JP3763286B2

JP3763286B2 - How to recover high-quality rhodium powder

Info

Publication number: JP3763286B2
Application number: JP2002129514A
Authority: JP
Inventors: 秀昌永井; 高裕山田; 隆至橋川
Original assignee: Sumitomo Metal Mining Co Ltd
Current assignee: Sumitomo Metal Mining Co Ltd
Priority date: 2002-05-01
Filing date: 2002-05-01
Publication date: 2006-04-05
Anticipated expiration: 2022-05-01
Also published as: JP2003321717A

Description

【０００１】
【発明の属する技術分野】
本発明は、ニッケル・銅原料中の貴金属元素を回収する工程において発生する王水にも不溶の難溶性残渣から、白金族元素精製工程における微粉のロジウムブラックを経て、高純度のロジウム粉を回収する方法に関する。
【０００２】
【従来の技術】
白金族元素は空気中で酸化され難く、酸化された状態になったとしても還元されやすいという特徴があるため、古くは宝飾品類として取扱われてきた。また、近年では単体以外の用途が拡大され、触媒や電極などの化学工業に欠くことのできない存在となってきている。
【０００３】
白金族元素のなかでロジウム（Ｒｈ）は、装飾品メッキの用途以外にも、熱電対（Ｒ系）や電気接点、自動車排ガス触媒（三元触媒）等として広く使用されている。また、これらの用途におけるロジウムには、ますます高純度の品質が要求されている。
【０００４】
従来、ニッケル・銅原料からの貴金属元素回収工程で発生する難溶性残渣中のロジウムを回収するには、白金族元素を高濃度で含有する難溶性残渣を鉄粉と共に還元焙焼して可溶性とし、還元焙焼物から硫酸で鉄を浸出した後、その浸出残渣を塩酸と過酸化水素水で溶解し、得られた溶解液をロジウム精製工程に供給して処理していた。
【０００５】
ロジウム精製工程では、上記溶解液から不純物を分離した後、化学的手段又は電気的手段により還元してロジウムブラックを得、これを真空乾燥することで製品としていた。真空乾燥する方法としては、真空乾燥機にて１週間から２週間程度乾燥する方法や、ロジウムブラックを乾燥後に水素気流中にて還元焙焼する方法等が知られている。
【０００６】
【発明が解決しようとする課題】
上記した従来のロジウム回収方法においては、難溶性残渣を鉄粉と還元焙焼した後、鉄を硫酸で浸出除去するが、それでも多くの鉄が還元焙焼物中に残っている。そのため、還元焙焼物を塩酸と過酸化水素水で溶解した溶解液は、各種の面倒な化学的処理により更に鉄を除去しなければ、ロジウム精製工程にて処理することが困難であった。
【０００７】
また、従来のロジウム精製工程から産出したロジウムブラックは、真空乾燥することにより製品ロジウムとされるが、酸素やナトリウムの品位が高く、また粒子の大きさが非常に小さいため、酸化されやすいという問題があった。
【０００８】
一方、ロジウムブラックを乾燥後、水素気流中にて還元焙焼する方法は、乾燥時にロジウムが酸化することや、水素を取扱うため水素爆発の危険性があるという問題があった。また、得られる還元焙焼物が融着して固まるため製品化が困難である、またロジウムブラックに付着していたナトリウム分が高温脱ガス時に石英の反応管を侵食するという問題があった。
【０００９】
本発明は、このような従来の問題点に鑑み、白金族元素を高濃度で含有する難溶性残渣からロジウムを回収するにあたり、還元焙焼に用いた鉄を簡単に効率良く除去することができ、また、酸素等のガス成分やナトリウム等の不純物の含有量を低く抑え、酸化され難い程度の粒度で高純度のロジウム粉を、簡単な操作で且つ工業的実施に有利な方法で回収することを目的とする。
【００１０】
【課題を解決するための手段】
上記目的を達成するために、本願請求項１の発明は、白金族元素を含有する難溶性残渣を鉄と共に焙焼還元し、硫酸で鉄を浸出した後、浸出残渣を塩酸と過酸化水素水で溶解した溶解液をロジウム精製工程に供給し、得られたロジウムブラックからロジウム粉を回収する方法において、前記溶解液中の大部分の鉄をジブチルカルビトールで抽出し、その抽出残液をロジウム精製工程に供給することを特徴とする高品位ロジウム粉の回収方法を提供する。
【００１１】
本願請求項２の発明は、白金族元素を含有する難溶性残渣を鉄と共に焙焼還元し、硫酸で鉄を浸出した後、浸出残渣を塩酸と過酸化水素水で溶解した溶解液をロジウム精製工程に供給し、得られたロジウムブラックからロジウム粉を回収する方法において、前記ロジウムブラックを不活性ガス雰囲気中で第１段の加熱焙焼を行い、湿式粉砕した後、第１段の加熱焙焼よりも高温で更に第２段の加熱焙焼を行うことを特徴とする高品位ロジウム粉の回収方法を提供する。
【００１２】
上記本願請求項２の発明においては、前記第１段の加熱焙温度は６００〜８００℃、及び第２段の加熱焙焼温度は９００〜１１００℃であることが好ましい。また、前記第１段の加熱焙焼と第２段の加熱焙焼の間で、焙焼物を湿式粉砕し、ナトリウム及び塩素などの不純物を洗浄除去することが好ましい。
