Method for co-processing chromium-containing aluminum mud and electrolytic aluminum overhaul slag

Abstract

The invention discloses a method for co-processing chromium-containing aluminum mud and electrolytic aluminum overhaul slag, which comprises the following steps of: oxidizing cyanide in the finely ground overhaul slag into carbon dioxide and nitrogen by using hexavalent chromium with strong oxidizing property in the chromium-containing aluminum mud under an acidic condition, and adding calcium oxide into decyanated slag to obtain trivalent chromium precipitate and insoluble villiaumite; and chloridizing the washed and dried precipitation slag by adopting aluminum chloride, carrying out multi-stage condensation separation and purification on the chloridized flue gas to respectively obtain ferric trichloride and aluminum trichloride, carrying out heat exchange and washing on the chloridized slag to obtain a chromium trichloride solution, and carrying out alkaline leaching to obtain sodium aluminate and tailings. According to the method, oxidation-reduction characteristics of the chromium-containing aluminum mud and the overhaul slag are utilized to cooperate with detoxification, a carbon-based wave-absorbing material in the overhaul slag is subjected to microwave heating for chlorination recovery of valuable elements, the heating rate is high, heating is uniform, the reaction efficiency is high, harmless treatment of the two hazardous wastes is achieved, the valuable elements such as chromium and aluminum in the hazardous wastes are effectively recovered, and the method is suitable for industrial production. And the energy utilization rate is high.

Description

Technical Field

[0001] The invention relates to the technical field of resource utilization of hazardous wastes, and in particular to a method for the coordinated disposal of chromium-containing aluminum mud and electrolytic aluminum overhaul slag. Background Art

[0002] There are two main methods for industrial production of sodium dichromate: calcium roasting method and calcium-free roasting method. Compared with calcium roasting method, calcium-free roasting method is cleaner and more efficient. However, aluminum silicon compounds in calcium-free roasting will react with soda ash to form more sodium silicate and sodium metaaluminate, which will enter the alkaline leaching solution and produce a large amount of chromium-containing aluminum mud, which is about 5-10 times that of calcium roasting method. Chromium-containing aluminum mud contains hexavalent chromium, which is highly toxic and is listed in the "National List of Hazardous Wastes". Stacking or direct discharge will cause serious harm to the environment. Chromium-containing aluminum mud contains rich chromium and aluminum resources. Through appropriate methods of comprehensive utilization, it can not only eliminate environmental pollution, but also effectively promote the green and sustainable development of my country's chromium salt industry.

[0003] Electrolytic aluminum overhaul slag refers to the material that is replaced due to the damage, deformation and rupture of the lining of the electrolytic aluminum tank caused by long-term erosion by electrolytes, high-temperature aluminum liquid, etc., and the electrolyte infiltration causes the lining to be damaged, deformed and broken. It mainly includes waste cathode carbon blocks, waste refractory materials and waste insulation materials. The electrolytic production of one ton of primary aluminum will produce 30-50kg of overhaul slag. my country's aluminum industry produces an average of more than 1.2 million tons of overhaul slag per year. Due to differences in factors such as the electrolyte composition, current capacity, operating procedures and lining replacement time of electrolytic aluminum plants, the specific composition of the overhaul slag varies, but the overall composition is basically the same, mainly including carbon, fluoride and a small amount of sodium, aluminum, calcium, iron, silicon and cyanide. The overhaul slag contains a large amount of soluble fluoride and cyanide, which is listed in the "National List of Hazardous Wastes". If it is directly stored or landfilled, it will seriously affect the environment and endanger human health. The harmless treatment and high-value utilization of overhaul slag are of great significance to the green and high-quality development of the aluminum industry. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention aims to provide a method for the coordinated disposal of chromium-containing aluminum mud and electrolytic aluminum overhaul slag.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A method for co-disposing chromium-containing aluminum mud and electrolytic aluminum overhaul slag comprises the following steps:

[0007] S1. Grinding: Grinding the electrolytic aluminum overhaul slag to obtain fine powder;

[0008] S2, decyanation: decyanation is performed by mixing chromium-aluminum mud and hydrochloric acid with the fine powder obtained in step S1 to obtain decyanation material, carbon dioxide and nitrogen;

[0009] S3, chromium precipitation and fluorine fixation: using calcium oxide to precipitate chromium and fluorine from the decyanated material obtained in step S2 to obtain a precipitate;

[0010] S4, washing and drying: washing and drying the precipitate obtained in step S3 with pure water to obtain a washing liquid and a dried material;

[0011] S5, chlorination: using gaseous aluminum chloride to chlorinate the dried material obtained in step S4 to obtain chlorinated slag and chlorinated flue gas, and the chlorinated flue gas is sent to the multi-stage condensation process in step S7;

[0012] S6, heat exchange: using the gaseous aluminum chloride to exchange heat with the chlorinated slag obtained in step S5, absorbing the heat in the chlorinated slag, the gaseous aluminum chloride after absorbing heat is sent to the chlorination process of step S5, and the cooled chlorinated slag is sent to the washing process of step S8;

[0013] S7, multi-stage condensation: the chlorinated flue gas obtained in step S5 is subjected to multi-stage condensation separation and purification to obtain solid-phase ferric chloride and solid-phase aluminum chloride respectively; the solid-phase aluminum chloride is gasified, and the obtained gaseous aluminum chloride is returned to the heat exchange process of step S6;

[0014] S8, washing: washing the cooled chlorinated slag obtained in step S6 with pure water to obtain a chromium trichloride solution and washed slag;

[0015] S9, alkali leaching: using sodium hydroxide to alkali-leach the washed slag obtained in step S8 to obtain a sodium aluminate solution and tailings.

