JPS63166937A - Recovering method for noble metal from fuel cell electrode waste material - Google Patents

Abstract

PURPOSE:To recover the noble metals with high efficiency without discharging harmful gas to the outside nor infiltrating fluorine into a platinum recovery solution system, by burning fuel cell electrode waste material, etc., together with alkali carbonate. CONSTITUTION:The fuel cell electrode waste material, etc., are crushed and then burnt together with carbonate of alkali such as soda ash. At this time, polytetrafluoroethylene, etc., contained in the above waste material are decomposed, so that harmful fluorine-containing gas is generated. This gas is fixed in the form of alkali fluoride by means of the above alkali carbonate, so that discharge to the outside is prevented. The resulting burnt product is treated with aqua regia so as to recover the noble metals such as platinum. At this time, it is desirable that alkali fluoride in the above burnt product is treated with boride such as boric acid, to undergo complexing of fluorine so as to prevent the deterioration in the recovery rate of platinum and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for recovering precious metals such as platinum contained therein from electrode waste materials of used fuel cells.

(Prior Art and its Problems) In recent years, various fuel cells have been actively manufactured and developed due to demands for energy conservation, new energy development, and the like. Among these types of fuel cells, especially phosphoric acid fuel cells, noble metals such as platinum are usually supported on carbon electrodes as catalyst activators, and therefore, such noble metals are removed from used electrodes. It will be necessary to collect it. To recover this precious metal, an acid extraction method typified by the aqua regia dissolution method can be used.

Fuel cell waste generally contains PTFB (polytetrafluoroethylene), so even if aqua regia is applied directly, the platinum extraction action of aqua regia is inhibited by the presence of PTPB. Collection efficiency is poor. Therefore,
In order to remove this PTFE, it is necessary to sinter the waste material in a step prior to aqua regia treatment. However, as mentioned above, fuel cell waste materials contain fluorine, and there is a problem in that harmful fluoride gas is generated during the firing process.

In view of these points, the present invention has been devised to provide a recovery method capable of efficiently recovering precious metals from fuel cell waste materials, etc., without emitting harmful gases to the outside and without introducing fluorine into the platinum recovery solution system. The purpose is to develop.

(Means for Solving the Problems) In order to achieve the above object, the present invention first uses the waste materials, etc., in the firing process performed when recovering precious metals such as platinum from the electrode waste materials of fuel cells. By firing with alkali carbonate, the fluorine-containing gas generated from the waste materials is fixed as alkali fluoride, thereby preventing the generation of harmful gases during the firing process.

Furthermore, the alkali fluoride produced by firing with alkali carbonate in the above firing process remains even if the fired product is thoroughly washed with water. In the step of forming an acid complex compound, generation of a platinum fluoride complex compound is prevented.

In other words, in the conventional method, the fluorine fixed as alkali fluoride is reversibly changed by hydrochloric acid to become harmful hydrogen fluoride gas, which not only damages the reaction container such as glass but also dissolves in the aqua regia. It reacts with platinum ions to form a platinum fluoride complex compound with greater solubility than ammonium hexachloroplatinate, reducing the recovery rate of platinum from platinum solutions. Therefore, in the present invention, following the step of removing the generated alkali fluoride from the fired product, the fired product is treated with boric acid to convert the hydrogen fluoride gas generated by the action of hydrochloric acid into a complex. , a more stable and highly soluble borofluoride is used to prevent fluoride from being mixed into the platinum solution system as much as possible.

(Effects of the Invention) As described above, according to the method of the present invention, in the firing step that is performed prior to the platinum extraction process, fuel cell waste materials are fired together with excess alkali carbonate. Fluorine-containing gas generated from waste materials and the like is fixed as alkali fluoride and can be prevented from being released to the outside.

The second major effect is that, in the present invention, boride is added in the step of removing residual alkali fluoride from the fired product, so that it is once fixed as alkali fluoride by the hydrochloric acid used in this step. Fluorine is complexed to prevent it from turning back into harmful hydrogen fluoride.

Therefore, it is possible to eliminate the problem of the generation of platinum fluoride complex compounds caused by the generated hydrogen fluoride, which reduces the recovery rate of platinum, and also prevents the glass containers used in the subsequent process from being immersed in the generated fluorine gas. It is also possible to eliminate the negative effects caused by If this second effect does not exist, even if fluorine pollution-free treatment is carried out by co-firing soda ash, the fluorine compounds produced as a by-product will mix into the platinum recovery solution system and reduce the platinum recovery rate. If we lower it, we will lose the original purpose, so we can see how important this second effect is.

