A harmless treatment device and method for electrolytic aluminum ash

Abstract

The present application belongs to the technical field of electrolytic aluminum ash treatment, and discloses a harmless treatment device for electrolytic aluminum ash, which comprises a raw material preparation reaction system and a ore slurry treatment system, 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 ore slurry treatment system comprises a vacuum belt filter, a light brine tank, a second calcium chloride tank, a concentrated brine tank, a lye tank, a precipitate slurry tank, an air compressor and an MVR evaporator. The present application uses dust removal ash and dilute hydrochloric acid to obtain soluble calcium salt, makes calcium chloride react with fluoride in electrolytic aluminum ash to obtain calcium fluoride precipitation, so that most of the fluorine can be removed, the occurrence of MVR pipeline corrosion, scaling and blockage is greatly reduced, the service life of the equipment is prolonged, and the salt content is improved by circulating and enriching the light brine, so that the MVR energy consumption is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrolytic aluminum ash treatment and relates to a harmless treatment device and method for electrolytic aluminum ash. BACKGROUND

[0002] The electrolytic aluminum ash contains fluoride ions, aluminum nitride and about 5% of salt. Generally, when the electrolytic aluminum ash is harmlessly treated, calcium hydroxide is added to the electrolytic aluminum ash for hydrolysis reaction, so as to reduce the content of aluminum nitride in the aluminum ash, reduce the fluoride content and salt content of the aluminum ash immersed, and reach the harmless standard. However, this treatment will produce a large amount of high-fluorine salt water, and the salt content is only about 3%. If the salt is extracted, the energy consumption of the MVR is particularly large, and the fluoride content is high, which corrodes the MVR and affects the service life of the equipment.

[0003] In addition, sulfur-containing flue gas will be generated when the primary aluminum ash is added with a composite salt for refining in a rotary furnace. The calcium hydroxide method is currently used for desulfurization of this part of flue gas, and calcium addition dust removal ash will be generated in the desulfurization process, which contains about 20-30% of calcium hydroxide. However, it is generally treated as hazardous waste, which causes resource waste. SUMMARY

[0004] The application aims at the technical problem that the existing electrolytic aluminum ash treatment cannot effectively remove fluoride, resulting in high process energy consumption and short service life of equipment, and provides a harmless treatment device and method for electrolytic aluminum ash, which obtains soluble calcium salt by using dust removal ash and dilute hydrochloric acid, so that calcium chloride reacts with fluoride in the electrolytic aluminum ash to obtain calcium fluoride precipitation, so that most of the fluoride is removed, the occurrence of MVR pipeline corrosion, scaling and plugging is greatly reduced, and the service life of the equipment is prolonged. At the same time, the salt content is improved by circulating and enriching the dilute brine, and the energy consumption of the MVR is reduced.

[0005] To achieve the above-mentioned purpose, the following technical solutions are adopted in the application.

[0006] The application provides a harmless treatment device for electrolytic aluminum ash, which comprises a raw material preparation reaction system and a ore slurry treatment system. The raw material preparation reaction 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 ore slurry treatment system comprises a vacuum belt filter, a dilute brine tank, a second calcium chloride tank, a concentrated brine tank, a lye tank, a precipitate slurry tank, an air compressor and an MVR evaporator.

[0007] The bottom outlet of the semi-finished ash bin, the first calcium chloride tank and the raw brine tank is 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 inlet of the dilute brine tank and the concentrated brine tank, the top brine inlets of the dilute brine tank and the concentrated brine tank are respectively connected to the top brine inlets of the dilute brine tank and the concentrated brine tank, the bottom outlets of the dilute brine tank and the concentrated brine tank are connected to the top inlet of the precipitate slurry tank, the bottom outlet of the precipitate 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 pure 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.

[0008] In the technical scheme of the present application, the bottom outlet pipelines of the dilute brine tank and the concentrated brine tank are divided into a gas pipeline and a slurry pipeline, the gas pipeline is connected to the gas outlet of the air compressor, and the slurry pipeline is connected to the top inlet of the precipitate slurry tank.

