JP3968577B2 - Method and apparatus for recovering precious metals from waste - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a method for recovering noble metals, particularly platinum, from waste while suppressing generation of harmful gases.
[0002]
[Prior art]
Fuel cells that use oxygen or air for the positive electrode and hydrogen, methanol, hydrocarbons, etc. for the negative electrode as active substances can be expected to have high conversion efficiency because they directly convert chemical energy into electrical energy. Due to the absence of emissions, it is highly environmentally friendly and attracts attention as a future energy source. In the fuel cell, a catalyst made of a noble metal such as silver, platinum, or palladium is used to promote the electrode reaction.
In addition, detoxifying substances such as HC, CO and nitrogen oxides present in exhaust gases of automobiles and the like are made harmless by a catalyst. Exhaust treatment catalysts used for this purpose are generally purified by using a porous inorganic substance such as alumina as a carrier, carrying a noble metal such as platinum dispersed on the carrier, and contacting the catalyst with harmful substances. It is carried out.
[0003]
As described above, since the fuel cell and the exhaust treatment catalyst contain a noble metal such as platinum as a constituent component, it is extremely important to recover the noble metal from the used waste from the viewpoint of effective utilization of rare resources. However, these precious metals are speculative, so the price is unstable, and the recovery of precious metals from waste currently being carried out is not stable, and the benefits of recovery are very high. Is unstable. Therefore, in order to maintain a precious metal recycling system, it is important to reduce the cost required for recovery as much as possible.
[0004]
As a method for recovering precious metals from waste, generally, the waste is calcined to reduce the weight, the calcined residue is pulverized, then extracted with a strong acid such as aqua regia, and this is reduced and returned to the metal. Has been done. However, when the method is applied to a used fuel cell as it is, the fluorocarbon, which is a constituent material of the fuel cell, such as an electrolyte membrane of the fuel cell is decomposed to generate a fluorine-containing harmful gas such as hydrogen fluoride gas. Also, the addition of a strong acid during extraction also decomposes the sulfone group-containing side chains in the resin constituting the fuel cell element to generate sulfur-containing harmful gases.
[0005]
As a method for recovering noble metals from spent fuel cells while suppressing the generation of harmful gases, the alkaline earth metal compound is added to the fuel cell elements, and then the fuel cell elements are fired to reduce the volume. It is known to recover noble metals by dissolving in an acidic solution. In this method, in the step of firing the fuel cell element, fluorine-containing harmful gas and alkaline earth metal compound are reactively bonded and fixed to the firing residue to suppress discharge as a gas (see, for example, Patent Document 1) ).
[0006]
[Patent Document 1]
Japanese Patent Publication No. 2-50775 (pages 1 to 5)
[0007]
[Problems to be solved by the invention]
However, in the above recovery method, the cost of the alkaline earth metal compound is added, so that the recovery cost increases. Moreover, in order to efficiently capture harmful gases, it is advantageous that the specific surface area of the alkaline earth metal compound to be added is large, but the specific surface area of the alkaline earth metal compound is usually about several m ² / g. In order to fix all harmful gases generated by firing, it was necessary to add a large excess of alkaline earth metal compound.
[0008]
It is also possible to simply pulverize the fuel cell element without performing such firing and extract the noble metal with a strong acid. In this case, since the fluorocarbon is not decomposed, generation of fluorine-containing harmful gas is suppressed. . However, generation of sulfur-containing harmful gases due to decomposition of the sulfone group-containing side chain is inevitable.
[0009]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a method and an apparatus for recovering noble metal from waste such as spent fuel cell elements with high efficiency and low cost.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, a method for recovering noble metal from waste according to claim 1 of the present invention includes a noble metal-containing waste, an alkali metal source and / or an alkaline earth metal source and / or porous Al _2. Calcination in the presence of O ₃ , and at this time, fluorine-containing harmful gas generated by the calcination is reacted with the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ to obtain a fluorine-containing solid material. Then, in the method for recovering noble metal from waste, the noble metal is extracted from the firing residue with a strong acid, and further reduced and recovered.
