CN116605899A - Method for producing high-quality cryolite by-product of aluminum fluoride and its production system - Google Patents

Abstract

The invention provides a method for producing aluminum fluoride byproduct high-quality cryolite, and belongs to the technical field of aluminum fluoride production. The method for producing the aluminum fluoride byproduct high-quality cryolite comprises the following steps: absorbing tail gas and preparing mother liquor: sucking tail gas discharged from the fluidized bed into water in a negative pressure mode to form mother liquor; preparing slurry: sodium aluminate is added into the mother liquor, so that hydrogen fluoride in the mother liquor is fully absorbed to generate cryolite slurry; and (3) filtering and drying: filtering cryolite slurry to obtain filter residues and filtrate; preparing a backwash liquid: adding hydrofluoric acid into the filtrate, and adjusting the pH of the filtrate to 5-6 to form a backwashing liquid; backwashing: adding a reverse washing liquid into the filter residue, repeatedly washing to remove impurities in the cryolite, and then filtering again to obtain the white powder cryolite. The iron fluoride impurity removal is carried out by backwashing, new components are not introduced while the impurity is removed, and the prepared cryolite has high purity and meets the requirements on appearance.

Description

Method for producing high-quality cryolite by-product of aluminum fluoride and its production system

technical field

The invention relates to the technical field of aluminum fluoride production, in particular to a method for producing high-quality cryolite as a by-product of aluminum fluoride and a production system thereof.

Background technique

Existing exhaust gas from the fluidized bed producing aluminum fluoride contains a large amount of hydrogen fluoride gas and aluminum fluoride dust, and these fluorine-containing emissions are finally absorbed by the tail gas purification system. After absorption, fluoride is in an ionic state and is difficult to recycle. In the prior art, there is also a process of using water to absorb tail gas to produce mother liquor and then by-product cryolite, as recorded in Patent No. 101891228, and there is also a process of using mother liquor to by-produce cryolite. In the production process of this process, the slurry preparation step is carried out under weakly acidic or weakly alkaline conditions, and the pH is generally controlled between 6-8 to obtain cryolite products. However, in actual production, the production equipment used for tail gas absorption treatment will also have reduced anti-corrosion performance due to the aging of the anti-corrosion layer, and the acidic solution can penetrate into some weak positions, causing metal corrosion, especially iron elements will come into contact with the acidic solution. At the same time, the water in the mother liquor generally comes from tap water, and tap water generally also contains trace amounts of iron oxide. Hydrofluoric acid can react with iron and iron oxide to produce iron fluoride. At the same time, in the actual process of preparing cryolite, the pH is not stable. When the pH of the solution is too small and in an acidic environment, the formation of ferric fluoride will be promoted. When the pH of the solution is adjusted to neutral later, the formed Ferric fluoride will precipitate with cryolite at the same time in a neutral environment, resulting in dark or yellow color of cryolite. As a result, the impurity content and appearance of cryolite products do not meet user requirements.

Contents of the invention

In view of this, the present invention provides a method for producing aluminum fluoride as a by-product of high-quality cryolite, so as to solve the problem of high impurity content in cryolite products. In addition, the present invention also provides a production system for producing high-quality cryolite by-product of aluminum fluoride.

A method for producing aluminum fluoride by-product high-quality cryolite comprises the following steps:

step one:

Absorb tail gas and prepare mother liquor: suck the tail gas discharged from the fluidized bed into water through negative pressure to form mother liquor;

Step two:

Preparation of slurry: adding sodium aluminate to the mother liquor, so that the hydrogen fluoride in the mother liquor is fully absorbed to form a cryolite slurry;

Step three:

Filtration and drying: filter the cryolite slurry to obtain filter residue and filtrate;

Step four:

Prepare the backwash solution: add hydrofluoric acid to the filtrate to adjust the pH of the filtrate to 5-6 to form a backwash solution;

Step five:

Backwashing: add backwashing solution to the filter residue, wash repeatedly to remove impurities in cryolite, and then filter again to obtain white powder cryolite.

A production system for producing high-quality cryolite by-product of aluminum fluoride includes a negative pressure device, an exhaust gas absorption device, a reaction kettle, a separation device, a backwash liquid tank, a backwash device, and a drying device. The outlet end of the negative pressure device is sealed and connected with the tail gas pipeline of the fluidized bed, and the gas outlet end of the negative pressure device is located at the bottom of the tail gas absorption device to pass the tail gas into the tail gas absorption device. The reaction kettle is provided with a mother liquid inlet and a sodium aluminate liquid inlet. mouth, to add mother liquor and sodium aluminate, the mother liquor inlet is connected to the tail gas absorption device through pipelines, the bottom of the reaction kettle is connected to the separation device, and the liquid discharge port of the separation device is connected to the backwash liquid tank through pipelines to The filtrate is introduced into the backwashing liquid tank, and the liquid inlet of the backwashing device is connected with the backwashing liquid tank through pipelines to flush the filter residue in the backwashing device. The slag port is connected with the feed port of the drying device to dry the filter residue.

