Harmless treatment device and method for electrolytic aluminum ash

Abstract

The invention belongs to the technical field of electrolytic aluminum ash treatment, and discloses an electrolytic aluminum ash harmless treatment device which comprises a raw material preparation reaction system and an ore pulp treatment system, and the raw material preparation reaction system comprises a semi-finished product ash bin, a first calcium chloride tank, a raw material saline water tank, a batching tank and a reaction tank; the ore pulp treatment system comprises a vacuum belt filter, a light salt brine tank, a second calcium chloride tank, a strong salt brine tank, an alkali liquor tank, a sediment slurry tank, an air compressor and an MVR evaporator. According to the method, soluble calcium salt is obtained by utilizing the fly ash and diluted hydrochloric acid, calcium chloride reacts with fluoride in the electrolytic aluminum ash to obtain calcium fluoride sediment, most fluorine is removed, the phenomena of corrosion and scaling blockage of an MVR pipeline are greatly reduced, the service life of equipment is prolonged, meanwhile, the salt content is increased through light salt brine circulation enrichment, and the MVR energy consumption is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of electrolytic aluminum ash treatment, and relates to a device and method for harmless treatment of electrolytic aluminum ash. Background Art

[0002] Electrolytic aluminum ash contains fluoride ions, aluminum nitride, and about 5% salt. In general, when electrolytic aluminum ash is treated harmlessly, calcium hydroxide is added to the electrolytic aluminum ash for hydrolysis reaction to reduce the aluminum nitride content in the aluminum ash, reduce the fluorine content and salt content of the aluminum ash leaching, and meet the harmless standard. However, this treatment will produce a large amount of high-fluoride salt water, the salt content of which is only about 3%. If these salts are to be extracted, the MVR energy consumption is particularly large, and the high fluorine content will corrode the MVR and affect the service life of the equipment.

[0003] In addition, when primary aluminum ash is refined by adding composite salt in a rotary furnace, sulfur-containing flue gas will be generated. This part of the flue gas is currently desulfurized by the calcium hydroxide method. The desulfurization process will produce calcium-added dust ash, which contains about 20-30% calcium hydroxide, but it is generally classified as hazardous waste, resulting in waste of resources. Summary of the invention

[0004] The present invention aims at the technical problem that the existing electrolytic aluminum ash treatment cannot effectively remove fluorine, resulting in high process energy consumption and short equipment service life. The present invention provides an electrolytic aluminum ash harmless treatment device and method. Dust removal ash and dilute hydrochloric acid are used to obtain soluble calcium salt, and calcium chloride is reacted with fluoride in the electrolytic aluminum ash to obtain calcium fluoride precipitation, so that most of the fluorine can be removed, which greatly reduces the occurrence of MVR pipeline corrosion and scaling blockage, prolongs the service life of the equipment, and at the same time, the salt content is increased by circulating and enriching the dilute brine, thereby reducing the MVR energy consumption.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The present invention provides a harmless treatment device for electrolytic aluminum ash, comprising a raw material preparation reaction system and a slurry treatment system, wherein the raw material preparation system comprises a semi-finished product ash bin, a first calcium chloride tank, a raw material brine tank, a batching tank and a reaction tank; the slurry treatment system comprises a vacuum belt filter, a light brine tank, a second calcium chloride tank, a concentrated brine tank, an alkali liquid tank, a precipitation slurry tank, an air compressor and an MVR evaporator; The bottom outlets of the semi-finished product ash bin, the first calcium chloride tank, and the raw brine tank are connected to the raw material inlet of the batching tank, the bottom liquid outlet of the batching tank is connected to the liquid inlet of the reaction tank, the top gas outlet of the reaction tank is connected to the ammonia recovery system, the bottom liquid outlet of the reaction tank is connected to the raw material inlet of the vacuum belt filter, the brine outlet of the vacuum belt filter is connected to the top brine inlets of the dilute brine tank and the concentrated brine tank, the second calcium chloride tank and the alkali solution tank are connected to the top brine inlets of the dilute brine tank and the concentrated brine tank respectively, the bottom outlets of the dilute brine tank and the concentrated brine tank are connected to the top inlet of the precipitation slurry tank, the bottom outlet of the precipitation slurry tank is connected to the raw material inlet of the vacuum belt filter, the upper liquid outlet of the dilute brine tank is connected to the liquid inlet of the raw brine tank, the side net brine outlet of the concentrated brine tank is connected to the MVR evaporator, and the gas outlet of the air compressor is connected to the bottom outlets of the dilute brine tank and the concentrated brine tank.

