JP2001032025A - Method for recovering platinum group metal from platinum group metal-containing solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily recover almost all platinum group metals contained in a soln. by adding a soln. contg. platinum group metals typically as colloidal particles, for instance, a catalytic soln. contg. palladium with a reducing agent, forming the particles of platinum group metals and separating and recovering them. SOLUTION: A catalytic soln. of pH<=5 contg. platinum group metals or the compd. thereof, particularly, a used catalytic soln. of a palladium colloidal particle suspension exhausted in a catalyzing stage at the time of subjecting plastics or the like to electroless plating treatment is added with a reducing agent. As this reducing agent, sodium borohybride is preferable, and it is charged as an aq. soln. of about 0.1 to 40%. By the addition of this reducing agent, the colloidal state of the platinum group metallic particles, e.g. of about 10 to 20 Å potentially stable in the soln. is potentially destroyed, and they are flocculated to about 1 to 100 μm. This particles made to be filterable are separated and recovered, and expensive platinum group metals are recovered so as to be reutilizable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering a platinum group metal from a solution containing a platinum group metal or a compound thereof, and more particularly, to a used catalyst solution discharged in a catalyzing step of electroless plating. And a method for recovering palladium from methane.

[0002]

2. Description of the Related Art Recently, non-conductive materials such as plastics and ceramics have been
It is common practice to plate metals such as copper and nickel and various alloys. For example, metal parts are applied to daily necessities for design reasons, and some automobile parts and electric products are used for the purpose of imparting corrosion resistance and blocking electromagnetic waves.
Such metal plating is generally performed. Further, a similar metal plating technique is used in the manufacture of a printed wiring board and the like. However, in these plating processes, since the object is a non-conductive material such as plastic, normal electroplating cannot be applied immediately. Therefore, in order to impart conductivity in advance to the surface of such a non-conductive material,
Usually, a chemical plating process, that is, an electroless plating process is performed.

[0003] Electroless plating refers to plating performed without applying electric energy to the aqueous solution from the outside. When plating on the surface of a non-conductive material, the principle of plating metal plating on the surface is, for example, reduction of the plating metal salt. If the metal deposition principle is based on reduction, such electroless plating can be performed simply by a reduction reaction. However, the plating metal can be easily and / or strongly applied to the surface to be plated. Given the join,
The use of a catalyst is preferred and is usual. That is, in a typical electroless plating process, a catalyst of a platinum group metal or the like (for example, palladium) serving as a nucleus of a catalytic reaction is applied to the surface of a base material in advance, and then used as a nucleus for the catalytic reaction. And depositing a plating of copper, nickel or the like on the base material. Thereby, metal can be plated on the surface of the non-conductive material.

[0004] Usually, the electroless plating is performed according to the following procedure. That is, first, a degreasing step is performed using an alkaline degreasing liquid containing a surfactant for the purpose of removing oil and dirt attached to the surface of the non-conductive member to be treated and improving the wettability of the material surface. Then
An etching step of roughening the surface of plastic or the like with an etching agent is performed. By this step, the treated surface is roughened, and the adhesion after plating between the metal to be plated and a member such as plastic can be enhanced.

Next, a step of applying a catalyst for a deposition reaction of electroless plating to the surface of the base material, that is, a so-called catalyzing step is performed. The reason that this step is required is that the metal to be electrolessly plated is unlikely to be deposited on materials other than the catalytic substance, and therefore, in order to perform electroless plating on a non-conductive base material, the surface must first be coated. This is because it is necessary to adsorb the catalyst. In this step, in order to perform such catalyst application, a colloidal acidic solution (that is, a catalyst solution) in which tin and palladium are mixed, which is generally called a “catalyzer” or a “catalyst”, is used. ing. In the electroless plating process, after this catalyzing step, if necessary, an activation process for removing the influence of tin is performed, and then the base material is placed in an electroless plating solution containing copper, nickel, or the like. The substrate is immersed and electroless plating is performed on the surface of the substrate.

