JP2011006749A - Method for separating and collecting element coexisting in iron scrap - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for effectively and economically separating and collecting elements such as copper which coexists in iron scrap.SOLUTION: This separation and collection method includes: melting the iron scrap; bringing the obtained melt of the iron scrap into contact with molten Ag to migrate the elements coexisting in the iron scrap to the molten Ag, on the basis of distribution equilibrium between the melt of the iron scrap and the molten Ag; and oxidizing the elements which have migrated to the molten Ag and removing the elements from the molten Ag. The melt of the iron scrap preferably contains C, and further preferably the C is dissolved and saturated in the melt.

Description

  The present invention relates to a method for separating and recovering an element coexisting with iron in iron scrap, particularly a metal element such as a playing card element.

  The accumulation of iron scrap in Japan is increasing year by year, reaching about 1.8 billion tons in 2020, and 50 million tons of iron scrap is expected to be generated annually. In commercial iron scrap, it is difficult to remove from iron, and impurity components other than small iron (Cu, Ni, Cr, Sn) called trump elements that adversely affect the quality or manufacturing process of steel materials. , Zn, etc.) are often contained, and the use as a raw material for high-grade steel materials that the Japanese steel industry is good at is restricted.

  Recently, problems of soaring and depletion of useful rare metals have emerged in addition to iron resources, and even from this point of view, in addition to the above copper and chromium, useful metals (W, Mo, Co, Ni, V, Nb, etc.), and if it becomes possible to efficiently separate and recover the components other than the minute iron contained in the iron scrap, It is possible to expand domestic use without exporting the generated iron scrap.

  As a method for removing copper from iron scrap, there is a technique for removing copper from molten iron by utilizing copper distribution between iron-alkali metal and alkaline earth metal sulfides and carbon-saturated iron (non-patent). Reference 1).

  In this method, a copper removal rate of 65 to 75% can be achieved with a flux unit of 100 kg / t-metal, but the copper removal efficiency is not sufficient, and in order to further improve the copper removal rate, the amount of flux is increased. There is a problem from an economic point of view.

Further, since a sulfide flux containing a large amount of alkali metal is used, the flux processing also becomes a problem.
Patent Document 1 reports a method of selectively reacting copper with iron using chlorine gas and removing it as a gas. However, since chlorine gas is used, the reaction vessel is made completely sealed. In addition to the necessity, the material of the reaction vessel that does not react with chlorine becomes a problem.

  An evaporative refining method for selectively evaporating copper under vacuum has also been proposed, but in order to increase the evaporation rate, a high temperature of 1873 K or higher and a high vacuum of at least 100 Pa are required. Moreover, the reaction interface area sufficient for practical use calculated from the evaporation rate is enormous, and development to an actual process is difficult (Non-Patent Document 2).

Patent Document 2 devises a technique for removing copper by once transferring copper in iron scrap to a lead alloy and then transferring copper in the lead alloy to a metal melt containing aluminum.
However, in this prior art, it is necessary to separately carry out the transfer of copper from iron scrap to lead alloy and the transfer of copper from lead alloy to a metal melt containing aluminum with respect to molten iron. Can't progress.

Also, in the transfer of copper from iron scrap to lead alloy, the distribution of copper to the lead alloy relative to iron (equilibrium distribution ratio of copper = [mass% Cu] _{in Pb} / [mass% Cu] _{in Fe-C} , here [Mass% Cu] _{in Pb} means the copper concentration in lead, and [mass% Cu] _{in Fe-C} means the copper concentration in iron.) Is as small as about 2: 1. There is a problem that a large amount of lead alloy is required for removal.

  As described above, the conventionally proposed methods for removing copper from iron scrap have problems from the viewpoint of efficiency and economy, and have not been put into practical use.

JP-A-6-248364 JP-A-10-110224

Oshio, Tetsuya Nagasaka, Hikaru Hino, Shiro Sugaya: Iron and Steel, 77 (1991), 644-651. H. Ono-Nakazato, K .; Taguchi, Y .; Seike and T.W. Usui: ISIJ International, 43 (2003), 1691-1697.

  The present invention proposes a method for efficiently and economically separating and recovering elements such as copper coexisting in iron scrap, and an object thereof is to expand the use of iron scrap.

