JP4783310B2 - Recovery and purification of platinum group metals by molten salt electrolysis - Google Patents

Description

  The present invention relates to a method for recovering a platinum group metal from waste containing a platinum group metal such as ruthenium and iridium by a molten salt electrolysis method.

  Platinum group noble metals such as ruthenium and iridium (hereinafter sometimes referred to as noble metals) have high heat resistance and high corrosion resistance, so they have electrical properties in addition to structural materials such as crucibles for melting various inorganic materials. In addition, it is also used as an electrode material for electronic parts. On the other hand, since these noble metals are rare and expensive, they require efficient use and consumption without waste, and the development of recycling technology is required.

The applicant of the present application has a processing technique using a molten salt in a technique for recovering and purifying precious metals, and discloses, for example, the following method.
Japanese Patent Laid-Open No. 2004-99975

  The method of recovering platinum group metals from waste by the applicant of the present application is to dissolve a waste containing a noble metal such as iridium in a molten chloride salt containing a cesium salt, and to convert the noble metal in the waste into a cesium chloride iridate. And a step of separating and recovering cesium chloride iridate by mixing the molten salt after reaction and water. This technique using the molten salt can recover the platinum group metal in a relatively small number of steps.

In addition to the technique for recovering the noble metal in the chloride molten salt in the form of a compound as described above, the applicant of the present application also discloses a method for electrolyzing the chloride molten salt to precipitate the noble metal.
JP 2001-089890 A JP 2001-152381 A

  In such precious metal recovery by the molten salt electrolysis method, the waste to be treated is used as an anode, an insoluble electrode such as carbon is used as a cathode, and these are used as chloride molten salts (sodium chloride, potassium chloride, cesium chloride, etc.). A single salt or mixed salt of an alkali metal chloride is often used). As a result, the noble metal in the anode is eluted into the molten salt, and is deposited on the surface of the cathode and can be recovered. Such a molten salt electrolysis method has an advantage that the precious metal can be directly recovered and its purity is high.

  By the way, the collection efficiency of the noble metal using the molten salt varies depending on the content of the noble metal dissolved in the molten salt, that is, the amount of the object to be treated containing the noble metal dissolved in the molten salt.

  However, the dissolution rate of the noble metal in the object to be treated can be adjusted to some extent by the temperature of the molten salt, but the range is limited. Moreover, even if it can be adjusted, there is a limit to the dissolution rate, and a method for more efficient dissolution under the same conditions is required.

  The present invention has been made under the background as described above, and in the method for recovering a noble metal using a molten chloride salt, the dissolution rate of the noble metal from the object to be processed is increased, thereby efficiently recovering the noble metal. It is an object of the present invention to provide a method that can be carried out in the future and an apparatus therefor.

  The present invention for solving the above-mentioned problems is a recovery of a platinum group metal including a dissolving step of immersing a treatment object containing a platinum group metal in a chloride molten salt and dissolving the platinum group metal in the chloride molten salt. -It is a refinement | purification method, Comprising: The said melt | dissolution process is a collection | recovery / refinement | purification method of the platinum group metal which is electrolyzed while blowing chlorine in the said chloride molten salt.

  The dissolution of the noble metal in the molten salt is based on the ionization of the noble metal and the reaction between the generated noble metal ion and chlorine ion to form a chloride. Since these reactions are in an equilibrium relationship, it is necessary to increase the concentration of noble metal ions and increase the concentration of chlorine ions in order to promote dissolution of the noble metal. In the present invention, the equilibrium relationship is shifted to the chloride production side by increasing the concentration of noble metal ions and chlorine ions by electrolysis of molten salt and increasing the chlorine ion source by blowing in chlorine gas.

  Hereinafter, the present invention will be described in detail. In the present invention, the object to be treated containing a noble metal acts as an anode, but the content of the noble metal is not particularly limited. The shape is not particularly limited as long as it can be energized as an anode. Moreover, you may use what once melted and cast the scrap containing a noble metal. The cathode is preferably an insoluble electrode and is preferably made of carbon. Note that platinum, iridium, ruthenium, rhodium, and osmium can be recovered and purified as belonging to the platinum group metal that is the subject of the present invention.

