JP4296372B2 - Recycling method of Nd-based rare earth magnet scrap - Google Patents
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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
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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
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
Description
【０００１】
【発明の属する技術分野】
本発明は、Ｎｄ系希土類磁石製造工程で発生するＮｄ系希土類磁石スクラップのリサイクル方法に関するものである。
【０００２】
【従来の技術及び発明が解決しようとする課題】
Ｎｄ系希土類磁石は、一般家電製品から大型コンピュータの周辺端末機や医療用機器まで幅広い分野で使用されており、先端技術の鍵を握る極めて重要な電気・電子材料の一つである。近年、コンピュータや通信機器の小型軽量化に伴いＮｄ系希土類磁石の小型化、高精密化が進み、さらに今後の使用用途の拡大によりその需要も急速に増大する可能性がある。
【０００３】
Ｎｄ系希土類磁石の製造方法は粉末冶金法で行われているが、粉末から製品とするまでには成形、焼結、加工、表面処理等の工程が必要であり、これらの工程中では成形不良、焼結不良、機械加工時の端材等のスクラップ及び研削粉等のスラッジが発生する。工程中で発生したスクラップ及びスラッジの回収方法として種々の方法が提案されている。例えば、Ｎｄ系希土類磁石スクラップを硝酸−硫酸水溶液中に溶解し、得られた溶液にアルコールを添加して希土類硫酸塩を選択的に晶析させ、希土類元素を分離回収する方法（特許第２７６５４７０号）やコバルトを含む希土類−鉄系合金のスラリーに硝酸を添加し、得られたコバルトおよび希土類を含有する溶液に蓚酸又はフッ素化合物を添加し、希土類化合物とコバルトを分離回収する方法（特開平９−２１７１３２号公報）などが提案されている。しかしこれらの方法では処理工程が複雑であり、同時に生成する水酸化鉄等の処理でコストがかかるなどの問題がある。また、スクラップを高周波溶解炉等で加熱溶解、合金として回収する方法（特開平８−３１６２４号公報）では、合金とスラグの分離が難しく、スクラップに含有されている酸素や炭素が合金中に混入すること、溶解後の合金の組成が不安定であることから、そのまま希土類磁石原料として使用できない等の問題がある。
【０００４】
これまで提案されてきたＮｄ系希土類磁石スクラップのリサイクル方法では、磁石スクラップから希土類元素のみを分離し、高純度の希土類酸化物もしくはフッ化物を回収するもので、さらにＮｄ系希土類磁石スクラップ中に含まれる有価遷移金属を分離回収するには、より複雑な処理工程を必要とすることから、効率的に希土類元素及び有価遷移金属を簡便かつ経済的に再生、再利用する方法が望まれていた。
【０００５】
本発明の目的は、Ｎｄ系希土類磁石スクラップ中に含有する希土類元素及び有価遷移金属を同時に再生することが可能であり、さらにＮｄ系希土類磁石スクラップ中の希土類酸化物又は固溶酸素を効率的に還元又は脱酸することで、高純度の希土類−遷移金属−ボロン合金を簡便かつコスト的に有利にリサイクルする方法を提供しようとするものである。
【０００６】
【課題を解決するための手段及び発明の実施の形態】
本発明者らは、かかる課題を解決するために鋭意検討を行った結果、溶融塩電解還元法に着目し、Ｎｄ系希土類磁石スクラップの再利用に溶融塩電解が有効であることを見出した。即ち、溶融塩電解還元法により希土類金属又は希土類−遷移金属合金を製造するに際し、Ｎｄ系希土類磁石スクラップを電解浴に投入し、電解浴中にて該スクラップを希土類酸化物と磁石合金に溶融分離させ、電解浴に溶解した希土類酸化物を電解により希土類金属に還元し、さらに電解浴への溶解度が小さい磁石合金を電解還元により生成し電解浴底部に溜まった希土類金属と合金化し、希土類−遷移金属−ボロン合金として再生する方法により、Ｎｄ系希土類磁石スクラップ中に含有する希土類元素及び有価遷移金属を同時に再生することが可能であり、さらにＮｄ系希土類磁石スクラップ中の希土類酸化物又は固溶酸素を効率的に還元又は脱酸することで、高純度の希土類−遷移金属−ボロン合金を簡便かつコスト的に有利にリサイクルできることを知見し、本発明をなすに至ったものである。
