JP7499600B2 - How to recover rare metals - Google Patents

Description

The present invention relates to a method for recovering rare metals, and more specifically, to a method for recovering Sc, which is a type of rare metal.

Titanium is produced from titanium ore by the Kroll process. In this process, titanium ore and coke are fed into a fluidized bed reactor, and chlorine gas is blown into the reactor from the bottom. This results in the production of gaseous titanium tetrachloride, which is recovered and reduced with magnesium or other substances, ultimately producing titanium sponge. This series of reactions produces a by-product, a chlorination residue, which still contains useful materials, and various attempts are being made to recover these useful materials.

Patent Document 1 discloses a method for recovering titanium oxide and/or coke from chlorination residue. Patent Document 1 also discloses classification of the chlorination residue, and uses a liquid cyclone and a wet sieve as classification means. Patent Document 2 discloses a method for recovering Sc from chlorination residue, and discloses that the chlorination residue is classified during the process.

JP 2018-168448 A International Publication No. 2017/199887

When recovering Sc, various processes are carried out. Examples of such processes include classification, leaching, solid-liquid separation, and solvent extraction. There are many different flows for recovering Sc, and some of them include a filtration process. From the viewpoint of production efficiency, it is desirable to carry out the filtration process smoothly. However, while substances derived from chlorination residues of one lot can be filtered smoothly, substances derived from chlorination residues of another lot cannot be filtered smoothly. Specifically, the filtration speed was sometimes slow.

Such delays in filtration result in reduced productivity. Therefore, the present invention aims to provide a method for achieving smooth filtration processing.

After extensive research, the inventors discovered a difference between substances that can be filtered smoothly and those that cannot. More specifically, they discovered that slurries that cannot be filtered smoothly contain a large amount of Zr. Therefore, when the Zr concentration in the slurry was reduced before filtration, the filtration speed improved.

The present invention has been completed based on the above findings, and in one aspect includes the following invention.
(Invention 1)
1. A method for recovering Sc, comprising:
providing a chloride residue;
A filtering step;
Including,
The subject of the filtering step is a suspension or a slurry,
The suspension or slurry is derived from the chlorination residue, contains Sc and Zr, and has a pH of 3.5 or less;
The filtering step includes filtering in a state in which the Zr concentration in the suspension or slurry is reduced.
Method.
(Invention 2)
The method according to claim 1, wherein filtering in a state in which the Zr concentration is reduced includes filtering in a state in which the Zr concentration is reduced to 50 mg/L or less.
(Invention 3)
In the method according to the first or second aspect of the present invention, the method further comprises:
Prior to the filtration step, the method includes a step of flocculating Zr in the suspension or slurry with a flocculant;
The flocculant is sulfuric acid or a salt thereof;
Method.
(Invention 4)
A method according to claim 3, comprising the steps of:
The suspension or slurry further comprises at least one of Ti and Th;
The step of aggregating with the aggregating agent includes aggregating at least one of Ti and Th.
Method.
(Invention 5)
5. The method according to any one of claims 1 to 4, wherein the chlorination residue is generated during the production of titanium tetrachloride from titanium ore.

In one aspect, the method of the present invention includes filtering the suspension or slurry at a reduced Zr concentration, thereby increasing the filtration rate.

In one embodiment, an example in which the filtration rate varies from lot to lot is shown. The vertical axis indicates the time required for filtration (unit: hours). The horizontal axis indicates the number of batches. The dotted line indicates the planned value of the filtration time. The solid line indicates the actual value of the filtration time. In one embodiment, the relationship between the amount of flocculant added and the change in concentration of Zr, etc. is shown. In one embodiment, the relationship between Zr concentration and filtration time (without addition of a flocculant) is shown. The vertical axis indicates the time required for filtration (unit: hours). The horizontal axis indicates the Zr concentration. In one embodiment, the relationship between Zr concentration and filtration time (with addition of a flocculant) is shown. The vertical axis indicates the time required for filtration (unit: hours). The horizontal axis indicates the Zr concentration. In one embodiment, the pH and Zr concentration of the chlorinated residue slurry vary from lot to lot. The vertical axis represents Zr concentration. The horizontal axis represents pH.

