JP4287749B2

JP4287749B2 - Method for recovering useful elements from rare earth-transition metal alloy scrap

Info

Publication number: JP4287749B2
Application number: JP2003576661A
Authority: JP
Inventors: 浩生頼; 英雄横井
Original assignee: Santoku Corp
Current assignee: Santoku Corp
Priority date: 2002-03-19
Filing date: 2003-03-18
Publication date: 2009-07-01
Anticipated expiration: 2023-03-18
Also published as: CN100339495C; AU2003221047A1; WO2003078671A1; CN1656239A; JPWO2003078671A1

Description

技術分野
本発明は、希土類−遷移金属合金スクラップから希土類元素等の有用元素を経済的、且つ安全に回収することができる有用元素の回収方法に関する。
背景技術
希土類−遷移金属合金の分野で実用化されている代表的な製品に、希土類−コバルト系及び希土類−鉄−ホウ素系の永久磁石がある。特に後者は優れた磁気特性を示すことからその使用量が近年著しく増加してきている。該磁石は、通常、例えばＮｄ、Ｐｒ、Ｄｙ等の希土類元素を約３０〜３５重量％、鉄を約６０〜６５重量％、ホウ素を１〜２重量％含有し、必要に応じて、Ｃｏ、Ａｌ等を含む合金（以下、希土類−鉄系合金ということがある）を原料とし、粉砕後に成形・焼結して焼結磁石とするか、或いは樹脂と混練・射出成形によりボンド磁石としている。
ところで、希土類−遷移金属合金を用いて磁石を製造する場合、粉砕、成形、焼結、不要部の切除又は研削、検査等の工程で大量の合金屑や研磨屑等のスクラップが発生し、その量は製品重量の３０〜４０％にも及ぶ。ここで、研磨屑等の粉末が研磨液や水等でスラリー状態にあるスクラップを、以下特にスラッジという。また、原料合金の製造過程においても、溶解スラグのロスや鋳造歩留まり、粉砕歩留まりの面から不可避的に屑が発生する。これらスクラップ成分の約３０重量％は、高価かつ有用な希土類元素であり、その回収は資源の有効利用の観点からも、経済性の観点からも強く要請されている。
そこで、磁石合金からの希土類元素の化学的な分離・回収法について、（１）酸溶解法（特開昭６２−１８７１１２号公報、特開昭６３−４０２８号公報）、（２）燃焼酸化−酸浸出法（特公平５−１４７７７号公報）、（３）ｐＨ制御−酸浸出法（特公平７−７２３１２号公報、特開平９−２１７１３２号公報）が提案されている。
前記（１）酸溶解法は、スクラップの全量を酸で溶解し、溶解液からフッ化希土、シュウ酸希土等の形で希土類化合物を回収する方法である。しかし、該方法では、初めの溶解過程において、硫酸、塩酸、硝酸等の鉱酸を高濃度で且つスクラップに対して当量以上に投入する必要がある。特に、スクラップが磁石成形時の切り捨て部分や不良磁石体等の塊状の固形物であるか、それら塊状の固形物が混在したスラッジである場合には、鉱酸に極めて溶解し難く更に高濃度の酸を多く投入するか、予めスクラップ形態の選別又はスクラップの粉砕工程を組入れる必要がある。またスクラップの溶解過程においては、酸ミスト、水素ガス、ＮＯｘガスが生じるため、作業環境上の安全性の問題もある。
前記（２）燃焼酸化−酸浸出法は、スクラップを一旦燃焼酸化して酸化物とし、強酸を用いて主に希土類元素を溶出させ、その溶液からシュウ酸希土、炭酸希土等の形で希土類化合物を回収する方法である。該方法においては、スクラップが、発火性を有する研磨屑等のスラッジである場合、乾燥後に加熱・燃焼装置で一旦着火すれば酸化を進行させることができる。しかし、該スラッジの乾燥・焼成は、設備、エネルギーの点でコストがかさみ、焼成後に酸化物の粉砕が必要になる等作業効率も低い。また塊状の固形物を含有するスクラップの場合、該固形物の芯まで酸化させることは容易でないため、別途予備粉砕が必要であり、作業工程が更に長くなる。
前記（３）ｐＨ制御−酸浸出法は、スラッジを塩酸等に投入し、ｐＨを３〜５に維持して希土類元素を溶出させる方法（特公平７−７２３１２号公報）、或いはｐＨを５以上に維持しつつ希硝酸で希土類元素を溶出させる方法（特開平９−２１７１３２号公報）である。これらの方法では、空気を吹き込むことにより、鉄を水酸化鉄として固相に残すため、前記（１）酸溶解法に比べて酸の使用量は減るが、その効果は十分でなく、やはりこの場合も塊状の固形物が混在すると、予備粉砕工程が不可欠となる。
以上のように、従来提案されている化学的な分離・回収法では、いずれを採用する場合であっても、多量に高濃度の酸を必要とし、特に塊状の固形物からなるスクラップ或いは塊状の固形物の混在するスラッジに対しては、そのまま対応できず、事前選別や予備粉砕工程が必要となるためコスト面からも大量処理の実施を困難としている。
発明の開示
本発明の目的は、希土類−鉄系、希土類−コバルト系、希土類−鉄−コバルト系等の希土類−遷移金属合金、特に希土類−鉄−ホウ素系永久磁石合金等を含むスクラップから希土類元素等の有用元素を、多量の酸を消費することなく、また、スクラップ形態の事前選別や予備粉砕工程を必要とせずに、経済的、且つ安全に有用元素を回収しうる回収方法を提供することにある。
本発明によれば、希土類−遷移金属合金スクラップを、鉱酸のアンモニウム塩水溶液（以下、ＭＡＳ水溶液という）に浸漬する工程（Ａ）と、工程（Ａ）におけるＭＡＳ水溶液に酸素を含む気体を流通させ、スクラップを酸化させて酸化物及び水酸化物の少なくとも１種を主体とする粉末を含む沈澱物を得る工程（Ｂ）と、工程（Ｂ）で得られた沈澱物を、ＭＡＳ水溶液から分離する工程（Ｃ）と、工程（Ｃ）で分離した沈澱物から希土類元素を回収する工程（Ｄ）とを含む希土類−遷移金属合金スクラップからの有用元素の回収方法が提供される。
発明の好ましい実施の態様
以下本発明を更に詳細に説明する。
本発明の回収方法において、回収の対象とされる希土類−遷移金属合金としては、希土類−コバルト系永久磁石合金、希土類−鉄−ホウ素系永久磁石合金、該希土類−鉄−ホウ素系永久磁石合金のホウ素を炭素、窒素等で置換した永久磁石合金、光磁気記録薄膜形成用希土類−鉄−コバルト系合金、スパッタリングターゲット材等の磁性材料が代表的であり、これら合金に通常含有されることがあるＡｌ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｎｉ、Ｃｕ、Ｚｒ、Ｈｆ、Ｎｂ、Ｔａ、Ｍｏ、Ｇｅ、Ｓｂ、Ｓｎ、Ｂｉ、Ｗ等の少なくとも１種、並びに不可避的な不純物元素が含有されたものであっても良い。希土類元素は、Ｎｄ、Ｐｒ、Ｓｍ等の軽希土類、Ｇｄ、Ｔｂ、Ｄｙ等の重希土類又はこれらの混合物のいずれでもよい。