Beneficial effects: In the method for producing high-quality cryolite by-product of aluminum fluoride of the present invention, the impurity removal of ferric fluoride is carried out by backwashing, while removing impurities, no new components are introduced, and the purity of the prepared cryolite is Very tall and the look fits the bill.

Description of drawings

Fig. 1 is the process flow chart of the production system of aluminum fluoride by-product high-quality cryolite of the present invention.

Fig. 2 is a schematic structural view of the backwashing device of the present invention.

In the figure: negative pressure device 10, tail gas absorption device 20, spray tower 201, mother liquid pool 202, reaction kettle 30, separation device 40, backwash liquid tank 50, backwash device 60, acid-proof filter bag 601, backwash tank 602 , an ultrasonic vibrator 603 , a drying device 70 , and a fluidized bed 80 .

Detailed ways

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings that need to be used in the embodiments. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. Ordinary technicians can also obtain other drawings based on these drawings on the premise of not paying creative work.

A method for producing aluminum fluoride by-product high-quality cryolite comprises the following steps:

step one:

Absorb tail gas to prepare mother liquor: suck tail gas discharged from fluidized bed 80 into water to form mother liquor;

Step two:

Preparation of slurry: adding sodium aluminate to the mother liquor, so that the hydrogen fluoride in the mother liquor reacts with it to form a cryolite slurry;

Step three:

Filtration and drying: filter the cryolite slurry to obtain filter residue and filtrate;

Step four:

Prepare the backwash solution: add hydrofluoric acid to the filtrate to adjust the pH of the filtrate to 5-6 to form a backwash solution;

Step five:

Backwashing: add backwashing solution to the filter residue, wash repeatedly to remove impurities in cryolite, and then filter again to obtain white powder cryolite.

In a preferred embodiment, the sodium aluminate in step 2 is prepared from sodium hydroxide solution and aluminum hydroxide.

Fluidized bed 80 is used to produce aluminum fluoride. The tail gas discharged from the fluidized bed 80 can be fully absorbed by the form of negative pressure, preventing the tail gas from escaping from the gaps at the joints of the pipes. At the same time, the absorption rate of exhaust gas can also be improved. The main component in the exhaust gas is hydrogen fluoride, which forms hydrofluoric acid after being absorbed by water. Although hydrofluoric acid is a weak acid, it is extremely corrosive and can strongly corrode metals, glass and silicon-containing objects. Iron oxide is easy to react with hydrofluoric acid to form ferric fluoride, which can be dissolved in hydrofluoric acid to form ferric fluoride. When the synthesis end point reaches neutral, ferric fluoride reacts with cryolite in the form of ferric fluoride Precipitate together, resulting in darker or yellowish appearance of cryolite. In the present invention, part of the filtrate is added with hydrofluoric acid to make a backwash solution. Under the action of the backwash solution, the ferric fluoride in the cryolite will become fluoroferric acid. In the solution, so as to remove the ferric fluoride in the cryolite, improve the quality and appearance of the cryolite product.

Cryolite cleaning effect of the present invention is as table 1:

Table 1: Main substance content of cryolite products

Wherein, the main content is the mass percentage of cryolite in the cryolite test sample.

It can be seen from the data in the table that the content of iron in cryolite can be effectively reduced through backwashing measures, and the content of calcium oxide can also be reduced. Before backwashing, the main content of cryolite is lower than the national standard. After backwashing, the content of iron element is effectively reduced, so that the purity of cryolite increases, thus meeting the national standard.

The filtrate and the waste liquid after backwashing in the present invention can be recycled into the tail gas absorption device 20 for use. Adding the waste liquid after backwashing to the tail gas absorption device 20 has two advantages. The first advantage is that the hydrogen fluoride in the waste liquid is effectively utilized. The second advantage is that the pH of the water in the tail gas absorption device 20 is relatively higher than that of the waste liquid. Able to participate in the subsequent process of preparing cryolite.

Of course, as the number of cycles increases, the content of ferric fluoride in the mother liquor will gradually increase. In this way, in the subsequent process of preparing cryolite, when the solution environment is neutral or slightly alkaline, there will be ferric fluoride again. It is precipitated at the same time as cryolite. Therefore, after the backwash solution is used for a period of time, the pH can be adjusted to be neutral or slightly alkaline, so that ferric fluoride can be precipitated in advance, thereby removing the ferric fluoride in the backwash solution, and then entering the exhaust gas The absorption device 20 purifies the exhaust gas.

