JP2014169484A - Method for producing platinum powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing platinum powder substantially free of potassium and chlorine in a very high yield.SOLUTION: A method includes reducing ammonium chloroplatinate as a feedstock to produce platinum powder by a wet process. The method comprises at least: a first step of adding a hydrazine compound as a reducing agent and an ammonia compound as a neutralizing agent to the feedstock to produce Magnus' green salt at 10-60°C; a second step of adding a hydrazine compound to the resultant Magnus' green salt and reducing it to platinum powder at 40-60°C; and a third step of calcining the resultant platinum powder at a calcining temperature of preferably 700-950°C. It is preferable that a mole amount of the ammonia compound added at the first step is 4 to 12 times a mole amount of the platinum including in the ammonium chloroplatinate as the feedstock.

Description

  The present invention relates to a method for producing platinum powder by reducing a platinum compound by a wet method, and in particular, producing platinum powder having a low content of sodium and chlorine by reducing ammonium chloroplatinate as a raw material by a wet method. Regarding the method.

  Platinum is widely used in applications such as jewelry materials, semiconductor materials, electronic materials, and automobile catalysts, but because it is a rare metal, it is used in automobile scrap catalysts, platinum-containing scrap, copper smelting and nickel smelting. Recovery from electrolytic slime generated in the electrolysis process is performed. Such platinum recovery is generally performed in the form of platinum powder whose particle size can be easily adjusted. In particular, when platinum is used as an electronic material, recovery in the form of platinum powder is preferable.

  As a method for recovering in the form of platinum powder, first, ammonium chloride is added to a hydrochloric acid acidic platinum solution to precipitate and recover ammonium chloride chloroplatinate, or chloroplatinic acid using an organic solvent. Platinum is recovered as a purified ammonium chloroplatinate by a solvent extraction method for recovering ammonium or a combination of these, and then the recovered ammonium chloroplatinate is reduced by a dry method or a wet method to obtain platinum. Methods for obtaining powder are conventionally used.

  Among these, in the reduction by a wet method, conventionally, after adding water to ammonium chloroplatinate and suspending it, a method of reducing with a hydrazine compound has been used. In this method, sandy platinum is obtained from a solution acidified with hydrochloric acid generated by reduction. For example, Patent Document 1 discloses a method in which a solution in which an ammonia compound as an additive and a hydrazine compound as a reducing agent are mixed is directly added to ammonium chloroplatinate and reduction is performed at a high temperature of 50 ° C. or higher. .

JP-A-2-294416

  When producing platinum powder for electronic materials, it is generally performed to manage the content of impurities contained in the platinum powder as a product as an acceptable standard value for Na at 100 ppmw or less and for Cl at 100 ppmw or less. Yes. In this respect, it can be said that the method of Patent Document 1 is suitable because an additive not containing sodium is used when obtaining platinum powder. However, in the method of Patent Document 1, foil-like platinum may be deposited on the inner wall of the reaction tank or the blades of the stirrer, and not only the yield of platinum powder is deteriorated, but also the recovery of platinum attached to the inner wall of the reaction tank. Since the work is very time consuming, there has been a problem that productivity is lowered.

  Therefore, in order to suppress the problem of the adhesion of the platinum powder, a method has been proposed in which the hydrochloric acid generated by the reduction reaction is neutralized with caustic soda and the platinum is reduced within the alkaline range. The platinum powder obtained by this method is powdery and has good handling properties, and the hydrazine compound used for the reduction has the advantage that the reaction can be terminated even when added in a theoretical amount.

  However, it was not possible to avoid that the platinum powder obtained by this method contains about 300 to 1000 ppmw of sodium and about 100 to 1000 ppmw of chlorine. Since these sodium and chlorine are contained almost uniformly when observed with EPMA, it is considered that sodium chloride produced by the reaction is mixed in the platinum powder. As a method for removing the salt from the platinum powder, repulp washing and roasting with warm water can be considered.

