JP2001240853A - Method of regenerating acid sulfide rare earth fluorescent substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of regenerating an acid sulfide rare earth fluorescent substance as rare earth oxide raw material by efficiently dissolving the acid sulfide rare earth fluorescent substance in a simple reacting container in a short time. SOLUTION: This method for regenerating an acid sulfide rare earth fluorescent substance comprises (a) a step for dissolving a fluorescent substance by dispersing the acid sulfide rare earth fluorescent substance into hydrochloric acid and then gradually adding nitric acid to the dispersion, (b) a step for producing rare earth salt of oxalic acid by adding oxalic acid or dimethyl oxalate to the above fluorescent solution and (c) a step for obtaining a rare earth oxide by heat-treating the produced rare earth salt of oxalic acid in this order.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for decomposing a rare-earth oxysulfide phosphor such as europium-activated yttrium oxysulfide phosphor (Y ₂ O ₂ S: Eu) and regenerating it as a rare-earth oxide.

[0002]

As a red-emitting phosphor of a color cathode ray tube, a oxysulfide rare phosphor Y ₂ O ₂ S: although Eu phosphor has been widely used, they are expensive for the rare earth element as a raw material , To collect and reuse this,
This is important from the viewpoint of not only effective use of resources but also reduction of manufacturing costs.

[0003] For this reason, various recovery and regeneration techniques have been developed for oxysulfide rare earth phosphors.

[0004] However, most of these methods physically recover and regenerate the phosphor from excess phosphor slurry containing a high concentration of the phosphor generated in the process of developing the phosphor film of the color cathode-ray tube. Although it is useful as a method for collecting and regenerating phosphors that are not
It is unsuitable for recovery from sludge having a low phosphor-containing concentration such as scattered phosphor slurry or suspended particles of phosphor particles generated in the process of producing the phosphor.

[0005] With respect to such degraded phosphors, it is necessary to chemically decompose the collected phosphors and regenerate them as a rare earth oxide raw material. For example, oxysulfide rare earth phosphors are converted to hydrochloric acid, nitric acid, After dissolving with a mineral acid such as sulfuric acid and selectively precipitating and removing heavy metals as a rare earth ion solution,
It has been reported that oxalic acid is used to precipitate a rare earth salt using oxalic acid, dried, and then decomposed at a high temperature to obtain a rare earth oxide.

However, when hydrochloric acid is used to dissolve the oxysulfide rare earth phosphor, dissolution takes time, and nitric acid has a strong oxidizing power and the dissolution reaction proceeds rapidly. In addition, sulfur generated at the time of dissolution is oxidized, and the resulting sulfuric acid causes a rare earth sulfate to precipitate, resulting in a poor yield. Furthermore, when sulfuric acid is used,
As in the case of nitric acid, rare earth sulfate precipitates and the yield becomes poor.

[0007]

As described above, in order to reuse a degraded oxysulfide rare earth phosphor, it is necessary to chemically decompose the collected phosphor and regenerate it as a rare earth oxide raw material. However, conventional methods have drawbacks such as time-consuming dissolution of the phosphor, poor yield, and the need for a large-scale reaction vessel, and a simple and efficient regeneration method has been found. The fact is that they have not.

The present invention has been made in order to solve such a problem, and it is possible to efficiently dissolve a rare-earth oxysulfide phosphor in a simple reaction vessel in a short time and regenerate it as a rare-earth oxide raw material. An object of the present invention is to provide a method for regenerating an oxysulfide rare earth phosphor.

[0009]

According to a first aspect of the present invention, there is provided a method for regenerating an oxysulfide rare earth phosphor.
(A) dispersing the oxysulfide rare earth phosphor in hydrochloric acid, and then gradually adding nitric acid to the dispersion to dissolve the phosphor, (b) oxalic acid and / or It is characterized in that it includes a step of adding dimethyl oxalate to form a rare earth oxalate and a step (c) of heat-treating the resulting rare earth oxalate to obtain a rare earth oxide.

In the present invention, as described in claim 2, after the step (c), a step (d) of adding a flux to the rare earth oxide and firing may be performed.

In the above-mentioned method for regenerating an oxysulfide rare earth phosphor according to the present invention,
In the step (a), the rate of addition of nitric acid to the dispersion is
It is preferable to set 0.5 ml / min / kg of phosphor to 2.0 ml / min / kg of phosphor.