[0009] In the technical scheme of the present application, the reaction tank is provided with three.

[0010] In the technical scheme of the present application, the dilute brine tank and the concentrated brine tank are each provided with two.

[0011] The present application also provides an electrolytic aluminum ash harmless treatment method based on the above-mentioned electrolytic aluminum ash harmless treatment device, which comprises the following steps:

[0012] The raw material ash in the semi-finished ash bin is made of electrolytic aluminum ash by ball milling and screening, calcium hydroxide in the dust in the first calcium chloride tank reacts with dilute hydrochloric acid to obtain calcium chloride solution, the raw material brine from the raw brine tank, the calcium chloride solution and the raw material ash are sent into the batching tank for mixing and then into the reaction tank;

[0013] The generated gas in the reaction tank is sent into the ammonia recovery system, and the ore slurry in the reaction tank is sent into the vacuum belt filter for filtration, the precipitate enters the filter cake, and the filtered brine enters the dilute brine tank;

[0014] Calcium fluoride precipitate is obtained by adding calcium chloride solution from the second calcium chloride tank into the dilute brine tank and introducing high-pressure air for aeration and stirring from the bottom, the upper clear liquid is sent into the raw brine tank for batching after standing, high-pressure air is introduced again for aeration and stirring, the bottom precipitate is sent into the precipitate slurry tank and then into the vacuum belt filter for filtration, the precipitate enters the filter cake, and the batching, reaction and filtration are continuously carried out to enrich the salt, and the filtered brine is sent into the concentrated brine tank when the salt content in the filtered brine reaches 30%;

[0015] The alkali liquor from the alkali liquor tank is added into the concentrated brine tank, and high-pressure air is introduced into the bottom for aeration and stirring to obtain calcium carbonate precipitate, and after aging, the upper clean brine is sent into the MVR evaporator, high-pressure air is again introduced into the bottom of the concentrated brine tank for aeration and stirring, and then the bottom precipitate is sent into the precipitate slurry tank, and then the slurry is sent into the vacuum belt filter for filtration, the precipitate enters the filter cake, and the filtered brine enters the dilute brine tank, and with the continuous feeding, reaction and filtration, the salt is enriched, and when the salt content in the filtered brine reaches 30%, the filtered brine is sent into the concentrated brine tank, and the cycle is repeated.

[0016] In the technical scheme of the present application, the alkali liquor is a mixed solution of sodium hydroxide and sodium carbonate.

[0017] Compared with the prior art, the present application has the following beneficial effects:

[0018] In the present application, calcium chloride solution is added into the raw brine, and the calcium chloride reacts with the fluoride in the electrolytic aluminum ash to form calcium fluoride precipitate, thereby removing most of the fluoride; in the dilute brine tank, calcium chloride is again added to form calcium fluoride precipitate, further removing the fluoride in the dilute brine, and the fluoride content in the raw brine used for batching is at a minimum, thereby ensuring that the leaching fluoride content of the electrolytic aluminum ash after harmless treatment meets the standard, which greatly reduces the occurrence of MVR pipeline corrosion due to the presence of fluoride, and prolongs the service life of the equipment.

[0019] In the present application, the dilute brine is recycled and enriched to increase the salt content, so that the brine entering the MVR evaporator is close to saturation, greatly reducing the energy consumption of the MVR, and no excess wastewater is discharged. In addition, in the concentrated brine tank, alkali liquor is added to form calcium carbonate precipitate, so that excess calcium ions are removed, thereby avoiding the existence of calcium ions causing MVR pipeline fouling and blockage, thereby improving the crystallization efficiency and reducing the energy consumption. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a process flow diagram of the electrolytic aluminum ash harmless treatment method of the present application.

[0021] In the drawings, 1 is a semi-finished product ash bin, 2 is a first calcium chloride tank, 3 is a raw brine tank, 4 is a batching tank, 5 is a reaction tank, 6 is a vacuum belt filter, 7 is a dilute brine tank, 8 is a second calcium chloride tank, 9 is a concentrated brine tank, 10 is an alkali liquor tank, 11 is a precipitate slurry tank, 12 is an air compressor, and 13 is an MVR evaporator. DETAILED DESCRIPTION

[0022] The following examples are used to illustrate the present application, but are not used to limit the protection scope of the present application. If not specifically indicated, 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.

