JP2000087154A - Method for recovering rare earth element from used rare earth element type abrasive material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover a rare earth element from a used rare earth element type abrasive material as hydroxide or oxide in high purity at a relatively low cost. SOLUTION: A used rare earth element type abrasive material is treated with an aq. mineral acid soln. to dissolve the rare earth element and the resultant soln. is separated from the undissolved material and recovered. Oxalic acid and an aq. alkali oxalate soln. are added to the recovered soln. so that the soln. is adjusted to <=pH 5 and the rare earth element is deposited as oxalate. This oxalate is recovered by solid-liquid separation and converted into hydroxide by treatment with an aq. alkali hydroxide soln. The hydroxide of the rare earth element and an aq. alkali oxalate soln. formed by the treatment are recovered by solid-liquid separation. The recovered aq. alkali oxalate soln. is reutilized in the oxalate depositing step.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering rare earth elements from used rare earth abrasives, and more particularly, to a method for recovering rare earth elements from a rare earth abrasive used for polishing a glass surface or the like. Reusing.

[0002]

2. Description of the Related Art Rare earth element-based abrasives are obtained by pulverizing a bastnaesite concentrate obtained by removing foreign minerals from a rare earth mineral ore such as bastnaesite produced in the United States in a beneficiation process. It is manufactured through various processes such as chemical treatment, filtration, drying, roasting, pulverization, classification, and mixing of additives.

[0003] Rare earth element-based abrasives have excellent polishing properties, and are therefore used for glass substrates for liquid crystal display devices (LCDs), glass substrates used for hard disk storage devices for computers, optical glasses such as lenses, and semiconductor ICs. It is used for polishing glass substrates for masks and glass for cathode ray tubes (CRT).

[0004] In recent years, the demand for a glass substrate for a liquid crystal display device or a glass substrate used for a hard disk storage device for a computer, which is an object to be polished, has been increasing year by year. Current,
About 4000 tons of rare earth element-based abrasives are used annually for polishing glass substrates and optical lenses.

[0005]

At present, almost all of these rare earth element-based abrasives are discarded as industrial waste after use. Under the situation where the increasing industrial waste has become a serious social problem, there is an increasing demand for recycling of used rare earth element-based abrasives.

Further, these used rare earth element-based abrasives contain 20 to 80% by weight of a rare earth element oxide on a dry basis, and from the viewpoint of effective use of these resources, and depend on import. Recovery of rare earth elements from spent rare earth element-based abrasives is also an important issue from the viewpoint of securing stable rare earth element resources. Conventionally, various methods have been proposed for recovering rare earth elements from spent rare earth element-based abrasives.However, these recovery methods have problems in terms of purity of recovered products, cost, etc. No satisfactory recovery method has been proposed.

For example, a rare earth element is dissolved from a used rare earth element-based abrasive by treating with a mineral acid or anodizing, and a precipitant such as oxalic acid or an alkali oxalate is directly added to the solution to obtain a rare earth element. Is recovered in the form of an oxalate, and then the oxalate is oxidized and roasted to recover the rare earth element in the form of an oxide. However, the above-mentioned recovery method is a preferable method in terms of the purity of the rare-earth element oxide to be recovered, but has a drawback that the cost increases because expensive oxalic acid or alkali oxalate is consumed.

The present invention has been made in order to solve the above-mentioned drawbacks, and a method for recovering a rare earth element from a used rare earth element-based abrasive as a hydroxide or an oxide with high purity and at a relatively low cost. The challenge is to provide

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, after recovering a rare earth element in the form of an oxalate in the same manner as in the prior art, an aqueous alkali hydroxide solution was used. Treated to convert to rare earth element hydroxide and to generate an aqueous alkali oxalate solution, collect them by solid-liquid separation, and reuse the recovered aqueous alkali oxalate solution as a precipitating agent to obtain used rare earth element polishing The present inventors have found that rare earth elements can be recovered as hydroxide from the material with high purity and relatively low cost, and the present invention has been completed.