【００１３】
【発明の実施の形態】
白金族元素を高濃度に含有する難溶性残渣からロジウムを回収するには、まず鉄粉と混合して還元焙焼することにより可溶性の鉄合金とし、塩酸と過酸化水素水に溶解させる。この溶解液中にはロジウムと合金化していた鉄が多量に溶解しているため、そのままではロジウム精製工程で処理することは出来ない。
【００１４】
本発明方法では、この溶解液中の鉄をジブチルカルビトール（ＤＢＣ）で抽出することにより、大部分の鉄を分離除去することが可能である。ＤＢＣでの抽出条件としては、塩酸濃度４〜６Ｎ、酸化還元電位８００〜９００ｍＶ以上であることが、鉄の抽出率が高く望ましい。また、ＤＢＣは金も抽出するため、同時に除去することが出来る。この前処理を行うことにより、ロジウム精製工程にて処理可能な組成の液を簡単に得ることが出来る。
【００１５】
また、本発明方法においては、ロジウム精製工程で得られたロジウムブラックを、湿潤な状態で又は真空乾燥した後アルミナボートに詰め、窒素やアルゴン等の不活性ガス雰囲気中で第１段の加熱焙焼を行い、次に第１段の加熱焙焼よりも高温で更に第２段の加熱焙焼を行う。このとき、第１段の加熱焙焼と第２段の加熱焙焼の間で焙焼物を湿式粉砕し、付着していたナトリウム及び塩素などの不純物を洗浄除去することが好ましい。
【００１６】
第１段の加熱焙焼では焙焼温度を６００〜８００℃とし、ロジウムの微粒子を凝集させ粒成長させる。焙焼温度が６００℃未満では粒成長が起こらず活性なロジウム微粉となり、酸化されやすいためハンドリングに問題が生じる。また、焙焼温度が８００℃を超えると過剰な粒成長が起こると共に、ナトリウム分の揮発が始まり、焙焼時に使用している石英の反応管を侵食する恐れがある。この焙焼後は、長時間かけて徐冷することで再酸化を防止することが好ましい。これらの操作により、従来の問題点であった真空乾燥前後での空気酸化を抑制することが可能である。
【００１７】
上記第１段の焙焼後、湿式にて粉砕することで、凝集や焼結により粒径がある程度大きくなったものを解砕すると共に、付着していたナトリウム及び塩素などの不純物を洗浄除去する。この湿式粉砕による洗浄操作は何回も繰り返すほど効果が高く、通常は３回程度が好ましい。尚、ナトリウム及び塩素などの不純物を除去するには、第１段の焙焼前に洗浄しても粒径が細かく凝集したロジウム粒子内部に取り込まれているため十分除去できず、後の第２段の焙焼後に湿式粉砕して除去すると、更に乾燥工程を加える必要があるため好ましくない。
【００１８】
湿式粉砕により得られた粉砕物は、第２段の加熱焙焼を行うことにより、脱ガスと乾燥を行う。この際の焙焼温度は９００〜１１００℃が好ましい。９００℃未満の温度では脱ガスが不十分であり、また１１００℃を超えると焼結を起こすため後の取り扱いが困難となる。焙焼後は、長時間かけて徐冷することで再酸化を防止することが好ましい。尚、第２段の加熱焙焼における雰囲気は、特に限定されるものではないが、窒素やアルゴン等の不活性ガスが好ましい。
【００１９】
上記第１段及び第２段の焙焼温度を決定するにあたっては、ロジウムの酸化反応が重要である。即ち、ロジウムの酸化反応は下記化学式１であり、逆に酸素の解離反応は下記化学式２又は３であると考えられる。
【００２０】
【化１】
Ｒｈ＋Ｏ_２→ＲｈＯ_２
【００２１】
【化２】
ＲｈＯ_２→ＲｈＯ＋１／２Ｏ_２
【００２２】
【化３】
ＲｈＯ→Ｒｈ＋１／２Ｏ_２
【００２３】
ロジウム精製工程より得たロジウムブラックは、相当量の気体を含んでおり、その表面は必ず酸化されている。ロジウムブラックを真空中又は酸素中で加熱していくと更に酸化が進み、ある一定温度で急な重量増加を伴う酸化ロジウムの生成が起こる。
【００２４】
また、文献「白金族と工業的利用」（産業図書株式会社刊）によれば、「ロジウム塩を水素気流中で加熱還元して得たロジウムは、水素を吸収しているから、空気中に出せば空気中の酸素と吸収された水素とは触媒ロジウムの助けによって化合し、水分をロジウムの粒子面に凝縮生成している。もし水素で還元した後、空気のないところに置けば水分は生じない。つまり酸化しないといえる。」とある。
【００２５】
本発明のロジウムブラックからロジウム粉を回収する工程は、このようなロジウムの酸化及び分解の挙動に基づいて、酸化ロジウムが６００〜１１００℃まで加熱されると酸素を解離し、これを不活性ガス雰囲気中で徐冷すると再酸化が起こらない反応を利用して、２段階に温度を変えて加熱焙焼することによって、粒成長を促進すると共に、酸素及び塩素を分離するものである。
【００２６】
即ち、ロジウムブラックを不活性ガス雰囲気中にて６００〜８００℃で２時間程度焙焼し、徐冷の後、好ましくは、得られた焙焼物を湿式粉砕して解砕すると共に、ロジウムブラックに付着して持ち込まれたナトリウム等を除去する。湿式粉砕したものは９００〜１０００℃にて再度焙焼することにより、更に脱ガスを行い、酸素品位の低いロジウム粉を得ることができる。
【００２７】
【実施例】
実施例１
難溶性残渣の溶解液から、共存する鉄を抽出により除去する基礎試験を実施した。原料としては、下記表１に示す組成の難溶性残渣を使用した。
【００２８】
【表１】