[0023] Example 1

[0024] As Figure 1 shown in the process flow chart, the electrolytic aluminum ash harmless treatment device of the present application includes a raw material preparation reaction system and a slurry treatment system, wherein the raw material preparation reaction 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 dilute brine tank 7, a second calcium chloride tank 8, a concentrated brine tank 9, a lye tank 10, a precipitate slurry tank 11, an air compressor 12 and an MVR evaporator 13.

[0025] The bottom outlet of the semi-finished product ash bin 1, the first calcium chloride tank 2 and the raw material brine tank 3 is 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 5. The raw material ash in the semi-finished product ash bin 1 is obtained by ball milling and screening from the electrolytic aluminum ash, the batching water comes from the raw material brine tank 3, the calcium chloride solution is obtained by the reaction of the dust ash and dilute hydrochloric acid in the first calcium chloride tank 2 (generally, 10% dilute hydrochloric acid is selected, and the amount of dilute hydrochloric acid is determined according to the molar ratio of chloride ions to calcium ions in the dust ash being 2:1), the raw material brine and the raw material ash are added to the batching tank 4 at a mass ratio of 2:1, and in actual operation, the composition of the raw material ash is detected to control the amount of calcium chloride solution added.

[0026] After the raw material enters the reaction tank 5, the calcium chloride reacts with most of the soluble fluorides in the electrolytic aluminum ash to generate calcium fluoride precipitate, and the aluminum nitride in the electrolytic aluminum ash hydrolyzes to generate ammonia gas and aluminum hydroxide. Generally, three reaction tanks 5 are connected to each other to ensure sufficient reaction. The gas outlet at the top of the reaction tank 5 is connected to an 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 inlets of the dilute brine tank 7 and the concentrated brine tank 9. The second calcium chloride tank 8 and the lye tank 10 are respectively connected to the top brine inlets of the dilute brine tank 7 and the concentrated brine tank 9. The bottom outlets of the dilute brine tank 7 and the concentrated brine tank 9 are connected to the top inlet of the precipitate slurry tank 11. The bottom outlet of the precipitate 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 clean brine outlet of the concentrated brine tank 9 is connected to the MVR evaporator 13, and the gas outlet of the air compressor 12 is connected to the bottom outlets of the dilute brine tank 7 and the concentrated brine tank 9.

[0027] In an embodiment, the vacuum belt filter 6 generally adopts a five-stage vacuum belt filter, including a mother liquor zone, a four-stage leaching zone and a dry extraction zone, the liquid outlets of the mother liquor zone and the first-stage leaching zone correspond to the brine outlet, and the dry extraction zone corresponds to the filter cake ash outlet; the lye in the lye tank 10 is a mixed solution prepared by 7% sodium hydroxide and 21% sodium carbonate, wherein the sodium hydroxide is used to adjust the pH value of the concentrated brine, and the sodium carbonate is used to react with calcium ions to generate calcium carbonate precipitate to remove calcium ions.

[0028] Further, for the convenience of operation, the bottom outlet pipes of the dilute brine tank 7 and the concentrated brine tank 9 are divided into gas pipes and slurry pipes, and corresponding control valves are arranged on the pipes. The gas pipes are connected to the gas outlet of the air compressor 12, and the slurry pipes are connected to the top inlet of the precipitate slurry tank 11, so that the aeration and the discharge of the precipitate slurry do not affect each other.

[0029] As shown in the process flow chart, Figure 1 The harmless treatment method of the electrolytic aluminum ash of the present application specifically comprises the following steps:

[0030] (1) The raw ash in the semi-finished ash bin 1 is made of electrolytic aluminum ash by ball milling and sieving. In the first calcium chloride tank 2, calcium hydroxide in the dust is reacted with dilute hydrochloric acid to obtain a calcium chloride solution. After the raw brine from the raw brine tank 3, the calcium chloride solution, and the raw ash are mixed uniformly in the batching tank 4, they are sent to the reaction tank 5.