Specific embodiments for carrying out the present invention will be described below. The following description is intended to facilitate understanding of the present invention. In other words, it is not intended to limit the scope of the present invention.

1. Overview In one embodiment, the present invention relates to a method for recovering Sc, the method comprising at least the following steps:
A step of providing a chloride residue A step of filtering

In the above method, the subject of the filtering step is a suspension or a slurry. The suspension or slurry is derived from chloride residue. The suspension or slurry further contains Sc and Zr. The pH of the suspension or slurry is 3.5 or less.

In the above method, the filtering step includes filtering in a state where the Zr concentration in the suspension or slurry is reduced.

Each step is explained in detail below.

2. Providing a chloride residue
2-1. Origin of chlorinated residue The chlorinated residue may be derived from a substance generated during the production of titanium tetrachloride from titanium ore.

Traditionally, titanium has generally been refined from titanium ore using the Kroll process. As an example of the production flow, titanium ore and coke are fed into a fluidized bed reactor. Chlorine gas is then blown into the bottom of the fluidized bed reactor. The titanium ore reacts with the chlorine gas to produce titanium tetrachloride. Titanium tetrachloride is in a gaseous state at the temperature inside the reactor. This titanium tetrachloride in a gaseous state is sent to the next cooling system and cooled. The cooled titanium tetrachloride becomes liquid and is recovered.

When the gaseous titanium tetrachloride is sent to the subsequent cooling system, impurities in the form of fine powder are carried along with it in the air flow. These impurities include substances other than titanium (e.g., Sc, Th, etc.), unreacted ore, unreacted coke, etc. These impurities are recovered in the cooling system in solid form. In this specification, this recovered material is called chlorination residue. The chlorination residue may be made into a slurry or may be in the form of a dry particle group. Typically, Sc can be recovered using the slurry material.

The chloride residue may contain various metal elements other than Sc. For example, the chloride residue may contain Zr. Furthermore, the chloride residue may contain Ti and/or Th.

When recovering Sc from the chlorination residue, the chlorination residue can be provided in the form of a suspension or slurry.

3. Filtration process
3-1. A series of processes for recovering the substance Sc to be filtered includes a step of filtering a substance containing Sc. Here, the substance containing Sc is derived from the above-mentioned chlorination residue. The above-mentioned substance containing Sc further contains Zr. The substance containing Sc is in the form of a suspension or a slurry. Furthermore, Sc in the suspension or slurry may be present on the solid side, may be present on the liquid side, or may be present on both sides. Furthermore, Sc present on the solid side may be present in the form of a precipitate, or may be present suspended in the liquid as a colloid.

Whether Sc is present in the solid and/or liquid side may depend on the processing up until the time of filtration.

For example, if the above-mentioned slurry-form chloride residue is to be filtered, Sc will be present mainly in the solid side.

For example, if the slurry resulting from leaching Sc from a solid is to be filtered, Sc will be primarily present in the liquid side.

For example, if a specific fraction obtained after classification of the above-mentioned slurry-form chloride residue is to be filtered, Sc will be present mainly in the solid side.

In any case, the method of the present invention in one embodiment can be applied regardless of whether Sc is present on the solid side and/or the liquid side.

3-2. pH of the object to be filtered
As described above, the filtration target is a substance containing Sc, and the substance containing Sc is in the form of a suspension or a slurry. The pH of the suspension or slurry is 3.5 or less. This is because, when the pH is more than 3.5, Zr precipitates, which has little effect on the filtration rate. Preferably, the pH of the suspension or slurry (particularly, the pH of the suspension or slurry in the case of applying the method of filtering after lowering the Zr concentration) is 2.0 or less, and more preferably, 1.5 or less. This is because, when the pH is 2.0 or less or 1.5 or less, the amount of Ti and Th in the liquid increases. Another reason is that, when the pH is 2.0 or less or 1.5 or less, the Zr concentration tends to increase, which has a large effect on the filtration rate. The lower limit is not particularly limited, but is typically -1 or more, taking into account, for example, the pH during the leaching treatment.

3-3. Control of Zr concentration The filtering step includes filtering in a state in which the Zr concentration in the suspension or slurry is reduced. Therefore, the filtering step can include performing a treatment for reducing the Zr concentration in the suspension or slurry.