(Example) An embodiment of the present invention will be described in detail below.

The embodiment described below is based on a fuel cell electrode waste catalyst 1100.
(This is an example of platinum recovered from I. This recovered product 1000
g is the result of quantitative analysis, PTFE30.1%, Pt
It consisted of 9.25% and 60.6% carbon content.

The processing steps in this example roughly consist of the following 10 steps.

A: Dephosphorization, drying process B: Grinding process C: Alkali carbonate mixing step D = firing process E: Hydrolysis step F: Complexing step of residual NaF G: Aqua regia dissolution process H: Neutralization process ■: Platinum salt precipitation process J: Roasting and melting process Next, each step will be explained in detail.

A: Dephosphorization and drying step First, 1000 g of the above recovered product was thoroughly washed with water to remove phosphoric acid. Thereafter, the recovered product after washing was placed in an electric dryer and dried at 90° C. overnight. Weight after drying is 984
It was g. Note that the platinum contained in the above-mentioned washing water was once ionized and then reduced with zinc to obtain crude platinum.

B: Grinding process Next, the dried recovered product was ground in a grinder and then mixed in a mixer. After passing through this process, a portion of the recovered product was collected and quantitatively analyzed, and the above-mentioned values are the results.

C: Alkali carbonate mixing process Add 7 to 8 times more soda ash (Na
2CO3) and mixed these art materials.

After the recovered product mixed with soda ash was taken out from the mixer, it was placed in the main combustion chamber of the kiln, and soda ash powder was sprinkled over it so as to cover the surface of the recovered product.

D: Firing Step The firing furnace used in this example has a structure including a main combustion chamber, a sub-combustion chamber, and a combustion exhaust gas treatment tower. Firing is first performed in the main combustion chamber, and ash and unburned components scattered from the main combustion chamber during firing in the main combustion chamber are collected in the sub-combustion chamber. The unfired components collected in the secondary combustion chamber are refired here. This auxiliary combustion chamber ensures that the waste material is burned. On the other hand, the above-mentioned exhaust gas treatment tower is supplied with an absorption liquid made of Na2COi, and the exhaust gas generated from the main and auxiliary combustion chambers during firing comes into contact with this absorption liquid and is then discharged to the outside.

A firing process for recovered products using the firing furnace configured as described above will be explained. First, as mentioned above, the material to be burned that has been placed in the main combustion chamber and sprinkled with soda ash is
Calcined by electric heating under oxygen supply. The temperature during this firing was maintained at 600 to 700°C. The reason for this is 8
This is because if the temperature exceeds 00°C, Na2CO3 will melt and the combustion of carbon will be hindered.
This is because the reaction rate is slow and it takes too much time to burn the carbon.

Unfired components scattered from the combustion chamber during firing in the main combustion chamber are collected in the auxiliary combustion chamber and refired.

This recalcination achieved an improvement in the recovery rate of platinum. That is, as will be described later, in this example, 3% of the recovered platinum could be obtained by this re-firing.

The main reaction mechanism during firing is as shown in the following equation.

PTF[i +Na2CO3-NaF +CO2(1
) C+ 02 → CO□ (2) Here, HP or F generated in the above-mentioned PTBF thermal decomposition process
Most of the harmful gases such as No. 2 are fixed as NaF by the solid-gas phase core system (1) with Na2COs in the main combustion chamber. However, Na2CO remains unfixed in the exhaust gas and is introduced into the exhaust gas treatment tower.
Fixed by contact with +.

The reaction at this time can be expressed by the following formula.

8P + Na2CO, → NaF +
lI20 + CO□ (3) Fi
+ Na2Co3-+ NaF + CO2 (4)
E: Hydrolysis step Next, the fired products obtained in the above steps, that is, the fired products obtained in each of the main and auxiliary combustion chambers, were hydrolyzed to remove residual Na2CO+ and generated NaF. Thereafter, solid-liquid separation was performed to obtain a solid content containing platinum, ash, etc. as well as a slight amount of residual NaF.

F: Complexing step of residual NaF Add boric acid (83BO3) to the solid content obtained in the above step.
When NaF 2 remains in the solid content, it becomes soluble borofluoride and can be easily removed. To further completely decompose NaF, boric acid is reacted with hydrochloric acid, and the HP generated is complexed into a form such as 1BF4 (borofluoric acid), which is more stable and has higher solubility, as shown in the reaction formula below. Fluorine will not be mixed into the solution system.

