Method for recovering rare metal from waste optical glass

Abstract

To provide a method for recovering Ta, Nb, La, or Gd from waste optical glass by a relatively simple process and in an economical manner.SOLUTION: A method of the present invention comprises the steps of: (a) dissolving waste optical glass using nitric acid to provide a first solution; (b) filtering the first solution to provide a first precipitate and a second solution; (c) dissolving the first precipitate using sodium hydroxide and hydrogen peroxide to provide a third solution; (d) filtering the third solution to provide an insoluble residue and a fourth solution; and (e) crystallizing the fourth solution to provide a crystalline product containing Ta and Nb.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for recovering rare metals from waste optical glass, and more particularly to a method for recovering Ta, Nb, La, or Gd from waste optical glass. [Background technology]

[0002] Rare metal elements such as Ta, Nb, La, Gd, etc. (hereinafter referred to as "rare metals" in this specification) are almost entirely consumed through imports from overseas. This makes it difficult to ensure a stable supply, and they are also greatly affected by price fluctuations. Meanwhile, rare metals are currently being discarded after being used for various purposes. For example, although optical glass contains many types of rare metals, including the rare metals mentioned above, most of them are discarded during the manufacturing process, and less than half of the raw materials are used to make products. Given this current situation, there is a need for technology to efficiently and economically separate and recover rare metals from waste materials that contain rare metals.

[0003] As a technique for recovering rare metals, Patent Document 1 discloses a method for separating and recovering rare metals from waste optical glass by a chlorination volatilization method, while Patent Document 2 discloses a method for recovering rare metal components from optical glass sludge generated in an optical glass polishing and cleaning process and an associated wastewater treatment device by using sulfuric acid treatment or the like.

[0004] However, the method described in Patent Document 1 requires complicated control of chlorine supply and heating temperature, and the method described in Patent Document 2 uses optical glass sludge as the raw material. Neither method discloses a method for recovering Ta, Nb, La, or Gd from optical glass waste efficiently and economically, in other words, with a high recovery rate by a relatively simple method. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5504531 [Patent Document 2] Japanese Patent Application Publication No. 11-50168 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention aims to provide a method for recovering Ta, Nb, La, or Gd from waste optical glass in a relatively simple and inexpensive (economical) manner. [Means for solving the problem]

[0007] The present invention provides a method for recovering rare metals from waste optical glass, comprising the steps of (a) dissolving the waste optical glass with nitric acid to obtain a first solution, (b) filtering the first solution to obtain a first precipitate and a second solution, (c) dissolving the first precipitate with sodium hydroxide and hydrogen peroxide to obtain a third solution, (d) filtering the third solution to obtain an insoluble residue and a fourth solution, and (e) crystallizing the fourth solution to obtain a crystallized material containing Ta and Nb.

[0008] According to the present invention, Ta and Nb can be recovered as crystallized products containing them at a high recovery rate by a relatively simple chemical treatment using an acid and an alkali.

[0009] In one aspect of the present invention, the step (a) of obtaining the first dissolving solution includes the steps of (a1) dissolving the optical glass waste material using high-concentration nitric acid, and (a2) dissolving the dissolving solution using high-concentration nitric acid with nitric acid of a lower concentration than the high-concentration nitric acid. In this case, for example, the high-concentration nitric acid can have a concentration (M) approximately twice that of the low-concentration nitric acid.

[0010] According to one aspect of the present invention, the dissolution of the waste optical glass is carried out in two stages using high-concentration and low-concentration nitric acid, thereby making it possible to improve the solubility of the waste optical glass.

[0011] In one embodiment of the invention, the sodium hydroxide can be at a concentration of about 1 M and the hydrogen peroxide can be at a concentration of about 5-7% by weight.

[0012] According to one embodiment of the present invention, the recovery rates of Ta and Nb in the third solution can be approximately 95% or more and approximately 40% or more, respectively.

[0013] In one aspect of the present invention, the step of crystallizing the second solution includes the step of holding the fourth solution at a temperature in the range from room temperature to approximately 80 degrees.

[0014] According to one embodiment of the present invention, a crystallized material containing Ta and Nb can be obtained by a relatively simple process, such as leaving the fourth solution at room temperature or heating it according to a heating temperature and then cooling it.

[0015] In one embodiment of the present invention, the method further includes the steps of adjusting the pH of the second solution to a predetermined value using ammonia water, sodium hydroxide, or the like, filtering the second solution after the pH adjustment to obtain a fifth solution, and adding sodium sulfate to the fifth solution to obtain a sulfate salt containing La and Ga. In this case, the pH can be set to, for example, 3.

[0016] According to one embodiment of the present invention, in addition to Ta and Nb, La and Gd can be recovered as sulfates containing these metals by a relatively simple chemical treatment using acid and alkali.

[0017] In one embodiment of the invention, the ammonia water may have a concentration of approximately 20% by weight and the sodium sulfate may have a concentration of approximately 30% by weight.