That is, the method for recovering a rare earth element from a used rare earth element-based abrasive according to the present invention comprises a first step of treating the used rare earth element-based abrasive with a mineral acid aqueous solution to dissolve the rare earth element, A second step of solid-liquid separation of a solution in which the rare earth element produced in one step is dissolved and an undissolved substance to recover the solution, and oxalic acid so that the pH of the recovered solution is 5 or less. And a third step of adding an aqueous alkali oxalate solution to precipitate the rare earth element as an oxalate, a fourth step of recovering the rare earth element oxalate by solid-liquid separation, an aqueous alkali hydroxide solution of the recovered rare earth element oxalate A fifth step of converting to a rare earth element hydroxide and producing an aqueous alkali oxalate solution, and solid-liquid separation of the rare earth element hydroxide and the aqueous alkali oxalate solution produced in the fifth step, respectively. Includes a sixth step of yield, oxalate alkaline aqueous solution recovered in the sixth step, and wherein the reused as oxalic acid aqueous alkali solution to be added in the third step.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, "used rare earth element abrasive" as a source for recovering a rare earth element is a rare earth element oxide, particularly a rare earth element abrasive mainly composed of cerium oxide. Means a mixture of a rare earth element oxide and a glass powder to be cut which is produced when the surface of a glass substrate or the like is polished.

The rare earth element abrasive currently used for polishing a glass substrate contains 80 to 98% by weight of a rare earth element oxide.
Among them, cerium oxide is the largest, and accounts for 40 to 90% by weight of the entire rare earth element oxide. Further, it contains 5 to 9% by weight of fluorine. Fluorine is originally contained in bastnaesite ore [(Ce, La) (CO ₃ ) F], but it has an important chemical polishing effect together with physical polishing in glass polishing, so its content is reduced to 5 to 9% by weight. I am adjusting. The rare earth element-based abrasive preferably has an average particle size of 0.4 to 3.0 μm.

Further, a dried rare earth element-based abrasive slurry, or a used rare earth element-based abrasive slurry is agglomerated with an organic or inorganic coagulant, and then solid-liquid separated by a dehydration filter such as a filter press. When the composition of the dried solid (cake) after drying is examined, there is a difference depending on the material of the material to be polished and the polishing method, but the glass component, particularly silica (SiO ₂ ) is contained, for example, in an amount of 2 to 20% by weight. ing. The silica content in the rare earth-based abrasive before use is 2% by weight or less, and is generally considerably increased.

When polyaluminum chloride is used for coagulating the spent rare earth element-based abrasive slurry, alumina is also contained in an amount of 3 to 20% by weight. In the recovery method of the present invention, the used rare-earth-based abrasive contains 20 to 80% by weight of rare-earth element oxide on a dry basis.
Includes, but if the profitability aspect is important, 40% by weight
More preferably, the content is more preferably 60% by weight or more.

As a first step of the recovery method of the present invention, the used rare-earth-based abrasive is treated with a mineral acid, for example, an aqueous sulfuric acid solution to dissolve the rare-earth element. By this dissolving operation, a mixture consisting of a solution in which the rare earth element is dissolved and an undissolved substance is generated. The concentration of the sulfuric acid aqueous solution used at this time is a concentration that can dissolve the rare earth element, and the amount of the sulfuric acid aqueous solution used is also affected by the content of impurities. To 1.5 equivalents, preferably 1.1 to 1.3 equivalents of sulfuric acid. When the amount of sulfuric acid used is small, it takes a long time for the rare earth element to completely dissolve, or a part of the rare earth element tends to remain undissolved, and when the amount of sulfuric acid used is large Is wasteful and uneconomical. The temperature and time during the dissolution treatment are not critical, but if the temperature is low, the dissolution of the rare earth element oxide becomes difficult, and conversely, as the temperature increases, the dissolution rate increases.
Equipment will be expensive. For example, 50-70 ° C
For 3 to 5 hours.

In the second step of the recovery method of the present invention, the solution in which the rare earth element formed in the first step is dissolved and the undissolved matter are separated into solid and liquid, and the solution is recovered as a filtrate, for example, by filtration. I do. At the time of this filtration, the residue may be washed with water, and the washing may be combined with the filtrate. In addition, since the residue contains various components generated by polishing the glass, for example, silicon-based, boron-based, and phosphorus-based compounds, the residue can be discarded or solidified into blocks. .

In the third step of the recovery method of the present invention, the pH of the solution (filtrate or filtrate + washing liquid) recovered by solid-liquid separation in the second step is 5 or less, preferably 1 to 2.5. As described above, oxalic acid (usually an aqueous oxalic acid solution) and an aqueous alkali oxalate solution are added to precipitate rare earth elements as oxalates.
Since this precipitate is fine particles, it precipitates gradually. The addition amount of the aqueous oxalic acid solution and the aqueous alkali oxalate solution needs to be an amount sufficient to precipitate as much rare earth element as possible, but if the added amount is large, it is wasted. Uneconomical.