In this specification, the Zr concentration in the suspension or slurry means the Zr concentration in the filtrate obtained by performing a filter press under the following conditions, or the Zr concentration in the filtrate obtained by suction filtration using a 5C (equivalent to type 5C specified in JIS P 3801 [filter paper (for chemical analysis)]) filter paper.
Model: TFAP-7-14MKII (manufactured by Hitachi Zosen Corporation)
Filter area: 10.9 ^m2
Filtration pressure: 0.4Ma
Slurry volume: 1.5 ^m3 /batch Filter cloth: Specification: PJ-7 Weaving method: double weave Structure: multi-multi Air permeability: 0.3 cc/(sec· ^cm2 ·12.7 mmAq)

The Zr in the filtrate includes, for example, Zr dissolved in the solution and present in the form of ions, etc., and Zr present as colloids that have passed through the filter. The filtrate is sampled, the colloids are further dissolved with hydrochloric acid, and the Zr concentration is then measured by ICP atomic emission spectrometry.

Filtration is preferably carried out after the Zr concentration in the suspension or slurry has been reduced to 50 mg/L or less (i.e., after pretreatment so that the Zr concentration of the filtrate after filtration under the above conditions is 50 mg/L or less). This improves the filtration rate.

The means for reducing the Zr concentration is not particularly limited, but may include a means for selectively removing only Zr. For example, it may include agglomerating Zr with a flocculant. This causes Zr present as a colloid to aggregate.

3-3-1. Control of Zr concentration by flocculant The flocculant is preferably an inorganic flocculant, more specifically, it may be sulfuric acid (H ₂ SO ₄ ) or a salt thereof. Examples of sulfates include sodium sulfate and aluminum sulfate. Typically, the sulfate may be sodium sulfate.

The amount of flocculant to be added is not particularly limited, but it is preferable that the amount be such that Zr is flocculated and the Zr concentration is 50 mg/L or less. Typically, the amount of flocculant to be added is 1.5 g/L or more.

Although the following explanation is not intended to limit the present invention, the mechanism by which Zr affects the filtration rate is believed to be as follows. First, when Zr is present, Zr hydroxide colloids/fine particles are generated. These then cover the cake surface. It is believed that the presence of this coating on the cake surface causes a decrease in the filtration rate.

3-3-2. Effect of the flocculant on other metal elements The above-mentioned sulfuric acid (H ₂ SO ₄ ) or salts thereof can affect not only the Zr concentration but also the Ti and/or Th concentration. More specifically, sulfuric acid (H ₂ SO ₄ ) or salts thereof can promote the flocculation of Ti and/or Th, similar to Zr. On the other hand, the above-mentioned sulfuric acid (H ₂ SO ₄ ) or salts thereof hardly contributes to the flocculation of Sc. Therefore, the above-mentioned sulfuric acid (H ₂ SO ₄ ) or salts thereof may be useful for separating Sc. For example, when Sc and Zr, etc. (for example, Zr, Ti, and/or Th) are present as fine colloids in the liquid, the flocculant can flocculate metal elements other than Sc, thereby improving the purity of Sc.

3-4. Types of Filtration Methods There are no particular limitations on the types of filtration methods, but examples include pressure filtration (filter press), reduced pressure filtration, centrifugal filtration, natural filtration, etc. From the viewpoints of filtration speed, simplicity of equipment, etc., filter press is preferred.

The filtering conditions are not particularly limited. The effects of the present invention in one embodiment can be obtained with any area, any filter pore size, any filter material, any pressure, etc.

4. Other (applicable flows)
The method of the present invention in the above-mentioned embodiment can be applied to various flows for recovering Sc. For example, filtration may be performed in a state where Sc is mainly contained in the solid side of a liquid and a solid. In another example, filtration may be performed in a state where Sc is mainly contained in the liquid side of a liquid and a solid.

4-1. When Sc is contained in the solid side (A01) A chlorinated residue slurry is prepared (A02) The chlorinated residue slurry is classified (e.g., using a liquid cyclone, etc.) to obtain a slurry-like fraction containing the most Sc (A03) The slurry-like fraction is filtered to obtain a solid Sc-enriched raw material

The method of the present invention according to the embodiment described above is useful, for example, in the filtration step (A03). In addition, when a flocculant is used, the Sc in the colloid also flocculates and remains on the solid side, improving the recovery rate of Sc.