回収処理に供されるスクラップの形態としては、上記合金から磁石等の磁性材料に加工される過程で切り捨てられた圧粉体、焼結体、又は廃棄磁石体等の塊状の固形物；研磨屑等の合金粉末と研磨液、水、油等との懸濁廃棄物であるスラッジ；塊状の固形物が混在するスラッジ等が主に挙げられる。また、原料合金製造過程で派生した溶解スラグ等の固形物も本発明の対象に含まれる。
本発明者らは、多量の酸を使用することなく、有効元素を高率で回収する方法、また従来回収処理を実施するうえで大きな障害となっていた前記塊状の固形物の予備選別及び予備粉砕を省略し、人的、設備的負荷の少ない化学プロセスのみで対処し得る簡便な回収方法を追求した結果、スラッジ、塊状の固形物又は両者が混在するスラッジ等のスクラップを、特定条件の下でＭＡＳ水溶液と反応させることにより、スクラップ全体を、酸化物及び／又は水酸化物を主体とする粉末（以下、これらの粉末をまとめて酸化物粉末と略記する）に変化させ得ることができ、この酸化物粉末から希土類元素等の有用元素を容易に回収しうることを見出し、本発明を完成させた。
スクラップが上述の酸化物粉末に変化するのは、スクラップを浸漬したＭＡＳ水溶液中に酸素を含む気体を吹き込みながら（以下、エアレーションという）反応させることにより、スクラップが次第に表面から酸化され固形物が崩壊するためと考えられる。
本発明の回収方法では、まず、希土類−遷移金属合金スクラップを、ＭＡＳ水溶液に浸漬する工程（Ａ）を行う。
前記ＭＡＳ水溶液における鉱酸のアンモニウム塩としては、例えば、塩化アンモニウム（ＮＨ_４Ｃｌ）、硫酸アンモニウム（（ＮＨ_４）_２ＳＯ_４）、硝酸アンモニウム（ＮＨ_４ＮＯ_３）、フッ化水素アンモニウム（ＮＨ_４ＨＦ_２）等が挙げられる。これらのうち硫酸アンモニウムがスクラップの酸化・崩壊反応を促進する上で最も効果が大きい。
ＭＡＳ水溶液の濃度は、スクラップの形態、酸化・崩壊のし易さ、許容できる反応時間等により適宜決定できる。通常０．１〜２．０ｍｏｌ／ｌ、好ましくは０．２〜１．５ｍｏｌ／ｌである。該濃度が０．１ｍｏｌ／ｌ未満では反応速度が遅く実用的でなく、２．０ｍｏｌ／ｌを超えてもそれ以上の反応速度の向上は認められないので好ましくない。スクラップがスラッジの場合、ＭＡＳ水溶液濃度とは、スラッジ中の水分により希釈された後の濃度である。
工程（Ａ）において、スクラップをＭＡＳ水溶液に浸漬するには、例えば、上記濃度のＭＡＳ水溶液と適量のスクラップとを反応容器に収容して行うことができる。この際、スクラップがスラッジの場合は、必要によりその上澄み部分の水分、油分を除去してから収容できる。前記反応容器としてはＦＲＰ製等の汚染され難い材料の使用が適している。
前記容器に収容するスクラップの量とＭＡＳ水溶液量との合計量に対するスクラップの量、即ち、スクラップの濃度は特に限定されず、スクラップが該水溶液に浸され、後述するエアレーション、又はエアレーションと同時に攪拌を行った時に酸素を含む気体及びＭＡＳ水溶液がスクラップと十分に接触が可能であれば、広い範囲のスクラップの濃度が許容される。その機構は十分に明らかでないが、本発明に用いるＭＡＳ水溶液における鉱酸のアンモニウム塩が、恐らくスクラップが空気酸化される際の反応促進剤、或いは触媒として作用し、従来のスクラップを直接鉱酸に溶解する場合のような化学量論的に進行する反応とは異なる反応が生じているためと考えられる。
本発明では、前記工程（Ａ）におけるＭＡＳ水溶液に酸素を含む気体を流通させ、スクラップを酸化して酸化物粉末を含む沈澱物を得る工程（Ｂ）を行う。
前記酸素を含む気体としては、通常空気を使用できるが、所望の酸化物粉末が得られる程度の酸素量を含む気体であれば特に限定されない。このような気体をＭＡＳ水溶液中に流通させる方法は特に限定されず、例えば、該気体をバブリングする方法により実施できる。この際、必要に応じて公知の攪拌手段、混合手段を用いて酸素を含む気体及びＭＡＳ水溶液がスクラップと十分に接触するようにしても良い。
工程（Ｂ）において、スクラップを酸化させて酸化物粉末を得る際のＭＡＳ水溶液の温度、即ち、スクラップの酸化反応時の温度は、室温以上であれば良いが、反応を更に促進させる点から４０〜９０℃が好ましい。従って、工程（Ｂ）においては、ＭＡＳ水溶液の温度を少なくともスクラップを酸化させる際に上記好ましい温度範囲に保持することが望ましい。この際、ＭＡＳ水溶液の温度が４０℃未満では反応促進効果が小さく、一方、９０℃を超えても更に特段の反応促進効果は望めず、加熱負荷が増すのでメリットは少ない。このような温度保持手段としては、例えば、投げ込みヒーター、スチームの直接吹き込みが簡便で好ましい。
前記酸化反応に要する時間は、スクラップの形態、酸化・崩壊反応のし易さ、ＭＡＳ水溶液の濃度及び温度等により変わるが、通常１２〜９６時間程度であり、スクラップ中の固形物の大きさ等により更に短縮或いは延長することができる。塊状の固形物を含有するスクラップの場合、反応の終了は、スクラップ中の固形物がほぼ全量崩壊し、沈澱物に含まれる粉末の粒径が１ｍｍ以下となる段階が好ましい。このような段階は、例えば、目視或いは容器の底を棒等で探ることにより容易に判定できる。
前記スクラップ中の固形物がほぼ全量崩壊した段階における酸化物粉末の粒径は、通常、数１０μｍ以下であるが、得られる沈澱物中含まれる粉末の粒径はこれに限定されない。要するに、後述する工程（Ｄ）において有用元素の分離・回収効率が十分であれば、必ずしもスクラップを完全に粒度の低い粉末にさせる必要はなく、粒径数ｍｍ以下程度の固形物が残存していても良い。工業的な実用レベルにおいては、前記酸化反応の時間等によってこのような粒径の固形物が含まれる可能性が生じる。このような粒径の固形物の割合は少ない方が好ましいが、後述する工程（Ｄ）における酸の使用量や条件を適宜選択することにより有用元素を効率良く回収することは可能である。
本発明では、工程（Ｂ）で得られた酸化物粉末を含む沈澱物を、ＭＡＳ水溶液から分離する工程（Ｃ）を行う。該分離は、沈澱物相と水溶液相とを分離することにより行うことができる。分離方法は、傾斜法、フィルタープレス法等の公知の方法で実施でき、好ましくは分離した沈澱物に吸着している鉱酸のアンモニウム塩を水で洗浄することができる。洗浄後の沈澱物は特に乾燥する必要を要しない。
本発明においてＭＡＳ水溶液中の鉱酸のアンモニウム塩は、前述のように触媒的な働きをし、工程（Ｂ）における反応後もほとんど変化しないため、分離後の水溶液はそのまま、或いは必要により比重測定等を行って鉱酸のアンモニウム塩の濃度調整を行って次のバッチにリサイクル使用される。
前記分離された沈澱物は、そのほとんどがスクラップ中の金属元素を含む酸化物粉末である。該酸化物粉末は、酸化物及び／又は水酸化物を主体とする粉末であり、具体的には後述する実施例に示すように、スクラップ中の鉄はその全てがオキシ水酸化鉄（ＦｅＯ（ＯＨ））及び／又は水酸化第二鉄（Ｆｅ（ＯＨ）_３）として含有され、希土類元素の９０％以上が恐らくＲ（ＯＨ）_３として該粉末中に含有されている。従って、工程（Ｃ）において分離された沈澱物を分析することにより、工程（Ｂ）において得られた沈澱物が、本発明における所望の酸化物粉末を含んでいることが確認できる。