  As a result of investigations by the present inventors, among the elements coexisting in iron scrap, even if it is difficult to separate from molten iron by ordinary oxidation refining, molten Ag having a particularly low solubility in the molten iron scrap is obtained. The inventor obtained the knowledge that the above-mentioned problems can be solved by indirect oxidation removal as a medium.

  This knowledge will be described in detail using Cu as an example of an element that is harder to oxidize than Fe and difficult to separate from molten iron by conventional oxidation smelting. By blowing oxygen onto the surface of the molten Ag that is not in contact with the molten iron scrap through the molten Ag having a particularly low solubility in the molten iron scrap, Cu can be removed by oxidation and recovered.

  When Cu is contained in the Fe phase, Fe is preferentially oxidized with respect to Cu. For this reason, reaction of following formula (2) cannot be advanced normally.

  Therefore, by using the iron scrap melt and Ag having no solubility, the distribution of Cu between the iron scrap melt and the molten Ag (the following formula (3)) and the oxidation of Cu in the molten Ag (the following formula (4) )) Is continuously carried out, the reaction of the formula (3) + the formula (4) = the formula (2), that is, the oxidative refining of Cu in the iron scrap melt can be realized.

  The element that can be separated by the above principle is more easily oxidized than Ag and can be dissolved in the iron scrap melt and the molten Ag, that is, distributed at the interface between the iron scrap melt and the molten Ag. Element.

Moreover, when the iron scrap melt contains C, the above-described elements can be recovered more efficiently.
The present invention completed based on the above knowledge is as follows.

  (1) A method for separating and recovering elements coexisting in iron scrap, melting the iron scrap, and melting the element coexisting in the iron scrap by bringing the obtained iron scrap melt into contact with molten Ag A separation / recovery method characterized in that the element transferred to Ag is oxidized and removed from the molten Ag.

Here, when the iron scrap is melted and the obtained iron scrap melt is brought into contact with the molten Ag, from the iron scrap melt based on the distribution equilibrium between the iron scrap melt and the molten Ag. An element coexisting with iron in iron scrap (hereinafter also referred to as “coexisting element”) is transferred to molten Ag.
“Oxidation removal” refers to an element that is more easily oxidized than Ag among the elements contained in molten Ag by making the atmosphere near the surface of molten Ag a strong oxidizing atmosphere by means such as blowing oxygen. Oxidation refers to removal from the molten Ag phase as an oxide insoluble in molten Ag.

  (2) The separation / recovery method according to (1), wherein the iron scrap is melted and the iron scrap melt and the molten Ag are contacted in a non-oxidizing atmosphere.

(3) Separation / recovery method according to (1) or (2) above, wherein the iron scrap melt contains C and the concentration N _c (unit: mass%) satisfies the following formula (1):
N _C ≦ 10 ^{12.728 / T + 0.7271 × log T−3.049} (1)
Here, T is the temperature of the iron scrap melt, and satisfies 1426 <T <1873K.

  (4) The separation / recovery method according to the above (3), wherein the iron scrap is melted together with the carbon source to obtain an iron scrap melt containing C.

  (5) The separation / recovery method according to (4), wherein the melting of iron scrap and the contact between the iron scrap melt and molten Ag are performed in a graphite crucible, and C is saturated and dissolved in the iron scrap melt.

  (6) The separation / recovery method according to any one of (1) to (5), wherein the element to be separated / recovered includes a trump element.

  (7) The separation / recovery method according to any one of (1) to (6), wherein the element to be separated / recovered is one or more elements selected from the group consisting of W, Mo, Co, V and Nb. .

  In the present invention, elements coexisting in iron scrap can be oxidized and removed by using a melt of iron scrap and molten Ag having no solubility as a medium. For this reason, it is implement | achieved that a trump element and a useful rare element are efficiently collect | recovered from iron scrap. Accordingly, the use of iron scrap can be expanded by employing the method according to the present invention.

It is a figure which shows notionally the structure of an example of the reaction container for enforcing the separation / recovery method of the coexisting element which concerns on this invention. It is a figure which shows notionally the separation / recovery apparatus of the coexisting element used in the present Example. It is the result of having carried out X-ray diffraction (XRD) measurement of a part of surface of the collection | recovery area | region side in the solid Ag phase after completion | finish of the test of a present Example.