Also, as described in claim 4, (c)
In the step, the heat treatment temperature is preferably set to 700 ° C to 1100 ° C, and as described in claim 5,
In the step (c), it is desirable that the generated rare earth oxalate is washed with water, filtered and dried, and then heat-treated.

In the present invention, the phosphor can be dissolved in a short time by dispersing the oxysulfide rare earth phosphor in hydrochloric acid and then gradually adding nitric acid to the dispersion. That is, the dissolution time is significantly reduced as compared with the case of treating hydrochloric acid alone. In addition, since the oxidizing effect of nitric acid on sulfur generated at the time of dissolution is suppressed, the rare earth element is less likely to precipitate as a sulfate, and can be recovered and regenerated as a rare earth oxide with a high yield. In addition, although the dissolution time is shortened, the dissolution reaction does not proceed violently as in the case of treatment using conventional nitric acid alone, so that there is no need to use a large-scale reaction vessel and the cost for regeneration is reduced. can do.

[0014]

Embodiments of the present invention will be described below.

In the present invention, first, an oxysulfide rare earth phosphor is dispersed in hydrochloric acid, and then nitric acid is gradually added to the dispersion to dissolve the phosphor (step (a)).

The oxysulfide rare earth phosphor has a general formula:
Re ₂ O ₂ S (where Re is Y, La, Ce, Pr, N
d, Pm, Sm, Eu, Gd, Tb, Dy, Ho, E
and at least two rare earth elements selected from r, Tm, Yb and Lu). This oxysulfide rare earth phosphor may be recovered as a loss in the manufacturing process of the phosphor, or may be recovered as surplus or loss in the process of forming the fluorescent film of the color cathode ray tube. Is also good. Further, the phosphor may be a phosphor that has been subjected to a treatment such as removal of impurities from the phosphor, or may be a phosphor that has been recovered as a loss during the treatment process.

Such a phosphor is dispersed in pure water such as deionized water, if necessary, filtered to remove foreign substances, and then dispersed in hydrochloric acid. It is preferable to use hydrochloric acid having a concentration of 21% by weight to 38% by weight. The amount is usually 50 parts by weight to 150 parts by weight, preferably 80 parts by weight to 100 parts by weight, based on 100 parts by weight of the phosphor (in terms of solid content). If the amount is less than 50 parts by weight, the amount of sulfate increases and the yield of rare earth oxides decreases. If the amount exceeds 150 parts by weight, a radical reaction is likely to occur and a large-scale reaction vessel is required. Dispersion in hydrochloric acid can be performed by stirring, and during that time, it is preferable to heat and maintain the liquid temperature at 50 ° C to 90 ° C.

After the phosphor is dispersed in hydrochloric acid, nitric acid is gradually added to the dispersion, preferably while stirring the dispersion. Nitric acid is usually used at a concentration of 62% by weight to 72% by weight, and 0.5 ml / min / 1 kg of phosphor to 2.0 ml / min / 1 kg of phosphor,
Preferably 0.8 ml / min / phosphor 1 kg-1.2 ml / min / phosphor 1
At an addition rate of kg, the total amount is 50 to 150 parts by weight, preferably 80 to 100 parts by weight, per 100 parts by weight of the phosphor (in terms of solid content). If the addition rate is less than 0.5 ml / min / 1 kg of phosphor, it takes a long time to dissolve, and 2.0 ml / min /
If the phosphor exceeds 1 kg, the dissolution reaction becomes excessive and a large-scale reaction vessel is required. If the total amount of nitric acid is less than 50 parts by weight per 100 parts by weight of the phosphor (in terms of solid content), the dissolution will take a long time, and if it exceeds 150 parts by weight, the amount of sulfate increases and the yield of rare earth oxides decreases. . By continuing the stirring for about 0.5 to 3 hours after the addition, the phosphor is dissolved, and a rare earth element ion solution is obtained.

Next, oxalic acid and / or dimethyl oxalate are added to the rare earth element ion solution obtained in the above step and stirred to produce a rare earth oxalate salt (step (b)).

The rare earth element ion solution obtained in the step (a) may be transferred to a stationary tank and left standing to remove impurities by settling if necessary. The standing is usually performed for 24 hours or more. The rare-earth element ion solution from which the impurities have been removed in this manner may be subjected to a filtration treatment, if necessary, whereby the impurities can be more reliably removed.

