JPH0726223B2 - How to recover precious metals - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for dissolving precious metals from spent catalysts and the like using fluidized bed electrolysis or fixed bed electrolysis.

[0002]

BACKGROUND ART Precious metals such as platinum group metals are widely used as catalysts for purifying automobile exhaust gases, for various organic chemical reactions, as electrode catalysts for fuel cells, and as materials for electronic components such as ICs. Precious metals are expensive and resources are in short supply, so it is important to recover precious metals from various used materials.

Conventionally, when recovering such precious metals, the metals are dissolved together with the carrier using an oxidizing acid such as hot concentrated sulfuric acid or aqua regia, and a reducing agent is added to the resulting solution to deposit the precious metal in the solution, or the precious metals are electrolyzed in a low current density electrolytic cell to deposit them on the cathode.

[0004]

[Problem to be solved by the invention] When dissolving with acid,
Not only does it require a large amount of heat for heating, but the strong oxidizing acid is dangerous and difficult to handle. Aqua regia, which has traditionally been used to dissolve precious metals, generates nitrogen oxides (NOx), which can cause pollution problems, making disposal of these NOx a major issue. While cyanides such as sodium cyanide are also effective in dissolving precious metals, they are highly toxic and require careful handling and wastewater treatment.

Furthermore, when recovering precious metals from precious metal catalysts, a small amount of precious metal is supported on a carrier such as silica or alumina, and the amount of precious metal relative to the total catalyst volume is extremely small (approximately 1 gram of precious metal per 1 liter of apparent catalyst volume), so if the carrier is dissolved, the recovery rate decreases and a large amount of solution must be treated, which is uneconomical.

Furthermore, some of these precious metals may exist as oxides, and some precious metal oxides are hardly soluble in aqua regia. Therefore, there are drawbacks such as the need to carry out a reduction treatment before dissolution, or to carry out the dissolution operation in two separate steps, such as combining dissolution of the metal with an acid and dissolution of the oxide with an alkali (see, for example, Japanese Patent Laid-Open Publication No. 57-155333).

On the other hand, various methods for dissolving metals by electrolysis have been proposed (for example, Japanese Patent Application Laid-Open No. 51-37045).
No. 5,999,023, and the like), there has been no report yet on the application of electrolysis to dissolving precious metals from granular materials carrying metals or metal compounds such as precious metal catalysts.

Furthermore, since the concentration of precious metals in the solution from which the precious metals have been eluted is low, adding a reducing agent to the eluate requires a large amount of solution to be treated, which has the disadvantage of requiring a large-sized apparatus and high operating costs. Furthermore, in an electrolytic cell using ordinary flat electrodes, the solution concentration is low, making it impossible to efficiently recover the precious metals.

[0009]

The present invention utilizes the advantage of electrolysis, which does not require the use of oxidizing acids, to produce spent catalysts and fuel cell electrodes carrying metal particles or metal compound particles.
The purpose of this method is to recover metals by dissolving them in an electrolytic solution in the anode chamber of an electrolytic cell, and then depositing the resulting dilute solution on cathode particles in the cathode chamber of a fluidized bed electrolytic cell, without the problems of post-treatment that arise when oxidizing acids are used on crushed granules of electronic components.

In the present invention, the term "granular bodies" refers to spherical or cylindrical bodies such as catalyst carriers, as well as plate-shaped or conical bodies, amorphous bodies obtained by crushing or pulverization, and bodies obtained as ash after combustion, but is not limited to these.

The present invention will now be described in detail using a used catalyst as an example.

The process of dissolution of precious metals from non-conductive catalyst carriers is not fully understood, but it is believed that various factors contribute to the dissolution, such as anodic dissolution due to the passage of electricity from the anode to the precious metal components, dissolution due to the precious metal components of each granule acting as a bipolar electrode, and the action of chlorine generated by electrolysis of the components in the electrolyte.

The noble metals targeted by the present invention are not particularly limited, but include noble metals supported on spent catalyst substrates made of alumina, silica, silica-alumina, etc., electronic components such as ICs, and fuel cell electrodes, and include palladium, platinum, rhodium, ruthenium, iridium, silver, and gold.
The amount of metal or metal compound supported on the carrier varies depending on the use of the carrier, but in the case of a used catalyst, for example, it is about 0.1 g to 50 g per kg of carrier weight.

