JPH0382785A - Method and apparatus for refining iridium - Google Patents

Abstract

PURPOSE:To efficiently refine iridium while reducing labor and the amount of electric power consumption by subjecting iridium containing noble metal impurities to electrolytic refining and also refining and recovering irridium in the form of tetravalent iridium ions in the same electrolytic cell. CONSTITUTION:At the time of refining an Ir solution containing chloride ions by means of diaphragm electrolysis, an electrolytic cell is partitioned into an anode chamber and a cathode chamber by means of a diaphragm 1, and about 9.8g/l of Ir solution is added as an anolyte 4 to the anode chamber and about 10.2g/l of Ir solution containing noble metal impurities is added as a catholyte 5 to the cathode chamber. Subsequently, electrolysis is performed, and the noble metal impurities are electrodeposited on a cathode 3 and Ir is transformed into trivalent Ir ions. Then, the electrolyte is supplied via a connecting pipe 7 having a filtration filter 6 into the anode chamber by the working of a pump 8, and the trivalent Ir ions are oxidized into tetravalent Ir ions and these tetravalent Ir ions are recovered via a drawing-out pipe 10. By this method, Ir can be efficiently recovered.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides a method and apparatus for purifying iridium by electrolysis, particularly for removing precious metal impurities from an iridium solution containing trace amounts of other precious metal impurities and for purifying iridium. The present invention relates to a method and apparatus for purifying iridium to obtain it as a tetravalent iridium ion that is easily converted into other compounds.

(Prior art and its problems) Iridium is usually contaminated with noble metals such as gold, silver, platinum, palladium, rhodium, and ruthenium as impurities. Separation of these precious metals and iridium has been carried out by chemical precipitation methods and solvent extraction methods, but in each method, the operations are complicated and diverse, requiring a lot of labor and time.

It has been discovered that iridium can be purified by electrolyzing a portion of an iridium solution with a diaphragm to remove impurities on the cathode. However, in this method, the noble metal electrodeposited on the cathode is redissolved by the chlorine gas and oxygen gas generated from the anode side and mixed in, making the removal of trace impurities (less than a few ppm of impurities in the iridium solution) inefficient. It has disadvantages such as reduced purity and increased purification time.

In addition, the iridium purified in this way is usually converted into an iridium compound and used for other purposes, but the iridium obtained by purification by diaphragm electrolysis is a trivalent ion, and the trivalent iridium ion is converted into a tetravalent iridium ion. Compared to iridium ions, it is difficult to convert them into compounds, and the trivalent iridium ions obtained by diaphragm electrolysis cannot be provided for other uses after being oxidized to tetravalent iridium ions through a separate oxidation process. many.

However, installing an oxidation device in addition to the electrolytic device not only increases the number of steps but also increases the installation area and labor of the device. There is a need for a method for refining and recovering it.

(Object of the invention) The present invention solves the above-mentioned drawbacks, and provides an iridium purification method and a purification apparatus that can electrolytically purify iridium containing noble metal impurities and purify and recover it as tetravalent iridium ions in the same electrolytic cell. With the goal.

(Means for Solving the Problems) The present invention provides, firstly, a method for purifying an iridium solution containing chloride ions by diaphragm electrolysis, in which an iridium solution containing noble metal impurities is supplied to a cathode chamber of an electrolytic cell. electrolysis to deposit the noble metal impurities on the cathode and convert the iridium into trivalent iridium ions, supply the iridium solution from which the electrodeposited noble metal impurities have been removed by filtration to the anode chamber, and The present invention is an iridium purification method characterized by oxidizing and recovering the trivalent iridium ions into tetravalent iridium ions in a chamber, and secondly, an iridium purification apparatus that can be used in the method.

The present invention will be explained in detail below.

In electrolytic refining of iridium that contains the other noble metals mentioned above as impurities, all noble metal ions other than iridium are reduced to a metal state (zero valence) in a chloride system (
For example, Pt''''-Pt') metal is deposited on the cathode, whereas iridium is only reduced from tetravalent to trivalent and is not deposited on the cathode. Purification is performed by improving the purity of iridium in the iridium solution.

