JP2012107294A - Method for recovering platinum group metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of collecting a platinum group metal efficiently from a catalyst-containing wash coat by a simple treatment.SOLUTION: The method for collecting a platinum group metal comprises as follows. A catalyst-containing wash coat is leached by an inorganic acid, an inorganic acid soluble element is eluted, then a leachate in which a leaching residue is leached with aqua regia is used to be treated with an iron reduction bacillus, thereby a platinum group metal is collected efficiently.

Description

  The present invention relates to a platinum group metal recovery method for recovering a platinum group metal from a catalyst-containing washcoat.

  In recent years, most gasoline vehicles are equipped with an exhaust gas purification system using a three-way catalytic converter. This three-way catalytic converter converts carbon monoxide (CO), nitrogen oxide (NOX), and unburned hydrocarbons into carbon dioxide, nitrogen, and water to purify exhaust gas from a gasoline engine.

  The catalytic converter has a monolith (honeycomb) structure. The monolith is the basic structure of the converter and at the same time functions as a substrate for the catalyst coating. The catalyst coating is performed as follows. First, the surface of the monolith is covered with a thin film of washcoat (catalyst carrier holding material). A catalyst (mainly a platinum group metal such as platinum, palladium, or rhodium) is coated on the washcoat.

  In order to increase the catalytic ability, it is necessary to increase the surface area where the reaction occurs. This is obtained by a monolithic structure and a porous washcoat. As the material for the washcoat, inorganic oxides generally used as a catalyst carrier having a high surface area such as alumina, titania, zirconia, silica-alumina and the like are used. In particular, activated alumina is often used. Activated alumina often contains rare earth elements such as lanthanum and cerium and alkaline earth elements such as barium.

  Traditionally, catalytic converters have been discarded after use. The catalyst coated on the washcoat contains a high concentration of platinum group metal. Therefore, it is desirable to collect these and reuse them.

  The present inventors have attempted to recover a platinum group metal from a printed circuit board using iron-reducing bacteria (see, for example, Non-Patent Document 1). In the method described in this document, a metal containing a platinum group metal is leached from a printed circuit board or the like using aqua regia, and the platinum group metal is recovered from the leached solution using iron reducing bacteria. However, as described above, the catalyst-containing washcoat contains aluminum and other metals in the wetcoat layer. For this reason, if the catalyst-containing washcoat is simply leached using aqua regia, the leachate will gel, and subsequent processing cannot be performed. Therefore, it is necessary to consider new processing steps.

In the present specification, the “catalyst-containing washcoat” means a washcoat including a waste catalyst that is peeled off from the monolith surface of the three-way catalytic converter.
Yasuhiro Konishi, “Challenge to Rare Metal Recovery Utilizing Microbial Functions”, Chemical Engineering, Volume 74,

  That is, the present invention has been made in view of the above problems, and an object thereof is to provide a method for efficiently recovering a platinum group metal from a catalyst-containing washcoat by a simple treatment.

  The present inventors examined a pretreatment method for a catalyst-containing washcoat, leached the catalyst-containing washcoat with an inorganic acid, eluted an inorganic acid-soluble element, and then obtained a leachate obtained by leaching the leaching residue with aqua regia. It was found that platinum group metals can be efficiently recovered by treating with iron-reducing bacteria, and the present invention has been completed. That is, the present invention is as follows.

  The platinum group metal recovery method of the present invention includes a step of leaching a catalyst-containing washcoat with an inorganic acid to obtain a leaching residue, a step of leaching the leaching residue with aqua regia to obtain a leachate, and Treating with reducing bacteria.

  The platinum group metal recovery method of the present invention includes a neutralization step of neutralizing the leachate after leaching using the aqua regia, and recovers platinum.

  The iron-reducing bacterium used in the platinum group metal recovery method of the present invention is preferably Shiwanella algae.

In the method of the present invention, the catalyst-containing washcoat is first leached with an inorganic acid to leach inorganic acid soluble components. Thereby, when it is directly leached with aqua regia, an element that causes gelation of the leachate can be removed. Further, when leached with an inorganic acid, the platinum group metal hardly dissolves in an inorganic acid such as hydrochloric acid. On the other hand, platinum group metals are leached into aqua regia. Therefore, the platinum group metal can be leached with high selectivity when leaching with aqua regia by first treating with an inorganic acid. When this is treated with iron-reducing bacteria, the platinum group metal can be efficiently recovered.
Moreover, when the aqua regia leachate is neutralized, only platinum remains in the leachate. Therefore, when this solution is used, platinum can be recovered alone.

