Pd separation method

Abstract

To provide a Pd separation method in which Pd contained as a complex in organic waste liquid can be separated and recovered with simple treatment and efficiently at high purity.SOLUTION: Provided is a Pd separation method, which is a method in which, using an organic waste liquid containing mainly an organic solvent having a water content of less than 10 mass% as a liquid to be treated, Pd is selectively separated from the inorganic components contained in the liquid to be treated, and the method comprises a step of adding 10 equivalents or more of formic acid to Pd contained in the liquid to be treated, heating to a temperature in the range of 50 to 100°C in a state in which formic acid is mixed in the liquid to be treated to generate a precipitate, and subjecting the generated precipitate to solid liquid separation.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for separating palladium (Pd), and more particularly to a method for separating and recovering Pd dissolved as a complex in an organic wastewater, followed by purification. [Background technology]

[0002] Generally, when valuable metal components such as Pd and other precious metals are contained in wastewater or effluent discharged from industrial processes such as catalyst manufacturing or cutting, it is common to recover the precious metals from the wastewater or effluent. Methods for recovering valuable specific metals such as Pd and other precious metals from wastewater or effluent include precipitation separation, electrolytic deposition, solvent extraction, and adsorption.

[0003] Furthermore, when the wastewater is organic and contains organic solvents, the heat generated during the incineration process allows for incineration with low energy consumption, and so the wastewater is also incinerated to recover metals. However, due to the heat generated during the incineration process, only small amounts can be supplied to the incineration furnace, which makes efficient treatment difficult.

[0004] For example, Patent Document 1 discloses a method for recovering Pd from an aqueous solution containing Pd, in which Pd is adsorbed onto an adsorbent and then desorbed from the adsorbent using a reducing agent to recover Pd.

[0005] Furthermore, Patent Document 2 discloses a method for recovering platinum group metals such as Pd contained in wastewater such as catalyst wastewater from electroless plating, in which a reducing agent such as an aqueous solution of sodium borohydride is added to the catalyst wastewater to form platinum group metal particles, which are then separated and recovered.

[0006] Patent Document 3 discloses a method for recovering Pd from a Pd-containing aqueous solution, which comprises the steps of: (1) adjusting the pH of a palladium-containing aqueous solution containing inorganic sulfur oxide, which is at least one salt selected from sulfates, thiosulfates, dithionites, dithionates, sulfites, and hydrogen sulfites, to a pH of 0 or more and 2 or less; (2) adding a reducing agent such as sodium borohydride to the palladium-containing aqueous solution to reduce palladium; (3) A step of adding a cationic surfactant to the palladium-containing aqueous solution to coagulate and precipitate the reduced palladium, thereby recovering the palladium.

[0010] A method is disclosed comprising: [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2014-122397 [Patent Document 2] Patent Publication No. 2001-32025 [Patent Document 3] Patent Publication No. 2014-19921 Summary of the Invention [Problem to be solved by the invention]

[0008] As mentioned above, various methods have been developed for recovering valuable metals, such as Pd and other precious metals, from wastewater and effluents. Among these, solvent extraction is widely adopted due to its economical and easy operation. Solvent extraction consists of an extraction step in which an aqueous phase containing dissolved metal ions is brought into liquid-liquid contact with an organic phase containing dissolved metal ion extractant, thereby extracting the metal ions into the organic phase, and a stripping step in which the metal ions extracted into the organic phase are contacted with an aqueous phase containing dissolved stripping agent, thereby stripping and concentrating the metal ions into the aqueous phase.

[0009] However, when the liquid to be treated is organic and contains an organic solvent, Pd (metal) ion extractants are miscible with the organic wastewater and therefore cannot be used. Known solutions to this problem include using adsorbents with high metal ion adsorption capacity and precipitating specific metals using reducing agents such as sodium borohydride, as described in Patent Documents 2 and 3. However, methods using adsorbents have issues with the contamination of metal ions with components (sulfur and nitrogen) derived from the adsorbent or separating agent during metal ion recovery, which can reduce the purity of the precious metals themselves. Furthermore, the use of a desorbing agent increases the amount of wastewater. Precipitation separation methods have safety and impurity issues, such as the contamination of metals derived from additives during precious metal recovery. Methods using reducing agents can generate hydrogen in amounts equal to or greater than the amount of precious metals during the reduction reaction.

[0010] Because of these issues and because organic waste liquids can be incinerated with low energy because of the heat of combustion generated by the organic solvent during incineration, a method of recovering metal components by calcination without adding a third component is widely adopted. However, the method of recovering metal components by calcination has the problem that only small amounts can be supplied to the combustion furnace due to the heat of combustion generated by the organic solvent during calcination, making efficient treatment impossible. Furthermore, the incineration of organic waste liquids generates a large amount of carbon dioxide, which is problematic from the environmental and carbon-neutral perspectives.

[0011] As mentioned above, when calcining an organic effluent containing Pd, the heat generated by combustion of the organic solvent is generated, and only small amounts can be treated at a time. Therefore, the inventors investigated ways to improve the treatment efficiency by concentrating the effluent by distillation prior to the calcination treatment. However, distillation treatment poses safety issues, such as adhesion problems due to solid precipitation of substances other than the target precious metal, and hydrogen generation. Therefore, they concluded that it is difficult to achieve a concentration of more than about five times by distillation. Therefore, it is difficult to sufficiently improve the treatment efficiency with such concentration treatment by distillation.

[0012] Furthermore, when a reducing agent such as sodium borohydride disclosed in Patent Documents 2 and 3 was used on a concentrated solution of organic effluent containing Pd, it was possible to precipitate most of the Pd contained in the concentrated solution, but many non-volatile components other than Pd contained in the concentrated solution also precipitated at the same time, resulting in a significantly low Pd compound composition in the final solid content, for example, less than 50 mass%, and not resulting in the recovery of highly pure Pd. Furthermore, it was confirmed that the addition of a reducing agent also generated hydrogen in an amount equal to or greater than the amount of Pd, which was undesirable from a safety standpoint.