The amount of oxalic acid and / or dimethyl oxalate added in this step (b) is usually 110 to 390 parts by weight, preferably 120 parts by weight, per 100 parts by weight of the phosphor (in terms of solid content). Parts to 220 parts by weight. If the amount of addition is less than 110 parts by weight with respect to 100 parts by weight of the phosphor (in terms of solid content), the rare earth oxalate salt formation reaction does not proceed, and the yield of rare earth oxide decreases. On the other hand, if it exceeds 390 parts by weight, it becomes excessive addition not contributing to the rare earth oxalate salt formation reaction. It is desirable that the addition of oxalic acid and the like be performed while the solution is heated and maintained at 55 to 90 ° C. and the solution is stirred. By continuing stirring for about 0.5 to 2 hours after the addition, the rare earth element ion reacts with oxalic acid or the like to generate a rare earth oxalate.

Thereafter, the mixture is allowed to stand to sediment the rare earth oxalate, and the supernatant is removed. If necessary, it is washed with water, filtered and dried, and then heat-treated (step (c)).

In the water washing, it is preferable that the supernatant is repeatedly washed with pure water such as deionized water or distilled water until the pH of the supernatant becomes 5.0 or more. Dry at about 150 ° C. for about 12 hours to completely remove water.

The heat treatment is performed using a continuous roasting furnace or the like to separate the rare earth oxalate at 700 ° C. to 1100 ° C. for 1 hour to 4 hours, preferably at 800 ° C. to 1000 ° C. for 2 hours to 3 hours. .
As a result, a sufficiently purified rare earth oxide is obtained.

The rare earth oxide thus obtained is
By adding the flux and firing (step (d)), a reusable regenerated phosphor can be obtained.

For example, by using barium chloride, magnesium chloride, or the like as a flux and heating and firing in air at 1150 ° C. to 1500 ° C. for 1 hour to 6 hours, a rare earth oxide phosphor can be obtained.

Further, calcination is carried out by heating at 800 ° C. to 1250 ° C. for 1 hour to 6 hours in air using an alkali metal carbonate such as sodium carbonate or potassium carbonate, sulfur and potassium phosphate as a flux. A rare earth phosphor can be obtained.

If necessary, the obtained regenerated phosphor may be subjected to filtration, filtration, etc., as performed when a new phosphor is produced.
Final purification such as drying and sieving is performed as appropriate, and the product is put to practical use.

As described above, according to the method for regenerating an oxysulfide rare earth phosphor of the present invention, after the oxysulfide rare earth phosphor is dispersed in hydrochloric acid, nitric acid is gradually added to the dispersion. Dissolve the phosphor. Although this dissolution reaction proceeds promptly, it does not cause a rapid reaction as in the case where a phosphor is thrown into and dissolved in conventional nitric acid, and also suppresses the precipitation of rare earth sulfate, which is a general reaction. By using a simple reaction vessel, the oxysulfide rare earth phosphor can be efficiently decomposed in a short time and regenerated as a rare earth oxide in high yield.
In addition, a reusable regenerated phosphor can be obtained using the regenerated rare earth oxide as a raw material. The method for regenerating an oxysulfide rare earth phosphor of the present invention is particularly useful as a method for regenerating a degraded oxysulfide rare earth phosphor which is difficult to regenerate by a so-called physical regeneration method.

[0030]

EXAMPLES Next, specific examples of the present invention will be described, but the present invention is not limited to these examples.

EXAMPLE 100 kg (solid content) of europium-activated yttrium oxysulfide phosphor was put into 430 l (liter) of 21% hydrochloric acid housed in a reaction tank (1 tGL reactor), and the liquid temperature was reduced to 7%.
The mixture was stirred while maintaining the temperature at 0 ° C. When the phosphor is sufficiently dispersed, 67.5% nitric acid is dispersed in the dispersion at a rate of 100 ml / min.
100 l were added and stirring was continued for another 2 hours.

Next, the above-mentioned stirred liquid was transferred to a stationary tank and allowed to stand for 24 hours or more to precipitate impurities, and the supernatant was passed through a membrane filter and filtered.

