KR101736014B1 - Method for collecting palladium - Google Patents

Abstract

Palladium can be efficiently recovered from a palladium-containing waste liquid containing inorganic sulfur oxides such as sodium sulfite at a high recovery rate without requiring complicated operations. Containing aqueous solution containing an inorganic sulfur oxide to a pH of 2 or less, adding a reducing agent to the palladium-containing aqueous solution to reduce palladium, adding a cationic surfactant to the palladium-containing aqueous solution, And recovering palladium by flocculation and sedimentation.

Description

[0001] METHOD FOR COLLECTING PALLADIUM [0002]

The present invention relates to a method for recovering palladium, and more particularly, to a method for recovering palladium from a palladium-containing waste liquid containing an inorganic sulfur oxide.

Palladium (Pd) is widely used as a highly active and highly practical catalytic metal in fields such as organic synthesis and exhaust gas purification. Particularly, in the production of chemical products such as agricultural chemicals, medicines, fragrances and dyes, the palladium catalyst can be used for a wide range of reactions such as hydrogenation of olefins, ketones, aldehydes, hydrogenation of halogen compounds, Is an extremely useful catalyst in the field of organic synthesis and is one of the most commonly used transition metal catalysts.

However, as the use of palladium catalysts in organic synthesis has expanded, how to efficiently recover palladium from a solution (waste solution) after organic synthesis using a palladium catalyst has become a problem. Since palladium is a noble metal, it is scarce in resources and expensive, it is extremely important to recover palladium effectively from a waste liquid containing palladium at low cost from the viewpoint of reuse and stable supply of palladium.

Conventionally, as a method for recovering palladium from a palladium-containing liquid, various methods such as a solvent extraction method, an ion exchange method, and a bioconcentration method using a biological function of a microorganism are known.

However, although the solvent extraction method using the extraction of water and organic solvent is widely adopted from the viewpoints of economic efficiency and operability, it is difficult to select an appropriate extraction agent considering the extraction ability, extraction speed, durability, There is a problem in that it is necessary to dispose the used organic solvent appropriately. On the other hand, an adsorption method using an adsorbent such as activated carbon or an ion exchange resin generally requires a small amount of adsorption by the adsorbent, requires a troublesome process, and has a disadvantage that it is necessary to properly dispose the used adsorbent. Further, in the bioconcentration method, there are many problems to be solved, such as cost, in order to put the bio-concentration method into practical use, and further examination is required.

In addition to the above methods, various methods for recovering palladium have been reported by a number of researchers. For example, palladium can be recovered by a relatively simple operation. As a conventional technique, palladium ions are reduced to aggregate palladium A recovery method has been proposed. This method is based on the principle that when the reducing agent is added to the palladium-containing liquid, the stability of the palladium stably dispersed in the liquid is lost, and as a result, relatively large particles including palladium are formed. As a specific example of such a method, Patent Document 1 discloses a method in which particles of palladium are formed by adding a reducing agent such as sodium borohydride, lithium aluminum hydride, hydrogen, hydrazine or the like to an acidic solution in a colloidal state containing palladium or a compound thereof, And then recovering and recovering the palladium.

In Patent Document 2, an alkaline agent is added to a palladium acidic solution in a colloidal state obtained in various industrial processes, and the solution is made basic to at least pH 11 to form palladium particles, Or an anionic polymer flocculant is added to form an agglomerate of palladium particles, which is separated and recovered.

As a technique for reducing and recovering palladium by a simple operation without going through a complicated treatment process, a hydrogen absorbing alloy is caused to act on a palladium solution in which palladium is dissolved, whereby a metal in the palladium solution with atomic hydrogen occluded in the hydrogen absorbing alloy Wherein palladium is recovered by separating the insoluble palladium material from the palladium solution by adding a polyethyleneglycol-based surfactant to the palladium solution to produce an insoluble palladium material in which the palladium is insolubilized, Patent Document 3 discloses a palladium recovery method.