本発明では、工程（Ｃ）で分離した沈澱物から希土類元素を回収する工程（Ｄ）を行う。
工程（Ｄ）において、工程（Ｃ）で分離した酸化物粉末を含む沈澱物から希土類元素を回収する方法は、特に限定されず、従来公知の酸浸出法等を参照して行うことができる。例えば、特公平５−１４７７７号公報に記載された燃焼酸化−酸浸出法における燃焼酸化を除いた方法、特公平７−７２３１２号公報又は特開平９−２１７１３２号公報に示されたｐＨ制御−酸浸出法が、本発明に特に有利に採用し得るがこれに限定されない。このような酸浸出法が好ましい理由は、本発明における工程（Ｂ）によって前述のとおり合金中の鉄は、既にオキシ水酸化鉄、水酸化第二鉄等に変化しているため、該酸化物粉末を引き続いて酸と反応させる際に鉄の溶出がほぼ完全に抑制され、少ない量の酸で希土類元素を選択的に溶出させうるからである。
工程（Ｄ）において、上記酸浸出法により酸化物粉末を含む沈澱物から希土類元素の溶出を行った後、該希土類元素が溶出した溶液から希土類化合物を回収するには、公知の沈澱生成法等により行うことができる。例えば、前記溶液にフッ化物、シュウ酸塩、炭酸塩等の可溶性沈澱剤を添加し、フッ化希土、シュウ酸希土、炭酸希土等の希土類塩類の不溶性沈澱を生成させ、分離・乾燥する方法、或いは更に焼成を加えて希土類酸化物とする方法等により回収できる。
工程（Ｄ）において採用しうる、前記酸浸出法及び沈澱生成法の条件は特に限定されず、目的達成のために公知の条件等を勘案して適宜決定することができる。
例えば、酸浸出法の場合、工程（Ｃ）で得られた酸化物粉末を含む沈澱物を水に分散し、エアレーションしながら所望濃度の硫酸、塩酸、硝酸等の鉱酸を滴下する方法により行うことができる。この際、滴下時の沈澱物を含む溶液の温度は、室温以上、好ましくは４０〜６０℃程度である。鉱酸の滴下量や滴下時間は適宜選択でき、反応の終了は溶液のｐＨ測定等により決定できる。
本発明において、希土類−遷移金属合金スクラップの合金中にその他の有用金属、例えば、コバルトが含有されている場合、工程（Ｂ）のＭＡＳ水溶液による酸化により、コバルトもその９０重量％以上が酸化物粉末中に残留するので、工程（Ｄ）において採用しうる前述の酸浸出法、特に特開平９−２１７１３２号公報に記載の方法に準じて前記希土類元素と共にコバルトをも回収できる。
本発明では、特に、ＭＡＳ水溶液に酸素を含む気体を流通させ、スクラップを酸化して特定の酸化物粉末を含む沈澱物を得る工程（Ｂ）を行うので、希土類−遷移金属合金スクラップから希土類元素等の有用元素を、多量の酸を消費することなく、またスクラップ形態の事前選別や予備粉砕工程を必要としないで、経済的且つ安全に、しかも効率良く有用元素を回収することができる。
実施例
以下、試験例及び実施例により本発明を更に詳細に説明するが、本発明はこれらに限定されるものではない。尚、例中の％は「重量％」を示す。
試験例１〜５
塊状の固形物であるスクラップ試料として、寸法：２０．５ｍｍ×５２．５ｍｍ×約２．２ｍｍ、成分：希土類元素（Ｎｄ＋Ｐｒ＋Ｄｙ）３１．８％、Ｆｅ６５．９％、Ｂ１．０５％、Ｃｏ０．９０％の希土−鉄−ホウ素系焼結磁石の切り捨て部を用意した。ポリ容器に０．５ｍｏｌ／ｌのＭＡＳ水溶液４００ｍｌと約１７〜１８ｇのスクラップ試料（Ｗ^１）１個を入れ、攪拌機にて攪拌、エアーポンプにてエアレーションしながら室温（２５〜３０℃）にて放置し酸化処理を行った。２４時間毎に試料の未崩壊部の量（Ｗ^２）を秤量し、固形物の残存率（Ｗ^２／Ｗ^１×１００）を求めた。残存率の時間変化を図１に示す。
ここで、ＭＡＳ水溶液として、塩化アンモニウム（ＮＨ_４Ｃｌ）水溶液を用いた例を試験例１、硫酸アンモニウム（（ＮＨ_４）_２ＳＯ_４）水溶液を用いた例を試験例２、硝酸アンモニウム（ＮＨ_４ＮＯ_３）水溶液を用いた例を試験例３、フッ化水素アンモニウム（ＮＨ_４ＨＦ_２）水溶液を用いた例を試験例４、ＭＡＳ水溶液を用いずに純水を用いた例を試験例５とする。
図１より、ＭＡＳ水溶液の使用により、スクラップの酸化・崩壊が促進される傾向が明らかであり、時間の経過と共に試料は表面から酸化・崩壊し、容器の底に褐色粉末として拡がってゆく状況が見られた。中でも硫酸アンモニウム水溶液を用いた試験例２の効果が大きいことが判る。
試験例６
ＭＡＳ水溶液として、０．５ｍｏｌ／ｌの硫酸アンモニウム水溶液を用い、該水溶液の温度を２５℃、４０℃、６０℃、８０℃及び１００℃に代えた以外は、試験例１〜４と同様にして塊状の固形物であるスクラップ試料を酸化処理した。各温度について固形物の残存率が１０％以下になるまでの時間を測定した。結果を図２に示す。また６０℃、７２時間処理により完全に崩壊した試料について、沈澱物をろ過して回収し、１００℃で乾燥した粉末をＸ線回折で調査した。結果を図３に示す。
図２より、ＭＡＳ水溶液の温度を４０℃以上に上昇させると、顕著に反応が促進されることが分かる。
図３より、生成した粉末にはＦｅ（ＯＨ）_３、ＦｅＯ（ＯＨ）等の強い回折ピークが存在する。希土類化合物のピークは必ずしも明瞭でないが、これは恐らく結晶性の低い水酸化物として存在するためであると考えられる。
試験例７及び８
硫酸アンモニウム水溶液の濃度を、０．１〜２．０ｍｏｌ／ｌの範囲で変化させ、温度６０℃一定とした以外は、試験例１〜４と同様にして塊状の固形物であるスクラップ試料を酸化処理した。用いた硫酸アンモニウム水溶液の各濃度について固形物の残存率が１０％以下になるまでの時間を測定した（試験例７）。また、試験例８として、温度６０℃一定とし、エアレーション無しの条件とした以外は試験例２と同様にしてスクラップ試料を酸化処理した。この際の固形物の残存率が１０％以下になるまでの時間を測定した。これらの結果を図４に示す。但し、試験例８の結果のみ図中×印で示す。
図４から、硫酸アンモニウム水溶液を用いた場合、その濃度は、０．２ｍｏｌ／ｌ以上で酸化・崩壊促進効果が得られ、濃度上昇につれて効果が増し、１．５〜２．０ｍｏｌ／ｌ付近で飽和に及ぶこと、またエアレーションを行わない試験例８では著しく反応が遅れることが分かる。
実施例１
表１に示す組成の希土類−鉄−ホウ素系焼結磁石の製造過程で派生した切り捨て部（約１７ｇ／個）６個が混在する粉末状の研削屑含有スラッジ（乾燥重量１１９．７ｇ）を、濃度０．８ｍｏｌ／ｌの硫酸アンモニウム水溶液５００ｍｌに浸漬した。続いて、攪拌及びエアレーションしつつ７０℃にて３０時間の酸化処理を行ったところ、該スラッジから酸化物粉末の沈澱物が生成した。この酸化物粉末をろ過分離し、乾燥したところ１９２．５ｇであった。その一部を採取して組成を分析した。結果を表１に示す。
表１より、得られた粉末中には、該スラッジ中の希土類元素の９８％以上、またＣｏの９３％以上が移行していることが判る。
尚、表１及び表２中のＲはＮｄ、Ｐｒ及びＤｙの混合物を示し、表１の「その他」は酸素、水素、炭素、硫黄等のガス成分を示す。