[0006] The electroless plating treatment is usually carried out in the above-described procedure. In the catalyzing step, particularly, in the catalyzing step, copper is gradually contained in the plating treatment during the plating process. It may be mixed. In such a case, usually, when a certain copper concentration is reached, the catalyst liquid is to be disposed of as a waste liquid. In many cases, the amount of the catalyst metal (for example, palladium) contained in the waste liquid of the catalyst liquid is small. Therefore, conventionally, the catalyst liquid is finally mixed with other waste liquid and then disposed of by an external specialist. They have been disposed of or disposed of in-house wastewater treatment facilities to meet certain environmental standards before being disposed of. Therefore, attempts to separate and recover platinum group metals such as palladium contained in the catalyst solution generated by the electroless plating have been scarcely made.

In the above-mentioned catalyst solution,
It is known that a platinum group metal such as palladium forms a colloid and is stably dispersed in a liquid, and the colloid particles have a diameter smaller than 1 μm.
It is known that it is about 0 to 20 angstroms. For this reason, it was difficult to separate and collect by simple filtration, centrifugal sedimentation or the like.

[0008] On the other hand, in recent years, interest in recycling palladium contained in various kinds of waste has been increasing due to a rising price of palladium. In addition, due to the recent growing interest in environmental issues, many companies have put forth the philosophy of environmental recycling, and companies and organizations that emit the above-mentioned catalyst solution should also collect palladium in wastewater. Was desired.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a solution containing a platinum group metal, typically as colloidal particles, in particular, a catalyst solution containing palladium as colloidal particles, from a platinum solution contained therein. Group metals (especially palladium)
And a method of separating and recovering almost all of them by simple means.

[0010]

According to the present invention, when a reducing agent is added to a platinum group metal-containing liquid which has been conventionally discarded without being subjected to almost any recovery treatment, the liquid is stably dispersed in the liquid. It is based on the discovery that the stability of the platinum group metal is lost and relatively large particles containing the platinum group metal are formed.

<Summary> That is, the method for recovering platinum group metals according to the present invention comprises adding a reducing agent to a liquid containing a platinum group metal or a compound thereof to reduce the particle diameter of the platinum group metal particles in the liquid. Or forming platinum group metal particles and separating and recovering them.

<Effect> According to the method of the present invention, a platinum group metal can be easily and efficiently recovered from a liquid containing a platinum group metal or a compound thereof. Further, by the method of the present invention, it is possible to recover a relatively expensive platinum group metal in a catalyst solution, which has hardly been recovered conventionally, and as a result, it is possible to reuse it. Further, according to the method of the present invention, almost all of the platinum group metal contained in the liquid containing the platinum group metal can be easily recovered. The liquid containing a platinum group metal or a compound thereof, which is a target of the present invention, is typically a colloidal solution of a platinum group metal (details will be described later). It is of interest that the particle size is enlarged from the colloidal particles, so that the solid (platinum group metal) and the solution can be easily separated.

[0013]

DETAILED DESCRIPTION OF THE INVENTION <Platinum Group Metal-Containing Solution> A solution containing a platinum group metal or a compound thereof to be treated in the method of the present invention (hereinafter referred to as a platinum group metal-containing solution). "May be" means a liquid containing a platinum group metal (particularly in a colloidal state) or a compound thereof obtained in various industrial processes.
This does not exclude organic ones, although aqueous ones are common. Examples of such platinum group metal-containing solutions include:
Examples of the catalyst solution containing platinum group metal colloid particles used (or used) in various catalytic reactions are exemplified.
In the present invention, such a catalyst liquid is preferable. In addition,
In the present invention, the term "catalyst liquid" refers to a catalyst liquid used in a catalytic reaction (that is, a catalyst waste liquid) as described above.
In addition, a catalyst solution before use, a catalyst cleaning solution, and the like are also included. The platinum group metal-containing solution preferred in the present invention is used in a so-called catalyzing step in performing an electroless plating treatment, that is, a step of seeding an object to be plated with an active nucleus of a catalyst such as a platinum group metal (or Used) catalyst solution.

