JP3134189B2 - How to collect abrasives - Google Patents

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 an abrasive from a used abrasive waste generated after precision polishing of an optical glass or a crystal oscillator with an abrasive.

[0002]

2. Description of the Related Art Currently used abrasives for precisely polishing optical glass and quartz oscillators in a finishing process are mainly cerium oxide, and rare earth elements containing lanthanum oxide, neodymium oxide, praseodymium oxide, etc. Elemental oxides are used. As a conventional method for producing an abrasive containing cerium oxide as a main component, after pulverizing and classifying a rare earth ore, a method of producing a cake obtained by chemical treatment by drying and firing, and further pulverizing and classifying, From a rare earth chloride aqueous solution obtained by chemically treating a pulverized rare earth ore, a cerium concentrate containing cerium hydroxide as a main component is manufactured, dried, calcined, and further pulverized and classified to produce. And so on.

In the case of finish polishing an optical glass or a quartz oscillator, precision polishing is performed by pressing against a rotating polishing cloth while spraying a slurry of an abrasive mainly composed of cerium oxide. The abrasive slurry is repeatedly used while being circulated, and when the polishing performance gradually decreases due to mixing of glass powder, fibers of the polishing cloth, dust and the like, the abrasive is replaced with a new abrasive. The slurry of the used abrasive is precipitated by adding a coagulant to the slurry and dehydrated to obtain cake-like polishing waste. As described above, rare earth oxides such as cerium oxide used as an abrasive used for precision polishing of finishes are relatively soft, and it is conventionally thought that the particle shape is destroyed by polishing and polishing performance is reduced. Because it was
The used polishing waste was directly landfilled as industrial waste.

[0004] However, rare earth elements, which are the main constituent elements of abrasives, are unevenly distributed in the world, and Japan is entirely dependent on imports. Used polishing waste is 70-85% in cake form
Since it contains a large amount of water, the disposal costs for landfills are as high as tens of thousands of yen per ton, and the number of landfill sites is small, so future measures are needed.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, the present invention has conducted various studies. As a result, the particles of the abrasive recovered from the used polishing waste did not collapse even after polishing. The present invention provides a method for recovering abrasives that aims to reduce the amount of polishing waste and reduce disposal costs while at the same time finding that it can be reused and efficiently recovering it to save resources of rare earth elements. .

[0006]

According to a first aspect of the present invention, there is provided a method for recovering an abrasive, wherein a used abrasive slurry containing cerium oxide as a main component is recovered as an abrasive, and a coagulant is added thereto. After adding and condensing the solid content, dehydration treatment is performed to produce a dewatered cake-like polishing waste. Using this polishing waste as a raw material, an alkali metal hydroxide having a concentration of 6 mol /
After dissolving the soluble impurities by mixing the polishing waste with an aqueous solution of 1 liter or less, the aqueous solution in which the impurities were dissolved and the solid content were separated, and then the separated solid content was sieved to obtain glass powder. It is characterized by separating contaminants such as fibers and dust of polishing cloth and dust, and collecting fine abrasives.

Further, the method for recovering an abrasive according to the second aspect of the present invention is characterized in that, as the alkali metal hydroxide, sodium hydroxide or sodium hydroxide having a weight of 5 times or more of the polishing waste on a dry matter basis.
It is characterized by using potassium hydroxide twice or more times.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below in detail. The used polishing waste contains rare earth oxides such as lanthanum oxide, neodymium oxide and praseodymium oxide in addition to cerium oxide which is a main component of the abrasive. In addition, the polishing waste also includes a silicon compound that is a polished glass component, an aluminum compound of an added flocculant,
Glass powder that has been broken down into fine pieces, fibers of polishing cloth, dust and the like are mixed. As the flocculant to be used, polyaluminum chloride, aluminum sulfate, and a polymer flocculant are generally used, and these are used alone or in combination.

