WO2010098381A1 - Re-tm系混合物からの希土類元素の回収方法 - Google Patents
Re-tm系混合物からの希土類元素の回収方法 Download PDFInfo
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- WO2010098381A1 WO2010098381A1 PCT/JP2010/052947 JP2010052947W WO2010098381A1 WO 2010098381 A1 WO2010098381 A1 WO 2010098381A1 JP 2010052947 W JP2010052947 W JP 2010052947W WO 2010098381 A1 WO2010098381 A1 WO 2010098381A1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
- C22B7/001—Dry processes
- C22B7/002—Dry processes by treating with halogens, sulfur or compounds thereof; by carburising, by treating with hydrogen (hydriding)
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B59/00—Obtaining rare earth metals
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
- C22B7/001—Dry processes
- C22B7/003—Dry processes only remelting, e.g. of chips, borings, turnings; apparatus used therefor
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
- C22B9/02—Refining by liquating, filtering, centrifuging, distilling, or supersonic wave action including acoustic waves
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
- C22B9/05—Refining by treating with gases, e.g. gas flushing also refining by means of a material generating gas in situ
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Definitions
- the present invention heats and melts a compound and / or mixture containing a rare earth element and a transition metal such as sludge generated during processing and forming of an Nd—Fe—B magnet in a graphite crucible in an inert gas atmosphere.
- the present invention relates to a method of phase-separating into an oxide containing a rare earth element as a main component and an Fe alloy containing Fe and other transition metals, and recovering these separately.
- the RE-TM mixture means a compound and / or mixture containing a rare earth element and a transition metal containing Fe.
- RE means one or more elements selected from rare earth elements such as Nd, Dy, Pr, Tb, Sm, and Ce
- TM means Fe containing a transition metal such as Co. Means.
- Rare earth elements refer to a total of 17 elements including La to Lu, lanthanides, Sc and Y.
- transition metal means an element other than the rare earth elements described above among elements existing between Group 3 elements and Group 11 elements in the periodic table.
- the rare metal means a metal element other than Fe or Al, and specific examples include rare earth elements, Co, W, and the like. Processing / cutting waste generated in the manufacturing process of parts containing metal elements is called “sludge”. In particular, sludge generated during processing and forming of an Nd—Fe—B magnet is referred to as “Nd—Fe—B sludge”.
- rare metals used in important parts have increased dramatically in many industries.
- Parts and materials containing such rare metal components include Nd—Fe—B magnets used in motors for hard disk drives, hybrid cars, MRI, and acoustic equipment, and other magnets include Sm—Fe—N magnets.
- Examples of the hydrogen storage alloy include La, Ce, Nd, Ni, Co, Al, Mn and the like.
- the sludge generated during the processing / forming process includes not only Nd but also rare earth elements such as Dy, Pr, and Tb, and Fe as well as Co. Many other transition metal elements are contained. If the rare metal component can be separated and recovered from the Nd—Fe—B-based sludge at a high yield, high selectivity, and low cost, it can greatly contribute to the stable supply of the rare metal. For this reason, establishment of this separation / recovery technique is strongly desired.
- Nd—Fe—B sludge As an example.
- rare earth elements such as Nd, Dy, and Pr are oxides.
- Nd—Fe—B-based sludge is immersed in an acid aqueous solution, Fe dissolves in the acid but the rare earth element does not dissolve in the acid, so that Fe is separated into a liquid phase and rare earth is separated into a solid phase. If solid-liquid separation is performed by means such as filtration, the rare earth element compound that is a solid phase can be recovered.
- the wet method is actually a method having the following problems. It takes a lot of time to dissolve only Fe from a structure in which rare earth elements and elements other than rare earth elements (Fe and other transition metals) are finely mixed. Also, a large amount of acid is required to dissolve Fe. Furthermore, in order to dispose of the acidic solution, considerable processing is required, whether it is discarded or a component such as Fe is recovered.
- Patent Document 1 discloses a method of separating rare earth elements by separating them into alloys composed of elements other than these.
- this method has a problem from an economic point of view because it uses materials that have already been recycled in other processes, such as solid scrap, and very valuable materials, such as rare earth elements themselves.
