JP5021331B2 - Method for recovering platinum group metals from waste - Google Patents

Description

  The present invention relates to a method for recovering platinum group metals in a reusable state from wastes such as scraps containing platinum group metals such as ruthenium and iridium.

  Since platinum group metals such as ruthenium and iridium have high heat resistance and high corrosion resistance, they have excellent electrical properties in addition to structural materials such as crucibles for melting various inorganic materials, and are also used as electrode materials for electronic parts. in use.

On the other hand, since these platinum group metals are rare and expensive metals, they require efficient use and consumption without waste, and development of recycling technology is required. Various methods for recovering ruthenium and the like from solid-state waste containing platinum group metals are known. Among them, the applicant of the present application discloses the following recycling method using a processing technique using molten salt.
Japanese Patent Laid-Open No. 2004-99975

  According to the present applicant's platinum group metal recycling method from waste, a waste containing a platinum group metal (ruthenium, iridium) is dissolved in a molten salt composed of an alkali metal chloride containing at least a cesium salt, The platinum group metal in the waste is cesium chloride iridium chloride (ruthenium chloride cesium), which is sparingly soluble in water. The molten salt after the reaction is mixed with water, and cesium chloride iridium (ruthenate chloride). A step of separating and recovering cesium). This technique using the molten salt can recover the platinum group metal in a relatively small number of steps.

  By the way, wastes containing platinum group metals contain various elements according to their usage history. And in order to collect | recover platinum group metals from various wastes, it is preferable to apply the process according to the impurity element contained in it.

  From this point of view, the above-described conventional recycling method is suitable for recycling wastes having metal elements such as Fe, Ni, and Co as impurities. These metals easily form chlorides in the molten salt, and these chlorides are water-soluble. Therefore, mixing the molten salt after the reaction with water facilitates the recovery of the platinum group metal compound. It is because it can isolate | separate into.

  However, the waste does not contain only the above metals. This is naturally predicted from the fact that platinum group metals are used as crucible materials and electrode materials for electronic parts, and waste having such a use history often contains semimetals such as C and Si. . C and Si hardly generate chloride even in the molten salt, and separation and recovery are difficult by the above method.

  The present invention has been made under the background as described above, and it has been difficult to remove the platinum group metal from the waste containing platinum group metal such as iridium and ruthenium by the conventional method. It is an object of the present invention to provide a material that can be treated as waste containing impurities such as C, Si, or other semi-metal or an element that is difficult to produce a water-soluble chloride.

  The present invention for solving the above-mentioned problems is a method for recovering the platinum group metal from waste containing at least one platinum group metal of iridium, ruthenium, rhodium, palladium, osmium, and a molten salt comprising sodium chloride. In or in a molten salt consisting of sodium chloride and potassium chloride, after reacting the platinum group metal and chlorine contained in the waste to produce a platinum group metal chloride that is readily soluble in water, The platinum group metal recovery method includes a step of mixing the molten salt after the reaction with water and solid-liquid separation to obtain an aqueous solution of the platinum group metal.

  In the present invention, the platinum group metal in the waste is made into a water-soluble chloride, contrary to the conventional recovery method in which the platinum group metal is made into a hardly soluble chloride in the molten salt. Then, by mixing the molten salt after the reaction with water, insoluble impurities such as C and Si are separated in a solid state, and the platinum group metal for recovery is recovered in an aqueous solution state. Therefore, in this invention, the alkali metal salt which does not contain a cesium is applied as a structure of the molten salt used as a waste solvent. This is because it is difficult to separate the platinum group metal from insoluble impurities such as C and Si because cesium reacts with the platinum group metal in the molten salt to form a hardly soluble cesium salt from the examination of the prior art. Because it does.