As the fourth step of the recovery method of the present invention, the precipitated oxalate of the rare earth element is recovered by solid-liquid separation, for example, decantation. Since the precipitate composed of the oxalate of the rare earth element gradually settles in the dispersion medium, in order to shorten the operation time, a considerable amount of the dispersion medium becomes a supernatant before the precipitate completely settles. The supernatant is discarded by decantation to recover the rare earth oxalate. This waste liquid contains iron compounds, aluminum compounds,
It contains sodium sulfate and the like.

As a fifth step of the recovery method of the present invention, the rare earth oxalate recovered in the fourth step is treated with an alkali hydroxide aqueous solution to be converted into a rare earth hydroxide and an alkali oxalate aqueous solution is generated. . The addition amount of the aqueous alkali hydroxide solution needs to be an amount sufficient to convert as much of the oxalate of the rare earth element as a hydroxide, but if the addition amount is large, it is uneconomical. is there.

In the sixth step of the recovery method of the present invention, the hydroxide of the rare earth element and the aqueous alkali oxalate solution formed in the fifth step are recovered by solid-liquid separation, for example, decantation. In addition, since the hydroxide of the rare earth element is gradually settled in the aqueous alkali oxalate solution, a considerable amount of the aqueous alkali oxalate solution before the hydroxide of the rare earth element completely settles out is used for the purpose of shortening the operation time. At this stage, the hydroxide of the rare earth element and the aqueous alkali oxalate solution are recovered by decantation. Since the recovered aqueous alkali oxalate solution contains an effective oxalic acid component for precipitating rare earth elements as oxalates, it is used as the aqueous alkali oxalate solution to be added in the third step. The aqueous alkali oxalate solution recovered in the sixth step may be used by circulating it immediately in the third step, or may be stored and used as the aqueous alkali oxalate solution to be added in the third step. You may.

In the recovery method of the present invention, the aqueous alkali oxalate solution recovered in the sixth step is used as the aqueous alkali oxalate solution added in the third step as described above, that is, the oxalic acid component is recycled and used. The required amount of oxalic acid added in the third step may be an amount corresponding to the oxalic acid content lost in the fourth step and the sixth step.

Thus, the rare earth element is recovered in the form of oxalate and then consumed by oxidizing and roasting the oxalate, as compared with the prior art recovery method of recovering the rare earth element in the form of oxide. The amount of oxalic acid is reduced to less than half, and it is possible to recover rare earth elements as hydroxides or oxides from spent rare earth element-based abrasives with high purity and at low cost.

In the recovery method of the present invention, the hydroxide of the rare earth element recovered in the sixth step is treated with an acid, for example, hydrochloric acid, purified by washing with water, and then calcined to recover as an oxide. You can also. The oxide thus recovered can be reused as a rare earth element-based abrasive by blending it with other components necessary for forming the rare earth element-based abrasive.

[0024]

EXAMPLES Manufacturing Example Used rare earth element-based abrasive used for polishing a glass substrate (rare earth element oxide content: 70.29% by weight) 200
g (content of rare earth element oxide: 140.6 g) to 25%
The rare earth element was dissolved by performing extraction treatment in 612 ml of H ₂ SO ₄ at 60 ° C. for 4 hours. As a result of this dissolving operation, a mixture consisting of a solution in which the rare earth element was dissolved and an undissolved substance was produced.

The mixture comprising the dissolved solution in which the rare earth element is dissolved and the undissolved material is filtered to collect the dissolved solution as a filtrate, and the residue is washed with 705 ml of water, and the washed solution is combined with the filtrate. I made it. The total volume was 1200 ml. On the other hand, the amount of the residue was 172.9 g (the content of the rare earth oxide was 10.5 g) in a wet amount. This residue was discarded.

Dissolved solution (filtrate + washing solution) 1200 m
of oxalic acid in 1000 ml of water.
A solution in which 5 g was dissolved was added to precipitate the rare earth element as oxalate. At this time, the pH was 1.1. Since the precipitate composed of the oxalate of the rare earth element gradually settled out in the dispersion medium, in order to shorten the operation time, the supernatant liquid was decanted when about half of the dispersion medium became a supernatant liquid. Discarded. The waste amount was 800 ml.