[0013] As described above, in conventional Pd recovery technologies, when the wastewater to be treated is an organic wastewater, it is difficult to efficiently recover Pd contained in the wastewater with high purity. Furthermore, in light of the problems with these conventional Pd recovery technologies, the methods previously investigated by the present inventors have not yet achieved sufficient treatment efficiency or improved the purity of the recovered Pd to a satisfactory level.

[0014] Therefore, an object of the present invention is to provide a novel method for separating palladium (Pd). Another object of the present invention is to provide a method for separating Pd that can efficiently separate and recover Pd contained as a complex in organic effluent with high purity using a simple process. [Means for solving the problem]

[0015] As a result of extensive research by the present inventors in order to provide a method for separating Pd that solves the above-mentioned problems, they have surprisingly found that by concentrating an organic effluent containing Pd by distillation to an acceptable concentration range as described above, followed by adding a predetermined amount of formic acid as a reducing agent and performing a reduction treatment under predetermined temperature conditions, it is possible to selectively precipitate the Pd component from among the inorganic components contained in the organic effluent and to generate only a small amount of hydrogen, thereby arriving at the present invention.

[0016] That is, the present invention, which solves the above-mentioned problems, is a method for selectively separating Pd from inorganic components contained in a liquid to be treated, the liquid being an organic wastewater mainly containing an organic solvent and having a water content of less than 10 mass %, and the method comprises the steps of: adding 10 equivalents or more of formic acid or a derivative thereof to the Pd contained in the liquid to be treated; The liquid to be treated, in which formic acid or a derivative thereof is mixed, is heated to a temperature in the range of 50 to 100°C to generate a precipitate; The resulting precipitate is separated into solid and liquid, and then washed with a washing liquid. The present invention is characterized by including the following.

[0017] In one embodiment of the Pd separation method according to the present invention, when the Pd content in the treated liquid is 0.01 mass% or less, the treated liquid is concentrated by distillation prior to adding formic acid or a derivative thereof to the treated liquid.

[0018] In one embodiment of the method for separating Pd according to the present invention, the Pd content in the concentrated liquid to be treated obtained by the concentration treatment is set to 0.03 to 0.1 mass %.

[0019] In one embodiment of the Pd separation method according to the present invention, the liquid to be treated is mixed with formic acid or a derivative thereof, heated to a temperature in the range of 50 to 100°C, and treated with stirring for one hour or more to produce a precipitate.

[0020] In one embodiment of the method for separating Pd according to the present invention, the heating temperature is set to a range of 50 to 70°C.

[0021] In one embodiment of the Pd separation method according to the present invention, when the liquid to be treated is mixed with formic acid or a derivative thereof and heated to produce a precipitate, carbon dioxide is generated in the system in a molar ratio greater than or equal to the amount of hydrogen generated.

[0022] In one embodiment of the Pd separation method according to the present invention, formic acid or a derivative thereof is added to the treated liquid, and then the treated liquid is distilled to concentrate the treated liquid and produce a precipitate.

[0023] In one embodiment of the Pd separation method according to the present invention, the organic waste liquid to be treated is basic, and by adding 10 or more equivalents of formic acid or its derivative relative to the Pd contained in the liquid to be treated, and by adding any acid, the liquid to be treated is made neutral or acidic, at least when it is heated.

[0024] In one embodiment of the Pd separation method according to the present invention, the precipitate is subjected to solid-liquid separation, and then washed with water and recovered. This results in a recovery rate of 90% or more of the Pd contained in the treated liquid, and the Pd purity of the recovered and dried solid is 90% or more.

[0025] In one embodiment of the method for separating Pd according to the present invention, after the precipitate is subjected to solid-liquid separation, the precipitate is washed with at least one washing liquid selected from the group consisting of water, lower alcohols having 1 to 4 carbon atoms, and acetone.

[0026] In one embodiment of the method for separating Pd according to the present invention, the liquid to be treated contains at least an organic solvent capable of dissolving a Pd complex.

[0027] In one embodiment of the Pd separation method according to the present invention, the liquid to be treated contains at least one organic solvent selected from the group consisting of ketone organic solvents, alcohol organic solvents, ester organic solvents, ether organic solvents, amine organic solvents, alkoxysilane organic solvents, aromatic hydrocarbon organic solvents, aliphatic hydrocarbon organic solvents, and highly polar organic solvents. [Effects of the Invention]

[0028] The method for separating Pd according to the present invention can efficiently separate and recover highly pure Pd dissolved as a complex in an organic effluent using a simple process, and can also suppress the amount of hydrogen generated. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention will be described in more detail below based on embodiments.

[0030] (Organic wastewater containing Pd) In the Pd separation method according to the present invention, the composition of the "Pd-containing organic wastewater" as the liquid to be treated is not particularly limited, except that (a) it contains the Pd component to be recovered, and (b) the main component of the liquid phase is an organic solvent, and the water content is less than 10% by mass.

[0031] The reason why the liquid to be treated must satisfy condition (b) in addition to condition (a) above is that, for example, if the water content is 10% by mass or more, the separation method of the present invention is applicable, but is mainly due to the following reason: Pd complexes dissolved in organic solvents are soluble in organic solvents because the ligands coordinated to the Pd complexes are hydrophobic. Therefore, if the water content is high, the complex is partially hydrolyzed by heating and partially precipitates, making it unstable as a complex. On the other hand, if the water content is low, no precipitation occurs even when the liquid is concentrated, and palladium continues to dissolve as a complex, so a low water content is preferable. Note that a water content of less than 5% by mass, and even less than 1% by mass, is particularly preferable for treatment.