In addition, Patent Document 4 discloses a method in which an organic waste liquid is burned and converted into a primary soft material, and then the primary soft material is washed to remove at least a part of the salts in the primary soft material to form a cleaning material, A method for recovering palladium from an organic waste liquid characterized by carrying out leaching treatment of the ash, and recovering palladium by subjecting the leaching treatment liquid to a purification treatment and a reduction treatment.

Japanese Patent Application Laid-Open No. 2001-32025 Japanese Patent Application Laid-Open No. 2000-313927 Japanese Patent Application Laid-Open No. 2005-281830 Japanese Patent Application Laid-Open No. 2002-327220

When a palladium catalyst is used in the organic synthesis of various chemical products and their raw materials for production, inorganic sulfur oxides such as sodium sulfite are often used as a reaction terminator in order to stop the synthesis reaction.

However, even if palladium is recovered from the palladium-containing waste liquid generated by organic synthesis using such inorganic sulfur oxides by using the conventional palladium recovery method based on the principle of palladium reduction and agglomeration as described above, The reduction of palladium does not proceed sufficiently. Therefore, the aggregation of palladium after reduction becomes insufficient, and even when the reduction is sufficient, the inorganic sulfur oxide suppresses the aggregation reaction with the flocculant such as palladium and the surfactant There is a problem that the recovery rate of palladium is lowered because aggregation becomes insufficient. Therefore, development of a palladium recovery method capable of recovering palladium from a palladium-containing waste liquid containing inorganic sulfur oxides such as sodium sulfite at a high recovery rate has been desired.

In view of this situation, the present invention provides a palladium recovery method capable of recovering palladium from a palladium-containing aqueous solution containing inorganic sulfur oxides such as sodium sulfite at a high recovery rate without requiring a complicated operation We will do it.

The reason why the reduction and aggregation reaction of palladium is difficult to proceed in an aqueous solution containing palladium containing inorganic sulfur oxides such as sodium sulfite is that the inorganic sulfur oxides such as sodium sulfite present in the waste solution form a strong complex with palladium I think that it is the cause. As a result of intensive studies to prevent the formation of such complexes and to sufficiently reduce and coagulate palladium, it has been found that, in order to adjust the pH of the palladium-containing waste liquid to a predetermined range during the reduction of palladium and to accelerate agglomeration of the reduced palladium The present inventors have found that palladium can be recovered at a high recovery rate when palladium is sufficiently reduced and aggregated sufficiently by adding a cationic surfactant, and the present invention has been accomplished by further research based on this finding.

That is, the present invention is a method for recovering palladium from a palladium-containing aqueous solution, which comprises the following steps.

(1) a step of adjusting the pH of an aqueous palladium-containing solution containing inorganic sulfur oxides to 2 or less,

(2) a step of adding a reducing agent to the palladium-containing aqueous solution to reduce palladium,

(3) A step of adding a cationic surfactant to the palladium-containing aqueous solution and coagulating and precipitating the reduced palladium to recover palladium.

INDUSTRIAL APPLICABILITY According to the present invention, palladium can be efficiently recovered from a palladium-containing aqueous solution containing inorganic sulfur oxides such as sodium sulfite at a high recovery rate without requiring complicated operations.

The method of the present invention is characterized by including the steps (1) to (3) as described above. Hereinafter, each step will be described in detail.

For step (1)

The liquid to be subjected to the palladium recovery treatment in the method of the present invention is an aqueous solution containing palladium containing inorganic sulfur oxides, that is, an aqueous solution containing inorganic sulfur oxides and further containing palladium or a compound thereof. As a palladium-containing aqueous solution containing inorganic sulfur oxides, for example, a waste solution containing a palladium catalyst after the organic synthesis after using inorganic sulfur oxide as a reaction inhibitor is exemplified. Examples of the palladium catalyst include divalent palladium compounds such as palladium acetate, palladium chloride, palladium iodide, palladium nitrate, palladium oxide and dinitrodiamine palladium; Palladium complexes coordinated with ligands such as triphenylphosphine, tri-t-butylphosphine, acetonitrile, benzonitrile and the like; Palladium powder; Palladium activated carbon is exemplified.