  The composition of the molten chloride salt serving as the electrolyte is preferably an alkali metal chloride molten salt, and particularly preferably includes at least one of sodium chloride, potassium chloride, and cesium chloride from the viewpoint of handleability. A mixed salt obtained by mixing these can also be applied, and the melting point for melting the mixed salt can be adjusted by adjusting the mixing ratio. A preferable composition when three kinds of mixed salts are used is sodium chloride: potassium chloride: cesium chloride = 25 to 35 mol%: 20 to 30 mol%: 40 to 50 mol%. The temperature of the molten salt is preferably 490 to 540 ° C.

The conditions in the noble metal dissolution process, first, as the electrolysis conditions, 5 to 40 mA / cm ² cathode current density, preferably, preferably with 20~30mA / cm ^2. The chlorine gas blown into the molten salt is preferably one having a purity of almost 100%. The amount of chlorine gas blown depends on the electrode area and the cathode current density, and it is preferable to blow chlorine gas in an amount equivalent to or more than the equivalent amount of the electrochemical equivalent converted on the basis of the electrode area and the cathode current density. This is because if chlorine gas exceeding twice the electrochemical equivalent is blown, the partial pressure of chlorine in the reaction vessel rises, and the corrosion of the reaction vessel may be accelerated. Moreover, even if chlorine gas less than the electrochemical equivalent is blown, dissolution proceeds, but the speed is slow. At this time, even if the cathode current density is increased, noble metal is precipitated on the cathode side, and an increase in dissolution rate cannot be expected. Therefore, it is preferable to blow in chlorine gas having an electrical equivalent or more.

  In the melting step, it is preferable that the time for performing chlorine blowing and electrolysis under the above conditions is 8 to 24 hours. In consideration of the subsequent recovery efficiency of the precious metal, it is preferable to carry out the dissolving step until the precious metal concentration in the molten salt becomes 0.1 to 0.4 mol% with respect to the molten salt.

  In the present invention, after the noble metal is dissolved in the molten salt, the blowing of chlorine is stopped and the noble metal is recovered from the molten salt. For this recovery step, the molten salt after the dissolution step may be dissolved and recovered in the form of a noble metal compound, but preferably the molten salt after the dissolution step is electrolyzed to precipitate the noble metal. . This is because the electrolysis apparatus used in the dissolution process can be used as it is, and the recovery process can be promptly shifted from the dissolution process. Further, by performing electrolytic deposition, it is possible to recover a high-purity noble metal, and it becomes possible to purify simultaneously with the recovery.

The electrolytic conditions in the recovery step by this electrolytic deposition are 10 to 50 mA / cm ² , preferably 30 to 50 mA / cm ² . The reason why the current density is higher than the current density at the time of dissolving the noble metal is that the electrolysis at this stage is aimed at promoting the precipitation.

  The noble metal recovered by electrolytic deposition is deposited on the cathode in the melting step. The deposited metal is removed from the cathode and then recovered by washing or the like. You may perform a melt | dissolution process etc. as needed. The noble metal deposited by the molten salt electrolysis method has a high purity, and can be used as it is as a product (for example, a sputtering target) by washing and molding.

  As described above, according to the present invention, the noble metal in the processing object such as scrap containing noble metal such as ruthenium and iridium can be dissolved in the molten salt at a high dissolution rate. This makes it possible to efficiently recover and purify noble metals.

  In addition, high-purity noble metal can be efficiently recovered by electrolyzing the molten salt in which the noble metal is dissolved as described above. By combining such a dissolution step and electrolytic deposition, a product can be manufactured from waste in a small number of steps. ADVANTAGE OF THE INVENTION According to this invention, while aiming at the effective use of resources, the cost reduction of the product using a noble metal can be aimed at.

  Preferred embodiments of the present invention are shown below. In the present embodiment, a predetermined molten salt electrolysis apparatus was used, and a waste containing noble metal was treated as an object to be treated, and the noble metal was recovered through a dissolution step and a precipitation step.