[0016] Furthermore, in step S1, the particle size of the fine powder is less than 10 μm.

[0017] Furthermore, in step S2, the pH of the cyanide removal environment is 4-6.

[0018] Furthermore, in step S3, the pH of the chromium precipitation and fluorine solidification environment is 8-10.

[0019] Furthermore, in step S5, the chlorination temperature is 700-900°C, the chlorination time is 0.5-2h, and the chlorination reactor is a fluidized bed reactor, and the fluidized bed reactor is heated by microwaves.

[0020] Furthermore, in step S7, the gasification temperature is 190-300°C.

[0021] Further, in step S7, the chlorinated flue gas is first condensed at 190-290°C to obtain solid-phase ferric chloride, and then condensed at 20-170°C to obtain solid-phase aluminum chloride.

[0022] The beneficial effects of the present invention are:

[0023] 1. The present invention utilizes the highly oxidizing hexavalent chromium in the chromium-containing aluminum mud to oxidize the cyanide in the ground electrolytic aluminum overhaul slag into carbon dioxide and nitrogen under acidic conditions, and the hexavalent chromium is reduced to non-toxic trivalent chromium, thereby achieving the harmless treatment of two hazardous wastes;

[0024] 2. The present invention utilizes the abundant carbon and silicon carbide absorbing materials in the electrolytic aluminum overhaul slag and adopts microwave heating to provide the heat required for the chlorination reaction, with fast heating rate, uniform heating, fast chlorination reaction rate and high efficiency;

[0025] 3. The chlorination reaction in the present invention uses aluminum chloride as a chlorinating agent, which can selectively chlorinate the iron- and chromium-containing components to obtain iron trichloride and chromium trichloride without the introduction of impurities. In addition, the chlorination reaction in the present invention uses a fluidized bed reactor, which has good mixing contact between gas and solid phases, fast mass transfer and heat transfer rates, and high reaction efficiency. The carbon-based and silicon-based materials in the electrolytic aluminum overhaul slag can significantly improve the fluidization quality of the chromium-containing aluminum mud, effectively promoting the stable operation of the system;

[0026] 4. According to the difference in boiling points among aluminum chloride, chromium trichloride and ferric chloride, the present invention adopts one-step chlorination volatilization of aluminum chloride and multi-stage condensation of chlorinated flue gas to separate, purify and recover iron. The process is simple, the operation is simple, and the separation and purification efficiency is high. The chromium and aluminum components in the chlorinated slag are sequentially washed with water to obtain a chromium trichloride solution, and then leached with sodium hydroxide to obtain sodium aluminate. The product has high added value.

[0027] 5. The waste heat recovery rate of the present invention is high, which effectively improves the thermal efficiency of the overall process;

[0028] 6. The present invention can not only realize the coordinated "detoxification" of electrolytic aluminum overhaul slag and chromium-containing aluminum mud, but also effectively recover valuable elements such as chromium, aluminum and iron therein, with significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Flowchart of methods according to various embodiments of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to this embodiment.

[0031] Example 1

[0032] This embodiment provides a method for co-disposal of chromium-containing aluminum mud and electrolytic aluminum overhaul slag, such as Figure 1 As shown, the following steps are included:

[0033] S1. Grinding: Grinding the electrolytic aluminum overhaul slag to obtain fine powder with a particle size of less than 10 μm;

[0034] S2, decyanation: using chromium-aluminum mud and hydrochloric acid to carry out mixed reaction to remove cyanide from the fine powder obtained in step S1, the pH of the decyanation environment is 4, and decyanation material, carbon dioxide and nitrogen are obtained;

[0035] S3, chromium precipitation and fluorine fixation: adding calcium oxide to the decyanated material obtained in step S2 to perform chromium precipitation and fluorine fixation, the pH of the chromium precipitation and fluorine fixation environment is 8, and a precipitate is obtained;

[0036] S4, washing and drying: washing and drying the precipitate obtained in step S3 with pure water to obtain a washing liquid and a dried material;

[0037] S5, chlorination: the dried material obtained in step S4 is chlorinated by using gaseous aluminum chloride, the chlorination temperature is 700°C, the chlorination time is 2 hours, the chlorination reactor is a fluidized bed reactor, and the fluidized bed reactor is heated by microwaves. After the chlorination is completed, chlorinated slag and chlorinated flue gas are obtained, and the chlorinated flue gas is sent to the multi-stage condensation process in step S7;