  However, the repulp washing can hardly expect the removal effect of salt. Further, since the boiling point of sodium chloride is as high as 1413 ° C., 1400 ° C. or higher is required in order to perform sodium removal and dechlorination by volatilization removal by roasting. However, when roasting at 1400 ° C. or higher, platinum powder was sintered and became agglomerated, so that only those having poor handling properties were obtained.

  Thus, there is no method for successfully removing these sodium and chlorine from the platinum powder containing sodium and chlorine of about several hundred to 1000 ppmw to the above-mentioned acceptable standard value. Therefore, a method for producing platinum powder using the caustic soda. However, there is a problem that platinum powder cannot be obtained even if it is suitable as a method for producing platinum powder. The present invention has been made in view of the above-described conventional problems, and platinum powder that is hardly mixed with impurities such as sodium and chlorine is used for an inner wall of a reaction vessel or a stirring blade that is used in a step of obtaining platinum powder. An object of the present invention is to provide a method for producing platinum powder that can be recovered with extremely high yield without depositing foil-like platinum.

  In order to solve the above-mentioned problems, a method for producing platinum powder according to the present invention is a method for producing platinum powder by reducing ammonium chloroplatinate as a raw material by a wet method, comprising a hydrazine compound as a reducing agent and A first step of adding an ammonia compound as a neutralizing agent to the raw material to produce a magnus salt at 10 to 60 ° C., adding a hydrazine compound to the obtained magnus salt, and reducing to platinum powder at 40 to 60 ° C. The second step is to include at least a third step of roasting the obtained platinum powder.

  In the method for producing platinum powder of the present invention, the platinum powder is preferably roasted at a roasting temperature of 700 to 950 ° C. Moreover, it is preferable that the molar amount of the ammonia compound to be added is 4 to 12 times the molar amount of platinum contained in the ammonium chloroplatinate as the raw material.

  According to the present invention, it is possible to produce platinum powder containing almost no sodium or chlorine with a very high yield.

  Hereinafter, a specific example of the method for producing platinum powder of the present invention will be described. The manufacturing method of this one specific example is a method of manufacturing platinum powder by reducing ammonium chloroplatinate as a raw material by a wet method. First, in the first step, a reducing agent and ammonium chloride platinate as the raw material are added. A neutralizing agent is added, and a reaction is performed at 10 to 60 ° C. to produce a Magnus salt.

  In this way, by adding a reducing agent and a neutralizing agent to ammonium chloroplatinate and adjusting the temperature within a predetermined temperature range, a reduction reaction from Pt (IV) to Pt (II) occurs and is hardly soluble in water. Of Magnus salt. This magnus salt is produced even at a low temperature, but if the temperature is low, the viscosity of the slurry becomes high and the foam breakage becomes worse, or the produced magnus salt becomes difficult to handle. In order to suppress such a problem, the liquid temperature at the time of reaction shall be 10 degreeC or more.

  On the other hand, when the liquid temperature during the reaction exceeds 60 ° C., stable tetraammineplatinum (II) is produced in the presence of excess ammonia. As a result, when platinum is dissolved in the solution and the reduction of the dissolved platinum is advanced, foil-like platinum is deposited on the inner wall of the reaction vessel and the blade of the stirrer. Thus, when platinum adheres to a tank wall etc., it will take very much time to collect platinum obtained by precipitation. In order to suppress this problem, the upper limit of the liquid temperature during the production reaction of Magnus salt is set to 60 ° C. In particular, the upper limit is preferably set to 50 ° C. in consideration of variations in liquid temperature, measurement errors, and the like.

  In order to prevent impurities such as sodium from being mixed in the finally obtained platinum powder, it is desirable that the neutralizing agent and reducing agent used when producing the Magnus salt are free of impurities such as sodium. . For this reason, an ammonia compound is used as the neutralizing agent, and a hydrazine compound is used as the reducing agent.