【０００７】
従って、本発明は、Ｎｄ系希土類磁石スクラップを原料としてリサイクルする方法において、希土類酸化物を原料としてアルカリ、アルカリ土類及び希土類の混合フッ化物と共に融解させた溶融塩電解浴に該スクラップを投入し、電解浴中にて上記スクラップを希土類酸化物と磁石合金部に溶融分離させ、電解浴に溶解した希土類酸化物は電解により希土類金属に還元し、さらに磁石合金部は電解還元により生成される希土類金属と合金化させ、希土類金属−遷移金属−ボロン合金として再生することを特徴とするＮｄ系希土類磁石スクラップのリサイクル方法を提供する。
【０００８】
以下、本発明を詳細に説明する。
本発明で使用する溶融塩電解法は公知の方法で、例えば陰極に金属電極及び陽極に黒鉛電極を用い、希土類酸化物を原料としてアルカリ、アルカリ土類及び希土類の混合フッ化物と共に融解させた電解浴を使用した溶融塩電解法である。浴温度は７００〜１２００℃で、希土類酸化物の電解還元により希土類金属が陰極表面に連続的に析出され、析出した希土類金属は液状のまま浴底部に溜まり、一定の間隔で真空吸引を利用したタッピング装置等により系外へ回収する。回収の際、溶融希土類金属の装置内での凝固、吸引管の破損、さらに吸引管からの不純物の混入を抑制するために、磁石原料として使用される鉄などの遷移金属を添加することで合金の融点を低下させ、合金の回収を安全かつ効率的にすることができる。
【０００９】
本発明では、上記の目的で添加する遷移金属に替え、Ｎｄ系希土類磁石スクラップを添加することを特徴とする。Ｎｄ系希土類磁石スクラップを投入すると、該スクラップが浴底部まで沈降する間にスクラップ表面の酸化物は電解浴中に溶け込む。また、磁石合金の粒界に存在する希土類酸化物は連続投入され、電解還元により生成し浴底部に溜まった溶融希土類金属に溶け込んだ後、酸化物の熱拡散及び電解浴への酸素の溶解、電解浴と溶融金属中との酸素の活量の差による熱力学的な拡散により溶融合金−電解浴界面近傍に移動し、電解浴中に溶け込んでいく。電解浴に溶解しイオン化した希土類元素は、電解還元により再び陰極表面に金属として析出し、回収することができる。
【００１０】
なお、上記電解浴を構成する希土類酸化物としては、Ｎｄ系希土類磁石スクラップの希土類と同じ希土類の酸化物であることが好ましい。また、希土類酸化物とフッ化物との組成比は公知のものとすることができるが、通常、希土類酸化物をフッ化物に数ｗｔ％添加してもよい。フッ化物としては、アルカリ、アルカリ土類及び希土類の混合フッ化物が挙げられるが、具体的には、希土類フッ化物の他にフッ化リチウム、フッ化バリウム、フッ化カルシウム等が挙げられる。
【００１１】
本発明に用いるＮｄ系希土類磁石スクラップは、Ｒ−Ｔ−Ｂ系合金（ＲはＰｒ，Ｎｄ，Ｔｂ及びＤｙから選択される少なくとも１種類以上の希土類元素、ＴはＦｅあるいはＦｅと少なくとも１種類以上のＦｅ以外の遷移金属で、Ｒ：２７〜３５重量％、Ｂ：０．９〜１．３重量％、Ｔ：残部）であり、その形状はスクラップの発生する工程により様々であるが、電解浴に投入する形状は粒径が０．１〜１０ｍｍであることが好ましい。投入するスクラップの粒径が上記範囲内にあると、表面積が大きくなり、電解浴との接触面積が大きくなるため、スクラップ表面の希土類酸化物が効率的に溶解する。また、浴底部の溶融金属への溶解も促進され、合金内のスクラップの溶け残りを抑えることができる。
【００１２】
また、Ｎｄ系希土類磁石スクラップとして、機械加工工程で発生する粒径が１００μｍ以下の加工スラッジも利用することができる。スラッジは粒径が非常に小さいため、電解浴に投入すると、電解浴表面で燃焼し、スラグとして浴面に浮遊する。そのため、スラッジに含有する遷移金属も酸化され、浴面に溜まるスラグ量が増加するため、連続操業ができなくなる場合が生じ、生産性が低下する。そこで、スラッジを不活性ガスで吹き込み投入する方法や、スラッジの加圧成形体もしくはスラッジを１０００〜１２００℃で焼結後、上記の粒径にまで粉砕したものを電解炉に投入する方法で、スラッジもスクラップと同様の原理により再利用することができる。
【００１３】