- the present invention is a member containing a rare metal component of which Nd—Fe—B based sludge is shown as a typical example, particularly a rare earth element and a transition metal from a RE-TM mixture.
- An object of the present invention is to provide a method for efficiently and efficiently recovering a highly pure recycled material.
- the present inventor has investigated in detail the influence of the oxygen partial pressure of the atmosphere surrounding the RE-TM mixture on the phase present when the RE-TM mixture is heated. As a result, it was found that the rare earth element and the Fe alloy containing Fe or other transition metal can be phase-separated into two phases in the solid state (FIG. 1).
- the atmosphere surrounding the RE-TM mixture is controlled to an oxygen partial pressure that does not oxidize Fe or other transition metals.
- the RE-TM mixture is separated into a phase composed of an oxide containing a rare earth element as a main component and Fe including other transition metals is separated into a phase composed of Fe metal or an alloy.
- the carbon constituting the graphite crucible reacts quickly with oxygen so as to form a predetermined equilibrium state.
- the carbon constituting the graphite crucible is oxidized to form carbon monoxide even if the oxygen partial pressure of the gas introduced into the crucible is not strictly controlled.
- the oxygen partial pressure in the atmosphere in the graphite crucible is autonomously controlled.
- the rare earth in the RE-TM mixture is oxidized, and the transition metal such as Fe maintains its metallic state.
- the RE-TM mixture is phase-separated into an oxide containing a rare earth element as a main component and an Fe alloy containing Fe or another transition metal. Therefore, it is possible to individually collect the RE-TM mixture by heating and holding it in the graphite crucible.
- thermodynamic equilibrium reaction between carbon and oxygen is expressed by equation (3).
- ⁇ G o the standard free energy change (J) and T is the temperature (K).
- Patent Documents 1 to 5 specifically, Non-Patent Document 1 Fig. 5, Eq. [15], Non-Patent Document 2 Fig. 9, Eq. (15), Non-Patent Document 3 Fig. 2, Eq. (2), Non-Patent Document 4 Fig. 3, Eq. (8), and Non-Patent Document 5 Fig. 9, Eq. (14))
- the partial pressure is high, both rare earth elements and transition metal elements are present as oxides.
- the atmospheric oxygen partial pressure is low, both exist without being oxidized.
- the oxygen partial pressure of the atmosphere is between these, the rare earth element is oxidized, but the transition metal element is not oxidized.
- the oxygen partial pressure in the equilibrium state in the graphite crucible corresponds to the oxygen partial pressure that brings about the state in which this rare earth element is oxidized but the transition metal element is not oxidized. Therefore, the RE-TM mixture heated in the graphite crucible is stable in a state where the rare earth element becomes an oxide and the transition metal element becomes a metal or alloy. Therefore, they are phase-separated in the graphite crucible.
- FIG. 1 shows an equilibrium curve in the case where five kinds of rare earth elements coexist with Fe.
- the case where other rare earth elements and other transition metal elements other than Fe coexist with Fe is also generally shown. Similar to the equilibrium curve shown in FIG. 1, the oxygen partial pressure in the equilibrium state in the graphite crucible results in the rare earth element being oxidized but the transition metal element not being oxidized. Therefore, even when other rare earth elements and other transition metal elements other than Fe coexist with Fe, phase separation occurs in the graphite crucible.
- the present invention is based on a phenomenon in which the RE-TM mixture is autonomously phase-separated in the graphite crucible, and is based on the phenomenon that the phase-separated rare earth element as a main component and Fe metal or other transition metal Fe.
- An alloy is preferably melted and separated at 1623 to 1973K to provide a method for recovering each phase.
- the present invention is as follows. (1) A method for recovering a rare earth element and a transition metal, wherein a RE-TM mixture, which is a compound and / or mixture containing a rare earth element and a transition metal containing Fe, is charged into a graphite crucible. And heating the graphite crucible containing the RE-TM mixture to separate the RE-TM mixture into an oxide phase mainly composed of a rare earth element and a metal phase containing a transition metal. A separation step of melting the RE-TM-based mixture, and a recovery of separating the RE-TM-based mixture into an oxide containing a rare earth element as a main component and a metal or alloy containing a transition metal. A method comprising steps.
