JPH11147713A - Production of raw material for rare earth-based abrasion material from waste of abrasion material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a raw material for a rare earth- based abrasion material having the quality equal to the raw material for the rare earth-based abrasion material from ore, from the used rare earth-based abrasion material by a simple and economical step. SOLUTION: This method for producing a raw material for a rare earth-based abrasion material comprises a dissolving step for dissolving and removing a soluble impurity from a used rare earth-based abrasion material containing >=40 wt.% rare earth oxide expressed in terms of the dried material by using hydrofluoric acid, a solid-liquid separation step for carrying out a solid-liquid separation of the used abrasion material after dissolving treatment, and further additional component-regulating step for mixing a rare earth metal oxide or rare earth metal carbonate with the solid components obtained by the solid- liquid separation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for removing impurities from a rare earth waste abrasive used for polishing a glass surface or the like.
The present invention relates to a method for producing a rare earth-based abrasive raw material for recovering rare earth solids.

[0002]

2. Description of the Related Art At present, 4000 tons of rare earth abrasives are used annually for polishing glass substrates, optical lenses and the like. The rare earth-based abrasive contains at least 80% by weight of a rare earth oxide, of which 40 to 90% by weight is cerium oxide.

[0003] Rare earth-based abrasives are obtained by removing different kinds of minerals from a rare earth mineral ore such as bastnaesite produced in the United States in a beneficiation process and then pulverizing and chemically treating the obtained bastnaesite concentrate. , Filtration, drying, roasting,
Manufactured through each process of pulverization, classification, and mixing of additives (CMC “Latest application of rare earth” 1
985).

[0004] The rare-earth-based abrasives manufactured in this manner have excellent polishing properties and increase the production of glass substrates for liquid crystal display devices (LCDs) to be polished and hard disk storage devices for computers. The demand is increasing year by year.

[0005]

However, at present, almost all of these rare earth abrasives are discarded as industrial waste after use. Under the situation where the increasing industrial waste is becoming a serious social problem, there is an increasing demand for recycling of used rare earth abrasives. In addition, these rare earth waste abrasives contain 40% by weight or more of rare earth elements on a dry basis, and from the viewpoint of effective use of these resources, it is necessary to secure the stable use of rare earth resources that depend on imports. It is necessary to recover the raw materials of rare earth waste abrasive from the viewpoint of the surface.

[0006] Japanese Patent No. 2606156 discloses that a used abrasive is finely filtered to concentrate and remove coarse impurities to the concentrated liquid side, and the permeated liquid is concentrated by ultrafiltration. There has been proposed a method for collecting abrasive particles, which is characterized by being collected. However, the abrasive targeted by the above method has a fine particle size of several tens to 500 nm, and the particle size of the rare-earth-based abrasive which is the object of the present invention is 0.1 mm.
Since the thickness is 4 to 3.0 μm, the above method cannot be applied.

Japanese Patent Application Laid-Open No. 8-3543 discloses a chemical treatment step in which a polishing waste in which a used abrasive and impurities generated by polishing are mixed is used as a raw material, and a soluble impurity is removed from the polishing waste. There has been proposed a method for producing an abrasive, which comprises a physical treatment step of pulverizing the polishing waste to remove at least fine particles outside a specified value.
However, the abrasive particle size targeted by the above method is 5 to 2
0 μm, and the particle size of the rare earth-based abrasive targeted by the present invention is 0.4 to 3.0 μm, so the above method is inappropriate.

[0008] The present invention has been made in view of the above, and a rare earth-based abrasive having the same quality as a raw material of an abrasive from a rare-earth ore can be produced from used rare-earth-based abrasives in an economical process using simple equipment. An object is to provide a method for producing a raw material.

[0009]

To achieve the above object, the present invention provides a dissolving step of dissolving and removing soluble impurities from used rare earth waste abrasives using hydrofluoric acid.
And a solid-liquid separation step of performing solid-liquid separation after dissolution. A method for producing a rare earth-based abrasive raw material from waste abrasive is provided.

In the method for producing a rare earth-based abrasive material, a component adjusting step of mixing a rare earth oxide or a rare earth carbonate with the solid obtained in the solid-liquid separation step is added.

Further, the used rare-earth waste abrasive preferably contains at least 40% by weight of a rare-earth oxide on a dry basis. If the amount is less than 40% by weight, economical profitability is poor.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the "used rare earth-based abrasive" to be treated is a rare earth-based abrasive mainly composed of a rare earth oxide, particularly cerium oxide, for polishing a glass substrate surface or the like. It was done. Currently used rare earth abrasives for glass polishing are rare earth oxides of 80 ~
Among them, cerium oxide accounts for 40 to 90% by weight of the rare earth oxide. Further, it contains 5 to 9% by weight of fluorine F. Fluorine is originally contained in bastnaesite ore [(Ce, La) (CO3) F], but has a chemical polishing effect which is important together with physical polishing in glass polishing. I am adjusting. The average particle size of the rare-earth-based abrasive is 0.
4-3.0 μm is preferably used.

