JPS6058170B2 - Method for recovering gallium from dust generated in an aluminum electrolytic furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering gallium contained in dust generated from an electrolytic furnace during aluminum electrolytic smelting using molten cryolite.

Gallium has recently attracted attention as a semiconductor material such as gallium-arsenide (GaAs) or gallium-phosphide (GaP).

Although gallium exists widely on Earth, it is not produced as a high-grade mineral, so it has traditionally been recovered from Bayer fluid used in the production of alumina from bauxite or from zinc smelting leaching residue.

However, in these methods, since the gallium content in the raw material for gallium recovery is very low, recovery requires complicated steps and expensive processing costs.

For example, there are the lime method, carbonation method, and electrolytic method as methods for recovering from Bayer's liquid, and among these methods, the electrolytic method is industrially superior.

In this method, Bayer's solution is subjected to primary electrolysis using a mercury cathode and a nickel anode, the recovered crude gallium is treated with caustic soda, and the resulting solution is subjected to secondary electrolysis, but since mercury is used, it is a problem with pollution. There are drawbacks such as problems, and there is a demand for the development of a method that is simple in process and economically advantageous. In order to recover gallium efficiently and at low cost, it is necessary to use raw materials with a high gallium content.

Dust generated from an aluminum electrolytic furnace is a raw material that meets these conditions. The dust generated by Mazuko's aluminum electrolysis furnace will be explained in detail.

As mentioned above, the viar liquid contains gallium, and this gallium exhibits the same behavior as aluminum in the viar process, and almost the entire amount of S is contained in the alumina.

The gallium concentration in alumina varies from several tens of ppm to a maximum of 100 ppm, depending on the grade of bauxite in the raw ore.
It is about m. This gallium in alumina is mixed into the aluminum metal during alumina electrolysis, and some of it is included in the electrolytically generated dust. This dust is collected by a wet or dry dust collector such as an electrostatic precipitator, cyclone, or wet scrubber. The concentration of gallium in this dust ranges from 750 ppm to a maximum of 2000 ppm, which is several tens of times more concentrated than the concentration in alumina.There are no examples of such high concentrations of gallium being found, so it is difficult to obtain gallium. It is an excellent raw material. As a method for recovering gallium from dust generated during aluminum electrolysis, there is, for example, British Patent No. 1527981, which was also filed in West Germany and published as No. 2542642 in that country.

This method involves adding an excess of alkaline flux (5 times the weight of the dust in the example) to dust containing up to 0.2% gallium, followed by roasting at 500-800°C and soaking in water. broth,
There is a method of manufacturing metal gallium by adding metal powder such as aluminum or magnesium to molten gallium and fixing it. In this method, an expensive alkaline melting agent is added several times the amount of dust and roasted, so a large amount of alkaline melting agent is added. Fluxing agent is required.

In addition, since the dust contains a large amount of alkali-soluble components in addition to gallium, it is necessary to treat the waste liquid after gallium is collected, and there is no other way to dispose of the residue after leaching. There are still some issues that need to be solved for practical use, and it is also difficult to achieve economical results. The present inventors believe that one of the main drawbacks of the above method is that there are many dissolved components other than gallium in the dust, and these components are also treated at the same time as gallium, which complicates the process and increases processing costs. Focusing on this point, as a result of various studies, they found that flotation should be applied to reduce the dissolved components coexisting with the gallium component, and the present invention was completed.

That is, the present invention involves flotation of dust generated from an aluminum electrolytic furnace to separate and concentrate the gallium contained in the dust to obtain floss, then roasting the froth, and then treating the roasted product with high-temperature acid leaching using mineral acid. A reducing agent is added to the slurry to convert Fe3+ in the slurry to Fe2.
The present invention relates to a method for recovering gallium from dust generated in an aluminum electrolytic furnace, which comprises filtering the slurry after reduction to +, and adding an alkali to the resulting filtrate to precipitate the gallium component as hydroxide.