【００２９】
この難溶性残渣５０ｇと鉄粉１５０ｇをナイロン袋に入れてシール封印し、良く混合した後、混合粉を黒鉛ルツボに装入した。この黒鉛ルツボを小型の電気炉にて１０００℃まで加熱し、昇温後２時間保持した後、放冷した。
【００３０】
取り出した還元焙焼物をステンレスの乳鉢にて細かく粉砕し、１.５リットルの純水に薄硫酸（７９％）を０.２５リットル加えた溶液に加え、余分な鉄分を溶解させた。鉄溶解液（液量２リットル）の分析結果を下記表２に示す。添加した１５０ｇの鉄粉の約６割を除去でき、ロジウムのロスは殆どなかった。
【００３１】
【表２】

【００３２】
続いて、鉄溶解後の溶解残渣をビーカーに装入し、これに濃塩酸１リットルを添加し、７０℃まで昇温した後、過酸化水素水０.３リットルを徐々に添加した。このとき液温は１００℃近くまで上昇した。過酸化水素水の添加後は冷却し、溶解残渣を濾過した。
【００３３】
得られた溶解残渣は２ｇであった。得られた溶解液（液量１.６リットル）の組成を下記表３に示す。ロジウム浸出率は約９９％であり、Ｉｒ及びＲｕ等の浸出率も９５％を越えるという良好な結果を得た。
【００３４】
【表３】

【００３５】
硫酸による鉄溶解で取り切れなかった鉄はロジウム等と合金化しているものと考えられ、上記溶解液中の鉄濃度は非常に高い。これを更に除去するために、溶媒抽出を実施した。
【００３６】
即ち、溶解残渣を濾過した溶解液に、濃塩酸を０.５リットル添加することで塩酸濃度を６Ｎとした後、再度昇温し、過酸化水素を添加することで酸化処理を実施した。このときの酸化還元電位は約９００ｍＶとなった。
【００３７】
次に、酸化処理後の溶解液を５０ｍｌ採取し、１５０ｍｌのＤＢＣと混合し、撹拌することで鉄を抽出分離した。この操作を３回繰り返した後、得られた抽残液（４８ｍｌ）の分析結果を下記表４に示す。鉄及び金ともに十分抽出できており、ロジウム等のロスは比較的少なく、良好な結果であった。
【００３８】
【表４】

【００３９】
実施例２
難溶性残渣から高濃度の白金族溶解液を得る実施例１のスケールアップ試験を行った。下記表５に示す組成の難溶性残渣２.５ｋｇと、鉄粉７.５ｋｇをロッドミルにて混合し、混合粉を黒鉛ルツボに入れて蓋をし、電気炉にて１０００℃まで加熱した。昇温後３時間保持し、その後１５時間程度放冷した。この還元焙焼を３バッチ行い、合計３０ｋｇの焙焼物を確保し、これを全量粉砕機にて粉砕した。
【００４０】
【表５】

【００４１】
次に、脱鉄するために希硫酸にて溶解した。即ち、溶解槽に水１２０リットルと薄硫酸（７０％）４０リットルを張り、得られた粉砕物を徐々に添加した。こうして粉砕物３０ｋｇを装入した後、２時間撹拌した。鉄溶解液（液量３００リットル）の分析結果を下記表６に示す。添加した鉄２２.５ｋｇの約６０％（１３.７ｋｇ）を除去できた。尚、鉄溶解後の溶解残渣は容易に空気酸化するため、濾過後は直ちに槽内に戻し、湿潤な状態を保った。
【００４２】
【表６】

【００４３】
槽内に脱鉄後の溶解残渣を装入した後、濃塩酸１５０リットルを添加し、撹拌しながら７０℃まで昇温した後、過酸化水素水３０リットルを徐々に添加した。このとき液温は１００℃近くまで上昇した。過酸化水素水の添加後は冷却し、溶解残渣を濾過した。得られた溶解液（液量１５０リットル）の分析結果を下記表７に示す。ロジウム浸出率は約９６％であり、Ｉｒは８７％及びＲｕは８３％の浸出率であり、実施例１と同様の良好な結果が得られた。
【００４４】
【表７】