Ｎｄ系希土類磁石スクラップの投入量は、溶融塩電解浴温度に応じて回収する合金組成を決定し、調整して行う。前述のとおり電解浴の温度は７００〜１２００℃であり、浴底部に溜まった溶融合金の融点は電解浴の温度以下に保つ必要がある。このため、回収する合金の融点を電解浴温度より１００℃前後低めの組成になるようにスクラップの投入量を調整するのが望ましい。例えば、溶融塩電解による金属ネオジムの製造方法では、電解浴温度は１０００〜１１００℃で行われるため、回収する合金の融点を９００℃以下にすればよく、Ｎｄ−Ｆｅの状態図から回収する合金のＦｅ濃度が１〜３０重量％となるように磁石スクラップを投入するのが好ましい。Ｎｄ系希土類磁石スクラップの処理量を多くするにはＦｅ濃度のより高い方が効率的であるが、電解浴装置によって炉内温度分布が異なるため、炉にあわせて最適な投入量を決定していくことが望ましい。
【００１４】
得られる合金は、Ｒ−Ｔ−Ｂ（ＲはＰｒ，Ｎｄ，Ｔｂ及びＤｙから選択される少なくとも１種類以上の希土類元素、ＴはＦｅあるいはＦｅと少なくとも１種類以上のＦｅ以外の遷移金属）で表すことができ、それぞれＴ：１〜３０重量％、Ｂ：０．０１〜０．５重量％、Ｒ：残部であることが好ましい。Ｆｅ及びＣｏ等の遷移金属は全量、浴底部の溶融希土類金属中に溶解し、希土類−遷移金属−ボロン合金をつくり、磁石用原料として再利用できる。
【００１５】
上記の方法で回収し、得られる希土類−遷移金属−ボロン合金（Ｒ−Ｔ−Ｂ）の酸素濃度は、通常の溶融塩電解法で得られる合金の酸素濃度と同等である。投入するスクラップは一般に０．０５〜５．０重量％の酸素を含有しているため、浴底の溶融合金の酸素濃度は増加すると推測されるが、前述したように、溶融塩への希土類酸化物の溶解及び浴底に溜まった溶融金属中の酸素の電解浴への拡散等による還元あるいは脱酸反応が進行し、得られる合金の酸素濃度を低いレベルに抑制することができる。
【００１６】
得られた希土類−遷移金属−ボロン合金は、通常の磁石製造工程に戻し、再利用することができる。即ち、該回収合金を目的とするＮｄ−Ｆｅ−Ｂ合金に使用される希土類金属、遷移金属、Ｂ等磁石合金として必要な溶解原料に１〜５０ｗｔ％混合し溶解後、不活性ガス気流中で粉砕し、磁場中成形し、Ａｒ雰囲気又は真空中にて１０００〜１２００℃で焼結後、Ａｒ雰囲気中にて４００〜６００℃で熱処理することで希土類焼結磁石を製造することができる。
【００１７】
【実施例】
以下、実施例を示し、本発明を具体的に説明するが、本発明は下記の実施例に制限されるものではない。
【００１８】
［実施例１］
内径９００ｍｍφ、深さ１０００ｍｍの電解槽に、陽極として黒鉛電極、陰極としてＭｏ電極を挿入し、電解浴としてＮｄＦ3（６０ｗｔ％）−ＤｙＦ3（１５ｗｔ％）−ＬｉＦ（１５ｗｔ％）−ＢａＦ2（１０ｗｔ％）よりなる混合フッ化物浴に希土類酸化物としてＮｄ2Ｏ3（９０ｗｔ％）−Ｄｙ2Ｏ3（１０ｗｔ％）の混合酸化物を連続的に供給し、平均電圧１２．５Ｖ、平均電流８０００Ａ、平均浴温度１０８０℃の条件でＮｄ−Ｄｙ合金を製造している電解炉に、直径１０ｍｍ以下のＮｄ系希土類磁石スクラップ合計３５ｋｇを逐次投入しながら２４時間電解を行ったところ、２１１ｋｇの合金を回収した。その際、電解効率及び歩留は通常の操業とほとんど同等であった。得られた合金の組成は、表１に示す通りであり、Ｆｅ濃度９．７ｗｔ％、酸素濃度０．０２５ｗｔ％であった。Ｃｏ濃度及びＢ濃度はそれぞれ０．６１ｗｔ％及び０．１１ｗｔ％で、投入量から推測される濃度に近似し、ほぼ全量回収することができた。
【００１９】
得られたＮｄ−Ｄｙ合金をＮｄ−Ｄｙ−Ｆｅ−Ｃｏ−Ｂ−Ａｌからなる溶解原料に２５％添加、融解し、重量比（％）で２６．５Ｎｄ−１．５Ｄｙ−ＢＡＬ．Ｆｅ−１Ｃｏ−１Ｂ−０．５Ａｌの組成の母合金を作製した。得られた母合金に別途溶解した焼結助剤を適量混合し、窒素気流中のジェットミルで微粉砕して平均粒径３μｍ程度の微粉末を得た。その後、これらの微粉末を成形装置の金型に充填し，１２ｋＯｅの磁界中で配向させ、磁界に対して垂直方向に１ｔｏｎ／ｃｍ2の圧力でプレス成形した。得られた成形体を１１００℃で２時間焼結した後、冷却し、さらに５００℃で１時間、Ａｒ雰囲気中で熱処理して焼結磁石を作製した。得られた焼結磁石の磁気特性を測定したところ、Ｂｒ＝１３．０ｋＧ、ｉＨｃ＝１６．５ｋＯｅ、（ＢＨ）ｍａｘ＝４２ＭＧＯｅの特性が得られ、通常のＮｄ−Ｄｙ合金を用いた場合と同等の特性であった。
