WO2013128536A1

WO2013128536A1 - Method for separating rare earth elements from optical glass waste

Info

Publication number: WO2013128536A1
Application number: PCT/JP2012/054708
Authority: WO
Inventors: 佐久間幸雄; 渡邉俊貴
Original assignee: 株式会社アサカ理研
Priority date: 2012-02-27
Filing date: 2012-02-27
Publication date: 2013-09-06
Also published as: JP5678231B2; JPWO2013128536A1

Abstract

The present invention addresses the problem of separating with good efficiency the rare earths of La and Gd from optical glass waste. Carbon is added to pulverized optical glass waste and the mixture is subjected to reduction roasting in a nonoxidizing atmosphere in order to reduce the zinc oxide to zinc, and the zinc is selectively evaporated and removed. After the rare earth elements remaining in the roasting residue are eluted with hydrochloric acid or nitric acid, the Gd is extracted into the organic phase under acidic conditions at a pH of 2 or less using the extractant PC-88A (Daihachi Chemical Industry Co., Ltd., brand name). The La remaining in the aqueous phase is extracted into the organic phase under acidic conditions at a pH of 3 to 4 using the extractant PC-88A (Daihachi Chemical Industry Co., Ltd., brand name).

Description

Method of separating rare earth elements from optical glass waste

The present invention relates to a rare earth element separation method for separating and recovering La (lanthanum) and Gd (gadolinium) from zinc oxide-containing optical glass waste.

Optical glass is manufactured using oxides of rare earth elements such as lanthanum, gadolinium and tantalum (Ta) unlike ordinary silicon glass. These rare earth elements are difficult to separate from each other because of their similar physical and chemical properties, and are expensive metals. In addition, since the production area is limited, it is greatly affected by price fluctuations. However, although optical glass raw materials contain the above-mentioned rare earth elements, most of them are discarded as waste materials in the manufacturing process in the melting process, pressing process, polishing process, etc. It is half or less. Therefore, there is a need for a technique for efficiently separating and recovering rare earth elements from optical glass waste produced in the lens manufacturing process.

For separation of these rare earth elements, ion exchange resin method (solid-liquid extraction method), solvent extraction method (liquid-liquid distribution method), etc. are known, but solvents which can be mass-processed by continuous processes Extraction methods are preferred. In the solvent extraction method, an aqueous phase comprising an aqueous solution containing a metal element to be separated is brought into contact with an extractant for extracting the metal element and an organic phase comprising the dilution solvent thereof to extract the metal element into the extractant and separated. How to

Phosphorus compounds are mainly used as the extractant in the past. For example, di-2-ethylhexyl phosphoric acid (abbreviated as D2EHPA) or the like is used as the phosphoric acid ester, and as the phosphonic acid compound, 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (2 -ethylhexyl-phosphoric acid-mono-2-ethylhexyl ester (PC-88A: trade name of Daihachi Chemical Industry Co., Ltd.) is used. In addition, diglycol amic acid is also used as an extracting agent (for example, JP 2007-327085, JP 2011-1584).

Among the commercially available and commercially available extractants, the above-mentioned PC-88A is widely used as one having a high separation factor for rare earth elements, but it can be applied for separating rare earth elements from optical glass waste. It was not. The optical glass waste contains a considerable amount of zinc oxide, and zinc (Zn) derived from zinc oxide and lanthanum can not be efficiently separated by the extractant PC-88A.

The present invention has been made in view of such circumstances, and provides a separation method of rare earth elements capable of efficiently separating rare earth elements such as lanthanum and gadolinium from residues after zinc is removed from optical glass waste material in advance. The purpose is to

An object of the present invention is a separation method of rare earth elements for separating La, Zn, Gd from optical glass waste material containing rare earth elements containing at least La, Gd and Zn, and characterized by comprising the following steps: It is achieved by the separation method.
(a) A roasting process in which carbon is added to a pulverized product of optical glass waste material and heated to a temperature above the boiling point of metallic zinc in a non-oxidative atmosphere to reduce zinc oxide to zinc and volatilize and remove zinc ;
(b) dissolving the roasting residue obtained in step (a) with hydrochloric acid or nitric acid while heating;
(c) Gd is extracted into the organic phase by contacting the acid solution obtained in step (b) with the organic phase containing PC-88A as an aqueous phase under an acidic condition of pH 1 to 2, Leaving the water phase.