【００４５】
表７に示す組成の溶解液には、前工程で脱鉄したものの約６０ｇ／リットルの鉄を含んでいる。この鉄を除去し、ロジウム精製工程にて処理可能とするために溶媒抽出による脱鉄を実施した。溶媒はＤＢＣを使用し、ミキサセトラにて処理を実施した。得られた鉄抽出後の抽残液（３２０リットル）の分析結果を下記表８に示す。溶解液中の鉄は、６０ｇ／リットルから０.０３ｇ／リットルまで除去することができた。
【００４６】
【表８】

【００４７】
実施例３
真空乾燥したロジウムブラック各１０ｇを、アルゴン気流中にて、６００℃、７００℃、８００℃、９００℃までそれぞれ昇温し、１時間保持した後、徐冷した。得られた各焙焼物について、酸素、ナトリウム、塩素の分析結果、並びに灼熱減量、比表面積の測定結果を下記表９に示す。また、真空乾燥品についても併せて結果を示す。
【００４８】
【表９】

【００４９】
上記焙焼によりナトリウムと塩素については若干減少し、特に酸素が大幅に減少した。酸素品位は、焙焼前の真空乾燥品では１.９０％と高いが、焙焼温度に反比例するように減少し、焙焼物では０.０４〜０.６５％の間であった。これは、焙焼温度が高いほどロジウムからの酸素の解離反応が進み、また高温ほど粒成長が進むことで酸化が防止されるためである。しかし、９００℃で焙焼したものは過剰に粒成長し、硬く焼結してしまったため、酸素品位は低いものの製品とすることは困難であった。
【００５０】
また、比較のために、同じロジウムブラック１０ｇを大気中にて９００℃で焙焼したところ、焙焼物の酸素品位は１２.０％と非常に高く、且つ硬く焼結してしまったため、比表面積などの測定は不可能であった。
【００５１】
実施例４
ロジウムブラックの焙焼物について、湿式にて粉砕を実施し、洗浄によるナトリウムの除去率を求めた。即ち、ロジウムブラック１０ｇをアルゴン雰囲気中にて６００℃及び８００℃で焙焼した後、その粉砕物についてナトリウムを分析し、粉砕前の焙焼物のナトリウム濃度と共に下記表１０に示す。
【００５２】
【表１０】

【００５３】
湿式粉砕によるナトリウムの除去は、焙焼温度により若干差があり、６００℃よりも８００℃で焙焼した焙焼物の方が高いナトリウム除去率が得られた。
【００５４】
実施例５
ロジウムブラックを９００℃以上で焙焼すると硬く固まってしまうため、二段階に温度を変化させて焙焼を行った。焙焼時の雰囲気は窒素、炭酸ガス、アルゴンガス、大気と窒素の混合気の４種類について実施した。これらの２段階焙焼により得られた焙焼物の酸素品位を下記表１１に示す。
【００５５】
【表１１】

【００５６】
この結果から分るように、窒素あるいはアルゴン雰囲気において、第１段の焙焼温度を８００℃とし、第２段の焙焼温度を１０００℃としたとき、凝集が少なく比較的小さい粒径を維持しながら、酸素品位も低い良好な焙焼物が得られた。
【００５７】
次に、ロジウムブラックを、アルゴンガス雰囲気中で焙焼する際に、８００℃と１０００℃で２段階焙焼した（湿式粉砕無し）試料１と、８００℃と１０００℃で２段階焙焼し、その間に湿式粉砕を行った試料２について、それぞれ酸素品位を求めた。また、比較例として、同じロジウムブラックを真空乾燥した試料３についても、同様に酸素品位を求め、これらの結果を下記表１２に示す。
【００５８】
【表１２】