The platinum group metal in the present invention includes:
Among the Group VIII elements of the periodic table, palladium Pd, ruthenium Ru, rhodium Rh, osmium Os, iridium Ir, and platinum Pt are exemplified. In the present invention, palladium (Pd) is particularly preferred. Therefore, a preferred embodiment of the present invention relates to a method for recovering palladium from a catalyst solution. As a specific example of the catalyst liquid in a preferred embodiment of the present invention, “sensitizer HS-201
B (or HS-202B) "(manufactured by Hitachi Chemical). This is used to deposit palladium (catalyst) for initiating an electroless copper plating reaction on the surface of the substrate to be plated.

In a preferred embodiment of the present invention, the platinum group metal-containing solution is an acidic solution containing palladium or an acidic solution containing palladium and tin, and more specifically, an acidic catalyst solution containing palladium chloride or palladium chloride and tin. An acidic catalyst solution containing: In many cases, palladium is considered to be present in the liquid in a colloidal state. In this case, the colloidal particles are at least smaller than 1 μm in diameter,
It is known to be on the order of 20 angstroms. However, in this state, it is obviously difficult to separate by filtration with filter paper or the like, or to settle by centrifugation or the like.

The concentration of the platinum group metal in the platinum group metal-containing solution to be treated in the present invention may be any concentration as long as the solution contains at least the platinum group metal. For example, in the case of a catalyst solution in the catalyzing step of the electroless plating process, in terms of the amount of palladium chloride,
Usually, the amount is less than the catalyst liquid control range of 0.1 to 0.5 g / L. In addition, such a platinum group metal-containing solution may be subjected to the method of the present invention after being concentrated or diluted in advance by using various conventional concentration or dilution means, if necessary. Further, the platinum group metal-containing solution to be treated according to the present invention is usually an acidic solution, and specifically, the pH is usually lower than 5;
It is about 3.

When the platinum group metal-containing solution to be treated in the present invention is a used catalyst solution, various contaminants accompanying use in the pretreatment step of the catalytic reaction are mixed in the catalyst solution. Often. Therefore, the catalyst liquid to be treated in the present invention usually contains various contaminants.
For example, in the catalyst solution used in the catalyzing step of the electroless plating process, with repeated use in this step, impurities such as copper, glass, resin and other plating base components increase, and gradually. The efficiency of the catalysis step may be reduced. In such a case, in order to prevent a decrease in the efficiency of the catalyzing step, the catalyst liquid is often replaced with a new one at the time when the impurities increase to some extent, and the catalyst liquid targeted in the present invention is such a case. It can be a catalyst liquid discharged to.

For example, it is known that when an electroless copper plating process is performed in the manufacture of a printed wiring board or the like, the copper concentration in the catalyst solution increases with use. In such a case, the catalyst solution is usually replaced with a new one when the copper concentration exceeds about 2000 ppm. Therefore, in a particularly preferred embodiment of the present invention, the platinum group metal-containing solution to be treated in the present invention,
A catalyst solution comprising palladium or palladium and tin, which may comprise more than 2000 ppm of copper. In addition, such a liquid is often brownish black.

<Reducing Agent> As the reducing agent used in the present invention, any one capable of breaking the colloidal state of the platinum group metal, which is considered to be formed in the containing liquid, by its reducing action. , Any of which can be used. Thus, examples of such reducing agents include sodium borohydride, lithium aluminum hydride, hydrogen, hydrazine, hydrazine salts (e.g., hydrazine sulfate, etc.), oxides of elements having lower than normal valences, or Oxygen acids and their salts (eg, CO, SO ₂ , sulfites), metals that tend to donate electrons (eg, alkali metals, alkaline earth metals, Zn, Cu, Hg) and their amalgams, low valent metal ions (eg, Fe ²⁺⁾ , Sn ²⁺ ,
Examples thereof include salts containing Ti ³⁺ and Cr ²⁺ ), sulfur compounds (eg, sodium sulfide, ammonium sulfide, etc.), and organic substances such as formic acid, oxalic acid, aldehyde, and pyrogallol.