[0038] S6, heat exchange: using gaseous aluminum chloride to exchange heat with the chlorinated slag obtained in step S5, absorbing heat in the chlorinated slag, and the gaseous aluminum chloride after absorbing heat is sent to the chlorination process of step S5, and the cooled chlorinated slag is sent to the washing process of step S8;

[0039] S7, multi-stage condensation: the chlorinated flue gas obtained in step S5 is subjected to multi-stage condensation separation and purification, first condensed at 190°C to obtain solid-phase ferric chloride, and finally condensed at 20°C to obtain solid-phase aluminum chloride; the solid-phase aluminum chloride is gasified at a gasification temperature of 190°C, and the obtained gaseous aluminum chloride is sent to the heat exchange process of step S6;

[0040] S8, washing: washing the cooled chlorinated slag obtained in step S6 with pure water to obtain a chromium trichloride solution and washed slag;

[0041] S9, alkali leaching: using sodium hydroxide to alkali-leach the washed slag obtained in step S8 to obtain a sodium aluminate solution and tailings.

[0042] Example 2

[0043] The method flow of this embodiment is basically the same as that of embodiment 1, except that: in step S2, the pH of the cyanide removal environment is 6. In step S3, the pH of the chromium precipitation solid fluorine environment is 10. In step S5, the chlorination temperature is 900°C and the chlorination time is 0.5h. In step S7, solid phase ferric chloride is first condensed at 290°C, and finally solid phase aluminum chloride is condensed at 170°C, and the temperature of solid phase aluminum chloride gasification is 300°C.

[0044] Example 3

[0045] The method flow of this embodiment is basically the same as that of embodiment 1, except that: in step S2, the pH of the cyanide removal environment is 5. In step S3, the pH of the chromium precipitation and solid fluorine environment is 9. In step S5, the chlorination temperature is 800°C and the chlorination time is 1h. In step S7, solid phase ferric chloride is first condensed at 250°C, and finally solid phase aluminum chloride is condensed at 100°C, and the temperature of solid phase aluminum chloride gasification is 250°C.

[0046] For those skilled in the art, various corresponding changes and modifications can be made according to the above technical solutions and concepts, and all of these changes and modifications should be included in the protection scope of the claims of the present invention.

Claims

1. A method for the coordinated disposal of chromium-containing aluminum mud and electrolytic aluminum overhaul slag, characterized in that: The following steps are involved: S1. Grinding: Grinding the electrolytic aluminum overhaul slag to obtain fine powder; S2, decyanation: decyanation is performed by mixing chromium-aluminum mud and hydrochloric acid with the fine powder obtained in step S1 to obtain decyanation material, carbon dioxide and nitrogen; S3, chromium precipitation and fluorine fixation: using calcium oxide to precipitate chromium and fluorine from the decyanated material obtained in step S2 to obtain a precipitate; S4, washing and drying: washing and drying the precipitate obtained in step S3 with pure water to obtain a washing liquid and a dried material; S5, chlorination: using gaseous aluminum chloride to chlorinate the dried material obtained in step S4 to obtain chlorinated slag and chlorinated flue gas, and the chlorinated flue gas is sent to the multi-stage condensation process in step S7; S6, heat exchange: using the gaseous aluminum chloride to exchange heat with the chlorinated slag obtained in step S5, absorbing the heat in the chlorinated slag, the gaseous aluminum chloride after absorbing heat is sent to the chlorination process of step S5, and the cooled chlorinated slag is sent to the washing process of step S8; S7, multi-stage condensation: the chlorinated flue gas obtained in step S5 is subjected to multi-stage condensation separation and purification to obtain solid-phase ferric chloride and solid-phase aluminum chloride respectively; the solid-phase aluminum chloride is gasified, and the obtained gaseous aluminum chloride is returned to the heat exchange process of step S6; S8, washing: washing the cooled chlorinated slag obtained in step S6 with pure water to obtain a chromium trichloride solution and washed slag; S9, alkali leaching: alkali leaching the washed slag obtained in step S8 with sodium hydroxide to obtain a sodium aluminate solution and tailings.

2. The method according to claim 1, characterized in that In step S1, the particle size of the fine powder is less than 10 μm.

3. The method according to claim 1, characterized in that In step S2, the pH of the cyanide removal environment is 4-6.

4. The method according to claim 1, characterized in that In step S3, the pH of the chromium precipitation and fluorine solidification environment is 8-10.

5. The method according to claim 1, characterized in that: In step S5, the chlorination temperature is 700-900° C., the chlorination time is 0.5-2 h, and the chlorination reactor is a fluidized bed reactor, which is heated by microwaves.

6. The method according to claim 1, characterized in that In step S7, the gasification temperature is 190-300°C.

7. The method according to claim 1, characterized in that In step S7, the chlorinated flue gas is first condensed at 190-290°C to obtain solid ferric chloride, and then condensed at 20-170°C to obtain solid aluminum chloride.

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