- the carbon-containing material is charged into the graphite crucible so that the amount of carbon contained in the carbon-containing material and the amount of Fe charged in the graphite crucible satisfy the following formula (iii):
- the rare earth element in the RE-TM mixture is converted into an oxide by a simple and economical method of heating the RE-TM mixture in a graphite crucible in an inert gas atmosphere.
- a metal or alloy containing a transition metal such as Fe it can be separated and recovered with high purity.
- FIG. 1 It is a graph which shows the oxygen partial pressure which Fe and an oxide isolate
- FIG. 2 It is a figure which shows the cross-sectional observation result after cooling of the sample which concerns on Example 2.
- FIG. It is a figure which shows the external appearance observation result after cooling of the sample which concerns on Example 3.
- FIG. It is a figure which shows the external appearance observation result after cooling of each sample which concerns on Example 4.
- the RE-TM-based mixture is charged into a graphite crucible, and the graphite crucible is heated to separate it into an oxide phase containing a rare earth element as a main component and a metal phase containing a transition metal.
- the RE-TM mixture is melted.
- the order of phase separation and melting does not matter.
- the oxide is separated into an oxide containing a rare earth element as a main component and Fe containing metal Fe or another transition metal.
- the method according to the present invention includes a charging step of charging a RE-TM mixture, which is a compound and / or mixture containing a rare earth element and a transition metal containing Fe, into a graphite crucible,
- the graphite crucible charged with the mixture is heated to separate the RE-TM mixture into an oxide phase mainly composed of rare earth elements and a metal phase containing a transition metal, and the RE-TM system.
- the atmosphere in the graphite crucible is autonomously controlled, essentially no external operation for controlling the atmosphere is required.
- a gas having an oxygen content concentration of 1 ppm or more and 1% or less and the balance of an inert gas such as Ar or N 2 is introduced into the graphite crucible, and the graphite is formed in the atmosphere. It is desirable to carry out separation / recovery treatment by heating the RE-TM mixture together with the crucible.
- the oxygen partial pressure in the atmosphere is preferably 1 ppm or more.
- the method for supplying the inert gas is not particularly limited. What is necessary is just to adjust with an appropriate method so that oxygen concentration may become said range.
- industrially used inert gas contains about 1 to 10 ppm of oxygen as an impurity. Therefore, if a generally available inert gas is obtained and it is confirmed that the oxygen concentration contained therein is within the above range, the present invention can be carried out by supplying the inert gas as it is. it can.
- the carbon from the graphite crucible penetrates into Fe, so the melting point of Fe, which is 1811K, decreases. For this reason, the melt separation temperature is lowered, which is advantageous in terms of energy cost.
- the melting temperature of the rare earth oxide is about 1623K, which is the lower limit temperature of the separation.
- the melting temperature is preferably set to 1973K or less from the viewpoint of energy cost.
- the shape of the RE-TM mixture charged in the graphite crucible is not particularly limited.
- the present invention uses a phenomenon in which the oxygen partial pressure in the atmosphere in the graphite crucible is autonomously controlled so as to approach a specific equilibrium state, and the difference in stable state between the rare earth element and the transition metal element at the oxygen partial pressure is calculated. Since the phase separation per unit mass of the input RE-TM system mixture is larger, the interaction between the rare earth element and the fiber metal element and oxygen is more likely to occur. Separation phenomenon tends to occur. That is, from the viewpoint of the likelihood of phase separation, the smaller the diameter of the RE-TM mixture, the more advantageous. Therefore, when the RE-TM mixture is in the form of a lump, it is preferably processed after being pulverized into a powder.
- the average particle size of the RE-TM mixture to be added is preferably 5 to 100 ⁇ m, more preferably 5 to 50 ⁇ m, and particularly preferably 10 to 20 ⁇ m.
- the mixing amount of the carbon-containing substance is excessively large, there is a concern that carbon is mixed into the oxide containing a rare earth element as a main component. If this carbon does not affect the quality of the reused application, there is no problem, but if the mixed carbon may affect the quality of the product, the amount of carbon-containing material mixed according to the application Is preferably controlled.