Rare earth abrasives are used for polishing glass substrates used for liquid crystal display devices and hard disk storage devices of computers, optical glasses such as lenses, glass substrates for photomasks for semiconductor ICs, and glass for cathode ray tubes (CRT). in use.

[0014] Dried rare earth waste abrasive slurry, or solid content (cake) after agglomeration of rare earth waste abrasive slurry with an organic or inorganic coagulant and solid-liquid separation with a dehydration filtration device such as a filter press Inspection of the composition of the dried product shows that there is a difference depending on the object to be polished and the polishing method.
-20% by weight. The silica in the abrasive before use is less than 2% by weight, which has increased considerably.

When polyaluminum chloride (PAC) is used for coagulating the waste abrasive slurry, alumina (Al 2 O 3) is contained in an amount of 3 to 20% by weight.

In the present invention, the slurry of the rare-earth waste abrasive or the cake obtained by dewatering and filtering the slurry is placed in a reaction tank containing an aqueous solution containing 10 to 55% by weight of hydrofluoric acid, and then the slurry is placed in a reaction vessel. Stir at room temperature for 8 hours. The amount of hydrofluoric acid is determined such that the ratio of the weight of hydrofluoric acid to the content of silica is the required amount. That is, the ratio of Si / F is set to 1/3 to 1/8, preferably 1/4 to 1/6. When the alumina component is mixed in the waste abrasive, it is necessary to further increase the hydrofluoric acid by setting the Al / F ratio to 1/2 to 1/4.

The slurry concentration of the rare earth waste abrasive is 100
~ 300 g / l is desirable. Slurry concentration of 300g /
If it is 1 or more, the viscosity increases and the workability decreases. When the slurry concentration is 100 g / l or less, the processing capacity is reduced.

After the dissolution step, the suspension in the reaction tank is subjected to solid-liquid separation by a dehydration filter such as a filter press. Most of the silica in the waste abrasive is eluted by the above method, and the silica concentration in the residual solid (cake) can be 2% by weight or less on a dry basis. When the ratio of Si / F is larger than 1/3 (the amount of hydrofluoric acid is small), the removal of silica is not sufficient, and when the ratio is smaller than 1/8, fluorine in the cake after solid-liquid separation becomes excessive, which is not preferable. . Even when the rare earth waste abrasive contains 3 to 20% by weight of alumina component on a dry basis, the alumina component is reduced to 2% by weight or less by the above process.

As a dissolving solution for removing impurities in the dissolving step, there is a mixed aqueous solution of ammonium fluoride and sulfuric acid, or a mixed aqueous solution of ammonium fluoride and nitric acid. It is necessary to remove nitrogen components in wastewater to strengthen regulations. This requires expensive equipment and is not economical. Therefore, the present invention uses an aqueous solution of hydrofluoric acid that can easily treat wastewater.

The cake obtained by the solid-liquid separation step contains 75% by weight or more of a rare earth oxide on a dry basis. However, as a raw material for abrasives, a rare earth oxide of 80% by weight or more on a dry basis is required. Further, since the amount of fluorine contained in the cake may be out of the specified range, a component adjusting step of adding rare earth oxide or rare earth carbonate to adjust the component may be necessary. Rare earth oxides and rare earth carbonates are intermediate raw materials produced from ores. The rare earth oxide is a mixed oxide of various rare earth elements, and contains 50 to 99.9% by weight of cerium oxide. Rare earth carbonate is a mixed carbonate of various rare earth elements. Both are commercially available.

After the used rare-earth-based abrasive is subjected to an impurity dissolving treatment with hydrofluoric acid, the composition (the content of rare-earth oxide and fluorine) of the recovered rare-earth-based abrasive is determined by solid-liquid separation. If it falls within the above specified range, it is introduced into an abrasive production process using ore as a raw material without going through the above component adjustment process. When the composition of the rare earth-based abrasive raw material recovered by the solid-liquid separation is not included in the specified range, the rare earth oxide or the rare earth carbonate is added and mixed,
Perform component adjustment. The ratio of the rare earth oxide or rare earth carbonate to be mixed is determined according to the composition of the recovered rare earth-based abrasive raw material, the intended use of the product, and the specifications.

When the rare earth waste abrasive does not contain coarse particles having a particle size of 3 μm or more, the component adjusting step is performed after the pulverizing step which is the first step of the abrasive material manufacturing step using ore as a raw material. .

