, 130℃, 150℃, 170℃, 190℃, 210℃, 230℃, 250℃, 270℃ or 290℃.

[0073] The temperature of the second cooling section can be 20℃, 25℃, 30℃, 35℃, 40℃, 45℃ or 50℃.

[0074] In some optional embodiments, the second multi-stage condensation includes a third cooling section and a fourth cooling section. The third cooling section is used to condense the second chlorinated flue gas containing aluminum and fluorine to obtain an aluminum-containing solid phase. The fourth cooling section is used to condense the second chlorinated flue gas containing aluminum and fluorine to obtain a second gaseous silicon tetrafluoride and a second circulating liquid silicon tetrachloride, respectively. The temperature of the third cooling section is 70°C to 170°C, and the temperature of the fourth cooling section is 20°C to 50°C.

[0075] In some embodiments, the second multi-stage condensation may include a third cooling stage. The third cooling stage can be used to condense the second chlorinated flue gas containing aluminum and fluorine to obtain an aluminum-containing solid phase. The temperature of the third cooling stage can be 70°C to 170°C. Based on the boiling point difference between the aluminum chloride component and other components of the second chlorinated flue gas, the aluminum chloride component can be condensed into an aluminum-containing solid phase to achieve aluminum recovery. Alternatively, the second multi-stage condensation may include a fourth cooling stage. The fourth cooling stage can be used to condense the second chlorinated flue gas containing aluminum and fluorine to obtain a second gaseous silicon tetrafluoride and a second circulating liquid silicon tetrachloride, respectively. The temperature of the fourth cooling stage can be 20°C to 50°C. Based on the boiling point difference between silicon tetrafluoride and silicon tetrachloride in the second chlorinated flue gas, the silicon tetrachloride component can be condensed into a second circulating liquid silicon tetrachloride to achieve separation of silicon tetrafluoride and silicon tetrachloride, facilitating subsequent regeneration of silicon tetrachloride via gasification, thereby promoting the recycling of silicon tetrachloride.

[0076] The temperature of the third cooling section can be 70℃, 90℃, 110℃, 130℃, 150℃ or 170℃.

[0077] The temperature of the fourth cooling section can be 20℃, 25℃, 30℃, 35℃, 40℃, 45℃ or 50℃.

[0078] In some optional embodiments, before washing the second chromium-containing chloride residue to obtain a trivalent chromium-containing solution, and after vaporizing the first circulating liquid-phase silicon tetrachloride and the second circulating liquid-phase silicon tetrachloride 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:

[0079] S601. Silicon tetrachloride is vaporized and sorted to obtain first vapor-phase silicon tetrachloride and second vapor-phase silicon tetrachloride, respectively;

[0080] S602. Heat exchange is performed by introducing first gaseous silicon tetrachloride and first circulating gaseous silicon tetrachloride into the first chromium-containing chloride slag to obtain first preheated silicon tetrachloride; and

[0081] S603. The second fumed silicon tetrachloride and the second circulating fumed silicon tetrachloride are introduced into the second chromium-containing chlorinated slag for heat exchange to obtain the second preheated silicon tetrachloride.

[0082] In some embodiments, silicon tetrachloride can be vaporized and sorted. The first and second circulating gaseous silicon tetrachloride are fed according to the actual consumption of silicon tetrachloride in the first and second chlorination reactions. Furthermore, the heat of the first chromium-containing chlorinated slag can be recovered through heat exchange between the first and second circulating gaseous silicon tetrachloride and the first chromium-containing chlorinated slag; similarly, the heat of the second chromium-containing chlorinated slag can be recovered through heat exchange between the second and second circulating gaseous silicon tetrachloride and the second chromium-containing chlorinated slag. In other words, the heat from the first chromium-containing chlorinated slag can be used to preheat the first and second circulating gaseous silicon tetrachloride to obtain first preheated silicon tetrachloride, and the heat from the second chromium-containing chlorinated slag can be used to preheat the second and second circulating gaseous silicon tetrachloride to obtain second preheated silicon tetrachloride, thereby recovering the heat from the first and second chlorination reactions. This reduces the overall energy consumption of the method and improves its thermal efficiency.