- the amount of carbon contained in the carbon-containing material to be mixed (hereinafter abbreviated as “added carbon amount”) is the upper limit of the amount of carbon dissolved in Fe in the Nd—Fe—B-based sludge, that is, saturated carbon. It is desirable not to exceed the amount. From the above, it is desirable that the amount of added carbon Wc g be in the range given by the equation (1).
- W Fe (g) the amount of Fe charged in the graphite crucible
- T (K) the temperature in the graphite crucible in the separation step, which fluctuates in the range of more than 1623 K and less than 1973 K
- M Fe (g) Atomic weight of Fe 55.85
- M C (g) Atomic weight of C 12
- N C Saturated solubility in terms of mole fraction of carbon in Fe in Fe-C system
- N Fe 1-N C.
- the addition amount of carbon formula (1), (2) be in the above range given, it is further desirable to further the range of 0.017 W Fe ⁇ W C ⁇ 0.048 W Fe.
- the reason is as follows. When the amount of added carbon is small, the effect of shortening the time is small, so the meaning of adding becomes small. On the other hand, if the amount of added carbon is large, there is a possibility that a partial adverse effect may occur due to uneven carbon addition.
- the sludge itself contains components considered as a carbon-containing substance such as an organic agent used when storing the sludge, it is not necessary to consider it as a carbon-containing substance because it can be removed by washing with water.
- the rare earth oxide recovered by the method according to the present invention can be reused as a raw material for Ca reduction and molten salt electrolysis, and a transition metal or alloy can be recycled as a raw material for Fe, for example.
- Nd—Fe—B based sludge sample The samples used in the examples are all Nd—Fe—B sludge generated in the machining and cutting processes. Its composition is, by mass, Nd: 19.91%, Pr: 5.65%, Dy: 4.41%, Tb: 0.01%, Fe: 53.87%, B: 0.77%, Co: 0.08%, C: 1.36%, Al: 0.19%, and the remaining impurities.
- This Nd—Fe—B-based sludge was washed with ultrapure water, dried in air and sufficiently removed, and then pulverized to an average particle size of 10 to 20 ⁇ m and used in the experiment. .
- the pretreated Nd—Fe—B based sludge is referred to as “Nd—Fe—B based sludge sample”.
- Example 1 An Nd—Fe—B-based sludge sample (21.2 g) was placed in a graphite crucible, and industrial electric Ar (purity 99.99 vol%, oxygen concentration 10 ppm) was charged at 50 mL / min. (Standard state conversion), heated to 1823 K at 300 K / h, and held for 3 hours. Thereafter, the sample was taken out of the furnace and cooled by blowing Ar gas.
- industrial electric Ar purity 99.99 vol%, oxygen concentration 10 ppm
- FIG. 2 shows a cross-sectional photograph of the sample after cooling. It can be confirmed that two phases of a metal phase and an oxide phase exist.
- Table 1 shows the composition of the recovered metal phase (indicated by “alloy Fe” in the table) and oxide phase (indicated by “rare earth oxide” in the table).
- the metal phase is a phase mainly composed of Fe
- the oxide phase is a phase mainly composed of rare earth elements Nd, Dy, and Pr.
- the numerical values in Table 1 mean the content of each element (unit: mass%) when the mass of each phase is 100%.
- the concentration of transition metal element (Fe + Co) is 99.8%
- the concentration of rare earth element (Nd + Dy + Pr) is 96.8%, which is a very high value.
- Tables 2 and 3 are obtained by transcribing Tables 1 and 2 of Patent Document 1, which is a conventional technology, and are approximately the same amount as the pure content of rare earth elements in the sludge (0.75 by weight or 1 in weight ratio). The results obtained by adding the expensive Nd metal scrap of .1) are shown in these tables.
- the concentration of the transition metal element (Fe + Co) in the alloy is 99.7 or 99.8%, and the rare earth element in the recovered slag ( The concentration of (Nd + Dy + Pr) was 88.9 or 95.9%.
- rare earth elements (Nd, Dy, Pr) and transition metals (Fe, Co) were recovered with the same or higher purity.