The filtrate was transferred to a reaction vessel and heated to a temperature of 60 ° C.
After heating to 130 kg of solid oxalic acid with stirring
Was added and stirring was continued for another hour. Thereafter, the reaction product was allowed to settle by standing, and the supernatant was removed from the system.
Next, washing with water was repeatedly performed using pure water until the pH of the supernatant became 5.0 or more.

[0034] The washed reaction product is filtered and dried at 150 ° C for 12.
After drying for 0 hours, the mixture is put into an alumina tray and roasted in a continuous roasting furnace at 900 ° C. for 3 hours, and 90 kg (theoretical yield value 93
kg (equivalent to 96.8%) of rare earth oxides (Y ₂ O ₃ .Eu)
₂ O ₃ ) was obtained.

To 100 g of the obtained rare earth oxide, 35 g of sodium carbonate, 35 g of sulfur and 8 g of potassium phosphate were added as fluxes and mixed well. This mixture was filled in a quartz crucible and fired in air at 1150 ° C. for 240 minutes.

The fired product is washed with pure water several times, and then
After washing with a 0.5% mineral acid aqueous solution, the washing was repeated with pure water until the pH of the supernatant became 5.2 or more, followed by filtration, drying and sieving to obtain a europium-activated yttrium oxysulfide phosphor (Y ₂ O ₂ S: Eu) was obtained.

Examination of the luminescent properties of the obtained phosphor revealed that it was comparable to the newly manufactured phosphor, and could be sufficiently used as a regenerated phosphor.

COMPARATIVE EXAMPLE The same europium-activated yttrium oxysulfide phosphor 100 kg (in terms of solid content) as used in the examples was charged into 430 liters (liters) of 21% hydrochloric acid contained in a reaction vessel. 7
The mixture was stirred for 48 hours while maintaining the temperature at 0 ° C. However, the phosphor was hardly dissolved and could not be used for regeneration.

[0039]

As described above, according to the method for regenerating an oxysulfide rare earth phosphor of the present invention, nitric acid is gradually added to the dispersion after the oxysulfide rare earth phosphor is dispersed in hydrochloric acid. Since it is added and dissolved, the oxysulfide rare earth phosphor can be efficiently dissolved in a simple reaction vessel in a short time, and the yield of the obtained rare earth oxide can be increased.

Continued on the front page F term (reference) 4G076 AA02 AA13 AB08 AB28 BB08 BC07 BE09 BF09 DA11 4H001 CA06 CF01 CF02 XA00 XA08 XA16 XA39

Claims (7)

[Claims] (A) dispersing an oxysulfide rare earth phosphor in hydrochloric acid, and then gradually adding nitric acid to the dispersion to dissolve the phosphor; (b) adding a phosphoric acid solution to the phosphor solution; A step of adding oxalic acid and / or dimethyl oxalate to generate a rare earth oxalate; and (c) a step of heat-treating the generated rare earth oxalate to obtain a rare earth oxide. A method for regenerating an oxysulfide rare earth phosphor. 2. The regeneration of an oxysulfide rare earth phosphor according to claim 1, further comprising, after the step (c), a step of (d) adding a flux to the rare earth oxide and firing the rare earth oxide. Method. 3. The rate of addition of nitric acid to the dispersion in the step (a) is 0.5 ml / min / phosphor 1 kg to 2.0 ml / min /
3. The method for regenerating an oxysulfide rare earth phosphor according to claim 1, wherein the phosphor is 1 kg. 4. The heat treatment temperature in the step (c) is
The temperature is from 700 ° C. to 1100 ° C.
The method for regenerating an oxysulfide rare earth phosphor according to any one of the above. 5. The method according to claim 1, wherein in the step (c), the generated rare earth oxalate is washed with water, filtered, dried, and then subjected to a heat treatment.
The method for regenerating an oxysulfide rare earth phosphor according to the above item. 6. The oxysulfide rare earth phosphor has a general formula: Re
₂ O ₂ S (where Re is Y, La, Ce, Pr, Nd, P
m, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
The method for regenerating an oxysulfide rare earth phosphor according to any one of claims 1 to 5, wherein the phosphor is substantially represented by at least two kinds of rare earth elements selected from m, Yb and Lu). 7. The method for regenerating an oxysulfide rare earth phosphor according to claim 6, wherein the oxysulfide rare earth phosphor is a europium-activated yttrium oxysulfide phosphor.