[0083] 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, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0084] Example 1

[0085] As shown in Figure 2, a method for the synergistic recovery of valuable elements from overhaul slag and chromium-containing aluminum sludge is described. The overhaul slag contains fluorides, cyanides, iron, and carbon, while the chromium-containing aluminum sludge contains aluminum, iron, and hexavalent chromium.

[0086] S1. Inorganic acid, chromium-containing aluminum sludge and overhaul slag (particle size less than 10μm) are mixed to allow hexavalent chromium to undergo a redox reaction with cyanide in an acidic environment, resulting in a decyanated material containing fluoride, carbon, aluminum, iron and chromium.

[0087] S2. Use calcium oxide to precipitate the decyanated material to obtain a precipitate containing carbon, aluminum, chromium, iron and fluorine;

[0088] S3. The first preheated silicon tetrachloride is mixed with the precipitate so that, under the action of carbon in the precipitate, the first preheated silicon tetrachloride reacts with iron and fluorine in the precipitate to produce the first chlorination reaction, which yields the first chlorinated flue gas containing iron and fluorine and the first chromium-containing chlorinated slag containing chromium, aluminum, carbon and fluorine.

[0089] S4. The second preheated silicon tetrachloride is mixed with the first chromium-containing chlorinated slag, so that under the action of carbon in the first chromium-containing chlorinated slag, the second preheated silicon tetrachloride reacts with chromium, aluminum and fluorine in the first chromium-containing chlorinated slag to obtain the second chlorinated flue gas containing aluminum and fluorine and the second chromium-containing chlorinated slag.

[0090] S501. The first chlorinated flue gas containing iron and fluorine is subjected to first multi-stage condensation to obtain an iron-containing solid phase, a first circulating liquid phase silicon tetrachloride, and a first gas phase silicon tetrafluoride.

[0091] S502. The second chlorinated flue gas containing aluminum and fluorine is subjected to a second multi-stage condensation to obtain an aluminum-containing solid phase, a second circulating liquid phase of silicon tetrachloride, and a second gaseous phase of silicon tetrafluoride.

[0092] S503. Combine the first fumed silicon tetrafluoride and the second fumed silicon tetrafluoride to obtain silicon tetrafluoride;

[0093] S504. The first circulating liquid silicon tetrachloride and the second circulating liquid silicon tetrachloride are vaporized to obtain the first circulating gaseous silicon tetrachloride and the second circulating gaseous silicon tetrachloride.

[0094] S601. Silicon tetrachloride is vaporized and sorted to obtain first vapor-phase silicon tetrachloride and second vapor-phase silicon tetrachloride, respectively;

[0095] S602. Heat exchange is performed by introducing first gaseous silicon tetrachloride and first circulating gaseous silicon tetrachloride into the first chromium-containing chlorination slag to obtain first preheated silicon tetrachloride;

[0096] S603. A second fumed silicon tetrachloride and a second circulating fumed silicon tetrachloride are respectively introduced into the second chromium-containing chloride slag for heat exchange to obtain a second preheated silicon tetrachloride; and

[0097] S6. Wash the second chromium-containing chloride residue to obtain a solution containing trivalent chromium.

[0098] The temperature of the first chlorination reaction is 500℃, and the time of the first chlorination reaction is 2 hours.

[0099] The temperature of the second chlorination reaction is 800℃, and the reaction time is 2 hours.

[0100] Both the first and second chlorination reactions were carried out using microwave heating.

[0101] The pH of the redox reaction is 4, and the reaction time is 0.5 h.

[0102] 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.

[0103] The pH of the precipitation reaction is 8.

[0104] The first multi-stage condensation includes a first cooling section and a second cooling section. The first cooling section is used to condense the first chlorinated flue gas containing iron and fluorine to obtain an iron-containing solid phase. The second cooling section is used to condense the first chlorinated flue gas containing iron and fluorine to obtain a first gaseous silicon tetrafluoride and a first circulating liquid silicon tetrachloride, respectively. The temperature of the first cooling section is 70°C, and the temperature of the second cooling section is 20°C.

