JP3560121B2 - Method for producing rare earth-based abrasive raw materials from waste abrasive - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a rare-earth-based abrasive raw material for removing a rare-earth-based solid content after removing impurities from a rare-earth-based waste abrasive used for polishing a glass surface or the like.
[0002]
[Prior art]
Currently, 4000 tons of rare earth-based abrasives are used annually for polishing glass substrates and optical lenses. 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, for example, after removing foreign minerals from the ore of rare earth minerals such as bastnaesite produced in the United States in a beneficiation process, using the obtained bastnaesite concentrate as a raw material, pulverization, chemical treatment, filtration, It is manufactured through the steps of drying, roasting, crushing, classification, and mixing of additives (the latest applied technology of rare earth published by CMC, 1985).
[0004]
The rare earth-based abrasives manufactured in this manner are used for their excellent polishing properties and for increasing 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]
[Problems to be solved by the invention]
However, at present, almost all of these rare earth-based abrasives are discarded as industrial waste after use. Under the situation where increasing industrial wastes are becoming a serious social problem, there is an increasing demand for recycling of used rare earth-based 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 ensure the stability of rare earth resources that depend on imports. From the viewpoint of this, it is necessary to recover the raw materials of rare earth waste abrasives.
[0006]
Japanese Patent No. 2606156 discloses that a used abrasive is finely filtered to concentrate and remove coarse impurities to a concentrate side, and the permeate is concentrated by ultrafiltration to recover the concentrate. There has been proposed a method for collecting abrasive particles characterized by the following. However, the abrasive used in the above method has a fine particle size of several tens to 500 nm, and the rare earth-based abrasive targeted in the present invention has a particle size of 0.4 to 3.0 μm. Cannot be applied.
[0007]
Japanese Patent Application Laid-Open No. 8-3543 discloses a chemical treatment step of removing a soluble impurity from a polishing waste by using a polishing waste in which a used abrasive and an impurity generated by polishing are mixed as a raw material; There has been proposed a method for producing an abrasive, which comprises a physical treatment step of pulverizing an object to remove at least fine particles outside a specified value. However, the above method is inappropriate because the particle size of the abrasive targeted by the above method is 5 to 20 μm, and the particle size of the rare earth-based abrasive targeted by the present invention is 0.4 to 3.0 μm. .
[0008]
The present invention has been made in view of the above, and produces a rare earth abrasive material of the same quality as a raw material of an abrasive material from a rare earth ore from a used rare earth abrasive material by an economical process using simple equipment. It is intended to provide a method for doing so.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a dissolving step of dissolving and removing soluble impurities from used rare earth waste abrasive using hydrofluoric acid, and a solid-liquid separation step of performing solid-liquid separation after dissolution. The present invention provides a method for producing a rare earth-based abrasive raw material from waste abrasive, characterized by comprising:
[0010]
Further, in the method for producing a rare earth-based abrasive raw 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.
[0011]
Further, it is desirable that the used rare earth waste abrasive contains 40% by weight or more of a rare earth oxide on a dry basis. If the amount is lower than 40% by weight, economical profitability is poor.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, the "used rare earth waste abrasive" to be treated is a rare earth abrasive mainly composed of a rare earth oxide, particularly cerium oxide, used for polishing a glass substrate surface or the like. Currently used rare earth-based abrasives for glass polishing contain 80 to 98% by weight of rare earth oxides, of which cerium oxide accounts for 40 to 90% by weight of the rare earth oxides. 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 preferably 0.4 to 3.0 μm.
[0013]
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). I have.
[0014]
Drying of rare earth waste abrasive slurry, or solid content (cake) after solidifying the rare earth waste abrasive slurry with an organic or inorganic coagulant and solid-liquid separation with a dehydration filter such as a filter press Examining the composition of the polished material shows a difference depending on the object to be polished and the polishing method, but the glass component, particularly silica (SiO2), is contained in an amount of 2 to 20% by weight. The silica in the abrasive before use is significantly increased since it is less than 2% by weight.
[0015]
In addition, when polyaluminum chloride (PAC) is used for coagulating the waste abrasive slurry, alumina (Al2O3) is also contained in an amount of 3 to 20% by weight.
[0016]
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 the mixture is kept at room temperature for 0.5 to 8 hours. And stir. The amount of hydrofluoric acid is determined so 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 be 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.