  Hereinafter, the present invention will be described in detail. In the present invention, first, a molten salt is used as a solvent, and a waste to be treated is dissolved in the solvent while reacting with chlorine. The waste to be treated is scrap or the like containing a platinum group metal to be collected, but the content is not particularly limited. However, as will be described later, the amount of platinum group metal in the molten salt affects the reaction rate.

  In the reaction step with chlorine using a molten salt, the molten salt serving as a solvent is a molten salt composed of sodium chloride or a molten salt obtained by mixing two alkali metal chlorides of potassium chloride and sodium chloride. As the molten salt described in Patent Document 1, K-Na-Cs mixed salt containing cesium chloride in addition to potassium chloride and sodium chloride is applied. As described above, cesium is a platinum group metal. In the present invention, the application of a cesium salt is excluded because it produces a hardly soluble chloride.

  Potassium and sodium constituting the molten salt each generate a different type of chloride for the platinum group metal to be treated. Sodium produces sodium chloride (sodium chloroiridate, sodium chloride ruthenate, etc.) and potassium produces potassium chloride (potassium iridate, potassium ruthenate, etc.). Platinum group metal chlorides containing each alkali metal have different formation rates (reaction rates with platinum group noble metals) and solubility in water. According to the present inventors, as for the production rate, potassium chloride has a higher production rate than sodium chloride, while sodium chloride has a higher solubility than potassium salt in terms of water solubility.

  In particular, when a molten salt obtained by mixing sodium chloride and potassium chloride is applied, the composition affects the dissolution rate of the platinum group metal in the waste and the water solubility of the molten salt after the reaction. For example, when the proportion of the potassium salt is increased, the dissolution rate of the platinum group metal can be increased, but the solubility of the molten salt (the platinum group metal salt therein) after the reaction is decreased. In this regard, from the viewpoint of work efficiency (dissolution rate) and platinum group metal recovery rate (solubility), the composition of the molten salt preferably has a sodium chloride concentration of 50 mol% or more, preferably 75 to 90 mol%. A molten salt composed of sodium chloride and 10 to 25 mol% of potassium chloride is more preferable.

  In molten salt with the same composition, the reaction rate of the platinum group metal also varies depending on the amount of platinum group metal in the molten salt (the amount of platinum group metal in the waste). Increases speed. This is considered to accompany an increase in the reaction area. Therefore, the molar amount of the platinum group metal to be reacted is preferably 15 to 80 mol%, particularly preferably 30 to 60 mol%, based on the molar amount of the molten salt serving as a solvent. If the platinum group metal is less than this range, the reaction rate decreases, and it takes time to dissolve a sufficiently economical amount of the platinum group metal. This is because the platinum group metal that does not contribute to the reaction is excessively held, which is economically disadvantageous. The preferred range here is the weight of the platinum group metal, not the total weight of the waste. Therefore, it is preferable to analyze the platinum group metal concentration by ICP or the like and make the concentration known for wastes whose platinum group metal concentration is not easily estimated.

  The temperature for reacting the platinum group metal salt in the molten salt needs to be set on the premise that the mixed salt of sodium chloride and potassium chloride constituting the molten salt is melted. In this regard, the melting point of sodium chloride is about 800 ° C., the melting point of potassium chloride is about 776 ° C., and the ratio of both is equal (50%: 50%), the melting point of the mixed salt is about 658 ° C. If it deviates from this composition, the melting point increases. According to the present inventors, the temperature of the molten salt is preferably 750 to 850 ° C. The reason why such a temperature range is a preferable range is that sufficient fluidity of the molten salt is obtained in this temperature range, and when chlorine gas is blown, the stirring effect by the bubbles can be expected. Further, the reaction rate in the molten salt and the dissolution rate of the produced platinum group metal chloride are sufficient.

