JP7196669B2 - Gallium recovery method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for recovering gallium from an object to be treated containing at least iron, cobalt and gallium.

An RTB system permanent magnet (R is at least one rare earth element and must contain Nd, T is at least one transition metal element and must contain Fe, and B is boron) has excellent magnetism. Because of its properties, it is used in various fields such as automobiles, industrial machinery, and electronic equipment. Its usage is expected to increase due to the spread of electric vehicles and electronic devices. On the other hand, along with the increase in the production of magnets, the amount of processing waste (hereinafter referred to as "magnet sludge") such as cutting waste and grinding waste generated in the magnet manufacturing process is also increasing. Since magnet sludge contains valuable metal elements, it is an important technical issue to recover and reuse it. In particular, since rare earth elements are expensive, they are actively recycled.

Some RTB system permanent magnets use gallium (Ga) as an additive. Gallium is mainly produced as a by-product of aluminum smelting, but its production volume is small, and long-term stable procurement is a concern. Therefore, recovering and reusing gallium, which is a rare metal, from waste such as magnet sludge is an important issue from the viewpoint of procurement of raw materials.

Known methods for separating and recovering gallium from compounds containing gallium include the electrolytic refining method described in Patent Document 1 and the method of mixing and dissolving alkali metal hydroxides described in Patent Document 2. there is

In the electrolytic refining method described in Patent Document 1, an aqueous solution containing an electrolyte is used, and electrolysis is performed using a raw material containing gallium as an anode. Gallium eluted from the anode is electrodeposited on the cathode, but by setting the temperature of the electrolytic solution to the melting point of gallium or higher, the electrodeposited gallium can be melted, dropped, and recovered as a liquid. However, it is very difficult to treat powders such as magnet sludge that have been oxidized by this method due to their low electrical conductivity.

The method described in Patent Document 2 is a method in which a raw material containing gallium as a main component is mixed with an alkali metal hydroxide, heated, converted to a hydroxide, and then dissolved in water for recovery. However, when the content of gallium is small, such as magnet sludge, it is difficult to efficiently convert gallium into hydroxide.

In addition, magnet sludge contains components such as cobalt (Co) that are eluted in a strongly alkaline aqueous solution. After gallium is eluted from the object to be treated, it is reduced to metal gallium by electrolysis or the like. Since the melting point of gallium is 29.78° C., if gallium can be electrodeposited as a metal element, gallium can be easily recovered as a liquid with only a slight temperature rise. However, if a metal such as cobalt, which is more noble than gallium, is present in the solution, it may be reduced preferentially over gallium, forming a cobalt-gallium alloy or the like. In a gallium-cobalt alloy, a two-phase coexistence state of Ga phase and Ga ₃ Co phase is stable up to a cobalt concentration of 22 wt %. On the other hand, if the cobalt concentration exceeds 22 wt %, the Ga phase cannot exist stably and the melting point of the product increases, making it difficult to recover gallium at low temperatures. In order to efficiently separate the liquid Ga phase and the solid Ga ₃ Co phase, it is preferable that the Ga phase is larger than the Ga ₃ Co phase. For this purpose, it is necessary to adjust the ratio of cobalt to the sum of gallium and cobalt when eluting gallium so that it is less than 11%.

JP-A-6-192877 Japanese Patent No. 5002790

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for recovering gallium while suppressing contamination of cobalt from an object to be treated.

The gallium recovery method of the present invention, which has been made in view of the above points, is an exemplary embodiment 1 in which an object to be treated containing at least iron, cobalt and gallium is treated at a temperature of 70 ° C. or higher and lower than 150 ° C. A gallium recovery method in which gallium is immersed in an aqueous solution containing 01 mol/L or more and 5.6 mol/L or less of an oxidizing agent and 1.0 mol/L or more and 13.8 mol/L or less of an alkali metal hydroxide. be.
In aspect 2, the method for recovering gallium according to aspect 1, wherein the oxidizing agent is 0.01 mol/L or more and less than 1.18 mol/L.
Aspect 3 is the method for recovering gallium according to Aspect 2, wherein the oxidizing agent is 0.35 mol/L or more and less than 1.18 mol/L.
In aspect 4, the method for recovering gallium according to aspects 1 to 3, wherein the oxidizing agent is sodium nitrate or sodium nitrite.
Aspect 5, Aspect 1 to Aspect 4, wherein the object to be treated is magnet sludge of an RTB permanent magnet or a residue containing iron oxide as a main component obtained by removing rare earth elements from the magnet sludge. A method for recovering gallium as described.

