CN115924848A - Method for recovering fluorine from anode carbon slag - Google Patents

Abstract

The invention discloses a method for recovering fluorine from anode carbon slag, which comprises the steps of fully grinding the anode carbon slag by a ball mill, removing and recovering metals and metal oxides through screening and separation, dissolving fluoride salt in the screened powder anode carbon slag through sulfuric acid pickling, filtering and separating and recovering solid carbon powder, and respectively carrying out defluorination and dealumination on the filtered pickling solution to realize the recovery of fluorine and aluminum as hydrofluoric acid and aluminum hydroxide. The method can completely separate the components in the anode carbon slag one by one, realizes recycling, and has high purity of the recycled hydrofluoric acid product.

Description

Method for recovering fluorine from anode carbon slag

Technical Field

The invention belongs to the fields of chemical industry and environmental protection, and particularly relates to a method for recovering fluorine from anode carbon slag.

Background

The anode carbon residue is generated from fluoride salt-containing residue in the electrolytic aluminum production process, and mainly comprises fluoride salt, carbon and a small amount of metal oxide, wherein the generated amount accounts for about 0.1-2% of the aluminum yield.

The existing method for treating the anode carbon slag is single, and some methods use the anode carbon slag as fuel, and all contained electrolytes enter ash slag, so that not only is fluoride in the carbon slag influence the environment, but also electrolyte with considerable value is wasted. And the other method adopts a roasting method and a flotation method to treat the anode carbon residue, the flotation method obtains carbon materials and electrolyte, but the purity is not high, the carbon materials and the electrolyte cannot be used as return materials, and the obtained electrolyte contains carbon and cannot be returned to an electrolysis workshop for use.

CN109650343A discloses a high temperature purification method of fluoride in anode carbon residue, which adopts a crushing and screening way to carry out pretreatment, and then the fluoride is melted by heating through an electrolytic tank, thereby realizing the separation of the fluoride and carbon and preparing fluoride products. The method has the problems that molten fluoride salt and carbon are not completely separated, the energy consumption is high, the carbon slag is not realized in benefits and the like.

CN109161930A discloses a separation process of electrolytic aluminum anode carbon residue and electrolyte, which adopts a two-stage crushing and two-stage separation process to sufficiently grind the anode carbon residue, and then realizes the separation of carbon and fluoride salt by a magnetic separation and fractional precipitation method. The method is a physical sorting method, the carbon content in the recovered fluoride is high, the reutilization is difficult to realize, and the fluoride content in the recovered carbon is also high, so the application is difficult.

Through comparative analysis and actual production experience, the following problems are found in the prior art:

the production amount of the anode carbon slag is large, the components are complex, and effective treatment of the anode carbon slag is difficult to realize by a simple separation method; the key to the treatment of the anode carbon slag is to solve the problem of the reutilization quality of main fluoride and carbon in the anode carbon slag.

Disclosure of Invention

The invention aims to provide a method for recovering fluorine from anode carbon slag. The method comprises the steps of fully grinding anode carbon slag by adopting a ball mill, grinding metals and metal oxides remained in the carbon slag into thin pieces, then screening and separating, wherein screened powder mainly comprises fluoride salt and carbon, the fluoride salt is dissolved by acid pickling to achieve the purpose of separating from the carbon, and the acid pickling solution realizes the recovery of fluorine and aluminum as hydrofluoric acid and aluminum hydroxide through defluorination and dealumination respectively.

To achieve the object of the present invention, the following embodiments are provided:

in one embodiment, the method for recovering fluorine from anode carbon residue comprises the following steps:

1) Grinding the anode carbon slag, sieving the metal and the metal oxide in the anode carbon slag into thin pieces, separating and recovering the metal and the metal oxide, wherein the sieved powder anode carbon slag contains fluoride salt and carbon;

2) Carrying out acid washing reaction on the powder anode carbon residue by using sulfuric acid, converting the acid residue into sulfate and hydrogen fluoride water solution, filtering by using a plate frame, taking the filtrate as acid washing solution to carry out next step of treatment, drying the residual solid which is carbon powder, and recovering;

3) Removing hydrogen fluoride from the pickling solution obtained in the step 2) through a defluorination tower in a vacuum manner, separating a mixed gas of the hydrogen fluoride and water vapor from the top of the tower, and condensing to form a hydrofluoric acid product, wherein the concentration of the hydrofluoric acid is 35-46%;

4) Adjusting pH value of acid washing solution in the defluorination tower in the step 3) by adopting NaOH solution with the concentration of 30 percent to ensure that aluminum in the acid washing solution forms Al (OH) 3 precipitate, filtering and recovering solid Al (OH) ₃ ；

5) Concentrating the filtrate by evaporation to recover Na ₂ SO ₄ And (5) producing the product.