次いで、硝酸を用いた酸浸出法により、前記粉末からの希土類元素の回収を試みた。前記酸化物粉末１７０．０ｇを水２００ｍｌに分散させ、エアレーションしながら５Ｎの硝酸水溶液を滴下した。温度は４０〜５０℃に保持した。反応の進行と共にｐＨは７付近から次第に低下し、ｐＨ５．３となった時点で滴下を終了した。総滴下量は３７０ｍｌ、所要時間は８時間であった。得られた液をろ過・洗浄し、沈澱物と溶液に分離した。ろ液の分析結果を表２に示す。表２より、酸化物粉末中の希土類元素の９８．９％、Ｃｏの８８．０％がろ液中に移行していることが判る。

上記ろ液に、フッ化物、蓚酸塩、水酸化物、炭酸塩等の水溶液を添加して行う沈澱生成法又は溶媒抽出法等により、希土類元素とコバルトを選択的に回収することができる。
実施例２
実施例１と同組成の希土類−鉄−ホウ素系焼結磁石の製造過程で派生した研削屑を含有したスラッジ３５０ｇ（乾燥重量１７５ｇ）を濃度０．２ｍｏｌ／ｌの硫酸アンモニウム水溶液５００ｍｌに浸漬した。続いて、攪拌・エアレーションをしつつ７０℃にて１２時間の酸化処理を行い、生成した酸化物粉末をろ過・分離した。次いで、得られた酸化物粉末の全量を水２００ｍｌに分散させ、攪拌・エアレーションしながら５Ｎの硝酸水溶液を滴下した。温度は４０〜５０℃に保持した。反応の進行と共にｐＨは７付近から次第に低下し、ｐＨ３となった時点で滴下を終了した。総滴下量は１４０ｍｌ、所要時間は８時間であった。次いで、沈澱物をろ過し、得られた沈澱物を水で洗浄した。ろ液と沈澱物を洗浄した水を混合し、硝酸浸出ろ液１０００ｍｌとし、ろ液の分析を行った。スラッジ中の希土類元素含有量は３１．５ｇ、前記硝酸浸出ろ液中の希土類元素含有量は３０．９ｇであり、希土類元素の回収率は９８．０％であった。
比較例１
実施例２で用いたのと同じスラッジ３５０ｇ（乾燥重量１７５ｇ）を硫酸アンモニウム水溶液での酸化処理を行わず、攪拌・エアレーションしながら５Ｎの硝酸水溶液を滴下した。温度は４０〜５０℃を保持した。反応の進行と共にｐＨは１１付近から次第に低下し、ｐＨ３となった時点で滴下を終了した。総滴下量は３００ｍｌで、所要時間は３０時間であった。次いで、沈澱物をろ過し、得られた沈澱物を水で洗浄した。ろ液と沈澱物を洗浄した水を混合し、硝酸浸出ろ液１０００ｍｌとし、ろ液の分析を行った。スラッジ中の希土類元素含有量は３１．５ｇ、前記硝酸浸出ろ液中の希土類元素含有量は２５．２ｇであり、希土類元素の回収率は８０．０％であった。
【図面の簡単な説明】
図１は、試験例１〜５で行った酸化処理において、ＭＡＳ水溶液の種類の相違による、固形物残存率と浸漬時間との関係を示すグラフである。
図２は、試験例６で行った酸化処理において、固形物の残存率が１０％以下になるまでの浸漬温度と時間との関係を示すグラフである。
図３は、試験例６で調製した酸化物粉末試料のＸ線回折の測定結果を示すグラフである。
図４は、試験例７及び８で行った酸化処理において、固形物の残存率が１０％以下になるまでの硫酸アンモニウムの濃度と浸漬時間との関係を示すグラフである。TECHNICAL FIELD The present invention relates to a useful element recovery method capable of economically and safely recovering useful elements such as rare earth elements from rare earth-transition metal alloy scrap.
BACKGROUND ART Typical products that are put into practical use in the field of rare earth-transition metal alloys include rare earth-cobalt based and rare earth-iron-boron based permanent magnets. In particular, since the latter exhibits excellent magnetic properties, the amount used has increased remarkably in recent years. The magnet usually contains, for example, about 30 to 35% by weight of rare earth elements such as Nd, Pr, Dy, about 60 to 65% by weight of iron, and 1 to 2% by weight of boron. An alloy containing Al or the like (hereinafter sometimes referred to as a rare earth-iron alloy) is used as a raw material, and after pulverization, it is molded and sintered into a sintered magnet, or a bonded magnet is formed by kneading and injection molding with a resin.
By the way, when a magnet is manufactured using a rare earth-transition metal alloy, a large amount of scraps such as alloy scraps and polishing scraps are generated in processes such as pulverization, molding, sintering, cutting or grinding of unnecessary portions, inspection, etc. The amount ranges from 30 to 40% of the product weight. Here, the scrap in which the powder such as polishing scraps is in a slurry state with a polishing liquid or water is hereinafter referred to as sludge. Also, in the production process of the raw material alloy, waste is inevitably generated from the viewpoints of loss of molten slag, casting yield, and pulverization yield. About 30% by weight of these scrap components are expensive and useful rare earth elements, and their recovery is strongly demanded from the viewpoint of effective use of resources and from the viewpoint of economy.
Therefore, the chemical separation / recovery method of rare earth elements from magnet alloys is as follows: (1) Acid dissolution method (Japanese Patent Laid-Open Nos. 62-187112 and 63-4028), (2) Combustion oxidation- An acid leaching method (Japanese Patent Publication No. 5-14777), (3) pH control-acid leaching method (Japanese Patent Publication No. 7-72312, JP-A-9-217132) has been proposed.
The (1) acid dissolution method is a method in which the entire amount of scrap is dissolved with an acid, and the rare earth compound is recovered from the solution in the form of rare earth fluoride, rare earth oxalate, or the like. However, in this method, it is necessary to add a mineral acid such as sulfuric acid, hydrochloric acid, and nitric acid at a high concentration and in an equivalent amount or more with respect to scrap in the initial dissolution process. In particular, if the scrap is a lump solid material such as a cut-off portion or a defective magnet body at the time of magnet molding, or sludge mixed with such lump solid material, it is very difficult to dissolve in mineral acid, and even higher concentration It is necessary to add a large amount of acid or to incorporate a scrap form sorting or scrap grinding process in advance. Further, in the melting process of scrap, acid mist, hydrogen gas, and NOx gas are generated, and there is a problem of safety in the working environment.
In the (2) combustion oxidation-acid leaching method, scrap is once burnt and oxidized to form an oxide, and a rare earth element is mainly eluted using a strong acid, and the solution is used in the form of rare earth oxalate, rare earth carbonate, etc. This is a method for recovering a rare earth compound. In this method, when the scrap is sludge such as abrasive debris having ignitability, the oxidation can be advanced once it is ignited by a heating / combustion device after drying. However, the drying and firing of the sludge is costly in terms of equipment and energy, and the work efficiency is low, such as the need to grind the oxide after firing. Further, in the case of scraps containing massive solids, it is not easy to oxidize the cores of the solids, so separate preliminary pulverization is required, and the work process becomes longer.
The (3) pH control-acid leaching method is a method in which sludge is introduced into hydrochloric acid or the like and the pH is maintained at 3 to 5 to elute rare earth elements (Japanese Patent Publication No. 7-72312), or the pH is 5 or more. In this method, a rare earth element is eluted with dilute nitric acid while maintaining the temperature (JP 9-217132 A). In these methods, since air is blown to leave iron in the solid phase as iron hydroxide, the amount of acid used is reduced as compared with the above (1) acid dissolution method, but the effect is not sufficient. Even in the case where a lump of solid matter is mixed, a preliminary pulverization step becomes indispensable.
As described above, the conventionally proposed chemical separation / recovery method requires a large amount of high-concentration acid regardless of which method is employed, and particularly scrap or lump made of lump solid matter. The sludge mixed with solid matter cannot be dealt with as it is, and pre-selection and pre-grinding processes are required, making it difficult to carry out mass processing from the viewpoint of cost.
DISCLOSURE OF THE INVENTION An object of the present invention is to provide rare earth elements from scrap containing rare earth-iron-based, rare earth-cobalt-based, rare earth-iron-cobalt-based rare earth-transition metal alloys, particularly rare earth-iron-boron permanent magnet alloys. To provide a recovery method that can recover useful elements economically and safely without consuming a large amount of acid, and without requiring pre-screening and pre-grinding of scrap forms. It is in.
According to the present invention, a step (A) of immersing a rare earth-transition metal alloy scrap in an aqueous solution of an ammonium salt of mineral acid (hereinafter referred to as an MAS aqueous solution), and a gas containing oxygen in the MAS aqueous solution in the step (A) is circulated. And (b) obtaining a precipitate containing powder mainly composed of at least one of oxide and hydroxide by oxidizing the scrap, and separating the precipitate obtained in step (B) from the MAS aqueous solution. There is provided a method for recovering useful elements from a rare earth-transition metal alloy scrap, which includes a step (C) of recovering rare earth elements from the precipitate separated in the step (C) (D).
Preferred Embodiments of the Invention The present invention will be described in more detail below.
In the recovery method of the present invention, the rare earth-transition metal alloys to be recovered include rare earth-cobalt permanent magnet alloys, rare earth-iron-boron permanent magnet alloys, and rare earth-iron-boron permanent magnet alloys. Typical examples include permanent magnet alloys in which boron is replaced with carbon, nitrogen, etc., rare earth-iron-cobalt alloys for forming magneto-optical recording thin films, sputtering target materials, and the like, and these alloys are usually contained. Contains at least one of Al, Ti, V, Cr, Mn, Ni, Cu, Zr, Hf, Nb, Ta, Mo, Ge, Sb, Sn, Bi, W, and inevitable impurity elements It may be. The rare earth element may be a light rare earth such as Nd, Pr, or Sm, a heavy rare earth such as Gd, Tb, or Dy, or a mixture thereof.