FIG. 1 is a graph showing the concentration of elements in each of the above leachates by ICP analysis. FIG. 2 is a graph showing the leaching rate of elements in each of the above leaching solutions by ICP analysis. FIG. 3 is a graph showing the platinum concentration (FIG. 3 (a)) and the remaining rate of platinum (FIG. 3 (b)) in each of the above culture solutions by ICP analysis.

  The present invention is described in detail below. According to the platinum group metal recovery method of the present invention, the platinum group metal can be recovered by the following steps.

[Iron-reducing bacteria]
The iron-reducing bacterium used in the present invention is a bacterium that receives iron from an electron donor and reduces iron. Examples of such iron-reducing bacteria include Geobacter genus (Representative species: Geobacter metalreducens: Geobacter metalylreducence, ATCC (American Type Culture Collection) 53774 strain), Desulfomonas sulphonis genus (Representative species: Desulfuromonas sulphomonas de Sulfomonas de Sulfomonas de Sulfomonas sp. Monas palmitatis: ATCC 51701 strain), Desulfomusa genus (Representative species: Desulfuromusa kysingii: Desulfche sammung von Mikroengen und Zellkulturen) Venetian: ATCC 2394 strain), Shewanella algae (hereinafter referred to as “S. algae”): ATCC 51181 strain, Shewanella oneidensis: Shiwanella oneidensis: (hereinafter referred to as “S. Genus (Ferrimonas balearica: Ferrimonas valerica: DSM9799 strain), Aeromonas genus (Aeromonas hydrophila: Aeromonas hydrophila: ATCC 15467 strain), Sulfurospirillum spp. : C Linella Susinogenes: Wolinella succinogenes: ATCC 29543 strain), Desulfobibrio genus (representative species: Desulfovibrio desulfuricans: Desulfobibrio desulfuricans: ATCC29577 strain), Geotricus genus (representative species: Geofolith genius trieogenis Bacter genus (representative species: Deferribacter thermophilus: Deferibacter thermophilus: DSM14813 strain), Geovibrio genus (representative species: Geovibrio ferriducens: Geobibrio ferrireducence: ATCC 51996 strain), pirobulum p slandicum: Thermoproteus islandicam: DSM4184 strain), Thermotoga genus (representative species: Thermotoga maritima: Thermotoga maritima: DSM3109 strain), Alkaeglobus genus (representative species: Archaeoglobus fulgidus: 58 Alkaeglobus AT. (Representative species: Pyrococcus furiosus: Pyrococcus furiosus: ATCC43587 strain), Pyrodictium genus (representative species: Pyrodictium abyssi: DSM6158 strain) and the like. These iron-reducing bacteria are anaerobic bacteria.

The iron-reducing bacteria used in the present invention may be grown and maintained using a medium suitable for the bacteria. For example, S.W. For example, algae has a pH of 7.0, contains sodium lactate (32 mol / m ³ ) as an electron donor, and Fe (III) ions (56 mol / m ³ ) as an electron acceptor. Using ferric medium (ATCC No. 1931), grow and maintain batch culture in anaerobic atmosphere. In this example, the iron ion salt is citrate, but may be appropriately selected depending on the medium used and the type of iron-reducing bacteria used. S. algae can also be aerobically cultured using TSB (tryptosoy broth) liquid medium (pH 7.2).

  Among the iron-reducing bacteria used in the present invention, particularly preferred iron-reducing bacteria are S. cerevisiae. algae.

[Catalyst-containing washcoat]
In the present invention, the treatment target is a catalyst-containing washcoat.

  The catalyst-containing washcoat is recovered from the used three-way catalytic converter. The washcoat layer containing the waste catalyst is peeled off from the three-way catalytic converter. Therefore, in addition to the catalyst and the washcoat material, components constituting a monolith such as iron are also included. The catalyst-containing washcoat may be pulverized or the like as necessary in the leaching process. The pulverization method is not particularly limited, and may be pulverized using a known method. Examples of the pulverization method include a method using a roller pulverizer (fret mill), a vibration mill, a ball mill, a pot mill, a mortar, and an automatic mortar.

[Recovery of platinum group metals]
(Leaching with inorganic acid)
The catalyst-containing washcoat is first leached with an inorganic acid to obtain a leaching residue. Examples of inorganic acids that can be used include hydrochloric acid, nitric acid, sulfuric acid and the like. A preferred inorganic acid is hydrochloric acid. What is necessary is just to determine the density | concentration of the inorganic acid to be used suitably from the processing amount of a catalyst containing washcoat, for example, is 1-5 mol / L.

The catalyst-containing washcoat and the inorganic acid may be mixed at a solid / liquid mixing ratio of 100 to 300 kg / m ³ , for example. Moreover, although mixing may be performed by heating, it is preferable to perform at normal temperature.

