JP5556681B2 - Method for producing readily soluble sponge platinum - Google Patents

Description

  The present invention relates to a method for producing platinum powder, and more particularly to a method for producing platinum powder in which a dissolution residue is not substantially generated when dissolved in aqua regia.

Conventionally, as a method for producing platinum powder (hereinafter referred to as sponge platinum), ammonium chloride is added to an acidic platinum solution by adding ammonium chloride (also referred to as platinum cake: (NH ₄ ) ₂ PtCl ₆ ). This is dissolved by adding an alkali such as sodium hydroxide (caustic soda), and a reducing agent such as hydrazine is added to this solution to precipitate platinum, filtered and washed, and then dried to obtain sponge platinum. It has been done.

  Sponge platinum produced by the above wet method is often obtained as a fine powder having a particle size of approximately 10 μm, and the wet sponge platinum is washed and dried to produce a product. Further, when a paste is produced by mixing sponge platinum with other powders, those having a particle size of about 10 μm are preferred because they have good mixing properties. Furthermore, sponge platinum having a particle size of about 10 μm is featured in that it can be easily handled as an intermediate product for producing a compound containing platinum by dissolving in aqua regia. For this reason, the particle size of sponge platinum is often about 10 μm.

  However, the surface of fine powder particles of about 10 μm is easily oxidized. Therefore, even in the case of sponge platinum having a particle size of about 10 μm obtained by the above conventional method, it is substantially difficult to completely prevent the formation of oxide on the surface. As a result, when the surface of the sponge platinum is oxidized, it is difficult to dissolve when the aqua regia is added and dissolved, and a dissolution residue is generated. As a specific example, in the case of sponge platinum having a particle size of about 10 μm, it is known that approximately 2 to 10% by weight of the sponge platinum exists in an oxide state that does not dissolve in aqua regia.

  When a dissolved residue is generated when sponge platinum is dissolved in aqua regia, it is necessary to separate the dissolved residue from the solution, and it is necessary to repeatedly process the dissolved residue again. For this reason, it takes a lot of time and reprocessing the dissolved residue, resulting in an increase in cost and a decrease in productivity.

  In order to suppress the generation of dissolution residues, it is desirable to suppress the generation of oxide in sponge platinum as much as possible and return the generated oxide to metal. For example, in Patent Document 1, as a technique for reducing the dissolution residue of platinum, sponge platinum is coarsely pulverized to 2 mm or less in advance, and is placed in a reduction furnace and maintained at a temperature of 600 to 800 ° C. while flowing hydrogen gas. A method for performing deoxygenation is described. According to this method, since the oxide in the sponge platinum is removed, the dissolution rate when dissolved in aqua regia is improved, and the dissolution residue can be reduced.

  However, operating in a reducing furnace using hydrogen gas at a high temperature as in Patent Document 1 has a risk of explosion of hydrogen gas, so use of explosion-proof equipment and installation of alarm devices and shut-off devices In addition, strict safety measures such as ventilation are required. For this reason, capital investment and management costs increase, and the cost of hydrogen gas itself cannot be ignored. Therefore, it cannot be said that the method can be easily implemented industrially.

  In addition, when reduction using hydrogen is used for the treatment of metals that easily store hydrogen, such as platinum, the supplied hydrogen is stored in platinum metal, and it generates heat or ignites when it comes into contact with the atmosphere after the reaction is completed. Reoxidation may be promoted. For this reason, after the hydrogen reduction is completed, it is necessary to perform a process of releasing the hydrogen gas occluded in platinum by using a method such as depressurizing the inside of the furnace or replacing the furnace with an inert gas.

JP 2006-089808 A

  In view of the above-described problems in the conventional method for producing sponge platinum, the present invention is easy to operate, has no risk regarding safety during operation, is advantageous in terms of cost, and is simple when dissolved in aqua regia. It is an object of the present invention to provide a method for producing easily soluble sponge platinum which is not dissolved in a solution and does not generate a dissolution residue.