[0006] In the above technical solution of the present invention, the bottom outlet pipes of the brine tank and the concentrated brine tank are divided into a gas pipe and a slurry pipe, the gas pipe is connected to the gas outlet of the air compressor, and the slurry pipe is connected to the top inlet of the sedimentation slurry tank.

[0007] In the above technical solution of the present invention, the number of reaction tanks is three.

[0008] In the above technical solution of the present invention, the number of the dilute salt water tank and the number of the concentrated salt water tank are both two.

[0009] The present invention also provides a method for harmless treatment of electrolytic aluminum ash based on the above-mentioned electrolytic aluminum ash harmless treatment device, comprising the following steps: The raw ash in the semi-finished product ash bin is made of electrolytic aluminum ash through ball milling and screening. The calcium hydroxide in the dust removal ash in the first calcium chloride tank reacts with dilute hydrochloric acid to obtain a calcium chloride solution. The raw brine from the raw brine tank is sent to the batching tank together with the calcium chloride solution and the raw ash for mixing and then sent to the reaction tank; The gas generated in the reaction tank is sent to the ammonia recovery system, the slurry in the reaction tank is sent to the vacuum belt filter for filtration, the precipitate enters the filter cake, and the filtered brine enters the desalinated brine tank; Add the calcium chloride solution from the second calcium chloride tank to the light brine tank and introduce high-pressure air from the bottom for aeration and stirring to obtain calcium fluoride precipitation. After standing, send the upper clear liquid to the raw brine tank for batching. After introducing high-pressure air for aeration and stirring again, send the bottom precipitate to the precipitation slurry tank, and then send it to the vacuum belt filter for filtration. The precipitate enters the filter cake. As the batching, reaction and filtration are continuously carried out, the salt is enriched. After the salt content in the filtered brine reaches 30%, the filtered brine is sent to the concentrated brine tank; Add alkali solution from the alkali solution tank into the concentrated brine tank and introduce high-pressure air from the bottom for aeration and stirring to obtain calcium carbonate precipitate. After aging, send the upper clean brine to the MVR evaporator, introduce high-pressure air to the bottom of the concentrated brine tank for aeration and stirring again, and then send the bottom precipitate to the precipitation slurry tank, and then send the slurry to the vacuum belt filter for filtration, and the precipitate enters the filter cake. The filtered brine enters the desalinated brine tank. With the continuous progress of batching, reaction and filtration, the salt is enriched. When the salt content in the filtered brine reaches 30%, the filtered brine is sent to the concentrated brine tank, and the cycle is repeated.

[0010] In the above technical solution of the present invention, the alkali solution is a mixed solution of sodium hydroxide and sodium carbonate.

[0011] Compared with the prior art, the present invention has the following beneficial effects: The present invention adds a calcium chloride solution to the raw salt water, and the calcium chloride reacts with the fluoride in the electrolytic aluminum ash to generate a calcium fluoride precipitate, thereby removing most of the fluorine; in the salt water tank, calcium chloride is added again to generate a calcium fluoride precipitate, and the fluorine in the salt water is further removed, so that the fluorine content in the raw salt water used for batching is at the lowest state, thereby ensuring that the leached fluorine content after the harmless treatment of the electrolytic aluminum ash meets the standard, thereby greatly reducing the occurrence of MVR pipeline corrosion caused by the presence of fluorine, and extending the service life of the equipment.