【００５９】
表１２の結果から、真空乾燥品の試料３は、乾燥後の取り出し時に空気中で酸化されるため、酸素量が非常に高くなっている。これに対し、アルゴン気流中で焙焼した試料１及び２は、いずれも１００ｐｐｍと低い酸素品位を示した。
【００６０】
また、２段階焙焼で湿式粉砕無しの試料１のケイ素品位が高いのは、ロジウムブラックに付着したナトリウムが１０００℃焙焼時に揮発することにより、石英の反応管が侵食され、ケイ酸ソーダが製品に混入したものである。このため、ナトリウム品位については真空乾燥品よりも低下している。
【００６１】
２段階焙焼で間に湿式粉砕した試料２では、湿式粉砕の効果によりナトリウムが低減できており、このためケイ素の混入も低く抑えられている。湿式粉砕は同時に塩素の低減についても効果が見られた。最終的な純度は、試料２の２段階焙焼品（８００℃＋１０００℃、湿式粉砕有り）が９９.９５％以上と最も高く、次いで試料１の２段階焙焼品（８００℃＋１０００℃、湿式粉砕無し）、試料３の真空乾燥品の順であった。
【００６２】
【発明の効果】
本発明によれば、白金族元素を含有する難溶性残渣からロジウムを回収するにあたり、還元焙焼に用いた鉄を溶媒抽出により簡単に効率良く除去して、ロジウム精製工程に供給可能な溶解液を得ることができる。また、ロジウム精製工程で得られたロジウムブラックから、簡単な操作で且つ工業的実施に有利な方法によって、酸素等のガス成分やナトリウム等の不純物の含有量が低く、酸化され難い程度の粒度で高純度のロジウム粉を効率良く回収することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention recovers high-purity rhodium powder from the hardly soluble residue insoluble in aqua regia generated in the process of recovering precious metal elements in nickel and copper raw materials, through fine powder of rhodium black in the platinum group element refining process On how to do.
[0002]
[Prior art]
Since platinum group elements are not easily oxidized in the air and are easily reduced even when they are in an oxidized state, they have been treated as jewelry. In recent years, applications other than simple substances have been expanded and become indispensable to the chemical industry such as catalysts and electrodes.
[0003]
Among platinum group elements, rhodium (Rh) is widely used as a thermocouple (R system), an electrical contact, an automobile exhaust gas catalyst (three-way catalyst), etc., in addition to the use for decorative plating. In addition, rhodium in these applications is increasingly required to have high purity quality.
[0004]
Conventionally, in order to recover rhodium in poorly soluble residues generated in the process of recovering precious metal elements from nickel / copper raw materials, a poorly soluble residue containing a high concentration of platinum group elements is reduced and roasted together with iron powder to make it soluble. After leaching iron from the reduced roasted product with sulfuric acid, the leaching residue was dissolved with hydrochloric acid and hydrogen peroxide, and the resulting solution was supplied to the rhodium purification step for treatment.
[0005]
In the rhodium purification step, impurities were separated from the solution, and then reduced by chemical means or electrical means to obtain rhodium black, which was dried in vacuum to obtain a product. As a method of vacuum drying, a method of drying for about 1 to 2 weeks in a vacuum dryer, a method of reducing and roasting rhodium black in a hydrogen stream after drying, and the like are known.
[0006]
[Problems to be solved by the invention]
In the conventional rhodium recovery method described above, after the poorly soluble residue is reduced and roasted with iron powder, the iron is leached and removed with sulfuric acid, but still a lot of iron remains in the reduced roasted product. Therefore, it is difficult to treat the solution obtained by dissolving the reduced roasted product with hydrochloric acid and hydrogen peroxide solution in the rhodium purification step unless iron is further removed by various troublesome chemical treatments.
[0007]
In addition, rhodium black produced from the conventional rhodium refining process is made into product rhodium by vacuum drying, but it has high oxygen and sodium quality, and the size of the particles is very small, so it is prone to oxidation. was there.
[0008]
On the other hand, after the rhodium black is dried, the reduction roasting in a hydrogen stream has a problem that rhodium is oxidized at the time of drying and there is a risk of hydrogen explosion due to handling of hydrogen. In addition, there is a problem that the resulting reduced roasted product is hardened by fusing and is difficult to produce, and the sodium content attached to the rhodium black corrodes the quartz reaction tube during high temperature degassing.
[0009]
In view of such conventional problems, the present invention can easily and efficiently remove iron used for reduction roasting when recovering rhodium from a sparingly soluble residue containing a platinum group element at a high concentration. In addition, the content of gas components such as oxygen and impurities such as sodium should be kept low, and high-purity rhodium powder having a particle size that is difficult to oxidize can be recovered by a simple operation and in an advantageous manner for industrial implementation. With the goal.
[0010]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the invention of claim 1 of the present application is to reduce the insoluble residue containing a platinum group element together with iron, leaching the iron with sulfuric acid, and then leaching the leaching residue with hydrochloric acid and hydrogen peroxide solution. In the method of supplying the dissolved solution dissolved in the rhodium purification step and recovering the rhodium powder from the obtained rhodium black, most of the iron in the dissolved solution is extracted with dibutyl carbitol, and the extraction residue is rhodium. Provided is a method for recovering high-grade rhodium powder, which is supplied to a purification process.
[0011]
In the invention of claim 2, the poorly soluble residue containing the platinum group element is roasted and reduced together with iron, and after leaching iron with sulfuric acid, the solution obtained by dissolving the leached residue with hydrochloric acid and hydrogen peroxide solution is subjected to rhodium purification. In the method of recovering rhodium powder from the obtained rhodium black supplied to the process, the rhodium black is heated and roasted in the first stage in an inert gas atmosphere, wet pulverized, and then heated in the first stage. Provided is a method for recovering high-grade rhodium powder, characterized by further performing second-stage heating and roasting at a higher temperature than firing.
[0012]