In the actual production process, affected by factors such as impurity composition and impurity removal efficiency, special equipment is required to produce cryolite.

Therefore, please refer to Fig. 1, the present invention provides a kind of production system of aluminum fluoride by-product high-quality cryolite, comprise negative pressure device 10, tail gas absorption device 20, reactor 30, separating device 40, backwash liquid tank 50, Backwashing device 60, drying device 70, the inlet end of described negative pressure device 10 is sealed and connected with the tail gas pipeline of fluidized bed 80, and the gas outlet end of negative pressure device 10 is connected with tail gas absorption device 20, to absorb tail gas, so The reactor 30 is provided with a mother liquor inlet and a sodium aluminate inlet to add the mother liquor and sodium aluminate. The mother liquor inlet is connected to the tail gas absorption device 20 through a pipeline, and the bottom of the reactor 30 is connected to the separation device 40 In communication, the drain port of the separation device 40 is communicated with the backwash tank 50 through a pipeline, so that the filtrate is introduced into the backwash tank 50, and the liquid inlet of the backwash device 60 is connected with the backwash tank 50 through a pipeline to The filter residue in the backwashing device 60 is washed. The backwashing device 60 is provided with a slag discharge port and a liquid discharge port, and the slag discharge port is connected with the feed port of the drying device 70 to dry the filter residue.

The negative pressure device 10 is used to provide negative pressure so that the tail gas enters the tail gas absorption device 20 from the fluidized bed 80 . In a preferred embodiment, the negative pressure device 10 includes a sealing joint, an air inlet pipe, a negative pressure fan, and an air outlet pipe, and the sealing joint is arranged between the air inlet pipe and the tail gas pipe of the fluidized bed 80, and further The gas pipeline is connected with the air inlet of the negative pressure fan, the gas outlet of the negative pressure fan is connected with the outlet pipeline, and the outlet pipeline is also communicated with the bottom of the tail gas absorption device 20 .

In a preferred embodiment, the tail gas absorbing device 20 includes a spray tower 201, a spray nozzle, and a mother liquor pool 202, the middle end of the spray tower 201 is provided with an air inlet, and the air inlet of the spray tower 201 is connected to the The gas outlet of the negative pressure device 10 is connected through a pipeline, the spray head is located above the air inlet of the spray tower 201 , and the mother liquid pool 202 is located directly below the spray tower 201 .

By spraying, hydrogen fluoride and dust particles in the exhaust gas can be fully absorbed.

In addition to hydrogen fluoride, the exhaust gas also contains aluminum fluoride and iron oxide dust. The mother liquor pool 202 of the present invention has two functions. The first function is that after the water absorbs the tail gas, the fluoride ion content in the mother liquor can reach a relatively stable state, so that the concentration of hydrogen fluoride entering the reactor 30 can be kept consistent, so as to facilitate control The amount of sodium aluminate added. Another function is to play the role of static precipitation, so that the dust such as aluminum fluoride and iron oxide in the exhaust gas can be precipitated, preventing it from participating in subsequent reactions, or being mixed into cryolite and difficult to remove. At the same time, the product collected by static precipitation is also a product in the production process of aluminum fluoride, which can be recycled.

In a preferred embodiment, the separation device 40 is a conventional solid-liquid separator, such as a centrifuge, a stack filter or a filter screen.

In a preferred embodiment, the liquid inlet of the backwash tank 50 is also communicated with the tail gas absorbing device 20 through a pipeline, so that the mother liquor is added into the backwash tank 50 to adjust the pH.

In a preferred embodiment, please refer to FIG. 2, the backwashing device 60 includes an acid-proof filter bag 601, a backwash tank 602, and an ultrasonic vibrator 603, and the acid-proof filter bag 601 is suspended in the backwash tank 602 The anti-acid filter bag 601 contains cryolite to be removed, and the vibration end of the ultrasonic vibrator 603 is set in the backwash tank 602. During cleaning, the backwash liquid sinks through the acid-proof filter bag 601, so that the backwash liquid enters the In the anti-acid filter bag 601, the cryolite is cleaned by high-frequency vibration. After cleaning, the anti-acid filter bag 601 is suspended above the backwash tank 602, and is naturally controlled to dry.

After the natural control drying reaches the predetermined time, the acid-proof filter bag 601 is removed, and then put into the drying device 70 for drying. The drying device 70 is a conventional drying chamber or dryer, which will not be described again.