Preferred as the reducing agent of the present invention are the above-mentioned reducing agents. These are, for example, a chemical change (chemical reduction reaction or oxidation reaction) that imparts an electron to an element or an ion to reduce or eliminate a positive charge. (Reduction reaction). Particularly preferred in the present invention, sodium borohydride (NaBH ₄₎ is a (hereinafter, sometimes abbreviated as SBH).

When the above-mentioned reducing agent is used, if the reducing agent is available in a solid form, it may be used as it is or pulverized, and then it is directly introduced into the catalyst solution. However, the preferred reducing agent in the present invention is one that is soluble in the target catalyst solution, specifically, one that is water-soluble, and thus, for example, when the reducing agent is sodium borohydride, it is necessary to prepare an aqueous solution. It is preferable to add the catalyst solution to the catalyst solution. This can be said to be advantageous from the viewpoint of ease of handling and reactivity. Accordingly, a particularly preferred reducing agent used in the present invention is an aqueous sodium borohydride solution.

When the reducing agent is an aqueous solution, it is preferable to use a high-concentration solution of the reducing agent because the higher the concentration of the aqueous solution, the smaller the amount of the processing solution in the subsequent treatment can be reduced. For example, when using an aqueous solution of sodium borohydride as the reducing agent, for example, 0.1 to 40%,
It is desirable to use a 1 to 20%, particularly preferably 12%, aqueous solution of sodium borohydride.

As such a reducing agent, a commercially available product for the purpose of a reducing agent or the like is obtained from a supplier, and is used as it is or, if necessary, dissolved / diluted in a solvent such as water. , May be used. In the present invention,
A commercially available Vencil stock solution (manufactured by Morton International) containing sodium borohydride can be used. The Vencil stock solution is generally used for the purpose of reducing metal ions, and usually contains about 12% of sodium borohydride and about 40% of sodium hydroxide. .

By introducing the reducing agent into the catalyst solution,
The colloidal state of a platinum group metal (particularly, palladium), which is stable in potential, is broken down in potential, and the colloid of the platinum group metal is converted into solid particles (platinum group metal Particles). Thereby, the platinum group metal is precipitated as solid particles having a relatively large size, which is considered to be more advantageous for platinum group metal recovery. In this case, the particles of the platinum group metal generated by the introduction of the reducing agent are at least larger than the size of the colloidal particles before the introduction, and are usually particles having a diameter of about 1 to 100 μm, and a filter such as filter paper. It is a size that can be separated by filtration using
Catalyst solution (especially catalyst solution containing palladium in colloidal state)
Is observed to change from brownish black to almost colorless and transparent by the addition of the reducing agent. Then, it is also observed that black fine particles precipitate and float in the transparent liquid.

<Method of recovering platinum group metal (chemical reduction method)>
The following description relates to the procedure of the platinum group metal recovery method of the present invention. A platinum group metal-containing solution to be subjected to the platinum group metal recovery method of the present invention is provided from various production steps and treatment processes. For example, when the solution to be treated is the catalyst solution used in the catalyzing step of the electroless plating, the pH is usually about 2 and the liquid color is brown-black.

<< Addition of Reducing Agent >> First, a reducing agent is added to the obtained platinum group metal-containing solution. The reducing agent is preferably added in the form of an aqueous solution, as already mentioned above.
The amount of the reducing agent to be charged is preferably at least such that the colloid of the platinum group metal, which is considered to be present in the catalyst solution to be treated, is broken to generate platinum group metal particles. As long as the amount of the condition is satisfied, the amount of the reducing agent to be charged can be variously changed depending on the amount of the solution to be treated, the form of charging the reducing agent, the concentration of the reducing agent liquid to be used, and the like. For example, specifically, the catalyst solution to be treated (Pd
Amount 231 mg / L, pH 2.1)
The amount of reducing agent used is the Vencil stock solution (ie, 12% aqueous sodium borohydride) as the reducing agent.
When using is about 13 ml. In addition, the catalyst solution to be treated (Pd amount 144 mg / L, pH 0.1 or less) is 5
If there is 00 ml, the amount of reducing agent used (reducing agent is the same as above) is about 7 ml.

