KR101671178B1 - Recycling method of waste fuel cell - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for recycling a spent fuel cell, and more particularly, to a technique for recycling a scrap used in a steelmaking process, a valuable metal source, steelmaking slag, or the like using a waste fuel cell.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a recycling method of waste fuel cells,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for recycling a spent fuel cell, and more particularly, to a technique for recycling a scrap used in a steelmaking process, a valuable metal source, steelmaking slag, or the like using a waste fuel cell.

A steelmaking process for producing molten steel using an electric furnace or the like is usually performed by dissolving scrap and adjusting the metal components required for the steelmaking.

The scab is commonly referred to as brittle, scrap iron, etc., and is typically used by recycling iron products. On the other hand, in the steelmaking process, a large amount of valuable metals such as Ni and Cr is required in order to produce the required steel.

However, recently, the demand for metal resources has increased and the risk of depletion of reservoirs has been increasing. In some resource producing countries, resources are becoming more and more weaponized. Therefore, efforts are continuously being made to reduce the use of metal resources worldwide, and attempts to recover and recycle valuable metals from by-products and wastes are continuing.

On the other hand, a fuel cell is defined as a cell in which the chemical energy of fuel (hydrogen) is directly converted into electric energy to produce a direct current, and an oxidant (for example, oxygen) (For example, hydrogen) to generate electricity by electrochemically reacting with a fuel cell, which is different from a conventional battery, to produce electricity continuously by supplying fuel and air from the outside.

Examples of fuel cells include a Molten Carbonate Fuel Cell (MCFC), a Solid Oxide Fuel Cell (SOFC), and a Phosphoric Acid Fuel (PAFC), Alkaline Fuel Cell (AFC), Proton Exchange Membrane Fuel Cell (PEMFC), and Direct Methanol Fuel Cells (DEMFC).

The fuel cell includes a cathode, a cathode, an anode, and an electrolyte between the cathode and the anode. The fuel cell includes a stack of unit cells, And a separator for electrical connection of the separator. Stainless steel (STS), Ni-based alloy (Ni-metal), or the like is generally used as the material used for the fuel cell.

Some attempts have been made to recover a valuable metal from a battery (ex, lithium secondary battery) other than a fuel cell (Patent Document 1). However, to date, focusing on improving the performance of the fuel cell itself has been focused on the fuel cell, and the technology development is proceeding, and no attempt is made to recycle the spent fuel cell.

Korean Patent Laid-Open No. 2001-0106562

The present invention provides a technology for recycling waste fuel cells to scrap steelmaking processes and reusing them as a source of valuable metals, thereby providing a technology that can reduce resources and prevent environmental pollution.

One aspect of the present invention provides a method for preparing a waste fuel cell comprising the steps of: preparing a waste fuel cell;

Washing the spent fuel cell with water;

Forming a sludge by adding a reducing agent to washing water washed by the waste fuel cell; And

And using the washed waste fuel cell in a steelmaking process.

According to the present invention, not only an electric furnace but also a scrap that can be used in various steelmaking processes and a source of a valuable metal can be provided. In addition, by recycling the spent fuel cell, the problem of environmental pollution that may occur due to the discarded waste fuel cell and the cost of reprocessing at the time of disposal can be advantageously reduced.

FIG. 1 is a photograph showing a cross section of a spent fuel cell having reached the end of its life; FIG.
Fig. 2 is a schematic view showing the present invention. Fig.
Fig. 3 (a) is a view showing an example of the water-washing water tank of the present invention, and Fig. 3 (b)
FIG. 4 is a schematic view showing dissolution of a water-washed waste fuel cell and electrolytic iron in the embodiment of the present invention. FIG.
Fig. 5 (a) is a photograph of the dissolution process of Fig. 4, and Fig. 5 (b) is a photograph of a steel after dissolution.

Fuel cells generally consist of a unit cell made up of an electrode layer and an electrolyte layer, and a separator plate that electrically connects the unit cells and controls the flow of fuel and gas. The fuel cell typically uses a metal-based material, and in particular, Ni and Cr-based metals are used in many cases, and stainless steel (STS) is often used as an iron-based material.

Accordingly, there is a desperate need for a method of recycling a fuel cell having a shortened lifetime or a performance problem as a scrap of a steelmaking process or a supply source of a valuable metal such as Ni or Cr. The present invention has been derived.