The form of scrap to be subjected to the recovery process is a solid compact such as a green compact, a sintered body, or a discarded magnet body that has been cut off in the process of processing from the above alloy into a magnetic material such as a magnet; Sludge that is a suspended waste of an alloy powder such as an abrasive liquid, water, oil, etc .; sludge in which massive solids are mixed is mainly mentioned. Further, solid objects such as molten slag derived in the raw material alloy manufacturing process are also included in the subject of the present invention.
The inventors of the present invention provide a method for recovering effective elements at a high rate without using a large amount of acid, and preliminarily sorting and preliminarily collecting the massive solid matter, which has been a major obstacle to the conventional recovery process. As a result of pursuing a simple recovery method that can be handled only by chemical processes with less human and equipment load, without crushing, scrap such as sludge, lump solids, or sludge mixed with both under specific conditions By reacting with the MAS aqueous solution, the entire scrap can be changed into a powder mainly composed of oxide and / or hydroxide (hereinafter, these powders are collectively abbreviated as oxide powder), It has been found that useful elements such as rare earth elements can be easily recovered from this oxide powder, and the present invention has been completed.
The scrap changes to the above-mentioned oxide powder because the scrap is gradually oxidized from the surface and the solids are collapsed by reacting the gas containing oxygen into the MAS aqueous solution in which the scrap is immersed (hereinafter referred to as aeration). It is thought to do.
In the recovery method of the present invention, first, the step (A) of immersing the rare earth-transition metal alloy scrap in the MAS aqueous solution is performed.
Examples of the ammonium salt of the mineral acid in the MAS aqueous solution include ammonium chloride (NH ₄ Cl), ammonium sulfate ((NH ₄ ) ₂ SO ₄ ), ammonium nitrate (NH ₄ NO ₃ ), and ammonium hydrogen fluoride (NH ₄ HF _2). ) And the like. Of these, ammonium sulfate is most effective in promoting the oxidation and decay reactions of scrap.
The concentration of the MAS aqueous solution can be appropriately determined depending on the form of scrap, ease of oxidation / disintegration, acceptable reaction time, and the like. Usually, it is 0.1-2.0 mol / l, preferably 0.2-1.5 mol / l. If the concentration is less than 0.1 mol / l, the reaction rate is slow and not practical, and if it exceeds 2.0 mol / l, no further improvement in the reaction rate is observed, which is not preferable. When the scrap is sludge, the MAS aqueous solution concentration is a concentration after being diluted with moisture in the sludge.
In the step (A), in order to immerse the scrap in the MAS aqueous solution, for example, the MAS aqueous solution having the above concentration and an appropriate amount of scrap can be accommodated in a reaction vessel. At this time, if the scrap is sludge, it can be accommodated after removing moisture and oil from the supernatant as necessary. As the reaction vessel, it is suitable to use a material that is hardly contaminated, such as FRP.
The amount of scrap relative to the total amount of scrap contained in the container and the amount of MAS aqueous solution, that is, the concentration of scrap, is not particularly limited, and the scrap is immersed in the aqueous solution, and aeration described later or agitation at the same time as aeration is performed. A wide range of scrap concentrations is acceptable provided that the gas containing oxygen and the aqueous MAS solution can be in sufficient contact with the scrap when done. Although the mechanism is not clear enough, the ammonium salt of mineral acid in the MAS aqueous solution used in the present invention probably acts as a reaction accelerator or catalyst when the scrap is air-oxidized, and the conventional scrap is directly converted into mineral acid. This is probably because a reaction different from the stoichiometrically proceeding reaction such as the case of dissolution occurs.
In the present invention, the step (B) is performed in which a gas containing oxygen is circulated in the MAS aqueous solution in the step (A) to oxidize scrap to obtain a precipitate containing oxide powder.
As the gas containing oxygen, air can be usually used, but it is not particularly limited as long as it contains a sufficient amount of oxygen to obtain a desired oxide powder. A method of circulating such a gas in the MAS aqueous solution is not particularly limited, and for example, it can be performed by a method of bubbling the gas. At this time, if necessary, the gas containing oxygen and the MAS aqueous solution may be sufficiently brought into contact with the scrap by using known stirring means and mixing means.
In the step (B), the temperature of the MAS aqueous solution at the time of oxidizing the scrap to obtain oxide powder, that is, the temperature at the time of the oxidation reaction of the scrap may be room temperature or higher, but it is 40 from the point of further promoting the reaction. ~ 90 ° C is preferred. Therefore, in the step (B), it is desirable to maintain the temperature of the MAS aqueous solution within the above preferable temperature range at least when oxidizing the scrap. At this time, when the temperature of the MAS aqueous solution is less than 40 ° C., the reaction promoting effect is small. On the other hand, if the temperature exceeds 90 ° C., no particular reaction promoting effect can be expected, and the heating load increases, so there is little merit. As such a temperature holding means, for example, a throwing heater and direct blowing of steam are simple and preferable.
The time required for the oxidation reaction varies depending on the form of the scrap, the ease of the oxidation / disintegration reaction, the concentration and temperature of the MAS aqueous solution, and is usually about 12 to 96 hours, such as the size of solids in the scrap Can be further shortened or extended. In the case of scraps containing massive solids, the reaction is preferably terminated at a stage where almost all of the solids in the scraps are disintegrated and the particle size of the powder contained in the precipitate is 1 mm or less. Such a stage can be easily determined, for example, visually or by searching the bottom of the container with a stick or the like.
The particle size of the oxide powder at the stage where almost all of the solid matter in the scrap has collapsed is usually several tens of μm or less, but the particle size of the powder contained in the resulting precipitate is not limited thereto. In short, if the separation / recovery efficiency of useful elements is sufficient in the step (D) described later, it is not always necessary to make the scrap into a powder having a low particle size, and solid matter having a particle size of several millimeters or less remains. May be. At an industrial practical level, there is a possibility that a solid substance having such a particle size is included depending on the time of the oxidation reaction or the like. Although it is preferable that the ratio of solids having such a particle size is small, it is possible to efficiently recover useful elements by appropriately selecting the amount and conditions of acid used in the step (D) described later.
In this invention, the process (C) which isolate | separates the deposit containing the oxide powder obtained at the process (B) from MAS aqueous solution is performed. The separation can be performed by separating the precipitate phase and the aqueous solution phase. The separation method can be carried out by a known method such as a gradient method or a filter press method. Preferably, the ammonium salt of the mineral acid adsorbed on the separated precipitate can be washed with water. The precipitate after washing does not need to be dried.
In the present invention, the ammonium salt of the mineral acid in the MAS aqueous solution acts as a catalyst as described above, and hardly changes after the reaction in the step (B). Etc. to adjust the concentration of the ammonium salt of the mineral acid to be recycled for the next batch.
Most of the separated precipitates are oxide powders containing metal elements in scrap. The oxide powder is a powder mainly composed of oxide and / or hydroxide. Specifically, as shown in the examples described later, all of the iron in the scrap is iron oxyhydroxide (FeO ( OH)) and / or ferric hydroxide (Fe (OH) ₃ ), and more than 90% of the rare earth elements are probably contained in the powder as R (OH) ₃ . Therefore, by analyzing the precipitate separated in the step (C), it can be confirmed that the precipitate obtained in the step (B) contains the desired oxide powder in the present invention.