[0012] The present invention increases the salt content by circulatory enrichment of the light brine, so that the brine entering the MVR evaporator is close to saturation, greatly reducing the MVR energy consumption, and no excess wastewater is discharged. In addition, in the concentrated brine tank, alkali solution is added to generate calcium carbonate precipitation, so that excess calcium ions can be removed, thereby avoiding the scaling and blockage of the MVR pipeline caused by the presence of calcium ions, thereby improving the crystallization efficiency and reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The figure is a schematic diagram of the process flow of the harmless treatment method of electrolytic aluminum ash of the present invention.

[0014] Markings in the attached figure: 1 is a semi-finished product ash bin, 2 is a first calcium chloride tank, 3 is a raw material brine tank, 4 is a batching tank, 5 is a reaction tank, 6 is a vacuum belt filter, 7 is a light brine tank, 8 is a second calcium chloride tank, 9 is a concentrated brine tank, 10 is an alkali liquid tank, 11 is a precipitation slurry tank, 12 is an air compressor, and 13 is an MVR evaporator. DETAILED DESCRIPTION

[0015] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means known to those skilled in the art. The test methods in the following examples are conventional methods unless otherwise specified.

[0016] Embodiment 1 like Figure 1 As shown in the process flow chart, an electrolytic aluminum ash harmless treatment device of the present invention includes a raw material preparation reaction system and a slurry treatment system, wherein the raw material preparation system includes a semi-finished product ash bin 1, a first calcium chloride tank 2, a raw material brine tank 3, a batching tank 4 and a reaction tank 5; the slurry treatment system includes a vacuum belt filter 6, a light brine tank 7, a second calcium chloride tank 8, a concentrated brine tank 9, an alkali solution tank 10, a precipitation slurry tank 11, an air compressor 12 and an MVR evaporator 13.

[0017] The bottom outlets of the semi-finished product ash bin 1, the first calcium chloride tank 2 and the raw material brine tank 3 are connected to the raw material inlet of the batching tank 4, and the bottom liquid outlet of the batching tank 4 is connected to the liquid inlet of the reaction tank 2. The raw material ash in the semi-finished product ash bin 1 is made of electrolytic aluminum ash through ball milling and screening, the batching water comes from the raw material brine tank 3, the dust removal ash in the first calcium chloride tank 2 reacts with dilute hydrochloric acid to obtain a calcium chloride solution (generally, dilute hydrochloric acid with a concentration of 10% is selected, and the amount of dilute hydrochloric acid added is determined according to the molar ratio of chloride ions to calcium ions in the dust removal ash of 2:1), and the raw material brine and raw material ash are added to the batching tank 4 at a mass ratio of 2:1. In actual operation, the composition of the raw material ash is detected to control the amount of calcium chloride solution added.

[0018] After the raw materials enter the reaction tank, calcium chloride reacts with most of the soluble fluorides in the electrolytic aluminum ash to form calcium fluoride precipitation, and the aluminum nitride in the electrolytic aluminum ash is hydrolyzed to form ammonia and aluminum hydroxide. Generally, three interconnected reaction tanks 5 are set to make the reaction sufficient. The gas outlet at the top of the reaction tank 2 is connected to the ammonia recovery system, the bottom liquid outlet of the reaction tank 5 is connected to the raw material inlet of the vacuum belt filter 6, and the brine outlet of the vacuum belt filter 6 is connected to the top brine inlet of the brine tank 7 and the concentrated brine tank 9. The second calcium chloride tank 8 and the alkali liquid tank 10 are connected to the top brine inlet of the brine tank 7 and the concentrated brine tank 9 respectively. The bottom outlets of the brine tank 7 and the concentrated brine tank 9 are connected to the top inlet of the precipitation slurry tank 11. The bottom outlet of the precipitation slurry tank 11 is connected to the raw material inlet of the vacuum belt filter 6, the upper liquid outlet of the brine tank 7 is connected to the liquid inlet of the raw material brine tank 3, the side net brine outlet of the concentrated brine tank 9 is connected to the MVR evaporator 8, and the gas outlet of the air compressor 10 is connected to the bottom outlet of the brine tank 7 and the concentrated brine tank 9.