Specific examples of the inorganic sulfur oxides include at least one or more salts selected from sulfates, thiosulfates, sub dithionates, dithionates, sulfites and hydrogen sulfites. The inorganic sulfur oxide is generally used as a reaction terminator in organic synthesis.

In the palladium-containing aqueous solution to be subjected to the palladium recovery treatment, the contained concentration of palladium is not particularly limited and may be any concentration. The concentration of palladium in the aqueous solution containing palladium after organic synthesis using inorganic sulfur oxides as a reaction terminator is usually 0.05 to 5 g / L in terms of palladium metal powder.

The concentration of the inorganic sulfur oxide in the palladium-containing aqueous solution to be subjected to the palladium recovery treatment is not particularly limited, but it is preferably 10 to 200 g / L based on the volume of the palladium-containing aqueous solution in order to improve the recovery rate of palladium , Particularly 30 to 150 g / L.

In the step (1), the pH of the palladium-containing aqueous solution to be treated according to the present invention is adjusted to 2 or less, preferably 0 to 2, more preferably 1 to 2. By combining the steps of adjusting the pH of the palladium-containing aqueous solution to 2 or less, reducing the palladium by the reducing agent, adding the cationic surfactant, and coagulating and precipitating the reduced palladium in this manner, a palladium-containing aqueous solution It is possible to remarkably improve the recovery rate of palladium from the catalyst. If the pH is more than 2, even if a large amount of a reducing agent is added, the reduction reaction does not sufficiently proceed and the recovery rate is lowered. For example, since palladium acetate-derived acetic acid forms an acetic acid salt in a basic aqueous solution to buffer the palladium, the palladium reduction reaction does not proceed sufficiently. On the other hand, if the pH is lower than 0, a large amount of sulfur dioxide may be generated, and the reducing agent may be decomposed, which may necessitate the addition of a large amount of reducing agent after pH adjustment. The pH of the palladium-containing aqueous solution after the organic synthesis using the inorganic sulfur oxide as the reaction terminator is usually in the range of 4 to 5.

In order to adjust the pH of the palladium-containing aqueous solution to 2 or less, a pH adjuster may be added to the aqueous palladium-containing solution. The pH adjusting agent is not limited, and examples thereof include hydrohalogenic acids such as hydrochloric acid and hydrofluoric acid, inorganic acids such as sulfuric acid and carbonic acid, and organic acids such as citric acid, acetic acid, propionic acid, oxalic acid and adipic acid. Preferably, hydrogen halide acid which suppresses generation of sulfur dioxide and the like and is economically advantageous is used. There is no particular limitation on the timing of the adjustment of the pH, either simultaneously with the addition of the reducing agent or before or after the addition of the reducing agent. Preferably, when the pH is adjusted after or simultaneously with the reducing agent, a part of the reducing agent may lose the reducing function, and an excessive reducing agent may be required. Therefore, the pH is adjusted before adding the reducing agent.

About Process (2)

The combination of the adjustment of the palladium-containing aqueous solution in the step (1) to a pH of 2 or less, the addition of the reducing agent to the aqueous solution, and the step (2) of reducing palladium in the aqueous solution yield a high reduction efficiency.

As the reducing agent to be used, for example, hydrazine compounds such as sodium borohydride, lithium aluminum hydride, hydrazine and hydrazine hydrate, hydrogen, alcohol and the like are used. Particularly, sodium borohydride is preferably used. Since the palladium-containing aqueous solution to be treated according to the present invention contains an inorganic sulfur oxide, precipitation of palladium is still only slightly recognized at this stage.

The amount of the reducing agent to be added is suitably in the range of 1 to 20 times the theoretical amount required for reducing the palladium metal compound to metallic palladium.

The reducing treatment in the step (2) is usually carried out at normal temperature, depending on the kind of the reducing agent, and if necessary, heating is performed. The treatment time in the case of carrying out the reaction at room temperature is usually about 15 to 60 minutes. Also, there is no particular limitation on the timing of the addition of the reducing agent, and it may be either before or after the pH adjustment. Preferably, when the reducing agent is added at the same time as the pH adjustment or before the pH adjustment, a part of the reducing agent may lose the reducing function, and an excess of the reducing agent may be required. Therefore, the reducing agent is added after the pH adjustment.