According to the method of the present invention, gallium can be recovered from an object to be treated containing at least iron, cobalt and gallium while suppressing the amount of cobalt mixed therein.

In the gallium recovery method of the present invention, an object to be treated containing at least iron, cobalt and gallium is treated at a temperature of 70° C. or higher and lower than 150° C. with an oxidizing agent of 0.01 mol/L or higher and 5.6 mol/L or lower. and an alkali metal hydroxide of 1.0 mol/L or more and 13.8 mol/L or less, thereby eluting gallium while suppressing elution of cobalt. .
The details of the present invention are described below.

First, the object to be treated containing at least iron, cobalt and gallium to which the method of the present invention is applied may contain other elements such as rare earth elements and boron. Specifically, an RTB system permanent magnet can be mentioned. In particular, it can be suitably applied to magnet sludge generated in the manufacturing process.

At this time, the magnet sludge may be in a completely oxidized state or in an unoxidized state. The concentrations of gallium, cobalt, and iron contained in the magnet sludge are, for example, 0.02-0.6 wt%, 0.76-1.46 wt%, and 34.6-54.8 wt%.

Alternatively, it may be a residue after recovering (removing) the rare earth element from the magnet sludge. As a method for recovering (removing) the rare earth elements, for example, magnet sludge is completely oxidized in a rotary kiln, dispersed in water, and recovered (removed) by dropping acid while adjusting the pH to 3 or more. )do it. In addition, the completely oxidized magnet sludge is immersed in an acid containing slightly more hydrogen ions than 3.0 times the number of moles of rare earth elements contained in the magnet sludge, and heated at 60° C. or higher for 8 hours or longer. It can also be recovered (removed) by treatment. The main component of the residue obtained by these operations is iron oxide. Gallium and cobalt concentrations in the residue are, for example, 0.03-0.32 wt % and 1.09-2.09 wt %.

In order to sufficiently exhibit the effect of the present invention on the object to be treated, it is desirable that the object to be treated is in the form of powder having a particle size d50 of 10 μm or less. If the particle size d50 of the object to be treated exceeds 10 μm, gallium inside the particles may not be sufficiently eluted.

As the alkali metal hydroxide used in the present invention, sodium hydroxide or potassium hydroxide can be used. One or two of these alkali metal hydroxides are used by dissolving them in water (this aqueous solution is hereinafter referred to as "treatment liquid"). At this time, the concentration of the alkali metal hydroxide is preferably 1.0 mol/L or more and 13.8 mol/L or less. If the concentration of alkali metal hydroxide exceeds 13.8 mol/L, the solubility at room temperature will be exceeded, and the addition will be useless. When the alkali metal hydroxide concentration is less than 1.0 mol/L, the effect of eluting gallium is reduced.

As the oxidizing agent used in the present invention, sodium nitrate, sodium nitrite and the like can be used. One or two of these oxides are used by dissolving them in the treatment liquid. At this time, the concentration of the oxidizing agent is preferably 0.01 mol/L or more. When the concentration of the oxidizing agent is less than 0.01 mol/L, the effect of suppressing the elution of cobalt is reduced. Further, considering variations in the effect due to stirring or the like, it is more preferable that the concentration of the oxidizing agent is 0.35 mol/L or more. On the other hand, the upper limit of the concentration of the oxidizing agent is preferably 5.6 mol/L or less. This is because if the concentration of the oxidizing agent exceeds 5.6 mol/L, the effect of suppressing the elution of cobalt becomes saturated, and the addition is useless. Further, when gallium is recovered by electrolysis from an aqueous solution in which gallium is eluted, the concentration of the oxidizing agent is more preferably less than 1.18 mol/L. When the concentration of the oxidizing agent is 1.18 mol/L or more, the reduction product obtained in the electrolysis step is immediately oxidized, and the reduction cannot be efficiently performed. In such a case, gallium hydroxide can be efficiently reduced to a metal by adjusting the pH using a mineral acid such as hydrochloric acid or sulfuric acid to precipitate gallium hydroxide, recovering it, and subjecting it to a thermal reduction treatment with hydrogen or the like. . Note that the thermal reduction treatment may be applied even when the concentration of the oxidant is less than 1.18 mol/L.