[0019] In one embodiment, the vacuum belt filter 6 generally adopts a five-stage vacuum belt filter, including a mother liquor zone, a four-stage elution zone and a draining zone, the liquid outlet of the mother liquor zone and the liquid outlet of the first-stage elution zone correspond to the brine outlet, and the draining zone corresponds to the filter cake ash outlet; the alkali solution in the alkali solution tank 10 is a mixed solution prepared by 7% sodium hydroxide and 21% sodium carbonate, wherein sodium hydroxide is used to adjust the pH value of the concentrated brine, and sodium carbonate is used to react with calcium ions to generate calcium carbonate precipitate to remove calcium ions.

[0020] Furthermore, for the convenience of operation, the bottom outlet pipes of the salt water tank 7 and the concentrated salt water tank 9 are divided into a gas pipe and a slurry pipe, and corresponding control valves are arranged on the pipes. The gas pipe is connected to the gas outlet of the air compressor 10, and the slurry pipe is connected to the top inlet of the sedimentation slurry tank 11, so that aeration and discharge of the sedimentation slurry do not affect each other.

[0021] like Figure 1 As shown in the process flow chart, the harmless treatment method of electrolytic aluminum ash of the present invention specifically comprises the following steps: (1) The raw ash in the semi-finished product ash bin 1 is obtained by ball milling and screening the electrolytic aluminum ash. The calcium hydroxide in the dust removal ash reacts with dilute hydrochloric acid in the first calcium chloride tank 2 to obtain a calcium chloride solution. The raw brine from the raw brine tank 3 is sent to the batching tank 4 together with the calcium chloride solution and the raw ash for mixing and then sent to the reaction tank 5.

[0022] (2) In the reaction tank, calcium chloride reacts with most of the soluble fluorides in the electrolytic aluminum ash to form calcium fluoride precipitation, and aluminum nitride in the electrolytic aluminum ash is hydrolyzed to form ammonia and aluminum hydroxide. The gas generated in the reaction tank 5 is sent to the ammonia recovery system after exiting from the top outlet, and the slurry in the reaction tank 5 is sent to the vacuum belt filter 6 for filtration, the calcium fluoride precipitation enters the filter cake, and the filtered brine enters the desalinated brine tank 7.

[0023] (3) Add an excess of calcium chloride solution from the second calcium chloride tank 8 to the salt water tank 7 and introduce high-pressure air from the bottom for aeration and stirring for 5 minutes to obtain calcium fluoride precipitation. After standing for 12 hours, send the upper clear liquid to the raw salt water tank 3 for batching. After introducing high-pressure air for aeration and stirring for 5 minutes again, send the bottom precipitate to the precipitation slurry tank 11, and then send it to the vacuum belt filter 6 for filtration. The precipitate enters the filter cake, and the salt is enriched as the batching, reaction and filtration continue. After the salt content in the filtered salt water reaches 30%, the filtered salt water is sent to the concentrated salt water tank 9. In actual operation, the fluoride ion concentration in the salt water is detected to control the addition amount of calcium chloride solution.