  The catalyst-containing washcoat and the inorganic acid are mixed, and the inorganic acid-soluble component of the catalyst-containing washcoat is leached. The leaching residue is separated by a known method. In the leaching treatment with an inorganic acid, many of the metals that interfere with the direct aqua regia treatment such as aluminum, iron, and nickel can be removed.

(Leaching with aqua regia)
Next, the obtained leaching residue is leached using aqua regia. Aqua regia is a liquid formed by mixing concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3: 1. The concentration of aqua regia may be appropriately determined from the amount of leach residue treated, and is, for example, 1 to 5 mol / L. In addition, the solid-liquid mixing ratio of the leaching residue and aqua regia is not particularly limited as long as the platinum group metal including platinum is sufficiently eluted from the leaching residue, and may be 10 kg / m ³ or more. . From the viewpoint of processing efficiency, it is preferably 400 kg / m ³ or more. Moreover, although mixing may be performed by heating, it is preferable to perform at normal temperature.

  By leaching treatment with aqua regia, most platinum contained in the catalyst-containing washcoat and most of platinum group metals such as palladium and rhodium can be leached into aqua regia. This aqua regia leachate may be directly treated with iron-reducing bacteria, or neutralized and then treated with iron-reducing bacteria.

(Neutralization treatment)
The leachate from the aqua regia may be neutralized. When neutralization is performed, metals other than platinum are removed as neutralization waste. Therefore, when the leachate from which neutralization waste has been removed is treated with iron-reducing bacteria, high-purity platinum can be recovered.

(Treatment with iron-reducing bacteria)
The number of iron reducing bacteria used in the platinum group metal recovery method of the present invention is not particularly limited. Generally, the smaller the number of cells, the longer the processing time. The number of iron-reducing bacteria is, for example, 1.0 × 10 ¹⁴ cells / m ^{3 to} 1.0 × 10 ¹⁶ cells / m ³ , preferably 1.0 × 10 ¹⁵ cells / m ^{3 to} 8.0 × 10 ^16. What is necessary is just about cells / m ³ .

  In the platinum group metal recovery method of the present invention, the leachate obtained by the above leach treatment with aqua regia is used. For the preparation of the iron-reducing bacteria suspension, first, the iron-reducing bacteria culture solution that has reached the end of exponential growth is collected in a glove box made anaerobic with nitrogen gas and collected with a centrifuge. The collected bacterial solution is adjusted to a predetermined concentration using water (including distilled water, ion-exchanged water, pure water, etc.).

  The aqua regia leachate and iron-reducing bacteria suspension are mixed in an anaerobic atmosphere at room temperature, and the platinum group is recovered by stirring with a stirrer or bubbling with gas.

In a suspension of aqua regia leachate and iron-reducing bacteria, for example, an organic substance having 1 to 7 carbon atoms [carboxylate (fatty acid carboxylate (fatty acid salt): aromatic carboxylate such as formate, acetate, etc. : Benzoate, etc., oxocarboxylate: pyruvate, etc., other carboxylate: lactate, etc., alcohol (ethanol, etc.), unsaturated aromatic (toluenephenol, etc.)], or hydrogen gas (molecular) An electron donor such as hydrogen) may be added. The electron donor to be used varies depending on the type of iron-reducing bacteria to be used, and an optimal one may be selected as appropriate. For example, S.M.
In algae, an organic acid salt can be used as an electron donor.

  The mixing ratio of the aqua regia leachate and the iron-reducing bacteria suspension may be about 1 to 5/15 in volume ratio. The pH of the mixed solution of the aqua regia extract and the iron-reducing bacteria suspension varies depending on the amount of aqua regia leachate added and the electron donor to be added, but is preferably about 6.0 to 9.5, for example. .

  In the platinum group metal recovery method of the present invention, the treatment time is not particularly limited. Considering the treatment efficiency, the concentration of the platinum group metal and the number of iron-reducing bacteria to be used may be adjusted so that the recovery rate of the platinum group metal is increased.

  The platinum group metal recovered by the iron-reducing bacteria can be recovered by removing the organic substances by, for example, baking.

  By using the platinum group metal recovery method of the present invention, it is possible to recover the platinum group metal in a short time and with high efficiency by an extremely simple operation. Therefore, the platinum group metal can be recovered from the three-way catalytic converter and reused effectively by a simpler method than the conventional method and at a low cost.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to this Example.

  To prepare the suspension of iron-reducing bacteria, first, the iron-reducing bacteria culture solution that reached the end of exponential growth was collected in a glove box made anaerobic with nitrogen gas and collected with a centrifuge. Next, the collected bacterial solution was resuspended with ion-exchanged water and adjusted to a predetermined concentration.