  FIG. 1 shows the configuration of the molten salt electrolysis apparatus used in this embodiment. The molten salt electrolysis apparatus 1 includes a graphite inner container 20 that houses the molten salt 10, a graphite container 30 that houses the inner container 20, and a stainless outer container 40 that houses the container 30. The inner container 20 is hermetically sealed with a graphite shielding plate 21, and further, a chlorine introduction pipe 50 and an exhaust pipe 51 that penetrate the outer container 40 and the shielding plate 21 are provided. An anode 60 is laid on the bottom of the inner container 20, and a cathode 61 is immersed so as to face the anode 60.

  The outer container 40 is provided with an inert gas introduction pipe 52 in order to fill the outer container with an inert gas (in this embodiment, argon is used). Since chlorine is handled in the present invention, there is a concern about corrosion of the apparatus. In the present invention, the inner container 20 that holds the molten salt that cannot be contacted with chlorine is made of graphite, and the inner container 20 is sealed with a shielding plate 21. And since the outer container 40 holding the whole apparatus requires strength and toughness, it is made of stainless steel, and the outer container is filled with an inert gas to suppress corrosion. The cathode 61 may be driven up and down for adjusting the distance between the electrodes, and may be rotatable in order to make the film thickness of the precipitate during electrolysis uniform.

  As the chloride molten salt, a mixed molten salt having the following composition was used. A used ruthenium target was used as the anode.

Sodium chloride 3140 g (53.7 mol)
3250 g (43.6 mol) of potassium chloride
Cesium chloride 13690g (81.3mol)
Temperature 520 ° C

  In the melting step in the present embodiment, first, 100% chlorine gas was blown into the molten salt at 0.2 L / min without performing electrolysis. Meanwhile, argon gas is injected into the outer container at 5 L / min. During this time, the ruthenium concentration in the molten salt was measured at predetermined intervals.

Then, when the chlorine blowing amount reached about 200 L, the molten salt was electrolyzed while continuing the chlorine blowing as it was. The electrolysis conditions were an electrode area of 1000 cm ² and a cathode current density of 20 mA / cm ² (20 A).

  FIG. 2 shows the change in the ruthenium concentration in the molten salt measured in the melting step as described above. As can be seen from FIG. 2, the ruthenium concentration in the molten salt with only chlorine blowing increased gradually, but a significant increase in the ruthenium concentration was observed by electrolysis. This is because the dissolution of ruthenium is accelerated by the action of both chlorine blowing and electrolysis.

Next, about the molten salt which passed through the melt | dissolution process, chlorine blowing was stopped, it electrolyzed and ruthenium was deposited. The electrolysis conditions at this time were a current density of 30 mA / cm ² and the deposition time was 240 hours. After electrolytic deposition, the deposit on the cathode was pickled with hydrochloric acid and separated from the graphite electrode. As a result, 9028 g of ruthenium was obtained, and its purity was measured and found to be 99.99% or more.

The outline of the molten salt electrolysis apparatus used in this embodiment. The figure which shows the change of the ruthenium density | concentration in molten salt in a melt | dissolution process.

Claims (3)

A method for recovering and purifying a platinum group metal comprising a dissolving step of immersing a treatment object containing a platinum group metal in a chloride molten salt and dissolving the platinum group metal in the chloride molten salt,
The method for recovering and purifying a platinum group metal, wherein the dissolving step is to perform electrolysis while blowing chlorine into the chloride molten salt. The method for recovering and purifying a platinum group metal according to claim 1, further comprising a precipitation step of precipitating the platinum group metal in the molten chloride salt by stopping the blowing of chlorine after the dissolving step and electrolyzing the molten chloride salt. A graphite inner vessel for containing the molten salt, and a stainless outer vessel for containing the inner vessel, a chlorine introduction pipe provided through the outer vessel and supplying chlorine to the molten salt, and An exhaust pipe provided through the outer container and exhausting from the inner container;
Furthermore, a molten salt electrolysis apparatus comprising: an inert gas introduction pipe provided through the outer container and filling the space between the inner container outer wall and the inner container outer wall with an inert gas.

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