- the present method does not use expensive Nd metal scrap, and can be carried out at an economically inexpensive cost using an inert gas and a graphite crucible. It turns out that it is the method of collect
- Example 2 A Pt crucible filled with 0.15 g of a Nd—Fe—B-based sludge sample was introduced into an electric furnace held at 1823 K, and held in air for 1 hour. Thereafter, the sample was taken out of the furnace and cooled by blowing Ar gas.
- FIG. 3 shows a cross-sectional photograph of the sample after cooling.
- a uniform oxide phase was confirmed without being separated into two phases of a metal phase and an oxide phase.
- Example 3 A graphite crucible filled with 1 g of an Nd—Fe—B-based sludge sample was introduced into an electric furnace held at 1823 K, and held in air for 1 hour. Thereafter, the sample was taken out of the furnace and cooled by blowing Ar gas.
- FIG. 4 shows the appearance of the sample taken out from the crucible after cooling. It was confirmed that the metal phase and the oxide phase were separated into two phases. That is, it can be seen that the oxygen partial pressure is controlled in the graphite crucible by the reaction between graphite and oxygen even in an air atmosphere.
- Example 4 Using an electric furnace maintained at 1823 K, industrial Ar, purity 99.99 vol%, oxygen concentration 10 ppm, 50 mL / min (St.T.p. (Standard Temperature and Pressure)) were introduced, and the following conditions Each of the Nd—Fe—B sludge samples was heat-treated in the graphite crucible under the following conditions (1) to (4).
- FIG. 5 shows the appearance of the sample obtained under the conditions (1) to (4) taken out from the crucible after cooling.
- the sample obtained under the condition (2) is separated into two phases of a metal phase and an oxide phase.
- the sample obtained under the condition (1) resulted in insufficient melting and complete separation.
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Abstract
Description
本発明において、「遷移金属」とは、周期表で第3族元素から第11族元素の間に存在する元素のうち、上記の希土類元素以外の元素を意味する。
金属元素を含有する部品の製造工程において発生した加工・切削屑を「スラッジ」という。特に、Nd-Fe-B系磁石の加工・成形過程で発生するスラッジを「Nd-Fe-B系スラッジ」という。