The residue after decantation was treated with water 25
00 ml was added and the mixture was stirred, and 80 ml of a 15N NaOH aqueous solution was added thereto to generate a rare earth element hydroxide and an alkali oxalate aqueous solution. The pH at this time was 12.0. Since the hydroxide of the rare earth element is gradually settled in the aqueous alkali oxalate solution, for the purpose of shortening the operation time, about three quarters of the aqueous alkali oxalate solution becomes a supernatant liquid, and the supernatant is removed by decantation. The liquid (aqueous alkali oxalate solution) was recovered. The recovered volume is 2510 ml
Met.

The liquid containing the rare earth element hydroxide remaining after the decantation treatment was added to 2500 ml of water.
Was added, the solution was neutralized with 38 ml of 5N hydrochloric acid, washed and filtered. The amount of the residue after filtration was 155.4 g in wet weight (the content of hydroxide of rare earth element was 5 as rare earth oxide).
8.9 g).

Example 1 A solution (filtrate + washing solution) 1200 recovered in the above-mentioned production example
In the remaining half (600 ml) of the ml, 2510 ml of the aqueous alkali oxalate solution recovered in the above-mentioned Preparation Example and 1000 parts of water
A solution in which 45 g of oxalic acid was dissolved in ml was added to precipitate a rare earth element as an oxalate. The pH at this time is 1.5
Met. In addition, since the precipitate composed of the rare earth element oxalate gradually settled in the dispersion medium, for the purpose of shortening the operation time, about four-fifths of the dispersion medium became a supernatant liquid by decantation. The supernatant was discarded. The waste volume was 3350 ml.

The residue after decantation was treated with water 25
00 ml was added and the mixture was stirred, and 80 ml of a 15N NaOH aqueous solution was added thereto to generate a rare earth element hydroxide and an alkali oxalate aqueous solution. The pH at this time was 12.9. Since the hydroxide of the rare earth element is gradually settled in the aqueous alkali oxalate solution, for the purpose of shortening the operation time, about three quarters of the aqueous alkali oxalate solution becomes a supernatant liquid, and the supernatant is removed by decantation. The liquid (aqueous alkali oxalate solution) was recovered. The recovered volume is 2570 ml
Met.

2500 ml of water is added to the liquid containing the rare earth element hydroxide remaining after the decantation treatment.
Was added, the solution was neutralized with 41 ml of 5N hydrochloric acid, washed and filtered. The amount of the residue after filtration was 141.8 g in terms of wet weight (the content of hydroxide of rare earth element was 6 as rare earth element oxide).
1.1 g).

Example 2 Spent Rare Earth Abrasive (Rare Earth Oxide Content 70.29% by Weight) Used for Polishing Glass Substrate 200
g (content of rare earth element oxide: 140.6 g) to 25%
Extraction treatment was performed in 612 ml of H ₂ SO ₄ at 60 ° C. for 4 hours to dissolve the rare earth elements. As a result of this dissolving operation, a mixture consisting of a solution in which the rare earth element was dissolved and an undissolved substance was produced.

The mixture consisting of the dissolved solution in which the rare earth element is dissolved and the undissolved material is filtered to collect the dissolved solution as a filtrate, and the residue is washed with 703 ml of water, and the washed solution is combined with the filtrate. I made it. The total volume was 1200 ml. On the other hand, the amount of the residue was 175.6 g (11.7 g of rare earth element oxide) in terms of wet weight. This residue was discarded.

Dissolved solution (filtrate + washing solution) 1200 m
To 1 half (600 ml) of 1 was added a solution obtained by dissolving 45 g of oxalic acid in 2570 ml of the aqueous alkali oxalate solution and 1000 ml of water recovered in Example 1 to precipitate a rare earth element as an oxalate. The pH at this time was 1.8. In addition, since the precipitate composed of the rare earth element oxalate gradually settled in the dispersion medium, in order to shorten the operation time,
When about 4/5 of the dispersion medium became a supernatant, the supernatant was discarded by decantation. The amount of waste is 3
It was 370 ml.

The residue after decantation is treated with water 25
00 ml was added and the mixture was stirred, and 80 ml of a 15N NaOH aqueous solution was added thereto to generate a rare earth element hydroxide and an alkali oxalate aqueous solution. The pH at this time was 12.7. Since the hydroxide of the rare earth element is gradually settled in the aqueous alkali oxalate solution, for the purpose of shortening the operation time, about three quarters of the aqueous alkali oxalate solution becomes a supernatant liquid, and the supernatant is removed by decantation. The liquid (aqueous alkali oxalate solution) was recovered. The collected volume is 2610ml
Met.