In the method of the present invention, preferably, in step 1), the particles are sieved to 10 meshes, and the particles which do not reach the fineness are ground again until reaching 10 meshes;

in the method of the present invention, preferably, the concentration of the sulfuric acid in the step 2) is 40%, and the addition amount is 1.2 times of the mass of the anode carbon residue;

in the above process of the present invention, preferably, the vacuum pressure of the defluorination tower in the step 3) is 10kpa;

in the method of the present invention, preferably, the concentration of the hydrofluoric acid recovered in the step 3) is 35 to 46%;

in the above-described method of the present invention, preferably, in the step 4), the pH is 10 to 10.5.

In one embodiment, the invention provides a method for recovering fluorine from anode carbon slag, which comprises the following steps:

1) Removing metal and oxide, namely fully milling the anode carbon slag by using a ball mill, grinding the metal and the metal oxide remained in the carbon slag into slices, and then screening and separating to remove and recover the metal and the oxide, wherein the rest powder substances mainly comprise fluoride salt and carbon;

2) Carbon powder recovery: feeding the screened powder solid into a vibrating pickling bed, adding sulfuric acid to react with the powder solid fully, fully converting fluoride salt into sulfate and aqueous hydrogen fluoride solution, filtering and separating by using a plate frame to obtain insoluble solid carbon powder, drying the insoluble solid carbon powder, recycling the dried solid carbon powder as a carbon powder product, and feeding the filtrate as pickling solution to the next step;

3) And (3) recovering hydrogen fluoride: the acid washing liquid is fully removed with hydrogen fluoride in a vacuum condition through a defluorination tower, and the mixed gas of the hydrogen fluoride and the water vapor is separated from the top of the tower and condensed to form a hydrofluoric acid product.

4) And (3) aluminum recovery: the pH value of the pickling solution after the hydrofluoric acid is recovered is adjusted by adopting NaOH solution, so that the aluminum in the pickling solution generates Al (OH) ₃ Precipitating, filtering, and recovering solid Al (OH) ₃ ；

5) Sodium salt recovery: evaporating and concentrating the filtrate filtered in the step 4) to recover Na ₂ SO ₄ And (5) producing the product.

In one embodiment, the invention relates to a method for recovering fluorine from anode carbon slag, which comprises the following steps:

1) Fully grinding the anode carbon slag by a ball mill, grinding the metal and the metal oxide remained in the carbon slag into thin pieces, and then screening and separating to remove the metal and the metal oxide, wherein the rest powder material is the anode carbon slag mainly containing fluoride salt and carbon;

2) Adding the anode carbon residue solid powder screened in the step 1) into a vibrating pickling bed, adding 40% sulfuric acid which is 1.2 times of the mass of the anode carbon residue to fully react with the anode carbon residue solid powder, fully converting fluoride salt into sulfate and aqueous hydrogen fluoride solution, filtering and separating through a plate frame to obtain insoluble carbon powder, drying and recovering a carbon powder product, wherein the filtrate is pickling solution;

3) Fully removing hydrogen fluoride from the pickling solution in the step 2) through a defluorination tower under the vacuum condition of 10kpa, separating mixed gas of the hydrogen fluoride and water vapor from the tower top, and condensing to form a hydrofluoric acid product, wherein the concentration of the hydrofluoric acid is 35-46%;

4) Adjusting the pH value of the pickling solution subjected to hydrogen fluoride removal in the step 3) to be 10-0.5 by using a 30% NaOH solution to ensure that the aluminum in the pickling solution is Al (OH) ₃ Is precipitated out ofFiltering and recovering Al (OH) ₃ A solid;

5) Recovering Na from the filtrate obtained in step 4) by evaporation and concentration ₂ SO ₄ And (5) producing the product.