According to the method for separating rare earth elements of the present invention, waste optical glass is previously heated in a nitrogen atmosphere to a temperature higher than the boiling point of metallic zinc and roasted, thereby reducing zinc oxide to zinc and selectively selecting zinc. Remove by volatilization. Therefore, gadolinium can be efficiently extracted from the rare earth element group remaining in the roasting residue using the extractant PC-88A. Lanthanum remaining in the water phase without being extracted can be extracted into the organic phase by changing the acidic conditions.

Outline of process of separation method of rare earth element from optical glass waste according to the present invention

The optical glass waste used in the present invention is a glass waste containing at least La, Gd and a rare earth element containing Zn and Zn, and other rare earth elements such as Ta (tantalum), Nb (niobium), Zr (zirconium) and the like. It may contain B (boron). Further, the optical glass waste includes not only the optical glass waste generated in the lens manufacturing process, but also the discarded optical lens itself.

It is preferable to grind | pulverize a glass waste material, to classify as needed, and to equalize a particle size. Carbon added in the roasting step (a) is an amount necessary to reduce zinc oxide contained in optical glass waste to zinc. The reduction reaction of zinc oxide is considered to proceed as follows.
2ZnO + C → 2Zn + CO ₂

Therefore, it is theoretically sufficient to add 1/2 molar amount of carbon of zinc oxide, but in order to make the reduction reaction of zinc oxide proceed more completely, carbon of equimolar amount or more of zinc oxide may be added. Is preferably added.

Further, in the roasting step, since it is necessary to promote the reduction of zinc oxide in the glass waste material, heating is performed in a non-oxidative atmosphere. For example, it can be performed in a nitrogen atmosphere. Any inert gas can be used as well. A gas such as a rare gas such as helium or a gas such as carbon dioxide which does not oxidize carbon which is a reducing agent during reduction roasting and does not change itself, or a gas atmosphere which itself is a reducing agent such as hydrogen or carbon monoxide Just do it.

In the roasting step (a), heating is performed to the boiling point (907 ° C.) or more of metallic zinc. It is desirable to heat at 1000 ° C. or higher in order to accelerate the evaporation of metallic zinc.

The roasting residue after the roasting step is dissolved with hydrochloric acid or nitric acid. Hydrochloric acid can be used either in concentrated hydrochloric acid or dilute hydrochloric acid, but the solubility is slightly better in dilute hydrochloric acid than in concentrated hydrochloric acid (12 N). However, dilute hydrochloric acid (about 1 N) having a large dilution degree is not preferable because the elution amount of Nb and Ta increases. Therefore, it is preferable to use 3 to 6 normal hydrochloric acid. When using nitric acid, it is preferable to use dilute nitric acid rather than concentrated nitric acid. When the roasting residue is dissolved with hydrochloric acid while heating, lanthanum (La), gadolinium (Gd), zirconium (Zr) and boron (B) dissolve. Niobium (Nb) and tantalum (Ta) do not dissolve in hydrochloric acid and can be separated as insolubles. Heating at the time of dissolution is preferably performed by heating under reflux, whereby the lanthanum is almost completely dissolved in hydrochloric acid. In addition, as described in Example 1 to be described later, in a simulated sample which is not an optical glass waste material but is merely mixed with lanthanum oxide, boron oxide, zinc oxide, etc. as an optical glass raw material, Although almost completely dissolved, the waste of optical glass produced by mixing and melting optical glass raw materials does not completely dissolve lanthanum in hydrochloric acid at about 40 ° C. heating. By heating and refluxing the reaction solution, the lanthanum can be dissolved almost completely in hydrochloric acid.

If the organic phase obtained in the solvent extraction step (c) is separated and brought into contact with the aqueous phase under highly acidic conditions, gadolinium in the organic phase can be efficiently backextracted into the aqueous phase.

Lanthanum remains in the extraction residue (aqueous phase) in the solvent extraction step (c), which can be extracted with an organic phase containing PC-88A under conditions of pH 3-4. If the organic phase obtained in this solvent extraction step (d) is separated and brought into contact with the aqueous phase under highly acidic conditions, the lanthanum in the organic phase can be efficiently extracted back to the aqueous phase . Boron (B) remains in the extraction residue (water phase) of the solvent extraction step (d). The outline of the separation method of the present invention is as shown in FIG.

A simulated sample was prepared based on the composition of the lanthanum-based optical glass "TaSF2" described in "Science of rare earth" (Adachi Takuya, 1st Edition, First Edition (1999), pp 737, Table 30.3). The composition described in the _{_{literature, B 2 O 3 22wt%,}} La 2 O 3 33wt%, Gd 2 O 5 14wt%, Ta 2 O 5 11wt%, Nb 2 O 5 3wt%, ZrO 2 5wt%, with ZnO 11 wt% However, here, a mock sample was prepared excluding ZrO ₂ . The amount and composition ratio of each oxide in the simulated sample are shown in Table 1. The value of B ₂ O _{3 in} the table is a value converted from the amount of boric acid (H ₃ BO ₃ ) collected.