In this invention, the process (D) which collect | recovers rare earth elements from the deposit isolate | separated at the process (C) is performed.
In the step (D), the method for recovering the rare earth element from the precipitate containing the oxide powder separated in the step (C) is not particularly limited, and can be performed with reference to a conventionally known acid leaching method or the like. For example, a method excluding combustion oxidation in the combustion oxidation-acid leaching method described in Japanese Patent Publication No. 5-14777, pH control-acid shown in Japanese Patent Publication No. 7-72312 or Japanese Patent Application Laid-Open No. 9-217132 The leaching method can be employed particularly advantageously in the present invention, but is not limited thereto. The reason why such an acid leaching method is preferable is that the iron in the alloy has already been changed to iron oxyhydroxide, ferric hydroxide, etc. as described above by the step (B) in the present invention. This is because when the powder is subsequently reacted with an acid, elution of iron is almost completely suppressed, and the rare earth element can be selectively eluted with a small amount of acid.
In the step (D), after the rare earth element is eluted from the precipitate containing the oxide powder by the acid leaching method, the rare earth compound is recovered from the solution from which the rare earth element is eluted. Can be performed. For example, a soluble precipitant such as fluoride, oxalate or carbonate is added to the solution to form an insoluble precipitate of rare earth salts such as rare earth fluoride, rare earth oxalate or rare earth carbonate, and separated and dried. Or a method of adding rare earth oxide by further baking.
The conditions of the acid leaching method and the precipitation generating method that can be employed in the step (D) are not particularly limited, and can be appropriately determined in consideration of known conditions and the like for the purpose.
For example, in the case of the acid leaching method, the precipitate containing the oxide powder obtained in the step (C) is dispersed in water, and a mineral acid such as sulfuric acid, hydrochloric acid or nitric acid having a desired concentration is dropped while aeration is performed. be able to. Under the present circumstances, the temperature of the solution containing the deposit at the time of dripping is room temperature or more, Preferably it is about 40-60 degreeC. The dropping amount and dropping time of the mineral acid can be appropriately selected, and the end of the reaction can be determined by measuring the pH of the solution.
In the present invention, when other useful metals such as cobalt are contained in the alloy of the rare earth-transition metal alloy scrap, cobalt is oxidized by 90% by weight or more by oxidation with the MAS aqueous solution in the step (B). Since it remains in the powder, cobalt can be recovered together with the rare earth element according to the above-described acid leaching method that can be employed in step (D), particularly the method described in JP-A-9-217132.
In the present invention, in particular, the step (B) is performed in which a gas containing oxygen is circulated in the MAS aqueous solution and the scrap is oxidized to obtain a precipitate containing a specific oxide powder. Such useful elements can be recovered economically, safely and efficiently without consuming a large amount of acid, and without requiring pre-screening and pre-grinding steps of scrap form.
EXAMPLES Hereinafter, the present invention will be described in more detail with reference to test examples and examples, but the present invention is not limited thereto. In addition,% in an example shows "weight%".
Test Examples 1-5
As a scrap sample which is a massive solid, dimensions: 20.5 mm × 52.5 mm × about 2.2 mm, components: 31.8% rare earth element (Nd + Pr + Dy), Fe 65.9%, B 1.05%, Co 0.90 % Of a rare earth-iron-boron based sintered magnet was prepared. Put 400 ml of 0.5 mol / l MAS aqueous solution and ^one scrap sample (W ¹ ) of about 17-18 g in a plastic container, stir with a stirrer, and aerate with an air pump at room temperature (25-30 ° C.) It was left to oxidize. The amount (W ² ) of the undisintegrated part of the sample was weighed every 24 hours, and the residual ratio of solid matter (W ² / W ¹ × 100) was determined. The time change of the remaining rate is shown in FIG.
Here, as an MAS aqueous solution, an example using an ammonium chloride (NH ₄ Cl) aqueous solution as Test Example 1, an example using an ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) aqueous solution as Test Example 2, ammonium nitrate (NH ₄ NO ₃₎ ) An example using an aqueous solution is Test Example 3, an example using an ammonium hydrogen fluoride (NH ₄ HF ₂ ) aqueous solution is Test Example 4, and an example using pure water without using an MAS aqueous solution is Test Example 5.
From FIG. 1, it is clear that the use of MAS aqueous solution promotes the oxidation / disintegration of scrap, and as time passes, the sample oxidizes / disintegrates from the surface and spreads as brown powder at the bottom of the container. It was seen. It turns out that the effect of Test Example 2 using an ammonium sulfate aqueous solution is particularly great.
Test Example 6
As an MAS aqueous solution, a 0.5 mol / l ammonium sulfate aqueous solution was used, and the mass of the aqueous solution was changed to 25 ° C., 40 ° C., 60 ° C., 80 ° C. and 100 ° C. in the same manner as in Test Examples 1 to 4. A scrap sample, which is a solid material, was oxidized. For each temperature, the time until the residual rate of solids became 10% or less was measured. The results are shown in FIG. Moreover, about the sample completely disintegrated by the process at 60 ° C. for 72 hours, the precipitate was collected by filtration, and the powder dried at 100 ° C. was examined by X-ray diffraction. The results are shown in FIG.
FIG. 2 shows that the reaction is remarkably accelerated when the temperature of the MAS aqueous solution is increased to 40 ° C. or higher.
As shown in FIG. 3, the generated powder has strong diffraction peaks such as Fe (OH) ₃ and FeO (OH). The peak of the rare earth compound is not always clear, but this is probably because it exists as a hydroxide with low crystallinity.
Test Examples 7 and 8
Except for changing the concentration of the ammonium sulfate aqueous solution in the range of 0.1 to 2.0 mol / l and keeping the temperature constant at 60 ° C., the scrap sample, which is a massive solid, was oxidized in the same manner as in Test Examples 1 to 4. did. For each concentration of the aqueous ammonium sulfate solution used, the time until the residual rate of solids became 10% or less was measured (Test Example 7). In addition, as a test example 8, the scrap sample was oxidized in the same manner as in the test example 2 except that the temperature was kept constant at 60 ° C. and no aeration was used. At this time, the time until the residual ratio of the solids became 10% or less was measured. These results are shown in FIG. However, only the result of Test Example 8 is indicated by a cross in the figure.
As shown in FIG. 4, when an aqueous ammonium sulfate solution is used, the concentration / acceleration-promoting effect is obtained when the concentration is 0.2 mol / l or more, and the effect increases as the concentration increases, and is saturated near 1.5 to 2.0 mol / l. In Test Example 8 where no aeration is performed, the reaction is remarkably delayed.
Example 1
Powdered grinding scrap containing sludge (dry weight 119.7 g) in which 6 cut-off parts (about 17 g / piece) derived from the manufacturing process of the rare earth-iron-boron sintered magnet having the composition shown in Table 1 are mixed, It was immersed in 500 ml of an aqueous ammonium sulfate solution having a concentration of 0.8 mol / l. Subsequently, an oxidation treatment was carried out at 70 ° C. for 30 hours while stirring and aeration. As a result, a precipitate of oxide powder was generated from the sludge. The oxide powder was separated by filtration and dried to find 192.5 g. A part of the sample was collected and analyzed for composition. The results are shown in Table 1.
From Table 1, it can be seen that 98% or more of the rare earth elements in the sludge and 93% or more of Co are transferred in the obtained powder.
In Tables 1 and 2, R represents a mixture of Nd, Pr, and Dy, and “Others” in Table 1 represents gas components such as oxygen, hydrogen, carbon, and sulfur.