The method of the invention has the advantages that:

1. the method can realize the recovery of all substances of the anode carbon slag;

2. the products recovered by the method are single substances which are respectively aluminum sheets, carbon powder, hydrofluoric acid, aluminum hydroxide and sodium sulfate, and have high purity and wide application market;

3. the method of the invention adopts vacuum condition to remove the hydrogen fluoride, and the hydrogen fluoride is mixed with the water vapor and condensed to directly form hydrofluoric acid aqueous solution.

Detailed Description

The following examples are disclosed as representative for further illustration and understanding of the spirit of the invention and are not intended to limit the scope of the invention in any way and all such changes and modifications that come within the spirit of the invention are desired to be protected.

EXAMPLE 1 Anode carbon sludge recovery

The process comprises the following steps:

1. recovery of metals and metal oxides

Fully milling the anode carbon slag by a ball mill, grinding the metal and the metal oxide remained in the carbon slag into slices, passing through a 10-mesh sieve, separating, removing and recovering the metal and the metal oxide, wherein the rest powder substances are mainly fluoride salt and carbon, and the unscreened coarse particles can be returned and milled again and pass through the 10-mesh sieve.

2. Recovery of carbon powder

Adding the screened powder solid into a vibration pickling bed, adding 40% sulfuric acid to fully react with the powder solid, then filtering and separating through a plate frame to obtain insoluble carbon powder, filtering, drying the obtained solid, recovering a carbon powder product, and carrying out next treatment on the obtained filtrate, wherein the filtrate is pickling solution.

3. Recovery of hydrofluoric acid

And (3) fully removing hydrogen fluoride from the pickling solution in the previous step through a defluorination tower under the vacuum condition of 10kpa, separating mixed gas of the hydrogen fluoride and water vapor from the tower top, condensing to form a hydrofluoric acid product, wherein the concentration of the hydrofluoric acid is 35-46% (the concentration can be adjusted according to actual needs after recovery), and the yield is 92-97%.

4. Recovery of aluminium hydroxide

Adjusting the pH value of the pickling solution which finishes the hydrogen fluoride removal to 10-0.5 by adopting 30 percent NaOH solution to ensure that all aluminum in the pickling solution is Al (OH) ₃ Is precipitated, filtered and the solid Al (OH) is recovered ₃ 。

5. Recovery of sodium sulfate

Separating the filtered filtrate of step 4 by evaporation concentration to obtain Na ₂ SO ₄ Wet product, drying to obtain Na ₂ SO ₄ And (5) producing the product.

Claims (7)

1. A method for recovering fluorine from anode carbon slag comprises the following steps:

1) Grinding the anode carbon slag until the metal and the metal oxide in the anode carbon slag become thin pieces, sieving the thin pieces, separating and recovering the metal and the metal oxide, wherein the sieved powder anode carbon slag contains fluoride salt and carbon;

2) Carrying out acid washing reaction on the powder anode carbon residue by using sulfuric acid, converting the acid residue into sulfate and hydrogen fluoride water solution, filtering, taking the filtrate as acid washing solution, carrying out next treatment, taking the residual solid as carbon powder, drying and recovering;

3) Removing hydrogen fluoride from the pickling solution obtained in the step 2) in vacuum through a defluorination tower, separating a mixed gas of the hydrogen fluoride and water vapor from the top of the tower, and condensing and recovering a hydrofluoric acid product;

4) In the step 3), pH value of the pickling solution in the defluorination tower is adjusted by adopting NaOH solution, so that aluminum in the pickling solution forms Al (OH) ₃ Precipitating, filtering to recover solid Al (OH) ₃ ；

5) The filtrate obtained by the filtration is evaporated and concentrated to recover Na ₂ SO ₄ And (5) producing the product.

2. The method as claimed in claim 1, wherein the sieving in step 1) is 10 mesh, and the particles which do not reach the fineness are milled again to obtain 10 mesh particles.

3. The method as claimed in claim 1, wherein in the step 2), the concentration of the sulfuric acid is 40%, and the addition amount of the sulfuric acid is 1.2 times of the mass of the anode carbon slag.

4. The method according to claim 1, wherein the vacuum pressure of the defluorinating tower in step 3) is 10kpa.

5. The method according to claim 1, wherein the concentration of the recovered hydrofluoric acid in the step 3) is 35-46%.

6. The method of claim 1, wherein in step 4), the concentration of the NaOH solution is 30%.

7. The method according to claim 1, wherein the pH value in step 4) is 10 to 10.5.