In the present invention, the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ is a used exhaust treatment catalyst, and is a powder having a specific surface area of 10 m ² / g or more. Calcination of the noble metal-containing waste in the presence of an alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ powder having a specific surface area of 10 m ² / g or more, It is possible to efficiently suppress generation of fluorine-containing harmful gas during firing.
[0011]
The method for recovering noble metal from waste according to claim 2 of the present invention is the method according to claim 1, wherein the noble metal-containing waste, the alkali metal source and / or alkaline earth metal source and / or porous Al _{2 are used.} Baking is performed in a state where O ₃ is mixed.
In the present invention, a noble metal-containing waste and an alkali metal source and / or an alkaline earth metal source and / or porous Al ₂ O ₃ are mixed before firing, whereby fluorine-containing harmful gas generated by firing is alkalinized. It can be reacted with a metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ to form a fluorine-containing solid.
[0012]
The method for recovering precious metals from waste according to claim 3 of the present invention is the method according to claim 1, wherein the amount of the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ is: It is characterized by being 2 to 5 equivalents of fluorine-containing harmful gas generated from the noble metal-containing waste.
In the present invention, since the specific surface area of the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O _{3 used} is large, it reacts with all the fluorine-containing harmful gases generated by firing from the metal-containing waste. In the stoichiometric amount of 2 to 5 equivalents, all the harmful gases generated can be sufficiently converted to a fluorine-containing solid.
[0013]
The method for recovering noble metals from waste according to claim 4 of the present invention is characterized in that in the method according to claim 1, the noble metal-containing waste is a spent fuel cell element.
In the present invention, a noble metal can be conveniently recovered from a spent fuel cell element containing a noble metal such as platinum as a catalyst and a resin having a fluorocarbon or sulfone group-containing side chain as an electrolyte membrane or the like.
[0014]
In the present invention, a used exhaust treatment catalyst having an alkali metal and / or alkaline earth metal supported on a carrier and having a large specific surface area is treated as an alkali metal source and / or an alkaline earth metal source and / or a porous material. By using it as Al ₂ O ₃ , the fluorine-containing harmful gas can be efficiently converted into a fluorine-containing solid. Further, since the exhaust treatment catalyst may be used, it is not necessary to prepare a new alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ , which is advantageous in terms of cost. .
[0015]
The method for recovering noble metal from waste according to claim 5 of the present invention is characterized in that in the method according to claim 1, the noble metal is platinum.
In the present invention, platinum (Pt) contained in the fuel cell element and / or the exhaust treatment catalyst and rare and expensive can be conveniently recovered.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The precious metal-containing waste to be treated according to the present invention is a waste containing precious metals such as platinum, gold, palladium, etc., and harmful gas is generated by addition of strong acid for extracting precious metals by firing. Is. One example is a spent fuel cell element. The fuel cell element contains a noble metal as a catalyst for promoting the electrode reaction, but at the same time, as an electrolyte membrane, a water-repellent membrane, etc. Includes resins having group-containing side chains.
[0019]
A feature of the present invention is that the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ is a powder having a specific surface area of 10 m ² / g or more . A alkali metal source and / or an alkaline earth metal source and / or a porous Al ₂ O ₃ is potassium, and the alkali metal and / or alkaline earth metals such as barium, a noble metal oxide of aluminum such as platinum, zinc oxide A used exhaust treatment catalyst supported on a carrier such as titanium oxide. The catalyst contains an alkali metal and / or alkaline earth metal and / or porous Al ₂ O ₃ and has a large specific surface area to purify harmful substances contained in exhaust gas by contact. Therefore, it is suitable as the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ of the present invention. In addition, the exhaust treatment catalyst may be used, and the precious metal present in the catalyst can be recovered simultaneously with the precious metal-containing waste. Examples of the exhaust treatment catalyst include a 3-way catalyst, an oxidation catalyst, a diesel catalyst, a NO _x storage reduction catalyst, and the like.