Further, the present invention will be explained in detail.

The dust generated from an aluminum electrolytic furnace contains up to 20% of fine carbon, and a considerable amount of this carbon floats as froth during flotation and is separated.

The present inventors discovered that when this carbon is floated, trace amounts of metal impurities such as gallium, iron, nickel, silicon, and vanadium are involved and separated at the same time. During flotation, it is necessary to add, for example, kerosene as a carbon scavenger and a commercially available foaming agent to the dust to form a slurry.
Furthermore, the dust concentration in the slurry was increased to 50 to 200y/e1.
Preferably, it is necessary to set it to 100 to 150 y/'. If it does not reach 50 y/e, there is less carbon to help foaming, so foaming does not occur much and the flotation operation does not proceed well.

If it exceeds 200y/', the amount of carbon increases, and a large amount of electrolytic bath components other than the carbon, which often foams, is mixed into the froth, resulting in a decrease in the separation efficiency of gallium.

As mentioned above, the separation efficiency of gallium into froth during flotation is affected by the carbon content, so the froth content should be adjusted to 10 to 50% by weight relative to dust at the beginning of flotation.
Circulation improves the separation efficiency of gallium from dust.

The yield of gallium during flotation in the method of the present invention is about 80%, which is about twice the concentration in the dust, and the concentration of gallium in the floss is 1,500 to 4,000.
ppm.

In this case, about 70% of dissolved components other than gallium are separated into the tail. The tail from flotation consists of electrolytic bath components such as alumina, cryolite, and aluminum fluoride.
Since most of the metal impurities have been separated, it is possible to reuse the electrolytic furnace by simply drying it, which is useful for waste management and
It also has excellent effects in terms of effective use of resources without waste. The floss is then roasted to increase the gallium concentration and increase the solubility of the gallium.

The gallium contained in the electrolytic furnace dust is assumed to be an oxide or fluoride. In the present invention, a high-temperature acid leaching treatment is performed in a later step, and although fluoride is difficult to dissolve even if the fluoride is subjected to a high-temperature acid leaching treatment, its solubility improves when it is roasted. Furthermore, due to roasting, the weight of the carbon content is reduced by 30 to 40%, and at the same time as the above-mentioned solubility is improved, gallium is also concentrated to about 3000 to 6000 ppm. In other words, the concentration was three to four times higher than the initial concentration in the dust. The appropriate roasting temperature is 500 to 800°C; lower temperatures will not allow the firing to proceed sufficiently, while higher temperatures will cause problems such as melting of the fired product. In either case, the effect of increasing solubility will be reduced. Therefore, no improvement in the leaching rate of gallium can be expected during high-temperature acid leaching treatment. That is, in order to increase the concentration and solubility of gallium, it is necessary to roast it at 500 to 800 degrees Celsius. Next, the roasted dust is subjected to high-temperature acid leaching treatment using a mineral acid such as sulfuric acid, hydrochloric acid, or nitric acid at a temperature ranging from 80C to 1000C.

This treatment dissolves about 80% of the gallium and other metal impurities (iron, nickel, silicon, vanadium) in the roasted product, and also dissolves aluminum, which is the main component in the roasted product.
A slurry in which considerable amounts of fluorine and sodium are also dissolved is obtained. In the present invention, the gallium component is ultimately hydrolyzed by addition of alkali to obtain hydroxide, but since almost the entire amount of Fe3+ is precipitated under the conditions for gallium hydroxide precipitation, this is To prevent this, it is necessary to convert Fe3+ into Fe2+ by adding a reducing agent such as iron powder or zinc powder. That is, a reducing agent is added to the slurry after high-temperature acid leaching to reduce Fe3+ to Fe2+, followed by filtration, and an alkali is added to the filtrate to precipitate the dissolved gallium component as hydroxide by hydrolysis.