[0024] (4) Add alkali solution from alkali solution tank 10 to concentrated brine tank 9 and introduce high-pressure air from the bottom for aeration and stirring to obtain calcium carbonate precipitation. After aging for 24 hours, the upper clean brine is sent to MVR evaporator 13 for crystallization of salt (if the clean brine contains a small amount of ash, it can be filtered through a stainless steel double filter with a pore size of 10μm before entering the MVR evaporator). After introducing high-pressure air to the bottom of concentrated brine tank 9 for aeration and stirring for 5 minutes, the bottom precipitate and ash are sent to precipitation slurry tank 11, and then sent to vacuum belt filter 6 for filtration. The precipitate enters the filter cake, and the filtered brine enters the dilute brine tank 7. With the continuous process of batching, reaction and filtration, the salt is enriched. After the salt content in the filtered brine reaches 30%, the filtered brine is sent to concentrated brine tank 9, and the cycle is repeated. In actual operation, the calcium ion concentration and pH value of the concentrated brine are detected to control the addition amount of calcium chloride solution.

[0025] In one possible implementation, two salt water tanks 7 and two concentrated salt water tanks 9 are provided, and operations such as salt water intake, reaction, sedimentation, and aging are performed alternately to ensure continuous and stable production.

[0026] The present invention first uses dilute hydrochloric acid to react with calcium hydroxide in dust removal ash to obtain soluble calcium chloride, instead of directly adding dust removal ash to the batching tank, so as to avoid that calcium hydroxide slightly soluble in water in dust removal ash cannot fully react with fluoride and affect the initial defluorination effect, thereby realizing the effective utilization of dust removal ash as a hazardous waste. Thereafter, calcium chloride solution is added to the raw brine, and calcium chloride reacts with fluoride in electrolytic aluminum ash to form calcium fluoride precipitate, thereby removing most of the fluorine; in the salt water tank 7, calcium chloride is added again to form calcium fluoride precipitate, further removing the fluorine in the salt water, so that the fluorine content in the raw brine used for batching is at the lowest state, thereby ensuring that the leached fluorine content meets the standard after the harmless treatment of electrolytic aluminum ash, thereby greatly reducing the occurrence of MVR pipeline corrosion caused by the presence of fluorine and extending the service life of the equipment.

[0027] The present invention increases the salt content by circulating and enriching the light brine, so that the brine entering the MVR evaporator 13 is close to saturation, which greatly reduces the MVR energy consumption and does not discharge excess wastewater. In addition, in the concentrated brine tank 9, alkali solution is added to generate calcium carbonate precipitation, so that excess calcium ions can be removed, thereby avoiding the scaling and blockage of the MVR pipeline caused by the presence of calcium ions, thereby improving the crystallization efficiency and reducing energy consumption.

[0028] The embodiments described above are only preferred embodiments of the present invention and are only used to explain the present invention, not to limit the scope of implementation of the present invention. For those skilled in the art, other implementation methods can certainly be easily made by replacement or modification based on the technical contents disclosed in this specification. Therefore, all changes and improvements made on the principles of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. A harmless treatment device for electrolytic aluminum ash, characterized in that: It comprises a raw material preparation reaction system and a slurry treatment system, wherein the raw material preparation system comprises a semi-finished product ash bin (1), a first calcium chloride tank (2), a raw material brine tank (3), a batching tank (4) and a reaction tank (5); the slurry treatment system comprises a vacuum belt filter (6), a light brine tank (7), a second calcium chloride tank (8), a concentrated brine tank (9), an alkali liquid tank (10), a precipitation slurry tank (11), an air compressor (12) and an MVR evaporator (13); The bottom outlets of the semi-finished product ash bin (1), the first calcium chloride tank (2), and the raw material brine tank (3) are connected to the raw material inlet of the batching tank (4); the bottom liquid outlet of the batching tank (4) is connected to the liquid inlet of the reaction tank (2); the top gas outlet of the reaction tank (2) is connected to the ammonia recovery system; the bottom liquid outlet of the reaction tank (5) is connected to the raw material inlet of the vacuum belt filter (6); the brine outlet of the vacuum belt filter (6) is connected to the top brine inlets of the dilute brine tank (7) and the concentrated brine tank (9); the second calcium chloride tank (8) and the alkali solution tank (10) are connected to the raw material inlet of the vacuum belt filter (6); The top brine inlets of the dilute brine tank (7) and the concentrated brine tank (9) are respectively connected; the bottom outlets of the dilute brine tank (7) and the concentrated brine tank (9) are connected to the top inlet of the precipitation slurry tank (11); the bottom outlet of the precipitation slurry tank (11) is connected to the raw material inlet of the vacuum belt filter (6); the upper liquid outlet of the dilute brine tank (7) is connected to the liquid inlet of the raw material brine tank (3); the side clean brine outlet of the concentrated brine tank (9) is connected to the MVR evaporator (8); and the gas outlet of the air compressor (10) is connected to the bottom outlets of the dilute brine tank (7) and the concentrated brine tank (9).