[0020]
From a stoichiometric viewpoint, in order to fix 2 mol of fluorine atoms (1 mol as F ₂ gas) as a fluoride, 1 mol of calcium hydroxide is required when calcium hydroxide is used. However, in the prior art method, an alkali metal source and / or an alkaline earth metal source and / or porous Al ₂ O ₃ having 50 equivalents or more of the generated fluorine atoms is used. This seems to be because the specific surface area of the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O _{3 used} is small and the gas-solid contact efficiency is poor. On the other hand, in the present invention, the specific surface area of the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O _{3 used} is 10 m ² / g or more. The generation of fluorine-containing harmful gas can be suppressed only by using the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ .
[0021]
In the method of the present invention, the amount of fluorine-containing harmful gas generated from a predetermined amount of noble metal-containing waste is determined in advance using ion chromatography or the like, and the required amount of alkali metal source and / or alkali is determined. It can also be carried out using an earth metal source and / or porous Al ₂ O ₃ .
[0022]
In the method of the present invention, the noble metal-containing waste and the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ may be premixed before firing, or separated from each other. It may be housed. When separated and contained, the harmful gas generated in the treatment tank containing the precious metal-containing waste by firing is an alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O. _It is sent to the treatment tank in which ₃ is accommodated by an air supply facility that communicates both.
[0023]
Many fluorine-containing solids formed by the reaction of fluorine-containing harmful gases generated from fluorocarbons and the like with alkali metal sources and / or alkaline earth metal sources and / or porous Al ₂ O ₃ have low solubility, Does not dissolve. However, potassium fluoride has a high solubility in water and may be dissolved during the subsequent recovery process, but even if dissolved, it can be easily recovered and removed by known methods.
[0024]
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram illustrating one embodiment of the device of the present invention, and FIG. 2 is a schematic diagram illustrating another embodiment of the device of the present invention.
[0025]
The apparatus of the embodiment illustrated in FIG. 1 includes a first crusher 2 that crushes noble metal-containing waste 1, and a crusher that crushes an alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ 3. A crusher 4, a kneading machine 5 for mixing a crushed noble metal-containing waste 1, a crushed alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ 3, and a kneaded product The processing tank 6 to be accommodated, the heater 8 for heating and baking the kneaded material in the processing tank 6, the extraction tank 10 for extracting noble metal from the baking residue by adding strong acid from the strong acid tank 9, and the extract are reduced. And a noble metal recovery means comprising a reduction tank 11 for recovering the noble metal.
[0026]
According to the embodiment illustrated in FIG. 1, individually ground precious metal-containing waste 1 and alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ 3 are mixed by a kneader 5. After that, it is baked by the heater 8. The calcination is performed, for example, at a temperature of 800 ° C. for 2 hours. If desired, drying can be performed at a low temperature, for example, 100 ° C. before the calcination. The amount of precious metal-containing waste 1 is reduced by firing to improve recovery efficiency.
[0027]
At the time of firing, a fluorine-containing harmful gas is generated from the fluorocarbon or the like contained in the noble metal-containing waste 1, and it is an alkali metal source and / or alkaline earth metal source and / or porous material mixed with the noble metal-containing waste 1. It reacts with the porous Al ₂ O ₃ 3 to form a fluorine-containing solid and the release as gas is suppressed.
[0028]
After firing, the firing residue is extracted in the extraction tank 10 by the addition of strong acid from the strong acid tank 9 according to known methods. Examples of the strong acid include aqua regia, which is a mixture of hydrochloric acid and hydrogen peroxide, and a 1: 1 mixture of nitric acid and sulfuric acid. After extraction, the extract is sent to the reduction tank 11 and the extraction residue 12 containing the fluorine-containing solid is discarded. And the extraction liquid from the extraction tank 10 is reduce | restored by the reduction tank 11, and the noble metal 13 is collect | recovered as a metal.