【００２０】
［実施例２］
実施例１と同一の電解槽、同一電解条件にて、平均粒径１００μｍ以下の加工スラッジを不活性ガス雰囲気下で成形し、１０００℃で２時間焼結して得られた塊状のスラッジ６３ｋｇを逐次投入しながら２４時間電解を行ったところ、２４９ｋｇの合金が得られた。電解効率及び歩留は通常の操業とほとんど同等であった。得られた合金の組成は表１に示す通りであり、Ｆｅ濃度１５．１ｗｔ％、酸素濃度０．０２１ｗｔ％であった。Ｃｏ濃度及びＢ濃度はそれぞれ０．９６ｗｔ％及び０．２２ｗｔ％で、投入量から推測される濃度に近く、ほぼ全量回収することができた。
【００２１】
このＮｄ−Ｄｙ合金をＮｄ−Ｄｙ−Ｃｏ−Ｂ−Ａｌからなる溶解原料に２５％添加、融解し、重量比（％）で２７．５Ｎｄ−１Ｄｙ−ＢＡＬ．Ｆｅ−１Ｃｏ−１Ｂ−０．１５Ａｌの組成の母合金を作製した。得られた母合金を実施例１と同様の方法で焼結磁石を作製した。得られた焼結磁石の磁気特性を測定したところ、Ｂｒ＝１３．９ｋＧ、ｉＨｃ＝１５ｋＯｅ、（ＢＨ）ｍａｘ＝４８ＭＧＯｅの特性が得られ、通常のＮｄ−Ｄｙ合金を用いた場合と同等の特性であった。
【００２２】
［実施例３］
実施例１と同一の電解槽、同一電解条件にて直径１０ｍｍ以下のＮｄ系磁石スクラップ量を３３〜６３ｋｇ／日に変化させ、逐次投入しながら２４時間電解を１０日間行った。操業中の電解効率及び歩留は通常の操業と同等であった。得られた合金の組成は表１に示す通りであり、Ｆｅ、Ｃｏ、Ｂ濃度は投入したスクラップ重量に比例し、それぞれ５〜１５ｗｔ％、０．２〜０．８ｗｔ％、０．１〜０．３ｗｔ％であった。酸素濃度はスクラップ投入量の増加に拘わらず０．０２〜０．０５ｗｔ％であった。
【００２３】
これらのＮｄ−Ｄｙ合金をＮｄ−Ｄｙ−Ｆｅ−Ｃｏ−Ｂ−Ａｌからなる溶解原料に２５ｗｔ％添加、融解し、重量比（％）で２６．５Ｎｄ−１．５Ｄｙ−ＢＡＬ．Ｆｅ−１Ｃｏ−１Ｂ−０．５Ａｌの組成の母合金を作製した。得られた母合金を実施例１と同様の方法で焼結磁石を作製した。得られた焼結磁石の磁気特性を測定したところ、Ｂｒ＝１３ｋＧ以上、ｉＨｃ＝１６ｋＯｅ以上、（ＢＨ）ｍａｘ＝４２ＭＧＯｅ以上の特性が得られ、通常のＮｄ−Ｄｙ合金を用いた場合と同等の特性であった。
【００２４】
【表１】
【発明の効果】
本発明によれば、Ｎｄ系希土類磁石スクラップに含有する全元素を同時に再生可能であり、得られた合金の酸素濃度も低減されている。また、従来の処理方法と比較しても工程は単純であり、経済的に連続して処理が可能であるため産業上、その利用価値は極めて高い。
【図面の簡単な説明】
【図１】スクラップ投入量と得られた希土類−遷移金属−ボロン合金中の酸素濃度の関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for recycling Nd-based rare earth magnet scrap generated in an Nd-based rare earth magnet manufacturing process.
[0002]
[Prior art and problems to be solved by the invention]
Nd-based rare earth magnets are used in a wide range of fields, from general home appliances to peripheral terminals of large computers and medical equipment, and are one of the most important electrical and electronic materials that hold the key to advanced technology. In recent years, Nd-based rare earth magnets have become smaller and more precise with the reduction in size and weight of computers and communication devices, and the demand for such use may increase rapidly due to future expansion of usage.