In the invention of claim 2, the first stage heating roasting temperature is preferably 600 to 800 ° C., and the second stage heating roasting temperature is preferably 900 to 1100 ° C. Moreover, it is preferable to wet-grind the roasted material between the first stage heating roasting and the second stage heating roasting to wash away impurities such as sodium and chlorine.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In order to recover rhodium from a poorly soluble residue containing a platinum group element at a high concentration, first, it is mixed with iron powder and reduced to roasted to form a soluble iron alloy, which is dissolved in hydrochloric acid and hydrogen peroxide solution. Since a large amount of iron alloyed with rhodium is dissolved in this solution, it cannot be treated in the rhodium purification process as it is.
[0014]
In the method of the present invention, most of iron can be separated and removed by extracting iron in the solution with dibutyl carbitol (DBC). As extraction conditions in DBC, a hydrochloric acid concentration of 4 to 6 N and an oxidation-reduction potential of 800 to 900 mV or higher are desirable because of a high iron extraction rate. Further, since DBC also extracts gold, it can be removed at the same time. By performing this pretreatment, a liquid having a composition that can be treated in the rhodium purification step can be easily obtained.
[0015]
Further, in the method of the present invention, the rhodium black obtained in the rhodium purification step is packed in an alumina boat after being wet or vacuum dried, and heated in the first stage in an inert gas atmosphere such as nitrogen or argon. Baking is then performed, followed by a second stage of heating and roasting at a higher temperature than the first stage of heating and baking. At this time, it is preferable that the baked product is wet pulverized between the first stage heating roasting and the second stage heating roasting to wash away impurities such as sodium and chlorine adhering thereto.
[0016]
In the first stage of heating and roasting, the roasting temperature is set to 600 to 800 ° C., and rhodium fine particles are aggregated to grow grains. When the roasting temperature is less than 600 ° C., grain growth does not occur and the active rhodium powder is formed, which is easily oxidized and causes a problem in handling. Further, when the roasting temperature exceeds 800 ° C., excessive grain growth occurs and the volatilization of sodium content starts, which may erode the quartz reaction tube used during roasting. After this roasting, it is preferable to prevent reoxidation by slow cooling over a long period of time. By these operations, it is possible to suppress air oxidation before and after vacuum drying, which was a conventional problem.
[0017]
After the first stage roasting, it is pulverized in a wet manner to crush the particles whose particle size has increased to some extent due to agglomeration and sintering, and to wash away impurities such as sodium and chlorine that have adhered. . The washing operation by wet pulverization is more effective as it is repeated many times, and usually about 3 times is preferable. Incidentally, in order to remove impurities such as sodium and chlorine, even after washing before the first stage of roasting, it cannot be sufficiently removed because the particles are taken into the agglomerated rhodium particles. If it is removed by wet pulverization after roasting of the plate, it is not preferable because a drying step needs to be added.
[0018]
The pulverized product obtained by wet pulverization is degassed and dried by performing second-stage heating and roasting. The roasting temperature at this time is preferably 900 to 1100 ° C. Degassing is insufficient at temperatures below 900 ° C., and sintering at temperatures above 1100 ° C. makes subsequent handling difficult. After roasting, it is preferable to prevent reoxidation by slow cooling over a long period of time. The atmosphere in the second stage heating and roasting is not particularly limited, but an inert gas such as nitrogen or argon is preferable.
[0019]
In determining the roasting temperatures of the first and second stages, the rhodium oxidation reaction is important. That is, it is considered that the oxidation reaction of rhodium is represented by the following chemical formula 1, and the dissociation reaction of oxygen is represented by the following chemical formula 2 or 3.
[0020]
[Chemical 1]
Rh + O ₂ → RhO ₂
[0021]
[Chemical 2]
RhO ₂ → RhO + 1 / 2O ₂
[0022]
[Chemical 3]
RhO → Rh + 1 / 2O ₂
[0023]
Rhodium black obtained from the rhodium purification step contains a considerable amount of gas, and its surface is necessarily oxidized. When rhodium black is heated in a vacuum or in oxygen, the oxidation further proceeds, and rhodium oxide is generated with a sudden weight increase at a certain temperature.
[0024]
According to the document “Platinum group and industrial use” (published by Sangyo Tosho Co., Ltd.), “Rhodium obtained by heating and reducing rhodium salt in a hydrogen stream absorbs hydrogen. The oxygen in the air and the absorbed hydrogen are combined with the help of the catalyst rhodium to condense the moisture onto the rhodium particle surface.If it is placed in a place without air after being reduced with hydrogen, It does not occur, that is, it cannot be oxidized. "
[0025]
The process of recovering the rhodium powder from the rhodium black of the present invention is based on the behavior of rhodium oxidation and decomposition. When the rhodium oxide is heated to 600 to 1100 ° C., oxygen is dissociated, and this is converted into an inert gas. Utilizing a reaction in which re-oxidation does not occur when it is gradually cooled in an atmosphere, it is heated and roasted by changing the temperature in two stages, thereby promoting grain growth and separating oxygen and chlorine.
[0026]
That is, rhodium black is roasted at 600 to 800 ° C. for about 2 hours in an inert gas atmosphere, and after slow cooling, the obtained roast is preferably crushed by wet pulverization, Remove sodium and other adhering substances. What was wet-pulverized can be further degassed by roasting again at 900 to 1000 ° C. to obtain rhodium powder having a low oxygen quality.
[0027]
【Example】
Example 1
A basic test was conducted to remove the coexisting iron from the solution of the hardly soluble residue by extraction. As the raw material, a hardly soluble residue having the composition shown in Table 1 below was used.
[0028]
[Table 1]