Fig. 1 is a photograph showing a cross section of a solid oxide fuel cell (SOFC) having an end of its lifetime as an example of a waste fuel cell. Fig. 1 is a graph showing the results of the component analysis of the region A to E in Fig. . In FIG. 1, A represents an electrode (cathode, anode) corresponding to a unit cell of a fuel cell and an electrolyte, and C represents a catalyst. On the other hand, B, D and E correspond to component parts of the separator plate.

division
(wt%) NiO Cr ₂ O ₃ Fe ₂ O ₃ Al ₂ O ₃ K ₂ O ZrO ₂ Remarks A 62.5 0.2 0.1 23.7 11.2 0.03 Solid molding C 67.3 0.1 0.2 19.0 1.8 8.8 Solid molding

(The remainder being inevitable impurities, 'solid molding' means being made by solid molding)

division
(wt%) Ni Cr Fe Al Si Mn Remarks B 90.1 0.3 0.1 1.2 0.1 0.1 Ni metal D 14.6 19.1 60.0 0.1 0.4 1.0 STS E 18.5 24.7 52.4 0.1 0.5 0.7 STS

(The remaining amount is an inevitable impurity)

As shown in Tables 1 and 2, it can be seen that a large amount of valuable metals such as Ni and Cr is contained in the waste fuel cell in addition to a large amount of Fe. Therefore, a method for recycling the metal component is needed.

However, the form of the since the sphere at the same time of the fuel cell is placed in a state of high temperature and high pressure, especially a chemical reaction to take place, the Cr component is oxidized to Cr ^{6 +,} typically K ₂ Cr ₂ O ₇ (potassium dichromate) Lt; / RTI > It is difficult to utilize the Cr ^{6 +} immediately in the steelmaking process, and the present invention has been made to solve the above problems.

Cr ^{6 +} is classified as a very harmful carcinogen, as is well known. Therefore, it is a substance that is legally prohibited from processing by disposing of it, and it is prohibited to come into direct contact with the human body.

Hereinafter, the present invention will be described in detail.

The present invention relates to a method for preparing a waste fuel cell, which comprises washing a waste fuel cell with water (water washing), reducing washing water from which the waste fuel cell is washed, using the washed waste fuel cell as scrap, The separated sludge is used as a source of the valuable metal. The present invention is briefly shown in Fig.

First, prepare a waste fuel cell. The type and form of the waste fuel cell to be applied to the present invention are not particularly limited and can be selected from the group consisting of Molten Carbonate Fuel Cell (MCFC), Solid Oxide Fuel Cell (SOFC) (PAFC), Alkaline Fuel Cell (AFC), Proton Exchange Membrane Fuel Cell (PEMFC), Direct Methanol Fuel Cells (PEMFC) DEMFC) may be used.

The prepared waste fuel cell is washed with water (water washing). As described above, a large amount of Cr < ^{6 + &} gt ^; is produced in the spent fuel cell during the operation. It is difficult to use it as it is. Accordingly, it is necessary to remove the Cr ^{6 +} . In the present invention, the Cr ^{6 +} can be removed by washing with water. Since the Cr ^{6 +} has a solubility in water of 60 to 90 g / cc, it is possible to remove Cr ^{6 +} from the spent fuel cell by washing with water. The temperature of the washing water in the washing process does not greatly affect the washing process. The present inventors of Cr at all temperatures without significant impact on the temperature of the wash water to 6 ℃ (Winter basis) and 25 ℃ (summer basis) results temperature washing the Cell To determine the number of cleaning performance of the ^{6 +} Cr ^{6 +} It was confirmed that water washing was possible.

On the other hand, the washing is not significantly influenced by the pH of the washing water. The present inventors conducted water washing at a pH of about 6 to 7 in general tap water, observed changes in Cr ^{6 +} concentration and changed pH to 6 to 9, but did not significantly affect the washing of Cr ^{6 +} Respectively.

On the other hand, FIG. 2 illustrates a washing water tank which can be used in the water washing of the present invention, and was actually used in the following embodiments. The washing water tank is designed to increase the increase of the AC flow between the waste fuel cell and water. Specifically, since the waste fuel cell has a multi-layer laminated structure, water must permeate smoothly between the layers of the waste fuel cell to dissolve Cr ^{6 +} . Therefore, by using the seesaw principle, (Water circulation structure). As a result, the cleaning time can be shortened.

The washing is preferably performed one or more times. It is desirable to wash Cr ^{6 +} in the waste fuel cell to a content of 1.5 mg / l. For this purpose, in the present invention, it is preferable to measure Cr ^{6 +} of the fuel cell after washing and to carry out additional washing when the content exceeds 1.5 mg / l.