The electrolytic cell used for dissolution is not particularly limited in structure or material, as long as it is divided into an anode chamber and a cathode chamber by a diaphragm; for example, a box-shaped, cylindrical, or other electrolytic cell can be used. The diaphragm must have the function of preventing the precious metal components dissolved in the anode chamber from permeating into the cathode chamber and depositing on the cathode. Therefore, when the precious metal components are present in the electrolyte as cations, this diaphragm is preferably an anion exchange membrane, which prevents the permeation of cations. However, since the precious metal components are not necessarily present as cations, it is preferable to use a neutral or cation exchange membrane, which has superior durability, depending on the composition of the electrolyte and the precious metal components to be dissolved.

In the recovery method of the present invention, the precious metals are first eluted in an electrolytic cell. Since the elution reaction mainly utilizes the reaction in the anode chamber, it is preferable to adjust the position of the diaphragm so that the capacity of the anode chamber is larger than the capacity of the cathode chamber.

The anode and cathode used in the electrolytic cell for elution can be any conventional anode and cathode, such as a dimensionally stable anode coated with a noble metal oxide or a titanium cathode, without any restrictions.
Both electrodes are preferably arranged so that the electrolysis voltage is minimized. In this case, if the cathode is made porous so that gas generated between the cathode and the diaphragm can be vented behind the cathode, operation at a lower voltage becomes possible.

As the electrolyte, various acids such as hydrochloric acid, nitric acid, sulfuric acid, mixed acid, etc. can be used, but from the viewpoint of waste liquid and waste gas treatment, hydrochloric acid is preferable because it is relatively easy to treat the waste gas and waste liquid. In addition, any concentration of about 5% to 35% can be used.

The used catalyst and the like are placed in the anode chamber of the electrolytic cell composed of these elements, and electrolysis is carried out while supplying the electrolytic solution to the anode chamber. In this case, the granular material may be maintained in a fluidized bed state or in a fixed bed state.

FIG. 1 shows an example of a fluidized-bed electrolytic cell. The electrolytic cell 1 is divided into an anode chamber 3 and a cathode chamber 4 using a corrosion-resistant diaphragm 2, such as a fluororesin anion-exchange membrane or a fluororesin cation-exchange membrane. The anode chamber is larger than the cathode chamber to increase the amount of lead introduced into the anode chamber. The anode 5 is a porous, dimensionally stable anode with a coating containing a noble metal oxide on a substrate such as titanium, while the cathode 6 is made of various metals such as stainless steel or titanium. A corrosion-resistant propeller 8, such as polytetrafluoroethylene, is preferably used in the anode chamber to agitate and fluidize the catalyst particles 7. To form a fluidized bed, electrolyte can be supplied from below into a cylindrical electrolytic cell without using such a mechanical agitator, and the upward force of the electrolyte can bring the carrier into a fluidized bed state. In this fluidized-bed electrolysis, the carrier particles constantly rotate, dissolving all of the metal or metal compound supported on their entire surfaces.

FIG. 2 shows an example of a fixed-bed type electrolytic cell.
The electrolytic cell 1 is divided by a diaphragm 2 into an anode chamber 3 and a cathode chamber 4. A dispersing element 9 having openings smaller than the size of the granules is provided at the bottom of the anode chamber so that the anolyte can act sufficiently on stationary granules such as catalyst particles 7 packed in the anode chamber, and the anolyte is circulated from the bottom.

When treating by fixed-bed electrolysis, the granular material is filled in the anode chamber and an electric current is applied. Since many of the granular material are non-uniform, it is often impossible to obtain a uniform fluidized state using the fluidized-bed electrolysis method described above, so it is preferable to operate under stable conditions using this fixed-bed electrolysis method.
On the other hand, in this fixed-bed electrolysis method, a large amount of solution must be circulated to dissolve all the metals and metal compounds on the carrier. Also, in the precious metal dissolution process, the electrolysis can be interrupted before all the precious metals are dissolved, the electrolyte from which the precious metals have dissolved is removed, and the solution is replaced with an acid that does not contain the precious metals, and then electrolysis is continued. This reduces the amount of metal remaining in the granules, and makes it possible to increase the elution rate of the precious metals.

After electrolysis, the electrolyte containing the dissolved metals is removed from the electrolytic cell together with the residue, and then subjected to press filtration and washing. By using the liquid used for washing in the dissolution process, it is possible to increase the elution rate of the precious metals, thereby increasing the recovery rate of the precious metals.

The solution from which the precious metals have been eluted is a dilute solution of about several hundred mg/L, so this solution can be used directly for the production of catalysts.
Since it cannot be used for plating or other applications, it is necessary to recover the precious metals by concentrating them or precipitating them from the solution.