[0003]
The manufacturing method of Nd-based rare earth magnets is performed by powder metallurgy, but processes such as molding, sintering, processing, and surface treatment are necessary to make a product from powder. Sintering defects, scraps such as scraps during machining, and sludge such as grinding powder are generated. Various methods have been proposed for recovering scrap and sludge generated in the process. For example, Nd-based rare earth magnet scrap is dissolved in a nitric acid-sulfuric acid aqueous solution, alcohol is added to the resulting solution to selectively crystallize the rare earth sulfate, and the rare earth element is separated and recovered (Japanese Patent No. 2765470). ) And cobalt-containing rare earth-iron alloy slurry, nitric acid is added, and oxalic acid or a fluorine compound is added to the resulting cobalt and rare earth-containing solution, thereby separating and recovering the rare earth compound and cobalt (Japanese Patent Laid-Open No. Hei 9). -217132) and the like have been proposed. However, in these methods, the processing steps are complicated, and there is a problem that costs are increased in the treatment of iron hydroxide or the like produced at the same time. Further, in the method of melting and melting scrap in a high-frequency melting furnace or the like and recovering it as an alloy (JP-A-8-31624), it is difficult to separate the alloy and slag, and oxygen and carbon contained in the scrap are mixed in the alloy. In addition, since the composition of the alloy after melting is unstable, there is a problem that it cannot be used as a raw material for rare earth magnets as it is.
[0004]
The Nd-based rare earth magnet scrap recycling methods that have been proposed so far separate only rare earth elements from the magnet scrap and recover high-purity rare earth oxides or fluorides, and are also included in Nd-based rare earth magnet scraps. In order to separate and recover the valuable transition metal, a more complicated processing step is required. Therefore, a method for efficiently regenerating and reusing the rare earth element and the valuable transition metal simply and economically has been desired.
[0005]
An object of the present invention is to simultaneously regenerate rare earth elements and valuable transition metals contained in Nd-based rare earth magnet scraps, and to efficiently remove rare earth oxides or solid solution oxygen in Nd-based rare earth magnet scraps. An object of the present invention is to provide a method for easily and cost-effectively recycling a high-purity rare earth-transition metal-boron alloy by reduction or deoxidation.
[0006]
Means for Solving the Problem and Embodiment of the Invention
As a result of intensive studies to solve such problems, the present inventors have focused on the molten salt electroreduction method and found that molten salt electrolysis is effective for the reuse of Nd-based rare earth magnet scraps. That is, when producing a rare earth metal or a rare earth-transition metal alloy by the molten salt electrolytic reduction method, Nd-based rare earth magnet scrap is put into an electrolytic bath, and the scrap is melted and separated into a rare earth oxide and a magnet alloy in the electrolytic bath. The rare earth oxide dissolved in the electrolytic bath is reduced to rare earth metal by electrolysis, and a magnet alloy having a low solubility in the electrolytic bath is formed by electrolytic reduction and alloyed with the rare earth metal accumulated at the bottom of the electrolytic bath, thereby causing the rare earth-transition. By the method of regenerating as a metal-boron alloy, it is possible to simultaneously regenerate the rare earth element and valuable transition metal contained in the Nd-based rare earth magnet scrap. Furthermore, the rare earth oxide or solid solution oxygen in the Nd-based rare earth magnet scrap Recycling of high-purity rare earth-transition metal-boron alloys conveniently and cost-effectively by efficiently reducing or deoxidizing It was found that, in which the present invention has been accomplished.
[0007]
Accordingly, the present invention provides a method of recycling the Nd-based rare earth magnet scrap as a raw material, a rare earth oxide as a raw material alkali, alkaline earth and the scrap in a molten salt electrolytic bath melted with mixing fluoride of the rare earth In the electrolytic bath, the scrap is melted and separated into a rare earth oxide and a magnet alloy part. The rare earth oxide dissolved in the electrolytic bath is reduced to a rare earth metal by electrolysis, and the magnet alloy part is generated by electrolytic reduction. The present invention provides a method for recycling Nd-based rare earth magnet scraps that is alloyed with a rare earth metal and recycled as a rare earth metal-transition metal-boron alloy.
[0008]
Hereinafter, the present invention will be described in detail.
The molten salt electrolysis method used in the present invention is a known method, for example, an electrolysis in which a metal electrode is used as a cathode and a graphite electrode is used as an anode, and a rare earth oxide is used as a raw material and fused with a mixed fluoride of alkali, alkaline earth and rare earth. This is a molten salt electrolysis method using a bath. The bath temperature is 700 to 1200 ° C., and the rare earth metal is continuously deposited on the cathode surface by electrolytic reduction of the rare earth oxide, and the deposited rare earth metal remains at the bottom of the bath as a liquid, and vacuum suction is used at regular intervals. Collect outside the system with a tapping device. An alloy by adding a transition metal such as iron used as a magnet raw material to suppress solidification of molten rare earth metal in the apparatus, breakage of the suction pipe, and contamination of impurities from the suction pipe during recovery. The melting point of the alloy can be lowered, and the recovery of the alloy can be made safe and efficient.