[0018] According to one embodiment of the present invention, the recovery rates of La and Gd in the sulfate can be, for example, approximately 85% or more and approximately 79% or more, respectively. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 illustrates the overall steps of a method according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a part of the process (Ta and Nb recovery process) of the method of one embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing a part of a process (a process for recovering La and Gd) of a method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] An embodiment of the present invention will be described with reference to the drawings. Figs. 1 to 3 are diagrams showing steps of a method according to one embodiment of the present invention. Fig. 1 shows an overview of the steps of a method according to one embodiment of the present invention. Fig. 2 corresponds to the content of step S4 in Fig. 1 and shows a series of steps for recovering Ta and Nb in a method according to one embodiment of the present invention. Fig. 3 corresponds to the content of step S5 in Fig. 1 and shows a series of steps for recovering La and Gd in a method according to one embodiment of the present invention. The steps in Figs. 2 and 3 can be carried out separately or in parallel, and can be carried out continuously or discontinuously (at a time interval).

[0021] In step S1 of FIG. 1, waste optical glass is prepared. The waste optical glass is glass waste that comes out of the manufacturing process of optical glass and contains rare elements including rare metals. In one embodiment of the present invention, waste optical glass is prepared that contains, for example, four elements Zn, Zr, B, and Si in addition to Ta, Nb, La, and Gd that are the subject of recovery. Note that the elements contained in addition to Ta, Nb, La, and Gd are not limited to these four elements, and the method of the present invention is applicable even when some of these elements or other elements are contained depending on the type of optical glass.

[0022] In step S2, the prepared optical glass waste is dissolved in nitric acid (HNO 3 ) to obtain the first solution. In this case, the dissolution can be performed in two steps. That is, the step S2 for obtaining the first solution can be divided into a step of dissolving the optical glass waste material using high-concentration nitric acid and a step of dissolving the solution obtained by dissolving the high-concentration nitric acid using nitric acid of a lower concentration than the high-concentration nitric acid.

[0023] The process of dissolving using low-concentration nitric acid can be carried out by adding water to a dissolving solution of high-concentration nitric acid to reduce the concentration of nitric acid to a low concentration, or by adding a low-concentration nitric acid solution to a dissolving solution of high-concentration nitric acid. In this case, for example, the high-concentration nitric acid can have a concentration (M) that is approximately twice that of the low-concentration nitric acid. When this two-stage dissolving process is adopted, the solubility of the optical glass waste can be further improved.

[0024] In step S3, the first solution is filtered to recover a first precipitate (step S4), and a second solution corresponding to the filtrate is obtained. The first precipitate is treated in the next step S4 to recover Ta and Nb. The second solution is treated in the next step S5 to recover La and Gd.

[0025] Steps S41 to S43 in FIG. 2 show the details of step S4 for recovering Ta and Nb in FIG. 1. In step S41, the first precipitate is treated with sodium hydroxide (NaOH) and hydrogen peroxide (H 2 O 2 ) to obtain a third solution. At this time, for example, the sodium hydroxide can be adjusted to a concentration of about 1 M, and the hydrogen peroxide can be adjusted to a concentration of about 5-7 wt %. In step S42, the third solution is filtered to remove insoluble residue, and a fourth solution is obtained.

[0026] In step S43, the obtained fourth solution is crystallized (recrystallized). The crystallization can be performed, for example, by leaving the fourth solution at room temperature, or by heating it at a predetermined heating temperature and then cooling it. The heating temperature is in the range of room temperature to about 80 degrees. In other words, the water (liquid) in the fourth solution is gradually evaporated at a temperature that does not boil. A crystallized material containing Ta and Nb can be obtained by the above-mentioned relatively simple chemical treatment using acid and alkali.

[0027] S51 to S54 in FIG. 3 show details of step S5 of recovering La and Gd in FIG. 1. In step S51, the pH of the second dissolution solution is adjusted by adding ammonia (NH 4The pH of the second solution is adjusted to a predetermined value using sodium hydroxide (OH) water. The predetermined value is, for example, pH=3. In step S52, the second solution after the pH adjustment is filtered to remove insoluble residues to obtain a fifth solution. In step S53, sodium sulfate (Na 2 SO 4 ) is added to obtain a sulfate containing La and Ga. In step S54, the sulfate containing La and Ga is fired to obtain an oxide containing La and Ga. By the above-mentioned relatively simple chemical treatment using an acid and an alkali, a sulfate / oxide containing La and Ga can be obtained.

[0028] The results of actually producing (recovering) a crystallized material containing Ta and Nb and a sulfate containing La and Ga using the method (steps) of one embodiment of the present invention shown in Figs. 1 to 3 are shown below as examples. EXAMPLES

[0029] We prepared 1000 kg of waste optical glass containing four elements, Zn, Zr, B, and Si, in addition to Ta, Nb, La, and Gd. The content (kg) and percentage (%) of each element in the 1000 kg of waste optical glass are shown in Table 1 below. [Table 1]