[0017]
The slurry concentration of the rare earth waste abrasive is desirably 100 to 300 g / l. When the slurry concentration is 300 g / l or more, the viscosity increases and the workability decreases. When the slurry concentration is 100 g / l or less, the processing capacity is reduced.
[0018]
After the dissolution step, the suspension in the reaction tank is subjected to solid-liquid separation by a dehydration filtration device 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 insufficient, and when the ratio is smaller than 1/8, fluorine in the cake after solid-liquid separation becomes excessive, which is not preferable. . When the rare earth waste abrasive contains 3 to 20% by weight of the alumina component on a dry basis, the alumina component is reduced to 2% by weight or less by the above process.
[0019]
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, but when these are used, the regulation of nitrogen components in factory wastewater is strengthened. Therefore, it is necessary to remove nitrogen components from wastewater. This requires expensive equipment and is not economical. Therefore, the present invention uses an aqueous solution of hydrofluoric acid that can easily treat wastewater.
[0020]
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. All are commercially available.
[0021]
After the used rare-earth waste abrasive is subjected to an impurity dissolving treatment with hydrofluoric acid, the composition of the rare-earth-based abrasive raw material recovered by solid-liquid separation (the content of rare earth oxides and fluorine) is within the above specified range. If it is contained in the material, it is put into an abrasive production process using ore as a raw material without going through the above-mentioned 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 to adjust the components. 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 and specifications of the product, and the like.
[0022]
When the rare earth waste abrasive does not contain coarse particles having a particle size of 3 μm or more, the component adjustment step is performed after the pulverization step, which is the first step of the abrasive material production step using ore as a raw material.
[0023]
When the rare earth waste abrasive contains coarse particles having a particle diameter of 3 μm or more, the abrasive is subjected to pulverization or sieving before the hydrofluoric acid treatment, or to an abrasive production process using ore as a raw material. It may be inserted before the pulverizing step which is the first step, and may pass through the pulverizing step.
[0024]
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.
[0025]
In addition, it is preferable from the viewpoint of profitability that the waste abrasive used in the above treatment contains rare earth oxides in an amount of 40% by weight or more on a dry basis.
[0026]
【Example】
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. 0.8 t of the waste abrasive was put into a reaction tank containing 136 kg of 80% 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 with a stirrer for 1 hour, 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 analyzed for 0.79 t, 79.0% by weight of rare earth oxide, 1.4% by weight of silica, and 11.5% of fluorine were determined on a dry basis. % By weight. Cerium oxide was 50.3% by weight of the rare earth oxide.
[0027]
The analysis method is as follows. The analysis of rare earth oxides (TREO, TotalRare EarthOxides) 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.
[0028]
After the solid-liquid separation step, the obtained rare earth-based abrasive raw material was mixed with a rare earth oxide in a ratio of 7: 3, and the components were adjusted. That is, in each of the steps of pulverization, chemical treatment, filtration, drying, roasting, pulverization, classification, and mixing of additives, the product was processed by a standard method, and the product was analyzed by the above 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.
[0029]
The particle size of the rare earth-based recovered abrasive obtained by the above-mentioned 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.
[0030]
The "abrasive power" of the rare earth-based recovered abrasive obtained by the above-described production method was evaluated using an Oscar type sander 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 times. Evaluation conditions were a pressure of 200 g / cm 2, a rotation speed of 120 rpm, a slurry supply amount 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]
[Effects of the present invention]
As described above, according to the present invention, it is possible to remove impurities from a rare earth waste abrasive which has been conventionally discarded as industrial waste, and to repeatedly use the rare earth abrasive as a raw material, thereby stably securing rare earth resources. To contribute. 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 significantly reduced without causing pollution due to chemicals used.

Claims (3)

The waste abrasive is characterized by comprising a dissolving step of dissolving and removing soluble impurities from used rare earth waste abrasive using hydrofluoric acid, and a solid-liquid separation step of performing solid-liquid separation after dissolution. For producing rare earth-based abrasive raw materials. 2. The method for producing a rare earth-based abrasive raw material according to claim 1, wherein 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. The method for producing a rare earth-based abrasive raw material according to claim 1, wherein the spent rare-earth-based waste abrasive contains at least 40% by weight of a rare-earth oxide on a dry basis.