At the time of adding the reducing agent, a necessary amount may be prepared in advance and may be added to the solution to be treated at once or at a constant rate, but depending on the progress of the aggregation state of the solution to be treated. The reducing agent may be added at a controlled rate. For example, if the solution to be treated is the catalyst solution used in the catalyzing step of the electroless plating process, the liquid color is initially brown-black, but when the colloidal state assumed by the introduction of the reducing agent is disrupted, The liquid color is seen to change to a blackish transparent color. Therefore, the amount of the reducing agent introduced may be adjusted based on such a change in the liquid color. In addition, while measuring the oxidation-reduction potential of the catalyst solution to be treated, the amount of the reducing agent introduced can be adjusted accordingly.

As described above, when the solution to be treated is the catalyst solution used in the catalyzing step of the electroless plating treatment, the liquid color is changed from brown black to blackish by adding a reducing agent (particularly Vencil stock solution). It changes to a transparent color. This is considered to be because the colloidal state of the platinum group metal (particularly palladium) was broken by the reducing agent, and substantially black fine particles of the platinum group metal (particularly palladium) were generated. Usually, the size of the generated fine particles is
It has a size of about 1 to 100 μm, and is a size that can be separated by filtration with a filter such as filter paper. In addition, in the case of the catalyst liquid, it is also observed that the oxidation-reduction potential becomes, for example, from about +300 mV to about -700 mV by adding the reducing agent.

In the present invention, the target platinum group metal can usually be sufficiently filtered off by adding only a reducing agent, but if necessary, an auxiliary agent such as a coagulant may be further added. Can also be added. Such auxiliary agents can be variously selected from conventional ones according to the reducing agent used, the state of the particles generated by the introduction of the reducing agent, or the type of the separation and recovery means.

After the introduction of the reducing agent, it is preferable to sufficiently stir the mixture so that the reducing agent sufficiently contacts the entire processing solution.
After stirring, the solution may be allowed to stand, preferably until the generated particles and the like settle to some extent (for example, at least about 2 hours).

<< Separation / recovery operation >> Next, the above solution is subjected to a separation filtration operation, preferably a suction filtration operation, to separate a solid-liquid in the solution. At this time, it is common to use a general filtration device or a suction filtration device, but if necessary, for example, various other conventional devices such as a pressure filter, a vacuum filter, a continuous filter and the like. A filtering device can also be used. Further, at the time of filtration, pressure may be separately applied to increase the filtration speed, or an auxiliary agent such as a filter aid may be used. When a filter paper, a filter cloth, or the like is used, a conventional one can be used.

By the above-described separation operation, the solution treated with the reducing agent can be separated into a solid (solid residue) and a liquid (filtrate). Of these, the target platinum group metal (particularly, palladium) is usually little or hardly present on the filtrate side. On the other hand, on the side of the solid residue, most or almost all of the platinum group metal (particularly palladium) existing in the liquid before the treatment is usually present.
The obtained solid residue may be further calcined if necessary, and further, aqua regia is added to the obtained solid residue,
The platinum group metal (particularly palladium) may be dissolved to recover the target platinum group metal. The recovered platinum group metal can be isolated by a conventional separation operation such as fusion electrolysis to obtain an isolated product. As described above, according to the present invention, by collecting the formed solid residue, almost or almost all of the platinum group metal contained therein can be recovered from the catalyst solution before the treatment.

[0033]

The following is a specific description of the present invention by showing examples of the present invention. The present invention is not limited to these.