As a carbon source, charcoal was ground in a mortar and classified to 150 μm or less by a standard sieve for test. Mix 0.2236 g of crushed carbon into a sample of 2.2294 g, place it on a 30 × 150 mm graphite boat, place it in a quartz tube (inner diameter 30 mm, length 1000 mm), and use an electric furnace under a stream of nitrogen to externally The temperature was heated to 1040 ° C. After reaching 1040 ° C., roasting was performed for 1 hour. The temperature was measured by bringing a thermocouple into contact with the outer surface of the quartz tube.

After completion of roasting, the deposit on the inner wall of the quartz tube was washed with about 100 mL of 6 N hydrochloric acid, and the amount of each element in the solution obtained was quantified by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometer). Meanwhile, the roasted residue was transferred to a 200 mL conical beaker, 50 mL of 6 N hydrochloric acid was added, and the mixture was dissolved by stirring at 40 ° C. for 3 hours. The amount of each element in the obtained roasting residue solution was quantified by ICP-AES. The residue which did not dissolve by treatment with 40 ° C. hydrochloric acid was separated by filtration, 50 mL of 6 N hydrochloric acid was further added, and the mixture was stirred at 100 ° C. for 2 hours to obtain a solution, and the amount of each element was quantified.

The recovered amount of the component volatilized by roasting, the component dissolved by treatment with 40 ° C. hydrochloric acid in the component remaining in the roasting residue, and the component dissolved by further treatment with hydrochloric acid at 100 ° C. was calculated. The results are shown in Table 2. The recovery amount is shown as a percentage of the amount of each element in the preparation amount.

As can be seen from this Table 2, zinc oxide was almost completely removed as volatile matter by reduction roasting, and about 90% of the lanthanum, which is the object of separation and recovery, was eluted by treatment with hydrochloric acid at 40 ° C. Also, about 60% of gadolinium was eluted in the hydrochloric acid solution. The elements eluted from the roasting residue into the hydrochloric acid solution were three, boron, lanthanum and gadolinium. Ta and Nb were in the roasting residue and insoluble in hydrochloric acid.

An aqueous solution consisting only of La and Gd was prepared, and separation of both was attempted by a solvent extraction method. In 400 mL of 0.1 N hydrochloric acid, 0.5376 g of LaCl ₃ · 7H ₂ O and 0.2071 g of GdCl ₃ · 6H ₂ O were dissolved to obtain an aqueous phase. The weight ratio of La to Gd was in agreement with the above-mentioned document in terms of oxide. As a result of preparation, the initial concentration in the aqueous phase was 502.7 ppm for La and 219.0 ppm for Gd.

As an organic phase, 6.14 g of PC-88A was diluted with 400 mL of n-decane to make a solution of 50.1 mmol / L (10 times the total molar concentration of La and Gd). In the extraction operation, the aqueous phase and the organic phase are placed in a 2 L beaker, the two phases are suspended by vigorously stirring with a magnetic stirrer, a pH meter is inserted into the solution, and an aqueous solution of NaOH and HCl is appropriately added to pH 1.5. The mixture was stirred for 20 minutes for extraction. The mixture was then allowed to stand and separated into an organic phase and an aqueous phase. The element (Gd) extracted into the organic phase was subjected to back extraction (100 mL × 3 times) using a 6N hydrochloric acid solution. The amount of each element in the aqueous solution and the back extracted hydrochloric acid solution was quantified by ICP-AES. The results are shown in Table 3.

From this result, the distribution coefficient of La, Log P _OW (Log P _OW = Log (C _O / C _W ), C _O , C _W is the concentration in the organic phase and the aqueous phase) is log P _La = -1.46, Gd The distribution coefficient of was obtained as log P _Gd = 1.84. When extraction simulation is performed using this distribution coefficient, as shown in Table 4, La becomes 99.99% in purity and 93.41% in yield at the second extraction, and La is completely separated and recovered in high yield. It turned out that it is possible.

A reduction roasting process was performed using optical glass waste. The waste material of the optical lens was roughly crushed with a hammer, then finely ground using a planetary ball mill, and classified to 45 μm or less with a standard sieve for test to obtain a glass waste material sample. As in the case of Example 1, carbon was obtained by grinding charcoal and classifying it into 150 μm or less.