At this time, it is preferable to selectively precipitate gallium hydroxide, and for this purpose, the pH at which gallium begins to precipitate as hydroxide must be lower than the pH at which aluminum, the main dissolved component, begins to precipitate. Using this, the pH is 4~
Just adjust it so that it becomes 5. When Fe3+ is reduced to Fe2+, the precipitation rate of gallium hydroxide tends to decrease somewhat, but at least 95% can be ensured. Finally, it is filtered to obtain a hydroxide mixture, and the gallium concentration in this mixture is 10% or more. That is, the gallium concentration is about 2 times lower than that of the roasted product, and the gallium concentration is about 100 f8 compared to the initially used dust. The hydroxide mixture thus obtained by the method of the invention is a good raw material for obtaining metallic gallium.

An example of a method for obtaining metallic gallium from this raw material is shown below. First, the hydroxide mixture is dissolved in hydrochloric acid, and then subjected to solvent extraction using esters to separate metals other than gallium.

This solvent is back-extracted with water, and after extraction, the gallium in the aqueous solution is hydrolyzed with an alkali to precipitate hydroxide. Then, by dissolving this hydroxide with sodium hydroxide and further performing aqueous electrolysis, highly pure metallic gallium can be easily obtained. The present invention has been described in detail above, and gallium in the dust generated from an aluminum electrolytic furnace, which was conventionally difficult to recover economically, can be economically recovered by a combination of simple steps, and it has extremely high industrial value. It's a big deal.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1 Dust generated from an aluminum electrolytic furnace collected by an electrostatic precipitator (composition: 0.152 gallium, 1.10 iron, 0.2 silicon, 0.28 nickel, 0.101 vanadium)
Sodium 13.5, Aluminum 16.5s Fluorine 2
6.2, Carbon 20.1) Water was added to 500y to adjust the dust concentration to 100y/' and slurry.

After adding 4,000 ppm of kerosene as a carbon scavenger to this slurry in terms of solid weight ratio, and 1,000 ppm of a foaming agent, flotation was performed. As a result, the floss content was 41%, the tail content was 44%, and the loss was 15%. The gallium concentration in the froth is 0.298%, and the decomposition efficiency of gallium by flotation is 80.4%, and the decomposition efficiency of other components is 71.8% for iron, 65.7% for silicon, and 79.9% for nickel.
8%, vanadium 76.6%, and carbon 84.4%. The composition of the tail is 42.5% cryolite, 18.6% aluminum fluoride, 27.7% alumina, and 7% carphone.
．． 1%, which was essentially only the electrolytic bath composition.
Next, it was roasted at 100°C for 2 hours.

As a result, the carbon content was almost completely burned out, the weight of the roasted product was 96y, and the gallium concentration was 0.463.
It was %. Furthermore, no scattering of gallium was observed due to roasting. Sulfuric acid was added to the roasted product 50y at a weight ratio of 0.7, and water was added to the slurry concentration of 150y/y.
After that, acid leaching treatment was performed at 95 to 100°C for 3 hours to obtain a slurry. Iron powder 2y was added to this slurry, and after stirring for 30 minutes to reduce Fe3+, it was separated. Gallium concentration in filtrate 0.5
7y/f, and 82% of the gallium of the roasted product in the filtrate.
% was dissolved. The total iron and aluminum concentrations in the roasted product are 3.8y/El5.78y/
It was e. A 10% aqueous sodium hydroxide solution was added to the filtrate and the pH was adjusted to 4.5 to precipitate hydroxide, and 0.87y of precipitated hydroxide was obtained by filtration. Of these, the gallium content was 21.6% and the iron content was 2.2%, and the precipitation rate of gallium from the slurry after acid leaching treatment was 98.0%. Reference Example In Example 1, when the froth was subjected to the same acid leaching treatment as in Example 1 without being roasted, the leaching rate of gallium was only 35%.