[0105] The second multi-stage condensation includes a third cooling section and a fourth cooling section. The third cooling section is used to condense the second chlorinated flue gas containing aluminum and fluorine to obtain an aluminum-containing solid phase. The fourth cooling section is used to condense the second chlorinated flue gas containing aluminum and fluorine to obtain a second gaseous silicon tetrafluoride and a second circulating liquid silicon tetrachloride, respectively. The temperature of the third cooling section is 70°C, and the temperature of the fourth cooling section is 20°C.

[0106] The vaporization temperature is 70℃.

[0107] Example 2

[0108] Based on the content disclosed in Example 1, the following changes were made to the reaction conditions:

[0109] The temperature of the first chlorination reaction is 700℃, and the time of the first chlorination reaction is 0.5h.

[0110] The temperature of the second chlorination reaction is 900℃, and the reaction time is 0.5h.

[0111] The pH of the redox reaction is 6, and the reaction time is 2 hours.

[0112] The pH of the precipitation reaction is 10.

[0113] The first multi-stage condensation includes a first cooling section and a second cooling section. The first cooling section is used to condense the first chlorinated flue gas containing iron and fluorine to obtain an iron-containing solid phase. The second cooling section is used to condense the first chlorinated flue gas containing iron and fluorine to obtain a first gaseous silicon tetrafluoride and a first circulating liquid silicon tetrachloride, respectively. The temperature of the first cooling section is 290°C. The temperature of the second cooling section is 50°C.

[0114] The second multi-stage condensation includes a third cooling section and a fourth cooling section. The third cooling section is used to condense the second chlorinated flue gas containing aluminum and fluorine to obtain an aluminum-containing solid phase. The fourth cooling section is used to condense the second chlorinated flue gas containing aluminum and fluorine to obtain a second gaseous silicon tetrafluoride and a second circulating liquid silicon tetrachloride, respectively. The temperature of the third cooling section is 170°C, and the temperature of the fourth cooling section is 50°C.

[0115] The vaporization temperature is 100℃.

[0116] Example 3

[0117] Based on the content disclosed in Example 1, the following changes were made to the reaction conditions:

[0118] The temperature of the first chlorination reaction is 600℃, and the time of the first chlorination reaction is 1 hour.

[0119] The temperature of the second chlorination reaction is 850℃, and the reaction time is 1 hour.

[0120] The pH of the redox reaction is 5, and the reaction time is 1 hour.

[0121] The pH of the precipitation reaction is 9.

[0122] The first multi-stage condensation includes a first cooling section and a second cooling section. The first cooling section is used to condense the first chlorinated flue gas containing iron and fluorine to obtain an iron-containing solid phase. The second cooling section is used to condense the first chlorinated flue gas containing iron and fluorine to obtain a first gaseous silicon tetrafluoride and a first circulating liquid silicon tetrachloride, respectively. The temperature of the first cooling section is 150°C, and the temperature of the second cooling section is 30°C.

[0123] The second multi-stage condensation includes a third cooling section and a fourth cooling section. The third cooling section is used to condense the second chlorinated flue gas containing aluminum and fluorine to obtain an aluminum-containing solid phase. The fourth cooling section is used to condense the second chlorinated flue gas containing aluminum and fluorine to obtain a second gaseous silicon tetrafluoride and a second circulating liquid silicon tetrachloride, respectively. The temperature of the third cooling section is 120°C, and the temperature of the fourth cooling section is 35°C.

[0124] The vaporization temperature is 85℃.

[0125] The relevant experimental data and results are as follows:

[0126] The yields of aluminum in the aluminum-containing solid phase, iron in the iron-containing solid phase, and chromium in the trivalent chromium solution obtained in each embodiment were statistically analyzed, and the recovery rates of valuable elements such as aluminum, iron, and chromium were calculated. In addition, the weight content of cyanide and hexavalent chromium in the decyanated material were statistically analyzed, and the results are shown in Table 1.

[0127] Table 1. Recovery rates of valuable elements and weight content of cyanide and hexavalent chromium in the decyanation feed for each embodiment.