  In the present invention, it is preferable to dissolve as much (high concentration) platinum group metal as possible in the molten salt. In the present invention, in the subsequent treatment, the molten salt is mixed with water to obtain a platinum group metal salt aqueous solution. To recover the platinum group metal efficiently, the concentration of the platinum group metal salt aqueous solution, that is, This is because it is preferable that the amount of platinum group metal in the molten salt is large. The target value of the platinum group metal concentration in the molten salt after this reaction is 5 to 30 mol% on the basis of the total molar amount of the alkali metal molten salt at the time of charging and the dissolved platinum group metal molar amount. It is preferable to set. If it is less than 5%, the recovery efficiency is deteriorated and the processing cost is lowered. In addition, it is theoretically difficult to produce a molten salt containing more than 30% of a platinum group metal, and the dissolution rate of the platinum group metal in the molten salt is lowered, which is economically disadvantageous.

  The reaction time for this target value is 8 to 40 hours, preferably 10 to 35 hours, more preferably 14 to 24 hours.

  In the present invention, since the platinum group metal and chlorine are reacted in the molten salt, it is necessary to supply chlorine to the molten salt during the reaction. This supply of chlorine is preferably by blowing chlorine gas into the molten salt. The blowing of chlorine gas is preferably performed so that the chlorine gas is in direct contact with the waste. Specifically, it is preferable to install a nozzle for supplying chlorine gas so that the tip thereof is located in the vicinity of the waste surface. The supply amount of chlorine gas is preferably 0.5 to 10 L / min.

  By the reaction of the platinum group metal and chlorine in the molten salt described above, a water-soluble platinum group metal salt (potassium chloroiridate, sodium ruthenate, etc.) is generated in the molten salt. The molten salt is cooled and mixed with water, whereby the platinum group metal salt becomes an aqueous solution, while insoluble impurities such as C and Si are dispersed and precipitated as a solid in the aqueous solution. The solid-liquid separation of the aqueous solution is preferably by filtration.

  In mixing the molten salt and water, it is preferable to adjust the amount of water so that the platinum group metal concentration in the solution is 10 to 100 g / L, preferably 20 to 80 g / L. This is because if the platinum group metal concentration is too low, the recovery efficiency is deteriorated, and if it is too high, the occurrence of precipitation (dissolved residue) is concerned. As described above, the amount of water mixed in the aqueous solution is based on the platinum group noble metal concentration of the aqueous solution after production as a standard / target, so the amount of platinum group metal in the molten salt before the aqueous solution, or It is preferable to measure the concentration.

  The platinum group metal salt (sodium chloride iridate, potassium chloride iridate, etc.) in the aqueous solution obtained by the above steps is useful in itself. By performing ion exchange, electrolysis, concentration, etc., this aqueous solution can be made into a higher purity platinum group metal salt solution or platinum group metal salt crystal and can be used as it is.

  It is also possible to recover the platinum group metal from this aqueous solution in the form of a pure metal. As a pure metal recovery method, it is preferable to reduce a platinum group metal salt obtained by concentrating an aqueous solution in a hydrogen atmosphere. The temperature condition for this hydrogen reduction is preferably in the range of 300 to 650 ° C. The platinum group metal after hydrogen reduction can be further purified by washing with pure water to remove sodium chloride and potassium chloride, and hydrogen reduction (secondary hydrogen reduction treatment) again. .

  As described above, according to the present invention, platinum group metals can be efficiently recovered from wastes such as scraps containing platinum group metals such as ruthenium and iridium. The method according to the present invention makes it possible to recycle wastes containing metalloids such as C and Si as impurities. According to the recycling system centering on the present invention, it is possible to effectively use resources and reduce the cost of products using platinum group metals.

  The present invention is particularly useful in the recovery of ruthenium and iridium. As for platinum, when a mixed salt of sodium chloride and potassium chloride is used, it is difficult to recover platinum by reacting it in the molten salt and dissolving it in an aqueous solution. This is because platinum produces a chloride that is difficult to dissolve in the molten salt in the reaction with potassium chloride. However, this is effective as a technique for separating platinum from waste containing platinum and other platinum group metals (ruthenium, iridium, etc.). In particular, since various platinum alloys (platinum-iridium alloy, platinum-rhodium alloy, etc.) are often used in recent years, iridium and the like are recovered while separating platinum from waste containing these alloys. In some cases, the present invention is useful.