[0030] 1000 kg of optical glass waste having the composition shown in Table 1 was dissolved in nitric acid (HNO 3 ) to obtain the first dissolution solution. 3 and 3M (mol / L) HNO 3 The elements were dissolved in two steps using a 2000 sieve. The dissolution temperature was 70°C. The obtained first solution was filtered to obtain a first precipitate (insoluble residue) and a second solution corresponding to the filtrate. The contents (kg) of elements in the first precipitate and their recovery rates (%) are shown in Table 2 below. The recovery rate (%) means the remaining rate relative to the content (kg) of each element in Table 1. It can be seen from Table 2 that Ta and Nb did not dissolve and were present 100% in the first precipitate. [Table 2]

[0031] The contents (kg) of elements in the second solution and their recovery rates (%) are shown in Table 3 below. The recovery rate (%) means the remaining rate relative to the content (kg) of each element in Table 1. It can be seen from Table 3 that La and Gd were dissolved in the second solution at a ratio of 100% and 85.5%, respectively. [Table 3]

[0032] The first precipitate of the composition in Table 2 is made of sodium hydroxide (NaOH) and hydrogen peroxide (H 2 O 2 ) to obtain a third solution. At that time, the sodium hydroxide was adjusted to a concentration of 1M, and the hydrogen peroxide was adjusted to a concentration of 6 wt%. The third solution was filtered to remove the insoluble residue, to obtain a fourth solution (filtrate). The contents (kg) of elements in the fourth solution and their recovery rates (%) are shown in Table 4 below. The recovery rate (%) means the remaining rate relative to the content (kg) of each element in the first precipitate in Table 2. It can be seen from Table 4 that Ta and Nb are dissolved in the second solution at a ratio of 96.4% and 40.7%, respectively. [Table 4]

[0033] The pH of the second solution having the composition in Table 3 was adjusted by adding ammonia (NH 4 The pH of the second solution was adjusted to 3 using (OH) water. After adjusting the pH of the second solution, it was filtered to remove insoluble residues to obtain a fifth solution (filtrate). The contents (kg) of elements in the fifth solution and their recovery rates (%) are shown in Table 5 below. The recovery rates (%) in Table 6 refer to the remaining rates relative to the contents (kg) of each element in the second solution in Table 3. It can be seen from Table 5 that La and Gd remained at rates of 88.2% and 81.8%, respectively. [Table 5]

[0034] The fifth solution in Table 5 was diluted with sodium sulfate (Na 2 SO 4 ) was added to obtain sulfates containing La and Ga. The contents (kg) of elements in the obtained sulfates and their recovery rates (%) are shown in Table 6 below. Recovery rate 1 (%) in Table 6 means the remaining rate relative to the content (kg) of each element in the fifth dissolving solution in Table 5. It can be seen that La and Gd were recovered from the fifth dissolving solution in Table 5 at 97.1% and 77.4%, respectively. Recovery rate 2 (%) means the remaining rate relative to the content (kg) of each element in the second dissolving solution in Table 3. It can be seen that La and Gd were recovered from the fifth dissolving solution in Table 5 at 85.6% and 79.6%, respectively. Recovery rate 3 (%) means the remaining rate relative to the content (kg) of each element in the optical glass waste in Table 1. It can be seen from recovery rate 3 (%) that La and Gd were recovered from the optical glass waste in Table 1 at a rate of 85.6% and 68.1%, respectively. [Table 6]

[0035] The embodiments of the present invention have been described with reference to the drawings. However, the present invention is not limited to these embodiments. The present invention can be implemented in various forms with improvements, modifications, and variations based on the knowledge of those skilled in the art without departing from the spirit of the present invention.

Claims

1. A method for recovering rare metals from waste optical glass, comprising the steps of: Dissolving the optical glass waste material using nitric acid to obtain a first solution; filtering the first solution to obtain a first precipitate and a second solution; dissolving the first precipitate using sodium hydroxide and hydrogen peroxide to obtain a third dissolved solution; filtering the third solution to obtain an insoluble residue and a fourth solution; and crystallizing the fourth solution to obtain a crystallized material containing Ta and Nb.

2. The step of obtaining the first solution includes: dissolving the optical glass waste using concentrated nitric acid; The method according to claim 1 , further comprising the step of dissolving the solution dissolved by the high concentration nitric acid using nitric acid having a lower concentration than the high concentration nitric acid.

3. 3. The method of claim 2, wherein the high concentration nitric acid has approximately twice the concentration of the low concentration nitric acid.

4. 2. The method of claim 1, wherein the sodium hydroxide is at a concentration of about 1 M and the hydrogen peroxide is at a concentration of about 5-7% by weight.

5. The method of claim 1 , wherein the step of crystallizing the fourth solution includes the step of maintaining the fourth solution at a temperature in a range from room temperature to approximately 80 degrees. The method of claim 1.

6. adjusting the pH of the second solution to a predetermined value using aqueous ammonia; filtering the second solution after the pH adjustment to obtain a fifth solution; The method of claim 1 , further comprising the step of adding sodium sulfate to the fifth solution to obtain sulfates containing La and Ga.

7. The method of claim 6 , wherein the predetermined value of pH is approximately 3.

8. 7. The method of claim 6, wherein the aqueous ammonia has a concentration of approximately 20% by weight.

9. 7. The method of claim 6, wherein the sodium sulfate has a concentration of approximately 30% by weight.

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