[0029]
50 g of this hardly soluble residue and 150 g of iron powder were placed in a nylon bag, sealed and mixed well, and then the mixed powder was charged into a graphite crucible. The graphite crucible was heated to 1000 ° C. in a small electric furnace, held for 2 hours after being heated, and then allowed to cool.
[0030]
The reduced roasted product taken out was finely pulverized in a stainless mortar and added to a solution obtained by adding 0.25 liters of thin sulfuric acid (79%) to 1.5 liters of pure water to dissolve excess iron. The analysis results of the iron solution (2 liters) are shown in Table 2 below. About 60% of the added 150 g of iron powder could be removed, and there was almost no loss of rhodium.
[0031]
[Table 2]

[0032]
Subsequently, the dissolution residue after iron dissolution was placed in a beaker, 1 liter of concentrated hydrochloric acid was added thereto, the temperature was raised to 70 ° C., and 0.3 liter of hydrogen peroxide solution was gradually added. At this time, the liquid temperature rose to nearly 100 ° C. After the addition of aqueous hydrogen peroxide, the mixture was cooled and the dissolved residue was filtered.
[0033]
The dissolution residue obtained was 2 g. The composition of the resulting solution (liquid volume 1.6 liter) is shown in Table 3 below. The rhodium leaching rate was about 99%, and the leaching rates of Ir, Ru and the like exceeded 95%, and good results were obtained.
[0034]
[Table 3]

[0035]
Iron that could not be removed by dissolution of iron with sulfuric acid is considered to be alloyed with rhodium and the like, and the concentration of iron in the solution is very high. To further remove this, solvent extraction was performed.
[0036]
That is, after adding 0.5 liters of concentrated hydrochloric acid to the solution obtained by filtering the dissolution residue, the hydrochloric acid concentration was adjusted to 6N, and then the temperature was raised again, and the oxidation treatment was performed by adding hydrogen peroxide. The oxidation-reduction potential at this time was about 900 mV.
[0037]
Next, 50 ml of the solution after the oxidation treatment was collected, mixed with 150 ml of DBC, and stirred to extract and separate iron. After repeating this operation three times, the analysis results of the obtained extraction residual liquid (48 ml) are shown in Table 4 below. Both iron and gold were sufficiently extracted, and the loss of rhodium and the like was relatively small, showing good results.
[0038]
[Table 4]

[0039]
Example 2
The scale-up test of Example 1 which obtains a high concentration platinum group solution from a hardly soluble residue was performed. 2.5 kg of poorly soluble residue having the composition shown in Table 5 below and 7.5 kg of iron powder were mixed in a rod mill, the mixed powder was put in a graphite crucible, covered, and heated to 1000 ° C. in an electric furnace. The temperature was raised for 3 hours and then allowed to cool for about 15 hours. Three batches of this reduction roasting were performed to secure a total of 30 kg of roasted material, and this was pulverized in a whole pulverizer.
[0040]
[Table 5]

[0041]
Next, it was dissolved with dilute sulfuric acid to remove iron. That is, 120 liters of water and 40 liters of thin sulfuric acid (70%) were added to the dissolution tank, and the obtained pulverized product was gradually added. After charging 30 kg of the pulverized product in this way, the mixture was stirred for 2 hours. Table 6 below shows the analysis results of the iron solution (liquid volume: 300 liters). Approximately 60% (13.7 kg) of 22.5 kg of added iron could be removed. Since the dissolution residue after iron dissolution easily oxidizes in air, it was immediately returned to the tank after filtration and kept moist.
[0042]
[Table 6]

[0043]
After charging the dissolution residue after deironing into the tank, 150 liters of concentrated hydrochloric acid was added, the temperature was raised to 70 ° C. with stirring, and 30 liters of hydrogen peroxide was gradually added. At this time, the liquid temperature rose to nearly 100 ° C. After the addition of aqueous hydrogen peroxide, the mixture was cooled and the dissolved residue was filtered. The analysis results of the resulting solution (liquid amount 150 liters) are shown in Table 7 below. The rhodium leaching rate was about 96%, Ir was 87%, and Ru was 83%. The same good results as in Example 1 were obtained.
[0044]
[Table 7]

[0045]
The solution having the composition shown in Table 7 contains about 60 g / liter of iron which has been deironed in the previous step. In order to remove this iron and make it possible to process in the rhodium purification step, deironation by solvent extraction was performed. DBC was used as the solvent, and the treatment was carried out with mixer setra. Table 8 below shows the analysis results of the extracted extraction liquid (320 liters) after iron extraction. Iron in the solution could be removed from 60 g / liter to 0.03 g / liter.
[0046]
[Table 8]

[0047]
Example 3
10 g of each vacuum dried rhodium black was heated to 600 ° C., 700 ° C., 800 ° C., and 900 ° C. in an argon stream, held for 1 hour, and then gradually cooled. Table 9 below shows the analysis results of oxygen, sodium, and chlorine, and the measurement results of loss on ignition and specific surface area of the obtained roasted products. The results are also shown for the vacuum-dried product.
[0048]
[Table 9]