[0032] Although not particularly limited, in the case of "organic effluent containing Pd" actually provided as the liquid to be treated, the target Pd component contained in the effluent is often less than 0.01% by mass, more typically 0.005 to 0.01% by mass, and even more typically about 0.006 to 0.01% by mass. In cases where the Pd component contained in the liquid to be treated is less than 0.01% by mass, it is desirable to first concentrate the liquid to be treated by distillation, as described below. Examples of organic effluents with such low Pd component contents include, for example, effluents from catalyst production processes and effluents used and discharged in cutting processes, but of course, the present invention is not limited to these.

[0033] On the other hand, when the target Pd component of the "Pd-containing organic wastewater" as the liquid to be treated is 0.01 mass % or more, it is not necessarily necessary to first carry out a concentration treatment by distillation.

[0034] Furthermore, although not particularly limited, the "Pd-containing organic wastewater" as the liquid to be treated generally often contains inorganic substances other than Pd as inorganic components, such as, but not particularly limited to, Na, P, Cu, Zn, Mg, Fe, Al, Si, etc. The content of these inorganic substances other than Pd is not particularly limited, but is, for example, about 0.001 to 0.5 mass%, more typically 0.001 to 0.2 mass%, and even more typically about 0.001 to 0.1 mass%.

[0035] Furthermore, the organic solvent contained in the "organic effluent containing Pd" as the liquid to be treated is not particularly limited, as long as Pd forms a complex, compound, etc. and is present in the liquid phase of the effluent as the overall composition of the organic effluent. Furthermore, the Pd separation method of the present invention is applicable without being significantly affected by the type of organic solvent contained, and representative examples include one or more of ketone organic solvents, alcohol organic solvents, ester organic solvents, ether organic solvents, amine organic solvents, alkoxysilane organic solvents, aromatic hydrocarbon organic solvents, aliphatic hydrocarbon organic solvents, and highly polar organic solvents.

[0036] Examples of ketone-based organic solvents include, but are not limited to, acetone, methyl ethyl ketone, and methyl isobutyl ketone. Examples of alcohol-based organic solvents include, but are not limited to, methanol, ethanol, and isopropanol. Examples of ester-based organic solvents include, but are not limited to, ethyl acetate, isopropyl acetate, and isobutyl acetate. Examples of ether-based organic solvents include, but are not limited to, diethyl ether, 1,4-dioxane, tetrahydrofuran (THF), and methyl tertiary butyl ether (MTBE). Examples of amine-based organic solvents include, but are not limited to, methylamine, ethylamine, ethylenediamine, and pyridine. Examples of alkoxysilane-based organic solvents include, but are not limited to, methyltrimethoxysilane, phenyltrimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, and trimethylethoxysilane. Examples of aromatic hydrocarbon organic solvents include, but are not limited to, benzene, toluene, xylene, etc. Examples of aliphatic hydrocarbon organic solvents include, but are not limited to, n-hexane, isohexane, cyclohexane, n-octane, isooctane, decane, dodecane, etc. Examples of highly polar organic solvents include, but are not limited to, 1,3-dimethyl-2-imidazolidinone (DMI), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMA), dimethylformamide (DMF), etc.

[0037] The organic solvent contained in the "Pd-containing organic effluent" actually provided as the liquid to be treated is often a complex composition containing two or more of the above-mentioned organic solvents rather than just one of them. Although not particularly limited, a typical example is a mixture of a hydrophilic organic solvent such as an alcohol solvent (methanol, ethanol, isopropanol) or a ketone solvent (acetone) with a hydrophobic organic solvent such as n-hexane, toluene, or tetrahydrofuran, containing a small amount of water in a content of less than 10% by mass, particularly less than 1% by mass.

[0038] Furthermore, the pH of the "Pd-containing organic wastewater" to be treated is not particularly limited, and any acidic, neutral, or basic wastewater can be treated by the Pd separation method of the present invention. However, if the liquid to be treated is basic (pH > 7.0), formic acid is used as a reducing agent in the Pd separation method of the present invention, as described below, but this formic acid may be consumed by the base of the liquid to be treated, inhibiting the precipitation of Pd.

[0039] Therefore, when the "Pd-containing organic wastewater" to be treated is basic, as described below, in addition to adding 10 or more equivalents of formic acid or its derivatives relative to the Pd contained in the liquid to be treated as a reducing agent, any amount of acid can be added to the liquid to be treated, as needed, to neutralize or acidify the liquid to a pH of 7.0 or less. The acid used for this neutralization or acidification treatment is not particularly limited and may be any. Formic acid added as a reducing agent can also be used as the acid for this neutralization or acidification treatment. In this case, the amount of formic acid used as a reducing agent is 10 or more equivalents relative to the Pd contained in the liquid to be treated, and an additional amount for the neutralization or acidification treatment is sufficient. In addition to formic acid, the acid used for this neutralization or acidification treatment can also be, for example, organic acids such as acetic acid and oxalic acid, or inorganic acids such as hydrochloric acid and phosphoric acid, but is not limited to these listed acids.

[0040] Furthermore, the timing of adding the acid used for neutralizing or acidifying the "Pd-containing organic wastewater" as the liquid to be treated is not particularly limited. However, in order to prevent the formic acid as the reducing agent from being consumed by the base, it is desirable to add the acid to the basic liquid to be treated at least simultaneously with or before the addition of formic acid as the reducing agent.

[0041] On the other hand, if the "Pd-containing organic wastewater" to be treated is originally neutral or acidic, there is no particular need for such neutralization or acidification treatment by adding an acid.

[0042] (Concentration treatment) The Pd separation method of the present invention requires the addition of formic acid to the liquid to be treated and the subsequent heat treatment to selectively precipitate Pd, as described in detail below. However, if the Pd content of the liquid to be treated is 0.01 mass % or less, it is preferable to concentrate the liquid to be treated by distillation before adding formic acid to the liquid to be treated.

[0043] This is because, when the Pd content of the liquid to be treated is 0.01% by mass or less, the treatment efficiency can be improved by concentrating the wastewater to a certain extent by distillation. Since the liquid to be treated contains only 0.01% by mass or less of Pd, it is best to concentrate it as much as possible. However, if it is concentrated too much, the solubility of the nonvolatile components may be exceeded, leading to precipitation, so there is a concentration limit. This non-selective precipitation of nonvolatile components makes it difficult to selectively recover the target Pd with high purity. Furthermore, excessive concentration treatment may cause safety problems, such as the generation of hydrogen during treatment.