Hereinafter, a method for separating and recovering an element (coexisting element) coexisting with iron in the iron scrap according to the present invention will be described in detail.
1. Separation / Recovery Principle The separation / recovery method of coexisting elements in iron scrap using Ag in the present invention is a two-liquid phase separation between a molten Fe phase and a molten Ag phase made of a melt obtained by melting iron scrap. In addition, it utilizes the property that they have almost no solubility and do not dissolve each other, and the property that the molten Ag phase, which is the medium phase, is a noble metal and thus does not easily react with oxygen.

FIG. 1 is a diagram conceptually showing an example of the structure of a reaction vessel for carrying out the coexisting element separation / recovery method according to the present invention.
Since the molten Ag phase has a higher specific gravity than the molten Fe phase, as shown in FIG. 1, the molten Ag phase is present in the lower layer as a reaction vessel for carrying out the method according to the present invention, and partially enters the molten Ag phase. There is a structure in which the molten Fe phase and the molten Ag phase are in contact with each other in one region partitioned by the partition, and oxygen is supplied to the surface of the molten Ag in the other region. Hereinafter, the one area is referred to as a “separation area”, and the other area is referred to as a “collection area”.

  Since Fe and Ag have little solubility to each other, the two-phase separation of the molten Fe phase and the molten Ag phase occurs in the separation region. For this reason, the coexisting elements in the iron scrap are distributed into a molten Fe phase and a molten Ag phase separated into two liquid phases.

  The coexisting elements distributed in the molten Ag phase diffuse into the recovery region beyond the partition and reach the vicinity of the surface of the molten Ag in this region. Since oxygen is supplied to the surface of the molten Ag in the recovery region, the recovery region has a strong oxidizing atmosphere. For this reason, the coexisting elements that have reached the vicinity of the surface of the molten Ag in the recovery region are rapidly oxidized. Here, the molten Ag that is a medium is a noble metal and thus is not easily oxidized. Therefore, the coexisting elements are preferentially oxidized and become oxides and removed from the molten Ag phase.

When the coexisting elements in the molten Ag phase are oxidized and removed in this manner, the concentration of the coexisting elements in the recovery region of the molten Ag phase is lowered, and this influence promotes the diffusion of the coexisting elements from the separation region to the recovery region. For this reason, the concentration of the coexisting elements in the separation region also decreases. Then, based on the distribution equilibrium of the coexisting elements between the molten Fe phase and the molten Ag phase, the coexisting elements move from the molten Fe phase to the molten Ag phase in the separation region. Even during the movement of the coexisting element, the concentration of the coexisting element is lowered in the recovery region. Therefore, the coexisting element that has moved into the molten Ag phase in the separation region further moves to the recovery region by diffusion, and the recovery region. Oxidation is removed in a strong oxidizing atmosphere.
Based on such a principle, the coexisting elements contained in the molten Fe phase made of the iron scrap melt are continuously reduced, and the coexisting elements are recovered as oxides on the molten Ag phase side.

2. Target element Since elements are separated and recovered based on the above principle (hereinafter referred to as “the present principle”), the element separated and recovered in the present invention is an element that is more easily oxidized than Ag as a medium. These elements include so-called trump elements such as Cu, Ni, Cr, Sn, and Zn, and useful rare metals such as W, Mo, Co, Ni, V, and Nb. In particular, elements that are less likely to be oxidized than iron (such as Cu) are not removed by conventional oxidative refining, but are efficiently separated and recovered by the method of the present invention based on this principle. In other words, among the non-ferrous metal elements contained in iron scrap, when the target is an element that is more easily oxidized than Ag and less oxidized than Fe, the benefit of the separation / recovery method of the present invention can be most enjoyed.

  Of course, metals (for example, REM such as Sm) that are more easily oxidized than iron, that is, can also be removed by conventional oxidative refining, can be recovered in the recovery region according to this principle. However, in order to efficiently recover such elements in the recovery region, it is preferable that the atmosphere of the separation region is a non-oxidizing atmosphere so that conventional oxidation refining does not proceed in the separation region. .

  As will be described later, elements such as C, Si, B and the like that have a thermodynamic affinity for Fe are difficult to move from the iron scrap melt to the molten Ag. It is difficult.