[0128]

[0129] As shown in Table 1, the method for synergistic recovery of valuable elements from overhaul slag and chromium-containing aluminum sludge provided in the embodiments of this disclosure, using chromium-containing aluminum sludge and overhaul slag as raw materials, can simultaneously increase the removal rate of toxic elements in overhaul slag and chromium-containing aluminum sludge to over 99.95% through redox reactions, precipitation reactions and multiple chlorination reactions, and increase the recovery rate of valuable elements such as aluminum, iron and chromium to over 95%.

[0130] In summary, the method for synergistically recovering valuable elements from 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 for synergistic "detoxification." Furthermore, this method recovers valuable elements such as aluminum, chromium, and iron through multiple chlorination reactions. 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, aluminum, and iron.

[0131] In addition, in the method for synergistic recovery of valuable elements from overhaul slag and chromium-containing aluminum sludge provided in the embodiments of this disclosure, the carbon in the overhaul slag and the first chromium-containing chloride slag has the characteristics of fast heating rate and uniform heating, which can improve the reaction rate and reaction degree of the first chlorination reaction and the second chlorination reaction, thereby promoting the full conversion of valuable elements such as aluminum, chromium, iron and fluorine in the precipitate into aluminum chloride salts, chromium chloride salts, iron chloride salts and silicon tetrafluoride.

[0132] In addition, the method for synergistic recovery of valuable elements from overhaul slag and chromium-containing aluminum sludge provided in the embodiments of this disclosure can also recover the heat from the chromium-containing chloride slag obtained from each stage of the chlorination reaction, and use the recovered heat to preheat silicon tetrachloride, thereby realizing the recycling of heat and improving energy utilization efficiency; in addition, the method can also regenerate silicon tetrachloride through separation and purification, thus having good economic and social benefits.

[0133] Compared with related technologies, the technical solutions provided by the embodiments of this disclosure have the following advantages:

[0134] This disclosure provides an embodiment of a method for the synergistic recovery of valuable elements from overhaul slag and chromium-containing aluminum sludge. The method aims to simultaneously process overhaul slag (containing fluorides, cyanides, iron, and carbon) and chromium-containing aluminum sludge (containing aluminum, iron, 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.

[0135] 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, iron, and chromium.

[0136] Precipitation reaction steps: Use an alkaline component (such as ammonia or calcium oxide) to carry out a precipitation reaction on the decyanated material to remove chromium, aluminum, iron and fluorides; in addition, the precipitation reaction forms precipitates such as calcium fluoride, aluminum hydroxide, and iron hydroxide, thereby achieving the separation of these elements and obtaining a precipitate containing carbon, aluminum, chromium, iron and fluorine (which may be partially unprecipitated).

[0137] Chlorination reaction steps: First, a preheated silicon tetrachloride is used to perform a first chlorination reaction on the precipitate, with carbon in the precipitate serving as the heating medium to promote the reaction of chromium, iron, and aluminum to form iron-containing chlorides, chromium-containing chlorides, and aluminum-containing chlorides. The first chlorination reaction produces a first chlorinated flue gas containing iron and fluorine, and a first chromium-containing chlorinated slag containing chromium, aluminum, carbon, and fluorine. The first chlorinated flue gas can be further purified in subsequent steps to obtain an iron-containing solid phase and silicon tetrafluoride. Second, a second chlorination reaction is performed on the first chromium-containing chlorinated slag, with carbon in the slag serving as the heating medium to promote the reaction of chromium and aluminum to form chromium-containing chlorides and aluminum-containing chlorides. The second chlorination reaction produces a second chlorinated flue gas containing aluminum and fluorine, and a second chromium-containing chlorinated slag containing chromium. The second chlorinated flue gas can be further purified in subsequent steps to obtain an aluminum-containing solid phase and silicon tetrafluoride. The second chromium-containing chlorinated slag can be washed to obtain a trivalent chromium solution, thereby achieving chromium recovery.

[0138] Therefore, this method removes toxic elements from overhaul slag and chromium-containing aluminum sludge through oxidation-reduction reactions, and then effectively recovers aluminum, iron and chromium through multiple chlorination processes.