[0009]
The present invention is characterized by adding Nd-based rare earth magnet scrap in place of the transition metal added for the above purpose. When the Nd-based rare earth magnet scrap is introduced, the oxide on the scrap surface dissolves into the electrolytic bath while the scrap settles to the bottom of the bath. In addition, the rare earth oxide present at the grain boundary of the magnet alloy is continuously charged, dissolved in the molten rare earth metal generated by electrolytic reduction and accumulated at the bottom of the bath, thermal diffusion of the oxide and dissolution of oxygen in the electrolytic bath, It moves to the vicinity of the molten alloy-electrolytic bath interface and dissolves in the electrolytic bath by thermodynamic diffusion due to the difference in oxygen activity between the electrolytic bath and the molten metal. The rare earth element dissolved and ionized in the electrolytic bath is again deposited as a metal on the cathode surface by electrolytic reduction and can be recovered.
[0010]
The rare earth oxide constituting the electrolytic bath is preferably the same rare earth oxide as the rare earth of the Nd-based rare earth magnet scrap. The composition ratio between the rare earth oxide and the fluoride may be a known one, but usually, the rare earth oxide may be added to the fluoride by several wt%. Examples of the fluoride include mixed fluorides of alkali, alkaline earth and rare earth, and specific examples include lithium fluoride, barium fluoride, calcium fluoride and the like in addition to the rare earth fluoride.
[0011]
The Nd-based rare earth magnet scrap used in the present invention is an RTB-based alloy (R is at least one kind of rare earth element selected from Pr, Nd, Tb and Dy, and T is Fe or Fe and at least one kind or more. Transition metal other than Fe, R: 27-35 wt%, B: 0.9-1.3 wt%, T: balance), and the shape varies depending on the process of generating scrap, The shape put into the bath preferably has a particle size of 0.1 to 10 mm. When the particle size of the scrap to be added is within the above range, the surface area increases and the contact area with the electrolytic bath increases, so that the rare earth oxide on the scrap surface is efficiently dissolved. In addition, dissolution of the bath bottom into the molten metal is promoted, and the undissolved residue of the scrap in the alloy can be suppressed.
[0012]
Further, as the Nd-based rare earth magnet scrap, machining sludge having a particle size of 100 μm or less generated in the machining process can also be used. Since sludge has a very small particle size, when it is put into the electrolytic bath, it burns on the surface of the electrolytic bath and floats on the bath surface as slag. Therefore, the transition metal contained in the sludge is also oxidized, and the amount of slag that accumulates on the bath surface increases, so that continuous operation may not be possible, and productivity is reduced. Therefore, a method of injecting sludge with an inert gas or a method of injecting a sludge pressure-formed product or sludge sintered at 1000 to 1200 ° C. and then pulverized to the above particle diameter into an electrolytic furnace, Sludge can be reused on the same principle as scrap.
[0013]
The input amount of the Nd-based rare earth magnet scrap is determined by determining and adjusting the alloy composition to be recovered according to the temperature of the molten salt electrolytic bath. As described above, the temperature of the electrolytic bath is 700 to 1200 ° C., and the melting point of the molten alloy accumulated at the bottom of the bath needs to be kept below the temperature of the electrolytic bath. For this reason, it is desirable to adjust the amount of scrap input so that the melting point of the alloy to be recovered is about 100 ° C. lower than the electrolytic bath temperature. For example, in the method for producing metal neodymium by molten salt electrolysis, since the electrolytic bath temperature is 1000 to 1100 ° C., the melting point of the alloy to be recovered may be 900 ° C. or less, and the alloy to be recovered from the Nd—Fe phase diagram It is preferable to introduce magnet scraps so that the Fe concentration of 1 to 30% by weight. To increase the amount of Nd-based rare earth magnet scrap, the higher the Fe concentration, the more efficient. However, the temperature distribution in the furnace differs depending on the electrolytic bath apparatus, so the optimum input amount is determined according to the furnace. It is desirable to go.
[0014]
The resulting alloy is R-T-B (R is at least one kind of rare earth element selected from Pr, Nd, Tb and Dy, T is Fe or Fe and at least one kind of transition metal other than Fe). It is preferable that T is 1 to 30% by weight, B is 0.01 to 0.5% by weight, and R is the balance, respectively. All transition metals such as Fe and Co are dissolved in molten rare earth metal at the bottom of the bath to form a rare earth-transition metal-boron alloy, which can be reused as a raw material for magnets.