2500 ml of water was added to the liquid containing the rare earth element hydroxide remaining after the decantation treatment.
Was added, the solution was neutralized with 44 ml of 5N hydrochloric acid, washed and filtered. The amount of the residue after filtration was 140.9 g in wet weight (the content of hydroxide of rare earth element was 6 as rare earth oxide).
0.9 g).

Example 3 Dissolution (filtrate + wash) 120 recovered in Example 2 above
In the remaining half volume (600 ml) of 0 ml,
2610 ml of aqueous alkali oxalate solution and water 10
A solution in which 45 g of oxalic acid was dissolved in 00 ml was added to precipitate a rare earth element as an oxalate. The pH at this time was 1.7. In addition, since the precipitate composed of the rare earth element oxalate gradually settled in the dispersion medium, for the purpose of shortening the operation time, about four-fifths of the dispersion medium became a supernatant liquid by decantation. The supernatant was discarded. The amount of waste was 3120 ml.

The residue after decantation was treated with water 25
00 ml was added and the mixture was stirred, and 80 ml of a 15N NaOH aqueous solution was added thereto to generate a rare earth element hydroxide and an alkali oxalate aqueous solution. The pH at this time was 12.7. In addition, since the hydroxide of the rare earth element is gradually settled in the aqueous alkali oxalate solution, in order to shorten the operation time,
When about three-fourths of the aqueous alkali oxalate solution became a supernatant, the supernatant (an aqueous alkali oxalate solution) was recovered by decantation. The recovered amount was 2520 ml.

2500 ml of water was added to the solution containing the rare earth element hydroxide remaining after the decantation treatment.
Was added, the solution was neutralized with 45 ml of 5N hydrochloric acid, washed and filtered. The amount of the residue after filtration was 159.5 g in terms of wet weight (the content of hydroxide of rare earth element was 6 as rare earth element oxide).
1.6 g).

As is clear from the above description of the production examples and Examples 1 to 3, in Examples 1 to 3,
Even when the amount of oxalic acid newly added is about half, the recovery of hydroxide of rare earth element is high. Therefore, the rare earth element can be recovered as hydroxide from the used rare earth element-based abrasive with high purity and low cost.

[0041]

According to the recovery method of the present invention, although it is a preferable precipitant in view of the purity of the rare earth element oxide to be recovered, the required consumption of expensive oxalic acid can be reduced to about half, so that the used rare earth element can be used. Rare earth elements can be recovered as hydroxides from elemental abrasives with high purity and low cost.

Claims (5)

[Claims] 1. A first step of dissolving a rare earth element by treating a spent rare earth element-based abrasive with an aqueous solution of mineral acid, and a dissolving solution dissolving the rare earth element generated in the first step and an undissolved substance. A second step of solid-liquid separation to recover the solution, and a third step of adding an aqueous solution of oxalic acid and an alkali oxalate to the recovered solution so as to have a pH of 5 or less to precipitate a rare earth element as an oxalate. A fourth step of recovering the rare earth oxalate by solid-liquid separation, treating the recovered rare earth oxalate with an aqueous alkali hydroxide solution to convert it into a rare earth hydroxide and producing an aqueous alkali oxalate solution A fifth step to include, and a sixth step of recovering the hydroxide of the rare earth element and the aqueous alkali oxalate solution generated in the fifth step by solid-liquid separation, respectively.
A method for recovering a rare earth element from a used rare earth element-based abrasive, wherein the aqueous alkali oxalate solution recovered in the sixth step is reused as the aqueous alkali oxalate solution added in the third step. 2. A rare earth element from a spent rare earth element abrasive according to claim 1, wherein the spent rare earth element abrasive contains 20 to 80% by weight of a rare earth element oxide on a dry basis. Collection method. 3. The method according to claim 1, wherein the third step is carried out in a pH range of 1 to 2.5. 4. The method according to claim 1, wherein the aqueous alkali oxalate solution collected in the sixth step is stored, and the stored aqueous alkali oxalate solution is used as an aqueous alkali oxalate solution to be added in the third step. 4. The method for recovering rare earth elements from spent rare earth element-based abrasives according to 2 or 3. 5. The spent rare earth element system according to claim 1, wherein the rare earth element hydroxide recovered in the sixth step is purified, calcined and recovered as an oxide. A method for recovering rare earth elements from abrasives.