On the other hand, the measurement of Cr ^{+ 6} in wash water it is preferred that analysis of the Cr ^{+ 6} by Automatic water analyzer (Automatic analyzer water). When the wash water Cr ^{+ 6} concentration is reduced to less than 1.5mg / l, and ends the washing of the spent fuel cell, it is preferred to wash the finalizing the Cr ^{+ 6} concentration by the completion of the Korea Cell waste dissolution test method. The Cr ^{6 +} elution water obtained by the Korean waste elution test method is analyzed by an automatic water analyzer.

A reducing agent is added to the washing water from which the waste fuel cell is washed to perform reduction treatment. The reduction process has two purposes. One is that the waste water treated with the wash water from which Cr ^{6 +} is eluted is treated with wastewater (over 150,000 won per ton). If it is discarded as it is, it will prevent serious environmental pollution. Another object is to extract and recycle other useful metals such as Cr dissolved in the washing water. In addition to elution of Cr ^{6 +} in the washing water, other useful metals are contained, so that they can be extracted and recycled, and the washing water can be used again.

The reduction is performed by adding a reducing agent to the washing water. The reducing agent may be FeSO ₄ , NaHSO ₃ , Na ₂ S ₂ O ₃ and the like, preferably FeSO ₄ . The reaction formula when FeSO ₄ is used as a reducing agent is shown below.

H ₂ Cr ₂ O ₇ + 6FeSO ₄ + 6H ₂ SO ₄ = Cr ₂ (SO ₄ ) ₃ + 3Fe ₂ (SO ₄ ) ₃ + 7H ₂ O

The amount of the reducing agent supplied varies depending on the amount of Cr ^{6 + in} the washing water. Under ideal conditions, the reduction effect should be at least FeSO ₄ per kg of Cr ^{6 +} 8.43 kg or more is required. However, it is preferable to include not less than 10 kg of FeSO ₄ per 1 kg of Cr ^{6 + in} order to obtain an appropriate reducing effect in an ideal condition.

An example of determining the amount of Cr ^{6 + in} the wash water is as follows. For example, if the concentration of Cr ^{6 + in} the wash water is 150 mg / L and the wash water is 1000 L, the amount of Cr ^{6 + in} the wash water is 0.15 kg.

The upper limit of the amount of the reducing agent is not particularly limited, but it is necessary to put an appropriate amount into consideration in consideration of economical efficiency.

After the reduction, the solidified material exists in the form of sludge after washing. Various kinds of oxides such as Cr ₂ O ₃ , NiO, and Fe ₂ O ₃ exist in the sludge. The sludge can be utilized as a slag flux in a steelmaking process, as described later.

On the other hand, preferred reducing agents were derived through the following experiment. First, 50 cc of two kinds of washing water having a Cr ^{6 +} concentration of 100 mg / l and 10 mg / l were prepared. Then, FeSO ₄ , NaHSO ₃ And Na ₂ S ₂ O ₃ were added in amounts as shown in Table ₃ , respectively, and the concentration of residual Cr ^{6 +} was measured (twice experiment).

solution Cr ^{6 +} 100 mg / l, 50 cc Cr ^{6 +} 10 mg / l, 50 cc reducing agent
(input) FeSO ₄
(1 g) NaHSO ₃
(1 g) Na ₂ S ₂ O ₃
(1 g) FeSO ₄
(0.05 g) NaHSO ₃ (0.05 g) Na ₂ S ₂ O ₃ (0.05 g) Residual Cr ^{6 +}
density <0.01 57.00 87.44 <0.01 <0.01 4.27 <0.01 55.86 77.22 <0.01 <0.01 3.61

As can be seen from the results of Table 3, when FeSO ₄ is added as a reducing agent, residual Cr ^{6 +} is the least, indicating that a large amount of reduction has been achieved. Therefore, it can be seen that FeSO ₄ is most effective as a reducing agent.

The washed waste fuel cell itself is utilized as a steelmaking process such as an electric furnace. The washed spent fuel cell may be used as a scab due to the contained Fe component, and may be used as a source of Ni to Cr in some cases. On the other hand, the sludge separated from the reduced washing water is used as a slag flux in a steelmaking process or the like. The slag flux is injected into the molten steel during the steelmaking process to prevent Ni, Cr, and the like from being oxidized in the molten steel. Since the sludge has a high oxide content such as Fe, Ni and Cr, it can be added as a slag flux to increase the slag saturation of molten steel.

In addition, the sludge may be separately subjected to a process such as melt-reduction, solid-phase reduction or refining to obtain a metal alloy such as Fe-Ni, Fe-Cr or Fe-Ni-Cr. The metal alloy thus obtained can be used as a raw material in the production of steel such as a separate alloy iron.