Next, recovery of rare earth elements from the powder was attempted by an acid leaching method using nitric acid. 170.0 g of the oxide powder was dispersed in 200 ml of water, and a 5N aqueous nitric acid solution was added dropwise while aeration. The temperature was kept at 40-50 ° C. The pH gradually decreased from around 7 with the progress of the reaction, and the dropping was terminated when the pH reached 5.3. The total dripping amount was 370 ml, and the required time was 8 hours. The obtained liquid was filtered and washed to separate a precipitate and a solution. The analysis results of the filtrate are shown in Table 2. From Table 2, it can be seen that 98.9% of the rare earth elements and 88.0% of Co in the oxide powder have migrated into the filtrate.

Rare earth elements and cobalt can be selectively recovered by a precipitation generation method or a solvent extraction method performed by adding an aqueous solution of fluoride, oxalate, hydroxide, carbonate or the like to the filtrate.
Example 2
350 g (dry weight 175 g) of sludge containing grinding scraps derived in the process of manufacturing a rare earth-iron-boron sintered magnet having the same composition as in Example 1 was immersed in 500 ml of an aqueous ammonium sulfate solution having a concentration of 0.2 mol / l. Subsequently, oxidation treatment was performed at 70 ° C. for 12 hours while stirring and aeration, and the generated oxide powder was filtered and separated. Next, the total amount of the obtained oxide powder was dispersed in 200 ml of water, and a 5N aqueous nitric acid solution was added dropwise with stirring and aeration. The temperature was kept at 40-50 ° C. The pH gradually decreased from around 7 as the reaction progressed, and the dropping was terminated when the pH reached 3. The total dripping amount was 140 ml, and the required time was 8 hours. The precipitate was then filtered and the resulting precipitate was washed with water. The filtrate and water from which the precipitate was washed were mixed to make a nitric acid leaching filtrate of 1000 ml, and the filtrate was analyzed. The content of rare earth elements in the sludge was 31.5 g, the content of rare earth elements in the nitric acid leaching filtrate was 30.9 g, and the recovery rate of the rare earth elements was 98.0%.
Comparative Example 1
350 g (dry weight 175 g) of the same sludge used in Example 2 was not oxidized with an aqueous ammonium sulfate solution, and a 5N aqueous nitric acid solution was added dropwise with stirring and aeration. The temperature was kept at 40-50 ° C. The pH gradually decreased from around 11 as the reaction progressed, and the dropping was terminated when the pH reached 3. The total dripping amount was 300 ml, and the required time was 30 hours. The precipitate was then filtered and the resulting precipitate was washed with water. The filtrate and water from which the precipitate was washed were mixed to make a nitric acid leaching filtrate of 1000 ml, and the filtrate was analyzed. The content of rare earth elements in the sludge was 31.5 g, the content of rare earth elements in the nitric acid leach filtrate was 25.2 g, and the recovery rate of the rare earth elements was 80.0%.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the solid matter remaining rate and the immersion time depending on the type of MAS aqueous solution in the oxidation treatment performed in Test Examples 1 to 5.
FIG. 2 is a graph showing the relationship between the immersion temperature and time until the solids remaining rate becomes 10% or less in the oxidation treatment performed in Test Example 6.
FIG. 3 is a graph showing measurement results of X-ray diffraction of the oxide powder sample prepared in Test Example 6.
FIG. 4 is a graph showing the relationship between the concentration of ammonium sulfate and the dipping time until the solids remaining rate becomes 10% or less in the oxidation treatment performed in Test Examples 7 and 8.

