JP7337609B2 - Metal recovery method from ceramics - Google Patents

Description

Embodiments relate to methods of recovering metals from ceramics.

Ceramics are used for various structural materials, electronic materials, etc., taking advantage of their excellent properties. However, there are very limited methods of collecting used ceramic products like metal products and plastic products and recycling them as new products.

Japanese Patent Application Laid-Open No. 2001-19534 (Patent Document 1) discloses a method of pulverizing ceramic waste, using an appropriate amount of clay as a binder, and reusing the ceramic waste as a raw material.
However, although these methods can use finished ceramics as products as members of new products, they have not reached the point of reusing the raw materials contained in the ceramics. Among ceramics, fine ceramics used for industrial purposes require high performance, so carefully selected raw materials and auxiliaries are used. Many rare earths are used for these raw materials and auxiliary raw materials, and they are not reused as new raw materials.

Japanese Unexamined Patent Application Publication No. 2001-19534

Since ceramics generally have high covalent and ionic bonding properties, they have high hardness and toughness, and are difficult to pulverize during waste treatment. In addition, ceramics often contain rare earths, and it is necessary to establish technology to separate and recover them as necessary.
For example, gadolinium oxysulfide (GOS: Gd2O2S) is used as a scintillator for X-ray CT devices, baggage inspection devices, and food inspection devices due to its characteristics such as high sensitivity, short afterglow, small temperature characteristics of sensitivity, and high X-ray stopping power. It is used for non-destructive inspection equipment using radiation, analysis equipment, etc. However, gadolinium (Gd), which is the main component, could not be recovered from the waste of gadolinium oxysulfide, although it is a valuable rare earth.

In addition, silicon nitride (Si3N4) has high strength, high rigidity, high heat resistance, light weight compared to metal, and does not cause electrolytic corrosion, corrosion, or rust. is used as In order to bring out the characteristics of these products, highly purified silicon nitride raw materials are required, and the raw materials themselves are expensive. In addition, since silicon nitride itself is strong, it is pulverized as a waste material and used as a pavement material, etc., and silicon nitride raw materials and rare earths added as auxiliary agents are not reused as raw materials.

A method for recovering ceramics according to an embodiment is for solving such a problem. and metal oxides.
After hydrolyzing the acidic mixed liquid in a subcritical water state, the metallic oxide is separated and recovered from the mixed liquid containing the acidic aqueous solution produced by the hydrolysis and the metallic oxide by solid-liquid separation means. do.

In the method for recovering ceramics according to the embodiment, hydrolysis of the metal salt in the waste liquid proceeds efficiently by making the acidic solution into a subcritical water state. As a result, the metal salt is converted into an acid and a metal oxide without adding any chemicals, and can be easily separated and recovered by solid-liquid separation means.

Diagram showing the method of separating metal oxides and acids from ceramics The figure which shows the processing flow concerning embodiment.

FIG. 1 shows a method for separating metal oxides and acids from ceramics according to an embodiment. First, an acid aqueous solution for dissolving ceramics is prepared. Hydrogen ions H+ and negative ions X−, which are constituents of acid, are present in an acid aqueous solution. In addition, the hydrogen ion H+ of water and the hydroxyl ion OH
- exists. Examples of recovered ceramics include positive ions M3+ of metal M, negative ions N- of nitrides, negative ions O2- of oxides, and negative ions S of sulfides.
2- and the like exist as constituent elements.

By dissolving the ceramics in acid, hydrogen ions H+ of water, hydroxyl ions OH-, hydrogen ions H+ of acid, and MX3, which is a metal salt of metal M, are present.

By bringing the acidic mixed solution of molten ceramics to a subcritical state, the metal salt is hydrolyzed into metal ions M3+ and acid ions X-, and water is converted into hydrogen ions H+ and hydroxyl ions OH.
- state. It then becomes the hydroxide M(OH)3 and the free acid HX of the metal M, respectively.

Solid-liquid separation separates the metal oxide or metal hydroxide from the free acid HX. In FIG. 1 the hydroxide M(OH)3 is isolated.

Next, an actual processing method will be described. Although the processing method according to the embodiment is not particularly limited as long as it has the above configuration, the following methods can be mentioned as methods for obtaining it efficiently.

FIG. 2 shows the flow of the method for recovering metals from ceramics according to the embodiment.
First, ceramics such as waste materials are dissolved in acid. In order to melt the ceramics efficiently, it is necessary to crush the ceramics, but care must be taken not to allow impurities to enter from tools and equipment when crushing. Ceramics containing no or almost no auxiliary component can be pulverized and dissolved as they are to recover a single metal component that constitutes the ceramics.