そのようなレアメタル成分を含有する部品や材料として、ハードディスクドライブ、ハイブリッド自動車等のモーター、MRI、音響機器などに用いられているNd-Fe-B系磁石、そのほか磁石としてはSm-Fe-N系磁石、La-Co系磁石、磁石以外には、Tb,Dy,Fe,Co等を含有する光磁気ディスク、Y,Fe,Co等を含有するYAGレーザー、La,Ce,Nd,Fe等を含有する発火石、およびLa,Ce,Nd,Ni,Co,Al,Mn等を含有する水素吸蔵合金が例示される。
炭素と酸素の熱力学的平衡反応は式(3)により表現される。
2C + O2 = 2CO
ΔGo = -223532 - 175.4T (3)
ここで、ΔGoは標準の自由エネルギー変化(J)であり、Tは温度(K)である。
ΔGo = -RTln{PCO 2/(aC 2・PO2)} (4)
ここで、Rは気体定数、PCOはCOの分圧、aCは炭素の活量、およびPO2は酸素の分圧である。
PO2 = P・(1 - α) / (1 + α) (5)
PCO = P・2α / (1 + α) (6)
で与えられる。全圧Pを1atmとし、温度ごとに式(3)、(5)、(6)を式(4)に代入してαの値を求め、このαを(5)式に代入して算出したPO2を図1上に示した。図1に示されるように、黒鉛坩堝内の酸素分圧は、平衡状態において10-15~10-18atm程度になるように自律的に制御される。
(1)希土類元素および遷移金属の回収方法であって、希土類元素とFeを含む遷移金属とを含有する化合物および/または混合物であるRE-TM系混合物を黒鉛坩堝内に装入する装入ステップ、当該RE-TM系混合物が内部に装入された黒鉛坩堝を加熱して、希土類元素を主成分とする酸化物相と遷移金属を含む金属相とに前記RE-TM系混合物を分離させるとともに、前記RE-TM系混合物を溶融させる分離ステップ、および前記RE-TM系混合物を、希土類元素を主成分とする酸化物と遷移金属を含む金属または合金とに分離して、それぞれを回収する回収ステップを備える方法。
(4)分離ステップにおいて、前記RE-TM系混合物を炭素含有物質とともに溶融させることを特徴とする上記(1)記載の回収方法。
0 < WC ≦ WFe × MC × NC / ( MC × NC+ MFe × NFe ) (i)
NC ≦ 1012.728 / T + 0.7271 × log T - 3.049 (ii)
ここで、WFe(g):黒鉛坩堝に装入されたFe量、T (K):分離ステップにおける黒鉛坩堝内温度であって、1623K超1973K未満の範囲で変動する、MFe(g):Feの原子量55.85、MC (g):Cの原子量12、NC:Fe-C系におけるFe中炭素のモル分率換算の飽和溶解度、およびNFe= 1 - NCである。
本発明においては、RE-TM系混合物を、黒鉛坩堝内に装入し、この黒鉛坩堝を加熱して、希土類元素を主成分とする酸化物相と遷移金属を含む金属相とに分離させるとともに、RE-TM系混合物を溶融させる。ここで、相分離、溶融の順序は問わない。こうして相分離・溶融を行うことによって、希土類元素を主成分とする酸化物と、金属Feあるいは他の遷移金属を含有するFeの合金に分離する。
NC ≦ 1012.728 / T + 0.7271 × log T - 3.049 (2)
ここで、WFe(g):黒鉛坩堝に装入されたFe量、T (K):分離ステップにおける黒鉛坩堝内温度であって、1623K超1973K未満の範囲で変動する、MFe(g):Feの原子量55.85、MC (g):Cの原子量12、NC:Fe-C系におけるFe中炭素のモル分率換算の飽和溶解度、およびNFe= 1 - NCである。
実施例で使用している試料はいずれも加工、切削工程で発生したNd-Fe-B系スラッジである。その組成は、質量%で、Nd:19.91%、Pr:5.65%、Dy:4.41%、Tb:0.01%、Fe:53.87%、B:0.77%、Co:0.08%、C:1.36%、Al:0.19%、および残部不純物である。このNd-Fe-B系スラッジは、超純水で洗浄した後、空気中で乾燥し水分を十分に除去した後、平均粒径は10~20μmになるように粉砕して、実験に用いた。以下、この前処理が施されたNd-Fe-B系スラッジを「Nd-Fe-B系スラッジ試料」という。
Nd-Fe-B系スラッジ試料21.2gを黒鉛坩堝に装入し、電気炉を用いて、工業用Ar(純度99.99体積%、酸素濃度10ppm)を50mL/min.(標準状態換算)で導入し、300K/hで1823Kまで加熱し、3時間保持した。その後、試料を炉から取り出し、Arガスを吹き付けて冷却した。
2CO + O2= 2CO2
ΔGo= -568000+ 175.48T (7)
測定されたCO分圧およびCO2分圧を式(7)に適用した結果、平衡の酸素分圧として1823Kで5×10-11atmが算出された。この値は、式(3)による平衡により決定される酸素分圧と同程度、すなわち、図1でNd、Pr、Dyが酸化し、Feが酸化しない酸素分圧の範囲内にある。