When the rare earth waste abrasive contains coarse particles having a particle size of 3 μm or more, the abrasive is crushed or sieved before the hydrofluoric acid treatment, or an abrasive made of ore is used as a raw material. It may be inserted before the pulverizing step, which is the first step in the manufacturing process, and may pass through the pulverizing step.

In the component adjusting step, two or more kinds of used rare earth waste abrasives having different compositions and particle sizes used under different polishing targets and different polishing conditions may be mixed.

It is preferred from the viewpoint of profitability that the waste abrasive to be subjected to the above treatment contains at least 40% by weight of a rare earth oxide on a dry basis.

[0026]

EXAMPLES The present invention will be described more specifically with reference to examples. Example 1 A cake obtained by solid-liquid separation of a rare earth waste abrasive slurry after polishing a glass substrate for a liquid crystal display device was used. The composition was 68.0% by weight of rare earth oxide, 14.0% by weight of silica, and 5.1% by weight of fluorine on a dry basis. 8
0.8 t of the above-mentioned waste abrasive was put into a reaction tank containing 136 kg of 0% hydrofluoric acid and 3.44 m3 of water on a dry basis to make a total of 4 m3. The slurry concentration became 200 g / l. After stirring the reaction tank for 1 hour with a stirrer, the suspension was pumped to a filter press to perform solid-liquid separation. Further, the cake was washed with 0.8 m3 of water. When 1.13 t of the cake obtained here was dried and 0.79 t was analyzed, 79.0 wt% of rare earth oxide, 1.4 wt% of silica and 11.5 wt of fluorine were used on a dry basis.
% By weight. Cerium oxide was 50.3% by weight of the rare earth oxide.

The analysis method is as follows. Rare earth oxides (TREO, TotalRareEarthOxide
The analysis of s) was performed based on JISM8404-1976. Silica was quantitatively analyzed by ICP after alkali melting treatment, and fluorine was quantitatively analyzed by ion meter after alkali melting. The analysis of cerium oxide was performed with a fluorescent X-ray analyzer.

After the solid-liquid separation step, rare earth oxide is added to the obtained rare earth-based abrasive raw material in a ratio of 7: 3 and mixed.
After the components were adjusted, they were put into a rare earth abrasive production process.
That is, in each of the steps of pulverization, chemical treatment, filtration, drying, roasting, pulverization, classification, and additive mixing, treatment was carried out by a standard method, and the product was analyzed by the above-mentioned method. As a result, on a dry basis, the rare earth oxide was 86.1% by weight, silica was 1.0% by weight, and fluorine was 8.1% by weight. Cerium oxide was 51.4% of the rare earth oxides.

The particle size of the rare earth-based recovered abrasive obtained by the above production method was measured by an air permeation method (Brain method). As a result, the average particle size was 1.4 μm, which was equivalent to the particle size of the rare earth-based abrasive produced using ore as a raw material.

The "abrasive power" of the rare-earth-based recovered abrasive obtained by the above-described production method was evaluated using an Oscar-type grinder under the following conditions. Abrasive power is defined as the thickness of the glass that has been polished after polishing a soda lime glass plate under predetermined conditions for 10 minutes, and the abrasive obtained by a standard abrasive production process manufactured using ore as a raw material. It is a numerical value obtained by multiplying the ratio of the glass thickness by 100. Evaluation conditions were a pressure of 200 g / cm 2, a rotation speed of 120 rpm, a slurry supply rate of 2 l / min, and a slurry concentration of 100 g / l.
The resulting polishing force was 97. The polishing power was almost the same as that of a rare earth abrasive produced from ore, and the same quality was obtained.

[0031]

As described above, according to the present invention, it is possible to remove impurities from rare earth waste abrasives conventionally discarded as industrial waste and to reuse them as rare earth abrasive raw materials, Contribute to the stable securing of rare earth resources. In addition, it is possible to produce an abrasive raw material of the same quality as an abrasive raw material from a rare earth ore in an economical process using existing simple equipment. In addition, there is an effect that the amount of waste can be greatly reduced without causing pollution due to chemicals used.

Claims (3)

[Claims] 1. A dissolving step for dissolving and removing soluble impurities from used rare earth waste abrasive using hydrofluoric acid, and a solid-liquid separating step for performing solid-liquid separation after dissolving. , A method for producing rare earth-based abrasive raw materials from waste abrasives. 2. A process for producing a rare earth-based abrasive material according to claim 1, further comprising a component adjusting step of mixing a rare earth oxide or a rare earth carbonate with the solid content obtained in the solid-liquid separation step. Method. 3. The method according to claim 1, wherein the used rare earth waste abrasive contains at least 40% by weight of a rare earth oxide on a dry basis.