  In order to achieve the above object, the method for producing a readily soluble sponge platinum provided by the present invention is obtained by adding alkali to ammonium chloroplatinate to dissolve it, and after adding a reducing agent to the resulting solution to obtain sponge platinum, The wet platinum sponge separated and recovered is heated to a temperature of 800 to 1000 ° C. and baked, and the obtained baked product is crushed.

  In the method for producing the readily soluble sponge platinum of the present invention, the roasting is preferably performed in an inert atmosphere. Moreover, when crushing the roasted product, it is preferable to crush so that the particle diameter is in the range of 1 to 3 mm.

  ADVANTAGE OF THE INVENTION According to this invention, sponge platinum which melt | dissolves easily in aqua regia and does not generate | occur | produce a melt | dissolution residue can be manufactured by a safe and cost-effective method.

1 is a drawing showing a manufacturing process of sponge platinum according to the present invention. It is drawing which shows the manufacturing process of the conventional sponge platinum.

  The present invention comprises a step of obtaining sponge platinum from ammonium chloroplatinate by a wet method, a step of roasting the obtained sponge platinum in a wet state, and a step of crushing the roasted product. More specifically, in the step of obtaining sponge platinum, according to a known wet method, ammonium chloroplatinate is dissolved in caustic soda to obtain an alkaline solution, and platinum is reduced by a reducing agent such as hydrazine, and the produced sponge platinum is obtained. Collect by solid-liquid separation.

  Sponge platinum obtained from ammonium chloroplatinate by a wet method is preferably washed before moving to the next roasting step. For example, the recovered sponge platinum is suspended in pure water and stirred to separate the attached reduced mother liquor. The wet sponge platinum thus obtained is supplied to the next roasting step.

  Here, the sponge platinum in a wet state refers to, for example, sponge platinum that has been subjected to solid-liquid separation or further washing at room temperature, and is in a moisture state in which the surface is coated with moisture. The specific moisture content of the sponge platinum in a wet state cannot be generally specified, but is preferably such that the surface of the sponge platinum is coated with moisture, specifically about several to 20% by weight. .

  In the next roasting step, the sponge platinum in the wet state is charged into a heating furnace or the like in a wet state, and heated to a temperature in the range of 800 to 1000 ° C. in an air atmosphere or an inert gas atmosphere. And roast it. By this roasting treatment, the moisture contained in the sponge platinum is thermally decomposed and separated. In addition, a normal electric furnace etc. can be used as a heating furnace.

  If the temperature of the roasting treatment (roasting temperature) is less than 800 ° C., the solubility of the resulting sponge platinum in aqua regia is poor. On the other hand, if the roasting temperature exceeds 1000 ° C., roasting proceeds too much to produce lump sponge platinum, which is not preferable because handling becomes difficult. The target roasting temperature may be obtained by conducting a roasting test with a small amount in advance and obtaining the roasting temperature at which the particle size after crushing of the obtained sponge platinum is optimum. Further, the temperature rise time from room temperature, that is, the temperature gradient at the time of temperature rise is not particularly limited.

  The time required for the roasting treatment (roasting time) varies depending on the moisture content of the sponge platinum and the roasting temperature, but it is preferable to hold at least 5 minutes after reaching the predetermined roasting temperature. The roasting atmosphere may be an atmosphere that does not promote oxidation extremely, such as supplying oxygen, and can be performed in a normal air atmosphere, but an inert gas atmosphere such as nitrogen or argon is more suitable. preferable.

  The roasted product obtained in the roasting step is in a state that can be easily crushed. In the final crushing step, the roasted product is crushed so as to have a particle size of 1 to 3 mm to obtain a product. The reason why the particle size of the sponge platinum is in the range of 1 to 3 mm is that if it is less than 1 mm, it easily adheres to the container or bag due to static electricity, and it becomes difficult to weigh. Furthermore, a fine powder of less than 1 mm causes a severe dissolution reaction during dissolution, which is also a safety problem. On the other hand, if the particle size exceeds 3 mm, it is difficult to disperse when mixing in the reaction tank, dissolution becomes difficult, and it is not preferable because it promotes wear and breakage of the dissolution tank.