38F + 83BO3→ )lBF3(OH)
+ 2820 (5) 118F3 (Kano) Ten liver → HBF4 + ) + 20 (6) Furthermore, )! , BO3, NaBO□, etc. may be used.

When removing NaF using only hydrochloric acid as in the conventional method, if the generated IF is left as is, this H
F generates a platinum fluoride complex compound, and these ions reduce the recovery rate of platinum and immerse the glass container 5102 used in subsequent steps. Therefore, complexing the remaining fluorine as in this step is an extremely effective means.

After the treatment with hydrochloric acid and boric acid as described above, the treated product is separated into solid and liquid, and a trace amount of platinum dissolved in the filtrate is removed.
It was recovered as crude platinum by adding zinc and hydrochloric acid. The solid content obtained through this solid-liquid separation is approximately 200g.
Met.

G: Dissolve the solid content obtained in the step before the aqua regia dissolution step in aqua regia to extract platinum,
This platinum was purified by known methods. That is, aqua regia 1.
The denitrification operation of adding 21 and dissolving it, then drying it and adding IIcI is repeated 2 to 3 times, and then HC
It was diluted with I (1:9) and filtered after cooling.

Note 1. The solid content that remained after this process was extracted with aqua regia again to elute the residual platinum, which was reduced using zinc and recovered as crude platinum.

H: The washing liquid used in the step before the neutralization treatment step and the obtained filtrate were subjected to a known neutralization treatment. That is, the pH of these solutions was adjusted to 7 to 8 using a Na leaf solution and an oxidizing agent, and impurities were precipitated as hydroxides.

Thereafter, the treated solution was subjected to solid-liquid separation to separate the precipitate, and the filtrate was sent to the next step.

I: Platinum salt precipitation step The above filtrate was acidified by adding hydrochloric acid to drive out the oxidizing agent, and a saturated solution of NLCI was added to the filtrate to precipitate (NH4) 2P tc16. Thereafter, solid-liquid separation was performed to remove the precipitate, and zinc and IIcI were added to the filtrate to recover a small amount of platinum contained in the filtrate as crude platinum. Meanwhile, the generated precipitate was thoroughly washed with a 5% 'NH,CI solution.

J: At the end of the roasting and melting process, after drying the above precipitate, heat it in a furnace for about 7 hours.
It was heated to about 00°C to obtain spongy platinum. This platinum was further melted to produce platinum buttons.

The amount of platinum obtained through the above process was 89.1 g (including 3 g recovered from the fired product formed in the sub-combustion chamber). In addition, each of the above steps A1F, G and I
The total amount of crude platinum obtained was 2.2 g. The results are summarized below.

Result a, platinum content 92.5 gb1 recovery amount From the sintered product in the main combustion chamber 86.1 g From the sintered product in the auxiliary combustion chamber 3.0 g (total) 91.1 g C1 recovery rate 98.5% 1. In this example described above, IIF generated in the process of removing residual NaF is complexed with Na2CO3,
Of course, other alkali carbonates may also be used. For example, the same effect can be obtained by using 2C (13 (potassium carbonate)).

For comparison, a similar experiment was conducted without using the complexing step F1, that is, without using the second effect of the present invention, and the platinum recovery rate was 8.
It was 6.5%.

Procedural amendment written by the Commissioner of the Japan Patent Office, Black 1) Yu Akira 1, Indication of case 1986 Patent Application No. 315190 2, Title of invention Method for recovering precious metals from fuel cell electrode waste materials, etc. 3, Amendment Relationship with the case filed by the applicant: Name of applicant: Tokuriki Honten Co., Ltd. 4, Agent: 5 Date of amendment order: Initiator: 6, Subject of amendment Detailed explanation of the invention in the specification The following places in the specification: Correct the errors as shown in the column above.

Claims (2)

[Claims] (1) A method for recovering precious metals such as platinum from fuel cell electrode waste materials, etc., which includes a step of fixing fluorine-containing gas generated from the waste materials as alkali fluoride by firing the waste materials with an alkali carbonate. A precious metal recovery method characterized by comprising: (2) A method for recovering precious metals such as platinum from fuel cell electrode waste materials, etc., including a step of fixing fluorine-containing gas generated from the waste materials as alkali fluoride by firing the waste materials with alkali carbonate. , a step of treating the alkali fluoride remaining in the fired product obtained by the firing with a boride.