Some of the precious metal impurities deposited on the cathode fall off from the cathode and float in the cathode chamber or are deposited on the bottom plate of the cathode chamber, but in the present invention, these precious metal impurities are deposited together with the iridium solution in the anode chamber. When the iridium solution is supplied to the anode chamber, the tetravalent iridium ions obtained in the anode chamber are mixed with other noble metal ions, so the electrodeposited noble metal impurities must be removed before the iridium solution is supplied to the anode chamber. The present invention employs filtration as the removal means, and the filtration operation may be performed in any form before the iridium solution is supplied to the anode chamber, but it is also possible to circulate the catholyte and filter it through the circulation path. It is desirable to install a filter to perform continuous or intermittent filtration, or to install a filtration filter in the supply route for the iridium solution from the cathode chamber to the anode chamber. In the former case, part of the catholyte circulation path is divided into a branch path that passes through the filtration filter and a branch path that does not pass through the filtration filter, and the circulating iridium solution is intermittently filtered through the filtration filter by operating a valve or the like. It is desirable to do so. This results in less contact with the iridium solution than in the case of continuous filtration, making it possible to more effectively prevent redissolution due to oxidation. Any type of filtration filter may be used. Cartridge type filters are suitable for the filtration of the present invention because they are easy to replace and the filtered precious metals can be easily recovered, but membrane filters are also suitable for filtration of small amounts. Since it is easy to use and can hold fine particles, it can be used appropriately depending on the purpose. In the latter case, a similar filter may be installed in the supply route.

The iridium solution to be purified containing trace amounts of precious metal impurities is added to the cathode chamber of the purification electrolytic cell used in the present invention, and an acid, base, or salt suitable for the necessary iridium compound is added to the anode chamber. Desirably, for example, hydrochloric acid or sodium chloride is added. Of course, the iridium ions may be recovered as tetravalent iridium ions in the anode chamber and converted into a predetermined compound outside the electrolytic cell. Note that the current can be used most effectively when the iridium ion concentration in the anode chamber and the iridium ion concentration in the cathode chamber are equal, so it is particularly preferable that the iridium concentrations in the two electrolytes at the start of electrolysis are approximately equal, and that the iridium concentration in the cathode chamber is equal. The concentration of the iridium solution is 0.01 to 6N in hydrochloric acid concentration (other acids or chloride salts may be added), and the iridium concentration is from looppm to 150 g/I! It is desirable that the iridium concentration in the anode chamber be approximately the same.

The electrode is not particularly limited, and any electrode made of any material that is resistant to the electrolyte used may be used.
For example, an insoluble platinum-titanium electrode can be used as the anode, and the platinum-titanium electrode, a stainless steel plate, a titanium plate, etc. can be used as the cathode.

It is preferable to use a cation exchange membrane as the diaphragm separating the two electrode chambers in order to prevent noble metal impurity ions in the cathode chamber from permeating into the anode chamber. ), Nafion (manufactured by DuPont), Neocepta (manufactured by Tokuyama Soda Co., Ltd.), etc.

When the electrolytic cell configured as described above is energized, noble metal impurities electrodeposited in the cathode chamber are removed by filtration, and an iridium solution containing trivalent iridium is supplied to the anode chamber, where the trivalent iridium ions are converted into tetravalent iridium ions. is recovered as iridium ions. In this case, it is sufficient that the amount of current applied is 1 to 2 times the stoichiometric amount, and if the amount is kept to about 1.2 times, gas generation from both electrodes is suppressed, and electrolytic refining can be performed efficiently.

(Examples) Next, examples of the present invention will be described, but these examples do not limit the present invention.

EXAMPLE An iridium solution was electrolytically purified using the electrolytic cell shown in the schematic diagram in FIG.