About Process (3)

A cationic surfactant is added to the palladium-containing aqueous solution to precipitate reduced palladium to recover palladium. The sulfurous acid remains in the palladium-containing aqueous solution, and the residual sulfurous acid interferes with the agglomeration effect of the palladium by the surfactant and interferes with the agglomeration of the palladium. It is necessary to add a cationic surfactant in order to inhibit the residual inhibitory effect by the sulfurous acid and aggregate the palladium.

The pH of the palladium-containing aqueous solution before adding the cationic surfactant is preferably in the range of 1 to 7. [ When the pH of the palladium-containing aqueous solution is in the above-mentioned range, the optimum function of the cationic surfactant is obtained, so that the agglomeration of palladium is promoted and the recovery rate is improved. Also, there is no particular limitation on the timing of the addition of the cationic surfactant, either before, after or simultaneously with the pH adjustment, before or after the addition of the reducing agent. Preferably, the surfactant is added after the pH adjustment and the reducing agent addition, and more preferably after the pH adjustment and the reduction reaction of the palladium after the reducing agent is completed, because a part of the surfactant may be decomposed.

As the cationic surfactant, it is preferable to use a cationic surfactant, particularly an ammonium cationic surfactant, in order to enhance the flocculation effect of palladium. Examples of the cationic surfactant include cationic polyacrylamide, cationic polyacrylic acid ester, cationic polymethacrylic acid ester, alkyltrimethylammonium salt, dialkyldimethylammonium salt, and alkylbenzyldimethylammonium salt. Particularly, the cationic polyacrylamide is suitable because it has excellent flocculation promoting action of palladium and can be used in a wide pH range.

The cationic surfactant may be prepared, for example, by adding a cationic surfactant into a container filled with water with stirring with an agitator, then adding water to adjust the concentration to a predetermined level, stirring the mixture until the cationic surfactant is dissolved .

In the step (3), the addition amount of the cationic surfactant is preferably such that the concentration of the cationic surfactant in the palladium-containing aqueous solution after the addition of the cationic surfactant is 0.5 to 100 mg / L. It is more preferable to add an amount of 1 to 40 mg / L. If it is lower than 0.5 mg / L, the coagulation promoting action of palladium may not be sufficiently obtained. On the other hand, if it is higher than 100 mg / L, the viscosity of the liquid becomes high and it takes time to separate the coagulated palladium by filtration have.

In the step (3), the addition amount of the cationic surfactant to the weight of palladium (in terms of metal powder) in the palladium-containing aqueous solution is usually in the range of 0.05 to 10% by weight, preferably 0.1 to 6% by weight. On the other hand, if it is higher than 10% by weight, the viscosity of the liquid becomes high, and it sometimes takes time to separate the coagulated palladium by filtration.

Example

Examples of the present invention and comparative examples are shown below. They are illustrative and do not limit the scope of the invention.

[Examples 1 to 7 and Comparative Examples 1 to 3]

Palladium in the undiluted solution was recovered by the following method using an aqueous solution discharged from a production process using palladium acetate as a catalyst for an organic reaction as a stock solution (the pH of the undiluted solution was 4 to 4.5). In addition, the raw liquid includes inorganic sulfur oxides and organic substances (about 14% by weight) shown in Table 1.

First, hydrohalogenic acid (hydrochloric acid) was added dropwise to the stock solution to adjust the pH.

Then, 12 wt% aqueous solution of sodium borohydride was added as a reducing agent to the pH-adjusted stock solution to reduce palladium in the stock solution.

Thereafter, 0.2% by weight of a predetermined aqueous solution of the cationic surfactant was added to the solution after the reduction, stirred for 5 minutes, and then allowed to stand for 5 minutes to agglomerate and precipitate palladium.

