Method for recovering valuable elements, method for producing hydroxides of valuable elements, and method for producing oxides of valuable elements

Abstract

To provide a novel method in which valuable element such as cobalt can be recovered from waste catalyst.SOLUTION: A substance containing at least molybdenum and cobalt is brought into contact with aqueous hydrogen peroxide to yield a leachate in which at least cobalt is leached from the substance. By filtering the leachate to separate the substance, a filtrate is obtained. The filtrate is subjected to alkali treatment, and the formed cobalt precipitate is separated by filtration.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for recovering valuable elements from a substance containing at least molybdenum and cobalt (e.g., a waste catalyst such as a used desulfurization catalyst used in oil refining), as well as a method for producing a hydroxide of a valuable element and a method for producing an oxide of a valuable element. [Background technology]

[0002] Conventionally, desulfurization using a desulfurization catalyst is performed in oil refining. More specifically, hydrodesulfurization is performed in which oil is reacted with high-pressure hydrogen on the desulfurization catalyst to remove sulfur content in the oil as hydrogen sulfide. As such desulfurization catalysts are used, they become gradually poisoned by heavy metals and tar contained in the petroleum, reducing their catalytic activity, and must therefore be replaced periodically, generating used desulfurization catalysts (spent catalysts). Conventionally, from the viewpoint of resource circulation, methods for recovering various elements contained in spent catalysts have been proposed (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-133233 A Summary of the Invention [Problem to be solved by the invention]

[0004] The desulfurization catalyst is, for example, a carrier such as alumina on which a metal element such as molybdenum (Mo) or cobalt (Co) is supported. Molybdenum is used in special steels and stainless steels because adding it to steel increases its mechanical strength and rigidity. Furthermore, it is used in greases and the like because it is malleable and ductile at high temperatures. In recent years, there has been a strong demand for recovering these elements (valuable elements) from waste catalysts such as used desulfurization catalysts.

[0005] Therefore, an object of the present invention is to provide a novel method for recovering valuable elements such as cobalt from substances such as spent catalysts. [Means for solving the problem]

[0006] As a result of extensive investigations, the present inventors have found that the above object can be achieved by employing the following configuration, and have completed the present invention.

[0007] That is, the present invention provides the following [1] to

[10] . [1] A method for recovering valuable elements, comprising the steps of: contacting a substance containing at least molybdenum and cobalt with a hydrogen peroxide solution to obtain a leachate in which at least cobalt has been leached from the substance; filtering the leachate to separate the substance to obtain a filtrate; subjecting the filtrate to an alkali treatment; and separating the resulting cobalt precipitate by filtration. [2] The method for recovering a valuable element according to [1] above, wherein the hydrogen peroxide solution contains hydrogen peroxide, and the amount of the hydrogen peroxide relative to the amount of the substance is 40 mass% or less. [3] The method for recovering valuable elements according to [2] above, wherein the amount of the hydrogen peroxide relative to the amount of the substance is 5 mass% or more. [4] The method for recovering a valuable element according to any one of [1] to [3] above, wherein the substance is pulverized prior to contacting with the hydrogen peroxide solution. [5] The method for recovering a valuable element according to any one of the above [1] to [4], wherein the mass ratio of the hydrogen peroxide solution to the substance (hydrogen peroxide solution / substance) is 2 / 1 or more. [6] The method for recovering a valuable element according to any one of the above [1] to [5], wherein the filtrate is subjected to the above alkali treatment to adjust the pH of the filtrate to 7 or higher. [7] The method for recovering valuable elements according to any one of the above [1] to [6], wherein the substance is a waste catalyst. [8] The method for recovering valuable elements according to the above [7], wherein the waste catalyst is a used desulfurization catalyst. [9] A method for producing a hydroxide of a valuable element, comprising obtaining a hydroxide of the valuable element by using the method for recovering a valuable element according to any one of the above items [1] to [8].

[10] A method for producing an oxide of a valuable element, comprising obtaining an oxide of the valuable element by using the method for recovering a valuable element according to any one of the above items [1] to [8]. Effect of the Invention

[0008] According to the present invention, valuable elements such as cobalt can be recovered from substances such as spent catalysts. [Brief description of the drawings]

[0009] [Figure 1] 1 is a flowchart showing the flow of a method for recovering valuable elements. [Diagram 2] 1 shows the particle size distribution of the crushed spent catalyst. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The method for recovering valuable elements of the present invention includes contacting a substance containing at least molybdenum and cobalt with hydrogen peroxide to obtain a leachate in which at least cobalt has been leached from the substance, filtering the leachate to separate the substance to obtain a filtrate, subjecting the filtrate to an alkali treatment, and separating the resulting cobalt precipitate by filtration. According to the present invention, cobalt can be easily recovered as a cobalt precipitate from a substance containing at least molybdenum and cobalt.