  In the present invention, as described above, the sponge platinum in a wet state is roasted in a wet state using a heating furnace or the like until the oxide contained in the sponge platinum starts thermal decomposition. Since moisture present on the surface of platinum acts as a kind of protective film, reoxidation of sponge platinum can be effectively prevented. Further, since sponge platinum is not added directly to a heating furnace or the like that has reached the roasting temperature, there is no fear of causing a steam explosion, and it can be operated safely.

[Example 1]
Ammonium chloride was added to a hydrochloric acid acidic platinum solution obtained by refining the raw material containing platinum to produce ammonium chloroplatinate, which was separated by filtration. As shown in FIG. 1, this ammonium chloroplatinate was dissolved in sodium hydroxide and then reduced by adding hydrazine to the solution to produce sponge platinum. The produced sponge platinum is filtered, purified water is added and washed with repulp, then filtered by suction with a vacuum pump using 5C filter paper and Nutsche, and water separated from sponge platinum is not dripped into the filter bottle. Then, the filtration was stopped.

  The obtained wet sponge platinum was put in a crucible, charged in an electric furnace, and heated from room temperature to 900 ° C. over 30 minutes. After reaching 900 ° C., it was held for 5 minutes and then allowed to cool. The recovered sponge platinum after roasting was well baked compared to the conventional dry product, but it can be easily crushed by hand using a pestle in a mortar, with a particle size of 1 to 3 mm. A powder could be obtained.

  Next, 5 g of sponge platinum powder obtained as described above was collected and placed in a beaker. To this, 40 ml of concentrated hydrochloric acid was added, and then 13 ml of concentrated nitric acid was gradually added while stirring to make aqua regia. As a result, the color of the solution became a transparent orange color, and sponge platinum was formed before stirring for 1 hour. It completely dissolved and no dissolution residue was observed at the bottom of the beaker.

[Comparative Example 1]
Roasting was performed under the same conditions as in Example 1 except that the set temperature during the roasting was set to 700 ° C. 5 g of the obtained sponge platinum powder was subjected to a dissolution test, 40 ml of concentrated hydrochloric acid was added in the same manner as in Example 1 above, and 13 ml of concentrated nitric acid was gradually added while stirring.

  However, since the sponge platinum was not completely dissolved, the beaker was placed on a hot plate and heated to 90 ° C. or higher. Even when the reaction seemed to be almost completed after 1 hour or more, the color of the solution was black and turbid and there was no transparency. The weight of the dissolution residue collected by filtration was 3% by weight with respect to the weight of sponge platinum subjected to the dissolution test.

[Comparative Example 2]
In the same manner as in Example 1, wet platinum sponge was obtained. Next, according to the conventional method shown in FIG. 2, the obtained sponge platinum was repulped with pure water and then put into a drier and kept at 105 ° C. for 24 hours to obtain completely dried sponge platinum. The particle size of the obtained sponge platinum was about 10 μm.

  5 g of sponge platinum obtained by the above-mentioned conventional method was collected and subjected to a dissolution test. After adding 40 ml of concentrated hydrochloric acid by the same method as in Example 1, 13 ml of concentrated nitric acid was gradually added while stirring. However, since the sponge platinum was not completely dissolved, the beaker was placed on a hot plate and heated to 90 ° C. or higher.

  Even in a state where the reaction was considered to be almost completed after 1 hour or more, the color of the solution was black and cloudy and there was no transparency. The weight of the dissolution residue collected by filtration was 5% by weight with respect to the weight of sponge platinum subjected to the dissolution test.

Claims (3)

After adding alkali to ammonium chloroplatinate and adding a reducing agent to the resulting solution to obtain sponge platinum, the surface after solid-liquid separation or further washing is coated with moisture. Moisture sponge platinum is charged into a heating furnace, and the moisture contained in the sponge platinum is obtained by raising the temperature from room temperature to 800 to 1000 ° C. in an air atmosphere or an inert atmosphere and baking it. A method for producing readily soluble sponge platinum, characterized by crushing the roasted product.   The method for producing readily soluble sponge platinum according to claim 1, wherein the roasting is performed in an inert atmosphere.   The method for producing readily soluble sponge platinum according to claim 1 or 2, wherein the baked product is crushed so that the particle diameter is in a range of 1 to 3 mm.

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