[0044] Therefore, it is desirable to concentrate the liquid to be treated by such distillation so that the Pd content of the concentrated liquid to be obtained is 0.03 to 0.1 mass %, more preferably 0.04 to 0.1 mass %. The concentration ratio is, for example, 3 to 10 times, more preferably 4 to 10 times, by volume.

[0045] Furthermore, since the concentration process is performed by distillation, the Pd content increases as described above, and the composition of the organic solvent contained in the treated liquid may also change. For example, if the organic solvent contains both a low-boiling point compound such as acetone and a relatively high-boiling point compound such as a highly polar organic solvent, the concentration process will reduce the proportion of low-boiling point compounds and increase the proportion of relatively high-boiling point compounds. In this way, the proportion of relatively high-boiling point compounds in the composition of the concentrated treated liquid obtained by the concentration process tends to increase, and the selective precipitation reaction of Pd by the addition of formic acid or its derivatives, as described below, tends to proceed more smoothly. Therefore, the concentration process is also desirable from this perspective.

[0046] The method of concentration in distillation is not particularly limited, but for example, a batch distillation apparatus consisting of a still, a condenser, and a distillate tank is charged with an organic effluent containing Pd as the raw material, and the still is heated to, for example, 100°C with steam under a pressure of, for example, 101 kPa to evaporate the low-boiling components in the organic effluent. The evaporated liquid is cooled in the condenser and becomes a liquid, which then enters the distillate tank. In such an apparatus, for example, 1,000 kg of organic effluent is charged into the still, and the still is heated to, for example, 100°C with steam under a pressure of, for example, 101 kPa, and 800 kg is distilled, thereby obtaining a liquid concentrated fivefold.

[0047] (Selective deposition treatment) Therefore, in the Pd separation method of the present invention, formic acid or its derivative is added to the liquid to be treated in an amount that is 10 equivalents or more relative to the Pd contained in the liquid to be treated, and the liquid to be treated, while mixed with formic acid, is heated to a predetermined temperature to produce a precipitate.

[0048] Thus, in the present invention, formic acid or its derivatives are used as a reducing agent to selectively precipitate Pd present as a complex in the solution to be treated. When the wastewater solution to be treated is primarily composed of an organic solvent, many compounds known to be used as reducing agents in aqueous wastewater systems are limited in their use due to their solubility in organic solvents. Furthermore, their strength as reducing agents is questionable. Using strong reducing agents is dangerous because they generate large amounts of hydrogen and heat. On the other hand, formic acid is preferred from the standpoint of reactivity, its ability to selectively extract Pd, its low hydrogen production, and its ability to generate large amounts of carbon dioxide, an inert gas. The mechanism by which Pd, among the various inorganic substances contained in the liquid to be treated, is selectively precipitated as a precipitate when formic acid is used as a reducing agent is not entirely clear. However, when Pd exists as a complex in an organic effluent, the Pd exists in a state in which it has a ligand attached, and the solubility of Pd in ​​the effluent is determined by the ligand. It is thought that the addition of formic acid in an amount greater than the specified amount described above significantly affects the stability of the Pd complex, among the various inorganic components contained in the liquid to be treated, resulting in precipitation.

[0049] In the present invention, the amount of formic acid or its derivative added is 10 or more equivalents relative to the Pd contained in the liquid to be treated. That is, in addition to using formic acid to selectively precipitate Pd, adding a relatively large amount, 10 or more equivalents relative to Pd, is an important condition for efficient Pd precipitation. This is because if the amount is less than 10 equivalents relative to Pd, the amount of Pd precipitated in the liquid to be treated is likely to be insufficient. The amount of formic acid added is more preferably 10 to 100 equivalents relative to the Pd contained in the liquid to be treated, and even more preferably 10 to 20 equivalents.

[0050] Furthermore, the particle size of the precipitate tends to increase as the amount of formic acid or its derivative added increases. Therefore, from the viewpoint of facilitating solid-liquid separation after precipitation, it is desirable to add a relatively large amount, 10 equivalents or more relative to Pd, as specified in the present invention.

[0051] The purity of the formic acid used in the present invention is not particularly limited. For example, purity of 95% by mass or more, more preferably 99% by mass or more, can be used as long as it satisfies the above-mentioned required equivalent. The formic acid derivatives that can be used in the present invention are not particularly limited as long as they exhibit substantially the same effect as formic acid with respect to Pd deposition. Examples of formic acid salts that can be used in the present invention include, but are not limited to, sodium formate and potassium formate. Examples of formic acid esters include, but are not limited to, esters of formic acid with alkyl groups having 1 to 10 carbon atoms, such as methyl formate, ethyl formate, and amyl formate. The formic acid or its derivatives used as reducing agents in the present invention are not limited to being used alone, but can also be used in combination of two or more. For example, formic acid and a formate salt can be used in combination, or formic acid and a formate ester can be used in combination.

[0052] Furthermore, in the present invention, a predetermined amount of formic acid or its derivative is added as a reducing agent, as described above, and the formic acid or its derivative is mixed with the liquid to be treated and heated at a predetermined temperature. The temperature conditions depend on the atmospheric pressure, but under conditions near atmospheric pressure (1013 hPa ± 100 hPa), it is desirable to heat the liquid to a temperature in the range of 50 to 100°C, preferably 50 to 70°C, and more preferably 60 to 70°C. Maintaining a temperature in the range of 50 to 100°C promotes the precipitation reaction, allowing for efficient precipitation within a few hours, compared to the 10 days or more required for precipitation to begin after adding 70 equivalents of formic acid at room temperature (25°C + 2°C). Furthermore, using an extremely high temperature can be undesirable from a safety standpoint, for example, in a liquid to be treated containing low-boiling-point components, due to the further volatilization and thermal decomposition of formic acid and the generation of hydrogen. However, this does not occur within the predetermined temperature range. Note that, when the heating treatment is carried out at a temperature of 50 to 70°C, the generation of hydrogen due to the volatilization and thermal decomposition of formic acid or its derivatives is significantly suppressed, and this is an especially desirable treatment condition. As the temperature conditions for the heat treatment, under pressure, for example, 1013 to 5000 hPa, higher temperature conditions than those near normal pressure, for example, 50 to 150° C., more preferably 80 to 120° C., can be adopted. However, since pressurization equipment such as a pressurized container is required, there is a risk of problems in terms of cost and safety, and therefore it is desirable to carry out the heat treatment near normal pressure as described above.