  As the ammonia compound as the neutralizing agent, for example, ammonium carbonate, ammonium bicarbonate, or aqueous ammonia can be used. Of these, ammonium carbonate and ammonium bicarbonate are liable to foam due to the volatilization of carbon dioxide released by neutralization as carbon dioxide gas, which may cause problems such as bumping in the reaction vessel. Therefore, it is preferable to use ammonia water with less foaming as the neutralizing agent. On the other hand, as the hydrazine compound as a reducing agent, for example, hydrazine sulfate, hydrazine hydrochloride, and hydrazine hydrate can be used. Among these, hydrated hydrazine is preferable from the viewpoint of price and ease of handling.

  When adding an ammonia compound, it is preferable to add it so that the molar amount of ammonia contained in the ammonia compound is 4 to 12 times the molar amount of platinum contained in ammonium chloroplatinate as a raw material. Four times the molar amount of platinum is a value derived from the theoretical amount, and 12 times the molar amount of platinum is a suitable value for completing the reaction quickly.

  On the other hand, when adding the hydrazine compound, a hydrazine compound having a hydrazine concentration of 30 to 70 wt% is added dropwise to 20 kg of ammonium chloroplatinate at an addition rate of about 1 to 10 liters / hour. The dripping is preferably terminated when the color changes to green indicating generation.

  In the 2nd process performed following the said 1st process, a hydrazine compound is added to the liquid containing the Magnus salt obtained at the 1st process, Preferably it is 40-50 degreeC within the liquid temperature range of 40-60 degreeC. Reduction within the liquid temperature range causes platinum powder to precipitate. When the liquid temperature during the reduction exceeds 60 ° C., tetraammineplatinum (II) is produced, and foil-like platinum is deposited on the inner wall of the reaction tank and the blades of the stirrer. On the other hand, if this temperature is less than 40 ° C., the reduction reaction is difficult to proceed.

  The hydrazine compound was added by dropping a hydrazine compound having a hydrazine concentration of 30 to 70 wt% to 20 kg of ammonium chloroplatinate at an addition rate of about 1 to 10 liters / hour, and the green slurry indicating the presence of magnus salt was black. The dripping is preferably terminated when the color changes. The platinum powder precipitated by reduction is recovered by a solid-liquid separation method such as filtration, and then washed with water and dried as necessary to remove impurities.

  In the third step, the platinum powder obtained in the second step is roasted. The platinum powder obtained by the reduction by the wet method can remove impurities to some extent by washing with water as described above, but contains a little ammonium chloride produced by the reduction reaction. The third step is intended to volatilize and remove ammonium chloride contained in this platinum powder by roasting, whereby a platinum powder satisfying the acceptance criteria is obtained.

  The roasting temperature is preferably in the range of 700 to 950 ° C. The reason for this is that ammonium chloride contained in platinum powder shows a weight loss between 450 ° C. and 700 ° C. when the mass change with respect to temperature is measured by differential thermal-thermogravimetric simultaneous measurement (TG-DTA). This is because almost no weight reduction is observed. That is, by setting the roasting temperature of the platinum powder to 700 ° C. or higher, the ammonium chloride mixed in the platinum powder can be almost completely volatilized and removed, and the quality of Cl contained in the platinum powder can be further reduced.

  On the other hand, the reason why a roasting temperature of 950 ° C. or lower is preferable is that if the roasting temperature is increased, the sintering of platinum powder proceeds, and if it exceeds 950 ° C., the powdery material contains agglomerates. This is because operations such as crushing are required.

Example 1
First, in a wet state, 20 kg of ammonium chloroplatinate (equivalent to about 8 kg of platinum) and 30 liters of 25% aqueous ammonia are placed in a glass lining tank with a capacity of 200 liters. Adjusted. At this time, the molar amount of added ammonia is 11 times the molar amount of platinum. When the pH and temperature of the slurry obtained by adjusting the liquid volume were measured, the pH was 10.6 and the temperature was 17 ° C.