Further, the liquid outlet of the backwash tank 602 is also connected to the spray head of the tail gas absorption device 20 through a pipeline, so that the backwashed waste liquid is used to absorb hydrogen fluoride in the tail gas.

What is disclosed above is only a preferred embodiment of the present invention, and certainly cannot limit the scope of rights of the present invention with this. Those of ordinary skill in the art can understand the whole or part of the process of realizing the above-mentioned embodiment, and make according to the claims of the present invention The equivalent changes still belong to the scope covered by the invention.

Claims (9)

1. a method for producing aluminum fluoride by-product high-quality cryolite, is characterized in that: comprise the following steps: step one: Absorb tail gas and prepare mother liquor: suck the tail gas discharged from the fluidized bed into water to form mother liquor; Step two: Preparation of slurry: adding sodium aluminate to the mother liquor, so that the hydrogen fluoride in the mother liquor is fully absorbed to form a cryolite slurry; Step three: Filtration and drying: filter the cryolite slurry to obtain filter residue and filtrate; Step four: Prepare the backwash solution: add hydrofluoric acid to the filtrate to adjust the pH of the filtrate to 5-6 to form a backwash solution; Step five: Backwashing: add backwashing solution to the filter residue, wash repeatedly to remove impurities in cryolite, and then filter again to obtain white powder cryolite. 2. The method for producing aluminum fluoride by-product high-quality cryolite as claimed in claim 1, characterized in that: the sodium aluminate in step 2 is prepared from sodium hydroxide solution and aluminum hydroxide. 3. The method for producing aluminum fluoride as a by-product of high-quality cryolite as claimed in claim 1, characterized in that: in step 5, the waste liquid after backwashing is added to the tail gas absorption device to absorb tail gas. 4. A production system for high-quality cryolite by-product of aluminum fluoride, characterized in that it comprises negative pressure device, tail gas absorption device, synthesis tank, separation device, backwash liquid tank, backwash device, drying device, all The inlet end of the negative pressure device is sealed and connected with the tail gas pipeline of the fluidized bed, the gas outlet end of the negative pressure device is located at the bottom of the tail gas absorption device, so as to pass the tail gas into the tail gas absorption device, and the synthesis tank is provided with a mother liquor inlet mouth and sodium aluminate liquid inlet to add mother liquor and sodium aluminate, the mother liquor liquid inlet is connected with the tail gas absorption device through pipelines, the bottom of the synthesis tank is connected with the separation device, and the liquid outlet of the separation device is connected with the backwash liquid The tank is connected through pipelines to introduce the filtrate into the backwash tank. The liquid inlet of the backwash device is connected to the backwash tank through pipelines to flush the filter residue in the backwash device. The backwash device is equipped with a slag discharge The port and the liquid discharge port, the slag discharge port is connected with the feed port of the drying device to dry the filter residue. 5. The production system of aluminum fluoride by-product high-quality cryolite as claimed in claim 4, characterized in that: the negative pressure device comprises a sealing joint, an air inlet pipe, a negative pressure fan, and an air outlet pipe, and the sealing joint Set between the inlet pipe and the tail gas pipe of the fluidized bed 80, the inlet pipe is connected to the inlet of the negative pressure fan, the outlet of the negative pressure fan is connected to the outlet pipe, and the outlet pipe is also connected to the bottom of the tail gas absorption device . 6. The production system of aluminum fluoride by-product high-quality cryolite as claimed in claim 4, characterized in that: the tail gas absorption device includes a spray tower, a shower nozzle, and a mother liquor pool, and the middle end of the spray tower is provided with There is an air inlet, the air inlet of the spray tower is connected with the outlet of the negative pressure device through a pipeline, the spray head is located above the air inlet of the spray tower, and the mother liquor pool is located directly below the spray tower. 7. The production system of aluminum fluoride by-product high-quality cryolite as claimed in claim 4, characterized in that: the liquid inlet of the backwash liquid tank is also communicated with the tail gas absorption device through pipelines to add the mother liquor to the backwash liquid The pH is adjusted in tank 50 . 8. The production system of aluminum fluoride by-product high-quality cryolite as claimed in claim 4, characterized in that: the backwashing device comprises an acid-proof filter bag, a backwash tank, an ultrasonic vibrator, and the acid-proof filter The bag is suspended in the backwash tank, and the anti-acid filter bag contains cryolite to be removed, and the vibration end of the ultrasonic vibrator is set in the backwash tank. 9. The production system of aluminum fluoride by-product high-quality cryolite as claimed in claim 8, characterized in that: the liquid outlet of the backwash tank is also connected with the nozzle of the tail gas absorption device through pipelines, so that the backwashed The waste liquid is used to absorb hydrogen fluoride in the tail gas.