[0029]
The apparatus of the embodiment illustrated in FIG. 2 includes a first crusher 2 that crushes the noble metal-containing waste 1 and a first crusher that crushes the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ 3. 2 crusher 4, 1st treatment tank 61 for storing crushed noble metal-containing waste 1, crushed alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ 3 The second treatment tank 62, the heater 8 for heating and firing the precious metal-containing waste 1 in the first treatment tank 61, and the gas generated in the first treatment tank 61 by the firing to the second treatment tank 62 It consists of a leading air supply facility 7, an extraction tank 10 for adding a strong acid from the strong acid tank 9 to extract the noble metal from the baked residue, and a reducing tank 11 for reducing the extract to recover the noble metal.
[0030]
According to the embodiment illustrated in FIG. 2, the pulverized noble metal-containing waste 1 and the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ 3 are contained in the first treatment tank 61 and the second treatment tank 61. Only the noble metal-containing waste 1 stored in the processing tank 62 and stored in the first processing tank 61 is fired by the heater 8.
[0031]
In the embodiment illustrated in FIG. 2, the fluorine-containing harmful gas generated by the firing of the noble metal-containing waste 1 is mixed with the water vapor from the water vapor generator 14 so as to be all converted into hydrogen fluoride, and then the second treatment tank 62. And fixed by reaction with an alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ 3. In this case, hydrogen fluoride can react with not only alkali metals and alkaline earth metals such as potassium and barium but also aluminum to form a fluorine-containing solid. The conversion of the fluorine-containing harmful gas into hydrogen fluoride can be performed by bubbling in water in addition to mixing with water vapor.
[0032]
【Example】
Example 1
280 g of electrode member of spent fuel cell element (composition, fluorocarbon 36 wt., Sulfur 1.5 wt.%, Platinum 0.25 wt.%, Carbon 62.25 wt.%), And spent monolithic NO _x storage reduction catalyst 10 kg (composition, potassium 0.95% by weight, barium 2.9% by weight, platinum 0.21% by weight, aluminum oxide 19.8% by weight, cordierite 76% by weight) were mixed and kneaded. .
The kneaded product was put in a ZrO ₂ ceramic processing tank, and 3.3 kg of NO _x storage reduction catalyst pulverized as shown in FIG. 3 was laminated on the kneaded product. Thereafter, it was dried at 100 ° C. for 1 hour and calcined at 800 ° C. for 2 hours.
The calcined residue was treated with 0.1 sodium borohydride to reduce platinum, and then extracted with a 10: 1 mixture of 25% hydrochloric acid 25% and 30% hydrogen peroxide.
As a result of analyzing the extract, it was found that 27.77 g of platinum was recovered. Since the electrode member before the treatment contained 0.7 g and the catalyst contained 27.93 g of platinum, the recovery rate was 97%.
Moreover, the presence or absence of generation | occurrence | production of the noxious gas at the time of baking was observed by installing the quartz rod on the process layer. That is, if a fluorine-containing harmful gas or the like is generated by pyrolysis of fluorocarbon, the gas dissolves quartz and attacks the surface of the quartz rod. However, in Example 1, there was no change in the surface of the quartz rod, indicating that no harmful gas was generated.
[0033]
Comparative Example 1
A spent fuel cell element similar to Example 1 was ground and mixed with 0.89 kg of the same molar amount of BaCO ₃ as Example 1.
The mixture was placed in a ZrO ₂ ceramic processing tank, and 300 g of BaCO ₃ was laminated on the kneaded product as shown in FIG. Thereafter, it was dried at 100 ° C. for 1 hour and calcined at 800 ° C. for 2 hours.
As a result of extracting platinum in the same manner as in Example 1, it was found that 0.7 g of platinum was recovered, and the recovery rate was 97%.
Further, in the same manner as in Example 1, the presence or absence of generation of harmful gas during firing was observed. As a result, uneven traces of corrosion / dissolution were observed on the surface of the quartz rod, indicating that fluorine-containing harmful gases were generated.