  Subsequently, 60% hydrazine was dropped into the tank at an addition rate of 2 liters / hour. As a result, the slurry in the tank changed from yellow to green indicating the formation of Magnus salt, and the temperature of the slurry increased to 50 ° C. by the reaction, and then gradually decreased. In addition, bubbles generated during the reaction gradually decreased. Since the temperature of the slurry was lowered to 46 ° C., the pH was measured to be 8.1. When a sample of this slurry was collected, the color of the supernatant liquid was almost colorless, with the original red color being pale yellow.

  Next, the temperature setting of the liquid in the tank was set to 40 ° C. to reduce the Magnus salt, and the addition was continued without changing the addition rate of 60% hydrazine. Since the green slurry indicating the presence of magnus salt in the tank turned black, it was judged that the reduction reaction of magnus salt by hydrazine was reduced, and the addition of 60% hydrazine was stopped. Thereafter, stirring was continued for 30 minutes.

  After 30 minutes of stirring, the slurry in the tank was extracted, and platinum powder was collected by suction filtration using a three-type filter paper and a Buchner funnel. The obtained platinum powder was powdery and had good handling properties such as filtration. When the inside of the tank after removing the slurry was observed, no adhesion of platinum powder to the inner wall or the stirring blade was observed. Further, when the filtrate separated by the filtration was analyzed with an inductively coupled high-frequency plasma spectrometer (ICP spectrometer), the platinum contained in the filtrate was less than 0.01 g / L, and the platinum recovery rate was 99% or more. Met.

  Next, the obtained platinum powder was put into an alumina crucible and roasted at 600 ° C. The capacity of the platinum powder after roasting was 20% less than that before roasting in the crucible, but it was powdery and easy to handle. In order to measure the content of impurities contained in the platinum powder, Na and Cl were measured with a glow discharge mass spectrometer (GD-MS apparatus). As a result, Na was 12 ppmw, Cl was 72 ppmw, and platinum powder satisfying the acceptance criteria was obtained.

(Example 2)
Platinum powder was prepared in the same manner as in Example 1, but the liquid temperature before addition of hydrazine was 10 ° C., and the temperature of the liquid was increased to 31 ° C. by adding 60% hydrazine, and then decreased. Moreover, the temperature of the liquid in the tank set to perform the reduction reaction of Magnus salt was changed to 40 ° C. instead of 40 ° C., and the temperature was raised to 60 ° C. by the reduction reaction.

  As a result, as in Example 1, the platinum powder did not adhere to the inner wall of the tank or the stirring blade, and the obtained platinum powder was powdery and had good handling properties such as filtration. Moreover, platinum in the filtrate separated by filtration was less than 0.01 g / L, and the recovery rate of platinum was 98% or more. Furthermore, Na contained in the platinum powder after roasting was 12 ppmw and Cl was 76 ppmw, and platinum powder satisfying the acceptance criteria was obtained.

(Example 3)
A platinum powder was produced in the same manner as in Example 1 except that the roasting temperature was changed to 700 ° C. instead of 600 ° C. As a result, Na contained in the obtained platinum powder was 2 ppmw, Cl was 22 ppmw, and platinum powder satisfying the acceptance criteria was obtained. By raising the roasting temperature as compared with Example 1, the Cl quality was lowered and a higher quality platinum powder was obtained. The recovery rate of platinum was 99% or more.

Example 4
A platinum powder was produced in the same manner as in Example 2 except that the roasting temperature was changed to 700 ° C. instead of 600 ° C. As a result, Na contained in the obtained platinum powder was 2 ppmw, Cl was 26 ppmw, and a platinum powder satisfying the acceptance criteria was obtained. By raising the roasting temperature as compared with Example 2, the Cl quality was lowered, and higher quality platinum powder was obtained. The recovery rate of platinum was 98% or more.