[0009] Further, the composition ratio of the polishing waste is about 60% by weight of a rare earth oxide as an abrasive, about 12% by weight of a silicon compound, about 20% by weight of an aluminum compound added as a coagulant, on a dry matter basis. Other examples include glass powder, polishing cloth fibers, and garbage.

The method will be described below. A polishing slurry containing cerium oxide as a main component, whose polishing performance has been gradually reduced after repeated use while being circulated, is recovered, and a coagulant is added thereto to obtain a solid content. Is condensed and dewatered to produce a dewatered cake-like abrasive waste having a water content of about 70 to 85% by weight. Next, a predetermined amount or more of alkali metal hydroxide is converted into an aqueous solution having a concentration of 6 mol / liter or less, and the polishing waste is mixed to dissolve soluble impurities.

In this case, it is inexpensive and effective to use, for example, sodium hydroxide or potassium hydroxide as the alkali metal hydroxide to be used. The mixing amount of the alkali metal hydroxide is 5 times or more based on the dry matter of the polishing waste with sodium hydroxide, and 7 times or more with potassium hydroxide, so that the silicon compound mixed with the polishing waste can be obtained. In addition, soluble impurities such as an aluminum compound added as a coagulant can be dissolved.

In this case, if the mixing amount of the hydroxide of the alkali metal is less than the specified amount, the soluble impurities cannot be sufficiently removed. When the alkali metal hydroxide concentration exceeds 6 mol / liter, M-Si-Al composite oxides (M; Na, K) and composite hydroxides are formed, and impurities are not dissolved. Also, the resulting composite product particles have a higher hardness than the rare earth oxide, and when this is mixed into the abrasive,
Since there is a problem of scratching the surface of the optical glass or the crystal oscillator in the finishing precision polishing step, the range is limited to the above range.

As described above, the aqueous solution of the alkali metal hydroxide is mixed with the polishing waste and subjected to chemical treatment to dissolve soluble impurities. Then, the aqueous solution and the solid content are separated by a centrifugal separator. In the separated aqueous solution, a silicon component, which is a polished glass component, and an aluminum component, which is an added coagulant, are dissolved.

[0014] The separated solid content contains, in addition to the abrasive particles, undissolved glass powder, fibers of a polishing cloth, dust, and the like. This solid content is washed with water until the washing liquid becomes neutral, and then dried and then sieved to separate abrasive particles of several μm or less from glass powder or fibers of a polishing cloth larger than this, and dust and the like. ,Remove. In this case, since the flocculant has already been decomposed with the aqueous solution of the alkali metal hydroxide, the solid content is easily broken and the dispersion is good, so that the sieving operation can be easily performed.

In the fine particles separated and recovered in this way, silicon and aluminum remaining as impurities are about 2% by weight in terms of oxide. In addition, microscopic observation of the recovered rare earth oxide particles such as cerium oxide confirmed that the particle shape was not distorted and was the same as that of a new product, and that the polishing performance was almost the same as that of the new product.

[0016]

Embodiments of the present invention will be described below. After pulverizing and classifying the rare earth ore, the cake obtained by the chemical treatment is dried and calcined, and then pulverized and classified, and the cerium content is about 45% by weight and the lanthanum content is about 25% by weight in terms of oxide.
The optical glass was polished with a new abrasive made of a mixed component containing about 10% by weight of neodymium and about 3% by weight of praseodymium. When the polishing performance of the abrasive slurry was reduced while being used while being repeatedly circulated, it was collected. Next, a polyaluminum chloride as a flocculant and a polymer flocculant are added to the recovered abrasive slurry to coagulate the solids contained in the slurry, and then dewatered to form a dewatered cake having a water content of about 85%. Polishing waste was obtained.