[0053] Furthermore, as one embodiment of the Pd separation method according to the present invention, when the Pd content of the liquid to be treated is 0.01% by mass or less as described above and a concentration treatment by distillation is performed, it is also possible to add formic acid as a reducing agent to the liquid to be treated prior to the concentration treatment, and to concentrate the liquid to be treated and produce a precipitate by distillation. However, since there is a concern that the amount of hydrogen generated during precipitation may increase if precipitation is performed at a high temperature as described above, it is preferable to once perform the concentration treatment by distillation, add formic acid or a derivative thereof as a reducing agent, and separately perform a heating treatment at the above-mentioned predetermined temperature, preferably a relatively low temperature of 50 to 70°C, to precipitate Pd.

[0054] (solid-liquid separation) In the method for separating Pd according to the present invention, the precipitate is recovered by solid-liquid separation from the solution to be treated in which the precipitate has formed as a result of the selective precipitation treatment as described above. The method for solid-liquid separation is not particularly limited, and can be carried out by any of the commonly used methods such as filtration using a filter, filter paper, or the like, or centrifugation. However, since the precipitate obtained has a relatively large particle size, and the particle size tends to increase particularly when the amount of formic acid added is increased, good separation is also possible by separation operation by filtration using a filter or filter paper, which is easy to operate.

[0055] The precipitate obtained by solid-liquid separation is then subjected to a washing treatment, if necessary, to remove any adhering residues of the treated liquid and any soluble substances. Washing is preferably performed using water, particularly pure water, but it is also possible to wash using a low-boiling organic solvent such as a lower alcohol having 1 to 4 carbon atoms, such as methanol, ethanol, isopropyl alcohol, or butyl alcohol, or other low-boiling organic solvents, such as acetone, diethyl ether, chloroform, tetrahydrofuran, ethyl acetate, hexane, or benzene. It is also possible to combine washing with such a low-boiling organic solvent with washing with water, particularly pure water.

[0056] (separated substance) In the present invention, the above-described procedure allows for efficient separation and recovery of Pd contained as a complex in an organic wastewater through a simple process. Typically, after water washing, the recovered and dried solid (separated product) has a Pd purity of 90% or more, and the recovery rate of Pd from the treated liquid can be 90% or more. Furthermore, since the present invention allows for the production of high-purity palladium without incineration, no large amounts of carbon dioxide are generated when organic components are incinerated, making it an environmentally friendly separation process. [Example]

[0057] The present invention will be described in more detail below with reference to examples.

[0058] Example 1 (Liquid to be treated) The organic effluent used in this example was provided from a catalyst production process. The composition of this organic effluent was measured by gas chromatography under the following conditions. Equipment: GC-2014 (Shimadzu Corporation) Detector: Hydrogen flame ion detector Column: G-100 (inner diameter: 1.2 mm, length: 40 m, film thickness: 3.0 μm) Column temperature rise conditions: 80°C → 10°C / min temperature rise → 240°C (hold for 44 minutes) Injection port conditions: 250°C, Carrier gas flow rate: 15 ml / min The results obtained are shown in Table 1. The solid content concentration was calculated by collecting a portion of the organic effluent as a sample in a petri dish, leaving it on a hot plate at 140°C for 12 hours, and then dividing the amount of solid content remaining on the petri dish by the amount of the collected sample.

[0059] As shown in Table 1, the organic solvent in this organic effluent was primarily acetone, and the nonvolatile content was 0.76% by mass. After measuring the nonvolatile content, the solid content was transferred to a crucible and baked in an electric furnace at 1000°C for 1 hour. The resulting residue was dissolved in aqua regia, and the resulting solution was analyzed using an ICP optical emission spectrometer (Spectro, ARCOS:MV130·FHM22). It was confirmed that Pd was dissolved in the organic effluent as a complex, with a Pd content of approximately 0.008% by mass.

[0060] (Concentrated liquid to be treated) Since the Pd content in the liquid to be treated was 0.01% by mass or less, the liquid to be treated was subjected to concentration treatment by distillation. The distillation conditions were as follows: the liquid to be treated was charged into a batch still, steam was used as the heating source, the pressure inside the batch still was set to 101 KPa, and the liquid was concentrated by about 5 times. The composition of the concentrated liquid to be treated thus obtained was also analyzed in the same manner as above. The results are shown in Table 1.

[0061] As shown in Table 1, the concentrated liquid to be treated contained DMI as the main organic solvent, and the nonvolatile content was 4.71% by mass. After this 5-fold concentration, the inorganic components contained in the liquid as complexes did not precipitate or settle, and the liquid remained in a homogeneous liquid phase. The pH of the concentrated liquid to be treated was measured using a HORIBA D-75 and found to be 8.7. [Table 1]

[0062] The Pd concentration in the concentrated treated liquid was confirmed to be 0.032 mass% by taking a sample of the concentrated treated liquid in a crucible, baking it at approximately 1000°C for 1 hour, dissolving the resulting residue in aqua regia, and analyzing the solution using the same ICP atomic emission spectrometer as above.

