KR100858551B1 - A method of extraction of platinum group metals from the spent catalysts by electrochemical processes - Google Patents

Abstract

The present invention relates to a method for extracting a platinum group metal from a spent catalyst by an electrochemical method, comprising: placing a material to be treated between positive electrodes of a flowing electrolyzer; Filling an electrolytic cell with an aqueous 0.3-10.0% hydrochloric acid solution with an electrolyte; Activating a platinum group metal with an inverted electrode of the polarity of the electrode in the state of power failure; After the activation process, the electrolyte is circulated from the anode to the cathode at a rate at which the hydrated anion chlorine complex of the precious metal is formed. By using the method of extracting the platinum group metal from the waste catalyst of the present invention, the technical process is simplified, the extraction cost of the platinum group metal is low, the productivity of the extracted precious metal is remarkably excellent, and the economic efficiency is excellent.

Waste catalyst, precious metals, extraction method, electrochemical method

Description

A method of extraction of platinum group metals from the spent catalysts by electrochemical processes}

1 is a schematic representation of an electrolyzer for extracting platinum group metals from spent catalyst.

2 shows the circulation of concentration streams of hydrochloric acid, dissolved chlorine and platinum group metals in an electrolytic cell.

* Description of the symbols for the main parts of the drawings *

1. Electrolyzer

2. Graphite Cathode

3. Anode formed of a large lattice with an IrO ₂ put layer

4. Peristaltic pump

5. Electric heater

6. Pipe for solution circulation

7. Porous Diaphragm

8. Aqueous Chlorine Solution

9. Waste catalyst particles

10. Activated Carbon Particles

11. Initial Electrolyte Solution

The present invention relates to a method for extracting a noble metal from the spent catalyst by an electrochemical method.

Platinum group metals (PGM), such as platinum (Pt) and palladium (Pd), have high dissolution temperatures, excellent corrosion resistance due to chemical erosion, and have unique chemical characteristics such as reduction catalysis. The global average annual production of platinum group metals is around 200 tonnes, with more than 90% produced in South Africa and the former Soviet Union, and about 6% in Canada, in South America, the United States, Australia and Japan. These platinum group metals are almost used as catalysts for automobiles and petrochemical industries except for electric and electronic industries such as platinum group metal circuits.

These catalysts and components are degraded over time and eventually discarded at the end of their lifetime, but especially since platinum group metals are expensive and imported in their entirety, it is not only economically beneficial to recover and reuse them. Can play a big role in the efficient use of

Several methods have been reported for the recovery of precious metals supported on catalyst carriers, but each has technical advantages and disadvantages. In particular, the platinum group metal has a very high ionization potential, making it difficult to dissolve the metal itself, and it is more difficult to extract and separate the platinum group metal due to the catalyst carrier and other catalyst components and contamination.

Generally, the amount of precious metal in spent catalyst is about 0.02-5.0%. Generally, the waste catalyst is pulverized by extracting platinum, palladium, rhodium, or a mixture thereof from the spent catalyst, the platinum group metal is dissolved with an inorganic acid such as aqua regia, and then the solution in which the tin and platinum group metal are dissolved is filtered and the electrolyte has an anion exchange membrane. The method of extracting and obtaining from this containing electrolytic cell is known. However, they require expensive ion-exchange membranes, and due to the precipitation of chlorine generated during the extraction process, the membranes have a short lifespan, which requires frequent replacements, and the separation of precious metals is complicated due to the low concentration of precious metals in the extracted liquid. The process costs a lot, and the extraction time is long. It also has the disadvantage that the process has to go through many steps.

In general, hydrochloric acid solution having a concentration of 5-35% is used as the electrolyte, and leaching is carried out in a fixed filtration layer of spent catalyst particles or in a fluidized bed during circulation of the electrolyte through the leach material layer. The precious metal is then surrounded by a solution reduced to carbon particles in a cathodic chamber of a second electrolyzer with a cation exchange membrane. Finally, the precious metals are leached back into the electrolyte solution in the fluidized bed.