[0015]
The oxygen concentration of the rare earth-transition metal-boron alloy (R-T-B) recovered and obtained by the above method is equivalent to the oxygen concentration of the alloy obtained by a normal molten salt electrolysis method. Since the scrap to be added generally contains 0.05 to 5.0% by weight of oxygen, it is estimated that the oxygen concentration of the molten alloy at the bottom of the bath is increased. Reduction or deoxidation reaction proceeds by dissolution of the substance and diffusion of oxygen in the molten metal accumulated at the bath bottom to the electrolytic bath, etc., and the oxygen concentration of the resulting alloy can be suppressed to a low level.
[0016]
The obtained rare earth-transition metal-boron alloy can be returned to the normal magnet manufacturing process and reused. That is, 1-50 wt% is mixed with a melting raw material required as a magnet alloy such as rare earth metal, transition metal, B used in the Nd—Fe—B alloy for the purpose of the recovered alloy, and dissolved in an inert gas stream. A rare earth sintered magnet can be produced by pulverizing, shaping in a magnetic field, sintering at 1000 to 1200 ° C. in an Ar atmosphere or vacuum, and then heat-treating at 400 to 600 ° C. in an Ar atmosphere.
[0017]
【Example】
EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.
[0018]
[Example 1]
A graphite electrode as an anode and a Mo electrode as a cathode are inserted into an electrolytic cell having an inner diameter of 900 mmφ and a depth of 1000 mm, and NdF 3 (60 wt%)-DyF 3 (15 wt%)-LiF (15 wt%)-BaF 2 ( 10 wt%) is continuously supplied with a mixed oxide of Nd 2 O 3 (90 wt%)-Dy 2 O 3 (10 wt%) as a rare earth oxide to a mixed fluoride bath comprising an average voltage of 12.5 V and an average current When electrolysis was performed for 24 hours while sequentially charging a total of 35 kg of Nd-based rare earth magnet scraps with a diameter of 10 mm or less into an electrolytic furnace producing an Nd-Dy alloy under the conditions of 8000 A and an average bath temperature of 1080 ° C., 211 kg of the alloy Was recovered. At that time, the electrolytic efficiency and the yield were almost the same as the normal operation. The composition of the obtained alloy is as shown in Table 1. The Fe concentration was 9.7 wt% and the oxygen concentration was 0.025 wt%. The Co concentration and B concentration were 0.61 wt% and 0.11 wt%, respectively, which approximated the concentration estimated from the input amount, and almost the entire amount could be recovered.
[0019]
25% of the obtained Nd-Dy alloy was added to a melting raw material composed of Nd-Dy-Fe-Co-B-Al and melted, and 26.5 Nd-1.5 Dy-BAL. A mother alloy having a composition of Fe-1Co-1B-0.5Al was prepared. An appropriate amount of a sintering aid separately dissolved in the obtained master alloy was mixed and pulverized by a jet mill in a nitrogen stream to obtain a fine powder having an average particle size of about 3 μm. Thereafter, these fine powders were filled in a mold of a molding apparatus, oriented in a magnetic field of 12 kOe, and press-molded at a pressure of 1 ton / cm 2 in a direction perpendicular to the magnetic field. The obtained compact was sintered at 1100 ° C. for 2 hours, then cooled, and further heat-treated at 500 ° C. for 1 hour in an Ar atmosphere to produce a sintered magnet. When the magnetic properties of the obtained sintered magnet were measured, the following properties were obtained: Br = 13.0 kG, iHc = 16.5 kOe, (BH) max = 42 MGOe, equivalent to the case of using a normal Nd-Dy alloy. It was the characteristic.
[0020]
[Example 2]
In the same electrolytic cell and the same electrolysis conditions as in Example 1, a sludge having an average particle diameter of 100 μm or less was molded in an inert gas atmosphere and sintered at 1000 ° C. for 2 hours to obtain 63 kg of massive sludge. When electrolysis was carried out for 24 hours while sequentially charging, 249 kg of alloy was obtained. The electrolytic efficiency and yield were almost equivalent to normal operation. The composition of the obtained alloy was as shown in Table 1. The Fe concentration was 15.1 wt% and the oxygen concentration was 0.021 wt%. The Co concentration and B concentration were 0.96 wt% and 0.22 wt%, respectively, which were close to the concentration estimated from the input amount, and almost the entire amount could be recovered.
[0021]
25% of this Nd-Dy alloy was added to a melting raw material made of Nd-Dy-Co-B-Al and melted, and the weight ratio (%) was 27.5Nd-1Dy-BAL. A mother alloy having a composition of Fe-1Co-1B-0.15Al was produced. A sintered magnet was produced from the obtained mother alloy in the same manner as in Example 1. When the magnetic properties of the obtained sintered magnet were measured, the properties of Br = 13.9 kG, iHc = 15 kOe, (BH) max = 48 MGOe were obtained, and the same properties as when using a normal Nd-Dy alloy were obtained. Met.