4-2. When Sc is contained in the liquid side As an example, the following flow can be mentioned.
(B01) Prepare a chlorinated residue slurry. (B02) Use a leaching solution containing hydrochloric acid (e.g., pH 0.9 or less at the start of leaching) to leach Sc from the chlorinated residue slurry (at this time, Zr, etc. are also leached).
(B03) The chlorination residue and the post-leaching liquid are filtered. (B04) The pH of the filtrate is adjusted to the neutral side (e.g., pH 4 or higher) to precipitate Sc, and an Sc-concentrated slurry is obtained. (B05) The Sc-concentrated slurry is filtered to obtain a solid Sc-concentrated raw material.

The method of the present invention according to the embodiment described above is useful, for example, in the filtration step (B03).

Another example is the following flow:
(C01) Obtain a solid Sc-enriched raw material shown in (A03). (C02) Use a leaching solution containing hydrochloric acid (e.g., pH 0.9 or less at the start of leaching) to leach Sc from the solid Sc-enriched raw material (at this time, Zr, etc. are also leached).
(C03) The leaching residue and the post-leaching liquid are filtered. (C04) The pH of the filtrate is adjusted to the neutral side (e.g., pH 1.3 to 3.5) to precipitate metal elements other than Sc (e.g., Th, etc.). (C05) The filtrate containing the precipitate is filtered.

The method of the present invention according to the embodiment described above is useful, for example, in the filtration step of (C03).

In addition, the solid Sc-enriched raw material obtained in (A03) and/or (B05) may be further subjected to solvent extraction of the leachate obtained by leaching Sc from the solid Sc-enriched raw material, and/or the filtrate obtained in (C05). After the solvent extraction, Sc can be recovered in the form of Sc(OH) ₃ , which can be further calcined and recovered in the form of _Sc2O3 . Alternatively, the obtained _Sc (OH) ₃ can be leached, and scandium can be precipitated in the form of scandium carboxylate using a carboxylic acid such as oxalic acid, _which can be further calcined and recovered in the form of _Sc2O3 .

Below, more specific examples are disclosed to facilitate understanding of the present invention.

The chlorination residue is a solid material recovered in a furnace for recovering titanium tetrachloride that has evaporated during titanium smelting. The chlorination residue was obtained from Toho Titanium Co., Ltd. The chlorination residue was in a slurry state that had been washed with water.

The amounts of Sc, Zr, Th, and Ti in the slurry, solid, and solution were analyzed using alkali fusion-ICP atomic emission spectrometry (ICP-AES, Seiko Instruments Inc., SPS7700).

5. Example 1 (Changes in filtration time depending on the lot)
The above-mentioned chloride residue slurry was poured into a leaching solution containing hydrochloric acid to leach Sc, etc. The leaching residue and the post-leaching liquid were subjected to a filter press.

The filter press conditions were as follows:
Model: TFAP-7-14MKII (manufactured by Hitachi Zosen Corporation)
Filter area: 10.9 ^m2
Filtration pressure: 0.4Ma
Slurry volume: 1.5 ^m3 /batch Filter cloth: Specification: PJ-7 Weaving method: double weave Structure: multi-multi Air permeability: 0.3 cc/(sec· ^cm2 ·12.7 mmAq)

The time it took for filtration to be completed was measured for each batch. The results are shown in Figure 1. As shown in Figure 1, it was shown that the filtration time differed from lot to lot (batch to batch).

6. Example 2 (Changes in Zr concentration, etc. due to addition of flocculant)
Next, a portion of the mixture of the post-leaching solution and the leaching residue was sampled. A flocculant was added to the mixture of the post-leaching solution and the leaching residue. _Sodium sulfate ( _Na2SO4 ) was used as the flocculant. The flocculant was added in such amounts that the final concentrations were 0.5 g/L, 1.5 g/L, and 2.0 g/L. The pH of the chloride residue slurry was 1.5. The slurry before and after the addition of the flocculant was suction filtered with 5C filter paper to obtain filtrate, and the concentrations of Sc, Zr, Ti, and Th in the filtrate (including the concentrations of Sc, Zr, Ti, and Th contained in the colloidal particles suspended in the filtrate and passed through the filter) were measured. The results are shown in FIG. 2. Furthermore, the results when the amount added was 2.0/L (final concentration) are shown in Table 1 below.