Next, as shown in Samples No. 1 to No. 3 in Table 1, 5 to 10 times the weight of sodium hydroxide (NaOH) based on the dry matter of the polishing waste was dissolved in distilled water to obtain 2 to 6 mol / liter. Was prepared, and 50 g of a dewatered cake of polishing waste was mixed and chemically treated. After dissolving the soluble impurities, the aqueous solution in which the impurities were dissolved and the solid content were separated by a centrifugal separator. Next, the solid content is washed with water until the washing liquid becomes neutral, dried, and then sieved to separate abrasive particles of several μm or less from glass powder, polishing cloth fibers, dust, etc. which are larger than this. And removed.

When the composition of the fine particles collected by sieving in this manner was analyzed, the mixing ratio of the rare earth compound mainly composed of cerium oxide serving as the abrasive and the remaining impurities was determined by the sample number in Table 1. No. 1 to No. 3. Distilled water was added to the recovered reclaimed abrasive for 1 hour.
A polishing slurry of 0% by weight was prepared, and the polishing performance was measured. The results are shown in Table 2. For the sake of comparison, the same measurement was carried out for a sodium hydroxide / waste weight ratio smaller than the specified value (No. 4), a sodium hydroxide aqueous solution concentration higher than the specified value (No. 5), and a new abrasive. The results are shown in Table 2.

The polishing conditions were as follows. Polishing sample: S-BSL7 glass sample manufactured by Ohara Corporation,
16 mmφ x 6 Polishing machine: 200 mm Polishing machine rotation speed: Approx. 150 rpm Polishing pressure: Approx. 210 g / cm2 Polishing time: 30 minutes Evaluation method: Groove having a depth of several tens μm by hydrogen fluoride etching on the surface of a mirror-polished glass sample The surface roughness before and after polishing and the depth of the groove were measured by a surface roughness profile measuring apparatus, and the polishing rate was measured from the change. The results are shown in Table 2.

[0020]

[Table 1]

[0021]

[Table 2]

From the results shown in the above table, the abrasives recovered and reclaimed according to the present invention (No. 1 to No. 3) have a low residual amount of impurities, and the polishing rate is very slightly inferior to that of a new abrasive in a polishing test. Roughness was almost as good as new. In addition, the sample of No. 4 in which the weight ratio of sodium hydroxide / waste is smaller than the specified value does not dissolve impurities sufficiently, has poor surface roughness, and has a low polishing rate. Further, the sample of No. 5 in which the concentration of the aqueous sodium hydroxide solution was higher than the specified value was Na-Si
-Al composite oxide, composite hydroxide and the like were generated, and it was confirmed that the polishing rate was high but the surface roughness was poor.

When potassium hydroxide was used in place of sodium hydroxide as the alkali metal hydroxide for dissolving impurities, the treatment conditions (Nos.
o7), a slurry was prepared from the recovered abrasive, and its polishing performance was measured. The results are shown in Table 4.

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

As a result of the above table, according to the method for recovering abrasives according to the present invention, rare earth oxide particles can be efficiently recovered from used polishing waste by an extremely simple method. We found that the particles of the rare earth oxides were not broken down and could be reused as an abrasive, and conserved resources of rare rare earth elements. Reprocessing costs were less than half that of new ones, and at the same time the amount of polishing waste was reduced. And reduction of waste disposal costs.

Claims (1)

(57) [Claims] 1. A used abrasive slurry containing cerium oxide as a main component as an abrasive is collected, a coagulant is added thereto to condense a solid content, and then a dewatering treatment is performed to form a dewatered cake. A waste is produced, and the polishing waste is used as a raw material, and the alkali metal hydroxide is mixed with an aqueous solution having a concentration of 6 mol / L or less to dissolve the soluble impurities. Separating the solid solution from the aqueous solution in which the impurities are dissolved, and then sieving the separated solid to separate contaminants such as glass powder, fibers of a polishing cloth, and dust, and recover fine abrasives. A method for collecting an abrasive. 2. The polishing method according to claim 1, wherein the alkali metal hydroxide is sodium hydroxide or potassium hydroxide that is at least 5 times the weight of the polishing waste on a dry matter basis. Material collection method.