[0011] A preferred embodiment of the present invention will now be described with reference to FIG. FIG. 1 is a flow chart showing the flow of a method for recovering valuable elements.

[0012] The substance containing at least molybdenum and cobalt is not particularly limited, but in the following description, a spent catalyst will be taken as an example.

[0013] <Preparation of spent catalyst> The spent catalyst is, for example, a used desulfurization catalyst that contains at least molybdenum and cobalt. The desulfurization catalyst supports metal elements such as molybdenum (Mo), cobalt (Co), and nickel (Ni) on a support such as alumina (Al2O3).

[0014] Crush As described later, the spent catalyst is brought into contact with hydrogen peroxide water, but it is preferable to crush it prior to this. This is expected to result in highly efficient leaching. This is particularly useful when the spent catalyst is a desulfurization catalyst having an alumina support (having an alumina skeleton). The method for pulverizing the spent catalyst is not particularly limited, and the spent catalyst can be easily pulverized by a known method using a ball mill, a jet mill, or the like. The particle size of the pulverized waste catalyst is preferably 1000 μm or less, and more preferably 500 μm or less.

[0015] Contact with hydrogen peroxide: Obtaining leachate The waste catalyst is optionally pulverized and then contacted with hydrogen peroxide (aqueous solution of hydrogen peroxide). The contact method is not particularly limited, and an example of the method is to immerse the waste catalyst in hydrogen peroxide to contact the two. As a result, at least the cobalt out of the molybdenum and cobalt contained in the spent catalyst is leached into the hydrogen peroxide solution. That is, the obtained leachate is a slurry containing the spent catalyst and cobalt, which is a component dissolved from the spent catalyst. This slurry is, for example, strongly acidic, as described later.

[0016] Incidentally, when a large amount of molybdenum as well as cobalt is leached into the leachate, when the alkali treatment described below is carried out, a certain amount of molybdenum is also coprecipitated, and the quality of the obtained cobalt precipitate is likely to decrease. Furthermore, since molybdenum is not generally an element that precipitates at alkaline pH levels, a large amount of molybdenum remains in the waste liquid before it is discarded, resulting in increased molybdenum loss.

[0017] As a result of the inventors' investigations, they found that when a high concentration of hydrogen peroxide solution is brought into contact with a waste catalyst, various metals such as molybdenum and cobalt are leached in large quantities, and that when the concentration of the hydrogen peroxide solution is reduced, mainly only cobalt is selectively leached. This is thought to be because cobalt is more susceptible to oxidation by hydrogen peroxide than other metal elements, and therefore by contacting the spent catalyst with dilute hydrogen peroxide, a leachate containing more cobalt than other metal elements (e.g. molybdenum) is obtained.

[0018] From the above points, in this embodiment, it is preferable to set the amount of hydrogen peroxide contained in the hydrogen peroxide solution that comes into contact with the spent catalyst to a certain value or less relative to the amount (dry mass) of the spent catalyst. Specifically, the amount of hydrogen peroxide relative to the amount of the spent catalyst (hereinafter, for convenience, also referred to as "amount of hydrogen peroxide p") is preferably 40 mass% or less, more preferably 30 mass% or less, and even more preferably 20 mass% or less, which makes it easier to selectively leach only cobalt from the spent catalyst.

[0019] On the other hand, if the amount of hydrogen peroxide p is too low, there is a risk that cobalt will not be leached sufficiently. For this reason, the amount p of hydrogen peroxide is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more.

[0020] For example, when the mass ratio (hydrogen peroxide solution / waste catalyst) described below is 10 / 1, if the concentration of hydrogen peroxide solution (the content of hydrogen peroxide in hydrogen peroxide solution) is 4 mass%, the amount of hydrogen peroxide p will be 40 mass%.

[0021] The mass ratio of the hydrogen peroxide solution to the waste catalyst (hydrogen peroxide solution / waste catalyst) is preferably 2 / 1 or more, and more preferably 3 / 1 or more, for the reason that efficient leaching can be achieved. On the other hand, the mass ratio (hydrogen peroxide solution / waste catalyst) is preferably 50 / 1 or less, and more preferably 30 / 1 or less, because this allows the amount of hydrogen peroxide solution used to be appropriate and prevents an increase in the reaction vessel and costs.