The temperature of the treatment liquid is preferably 70°C or higher and lower than 150°C. If the temperature of the treatment liquid is lower than 70° C., the yield of gallium is lowered and gallium cannot be recovered efficiently. On the other hand, when the temperature of the treatment liquid exceeds 150° C., the boiling point of the treatment liquid is exceeded. Therefore, if the object to be treated is powder, there is a possibility that the recovery rate of gallium may decrease due to scattering of the treatment liquid.

As described above, the treatment is performed by immersing the object to be treated in the treatment solution in which the concentrations of the alkali metal hydroxide and the oxidizing agent and the temperature are adjusted. At this time, in order to promote the reaction between the treatment liquid and the object to be treated, it is preferable to stir as necessary. As a stirring method, a stirring method using stirring blades or a stirring method using air bubbling can be used. In particular, the method of stirring by air bubbling is more preferable in that the oxygen in the air acts as an oxidizing agent to suppress the elution of cobalt.

The immersion time in the treatment liquid is preferably 10 minutes or more and 96 hours or less. If the immersion time is less than 10 minutes, the temperature of the material to be treated does not reach the set temperature, and gallium may not be sufficiently eluted. Further, when the immersion time exceeds 96 hours, the effect of gallium elution is saturated.

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention should not be construed as being limited to the following description.

Gallium concentration and cobalt concentration of the object to be treated Magnet sludge with a particle size of about 10 μm generated in the manufacturing process of the RTB permanent magnet, which is the object to be treated (stored in water to prevent spontaneous combustion) was dehydrated by suction filtration. This magnetic sludge was further heat-treated at 900° C. for 2 hours, and then subjected to ICP analysis (equipment used: ICPV-1017 manufactured by Shimadzu Corporation). As a result, the gallium concentration was 0.30 to 0.38 wt%, and the cobalt concentration was 0.58 to 0.61 wt%.

Comparative Examples 1 and 2, Examples 1 to 5:
The concentration of sodium nitrate was adjusted to be the concentration shown in Table 1, and the magnetic sludge (in a wet state) was suction-filtered into 100 ml of an aqueous solution containing 5.00 mol/L of sodium hydroxide (treatment liquid). ) was immersed and treated at a temperature of 100° C. or 110° C. for 6 hours. Comparative Examples 1 and 2 are cases where sodium nitrate is not added (0.00 mol/L), and Examples 1 to 5 are cases where sodium nitrate is added.

After that, the residue after the treatment was subjected to suction filtration, and each filtrate was subjected to ICP analysis. Table 1 shows the results. Table 1 shows specific numerical values for sodium nitrate concentration and treatment temperature, Ga concentration in filtrate, Co concentration, Ga yield, and mass% of Co in filtrate and Co in Ga alloy. .

From the results in Table 1, by adding 0.01 mol / L or more sodium nitrate, the mass% of Co in the filtrate and Co in the Ga alloy can be less than 11%, and furthermore, 0.59 mol / L It has been found that the above addition can reduce the Co concentration to a level that cannot be detected by ICP analysis.

Next, using the filtrates of Comparative Examples 1 and 2 and Examples 1 to 4 as the electrolyte, using a platinum-plated titanium wire as the anode and a copper plate as the cathode, constant current electrolysis was performed at a current density of 1 A/cm ² for 1 hour. did Table 2 shows the EDX analysis results of the film (reduction product) formed on the copper plate.

It was found that the concentration of cobalt in the reduction product produced by constant current electrolysis can be reduced to 1.5 wt % or less in a solution containing 0.01 mol/L or more of sodium nitrate. On the other hand, it was found that when the sodium nitrate concentration was 0.59 mol/L or more, the oxygen concentration increased although the cobalt concentration was low. This is probably because the sodium nitrate added in excess oxidized the reduction product. Therefore, when it is desired to obtain a reduction product with a low oxygen concentration, a mineral acid such as hydrochloric acid or sulfuric acid is used to adjust the pH to precipitate as a hydroxide, which is recovered and then subjected to a thermal reduction treatment with hydrogen or the like. is preferred. In particular, when the sodium nitrate concentration is 1.18 mol/L or more, the oxygen concentration of the reduction product rises sharply, so it is preferable to carry out when the sodium nitrate concentration is 1.18 mol/L or more. In addition, in Comparative Examples 1 and 2, the oxygen concentration was also high, but it is considered that part of cobalt was electrodeposited as an oxide.