3. The atmosphere in the separation region The atmosphere in the separation region where the molten Fe phase and the molten Ag phase are in contact is preferably a non-oxidizing atmosphere. In order to move the coexisting elements from the molten Fe phase to the molten Ag phase by utilizing the distribution of elements between the molten Fe phase and the molten Ag phase, the target element of the separation / recovery method based on this principle is It is required to be dissolved in the molten Fe phase. Therefore, when the oxygen partial pressure in the atmosphere of the separation region, that is, the atmosphere in the vicinity of the interface between the molten Fe phase and the molten Ag phase is high, some elements dissolved in the molten Fe phase may become oxides. If it becomes an oxide in the molten Fe phase, it becomes difficult to move to the molten Ag phase through the interface between the molten Fe phase and the molten Ag phase, and it becomes difficult to recover the element in the recovery region.

4). Composition of iron scrap melt As described above, when the iron scrap melt is a molten Fe phase, it is possible to separate the molten Ag phase and the two liquid phases, as described below, The molten iron scrap is preferably a molten Fe-C phase, and it is particularly preferable that C contained in the molten Fe-C phase is saturated and dissolved.

  When the Fe-Ag system containing no carbon is separated into two liquid phases, a temperature in the vicinity of the melting point of iron, that is, about 1800 K is required, depending on the type and concentration of the coexisting elements. However, increasing the temperature of the entire system increases the solubility of Ag in the molten Fe phase. For this reason, the Ag concentration in the iron scrap after carrying out the separation / recovery method according to the present invention tends to be relatively high as compared with the case where the temperature of the entire system is not increased. This also means that Ag, which is a medium after the implementation of the present invention, is relatively reduced, and causes an increase in process loss.

  On the other hand, when a carbon source is present in melting iron scrap, since C has a thermodynamic affinity with Fe, the iron scrap melt changes from a molten Fe phase to a molten Fe-C phase. For this reason, although the melting point of the melt depends on the type and concentration of the coexisting elements, it decreases to about 1500 K or less, and two-liquid phase separation at a relatively low temperature becomes possible. As described above, this leads to an improvement in the quality of post-process iron scrap and a reduction in process loss. In addition, the inclusion of C further reduces the solubility of Ag in the iron scrap melt. For this reason, the quality of the scrap iron after the process is improved and the process loss is reduced more than the melting point is simply lowered. Furthermore, since the activity coefficient of the coexisting elements in the molten Fe—C phase is increased, the concentration of the coexisting elements distributed to the molten Ag phase is high in the distribution of the coexisting elements between the molten Fe—C phase and the molten Ag phase. This is thermodynamically expected, that is, the movement of coexisting elements from the molten Fe—C phase into the molten Ag phase is promoted. In addition, since C is contained, the reaction between Fe and oxygen in the iron scrap melt is suppressed.

  Reactions corresponding to the above formulas (2) to (4) when the iron scrap melt is a molten Fe-C phase are as shown in the following formulas (2) 'to (4)'.

Table 1 shows the calculation result of the reduction limit value of the coexisting element concentration in the molten Fe-C phase (C concentration is 4.4% by mass) when it is brought into contact with the molten Ag phase under P _O2 = 1 atm control. .

  Table 1 shows that it is possible to reduce the concentration in the molten Fe-C phase of trump elements such as Cu and Ni. Table 1 also shows that the amount of metal elements such as W, Mo, Co, V, and Nb can be very small in the molten Fe-C phase. Thus, based on this principle, Table 1 shows that a coexisting element can be efficiently extracted from the molten Fe-C phase and separated and recovered.

The C concentration N _c (unit: mass%) in the molten Fe—C phase is not particularly limited, but the saturated dissolution molar fraction is determined by the temperature of the molten Fe—C phase, and is expressed by the following formula (1). It becomes a range.
N _C ≦ 10 ^{12.728 / T + 0.7271 × log T−3.049} (1)

  Here, T is the temperature of the iron scrap melt, and satisfies 1426K <T <1873K. When the temperature T of the iron scrap melt is 1426K or less, it becomes difficult for the Fe-C phase to exist as a liquid phase, so it is practically impossible to carry out the separation / recovery method based on this principle. It becomes. When the temperature T of the iron scrap melt is 1873 K or higher, the energy input to carry out the separation / recovery method based on the present principle becomes excessive, and the benefits of carrying out this method are substantially lost.