2. The harmless treatment device for electrolytic aluminum ash according to claim 1 is characterized in that: The bottom outlet pipes of the salt water tank (7) and the concentrated salt water tank (9) are divided into a gas pipe and a slurry pipe, the gas pipe is connected to the gas outlet of the air compressor (10), and the slurry pipe is connected to the top inlet of the sedimentation slurry tank (11).

3. The harmless treatment device for electrolytic aluminum ash according to claim 1 is characterized in that: The number of reaction tanks (5) is three.

4. The harmless treatment device for electrolytic aluminum ash according to claim 1 is characterized in that: The number of the dilute salt water tank (7) and the number of the concentrated salt water tank (9) are both two.

5. A method for harmless treatment of electrolytic aluminum ash based on the harmless treatment device for electrolytic aluminum ash according to any one of claims 1 to 3, characterized in that: The following steps are involved: The raw ash in the semi-finished product ash bin (1) is obtained by ball milling and screening electrolytic aluminum ash. The calcium hydroxide in the dust removal ash reacts with dilute hydrochloric acid in the first calcium chloride tank (2) to obtain a calcium chloride solution. The raw brine from the raw brine tank (3) is sent to the batching tank (4) together with the calcium chloride solution and the raw ash for mixing and then sent to the reaction tank (5). The gas generated in the reaction tank (5) is sent to the ammonia recovery system, the slurry in the reaction tank (5) is sent to the vacuum belt filter (6) for filtration, the precipitate enters the filter cake, and the filtered brine enters the desalinated brine tank (7); Adding the calcium chloride solution from the second calcium chloride tank (8) to the salt water tank (7) and introducing high-pressure air from the bottom for aeration and stirring to obtain calcium fluoride precipitate, after standing, sending the upper clear liquid to the raw salt water tank (3) for batching, introducing high-pressure air for aeration and stirring again, sending the bottom precipitate to the precipitation slurry tank (11), and then to the vacuum belt filter (6) for filtration, and the precipitate enters the filter cake, and the salt is enriched as the batching, reaction and filtration are continuously performed, and after the salt content in the filtered salt water reaches 30%, the filtered salt water is sent to the concentrated salt water tank (9); Alkali from the alkali liquid tank (10) is added to the concentrated brine tank (9) and high-pressure air is introduced from the bottom for aeration and stirring to obtain calcium carbonate precipitation. After aging, the upper clean brine is sent to the MVR evaporator (13). High-pressure air is introduced to the bottom of the concentrated brine tank (9) for aeration and stirring again, and the bottom precipitate is sent to the precipitation slurry tank (11). The slurry is then sent to the vacuum belt filter (6) for filtration, and the precipitate enters the filter cake. The filtered brine enters the dilute brine tank (7). As the ingredients, reaction and filtration are continuously carried out, the salt is enriched. When the salt content in the filtered brine reaches 30%, the filtered brine is sent to the concentrated brine tank (9), and the cycle is repeated.

6. The method for harmless treatment of electrolytic aluminum ash according to claim 5, characterized in that: The alkali solution is a mixed solution of sodium hydroxide and sodium carbonate.

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