[0031] (2) In the reaction tank, calcium chloride reacts with most of the soluble fluorides in the electrolytic aluminum ash to generate calcium fluoride precipitate, and aluminum nitride in the electrolytic aluminum ash hydrolyzes to generate ammonia gas and aluminum hydroxide. The gas generated in the reaction tank 5 is sent to the ammonia recovery system 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 precipitate enters the filter cake, and the filtered brine enters the dilute brine tank 7.

[0032] (3) Excess calcium chloride solution from the second calcium chloride tank 8 is added to the dilute brine tank 7, and high-pressure air is introduced from the bottom for aeration and stirring for 5 min to obtain calcium fluoride precipitate. After standing for 12 h, the upper clear liquid is sent to the raw brine tank 3 for batching. After aeration and stirring for 5 min again, the bottom precipitate is sent to the precipitate slurry tank 11 and then to the vacuum belt filter 6 for filtration. The precipitate enters the filter cake, and the batching, reaction, and filtration continue to enrich the salt. When the salt content in the filtered brine reaches 30%, the filtered brine is sent to the concentrated brine tank 9. In actual operation, the concentration of fluoride ions in the dilute brine is detected to control the amount of calcium chloride solution added.

[0033] (4) into the concentrated brine tank 9 from the alkali tank 10 and from the bottom into the high-pressure air aeration stirring, get calcium carbonate precipitate, aging 24h, the upper part of the clean brine into MVR evaporator 13 crystallization salt (if the clean brine contains a small amount of ash, can be filtered through the aperture 10 μm stainless steel double filter machine after entering the MVR evaporator), into the concentrated brine tank 9 bottom high-pressure air aeration stirring 5min after the bottom precipitate, ash into the precipitate slurry tank 11, then into the vacuum belt filter 6 filter, precipitate into the filter cake, filter brine into the brine tank 7, with the ingredients, reaction, filtration continuously to make the salt enrichment, when the filter brine salt content reaches 30% after the filter brine into the concentrated brine tank 9, so the cycle. In actual operation by detecting the concentration of calcium ions in the concentrated brine and pH, to control the amount of calcium chloride solution.

[0034] In one embodiment, the dilute brine tank 7 and the concentrated brine tank 9 are provided with two, alternating salt water, reaction, settling, aging and other operations, so that the production is continuous and stable.

[0035] The present application first uses dilute hydrochloric acid to react with calcium hydroxide in the fly ash to obtain soluble calcium chloride, instead of directly adding fly ash to the batching tank, so that the slightly soluble calcium hydroxide in the fly ash and fluoride cannot fully react, which affects the preliminary fluorine removal effect, and realizes the effective utilization of the fly ash, a hazardous waste. Subsequently, calcium chloride solution is added to the raw brine, calcium fluoride precipitate is generated by the reaction of calcium chloride and fluoride in the electrolytic aluminum ash, thereby removing most of the fluorine; in the dilute brine tank 7, calcium fluoride precipitate is generated again by adding calcium chloride, further removing fluorine in the dilute brine, and the fluorine content in the raw brine used for batching is in the lowest state, thereby ensuring that the leaching fluorine content of the electrolytic aluminum ash after harmless treatment meets the standard, which greatly reduces the occurrence of MVR pipeline corrosion due to the presence of fluorine, and prolongs the service life of the equipment.

[0036] The present application improves the salt content by circulating and enriching the dilute brine, so that the brine entering the MVR evaporator 13 is close to saturation, which greatly reduces the energy consumption of the MVR, and no excess wastewater is discharged. In addition, in the concentrated brine tank 9, calcium carbonate precipitate is generated by adding alkali, so that excess calcium ions are removed, thereby avoiding the existence of calcium ions causing MVR pipeline fouling and blockage, thereby improving the crystallization efficiency and reducing the energy consumption.