Therefore, in the method of the present invention, a solution containing a dilute precious metal is introduced into a fluidized bed electrolytic cell having fluidized cathode particles, where the precious metal is deposited on the cathode particles and recovered as a metal; or, when a solution of a predetermined concentration is required, such as in the production of a catalyst, the cathode particles on which the precious metal has been deposited are electrochemically eluted again in the anode chamber of an elution electrolytic cell. By undergoing the electrochemical process of precipitation or elution of the precious metal, the precious metal component can also be refined at the same time.

The fluidized bed electrolytic cell for depositing precious metals used in the present invention may be, for example, a fluidized bed electrolytic cell disclosed in Japanese Patent Application Laid-Open No. 60-200994 filed by the present applicant, U.S. Pat. No. 456,666,456, or the like.
An electrolytic cell such as that described in US Pat. No. 9729 may be used.

When depositing precious metals in a fluidized-bed electrolytic cell as described above, if the electrolytic acid has a high conductivity, electrolysis does not occur on the particles, but the metal deposition reaction occurs on the cathode, which acts as a current collector supplying electrolytic current to the particles, and therefore the solution obtained in the dissolution step must be diluted. If the washing solution used to wash the residue in the dissolution step is used for dilution, it is possible to increase the recovery rate of precious metals.

[0027]

[Function] The present invention makes it possible to electrolyze used catalysts and the like in the anode chamber of an electrolytic cell, dissolving the precious metal components in the electrolytic solution, and then electrochemically depositing the precious metals from the resulting dilute solution containing the precious metals in a fluidized bed electrolytic cell, thereby recovering the precious metals and obtaining a solution with increased purity and concentration of the precious metals, without using cyanides or oxidizing acids, which require careful handling.

[0028]

EXAMPLES The present invention will be explained in more detail below with reference to examples. Example 1: Using the fluidized bed electrolytic cell shown in Figure 1, platinum in an automobile exhaust gas purification catalyst was dissolved. The catalyst was made of alumina with an average particle size of 3 mm, on which platinum and a small amount of palladium were supported. The amount of supported platinum per 1 kg of catalyst was about 1.
The powder used had a mass of 0.65 g and an apparent density of 0.65 kg/l.

The electrolytic cell 1 is 85 mm long and 115 mm wide.
A box-shaped electrolytic cell 1 was used, 200 mm deep, and this electrolytic cell 1 was partitioned using a diaphragm 2 made of a fluororesin-based anion exchange membrane so that the ratio of the volume of the anode chamber 3 to the volume of the cathode chamber 4 was 17:6. A porous, dimensionally stable anode was used as the anode 5, and a stainless steel substrate coated with titanium was used as the cathode 6. 15 wt % hydrochloric acid was added to this cathode chamber 4, 0.8 kg of the catalyst particles 7 were placed in the anode chamber 3, and a total of 3.5 liters of 15 wt % hydrochloric acid was circulated and supplied at 2 liters/hour.

Polytetrafluoroethylene propeller 8
The catalyst particles 7 are stirred using a stirring
The electrolysis was carried out for 4 hours at a current of 1.0 V. After 2 hours, the platinum concentration was 1.0 V.
47 mg/l, and the platinum concentration at the end of electrolysis was 226 mg/
The palladium concentration was 17.1 mg/l, the platinum elution rate was 98.9%, and the current efficiency of platinum elution was 2.2%.

Example 2 Palladium in a catalyst for selective hydrogenation of cracked gasoline was dissolved using a fixed-bed electrolytic cell as shown in Figure 2. The catalyst was made by supporting palladium on alumina pellets with an average particle size of about 3.2 mm, with the amount of supported palladium being about 30 g per kg of catalyst and an apparent density of 0.6 kg/l. Prior to electrolysis, the catalyst was reduced to convert all of the metal oxides present into metal.

The electrolytic cell 1 is the same as that in Example 1,
A distribution plate 9 with a 10-mesh net (opening of 1.65 mm) laid thereon for holding the catalyst was provided at the bottom of the anode chamber 3. 1 kg of catalyst particles 7 was packed on the distribution plate 9, and 15
A total of 10 liters of 10 wt % hydrochloric acid was circulated and supplied to the anode chamber 3 at a flow rate of 2 liters/hour, and while the catalyst particles 7 were kept stationary,
Electrolysis was carried out for 4 hours at a current of 30 A. At the end of the electrolysis, the palladium concentration in the solution was 1465 mg/L, and the dissolution efficiency was 48.8%.