[0022] The time for which the spent catalyst is brought into contact with the hydrogen peroxide solution (contact time) is preferably 10 minutes or more, and more preferably 15 minutes or more, for the reason that the valuable elements inside the spent catalyst can be sufficiently leached out. On the other hand, if the contact time is excessively long, the leaching reaches a steady state and no improvement in the leaching rate can be expected, so the contact time is preferably 180 minutes or less, more preferably 120 minutes or less. Normally, if the spent catalyst is crushed beforehand, one hour is enough to sufficiently leach the valuable elements from within the spent catalyst.

[0023] By making the hydrogen peroxide solution acidic, valuable elements can be efficiently leached out from the spent catalyst. However, if the waste catalyst is a used desulfurization catalyst, it is not necessary to add acid to the hydrogen peroxide solution. This is because the sulfides in the waste catalyst are converted into sulfates by hydrogen peroxide, and the sulfate ions dissolve in the hydrogen peroxide solution, providing the same effect as adding sulfuric acid. In fact, when the waste catalyst (used desulfurization catalyst) is placed in hydrogen peroxide solution, the pH drops quickly.

[0024] Separation of spent catalyst by filtration: Obtaining filtrate Next, the leachate is filtered, whereby the solid content of the spent catalyst is separated from the leachate to obtain a filtrate, which contains at least cobalt, which is a component dissolved from the spent catalyst. The filtration method is not particularly limited as long as it can separate the target solid content and obtain the desired filtrate, and any conventionally known method can be appropriately used. This also applies to the filtration described below.

[0025] In the waste catalyst, which is the residue of the filtration, molybdenum remains without being leached, while cobalt is leached and removed. In other words, it was difficult to remove cobalt from the waste catalyst by conventional methods such as the dry method, but this can be achieved by the present embodiment. Therefore, the waste catalyst, which is the residue after filtration, can be used to produce ferromolybdenum, etc., and molybdenum can be recycled easily.

[0026] <Alkaline treatment: formation of cobalt precipitate> Next, the filtrate is treated with an alkali to produce a cobalt precipitate. That is, by adding an alkali such as sodium hydroxide or potassium hydroxide to the filtrate, the cobalt in the filtrate is precipitated as cobalt hydroxide. The filtrate is subjected to an alkali treatment to adjust the pH of the filtrate. In order to obtain a sufficient cobalt recovery rate, the pH is preferably 7 or more, more preferably 8 or more, and even more preferably 9 or more. On the other hand, the pH is preferably 13.5 or less because the amount of acid required for neutralization is small and therefore economical.

[0027] Recovery of cobalt precipitate by filtration Next, the filtrate containing the cobalt precipitate is filtered. This separates the solid cobalt precipitate from the filtrate. In this way, cobalt can be recovered from the spent catalyst as the cobalt precipitate. The recovered cobalt precipitate is, for example, a hydroxide of cobalt. Furthermore, by drying this hydroxide of cobalt, the cobalt can be converted into an oxide form (i.e., an oxide of cobalt). The drying method is not particularly limited, and a known method can be used. The filtrate (residual liquid) from which the cobalt precipitate has been separated is discarded as waste liquid.

[0028] As described above, according to this embodiment, cobalt can be selectively leached from the spent catalyst and recovered as a cobalt precipitate, while molybdenum can be recovered by leaving it in the spent catalyst. Therefore, according to this embodiment, the process can be simplified compared to, for example, a method in which molybdenum and cobalt are both leached from a spent catalyst and then separately recovered. Generally, when a multi-stage process is required, the equipment becomes complicated, and costs such as construction costs increase (for practical purposes, it is required to implement the process on a certain scale of equipment to enjoy economies of scale). For this reason, the present embodiment is also advantageous in terms of cost. In addition, in this embodiment, a heat treatment such as roasting, which would require a large-scale facility from the standpoint of thermal efficiency, is not performed, and therefore the facility can be simplified in this respect as well. EXAMPLES

[0029] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples described below.

[0030] Example 1 Following the flow explained based on FIG. 1, valuable elements were recovered from a spent catalyst, which is a substance containing at least molybdenum and cobalt.

[0031] <Preparation of spent catalyst> The waste catalyst used was a used indirect desulfurization catalyst provided by an oil refinery plant. This spent catalyst was cylindrical with a diameter of 2 to 3 mm and a length of about 3 to 5 mm, and various elements were supported on an alumina carrier. The composition of the spent catalyst was determined by ICP (inductively coupled plasma) emission spectrometry and is shown in Table 1 below.

[0032] [Table 1]

[0033] Shatter 10 kg of the prepared spent catalyst was mixed with 100 L of pure water and crushed for 120 minutes using a wet ball mill. The median diameter of the crushed spent catalyst was 12 μm. The particle size distribution of the crushed spent catalyst is shown in Figure 2.