Example 1
10 g of the catalyst-containing washcoat was leached with hydrochloric acid. Hydrochloric acid with 2 mol / L was used. The leaching was conducted at a leaching temperature of 25 ° C. for 24 hours at a solid / liquid mixing ratio of 200 kg / m ³ . The leaching residue after leaching with hydrochloric acid was 8.72 g.

Next, the leaching residues 0.2, 1.0, 2.0, and 4.0 g were leached with aqua regia, respectively. The aqua regia used was 2 mol / L. The leaching was carried out at a leaching temperature of 25 ° C. for 4 hours at a solid / liquid mixing ratio of 10, 100, 200, 400 kg / m ³ . The leaching residues after leaching with aqua regia were 0.186, 0.953, 1.848 and 3.799 g, respectively.

  Aluminum (Al), iron (Fe), nickel (Ni), cerium (Ce), lanthanum (La), neodymium (Nd), palladium (Pd), platinum contained in the hydrochloric acid leachate and each aqua regia leachate (Pt) and rhodium (Rh) were analyzed by Inductively Coupled Plasma (ICP). The results are shown in FIGS.

FIG. 1 is a graph showing the concentration of elements in each of the above leachates by ICP analysis. In FIG. 1, the horizontal axis represents each aqua regia leachate (for example, Wang 10 means aqua regia leachate and a solid-liquid mixing ratio of 10 kg / m ³ ), and hydrochloric acid leachate (salt 200). Means the element concentration (mg / L) contained in the solution. FIG. 2 is a graph showing the leaching rate of elements in each of the above leaching solutions by ICP analysis. In FIG. 2, the horizontal axis represents each aqua regia leachate (for example, Wang 10 means aqua regia leachate and a solid-liquid mixing ratio of 10 kg / m ³ ), and hydrochloric acid leachate (salt 200). Means the element leaching rate (%) contained in the liquid. The element leaching rate was determined from the amount of element contained in the original catalyst-containing washcoat used as a raw material. 1 and 2, among the elements contained in the catalyst-containing washcoat, many of aluminum (Al), iron (Fe), nickel (Ni), cerium (Ce), lanthanum (La), and neodymium (Nd) It can be seen that it leaches into hydrochloric acid. Moreover, it turns out that platinum (Pt) and rhodium (Rh) are leached in aqua regia without being leached with hydrochloric acid among platinum group metals. Also, the leaching rate was very good, almost 100% for platinum and nearly 80% for rhodium.

  In the following examples, the platinum group metal recovery process was performed as follows. First, a screw cap bottle with a valve was used as an incubator. The culture temperature was 303K.

Cell density of Shiwanella argue: 7.9 × 10 ¹⁵ cells / m ³ , aqua regia leachate (aqua regia leachate with solid / liquid mixing ratio 400 kg / m ³ ) were added 1, 2.5 and 5 mL, respectively. 15 mL was used. In the culture, sodium formate was added as an electron donor to a concentration of 50 mol / m ^3, and one without an electron donor was used. As a control experiment, an aqua regia leachate and an electron donor were added, but no Siwanella algae was added. The initial pH of each culture solution was as shown in Table 1.

  Each of the above solutions was cultured for 2 hours, and the platinum concentration and platinum content in the liquid after the culture were measured. The results are shown in FIG. FIG. 3 is a graph showing the platinum concentration (FIG. 3 (a)) and the remaining rate of platinum (FIG. 3 (b)) in each of the above culture solutions by ICP analysis. In FIG. 3, the horizontal axis indicates the amount of aqua regia leachate added, whether or not sodium formate is added, and the control group (sterile), and the vertical axis indicates platinum concentration (mg / L) (FIG. 3 (a)) It means rate (%) (FIG. 3B). In these figures, the lower the platinum concentration and the lower the platinum content, the more platinum is recovered by Shiwanella alge. It can be seen from FIG. 3 that 30% of platinum was recovered in the case where 5 mL of aqua regia leachate was added.

(Example 2)
Sodium hydroxide was added to the aqua regia leachate (aqua regia leachate with a solid / liquid mixing ratio of 400 kg / m ³ ) to adjust the pH to 5.6. Neutral soot was produced in the liquid. When the liquid from which the neutralized soot was removed was analyzed by ICP, the liquid contained almost no elements other than platinum.

Claims (3)

Leaching the catalyst-containing washcoat with an inorganic acid to obtain a leaching residue;
Leaching the leaching residue with aqua regia to obtain a leachate;
A method for recovering a platinum group metal, comprising a step of treating the leachate with iron-reducing bacteria. After leaching using the aqua regia, including a neutralization step of neutralizing the leachate,
The method for recovering a platinum group metal according to claim 1, wherein platinum is recovered. The method for recovering a platinum group metal according to claim 1 or 2, wherein the iron-reducing bacterium is Shiwanella algae.

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