Carbon of the amount shown in Table 5 is mixed with 2.0 g of a glass waste sample, put on a 30 × 150 mm graphite boat, put in a quartz tube (inner diameter 30 mm, length 1000 mm), and put in a nitrogen stream electric furnace to use quartz. The tube was heated to an external temperature of 1040 ° C. After reaching 1040 ° C., roasting was performed for 1 hour. The carbon content of 0.02 g in Example 3-3 shown in Table 5 is about 1/2 molar amount of zinc oxide contained in the lens waste material sample. 0.20 g of carbon in Examples 3-2 and 3-5 is about 5 times the molar amount of zinc oxide contained in the lens waste material sample, and similarly, 2.00 g of carbon in Example 3-1 is in the samples. It is about 50 times the molar amount of zinc oxide.

After completion of roasting, the deposit on the inner wall of the quartz tube was washed with about 100 mL of 6 N hydrochloric acid, and the amount of each element in the solution obtained was quantified by ICP-AES. As shown in Table 6, in Examples 3-1 and 3-2 in which the carbon content was 0.2 g or more and the roasting temperature was 1040 ° C., zinc could be almost completely removed by evaporation. Even in Example 3-5, although the heating temperature was higher than the boiling point (907 ° C.) of metallic zinc, since the measurement temperature is the temperature of the outer wall of the quartz tube, the actual roasting temperature did not reach the boiling point (907 ° C.) or more It can be guessed. Alternatively, it is considered that the temperature needs to be higher than the boiling point of zinc because activation energy is required for the cleavage and reduction reaction of the bond with the matrix. In addition, the amount of carbon to be added was not sufficient in the case of 1/2 molar amount (the example 3-3) of the theoretical amount (Example 3-3), and only about half the amount of zinc oxide could be reduced and removed by evaporation Therefore, at least equimolar amount or more seems to be necessary to completely reduce zinc oxide to metallic zinc.

Subsequently, each roasted residue was transferred to a 200 mL conical beaker, 50 mL of 6 N hydrochloric acid was added and dissolved by stirring overnight at 40 ° C. The amount of each element in the obtained solution was quantified by ICP-AES. As shown in Table 7, the recovery rates of La and Gd as main recovery target products were less than half.

Since La and Gd are not volatilized by roasting as shown in Table 5, it is apparent that they are present in the roasting residue. However, since it did not dissolve in hydrochloric acid treatment at 40 ° C., the temperature was raised further, and it was attempted to heat and dissolve 6 N hydrochloric acid until refluxing. That is, the insoluble matter after the 40 ° C. hydrochloric acid treatment in Example 3-2 in Table 6 was collected by filtration, 6 N hydrochloric acid was again added to this, and the mixture was heated under reflux for 2 hours. After heating and dissolving treatment with hydrochloric acid, the amount of elements in the solution was quantified. The results are shown in Table 8.

The solution of La dissolved only 44% when dissolved in 40 ° C. hydrochloric acid was further dissolved by about 44% by the solution treatment of hydrochloric acid at 100 ° C., and the total recovery of La was about 88%. In this point, in the simulated sample of Example 1, about 90% of La from the roasting residue was able to be dissolved in hydrochloric acid by the treatment with hydrochloric acid at 40 ° C. Although the cause of this difference is unknown, it can be considered as follows. The simulated sample is a mixture of zinc, boron and oxides of rare earth elements, and each oxide is fine although it is a particle and forms agglomerates. On the other hand, the optical glass which is the source of the lens waste material of Example 3 (3-1 to 3-5) is only the mixture of the oxides of zinc, boron and rare earth elements which are the raw materials of the simulated sample of Example 1. Instead, they are melted at high temperature to form a glass. It has a uniform structure and no agglomerated structure. For this reason, even if it becomes a waste glass material, each element oxide is a homogeneous mixture, and it is presumed that the interatomic bond is strong. For this reason, it is considered that each element is firmly bonded even after reduction roasting at 1000 ° C., and the treatment with 40 ° C. hydrochloric acid is insufficient for elution.

The optical glass waste was subjected to reduction roasting in substantially the same manner as in Example 3-2, and La and Gd were separated from the roasting residue by solvent extraction.

0.2 g of carbon is mixed with 2.0 g of crushed optical glass waste material (classification size, 45 μm or less) prepared by the same method as in Example 3 and placed on a 30 × 150 mm graphite boat, and a quartz tube (inner diameter 30 mm) The sample was put in a length of 1000 mm), and was heated in an electric furnace under nitrogen stream so that the outside temperature of the quartz tube became 1040 ° C., and roasted for 1 hour. After completion of roasting, the roasted residue was transferred to a 200 mL conical beaker, 50 mL of 6 N hydrochloric acid was added, and the mixture was heated under reflux to elute the contents.