Example 3: An IC substrate made of alumina plated with a noble metal (total weight 3
2 g) was crushed in a crusher to a particle size of 1.2 mm or less,
The granules were burned at 850°C for 12 hours. Gold was dissolved from the granules using a fluidized-bed electrolytic cell as shown in Figure 1. A total of 5 liters of 10 wt% hydrochloric acid was circulated and supplied to the anode chamber of the electrolytic cell at a flow rate of 2 liters/hour, and electrolysis was performed for 30 minutes at a current of 10 A while stirring the particles with a propeller. The gold concentrations in the electrolyte after 15 minutes and 30 minutes were 151 mg/L and 187 mg/L, respectively, and the current efficiency for gold dissolution was approximately 2.5%. Furthermore, no metal was detected in the granules after electrolysis was completed.

Example 4: Using the fluidized-bed electrolytic cell shown in Figure 1, palladium and platinum were dissolved in a catalyst for use in hydrogenation reactions, in which palladium and platinum were supported on carbon particles. This catalyst was burned prior to electrolysis, and the resulting ash with a particle size of 15 µm or less was sieved and collected. These components were oxides of palladium, platinum, iron, aluminum, silicon, calcium, and magnesium, as well as unburned carbon, with the amount of palladium oxide being approximately 25% and the amount of platinum oxide being approximately 2%.

The anode chamber of the electrolytic cell was filled with 26% by weight hydrochloric acid, and 330 g of the catalytic combustion ash (apparent volume 55
26% by weight hydrochloric acid was supplied to the anode chamber at a flow rate of 2 liters/hour, and electrolysis was carried out for 3 hours at a current of 30 A while stirring the catalytic combustion ash with a propeller to maintain it in a fluidized bed state. The concentrations of palladium and platinum contained in the electrolyte were 0 mg/L, 0 mg/L, and 0 mg/L, respectively, at the start of electrolysis.
After 1.5 hours, the levels were 8930 mg/l and 715 mg/
l, and at the end of electrolysis, 12750 mg/l and 980 mg/l
The remaining amounts of palladium and platinum in the catalytic combustion ash at the end of electrolysis were 12 ppm and 0 ppm, respectively.
Palladium and platinum could be dissolved almost quantitatively.

Example 5 Using the fixed-bed electrolytic cell shown in FIG. 2, noble metals in granular catalyst for purifying exhaust gas for automobiles were dissolved.

This catalyst is a so-called three-way catalyst, in which platinum, palladium and rhodium are supported on alumina, with platinum at about 300 ppm and palladium at about 100 ppm.
000 ppm and about 15 ppm of rhodium.

The electrolytic cell 1 is 180 mm long and 250 mm wide.
The electrolytic cell is a box-shaped electrolytic cell having a length of 1000 mm and a depth of 1000 mm.
A diaphragm 2 made of a fluororesin-based anion exchange membrane is used,
The chamber was partitioned so that the ratio of the volume of the anode chamber 3 to the volume of the cathode chamber 4 was 5:1. A porous, dimensionally stable anode was used as the anode 5, and titanium was used as the cathode 6. 30 wt % hydrochloric acid was added to the cathode chamber 4, and 22 kg of catalyst granules 7 crushed to 20 to 40 mesh was placed in the anode chamber 3. Electrolysis was performed for 6 hours at a current of 200 A while circulating and supplying a total of 45 liters of 30 wt % hydrochloric acid at a rate of 80 liters/hour.

The concentrations of the metal components in the electrolyte at the end of electrolysis were 118 mg/l for platinum, 347 mg/l for palladium, and 6 mg/l for rhodium. Analysis of the residue showed that 97% of platinum, 96% of palladium, and 6% of rhodium were still in the electrolyte.
9% was eluted.

Example 6 Four hours after the start of electrolysis, the current was temporarily interrupted and the anolyte and 35%
The dissolution was carried out under the same conditions as in Example 5, except that two-stage electrolysis was carried out in which the aqueous solution was replaced with hydrochloric acid and electrolysis was carried out for two hours.

Analysis of the residue after 4 hours of electrolysis in the first stage showed that the elution rates of platinum, palladium, and rhodium were 94%, 94%, and 59%, respectively.
After electrolysis for 2 hours, the results were 97%, 98%, and 7%, respectively.
The elution rates of palladium and rhodium were 4%, which was higher than in Example 5. Example 7 The solution containing palladium and platinum obtained in Example 4 was diluted about 50 times and electrolysis was carried out in a cylindrical fluidized bed electrolytic cell with an anode diameter of about 50 mm, a cathode diameter of about 140 mm, and a height of about 1000 mm, using carbon particles as the cathode particles and a cation exchange membrane as the diaphragm, at a current of 50 A while circulating the electrolyte. As a result, the elution rate of palladium in the electrolyte was 14 mg.
/l, and platinum was reduced to 13 mg/l.