However, in the case of ceramics containing a certain amount or more of auxiliary agent components, there are cases where the melting is carried out while containing the auxiliary agent components and where the melting is carried out after removing the auxiliary agent components as much as possible. In the former case, there is no pre-melting treatment, but depending on the acid and temperature used, the ceramics may be recovered while still containing the auxiliary agents. It will be reused in a state where the auxiliary agent component is still included. In the latter case, the tablets are dissolved after removal of tablet components at grain boundaries, for example, by etching. In this case, it is crushed to a size that is easy to dissolve after the process is performed to a size suitable for the etching process.
Thus, although the pretreatment is troublesome, it is possible to recover ceramics with high purity.

As the acid for dissolving ceramics, an acidic aqueous solution of one or more acids selected from phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid, oxalic acid, hydrofluoric acid, and acetic acid is used. The concentration of the acid is adjusted according to the situation, because the dissolution state changes depending on the type of ceramics and the particle size after pulverization.
In general, increasing the concentration of acid promotes dissolution, but care must be taken not to damage equipment due to rapid reaction.

Dissolution of the ceramics in acid is carried out at temperatures below 100°C. Desirably 20°C to 100°C
up to and above the saturated vapor pressure. This is because, in general, the higher the temperature, the greater the amount of metal that dissolves in the acid, and by keeping it under saturated vapor pressure, it reduces concentration changes by suppressing water evaporation and suppresses the adverse effects on the environment caused by acid volatilization. because it can

Next, the temperature of the acidic mixed liquid in which the ceramics are dissolved is raised to 100 to 300° C. under an environment of a saturated vapor pressure or higher to bring it into a subcritical state. This hydrolyzes the metal salt in the acid, converting it to a metal hydroxide or metal oxide and the free acid. In this case, if the temperature is lower than 100° C., hydrolysis becomes difficult, and if the temperature is higher than 300° C., the acid decomposes, resulting in poor recycling efficiency.
A temperature of 100 to 200° C. is preferable in order to achieve both the recycling efficiency of the metal oxide and the acid.

The free acid and the solidified metal oxide or metal hydroxide are subjected to solid-liquid separation and recovered. Solid-liquid separation means include a distillation method and the like. Since the mixed solution after subcritical treatment consists of nitric acid as a volatile component and metal oxides and metal hydroxides as non-volatile components, it can be separated by a simple distillation apparatus and requires no expensive consumables. It is possible to recover metal oxides from ceramics at low cost without needing it, and to recover the acid used as a solvent.

Since the acid salt of the metal in the mixed liquid becomes a metal oxide produced by hydrolysis, the solid-liquid separation means facilitates the separation of the acid and the metal oxide. As solid-liquid separation means, sedimentation separation, membrane separation, distillation, etc. are possible, and these may be performed alone or in combination. For example, depending on the combination, after roughly separating into an acidic aqueous solution and a metal oxide slurry by precipitation separation or membrane separation, the aqueous solution is distilled to preferentially vaporize the acid and separate and recover it. . Acid can be recovered at low cost without the need for expensive consumables.

Since the volatile components to be separated and recovered contain water, multi-stage distillation is desirable in order to increase the efficiency of separation from water. In addition, the membrane separation method can recover the nitric acid solution with less energy than distillation, but the separation membrane may be expensive. In particular, it is difficult to separate metals and nitric acid with reverse osmosis membranes.
It is considered unsuitable as a separation method for subcritical water treatment products because it requires replacement of expensive separation membranes due to deterioration due to impurities.

The solid-liquid separated free acid is reused to recover metal oxides from ceramics. Metal oxides and metal hydroxides are recycled as industrial raw materials.

(Example 1)
A waste material of gadolinium oxysulfide (Gd2O2S) that had been coarsely crushed in advance was pulverized by a powder mill. The pulverized gadolinium oxysulfide powder was passed through a sieve to obtain a gadolinium oxysulfide powder of 30 μm or less. The obtained powder of gadolinium oxysulfide was diluted with 35w of nitric acid (HNO3).
A nitric acid solution of gadolinium oxysulfide was prepared by dissolving in a t% aqueous solution. To hydrolyze gadolinium oxysulfide, the nitric acid solution was brought to a subcritical state at 250° C. for 1 hour.
The precipitate generated in the subcritical state was separated from the solution by the sedimentation separation method. Analysis of the resulting precipitate detected gadolinium hydroxide.
The reaction formula of gadolinium oxysulfide in the subcritical state is as follows.
Gd2O2S+4H2O→2Gd(OH)2+H2S