[0034]
Example 2
280 g of electrode member of spent fuel cell element (composition, fluorocarbon 36 wt., Sulfur 1.5 wt.%, Platinum 0.25 wt.%, Carbon 62.25 wt.%), And spent monolithic NO _x storage reduction catalyst 10 kg (composition, 0.95% by weight of potassium, 2.9% by weight of barium, 0.21% by weight of platinum, 19.8% by weight of aluminum oxide, 76% by weight of cordierite) was pulverized.
The pulverized electrode member and the pulverized catalyst were placed in different treatment tanks, the electrode member was dried at 100 ° C. for 1 hour, and calcined at 800 ° C. for 2 hours. Gas generated during firing was bubbled into 500 cc of water to form a hydrogen fluoride solution. The hydrogen fluoride solution was placed in a treatment tank containing a catalyst, and hydrogen fluoride was fixed as a fluorine-containing solid.
After treating the firing residue of the electrode member and the catalyst residue after HF fixation with 0.1 sodium borohydride to reduce platinum, the platinum was removed with a 10: 1 mixture of 25% hydrochloric acid 25% and 30% hydrogen peroxide. Extracted.
As a result of analyzing the extract, it was found that 2.72 g of platinum was recovered. Since the electrode member before the treatment contained 0.7 g and the catalyst contained 2.1 g of platinum, the recovery rate was 97%.
[0035]
【The invention's effect】
In the method for recovering precious metal from waste according to the present invention, the fluorine-containing harmful gas generated during the firing of the precious metal-containing waste is converted into an alkali metal source and / or alkaline earth whose powder has a specific surface area of 10 m ² / g or more. by fixing at a metalloid source and / or a porous Al ₂ O _3, effectively suppress the generation of noxious gas with a small amount of an alkali metal source and / or an alkaline earth metal source and / or a porous Al ₂ O ₃ can do.
[0036]
The recovery method of the present invention can be preferably applied to a spent fuel cell element containing platinum or the like as a noble metal to be recovered and containing fluorocarbon or the like as a source of harmful gas. Also, exhaust treatment catalysts that have been used as alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ can be advantageously used, which is not only cost-effective, This is very preferable because the noble metal can be recovered from the catalyst.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating one embodiment of an apparatus for a method for recovering noble metals from waste according to the present invention.
FIG. 1 is a schematic view illustrating another embodiment of an apparatus for a method for recovering noble metals from waste according to the present invention.
3 is a schematic view illustrating treatment tanks of Example 1 and Comparative Example 1. FIG.
[Explanation of symbols]
1 Precious metal-containing waste 3 Alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃
5 Kneading machine 6 Processing tank 61 First processing tank 62 Second processing tank 7 Air supply equipment 8 Heating machine 10 Extraction tank 11 Reduction tank

Claims (5)

The noble metal-containing waste is calcined in the presence of an alkali metal source and / or an alkaline earth metal source and / or porous Al ₂ O ₃ , and the fluorine-containing harmful gas generated by the calcining is calcined with the alkali metal source and Reacting with a source of alkaline earth metal and / or porous Al ₂ O ₃ to form a fluorine-containing solid, then extracting the precious metal from the calcined residue with a strong acid and further reducing and recovering the precious metal from the waste In the collection method,
The method according to claim 1, wherein the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ is a used exhaust treatment catalyst and is a powder having a specific surface area of 10 m ² / g or more. The method according to claim 1, wherein the precious metal-containing waste is calcined in a mixed state of the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ . The amount of the alkali metal source and / or alkaline earth metal source and / or porous Al ₂ O ₃ is 2 to 5 equivalents of fluorine-containing harmful gas generated from the noble metal-containing waste, The method of claim 1.   The method of claim 1, wherein the noble metal-containing waste is a spent fuel cell element.   The method of claim 1, wherein the noble metal is platinum.

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