In the following examples, the concentrations of palladium, copper and tin were determined by the following measuring methods. [Measurement method of palladium concentration] In a 100 ml volumetric flask, about 50 ml of pure water and a hydrochloric acid solution (concentrated hydrochloric acid: water = 1: 2) 1
0 ml are added, followed by 1 ml of hydrogen peroxide. Next, 2 ml of a sample solution containing palladium is added to this solution, and the solution is diluted 50-fold with pure water to obtain a measurement solution. For this measurement solution, the concentration of palladium in the solution is measured using an atomic absorption spectrophotometer to determine the concentration of palladium in the sample.

[Method of Measuring Copper Concentration] In the same manner as described above, a measurement solution containing a sample solution is obtained, and the copper concentration in the solution is measured using an atomic absorption spectrophotometer to determine the copper concentration in the sample. . [Measurement method of tin concentration] A measurement solution containing a sample solution is obtained in the same manner as described above, and the tin concentration in the solution is measured using an IPC emission spectrophotometer to determine the tin concentration in the sample.

According to the method of the present invention, palladium was recovered from the spent catalyst solution as follows.

Example 1 In the catalyzing step of the electroless plating treatment, an aqueous palladium (Pd) colloid solution containing no tin (Sn) was used as a catalyst solution. The catalyst solution after this treatment step (hereinafter referred to as catalyst solution A) was collected and used in the following test. The above catalyst solution A had a pH of 2.1 and a Pd concentration of 231 mg / L. The copper concentration was 37 ppm. 1 L of this catalyst liquid A (Pd amount 2
31 mg) and prepare sodium borohydride (hereinafter SB)
13 ml of Vencil stock solution (manufactured by Morton International) containing 12%
The catalyst liquid was thoroughly stirred. When the SBH was charged, it was observed that the catalyst solution foamed violently. Further, when the oxidation-reduction potential of the catalyst solution was measured, it was found that the value was about +300 mV at first, but about -850 mV by SBH injection. On the other hand, although the pH of the catalyst solution changed from 2.1 to 3.1, depending on the introduction of the reducing agent, the pH was changed.
Did not change significantly. Then, in the catalyst solution, it was observed that the particles aggregated at a stage where the pH was 3.1 and the oxidation-reduction potential was about -850 mV. The liquid color is
When SBH was introduced, a colorless and transparent liquid color was observed from the initial black color, and black particles were found to be floating in the liquid.

Next, after the SBH was introduced and stirred, the catalyst liquid was subjected to suction filtration. The suction filtration was performed using an aspirator-type suction filter, the pressure was reduced by a water stream, and the filtration was performed for about 2 minutes. At this time, when the filterability is observed, for example, (2) Even if filtration was performed with one filter paper, the filter paper was hardly damaged during the filtration, and the filterability was relatively good.
By this suction filtration, the catalyst solution was converted into a colorless and transparent filtrate (1 L in liquid volume) and a black floc-like solid residue (0.3 g).
And could be separated into About the obtained filtrate, P
When the amount of d was measured, the amount of Pd in the filtrate was 0 mg,
In this measurement, no Pd was found in the filtrate.

On the other hand, the solid residue obtained by suction filtration was dissolved in aqua regia (concentration 10%) so that the total amount was 1 L, and the palladium concentration in the solution was measured by atomic absorption spectrophotometry. The measured palladium concentration is 23
It was 1 mg / L. Therefore, the amount of Pd recovered from the solid residue was 231 mg. The above results are summarized in Table 1 below. The table shows the amount of palladium before and after the Pd recovery process of the present invention was performed using 1 L of the catalyst solution A as a sample as described above. Also, the amount of copper is shown in the same manner.

Table 1 <Results of Pd recovery test from Pd-containing (Sn-free) catalyst solution> Palladium (Pd) Copper (Cu) Before treatment (mg) After treatment (mg) Before treatment (mg) After treatment (mg) Sample catalyst solution 231--37--Filtrate--0--0 Solid residue by filtration- − 231 −− 37 Total 231 231 37 37

As can be seen from Table 1, with respect to palladium, the material balance was maintained before and after the recovery treatment of the present invention, and it was found that Pd loss due to the treatment operation was hardly observed. In addition, according to the present invention, it was found that almost 100% of palladium in the sample catalyst solution can be recovered as a solid residue.