[0034] Contact with hydrogen peroxide and filtration Next, hydrogen peroxide solution (concentration: 35% by mass) was added to the mixture of the crushed waste catalyst and pure water in an amount such that the above-mentioned hydrogen peroxide amount p was 15% by mass, and then the mixture was stirred for 15 minutes to obtain a leachate. The resulting leachate was filtered to separate the waste catalyst and obtain a filtrate. For the filtration (suction filtration), 5C filter paper (retention particle size: 1 μm) was used (same below).

[0035] Alkaline treatment and filtration The filtrate was subjected to an alkali treatment. That is, an aqueous solution of sodium hydroxide was added to the filtrate to adjust the pH of the filtrate to 12, and the filtrate was left for one hour. As a result, a cobalt precipitate was formed in the filtrate. The filtrate containing the cobalt precipitate was filtered to separate, recover, and dry the cobalt precipitate. The composition of the dried cobalt precipitate was determined by ICP emission spectrometry. The composition of the cobalt precipitate is shown in Table 2 below.

[0036] It is assumed that the metal elements are precipitated in the form of hydroxides; for example, cobalt precipitate is represented by the formula Co(OH)3·H2O.

[0037] "evaluation" The cobalt yield (unit: mass%) was calculated based on the following formula. The results are shown in Table 2. It can be evaluated that the larger the cobalt yield value, the more cobalt was recovered from the spent catalyst as cobalt precipitate. Cobalt yield = 100 x (amount of cobalt in the cobalt precipitate / amount of cobalt in the spent catalyst at the time of preparation)

[0038] Furthermore, molybdenum loss (unit: mass%) was calculated based on the following formula. The results are shown in Table 2 below. The smaller the molybdenum loss value, the more molybdenum was evaluated to have been recovered without being leached out of the spent catalyst and remaining in the spent catalyst. Molybdenum loss = 100 x {1 - (amount of molybdenum in the spent catalyst when it was separated from the leachate / amount of molybdenum in the spent catalyst when it was prepared)}

[0039] Example 2 Except for changing the amount of hydrogen peroxide p to 40 mass%, the cobalt precipitate was recovered, and the composition of the cobalt precipitate, the cobalt yield, and the molybdenum loss were determined in the same manner as in Example 1. The results are shown in Table 2 below.

[0040] Example 3 Except for changing the amount of hydrogen peroxide p to 50 mass %, the cobalt precipitate was recovered, and the composition of the cobalt precipitate, the cobalt yield, and the molybdenum loss were determined in the same manner as in Example 1. The results are shown in Table 2 below.

[0041] [Table 2]

[0042] <Summary of evaluation results> As shown in Table 2 above, in Example 1 (amount of hydrogen peroxide p: 15% by mass), the cobalt yield was 71% by mass, and the obtained cobalt precipitate was of such a quality that it could be recycled by refiners and the like as a high-quality cobalt raw material. In Example 2 (amount of hydrogen peroxide p: 40 mass %), the cobalt yield was significantly increased compared to Example 1. In Example 3 (amount of hydrogen peroxide p: 50 mass %), molybdenum loss was increased compared to Examples 1 and 2.

Claims

1. contacting a substance containing at least molybdenum and cobalt with hydrogen peroxide to obtain a leachate in which at least cobalt has been leached from the substance; filtering the leachate to separate the substances, thereby obtaining a filtrate; The filtrate is subjected to an alkali treatment, and the resulting cobalt precipitate is separated by filtration; The hydrogen peroxide solution contains hydrogen peroxide, The amount of hydrogen peroxide relative to the amount of the substance is 20% by weight or less; The substance is a spent catalyst, The method for recovering valuable elements, wherein the waste catalyst is a used desulfurization catalyst.

2. 2. The method for recovering valuable elements according to claim 1, wherein the amount of said hydrogen peroxide relative to the amount of said substance is 5 mass% or more.

3. 3. The method for recovering valuable elements according to claim 1, wherein the substance is pulverized prior to contacting with the hydrogen peroxide solution.

4. 4. The method for recovering a valuable element according to claim 1, wherein a mass ratio of the hydrogen peroxide solution to the substance (hydrogen peroxide solution / substance) is 2 / 1 or more.

5. 5. The method for recovering valuable elements according to claim 1, wherein the filtrate is subjected to the alkali treatment to adjust the pH of the filtrate to 7 or higher.

6. A method for producing a hydroxide of a valuable element, comprising obtaining a hydroxide of the valuable element by using the method for recovering a valuable element according to any one of claims 1 to 5.

7. A method for producing an oxide of a valuable element, comprising obtaining an oxide of a valuable element using the method for producing a hydroxide of a valuable element described in claim 6.

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