表1に回収された金属相(表中「合金Fe」で示されている。)、酸化物相(表中「希土類酸化物」で示されている。)の組成を示す。金属相はFeを主成分とする相、酸化物相は希土類元素Nd、Dy、Prを主成分とする相である。表1における数値は、各相の質量を100%としたときの各元素の含有量(単位:質量%)を意味する。
一方、表2および3は、従来技術である特許文献1の表1および2を転記したものであり、スラッジにスラッジ中の希土類元素の純分とほぼ同量(重量比で0.75または1.1)の高価なNd金属屑を添加して回収を行った結果がこれらの表に示されている。表2および3に示されるように、特許文献1に開示される技術によれば、合金中の遷移金属元素(Fe+Co)の濃度は99.7または99.8%、回収スラグ中の希土類元素(Nd+Dy+Pr)の濃度は88.9または95.9%であった。この結果と比較して、本発明に係る回収方法では、同等かそれ以上の純度で希土類元素(Nd、Dy、Pr)、遷移金属(Fe、Co)が回収された。
1823Kに保持した電気炉に、Nd-Fe-B系スラッジ試料0.15gを充填したPt坩堝を導入し、空気中で1時間保持した。その後、試料を炉から取り出し、Arガスを吹き付けて冷却した。
金属相と酸化物相の2相には分離せず均一な酸化物相が確認された。
(実施例3)
1823Kに保持した電気炉に、Nd-Fe-B系スラッジ試料1gを充填した黒鉛坩堝を導入し、空気中で1時間保持した。その後、試料を炉から取り出し、Arガスを吹き付けて冷却した。
金属相と酸化物相の2相に分離しているのが確認された。つまり、空気雰囲気中でも黒鉛坩堝内は黒鉛と酸素の反応により酸素分圧が制御されていることがわかる。
1823Kに保持した電気炉を用いて、工業用Ar、純度99.99vol%、酸素濃度10ppm、50mL/min (s.t.p.(Standard Temperature and Pressure))を導入し、以下のような条件でそれぞれNd-Fe-B系スラッジ試料を黒鉛坩堝中で以下の(1)~(4)の条件で熱処理した。
(2)Nd-Fe-B系スラッジ試料1gに黒鉛粉末0.02gを添加、保持時間2分間、
(3)Nd-Fe-B系スラッジ試料1g、保持時間10分間、
(4)Nd-Fe-B系スラッジ試料1gに黒鉛粉末0.02gを添加、保持時間10分間、
保持後、試料を炉から取り出し、Arガスを吹き付けて冷却した。
条件(2)により得られた試料は、金属相と酸化物相の2相に分離している。これに対し、条件(1)により得られた試料は、溶融が不十分で分離が完全には生じていない結果となった。
Claims (6)
- 希土類元素および遷移金属の回収方法であって、
希土類元素とFeを含む遷移金属とを含有する化合物および/または混合物であるRE-TM系混合物を黒鉛坩堝内に装入する装入ステップ、
当該RE-TM系混合物が内部に装入された黒鉛坩堝を加熱して、希土類元素を主成分とする酸化物相と遷移金属を含む金属相とに前記RE-TM系混合物を分離させるとともに、前記RE-TM系混合物を溶融させる分離ステップ、および
前記RE-TM系混合物を、希土類元素を主成分とする酸化物と遷移金属を含む金属または合金とに分離して、それぞれを回収する回収ステップ
を備える方法。 - 溶融ステップにおいて、前記RE-TM系混合物を溶融させるときに黒鉛坩堝に1ppm~1%の酸素を含む不活性ガスからなるガスを導入する請求項1記載の回収方法。
- 装入ステップにおいて黒鉛坩堝に装入される前記RE-TM系混合物の平均粒径が10~20μmである、請求項1記載の回収方法。
- 分離ステップにおいて、前記RE-TM系混合物を炭素含有物質とともに溶融させることを特徴とする請求項1記載の回収方法。
- 装入ステップにおいて黒鉛坩堝に装入される前記炭素含有物質における炭素含有量Wc(単位:g)の範囲は式(i)および(ii)で与えられる請求項4記載の回収方法:
0 < WC ≦ WFe × MC × NC / ( MC × NC+ MFe × NFe ) (i)
NC ≦ 1012.728 / T + 0.7271 × log T - 3.049 (ii)
ここで、WFe(g):黒鉛坩堝に装入されたFeの量、T (K):分離ステップにおける黒鉛坩堝内温度であって、1623K超1973K未満の範囲で変動する、MFe(g):Feの原子量55.85、MC (g):Cの原子量12、NC:Fe-C系におけるFe中炭素のモル分率換算の飽和溶解度、およびNFe= 1 - NCである。 - 装入ステップにおいて、前記炭素含有物質に含有される炭素量および黒鉛坩堝に装入されたFe量が下記式(iii)を満たすように、前記炭素含有物質は黒鉛坩堝に装入される請求項5記載の回収方法。
0.017 WFe< WC < 0.048 WFe (iii)
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