As the C concentration _Nc is higher, Ag is less likely to move to the molten Fe—C phase, and coexisting elements are more likely to move to the molten Ag phase. Therefore, C is preferably saturated in the molten Fe—C phase. Further, when the C concentration _Nc is high, even if oxygen supplied from the recovery region to the molten Ag phase reaches the separation region due to diffusion or the like, it is contained in the molten Fe-C phase that contacts the molten Ag phase. It is quickly removed from the system by C. For this reason, maintaining the isolation region in a non-oxidizing atmosphere is realized stably and easily. The C concentration _Nc at which the benefit of containing carbon becomes clear varies depending on the composition of the iron scrap melt.

  The method for supplying C to the iron scrap melt is not particularly limited. As shown in FIG. 1, a carbon source such as coal may be melted in the state of coexisting with iron scrap. As shown in FIG. 2, if the crucible for melting iron scrap is a graphite crucible, carbon is supplied from the graphite crucible and the atmosphere in the vicinity of the iron scrap melt can be easily changed to a non-oxidizing atmosphere. Therefore, it is preferable.

  As described above, the advantage of including C in the iron scrap melt has been described, but also when Fe and the element having a thermodynamic affinity, such as B or Si, are contained in the iron scrap melt as in C, The same effect as in the case of C can be obtained. If this is demonstrated from another viewpoint, when B and Si are contained in iron scrap as coexisting elements, it is difficult to separate and collect these elements according to the present principle.

5. Medium Phase Material In the present invention, a molten Ag phase is used as a moving medium phase for coexisting elements contained in iron scrap. The molten Ag phase is a medium phase interposed between the iron scrap melt and the oxygen-containing gas phase, and itself does not react with oxygen. By interposing the molten Ag phase in this way, the molten iron in the iron scrap melt is suppressed from directly causing an oxidation reaction. In addition, coexisting elements such as Cu that have moved from the iron scrap melt to the recovery zone through the molten Ag phase, which is the medium, are oxidized in the oxidizing atmosphere of the recovery zone and can be recovered as insoluble in the molten Ag phase. It becomes. For this reason, the molten Ag phase can be used continuously.

  In addition, other noble metals other than Ag can be used as the medium phase in principle, but noble metals other than Ag (Au, Pt, etc.) are extremely expensive, so they can coexist even though they can be used continuously. It is impractical to use them as media phase materials to move elements. Further, since Cu is often an element to be collected, it is preferable not to use it as a medium phase material.

  Although it is possible to use Pb only from the viewpoint of distributing and separating coexisting elements contained in iron scrap in the separation region, the medium itself is volatilized or oxidized by oxidation refining in the recovery region. Moreover, Pb is a metal with a large environmental load. For these reasons, Pb cannot be used.

6). About the case where the separation area and the collection area are integrated In the above description, the case where the separation area and the collection area are separated by a partition has been described in order to facilitate the understanding of this principle. Not required.

  The entire atmosphere may be an oxidizing atmosphere, and the molten iron scrap and the molten Ag may be brought into contact with each other. In this case, Fe and an element that is more easily oxidized than Fe are removed from the iron scrap melt as oxidation proceeds on the surface of the iron scrap melt. In addition, an element that is less likely to be oxidized than Fe and more likely to be oxidized than Ag is oxidized on the surface of the molten Ag, and is consequently removed from the molten iron scrap.

  In such a configuration, when the iron scrap melt contains C and is in the form of a molten Fe-C phase, the element that has been oxidized on the surface of the iron scrap melt when C is not contained Among them, an element that is less oxidized than C in the atmosphere can move from the molten iron scrap to the molten Ag, and as a result, is oxidized on the surface of the molten Ag. Of course, it is as described above that the separation / recovery method according to the present invention is more efficiently carried out, and furthermore, the oxidation of the molten iron in the iron scrap melt is suppressed by the contained C. It is realized to recover the Fe—C phase having a reduced amount in a higher yield.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.
An example in which Cu contained as a coexisting element in Fe is oxidized and removed using Ag as a medium will be described.