Example 2 Dust generated from an aluminum electrolytic furnace collected by a wet scrubber (composition: 0.083% gallium, 0.98% iron)
3%, silicon 1.10%, nickel 0.28%, vanadium 0.18%, sodium 10.8%, aluminum 20.8%, fluorine 21.4%, carbon 13.6%)
Water was added to 500y to adjust the slurry concentration to 130g/f.

After adding 4,000 ppm of kerosene and 1,000 ppm of a foaming agent by weight of solid content as a carbon scavenger to this slurry, flotation was performed. As a result, the floss content was 37%,
A tail portion of 57% was obtained with a loss of 6%. The gallium concentration in the floss is 0.171%, and the decomposition efficiency of gallium by flotation is 76.2%, and the decomposition efficiency of other components is 79.3% for iron, 71.8% for silicon, and 76.5% for nickel.
%, vanadium 81.2%, carbon 64%). The composition of the tail is 34.6% cryolite, 5.4% aluminum fluoride, 50.9% alumina, and 6.2% carbon.
Therefore, it was essentially only the electrolytic bath composition. then 10
Floss 150y dried at 0°C for 2 hours was roasted at 700°C for 2 hours. As a result, the carbon content was almost completely burnt out, the weight of the roasted product was 116 f, and the gallium concentration was 0.22%. Furthermore, no scattering of gallium was observed due to roasting. Sulfuric acid was added to the roasted product 50q at a weight ratio of 0.7 to the roasted product, and water was added so that the slurry concentration was 150 v/e, and then 95 to 1
A slurry was obtained by performing acid leaching treatment at 00°C for 3 hours. Iron powder 2y was added to this slurry, and after stirring for 30 minutes to reduce Fe3+, it was filtered. The gallium concentration in the filtrate was 0.284 y/f, and 86% of the gallium in the roasted product was dissolved in the filtrate. The total iron and aluminum concentrations in the roasted product are each 2
．． They were 26y/' and 6.4y/e. A 10% aqueous sodium hydroxide solution was added to the filtrate to raise the pH to 4.5 to precipitate hydroxide, and 0.67y of precipitated hydroxide was obtained by filtration. Of these, the gallium content was 21.6% and the iron content was 4.8%, and the precipitation rate of gallium from the slurry after the acid leaching treatment was 96%. Reference Example In Example 2, when the same acid leaching treatment as in Example 2 was carried out without roasting the froth, the leaching rate of gallium was only 42%.

Claims (1)

[Claims] 1. Dust generated from an aluminum electrolytic furnace is flotated to obtain a froth in which gallium contained in the dust is separated and concentrated, and then the froth is roasted, and the roasted product is heated at high temperature with mineral acid. Acid leaching treatment is performed to obtain a slurry, a reducing agent is added to the slurry to reduce Fe^3^+ in the slurry to Fe^2^+, the slurry is filtered, and an alkali is added to the resulting filtrate. A method for recovering gallium from dust generated in an aluminum electrolytic furnace, characterized in that the gallium component is precipitated as a hydroxide. 2. Flotation of dust generated from an aluminum electrolytic furnace is carried out by adjusting the dust to a slurry having a concentration of 50 to 200 g/l, and then adding a carbon scavenger and a foaming agent to the slurry. A method for recovering gallium from dust generated in an electrolytic furnace. 3. The method for recovering gallium from dust generated in an aluminum electrolytic furnace according to claim 1, wherein the froth is roasted at a temperature of 500 to 800°C. 4. High-temperature acid leaching treatment using mineral acid for the roasted product uses either sulfuric acid, hydrochloric acid, or nitric acid as the mineral acid, and the temperature is 80 to 10 ml.
A method for recovering gallium from dust generated in an aluminum electrolytic furnace according to claim 1, which is carried out at 0°C. 5. The method for recovering gallium from dust generated in an aluminum electrolytic furnace according to claim 1, wherein the alkali is added to the filtrate so that the pH becomes 4 to 5.