Platinum group metals are extracted from inorganic-containing materials such as spent catalysts, slimes, concentrates, etc. which are currently used in which leaching of platinum group metals and precipitation of platinum group metals in a charged cathode are performed simultaneously as one step. to be. This method has a problem in that the process is complicated because only a limited concentration of the filtrate can be obtained and separate technical blocks are used.

Accordingly, an object of the present invention is a method of extracting a platinum group metal from a spent catalyst, while the technical process is simple, and the extraction cost of the platinum group metal is remarkably economical and high in productivity. Its purpose is to provide a method.

In order to achieve the above object, the present invention comprises the steps of adding a waste catalyst between the positive electrode of the electrolytic cell; Activating the platinum group metal while regularly changing the polarity of the electrodes; Circulating an electrolyte from an anode to a cathode, thereby depositing a platinum group metal on a cathode, thereby providing an electrochemical extraction method of a platinum group metal from a spent catalyst.

The electrolyte provides an electrochemical extraction method of the platinum group metal from the spent catalyst, characterized in that an electrolyte capable of generating chlorine anions, for example, 0.3-10.0% aqueous hydrochloric acid solution.

The electrochemical leaching provides an electrochemical extraction method of a platinum group metal from a waste catalyst, which is activated by periodically changing the polarity of the electrode.

The circulation of the electrolyte occurs from the anode (anode) to the cathode (cathode), the electrolyte provides an electrochemical extraction method of the platinum group metal from the spent catalyst, characterized in that using 0.3-10.0% hydrochloric acid aqueous solution. The waste catalyst provides an electrochemical extraction method of the platinum group metal from the waste catalyst, characterized in that it is charged into the electrolytic cell in the form of pellets as it is not pulverized.

Hereinafter, the present invention will be described in detail.

The electrochemical extraction method of the platinum group metal of the present invention can be used when extracting valuable metals such as platinum group metals from a carrier catalyst in the form of particles containing valuable metals.

The waste catalyst may place waste catalyst particles containing 0.01-10.0%, preferably 0.1-5.0%, of precious metal between the positive electrodes of the electrolyzer.

The electrolyte uses an electrolyte capable of generating chlorine anions, for example, an aqueous solution of 0.3-10.0% hydrochloric acid.

The electrochemical leaching is activated by periodically changing the polarity of the electrode.

There is no circulation of the electrolyte in the electrochemical activation step.

As described above, the pretreatment process of periodically changing the polarity of the electrode activates the electrochemical leaching of the precious metal. Without this activation, the electrochemical leaching does not occur at the center of the particles, but only at the surface of the particles, so that the recovery rate is low. Thus, in the inactivation conditions, most of the precious metal remains in the carrier, and only a small amount is located on the negative electrode.

At the _{^{anode: Cl - + 2H 2 O -}} 4e - → ClO 2 + 4H +

The generation of chlorine dioxide will depend on the degree of reverse reaction process that generates chloride ions.

_{^{ClO 2 + 4H + → Cl -}} + 2H 2 O - 4e -

In the cathode: 4H ^{+ +} 4e ^- → 4H

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Pt ^{0 -} e - → Pt ⁺

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Circulation of the electrolyte of the present invention takes place from an anode to a cathode.

Circulating an electrolyte containing 0.3-10.0% HCl causes precipitation of the precious metal at the cathode and occurs from the anode to the cathode, which is the opposite of the movement of the anionic complexes of the precious metal.

The circulation of the electrolyte is provided by a pump. Circulation of the electrolyte activates the precipitation of all metals in the electrolyte.

Dissolved metals (hydrated anionic chlorine complexes of precious metals) are directed to the anode. The anionic complexes then collapse and the cations of the noble metal are directed to the cathode, where their precipitation takes place.

When the electrolyte is not circulated and the anolyte is exchanged, no abundant metal is produced on the negative electrode.

In the circulation of the electrolyte in the transport tank from the positive electrode to the negative electrode, intensive disposition of the metal occurs on the negative electrode, and the disposition rate of the metal is 2-5 times faster than in the static mode. This means that as the metal is oxidized and consumed, the anolyte is increased and chlorine is rich in activity. The electrolyte circulation may vary depending on the type of metal and the concentration of the electrolyte. When the electrolyte is circulated, the metal is smoothly precipitated.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are merely examples of the present invention, and the present invention is not limited thereto.