As shown in Figure 2 and Table 1, it was shown that the addition of a flocculant reduced the concentrations of Ti, Zr, and Th in the filtrate. When sodium chloride ( _NaCl ) was added instead of sodium sulfate ( _Na2SO4 ), no effect as a flocculant was obtained and no significant change in concentration was observed. Therefore, it is believed that the above-mentioned change in concentration was caused by the presence of sulfate ions.

It is worth noting that the concentration of Sc is not affected by the addition of the flocculant. Therefore, the addition of the flocculant is also useful from the viewpoint of improving the purity of Sc. In particular, adding the flocculant while Sc is dissolved in the solution can promote the flocculation and subsequent separation of Ti, Zr, and Th other than Sc.

7. Example 3 (Relationship between change in Zr concentration and filtration rate)
Next, the mixture of the post-leaching solution and the leaching residue was subjected to a filter press. The filter press conditions were the same as in Example 1. The time required for filtration was measured. The filtrate was then sampled to measure the Zr concentration in the filtrate. The results are shown in Figure 3.

Next, a flocculant was added to the mixture of the post-leaching liquid and the leaching residue. The mixture of the post-leaching liquid and the leaching residue was then subjected to a filter press. The filter press conditions were the same as in Example 1. The time required for filtration was measured. The filtrate was then sampled and the Zr concentration in the filtrate was measured. The results are shown in Figure 4.

As shown in Figures 3 and 4, the filtration time decreased rapidly when the Zr concentration of the filtrate was 50 mg/L or less. Therefore, it was shown that lowering the Zr concentration of the filtrate is advantageous for improving the filtration rate.

Furthermore, comparing Figures 3 and 4, it was shown that even with the same Zr concentration, the filtration rate improved by adding a coagulant.

8. Example 4 (Zr concentration and pH for each lot)
The above example is an example in which filtration was performed on the post-leaching liquid (and leaching residue) from which Sc was leached. In this example, the Zr concentration and pH of the chlorinated residue slurry itself before leaching are verified. The chlorinated residue slurry was filtered to measure the Zr concentration and pH in the filtrate. The results are shown in FIG. 5. It was shown that the Zr concentration and pH differed greatly for each lot. In particular, it was shown that there were many lots with Zr concentrations exceeding 50 mg/L. Therefore, it was shown that when the chlorinated residue slurry or a slurry in a fraction thereof after classification or the like is filtered, the filtration time may be delayed. Furthermore, it was shown that the filtration time may be shortened by performing a process to reduce the Zr concentration.

Figure 5 also shows that the Zr concentration tends to increase as the pH decreases. This shows that lowering the Zr concentration is highly effective when filtering slurries with low pH (especially when the pH is 3.5 or less).

Specific embodiments of the present invention have been described above. The above embodiments are merely specific examples of the present invention, and the present invention is not limited to the above embodiments. For example, a technical feature disclosed in one of the above embodiments can be applied to other embodiments. Furthermore, unless otherwise specified, for a particular method, the order of some steps can be interchanged with other steps, and an additional step can be added between two specific steps. The scope of the present invention is defined by the claims.

Claims (4)

1. A method for recovering Sc, comprising:
providing a chloride residue;
A filtering step;
Including,
The subject of the filtering step is a suspension or a slurry,
The suspension or slurry is derived from the chlorination residue, contains Sc and Zr, and has a pH of 3.5 or less;
The filtering step includes filtering in a state in which the Zr concentration in the suspension or slurry is reduced.
It is a method,
The method further comprises the step of flocculating the Zr in the suspension or slurry with a flocculating agent prior to the filtering step;
The flocculant is a sulfate.
Method . The method of claim 1, wherein filtering with the Zr concentration reduced includes filtering with the Zr concentration reduced to 50 mg/L or less. 2. The method of claim 1 ,
The suspension or slurry further comprises at least one of Ti and Th;
The step of aggregating with the aggregating agent includes aggregating at least one of Ti and Th.
Method. The method according to any one of claims 1 to 3 , wherein the chlorination residue is generated during the production of titanium tetrachloride from titanium ore.