[0063] Furthermore, to investigate the composition of inorganic components contained in the concentrated solution, the concentrated solution was placed in a crucible and fired at approximately 1000°C, and the composition of the resulting residue (solid content composition) was analyzed by X-ray fluorescence analysis (ZSX PrimusIV, manufactured by Rigaku Corporation). The results are shown in Table 2.

[0064] [Table 2] Of the elements listed in Table 2, Al and Si were considered to be contaminants from the crucible used during firing. Furthermore, O and C were present in large amounts because, for the X-ray fluorescence analysis, a tablet was made by adding residue to cellulose and analyzing it. Based on these findings, it was confirmed that the concentrated solution to be treated also contained 2.89 times the amount of P, 7.81 times the amount of Na, 0.05 times the amount of Ca, 0.03 times the amount of Mg, 0.08 times the amount of Fe, and 0.16 times the amount of S relative to Pd.

[0065] (Selective deposition treatment) To 699.9 g of the concentrated treated liquid prepared as described above, 12.74 g of formic acid was added, which was approximately 100 equivalents of the Pd contained in the concentrated treated liquid.The liquid to be treated, while still mixed with formic acid, was heated to 70°C and held for 2 hours to produce a precipitate.

[0066] The precipitate was collected using filter paper (No. 5C) and then dried in a dryer at 110°C. After drying for 12 hours, the solid content was analyzed by X-ray fluorescence analysis (Rigaku Corporation, ZSX PrimusIV). The results are shown in Table 3. After collecting the precipitate on filter paper, it was thoroughly washed with pure water and then dried in a dryer at 110°C. After drying for 12 hours, the solid content was analyzed by X-ray fluorescence analysis in the same manner. The results are shown in Table 4.

[0067] [Table 3]

[0068] [Table 4]

[0069] As mentioned above, of the elements shown in Tables 3 and 4, Al and Si are believed to be contaminants from the crucible used during calcination, while O and C are present in large amounts because cellulose was mixed with the residue during X-ray fluorescence analysis to form tablets for analysis. From this perspective, when examining the composition of the precipitates assuming calcination, with the O and C components thought to have been mixed in during analysis set to zero, it is clear that Pd is selectively precipitated as a precipitate. Furthermore, when washing with water after filtration was performed, the composition of the resulting precipitate was found to be 95% or more Pd as an inorganic component, demonstrating a recovery rate of 90% or more of Pd from the treated liquid.

[0070] Example 2, Reference Examples 1 to 3 To examine the effect of the amount of reducing agent used, the Pd separation procedure was carried out in the same manner as in Example 1, except that the amount of formic acid added as a reducing agent in Example 1 was changed to 1 equivalent (Reference Example 1), 2 equivalents (Reference Example 2), 5 equivalents (Reference Example 3), or 10 equivalents (Example 2). The effectiveness of the Pd separation was evaluated by sampling a portion of the supernatant after the precipitate had settled after a predetermined time had passed and analyzing the amount of Pd. The analytical method involved calcining each sample in a crucible at 1000°C, dissolving the calcined solution in aqua regia, and analyzing the diluted aqua regia solution using an ICP (Spectro, ACROS:MV130·FHM22) to quantify the amount of Pd in ​​the supernatant.

[0071] The conditions for the separation operation and the results obtained are shown in Tables 5 and 6. In Table 6, the solids separation performance when using a reducing agent, the Pd sedimentation rate, and the Pd purity were each evaluated on a four-level scale, represented by ◎, 〇, △, and ×. The evaluation criteria are as follows:

[0072] Solids separation × Slurry, oil △ Average particle size less than 1 μm Average particle size: 1 μm to less than 5 μm ◎ Average particle size 5μm or more

[0073] Pd sedimentation rate × Less than 30% △ 30% to less than 60% ○ 60% to less than 90% ◎ 90% or more

[0074] Pd purity (inorganic component ratio) × Less than 70% △ Less than 70% to 80% ○ Less than 80% to 90% ◎ 90% or more

[0075] As shown in Tables 5 and 6, as the amount of formic acid added increased, the sedimentation rate of Pd increased and the particle size of the resulting precipitate tended to increase. However, when the amount added was less than 10 equivalents, the sedimentation rate was less than 50%, indicating insufficient recovery efficiency.

[0076] Comparative Examples 1 to 4 To investigate the effect of the type of reducing agent used, Pd separation was performed in the same manner as in Example 1, except that NaBH4 was used as a precipitant instead of the formic acid used in Example 1, and the amount added was 1, 5, 10, or 20 equivalents relative to Pd (Comparative Examples 1 to 4). In the NaBH4 addition system, the amount of Pd in ​​the supernatant was confirmed when a predetermined amount of NaBH4 was added. It was confirmed that the solution became black and suspended when 1 equivalent of NaBH4 relative to Pd was added at room temperature. The separation conditions and results obtained are also shown in Tables 5 and 6. Furthermore, for the sample in which 20 equivalents of NaBH4 relative to Pd were added (Comparative Example 4), the precipitate was collected using filter paper (No. 5C) and then dried at 110°C in a dryer. After drying for 12 hours, the solid content was analyzed by X-ray fluorescence analysis (Rigaku Corporation, ZSX PrimusIV). The results are shown in Table 7. After collecting the precipitate on filter paper, the precipitate was thoroughly washed with methanol and then dried in a dryer at 110°C. After drying for 12 hours, the solid content was analyzed by X-ray fluorescence analysis in the same manner. The results are shown in Table 8.

[0077] As shown in Tables 5 and 6, the amount of sedimentation and particle size tended to increase with increasing NaBH4 addition. Furthermore, Pd analysis of the supernatant after NaBH4 addition showed that the Pd sedimentation rate reached 90% at 5 equivalents relative to Pd, and remained constant with subsequent additions. While a high precipitation effect was observed even with small additions, the composition of the precipitates, as shown in Table 7, showed that the precipitate composition using NaBH4, excluding organic components (C and O), consisted of Na (21.2%) as the main component, Cl (7.01%), and Pd (1.73%). Furthermore, washing the precipitate with methanol reduced the weight of the resulting precipitate by approximately 84.3 wt% compared to before washing, and Pd became the main component at 27.7%, as shown in Table 8. However, the inorganic components contained Na and Cl in amounts approximately half that of Pd, and other metal components were also present in significant amounts.