Example 2 In the catalyzing step of the electroless plating treatment, an aqueous palladium (Pd) colloid solution containing tin (Sn) was used as a catalyst solution. The catalyst solution after this treatment (hereinafter referred to as catalyst solution B) was collected and used in the following test. The catalyst liquid B has a pH of 0.1,
The Pd concentration was 144 mg / L. This catalyst solution B
Vencil stock solution (Morton International) prepared by preparing 00 mL (Pd amount: 72 mg) and containing SBH 12%
About 7 ml was added and the catalyst liquid was thoroughly stirred. When the SBH was charged, it was observed that the catalyst solution foamed violently. Also, when the oxidation-reduction potential of the catalyst solution was measured, it was about +300 mV at first, but by SBH injection,
It was found to be about -700 mV. Further, in the catalyst solution, the pH is 0.1 and the oxidation-reduction potential is -700 mV.
At some stage, it was observed to aggregate into particles. On the other hand, although the pH of the catalyst solution changed from 0.1 to 0.3, no significant change in the pH was observed by the introduction of the reducing agent. When the SBH was introduced, the liquid color was changed from an initial brown-black color to a colorless and transparent liquid color, and it was recognized that black particles were floating in the liquid.

Next, after charging SBH and stirring, the catalyst solution was subjected to suction filtration in the same manner as in Example 1. At this time, the filterability was as shown in
Was relatively good as well. By this suction filtration,
The catalyst solution could be separated into a colorless and transparent filtrate (liquid amount 500 mL) and a black floc-like solid residue (1.1 g).

When the amount of Pd in the obtained filtrate was measured, the amount of Pd in the filtrate was 0 mg, and no Pd was found in the filtrate in this measurement.

On the other hand, the solid residue obtained by suction filtration was dissolved in aqua regia (concentration: 10%) so that the total amount was 1 L, and the palladium concentration in the solution was measured by atomic absorption spectrophotometry. The measured palladium concentration is 72 m
g / L. Therefore, the Pd recovered from the solid residue
The amount was 72 mg. The above results are summarized in Tables 2 and 3 below. Table 2 shows the amount of palladium before and after the Pd recovery treatment of the present invention when 3 L of the catalyst solution B was used as a sample, as described above. Table 3 shows the results of measuring the amounts of copper and tin before and after the Pd recovery treatment.

Table 2 <Results of Pd recovery test from Sn-Pd containing catalyst solution> Before (mg) treatment with palladium (Pd) (mg) After treatment (mg) Sample catalyst solution 72 --- Filtrate ---- 0 Solid residue separated by filtration --- 72 Total 72 72

Table 3 Copper (Cu) Tin (Sn) Before treatment (mg) After treatment (mg) Before treatment (mg) After treatment (mg) Sample catalyst solution 329-4200 --- Filtrate --- 0 --- 3765 Filtration solid residue- - 329 - 435 total 329 329 4200 4200

As can be seen from Table 2, with respect to palladium, the mass balance was maintained before and after the recovery treatment of the present invention, and it was found that Pd loss due to the treatment was hardly observed. According to the present invention, it was found that almost 100% of palladium in the sample catalyst solution can be recovered as a solid residue.

[0049]

According to the method of the present invention, almost all of the platinum group metal can be easily and efficiently recovered from the liquid containing the platinum group metal or its compound, and further, the catalyst which has been hardly recovered in the past. The fact that a relatively expensive platinum group metal in a liquid can be recovered and reused has already been described in the section of [Summary of the Invention].

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[Procedure amendment]

[Submission date] April 18, 2000 (2004.1.
8)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

Claims (3)

[Claims] 1. A method for recovering a platinum group metal, comprising forming a particle of a platinum group metal by adding a reducing agent to a liquid containing a platinum group metal or a compound thereof, and separating and recovering the particles. . 2. The method of claim 1, wherein the platinum group metal is palladium.
The method described in. 3. The method according to claim 1, wherein the reducing agent is an aqueous solution of sodium borohydride.