Selemion C, a strongly acidic cation exchange membrane, is used as the diaphragm l.
Using MV (manufactured by Asahi Glass Co., Ltd.), an insoluble electrode plated with platinum on a titanium substrate was used as the anode 2, and a stainless steel plate was used as the cathode 3. A 9.8 g/l iridium solution was added as the anolyte 4 to the anode chamber, and 1012 g/l of iridium solution containing the noble metal impurities shown in Table 1 was added to the cathode chamber as the catholyte 5. The anode chamber and the cathode chamber are placed in the center with a hole diameter of 0.
It is connected by a connecting pipe 7 having a filtration filter 6 which is a 2 μm membrane filter, and the electrolytic voltage is 5 V while the catholyte is supplied to the anode chamber at a constant rate by a pump 8.
, electrolytic refining was performed for 4.5 hours at a current of 3A. No generation of chlorine gas from the anode chamber side was observed during electrolysis.

After the electricity was stopped, the concentration of precious metals in the anolyte was measured.
Each concentration is as shown in Table 1, and all of the iridium obtained was a tetravalent iridium ion.

Comparative example anolyte was 0. An iridium solution was electrolytically purified in the same manner as in Example except that the catholyte was not supplied to the anolyte in place of IN hydrochloric acid. During electrolysis, a large amount of chlorine gas was observed to be generated from the anode chamber side. Table 1 shows the concentrations of each noble metal after the energization was stopped. In addition, since all of the obtained iridium was trivalent iridium ions, the iridium was oxidized to tetravalent iridium by sputtering in a separate step.

Reference Example Electrolytic refining was carried out under the same conditions as in Example 1, except that filtration was not performed when the liquid was passed from the cathode to the anode. Precious metals other than iridium deposited at the cathode were peeled off from the electrode, mixed into the anolyte, and redissolved at the anode, resulting in recontamination with impurities.

Table 1 shows the concentration of each noble metal in the anolyte after the energization was stopped.

Table 1 (Effects of the Invention) The present invention, when refining an iridium solution by diaphragm electrolysis, electrolyzes the iridium solution containing noble metal impurities in the cathode chamber of an electrolytic cell to electrodeposit the noble metal impurities on the cathode. The electrodeposited noble metal is filtered and removed before the iridium solution is supplied to the anode chamber, and the iridium reduced to trivalent ions in the cathode chamber is oxidized to tetravalent ions that are easily converted into other compounds in the anode chamber. I am trying to recover it.

Therefore, the present invention includes a step of electrodepositing noble metal impurities from iridium ions containing noble metal impurities and removing them by filtration in a single electrolytic cell, and a step of electrodepositing the precious metal impurities from iridium ions containing noble metal impurities and removing them by filtration, and removing the iridium ions reduced to trivalent ions by the electrodeposition operation. A step of oxidizing and recovering as tetravalent ions can be performed. Compared to the case where the electrodeposition process and iridium oxidation process are performed in separate electrolytic tanks, not only the operational effort is reduced by almost half, but also the power consumption is reduced by almost half, making it extremely efficient. A method and apparatus for purifying iridium.

Furthermore, depending on the electrolysis conditions, gas generation can be completely eliminated, making this an innovative method and device with excellent workability.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an electrolytic cell used in an example of the present invention.

Claims (2)

[Claims] (1) In a method of purifying an iridium solution containing chloride ions by diaphragm electrolysis, an iridium solution containing noble metal impurities is supplied to the cathode chamber of an electrolytic cell, electrolysis is performed, and the noble metal impurities are electrodeposited on the cathode. and converting the iridium into trivalent iridium ions, supplying the iridium solution from which the electrodeposited noble metal impurities were removed by filtration to an anode chamber, and converting the trivalent iridium ions into tetravalent iridium ions in the anode chamber. A method for purifying iridium, characterized by recovering it by oxidizing it. (2) In an apparatus for purifying an iridium solution containing chloride ions by diaphragm electrolysis, a cathode chamber of an electrolytic cell is supplied with an iridium solution containing noble metal impurities, and the noble metal impurities electrodeposited in the cathode chamber are filtered. filtration means for removing the noble metal impurities, and an anode chamber supplied with an iridium solution from which the noble metal impurities have been removed, the noble metal impurities are electrodeposited on the cathode in the cathode chamber by electrolysis, and the iridium is trivalently deposited in the cathode chamber. The trivalent iridium ions in the iridium solution, from which the electrodeposited precious metal impurities have been removed by the filtration means, are converted into iridium ions of
An iridium purification device characterized by oxidizing and recovering iridium ions.