Example 1.

40 liters of spent catalyst carrying palladium in granite was filled between electrodes of an electrolytic cell of 20 cm in width, 20 cm in length, and 100 cm in length. The spent catalyst was used as it is without pretreatment in the form of fine particles having a palladium content of 0.3% by weight and a diameter of 5mm. A 2% aqueous HCl solution was used as the electrolyte, and the polarities of the electrodes were changed every 1 minute for 1 hour. At the time of electrolytic extraction, the electrode had a voltage of 21 V and a current of 6 A (current density: 0.015 A / cm ² ). The pump was used to continuously circulate from the positive to the negative electrode at a rate of 0.5 L / min. The temperature was kept at 70 ° C.

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As a result, flakes of the metal containing 85-90% of the precious metal were generated in the cathode. This flake could be easily removed from the cathode.

After operation for 10 hours, the concentration of palladium in the electrolyte was less than 1 ppm, and the spent catalyst after electrolytic extraction showed that the palladium content was 0.0015% or less and the degree of palladium extraction was 99.5%. The shape of the spent catalyst remained unchanged and the color turned white. No waste catalyst components were extracted except palladium. The electricity consumed was 1.25 kWh for electrolysis and 7.5 kWh for heating and circulation of the electrolyte.

Example 2.

Attempts have been made to extract more palladium from the chemically leached palladium-alumina catalyst. The content of palladium was 0.02-0.03%, which is similar to the concentration of palladium remaining on the carrier after treatment in US Pat. No. 4,775,452. The volume of the catalyst in the electrolyzer was 40 liters and had a cylindrical shape of 10 mm in diameter and 15 mm in height. 0.3% HCl aqueous solution was used as the electrolyte, and the volume ratio of the fixed and liquid phases was 1: 1. The electrode polarity was changed every 1 minute for the first hour for activation on the catalyst surface. Electrochemical extraction was carried out for 15 hours while circulating the electrolyte, and palladium metal was precipitated at the cathode. The reaction temperature was carried out at 60 ° C., and the current density was 0.06 A / cm ² . As a result, the palladium concentration in the carrier was 0.005% and the palladium component in the electrolyte was 1 ppm or less.

Example 3.

40 L of platinum-alumina spent catalyst containing 0.4% platinum pretreated to have a particle diameter of 3-5 mm in diameter was charged to the electrolyzer. A 4% aqueous HCl solution was used as the electrolyte, and the solid and liquid had a volume of 1: 1. The polarity of the electrode was changed every 1 minute for 1 hour so that leaching could be activated. The electrochemical leaching was carried out for 20 hours while circulating the electrolyte in the same manner as in Example 1 while maintaining a current density of 0.025 A / cm ² (current 10 A in the electrolytic bath) and the temperature at 80 ° C. As a result, 98% of platinum was extracted, and the content of platinum attached to the cathode as a powder aggregate was 60-70%.

According to the extraction method of the present invention, the platinum group metal can be extracted with high efficiency and high yield, the extraction process can be simplified, and the cost of the platinum group metal extraction can be significantly reduced, which is a very economical method. Extraction is a very useful invention for the recycling of platinum group metals that are dependent on imports.

Claims (4)

Adding a spent catalyst between positive electrodes of the electrolytic cell; Activating the platinum group metal while regularly changing the polarity of the electrodes; Circulating an electrolyte from an anode to a cathode to precipitate the platinum group metal on the cathode, wherein the electrochemical extraction method of the platinum group metal from the spent catalyst is carried out. The electrochemical extraction method of a platinum group metal from a spent catalyst according to claim 1, wherein the electrolyte is 0.3-10.0% aqueous hydrochloric acid. The electrochemical extraction method of a platinum group metal from a waste catalyst according to claim 1, wherein the waste catalyst is added between both electrodes of the electrolytic cell in the form of unpulverized particles. The electrochemical extraction method of a platinum group metal from a spent catalyst according to claim 1, wherein the electrolytic cell is a vertical or horizontal electrolytic cell.

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