As shown in FIG. 2, a cut-out alumina tube (outer diameter 17 mm, inner diameter 12 mm, height 55 mm) is placed in an alumina crucible (outer diameter 30 mm, inner diameter 24 mm, height 50 mm). About 30 g of Ag and Cu were prepared so that the Cu concentration was 1.8% by mass, and Ar (purity 99.99%) was supplied at 100 cm ³ / min (standard condition conversion) from the gas spray tube. Pre-melting was performed for 1 hour in an atmosphere, and the alumina crucible and the alumina tube were filled with an Ag—Cu alloy and cooled.

The reason why Cu was previously contained in the medium Ag is as follows.
When a molten phase composed only of Ag is brought into contact with a molten Fe phase containing Cu, the following two phenomena occur.

(1) Due to the distribution, Cu moves from the molten Fe phase to the molten Ag phase, and the Cu concentration in the molten Fe phase decreases (separation by distribution).
(2) When oxygen is blown to the molten Ag phase, the Cu concentration in the molten Fe phase further decreases (recovery by oxidation).
As described above, the Cu concentration in the molten Fe phase decreases due to both the separation and recovery phenomena, and thus both phenomena cannot be evaluated independently.

  On the other hand, when the molten Ag phase containing Cu is brought into contact with the molten Fe phase containing Cu at a concentration determined in advance by the distribution of the molten Fe phase and the molten Ag phase, ) Does not occur. For this reason, only the recovery phenomenon shown in (2) occurs, and the principle of the present invention can be confirmed more clearly.

  After the alumina crucible and the alumina tube are filled with the Ag—Cu alloy as described above, 4 g of a pre-dissolved Fe-4 mass% Cu—C (saturated) alloy is placed on the Ag—Cu alloy in the alumina tube. The periphery of the Fe-Cu-C alloy was covered with a graphite tube and a graphite lid.

The graphite tube and the graphite lid hold the periphery of the Fe—Cu—C alloy in a reducing atmosphere and play a role of supplying carbon into Fe.
In this state, the temperature was set to 1523 K and Ar was maintained in an atmosphere supplied from the gas spray tube at 100 cm ³ / min (converted to the standard state) for 1 hour, and then the supply from the gas spray tube was O ₂ (purity 99 0.5%) was switched to 100 cm ³ / min (converted to the standard state), and held for 3 or 7 hours for air cooling.

  Analysis of the Cu, Ag and C concentrations in the solid Fe phase of the sample obtained by air cooling to room temperature and the Cu concentration in the solid Ag phase were performed. Table 2 shows the results.

  Cu in Fe decreases from the initial concentration to a value close to the Cu concentration (0.26% by mass) obtained by thermodynamic equilibrium calculation, and from the Fe phase by using the separation / recovery method according to the present invention. It was confirmed that Cu could be selectively oxidized and removed to a concentration predicted by thermodynamic equilibrium calculation.

When a part of the surface on the recovery region side in the solid Ag phase after the test was measured by X-ray diffraction (XRD), a peak of Cu ₂ O was observed as shown in FIG. 3, and Cu was oxidized and removed. It was confirmed that

Claims (7)

A method for separating and recovering elements that coexist in iron scrap,
Melting iron scrap,
By bringing the obtained iron scrap melt into contact with molten Ag, the elements coexisting in the iron scrap are transferred to molten Ag,
A separation / recovery method characterized by oxidizing and removing elements transferred to molten Ag from molten Ag.   The separation / recovery method according to claim 1, wherein the melting of the iron scrap and the contact between the iron scrap melt and the molten Ag are performed in a non-oxidizing atmosphere. The separation / recovery method according to claim 1 or 2, wherein the melt of iron scrap contains C and the concentration N _c (unit: mass%) satisfies the following formula (1):
N _C ≦ 10 ^{12.728 / T + 0.7271 × log T−3.049} (1)
Here, T is the temperature of the iron scrap melt, and satisfies 1426K <T <1873K.   The separation / recovery method according to claim 3, wherein the iron scrap is melted together with a carbon source to obtain a melt of the iron scrap containing C.   The separation / recovery method according to claim 4, wherein the iron scrap is melted and the iron scrap melt and the molten Ag are contacted in a graphite crucible, and C is saturated and dissolved in the iron scrap melt.   The separation / recovery method according to claim 1, wherein the element to be separated / recovered includes a trump element.   The separation / recovery method according to claim 1, wherein the element to be separated / recovered includes one or more elements selected from the group consisting of W, Mo, Co, V and Nb.

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