Table 1 shows various conditions in each process described above. In Table 1, the concentration of the inorganic sulfur oxide was calculated from the content weight of the raw solution with respect to the volume of the palladium-containing aqueous solution. The addition concentration of the cationic surfactant was calculated from the addition weight to the total volume of the aqueous solution after the addition of the cationic surfactant and the addition weight to the weight of palladium (in terms of metal powder) in the stock solution, .

Aron Floc CX-213: {polyacrylic acid ester (weak to medium cationic), manufactured by Aqua Polymer Co., MT, trade name}

Aaron Floc CX-100: {polyacrylic ester (weak to medium cationic), manufactured by Aqua Polymer Co., MT, trade name}

Aaron Floc A-235: {modified polyacrylamide (medium cationic type), manufactured by MT Aqua Polymer Co., Ltd., trade name)

Health Floc N-217: {acrylic acid amide (non-ionic type), product of Water Agency)

[Agglomeration of palladium]

The aggregation state of palladium was evaluated as ○, the aggregation precipitate of palladium was observed but the dispersion was dispersed in a part of the liquid, the dispersion of palladium was not observed and the dispersion of the palladium in the whole liquid was evaluated as X Respectively. The results are shown in Table 2.

[Recovery rate of palladium]

The coagulated liquid was separated by filtration through an aqueous solution and palladium precipitation, and the amount of palladium metal contained in the aqueous solution and the undiluted solution of the filtrate was measured by an inductively coupled plasma atomic emission spectrometer (ICP-AES) to determine the recovery rate of palladium Lt; / RTI > The results are shown in Table 2.

As can be seen from the results shown in Table 2, in Comparative Example 1 and Comparative Example 2 in which an anionic and nonionic surfactants were respectively used, in Comparative Example 3 in which palladium did not aggregate and the pH was adjusted to 3, Cohesion was recognized, but the recovery rate was only 74.7%. In contrast, in Examples 1 to 7 relating to the method of the present invention, palladium in the aqueous solution was entirely coagulated and precipitated, and as a result, a high recovery rate (97.1 to 98.0%) of palladium was obtained.

Claims (9)

A method for recovering palladium from a palladium-containing aqueous solution, comprising the steps of:
(1) the pH of an aqueous solution containing palladium containing at least one or more kinds of inorganic sulfur oxides selected from sulfates, thiosulfates, dithionites, dithionates, sulfites and hydrogen sulfites is adjusted to 0 or more and 2 or less Adjusting process,
(2) a step of adding palladium-containing aqueous solution to at least one reducing agent selected from hydrazine compounds such as sodium borohydride, lithium aluminum hydride, hydrazine, and hydrazine hydride, hydrogen and alcohol to reduce palladium,
(3) A step of adding a cationic surfactant to the palladium-containing aqueous solution and coagulating and precipitating the reduced palladium to recover palladium. The method according to claim 1,
Wherein the concentration of the inorganic sulfur oxide in the palladium-containing aqueous solution containing inorganic sulfur oxides in the step (1) is 10 to 200 g / L based on the volume of the aqueous palladium-containing aqueous solution. delete 3. The method of claim 2,
Wherein the cationic surfactant is an ammonium cationic system. 3. The method of claim 2,
Wherein the added amount of the cationic surfactant is such that the contained concentration of the cationic surfactant is 0.5 to 100 mg / L relative to the entire volume of the palladium-containing aqueous solution after the cationic surfactant is added. The method according to claim 1,
Wherein the cationic surfactant is an ammonium cationic system. The method according to claim 1,
Wherein the added amount of the cationic surfactant is such that the contained concentration of the cationic surfactant is 0.5 to 100 mg / L relative to the entire volume of the palladium-containing aqueous solution after the cationic surfactant is added. 5. The method of claim 4,
Wherein the added amount of the cationic surfactant is such that the contained concentration of the cationic surfactant is 0.5 to 100 mg / L relative to the entire volume of the palladium-containing aqueous solution after the cationic surfactant is added. The method according to claim 6,
Wherein the added amount of the cationic surfactant is such that the contained concentration of the cationic surfactant is 0.5 to 100 mg / L relative to the entire volume of the palladium-containing aqueous solution after the cationic surfactant is added.