First Embodiment : Here, molten iridium salt treatment, aqueous solution, and hydrogen reduction were performed, and metal iridium was recovered from waste.

A: Treatment with Molten Salt FIG. 1 is a schematic view of the molten salt treatment apparatus used in this embodiment. This molten salt treatment apparatus includes a graphite crucible 10 serving as a container for the molten salt 100, a chamber with a lid for accommodating the crucible 10 (the main body 21 is made of quartz, and the lid 22 is made of Teflon (registered trademark)), and the crucible is covered with a lid. A plurality of shielding plates 30 (made of graphite, quartz, Pyrex (registered trademark)) and a nozzle 40 for introducing chlorine are provided. The tip of the nozzle 40 is close to the surface of the waste 50 in the crucible 10 so that chlorine gas is in direct contact with the waste 50.

  Using this molten salt processing apparatus 1, iridium was recovered and purified. First, 1989 g of sodium chloride as a solvent salt and 2537 g of potassium chloride were placed in a quartz container. Furthermore, carbon mixed scrap having an iridium content of 2001 g was added.

  The mixed salt was heated to 820 ° C. and melted. Next, 100% chlorine gas was blown into the molten salt at a flow rate of 2 L / min and reacted for 14.2 hours (851 minutes). A part of the molten salt after the reaction was collected and subjected to ICP analysis. As a result, the iridium concentration in the molten salt was 26.5% by weight.

  Table 1 shows the results of the treatment with the molten salt with the composition changed in the same process as above. Here, the result of the process by the molten salt which consists only of sodium chloride is also shown as a comparison.

  The following points can be understood from the results of the examples. First, regarding the composition of the molten salt used as the solvent, the reaction rate increases as the potassium chloride concentration of the solvent salt increases from the comparison between Example 1 and Example 2 in which the Ir input amount and the reaction time are approximated. I understand that In addition, from the comparison between Example 2 and Example 4 in which the reaction time is the same as the molten salt composition, the reaction rate tends to increase as the amount of iridium added increases. It should be noted that iridium can be recovered even using a molten salt consisting of only sodium chloride (Example 6), but since the reaction rate is lower than in the case of other compositions, only the reaction rate should be emphasized. In other words, it is more preferable to add and mix potassium chloride to the solvent salt.

B: Generation of platinum group metal salt aqueous solution Next, the molten salts after completion of the reactions of Examples 1, 3, 5, and 6 were mixed with water, and iridium was recovered from the molten salt in the form of an iridium salt aqueous solution. Here, based on the iridium density | concentration in molten salt, the quantity of water was changed and mixed so that the iridium density | concentration in aqueous solution might be 20 to 80%. And the aqueous solution after mixing water was analyzed, and while measuring the density | concentrations, such as iridium, the presence or absence of the dissolution residue was examined. Table 2 shows the results.

  Basically, a high-purity iridium salt aqueous solution could be produced regardless of the target value of the iridium concentration in the solution. However, as a general tendency, when the target value becomes high, a dissolved residue is generated, and a deviation from the actual concentration in the aqueous solution tends to increase. In this regard, Example 1 with 50% potassium chloride showed favorable results (dissolution rate, etc.) at the stage of molten salt treatment, but there were relatively many dissolution residues at the stage of aqueous solution, The difference between the target concentration of the aqueous solution and the actual concentration tends to increase. On the other hand, in the case where the molten salt consisting only of sodium chloride of Example 6 is applied, there is little difference between the dissolved residue and the concentration value. As described above, this is considered to be due to the fact that potassium chloride has a higher production rate of iridium salt than sodium chloride, but its solubility in water is low.