(Comparative Example 1)
After producing the Magnus salt at 70 ° C., platinum powder was prepared in the same manner as in Example 1 except that the Magnus salt was reduced at 80 ° C. and the roasting temperature was 700 ° C. As a result, Na contained in the obtained platinum powder was 2 ppmw, Cl was 23 ppmw, and platinum powder satisfying the acceptance criteria was obtained.

  However, when the filtrate obtained by filtering the liquid in the tank after completion of the reaction was measured with an ICP spectrometer, the platinum in the filtrate was 20 g / L. When the platinum recovery rate was calculated from the amount of platinum remaining in the filtrate and the amount of platinum powder recovered by filtration, it was 72.8%, and the recovery rate was poor. Furthermore, foil-like platinum was adhered to the stirring blade and the baffle plate in the tank.

(Comparative Example 2)
In a wet state, 400 g of ammonium chloroplatinate (equivalent to about 160 g of platinum) and 400 mL of 25% aqueous ammonia were placed in a 3 liter beaker, and water was added to adjust the liquid volume to about 2 liters. At this time, the molar amount of added ammonia is 7 times the molar amount of platinum. The temperature of the slurry obtained by adjusting the liquid volume was adjusted to 70 ° C., and 60% hydrazine hydrate was dropped into the tank at an addition rate of 40 mL / hour.

  Subsequently, addition was continued without changing the addition rate of 60% hydrazine while maintaining the temperature of the slurry at 70 ° C. As a result, the slurry in the tank was dissolved in a light yellow liquid, and platinum adhered to the inner wall surface of the beaker as a silver mirror. After further reduction for 1 hour, when the inside of the beaker was observed, platinum adhered to the inner wall surface of the beaker and the stirring blade in the form of a foil, and platinum powder was hardly obtained.

(Comparative Example 3)
In a wet state, 20 kg of ammonium chloroplatinate was placed in a 200 liter tank, water was added to adjust the volume to 100 liters, and then adjusted to pH 12 with 24% caustic soda. After the temperature of the resulting slurry was raised to 80 ° C., 60% hydrazine was added at an addition rate of 2 liters / hour.

  Since the generation of bubbles in the tank was reduced, it was judged that the reduction reaction by hydrazine was eliminated, and the addition of hydrazine was stopped. Thereafter, stirring was continued for 30 minutes, and after cooling to 30 ° C., the slurry was filtered to recover platinum powder. The recovered platinum powder was in a powder form with good handleability. Moreover, there was no adhesion of platinum, such as foil shape, in the tank. When the filtrate obtained by the above filtration was measured with an ICP analyzer, platinum in the filtrate was less than 0.01 g / L, and a recovery rate of 98% or more was obtained.

  Next, after the collected platinum powder was washed with warm water, it was put into an alumina crucible and roasted at 700 ° C. When Na and Cl contained in the platinum powder after roasting were measured using a GD-MS apparatus, Na was 940 ppmw and Cl was 140 ppmw, which did not satisfy the acceptance criteria.

Claims (3)

  A method of producing platinum powder by reducing ammonium chloroplatinate as a raw material by a wet method, comprising adding a hydrazine compound as a reducing agent and an ammonia compound as a neutralizing agent to the raw material at 10 to 60 ° C. A first step of producing a Magnus salt, a second step of adding a hydrazine compound to the obtained Magnus salt and reducing the platinum powder to 40-60 ° C., and a third step of roasting the obtained platinum powder. A method for producing platinum powder, characterized by comprising at least   The method for producing platinum powder according to claim 1, wherein the platinum powder is roasted at a roasting temperature of 700 to 950 ° C.   3. The production of platinum powder according to claim 1, wherein a molar amount of the ammonia compound to be added is 4 to 12 times a molar amount of platinum contained in ammonium chloroplatinate as the raw material. Method.