[0078] Comparative Examples 5 to 9 In order to investigate the effect of the type of reducing agent used, butyraldehyde (Comparative Example 5), benzaldehyde (Comparative Example 6), an aqueous oxalic acid solution (Comparative Example 7), an aqueous sodium thiosulfate solution (Comparative Example 8), or an aqueous sodium phosphinate solution (Comparative Example 9) was used as a precipitant instead of the formic acid used in Example 1, and the amount added was the equivalent amount relative to Pd shown in Table 5, but the same procedure as in Example 1 was repeated. The conditions for the separation operation and the results obtained are also shown in Tables 5 and 6.

[0079] As shown in Tables 5 and 6, in the systems where butyraldehyde (Comparative Example 5), benzaldehyde (Comparative Example 6), and an aqueous oxalic acid solution (Comparative Example 7) were added, the amount of sedimentation was small even when a relatively large equivalent amount relative to Pd was added, making it difficult to recover Pd by precipitation and sedimentation. In the systems where sodium thiosulfate solution (Comparative Example 8) and sodium phosphinate solution (Comparative Example 9) were added, the amount of sedimentation was large. Regarding the precipitate of the sodium phosphinate aqueous solution (Comparative Example 9), which showed a particularly large amount of sedimentation, the precipitate was collected with filter paper (No. 5C) and then dried in a dryer at 110°C in the same manner as in Example 1. The solid content after drying for 12 hours was analyzed by X-ray fluorescence analysis (ZSX PrimusIV, manufactured by Rigaku Corporation). The obtained results are shown in Table 9. After collecting the precipitate on filter paper, the precipitate was thoroughly washed with pure water and then dried in a dryer at 110°C. After drying for 12 hours, the solid content was similarly analyzed by X-ray fluorescence analysis. The results are shown in Table 10. As is clear from the results shown in Tables 9 and 10, when an aqueous sodium phosphinate solution was used, the Pd purity and separability after washing were lower than when using formic acid. In addition, sodium phosphinate produced a large amount of hydrogen in a gas generation confirmation test.

[0080] [Table 5]

[0081] [Table 6]

[0082] [Table 7]

[0083] [Table 8]

[0084] [Table 9]

[0085] [Table 10]

[0086] Example 3 and Comparative Example 10 A gas generation confirmation test was conducted using formic acid as a reducing agent in accordance with the present invention and the sodium phosphinate precipitation method, which showed relatively good results in terms of precipitation amount as shown in Comparative Example 9. The type and amount of gas generated during the reaction were confirmed. A four-neck flask was attached to a mantle heater, 200 g of the concentrated liquid raw material was charged, a stirrer was added, and a reducing agent was added in an amount equivalent to 76 Pd equivalents (3.2 g) of formic acid or 21 Pd equivalents (2.1 g) of sodium phosphinate. After adding the reducing agent, a Dimroth condenser was attached, cooling water was run through, and the liquid cooled and returned during heating (total reflux state). A gas sampling bag was attached to the outlet of the Dimroth condenser, and the mixture was heated to 70°C and gas was collected for 2 hours. After further heating at 70°C for 2 hours, the system was depressurized to 100 Torr (13,332.2 Pa) using a diaphragm pump. The gas in the system during depressurization was collected using a gas sampling bag attached to the outlet of the diaphragm pump. The collected gas was analyzed by gas chromatography (TCD) to determine its composition. The gas chromatography conditions were as follows: Equipment: GC-2014 (Shimadzu Corporation) Detector: Thermal conductivity detector SHIN CARBON ST Temperature conditions: 40°C (hold for 12 minutes) → 10°C / min temperature increase → 200°C (hold for 42 minutes) Injection port conditions: 200°C, Carrier gas flow rate: 45 ml / min

[0087] After analysis by gas chromatography, the gas in the gas sampling bag was extracted with a 200 ml syringe and the amount of gas in the sampling bag was measured. The results are shown in Table 11.

[0088] Example 4 Furthermore, when formic acid according to the present invention was used as a reducing agent, a gas generation confirmation test was conducted at various heating temperatures to confirm the type and amount of gas generated during the reaction. Using the same apparatus configuration as in Example 3 above, 200 g of the concentrated liquid raw material was added with formic acid (0.5 g) as a reducing agent, in an amount equivalent to 15 Pd equivalents. The mixture was heated to 80°C under total reflux conditions and gas was collected for 6 hours. After heating, the system was depressurized to 100 Torr (13,332.2 Pa) using a diaphragm pump. The gas in the system at the reduced pressure was collected using a gas sampling bag installed at the outlet of the diaphragm pump and analyzed by gas chromatography (TCD) in part as in Example 3 to determine the composition. The results are shown in Table 11.

[0089] [Table 11]

[0090] As a result, when heated at the same temperature of 70°C, when sodium phosphinate was used (Comparative Example 10), 25.1 ml of hydrogen was generated, which was 1.2 equivalents relative to Pd, a slightly higher amount, suggesting that other substances were also reduced. On the other hand, when formic acid was used (Example 3), 9.44 ml of hydrogen and 44.31 ml of carbon dioxide were generated, resulting in 0.5 equivalents of hydrogen relative to Pd and 2.2 equivalents of carbon dioxide relative to Pd. The low amount of hydrogen generated is due to the fact that when formic acid is consumed in the reduction reaction, the reaction occurs via a hydride complex. Since the reduction reaction proceeds via a mechanism that does not generate hydrogen, the present invention achieves a highly safe reduction reaction with reduced hydrogen generation. Compared to sodium phosphinate, when formic acid was used, the amount of hydrogen generated was lower, and 4.7 times the amount of carbon dioxide generated relative to hydrogen. Since hydrogen is diluted with carbon dioxide, an inert gas, it was confirmed that the process of the present invention, using formic acid as a reducing agent, is safer than the case using sodium phosphinate.