Example 8 The solution containing platinum, palladium and rhodium obtained in Example 5 was diluted about six times to form an anode with a diameter of about 30 mm.
Electrolysis was carried out in a cylindrical fluidized bed electrolytic cell with a cathode diameter of approximately 90 mm and a height of approximately 600 mm, carbon particles as cathode particles, and a cation exchange membrane as a diaphragm, at a current of 20 A while circulating the electrolyte.

As a result, platinum was 2 mg/l, palladium was 3 mg/l, and
The concentration was reduced to mg/l, and rhodium was below the detection limit.

Comparative Example 1: Under the same conditions as in Example 1, except that no current was applied to the electrolytic cell, 3.5 liters of 15% by weight hydrochloric acid was circulated and supplied to the fluidized-bed electrolytic cell at a rate of 2 liters/hour. After 2 hours, the platinum concentration in the solution was 9.9 mg/L, and at the end of electrolysis, the platinum concentration was 15.3 mg/L, the palladium concentration was 0 mg/L, and the platinum elution rate was 6.7%. Comparative Example 2: Under the same conditions as in Example 2, except that no current was applied to the electrolytic cell, 10% by weight hydrochloric acid was supplied to the electrolytic cell to dissolve palladium in the catalyst for selective hydrogenation of cracked gasoline. After 4 hours, the palladium concentration was 37 mg/L.

Comparative Example 3 Using the crushed particles of the IC substrate used in Example 3, an attempt was made to dissolve gold without passing a current in the fluidized bed electrolytic cell shown in Figure 1. After 15 minutes, no gold was detected in the electrolyte, and after 30 minutes,
After 10 minutes, only a small amount of metal was detected, and metal remained on the IC substrate.

Comparative Example 4 Palladium and platinum in the combustion ash of the catalyst used in the hydrogenation reaction were dissolved under the same conditions as in Example 4, except that no current was applied to the electrolytic cell.

The concentrations of palladium and platinum contained in the electrolyte were 0 mg/l and 0 mg/l, respectively, at the start of electrolysis.
After 1.5 hours, the concentration was 9.20 mg/l and 0 mg/
At the end of the electrolysis, the concentrations were 13.4 mg/l and 0 mg/l, and the dissolution rates were 0.2% and 0%, respectively.

[0048]

The present invention does not use cyanides or oxidizing acids, which require careful handling, and electrolyzes granular materials that hold or contain precious metals or precious metal compounds in the anode chamber of an electrolytic cell, dissolving the precious metal components in the electrolyte, and furthermore, from the obtained dilute solution containing the precious metals,
It is possible to deposit precious metals and obtain solutions with increased purity and concentration of precious metals, thereby shortening and simplifying the work process and improving economy.

[Brief explanation of the drawings]

1 is a schematic diagram of a fluidized bed electrolytic cell for elution.

FIG. 2 is a schematic diagram of a fixed-bed elution electrolytic cell.

[Explanation of symbols]

1. Electrolytic cell 2. Diaphragm 3. Anode chamber 4. Cathode chamber 7. Catalyst granules 8. Propeller 9. Dispersion plate

Claims (6)

[Claims] [Claim 1] A method for recovering precious metals, comprising: eluting a precious metal component from granular material holding or containing at least one precious metal or precious metal compound in an anode chamber of an electrolytic cell partitioned into an anode chamber and a cathode chamber by a diaphragm; then supplying the liquid containing the precious metal component to the cathode chamber of a fluidized bed electrolytic cell having cathode particles in a fluidized state, electrolyzing the liquid, and depositing the precious metal on the cathode particles. 2. The method for recovering precious metals according to claim 1, wherein an acid is used as the electrolyte. 3. A method for recovering precious metals according to claim 1, wherein the particulate material holding or containing at least one precious metal or precious metal compound is a spent catalyst. 4. A method for recovering precious metals according to any one of claims 1 to 3, wherein the particulate matter holding or containing at least one precious metal or precious metal compound is made of a non-conductive material. 5. A method for recovering precious metals according to any one of claims 1 to 4, wherein the particulate material holding or containing at least one precious metal or precious metal compound is a pulverized fuel cell electrode. 6. A method for recovering precious metals, comprising: eluting a precious metal component from granular material holding or containing at least one precious metal or precious metal compound in an anode chamber of an electrolytic cell partitioned into an anode chamber and a cathode chamber by a diaphragm; supplying a liquid containing the precious metal component to a cathode chamber of a fluidized bed electrolytic cell having cathode particles in a fluidized state and electrolyzing the liquid to deposit the precious metal on the cathode particles; and then re-eluting the liquid in the anode chamber of the electrolytic cell partitioned into an anode chamber and a cathode chamber by a diaphragm to obtain a solution of the precious metal having a predetermined concentration.