[0022]
[Example 3]
The amount of Nd-based magnet scrap having a diameter of 10 mm or less was changed from 33 to 63 kg / day under the same electrolytic cell and the same electrolysis conditions as in Example 1, and electrolysis was performed for 24 hours for 10 days while sequentially charging. Electrolytic efficiency and yield during operation were equivalent to normal operation. The composition of the obtained alloy is as shown in Table 1, and the Fe, Co, and B concentrations are proportional to the weight of the scrap input, and 5 to 15 wt%, 0.2 to 0.8 wt%, and 0.1 to 0, respectively. It was 3 wt%. The oxygen concentration was 0.02 to 0.05 wt% regardless of the increase in scrap input.
[0023]
25 wt% of these Nd—Dy alloys were added to a melting raw material made of Nd—Dy—Fe—Co—B—Al and melted, and 26.5 Nd-1.5 Dy-BAL. A mother alloy having a composition of Fe-1Co-1B-0.5Al was prepared. A sintered magnet was produced from the obtained mother alloy in the same manner as in Example 1. When the magnetic properties of the obtained sintered magnet were measured, the properties of Br = 13 kG or more, iHc = 16 kOe or more, and (BH) max = 42 MGOe or more were obtained, which is equivalent to the case of using a normal Nd-Dy alloy. It was a characteristic.
[0024]
[Table 1]
【The invention's effect】
According to the present invention, all elements contained in the Nd-based rare earth magnet scrap can be regenerated at the same time, and the oxygen concentration of the obtained alloy is reduced. In addition, the process is simple even compared with the conventional treatment method, and since the treatment can be performed continuously economically, its utility value is extremely high in industry.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the amount of scrap input and the oxygen concentration in the obtained rare earth-transition metal-boron alloy.
Claims (7)
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| JP5424352B2 (en) | 2008-03-26 | 2014-02-26 | 一般財団法人生産技術研究奨励会 | Rare earth element recovery method and recovery apparatus |
| JP4820423B2 (en) * | 2009-02-23 | 2011-11-24 | 有限会社レアメタルズ２１ | Method of recovering neodymium magnet from used equipment and neodymium magnet recovered or recycled by the method |
| JP5398369B2 (en) * | 2009-06-15 | 2014-01-29 | 株式会社東芝 | Rare metal production method and system |
| JP5993374B2 (en) | 2011-08-10 | 2016-09-14 | 住友電気工業株式会社 | Element recovery method |
| JP5647750B2 (en) * | 2012-07-19 | 2015-01-07 | Jx日鉱日石金属株式会社 | Rare earth recovery method from rare earth element containing alloys |
| KR101495531B1 (en) * | 2012-11-05 | 2015-02-26 | 공주대학교 산학협력단 | METHOD FOR RECYCLING NdFeB MAGNET |
| JP2015024347A (en) * | 2013-07-24 | 2015-02-05 | 株式会社東芝 | Recovery method of valuable metal contained in waste magnet, and recovery device therefor |
| DE102014206223A1 (en) | 2014-04-01 | 2015-10-01 | Fme Freiberger Metallrecycling Und Entwicklungsdienstleistungen Gmbh | Process for the recovery of rare earths from rare earth-containing compositions |
| DE102014224015B4 (en) | 2014-11-25 | 2019-07-04 | Fme Freiberger Metallrecycling Und Entwicklungsdienstleistungen Gmbh | Process for the recovery of rare earths from rare earth-containing phosphors |
| JP6668021B2 (en) * | 2015-09-03 | 2020-03-18 | 株式会社東芝 | Rare metal recovery method |
| CN108359798A (en) * | 2017-06-03 | 2018-08-03 | 江西离子型稀土工程技术研究有限公司 | A method of rapidly and efficiently recycling neodymium iron boron waste material |
| KR20210021028A (en) * | 2018-06-18 | 2021-02-24 | 에이비비 슈바이쯔 아게 | Method for producing magnetic powder |
| CN108977674A (en) * | 2018-07-31 | 2018-12-11 | 邳州市尕星医药技术服务有限公司 | A method of the Extraction of rare earth oxide from Rare Earth Electrolysis waste material |
| EP3795704B1 (en) * | 2019-09-17 | 2024-02-21 | Institut "Jozef Stefan" | A method for selective recovery of rare earth elements from nd-fe-b magnet scraps based on electrolysis |
| CN114101686B (en) * | 2021-11-09 | 2023-07-25 | 中磁科技股份有限公司 | Treatment method of neodymium iron boron oxidized blank |
| CN114974870B (en) * | 2022-06-15 | 2023-10-27 | 赣州市华新金属材料有限公司 | Method for preparing neodymium-iron-boron permanent magnet from neodymium-iron-boron powdery waste |
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