Comparative Examples 3 and 4, Examples 6 and 7
The concentrations of sodium nitrate were adjusted to 0.00 mol/L and 0.59 mol/L, respectively, and suction-filtered magnet sludge (wet 10 g of the raw material) was immersed and treated at 130° C. or 140° C. for 6 hours. Comparative Examples 3 and 4 are cases where sodium nitrate is not added, and Examples 6 and 7 are cases where sodium nitrate is added.

After that, the residue after the treatment was subjected to suction filtration, and the filtrate was subjected to ICP analysis. Table 3 shows the results. Table 3 shows specific numerical values for sodium nitrate concentration and treatment temperature, Ga concentration in filtrate, Co concentration, Ga yield, and mass% of Co in filtrate and Co in Ga alloy. .

When sodium nitrate is not added at a high temperature of 130°C or 140°C, the amount of cobalt eluted is large. % can be suppressed to less than 11%.

Next, using each filtrate as an electrolyte, constant current electrolysis was performed at a current density of 1 A/cm ² for 1 hour using a platinum-plated titanium wire as the anode and a copper plate as the cathode. Table 4 shows the EDX analysis results of the film (reduction product) formed on the copper plate.

It was found that the concentration of cobalt in the reduction product produced by electrolysis can be reduced to 2.1 wt % or less in a solution containing 0.59 mol/L of sodium nitrate.

Comparative Example 5, Examples 8 and 9
The concentrations of sodium nitrate were adjusted to 0.00 mol/L and 0.59 mol/L, respectively, and suction-filtered magnet sludge (wet 10 g of the raw material) was immersed and treated at 70° C. or 90° C. for 6 hours. Comparative Example 5 is the case where sodium nitrate is not added, and Examples 8 and 9 are the cases where sodium nitrate is added.

After that, the residue after the treatment was subjected to suction filtration, and the filtrate was subjected to ICP analysis. Table 5 shows the results. Table 5 shows specific numerical values for sodium nitrate concentration and treatment temperature, Ga concentration in filtrate, Co concentration, Ga yield, and mass% of Co in filtrate and Co in Ga alloy. .

In the treatment at 70 ° C., the amount of cobalt eluted is large when sodium nitrate is not added, but the addition of sodium nitrate can suppress the elution of cobalt. % can be suppressed.

Comparative Examples 6-8, Examples 10-12
The concentrations of sodium nitrate were adjusted to 0.00 mol/L and 0.59 mol/L, respectively, and 100 ml of an aqueous solution containing 2.5 to 10.0 mol/L of sodium hydroxide (treatment liquid) was added to the solution, which was subjected to suction filtration with a magnet. 10 g of sludge (while still wet) was immersed and treated at 110° C. for 6 hours. Comparative Examples 6 to 8 are cases where sodium nitrate is not added, and Examples 10 and 12 are cases where sodium nitrate is added.

After that, the residue after the treatment was subjected to suction filtration, and the filtrate was subjected to ICP analysis. Table 6 shows the results. Table 6 shows specific numerical values for sodium nitrate concentration and sodium hydroxide concentration, Ga concentration in filtrate, Co concentration, Ga yield, Co in filtrate and mass% of Co in Ga alloy. It is a thing.

When sodium nitrate was not added in the treatment at 110°C, the amount of cobalt eluted was large regardless of the concentration of sodium hydroxide. It was found that the mass % of Co in the alloy can be suppressed to less than 11%.

The present invention removes gallium, a rare metal whose production volume is small and whose long-term stable procurement is concerned, from objects to be treated that contain iron, cobalt, and gallium, such as magnet sludge from RTB permanent magnets. It has industrial applicability in that it can be recovered.

Claims (4)

1. An object to be treated containing at least iron, cobalt and gallium at a temperature of 70° C. or higher and 140 ° C. or lower and 0.01 mol / L or higher; 7 6 mol/L or less of sodium nitrate ; 2 . 5 mol/L or more, 1 2 . A method for recovering gallium by immersing in an aqueous solution containing 5 mol/L or less of sodium hydroxide . 2. The method for recovering gallium according to claim 1, wherein said sodium nitrate is 0.01 mol/L or more and less than 1.18 mol/L. 3. The method for recovering gallium according to claim 2, wherein the sodium nitrate is 0.35 mol/L or more and less than 1.18 mol/L. 4. The object to be treated according to any one of claims 1 to 3 , wherein the object to be treated is magnet sludge of an RTB permanent magnet or a residue composed mainly of iron oxide obtained by removing rare earth elements from the magnet sludge. gallium recovery method.