Using this hydrochloric acid eluate, separation of La and Gd was performed by solvent extraction. The aqueous phase was diluted with water to 400 mL and used as the aqueous phase. The concentration of each element in the aqueous phase was La: 526.0 ppm, Gd: 197.5 ppm, B: 91.8 ppm. As the organic phase, one prepared by dissolving 6.6 g of PC-88A in 400 mL of n-decane was used. In the extraction operation, the aqueous phase and the organic phase are placed in a 2 L beaker, the two phases are suspended by vigorously stirring with a magnetic stirrer, a pH meter is inserted into the solution, and the desired pH is adjusted using NaOH and HCl aqueous solution as appropriate. The mixture was then stirred for 20 minutes and then allowed to stand to separate into an organic phase and an aqueous phase.

The first extraction operation was performed under the condition of pH 1.5. After the organic phase was separated, 400 mL of a fresh organic phase was mixed with the remaining aqueous phase and stirred at pH 3.0 for 20 minutes to carry out a second extraction. After separating the organic phase of the second extraction, the remaining aqueous phase was further mixed with 400 mL of fresh organic phase, and the third extraction was performed at pH 4.0. The organic phase obtained by each extraction operation was subjected to back extraction (100 mL × 3 times) using a 6 N aqueous hydrochloric acid solution, and the amount of each element in the back extracted hydrochloric acid solution was quantified by ICP-AES. The amount of each element was also quantified by ICP-AES for the aqueous phase (extraction residue) after the third extraction operation. The results are shown in Table 9.

From this result, distribution coefficients Log P _OW at each pH were as shown in Table 10.

An extraction simulation at pH 1.5 is shown in Table 11 using this distribution coefficient. From this, it was found that La can be recovered in the aqueous phase (extraction residue) with a purity of 99.99% and a yield of 98.28% at the second extraction. Specifically, it was shown that La and Gd can be completely separated and recovered in high yield by using a two-stage mixer / settler.

In addition, B (boron) in optical glass waste will remain in the aqueous phase (extraction residue) together with La, but if solvent extraction using PC-88A under pH 4.0 conditions, only La is extracted As a result, boron and La can be almost completely separated in one extraction operation (see Table 9). Under pH 3.0 conditions, as can be understood from Table 9, boron and La can not be almost completely separated by one extraction operation, but if several extraction operations are repeated, for example, a multistage mixer It is completely separable by using Setra. The organic phase (containing La) separated from the boric acid solution is subjected to back extraction using a hydrochloric acid solution, and if carbonate or oxalate is added to the obtained aqueous phase (back extracted phase), lanthanum carbonate or oxalic acid is obtained. By filtering out as a precipitate of lanthanum, a highly pure La compound can be obtained.

Claims

A method for separating La, Zn, Gd from an optical glass waste material containing at least La, Gd, and a rare earth element containing Zn, the separation method comprising the following steps:
(a) A roasting process in which carbon is added to a pulverized product of optical glass waste material and heated to a temperature above the boiling point of metallic zinc in a non-oxidative atmosphere to reduce zinc oxide to zinc and volatilize and remove zinc ;
(b) dissolving the roasting residue obtained in step (a) with hydrochloric acid or nitric acid while heating;
(c) Gd is extracted to the organic phase by contacting the acid solution obtained in step (b) with the organic phase containing PC-88A under the acidic condition of pH 2 or less, using La as the aqueous phase Process to leave in water phase.
The method for separating rare earth elements according to claim 1, further comprising the following steps:
(d) A step of extracting La remaining in the aqueous phase into the organic phase by bringing the aqueous phase after step (c) into contact with the organic phase containing PC-88A under acidic conditions of pH 3 to 4. .
The method for separating a rare earth element according to claim 1, wherein the heating temperature in the step (a) is 1000 ° C. or higher.
The method for separating rare earth elements according to claim 1, wherein the non-oxidizing atmosphere in the step (a) is a nitrogen atmosphere.
The carbon added at the said process (a) is the separation | isolation method of the rare earth elements which are more than equimolar quantity of the zinc contained in optical glass waste material.
The method for separating rare earth elements according to claim 1, wherein the heating in the step (b) is carried out by heating and refluxing the reaction liquid.
The said optical glass waste material contains B, Ta, Nb further, The isolation | separation method of the rare earth elements of Claim 1 characterized by the above-mentioned.