Hereinafter, embodiments of the present invention will be described in detail. The following examples are for the understanding of the present invention and are not intended to limit the present invention.

(Example)

A waste solid oxide fuel cell (SOFC) having the components shown in Tables 1 and 2 was prepared, followed by water washing. The water washing was carried out using the washing water tank of Fig. FIG. 3 (a) is a schematic view of a washing water tank, and FIG. 3 (b) is a photograph showing water washing using an actually manufactured water tank.

On the other hand, the Cr ^{6 +} of the SOFC is washed in washing water, and then the cell is separated from the washing tank. FeSO ₄ is added to washing water as a reducing agent to wash water to reduce Cr ^{6 +} and solidify into an oxide form. At this time, the solidified material exists in the form of sludge in the washing water and the results of the analysis are shown in Table 4 below.

ingredient SiO ₂ Al ₂ O ₃ SO ₃ Fe ₂ O ₃ K ₂ O Cr ₂ O ₃ NiO Content (wt%) 1.19 2.48 1.69 78.53 1.65 2.14 10.27

(The remaining amount is an impurity)

As a result of the sludge analysis, it was confirmed that the sludge obtained by reducing the washing water can be sufficiently utilized as the slag flux. In addition, since Cr ⁶⁺ in the washing water is removed, the washing water itself can be recycled, and environmental pollution can be prevented even if the washing water is discarded.

On the other hand, in order to evaluate whether the washed waste fuel cell can be used as an appropriate scrap, the following experiment was conducted. First, an induction furnace as shown in the schematic diagram of FIG. 4 was prepared, and electrolytic iron (scrap, Fe 99.99%) and a washed spent fuel cell were charged and dissolved.

(Electrolytic iron + fuel cell) was cooled to room temperature to measure the weight before and after the dissolution. The results are shown in Table 5 below. The contents of N, O, C, and S that can be attributed to the reducing agent and the reducing agent are analyzed and the results are shown in Table 6.

All the specimens were analyzed to determine if the Ni and Cr of the spent fuel cell were homogeneously dissolved in the melt. 5 (a) is a photograph showing a crucible provided in an induction furnace, and electrolytic iron is injected into the crucible. (b) shows the shape of the steel obtained from the electrolytic iron and the waste fuel cell.

Before melting After melting Electrolytic iron Waste fuel cell all 1045 g 77g 1165g

division Ni Cr N O C S Content (wt%) 2.45 0.75 0.013 0.08 0.0038 0.001

As a result, it has been proved that when the molten steel is manufactured using the cleaned waste fuel cell, it can be used as a supply source of Ni and Cr sufficiently, and the concentration of impurities N, O, C and S is very low, Respectively.

On the other hand, although not disclosed in this embodiment, when the electrolytic iron is dissolved first in the induction furnace, then the washed waste fuel cell is charged, and when the washed waste fuel cell is dissolved and then the electrolytic iron is injected and dissolved, Which is a source of Ni and Cr.

Claims (9)

Preparing a waste fuel cell;
Washing the spent fuel cell with water;
Forming a sludge by adding a reducing agent to washing water washed by the waste fuel cell; And
The step of using the washed waste fuel cell for a steelmaking process
And recycling the waste fuel cell.
The method according to claim 1,
Wherein the washed waste fuel cell is used as at least one of a scrap of a steelmaking process and a source of a valuable metal.
The method according to claim 1,
Wherein the sludge is used as a slag flux in a steelmaking process.
The method according to claim 1,
The method of recycling a spent fuel cell according to claim 1, wherein the washed fuel cell has a Cr ^{6 +} content of 1.5 mg / l or less.
The method according to claim 1,
Wherein the temperature of the washing water is 6 to 25 占 폚.
The method according to claim 1,
The reducing agent to be used in the reduction process is FeSO ₄ in recycling of spent fuel cells.
The method according to claim 1,
Wherein the amount of the reducing agent is 8.43 kg or more per 1 kg of Cr ⁶⁺ in the washing water.
The method according to claim 1,
The waste fuel cell may include a molten carbonate fuel cell (MCFC), a solid oxide fuel cell (SOFC), and a phosphoric acid fuel cell (PAFC) A method of recycling a spent fuel cell, the method being any of Alkaline Fuel Cell (AFC), Proton Exchange Membrane Fuel Cell (PEMFC), and Direct Methanol Fuel Cells (DEMFC).
The method according to claim 1,
Further comprising the step of performing at least one selected from the group consisting of melting and reducing the sludge, solid-phase reduction and refining to obtain at least one of Fe-Ni, Fe-Cr and Fe-Ni-Cr alloy.

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