Second Embodiment : Here, the applicability of the method according to the present invention to the separation operation of platinum in waste was examined. In Examples 5 and 6 of the first embodiment, Table 3 shows the results when the platinum concentration in the aqueous solution after the aqueous solution was analyzed.

  From Table 3, it can be seen that in Example 5, the target iridium concentration was 80 g / L, so that the platinum concentration in the solution could be made below the detection limit and platinum could be separated. It is predicted that when the target concentration of the solution is increased, dissolution residues are more likely to occur, but platinum tends to remain in the dissolution residue rather than iridium, so that platinum entrainment in the solution was suppressed. Is done.

  In Example 6 (the molten salt composition is 100% sodium chloride), the platinum concentration in the solution having a target iridium concentration of 20 g / L is below the detection limit, rather than the platinum concentration being low. This is probably due to the fact that the total weight of noble metals including iridium was too small. This is predicted from the fact that in Example 6, the platinum concentration (platinum weight / (iridium weight + platinum weight)) hardly changed even when the target iridium concentration was increased. From the comparison between Example 5 and Example 6, in this embodiment, when the subject matter is to completely separate platinum, it is preferable to mix potassium chloride as the molten salt composition. It is done.

  Next, in order to confirm this examination result, a scrap metal containing 5.0% platinum was dissolved in a molten salt and made into an aqueous solution using the same apparatus and conditions as in the first embodiment.

  Also in Example 7, the platinum concentration in the iridium salt aqueous solution was extremely low, and it was confirmed that the separation from platinum can be efficiently performed simultaneously with the recovery of iridium.

Third Embodiment : Here, treatment with molten salt was performed on scrap containing ruthenium. Using the same molten salt treatment apparatus as in the first embodiment, the treatment was performed by changing the composition of the molten salt. The treatment conditions here were such that the molten salt temperature was 820 ° C. and chlorine was blown at a flow rate of 2 L / min. The scrap to be processed is ruthenium scrap containing 3% carbon. Table 5 shows the results.

  As a result, it was confirmed that ruthenium can be recovered even for scraps containing ruthenium. Also in this embodiment, Example 8 containing a relatively large amount (45 mol%) of potassium chloride was excellent in dissolution rate and the like.

  The molten salt in which ruthenium is dissolved in Example 9 is made into an aqueous solution (the target Ru concentration at the time of making the aqueous solution is 50 g / L), and the obtained ruthenium salt aqueous solution is concentrated with an evaporator to obtain a ruthenium salt. Was reduced in a hydrogen atmosphere. In this reduction treatment, the ruthenium salt was first heated at 600 ° C. for 6 hours as a primary treatment. Then, the obtained metal ruthenium was washed with pure water and subjected to secondary hydrogen reduction treatment by heating at 700 ° C. for 6 hours. The purity of the ruthenium powder after the treatment was as high as 99.97%.

The figure which shows the structure of the molten salt processing apparatus used by this embodiment.

Claims (4)

A method of recovering the platinum group metal from waste containing at least one platinum group metal of iridium, ruthenium, rhodium, palladium, and osmium,
In a molten salt composed of 75 to 90 mol% sodium chloride and 10 to 25 mol% potassium chloride, the platinum group metal and chlorine contained in the waste are reacted, and the platinum group metal is readily soluble in water. After producing
A method for recovering a platinum group metal comprising a step of mixing the molten salt after the reaction with water and solid-liquid separation to obtain an aqueous solution of the platinum group metal. The method for recovering a platinum group metal according to claim 1 , wherein the temperature of the molten salt is 750 to 850 ° C. The method for recovering a platinum group metal according to claim 1 or 2 , wherein chlorine is supplied as chlorine gas so that the chlorine gas and waste are in direct contact with each other. The method for recovering a platinum group metal according to any one of claims 1 to 3 , wherein the recovered filtrate is concentrated and dried, and then reduced to hydrogen to form a platinum group metal.

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