[0037] The above-described embodiments are only preferred embodiments of the present application, merely to explain the present application, and not to limit the scope of the present application. For those skilled in the art, of course, other embodiments can be easily made by substitution or change based on the technical content disclosed in the present application, therefore, any changes and improvements made on the principle of the present application shall be included in the scope of the patent application.

Claims

1. A device for the harmless treatment of electrolytic aluminum ash, characterized in that, The system comprises a raw material preparation and reaction system and a slurry treatment system, the raw material preparation and reaction 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 dilute brine tank (7), a second calcium chloride tank (8), a concentrated brine tank (9), a lye tank (10), a precipitate slurry tank (11), an air compressor (12) and an MVR evaporator (13); The bottom outlet of the semi-finished product ash bin (1), the first calcium chloride tank (2) and the raw material brine tank (3) is 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 (5), the gas outlet at the top of the reaction tank (5) is connected to an 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 lye tank (10) are respectively connected to the top brine inlets of the dilute brine tank (7) and the concentrated brine tank (9), the bottom outlets of the dilute brine tank (7) and the concentrated brine tank (9) are connected to the top inlet of the precipitate slurry tank (11), the bottom outlet of the precipitate 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 net brine outlet at the side of the concentrated brine tank (9) is connected to the MVR evaporator (13), and the gas outlet of the air compressor (12) is connected to the bottom outlets of the dilute brine tank (7) and the concentrated brine tank (9).

2. The device for harmless treatment of electrolytic aluminum ash according to claim 1, characterized in that, The bottom outlet pipelines of the dilute brine tank (7) and the concentrated brine tank (9) are divided into a gas pipeline and a slurry pipeline, the gas pipeline is connected to the gas outlet of the air compressor (12), and the slurry pipeline is connected to the top inlet of the precipitate slurry tank (11).

3. The device for harmless treatment of electrolytic aluminum ash according to claim 1, characterized in that, The reaction tank (5) is provided with three.

4. The device for harmless treatment of electrolytic aluminum ash according to claim 1, characterized in that, The dilute brine tank (7) and the concentrated brine tank (9) are each provided with two.

5. A method for harmless treatment of electrolytic aluminum ash based on the device according to any one of claims 1 to 4, characterized in that, The system comprises the following steps: The raw material ash in the semi-finished product ash bin (1) is obtained by ball milling and screening of electrolytic aluminum ash, calcium hydroxide in the dust in the first calcium chloride tank (2) reacts with dilute hydrochloric acid to obtain a calcium chloride solution, the raw material brine from the raw material brine tank (3), the calcium chloride solution and the raw material ash are mixed uniformly in the batching tank (4) and then sent to the reaction tank (5); The generated gas in the reaction tank (5) is sent to an ammonia recovery system, and the slurry in the reaction tank (5) is sent to the vacuum belt filter (6) for filtration, the precipitate is sent to the filter cake, and the filtered brine is sent to the dilute brine tank (7); The calcium chloride solution from the second calcium chloride tank (8) is added to the brine tank (7), and high-pressure air is introduced from the bottom to aerate and stir, to obtain calcium fluoride precipitate. After standing, the supernatant is sent to the raw material brine tank (3) for batching. After high-pressure air is introduced again to aerate and stir, the bottom precipitate is sent to the precipitate slurry tank (11), and then to the vacuum belt filter (6) for filtration. The precipitate enters the filter cake, and the batching, reaction, and filtration continue to enrich the salt. When the salt content in the filtered brine reaches 30%, the filtered brine is sent to the concentrated brine tank (9); The lye from the lye tank (10) is added to the concentrated brine tank (9), and high-pressure air is introduced from the bottom to aerate and stir, to obtain calcium carbonate precipitate. After standing, the supernatant is sent to the MVR evaporator (13). High-pressure air is introduced again to the bottom of the concentrated brine tank (9) to aerate and stir, and then the bottom precipitate is sent to the precipitate 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 brine tank (7). The batching, reaction, and filtration continue to enrich the salt. When the salt content in the filtered brine reaches 30%, the filtered brine is sent to the concentrated brine tank (9), and the cycle continues.

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

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