[0049]
The roasting slightly reduced sodium and chlorine, especially oxygen. The oxygen grade was as high as 1.90% in the vacuum-dried product before roasting, but decreased to be inversely proportional to the roasting temperature, and between 0.04 and 0.65% in the roasted product. This is because the higher the roasting temperature, the more the oxygen dissociation reaction from rhodium proceeds, and the higher the temperature, the more the grain growth proceeds, thereby preventing oxidation. However, what was roasted at 900 ° C. had excessive grain growth and was hard sintered, so that it was difficult to obtain a product with low oxygen quality.
[0050]
For comparison, when 10 g of the same rhodium black was roasted at 900 ° C. in the air, the oxygen quality of the roasted product was very high at 12.0% and was hard and sintered. Measurement such as was impossible.
[0051]
Example 4
The rhodium black baked product was pulverized in a wet manner, and the removal rate of sodium by washing was determined. That is, after 10g of rhodium black was roasted at 600 ° C and 800 ° C in an argon atmosphere, sodium was analyzed for the pulverized product, and the sodium concentration of the baked product before pulverization is shown in Table 10 below.
[0052]
[Table 10]

[0053]
The removal of sodium by wet pulverization is slightly different depending on the roasting temperature, and a higher sodium removal rate was obtained with the roasted product that was roasted at 800 ° C than at 600 ° C.
[0054]
Example 5
When rhodium black was roasted at 900 ° C. or higher, it hardened and solidified, and thus roasting was performed by changing the temperature in two stages. The atmosphere at the time of roasting was implemented about four types, nitrogen, a carbon dioxide gas, argon gas, and the air-nitrogen mixture. Table 11 below shows the oxygen quality of the roasted product obtained by these two-stage roasting.
[0055]
[Table 11]

[0056]
As can be seen from this result, in a nitrogen or argon atmosphere, when the first stage baking temperature is 800 ° C. and the second stage baking temperature is 1000 ° C., there is little aggregation and a relatively small particle size is maintained. However, a good roasted product with low oxygen quality was obtained.
[0057]
Next, when rhodium black was roasted in an argon gas atmosphere, it was roasted at 800 ° C. and 1000 ° C. in two stages (no wet pulverization) Sample 1, and at 800 ° C. and 1000 ° C. in two stages. In the meantime, oxygen quality was determined for each sample 2 that was wet pulverized. As a comparative example, oxygen quality was similarly determined for Sample 3 obtained by vacuum drying the same rhodium black, and the results are shown in Table 12 below.
[0058]
[Table 12]

[0059]
From the results shown in Table 12, since the sample 3 of the vacuum-dried product is oxidized in the air when taken out after drying, the amount of oxygen is very high. In contrast, Samples 1 and 2 that were roasted in an argon stream both showed low oxygen quality of 100 ppm.
[0060]
In addition, the silicon quality of sample 1 which is two-stage roasting and not wet pulverized is high because the sodium adhering to rhodium black volatilizes at the time of roasting at 1000 ° C., and the quartz reaction tube is eroded, soda silicate It is mixed in the product. For this reason, the sodium quality is lower than that of the vacuum-dried product.
[0061]
In the sample 2 that was wet pulverized in the two-stage roasting, sodium could be reduced by the effect of the wet pulverization, and therefore, silicon contamination was also kept low. Wet pulverization was also effective in reducing chlorine. The final purity of the two-stage roasted product of sample 2 (800 ° C. + 1000 ° C., with wet pulverization) is 99.95% or higher, followed by the two-stage roasted product of sample 1 (800 ° C. + 1000 ° C., wet) No pulverization), followed by the vacuum dried product of Sample 3.
[0062]
【The invention's effect】
According to the present invention, when recovering rhodium from a sparingly soluble residue containing a platinum group element, the iron used in the reduction roasting can be easily and efficiently removed by solvent extraction and can be supplied to the rhodium purification step. Can be obtained. In addition, from the rhodium black obtained in the rhodium purification step, the particle content is such that the content of gas components such as oxygen and impurities such as sodium is low and is not easily oxidized by a simple operation and a method advantageous for industrial implementation. High-purity rhodium powder can be efficiently recovered.

Claims

A poorly soluble residue containing a platinum group element was reduced and roasted together with iron, iron was leached with sulfuric acid, and then a solution obtained by dissolving the leached residue with hydrochloric acid and hydrogen peroxide was supplied to the rhodium purification step. In the method for recovering rhodium powder from rhodium black, the recovery of high-grade rhodium powder characterized in that most of the iron in the solution is extracted with dibutyl carbitol and the extraction residue is supplied to the rhodium purification step. Method.

A poorly soluble residue containing a platinum group element was reduced and roasted together with iron, iron was leached with sulfuric acid, and then a solution obtained by dissolving the leached residue with hydrochloric acid and hydrogen peroxide was supplied to the rhodium purification step. In the method of recovering rhodium powder from rhodium black, the rhodium black is first heated and roasted in an inert gas atmosphere, and further heated at a higher temperature than the first heat roasting. A method for recovering high-grade rhodium powder, characterized in that

The method for recovering high-grade rhodium powder according to claim 2, wherein the heating roasting temperature of the first stage is 600 to 800 ° C, and the heating roasting temperature of the second stage is 900 to 1100 ° C.

The roasted material is wet-pulverized between the first-stage heating roasting and the second-stage heating roasting to clean and remove impurities such as sodium and chlorine. Of high quality rhodium powder.