[0139] 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 the synergistic recovery of valuable elements from overhaul slag and chromium-containing aluminum sludge, wherein the overhaul slag contains fluorides, cyanides, iron, and carbon, and the chromium-containing aluminum sludge contains aluminum, iron, 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, iron, and chromium. The decyanated material is subjected to a precipitation reaction using an alkaline component to obtain a precipitate containing carbon, aluminum, chromium, iron and fluorine. The first preheated silicon tetrachloride is mixed with the precipitate, so that under the action of carbon in the precipitate, the first preheated silicon tetrachloride reacts with iron and fluorine in the precipitate to produce a first chlorinated flue gas containing iron and fluorine and a first chromium-containing chlorinated slag containing chromium, aluminum, carbon and fluorine. The second preheated silicon tetrachloride is mixed with the first chromium-containing chlorinated slag so that, under the action of carbon in the first chromium-containing chlorinated slag, the second preheated silicon tetrachloride reacts with chromium, aluminum and fluorine in the first chromium-containing chlorinated slag to obtain a second chlorinated flue gas containing aluminum and fluorine and a second chromium-containing chlorinated slag. The first chlorinated flue gas and the second chlorinated flue gas were separated and purified to obtain an aluminum-containing solid phase, an iron-containing solid phase and silicon tetrafluoride; as well as The second chromium-containing chloride residue was washed to obtain a solution containing trivalent chromium.

2. The method according to claim 1, wherein, The temperature of the first chlorination reaction is 500℃~700℃, and the reaction time is 0.5h~2h; and / or The temperature of the second chlorination reaction is 800℃~900℃, and the time of the second chlorination reaction is 0.5h~2h.

3. The method according to claim 1, wherein, Both the first chlorination reaction and the second chlorination reaction are carried out by 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 separating and purifying 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 comprises the following steps: The first chlorinated flue gas is subjected to a first multi-stage condensation to obtain an iron-containing solid phase, a first circulating liquid phase silicon tetrachloride, and a first gaseous phase silicon tetrafluoride. The second chlorinated flue gas is subjected to a second multi-stage condensation to obtain an aluminum-containing solid phase, a second circulating liquid phase silicon tetrachloride, and a second gas phase silicon tetrafluoride. The first fumed silicon tetrafluoride and the second fumed silicon tetrafluoride are combined to obtain the silicon tetrafluoride; as well as The first circulating liquid silicon tetrachloride and the second circulating liquid silicon tetrachloride are respectively vaporized to obtain the first circulating gaseous silicon tetrachloride and the second circulating gaseous silicon tetrachloride.

8. The method according to claim 7, wherein, The first multi-stage condensation includes a first cooling section and a second cooling section; the first cooling section is used to condense the first chlorinated flue gas containing iron and fluorine to obtain an iron-containing solid phase, and the second cooling section is used to condense the first chlorinated flue gas containing iron and fluorine to obtain a first gaseous silicon tetrafluoride and a first circulating liquid silicon tetrachloride, respectively; the temperature of the first cooling section is 70℃~290℃, and the temperature of the second cooling section is 20℃~50℃.

9. The method according to claim 7, wherein, The second multi-stage condensation includes a third cooling section and a fourth cooling section; the third cooling section is used to condense the second chlorinated flue gas containing aluminum and fluorine to obtain an aluminum-containing solid phase, and the fourth cooling section is used to condense the second chlorinated flue gas containing aluminum and fluorine to obtain a second gaseous silicon tetrafluoride and a second circulating liquid silicon tetrachloride, respectively; the temperature of the third cooling section is 70℃~170℃, 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 second chromium-containing chloride residue to obtain a trivalent chromium solution, and after vaporizing the first and second circulating liquid-phase silicon tetrachloride to obtain the first and second circulating gaseous-phase silicon tetrachloride, the method further includes: Silicon tetrachloride was vaporized and sorted to obtain first-phase silicon tetrachloride and second-phase silicon tetrachloride, respectively. The first fumed silicon tetrachloride and the first circulating fumed silicon tetrachloride are respectively introduced into the first chromium-containing chloride slag for heat exchange to obtain first preheated silicon tetrachloride; and The second flammable silicon tetrachloride and the second circulating flammable silicon tetrachloride are respectively introduced into the second chromium-containing chlorinated slag for heat exchange to obtain the second preheated silicon tetrachloride.

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