Claims

Step (A) in which rare earth-transition metal alloy scrap is immersed in an aqueous ammonium salt solution of mineral acid, and a gas containing oxygen is circulated in the aqueous ammonium salt solution of mineral acid in step (A) to oxidize the scrap and oxidize the scrap And a step (B) for obtaining a precipitate containing a powder mainly composed of at least one of hydroxides, and a step (C) for separating the precipitate obtained in the step (B) from an aqueous ammonium salt solution of a mineral acid. And a step (D) of recovering rare earth elements from the precipitate separated in step (C), and a method for recovering useful elements from rare earth-transition metal alloy scrap.

The scrap is a scrap containing one or more alloys selected from the group consisting of a rare earth-iron alloy, a rare earth-cobalt alloy, and a rare earth-iron-cobalt alloy derived from a magnetic material manufacturing process. The recovery method according to claim 1.

The recovery method according to claim 1, wherein the aqueous ammonium salt solution of mineral acid is an aqueous solution of one or more salts selected from the group consisting of ammonium chloride, ammonium sulfate, ammonium nitrate and ammonium hydrogen fluoride.

The method according to claim 1, wherein the aqueous ammonium salt solution of mineral acid is an aqueous ammonium sulfate solution.

In step (A), the concentration of the aqueous solution of ammonium salt of mineral acid is 0.1 to 2.0 mol / l, and in step (B), the temperature of the aqueous solution of ammonium salt of mineral acid is at least 40 when oxidizing scrap. The recovery method according to claim 1, wherein the method is maintained at ˜90 ° C.

The recovery method according to claim 1, wherein the step (D) is performed by an acid leaching method using a mineral acid.