(Example 2)
Alumina (Al2O3), yttria (Y2O3), titania (TiO2
) was pulverized and classified into sizes of 0.5 to 1.0 mm with a mesh. The obtained silicon nitride was boiled in a 30 wt % sodium hydroxide (NaOH) aqueous solution to etch away the glass component in the grain boundaries. After etching, the silicon nitride was washed with water, dried and pulverized to 20 μm or less with a fine powder mill. The pulverized silicon nitride powder was wet pulverized with a ball mill in an organic solvent to obtain a slurry. Silicon nitride powder obtained by drying the slurry was dissolved in a 60 wt % aqueous solution of nitric acid (HNO3) to prepare a hydrochloric acid solution of silicon nitride. To hydrolyze silicon nitride, the hydrochloric acid solution was brought to a subcritical state at 150° C. for 1 hour.
The precipitate generated in the subcritical state was separated from the solution by the sedimentation separation method. Silicon dioxide (SiO2) was detected when the resulting precipitate was analyzed.
The reaction formula of silicon nitride in the subcritical state is as follows.
Si3N4+6H2O→3SiO2+4HN3

(Example 3)
Waste material of aluminum nitride (AlN) products to which yttria (Y2O3) was added as a sintering aid was pulverized and classified into sizes of 0.5 to 1.0 mm by a mesh. The aluminum nitride was boiled in a 30 wt % sodium hydroxide (NaOH) aqueous solution to etch away the glass component in the grain boundaries. After etching, the aluminum nitride was washed with water, dried, and pulverized to 20 μm or less with a fine powder mill. The pulverized aluminum nitride powder was wet pulverized with a ball mill in an organic solvent to obtain a slurry. Aluminum nitride powder obtained by drying the slurry was dissolved in a 35 wt % hydrogen chloride aqueous solution to prepare a hydrochloric acid solution of aluminum nitride.
To hydrolyze aluminum nitride, the hydrochloric acid solution was brought to a subcritical state at 150° C. for 1 hour.
The precipitate generated in the subcritical state was separated from the solution by the sedimentation separation method. Analysis of the resulting precipitate detected aluminum hydroxide (Al(OH)3).
By heating this aluminum hydroxide, alumina (aluminum oxide: Al2O3
) was generated.
The reaction formula of silicon nitride in the subcritical state is as follows.
AlN+3H2O→Al(OH)3+HN3

(Comparative example 1)
In Example 1, the temperature of the nitric acid solution for hydrolyzing gadolinium oxysulfide was set to 80
The process was the same except that the temperature was changed to °C. In this comparative example, hydrolysis in the aqueous solution became difficult, and no precipitate was obtained in the aqueous solution.

(Comparative example 2)
In Example 1, the temperature of the nitric acid solution for hydrolyzing gadolinium oxysulfide was 35
The process was the same except that it was at 0°C. In this comparative example, hydrolysis due to decomposition of the hydrochloric acid solution was reduced, and separation and recovery of hydrochloric acid became difficult.
From these experimental results, it can be said that the examples are very excellent in recovering ceramics.

Although some embodiments of the present invention have been illustrated above, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments are
It can be embodied in various other forms, and various omissions, replacements, changes, etc. can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof. Moreover, each of the above-described embodiments can be implemented in combination with each other.

Claims (4)

A method for recovering metal oxides from ceramics composed of one or more metal elements, wherein the ceramics are dissolved in an acidic aqueous solution at a temperature of 20 to 100° C. under a pressure environment higher than the saturated vapor pressure and mixed with an acidic solution. After making the liquid, the acidic liquid and the metal oxide are separated by a solid-liquid separation means from the liquid mixture containing the acid and the metal oxide or metal hydroxide produced by hydrolyzing the acidic liquid mixture into a subcritical water state. method of recovery. Metal oxidation from ceramics, characterized in that the ceramics shown in claim 1 is dissolved in an acidic aqueous solution, and the acidic mixture contains any one of phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid, oxalic acid, hydrofluoric acid, and acetic acid. How to collect things. 2. The method for recovering metal oxides from ceramics according to claim 1, wherein the subcritical water state is set to a pressure higher than the saturated vapor pressure at 100.degree. C. to 300.degree. According to claim 1 , the solid-liquid separation means separates the acidic aqueous solution and the metal oxide slurry by sedimentation separation or membrane separation, and then separates the metal oxides from ceramics by a distillation method. collection method.

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