[0091] Furthermore, when formic acid was used, and the heating temperature and treatment time were increased (Example 4), 30.68 ml of hydrogen (1.37 equivalents relative to Pd) and 54.03 ml of carbon dioxide (2.40 equivalents relative to Pd) were generated at 80°C. Comparing the amounts of generated gases with those in Example 3 (heating temperature 70°C), the amount of carbon dioxide increased only about 1.1 times, while the amount of hydrogen increased by about 3 times. In Example 4, the amount of generated hydrogen was greater than in Example 3, despite the smaller amount of formic acid used. Therefore, even if the heating temperature condition was within the range of 50 to 100°C, a temperature below 70°C as in Example 3, i.e., the range of 50 to 70°C, was considered to be more preferable from the standpoint of safety.

[0092] Reference example 4 In Example 1, the precipitation treatment of Pd in ​​the solution to be treated was carried out in the same manner as in Example 1, except that the treatment temperature after the addition of formic acid as a reducing agent was changed to room temperature (25°C). However, under these temperature conditions, precipitation did not occur in a short time, and it took approximately 10 days for the first precipitation to occur, even though a relatively large amount of formic acid (72 equivalents) was added.

[0093] Example 5 To investigate the effect of the pH of the treated liquid on Pd precipitation, a Pd precipitation treatment was performed under conditions different from those used in Examples 1 to 4 (pH 8.7). To the concentrated treated liquid used in Examples 1 to 4, 234 equivalents of NaOH relative to Pd were added to prepare a basic concentrated treated liquid under conditions where an excess amount of base was present. The pH of this basic concentrated treated liquid was 12.0. To this basic concentrated treated liquid, 102 equivalents of formic acid relative to Pd were added. The treated liquid, with the formic acid mixed therein, was heated to 70°C and maintained for 2 hours to produce a precipitate. The composition was 11.5 g of the concentrated treated liquid, the same as in Example 1, to which 0.38 g of NaOH and 0.19 g of formic acid were added. As a result, a black precipitate was formed, and the Pd sedimentation rate was good, but the precipitate particles were small, resulting in a slightly lower evaluation from the perspective of solid separation ability. The pH after 2 hours of heating was 7.3. These results suggest that basic conditions produce formate, which also contains an aldehyde group, promoting the precipitation of Pd through reduction. However, under basic conditions, the precipitate particles stabilized, preventing particle growth and resulting in a finer particle size. Conversely, under acidic conditions, the particles became unstable, and growth (aggregation) occurred due to intermolecular interactions with other particles. Therefore, when the treatment solution is basic, it is preferable to add formic acid or a formic acid derivative in an amount equal to or greater than 10 equivalents of Pd, as well as any amount of acid (including formic acid), to maintain the pH of the treatment solution neutral or acidic for treatment.

Claims

1. A method for selectively separating Pd from inorganic components contained in an organic wastewater treatment solution containing an organic solvent as the main component and having a water content of less than 10% by mass, the method comprising: adding 10 equivalents or more of formic acid or a derivative thereof to the Pd contained in the liquid to be treated; When the liquid to be treated, in which formic acid or a derivative thereof is mixed, is heated to a temperature in the range of 50 to 100°C to generate a precipitate, carbon dioxide is generated in the system in a molar ratio greater than or equal to the amount of hydrogen generated, The resulting precipitate is subjected to solid-liquid separation. A method for separating Pd, comprising:

2. A method for separating Pd as described in claim 1, wherein, when the Pd content of the liquid to be treated is 0.01 mass% or less, the liquid to be treated is concentrated by distillation prior to adding formic acid to the liquid to be treated.

3. 3. The method for separating Pd according to claim 2, wherein the Pd content of the concentrated liquid to be treated obtained by the concentration treatment is 0.03 to 0.1 mass %.

4. The method for separating Pd according to any one of claims 1 to 3, wherein the liquid to be treated is mixed with formic acid or a derivative thereof, heated to a temperature in the range of 50 to 100°C, and treated with stirring for one hour or more, thereby producing a precipitate.

5. 5. The method for separating Pd according to claim 1, wherein the heating temperature is in the range of 50 to 70°C.

6. 2. The method for separating Pd according to claim 1, wherein formic acid or a derivative thereof is added to the liquid to be treated, and then the liquid to be treated is distilled to concentrate the liquid to be treated and produce a precipitate.

7. 7. The method for separating Pd according to claim 1, wherein the organic waste liquid to be treated is neutral or acidic.

8. The method for separating Pd according to any one of claims 1 to 7, wherein the organic waste liquid to be treated is basic, and 10 or more equivalents of formic acid or a derivative thereof relative to the Pd contained in the liquid to be treated are added, and in addition, any acid is added to make the liquid to be treated neutral or acidic at least when the liquid is heated.

9. The method for separating Pd according to any one of claims 1 to 8, wherein the precipitate is subjected to solid-liquid separation, and then washed with water and recovered, so that the recovery rate is 90% or more of the Pd contained in the treated liquid, and the Pd purity of the recovered and dried solid is 90% or more.

10. The method for separating Pd according to any one of claims 1 to 9, wherein the precipitate is subjected to solid-liquid separation and then washed with at least one washing liquid selected from the group consisting of water, a lower alcohol having 1 to 4 carbon atoms, and acetone.

11. 11. The method for separating Pd according to claim 1, wherein the liquid to be treated contains at least an organic solvent capable of dissolving the Pd complex.

12. The method for separating Pd according to any one of claims 1 to 11, wherein the liquid to be treated contains at least one organic solvent selected from the group consisting of ketone organic solvents, alcohol organic solvents, ester organic solvents, ether organic solvents, amine organic solvents, alkoxysilane organic solvents, aromatic hydrocarbon organic solvents, aliphatic hydrocarbon organic solvents, and highly polar organic solvents.

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