JP2004218012A

JP2004218012A - Method for recovering noble metal in platinum group

Info

Publication number: JP2004218012A
Application number: JP2003007522A
Authority: JP
Inventors: Tomonori Tawara; 朋典田原
Original assignee: Asahi Pretec Corp
Current assignee: Asahi Pretec Corp
Priority date: 2003-01-15
Filing date: 2003-01-15
Publication date: 2004-08-05
Anticipated expiration: 2023-01-15
Also published as: JP4274802B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering a noble metal with which cost effectiveness is improved by reducing the consumption of liquid chemical and the treated amount of waste solution from catalyst layer depositing alumina layer containing the noble metal in a platinum group on a ferritic stainless steel surface, and by making an apparatus compact. <P>SOLUTION: The stainless steel surface is dissolved by dipping the noble metal-containing catalyst layer into hydrochloric acid having 5.0-10.0 N concentration at 50-90°C for 10-30 min. The catalyst layer containing the noble metal is detached and recovered from the stainless steel surface with the erosion thereof and the development of hydrogen gas in this way. The noble metal contained in this catalyst layer is dissolved with the hydrochloric acid or aqua regia containing chlorine, and the noble metal is recovered from the obtained dissolved solution in this method. Further, in the process for applying the noble metal-containing catalyst layer into the hydrochloric acid and/or a process for washing after dipping, a method for applying an ultrasonic irradiation to the catalyst layer, is performed, too. Further, a process for recovering the noble metal with an electrolysis from the dissolved solution obtained by dissolving the noble metal-contained detached catalyst layer with the hydrochloric acid or the aqua regia containing the chlorine, is performed, too. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は使用済みのフェライト系ステンレス鋼の表面に、白金族の貴金属を含むアルミナ層を担持せしめた触媒層から、貴金属を回収する方法に関するものである。更に詳しく述べると、この触媒層を特定範囲の濃度及び温度の塩酸に浸漬することにより、触媒層を担持するステンレス鋼の表面の腐食と発生した水素ガスによって、触媒層を剥離・回収した後貴金属を塩素を含む塩酸等で溶解し、電気分解法等によって貴金属を回収する方法である。
【０００２】
【従来の技術】
現在貴金属含有触媒は化学工業や自動車排気ガス処理等に広く用いられている。貴金属は高価且つ有限でありまた資源保全の観点からも、廃触媒等からの貴金属の回収は重要な課題である。このため以前から研究され多くの回収方法が開示されている。
【０００３】
自動車排気ガス処理に用いられている触媒には、セラミックベースに担持させた触媒と金属ベースに担持させた触媒がある。金属ベースに担持させた触媒の担体は、主としてフェライト系ステンレス鋼（Ｆｅ−Ｃｒが主成分）の波箔と平箔を交互に巻いて円筒形としたハニカム構造体からなり、その表面に貴金属を含有させたアルミナがコーティングされている。このハニカム体は更に金属製の円筒形の外筒に装入して使用される。
【０００４】
金属ベースに担持させた貴金属触媒から貴金属を回収する方法としては、この触媒をアルカリ溶液中で熱処理して、貴金属を担持したアルミナを剥離、回収した後にアルミナ層を強酸処理して、貴金属を回収する方法が開示されている（例えば、特許文献１参照。）。
【０００５】
また、金属ベースに担持させた貴金属触媒を硝酸中で加熱溶解して、貴金属を担持したアルミナ層をメタル担体から剥離し、更に硝酸に塩酸を添加して貴金属を溶解、回収する方法が開示されている（例えば、特許文献２参照。）。
【０００６】
或いは、金属ベースに担持させた貴金属触媒の加熱と水冷を繰り返し、金属ベースとアルミナ層との熱膨張率の差を利用して、貴金属を担持したアルミナ層を剥離回収後、回収したアルミナ層を強酸処理して貴金属を回収する方法が開示されている（例えば、特許文献３参照。）。
【０００７】
【特許文献１】
特公平６−５５２７７号公報（第２頁）
【特許文献２】
特開平３−１５４６４０号公報（第２頁）
【特許文献３】
特開平１１−１５８５６３号公報（第２−３頁）
【０００８】
【発明が解決しようとする課題】
前述の様に、使用済みのフェライト系ステンレス鋼の表面に、白金族の貴金属を含むアルミナ層を担持せしめた触媒層から貴金属を回収するため、多くの方法が開示されている。しかし、これらの方法は何れも工程が複雑で薬液所要量が多く、廃液処理が容易でないか、或いは回収装置が大型でその構造が複雑でありコンパクト化が困難である等の問題点があった。本発明は薬液所要量及び廃液処理量の減少と装置のコンパクト化によって、経済性を高めた回収方法を提供しようとするものである。
【０００９】
【課題を解決するための手段】
フェライト系ステンレス鋼の表面に、白金族の貴金属を含むアルミナ層を担持せしめた触媒層（以下、貴金属含有触媒層という）から、貴金属を回収する方法の一つが前記の特公平６−５５２７７号公報に開示されている。しかし、この方法では、貴金属含有触媒層を剥離せしめた後貴金属を強酸で溶解するためには、アルカリを中和し更に酸を加えて貴金属を溶解する必要がある。このため工程が複雑化すると共に、薬液所要量と廃液処理量が増加する他、後述の比較例７にも示す様に、貴金属の回収率が低い難点がある。
【００１０】
また、特開平３−１５４６４０号公報に開示されている方法では、硝酸で触媒層を溶解・剥離後、硝酸に塩酸を添加して貴金属を溶解するため、溶解後の硝酸・塩酸混合廃液は循環使用ができず、この様な組成の薬液はその他の分野でも再利用できる用途は限られているため、結局薬液所要量及び廃液処理量が増加してコストアップが避けられない。
【００１１】
更に、特開平１１−１５８５６３に開示されている方法では、水蒸気爆発の危険性があり、またメタル担体のハニカム体のガス流路に水を１０〜５０リットル／分・ｃｍ^２注入するための複雑で大型な設備が必要となって、設備費が嵩むためコストアップが避けられない。
【００１２】
これらの方法は何れも担体のステンレス鋼を損傷せずに、触媒層を剥離・回収する方法であり、その中でも、薬液による剥離方法では薬液の循環・再使用ができないため、多量の薬液と廃液処理が必要となる。今後環境への配慮から廃液処理の費用及び設備費は益々増大すると考えられる。本発明者は担体のステンレス鋼を損傷させても、薬液所要量及び廃棄量を大幅に減少させれば、却って経済性を向上させ得る可能性があるとの観点から、塩酸で担体のステンレス鋼の表面を腐食することにより、触媒層を剥離・回収する方法について検討した。
【００１３】
その結果、触媒層が担持されているステンレス鋼表面の溶解に使用された塩酸を補充するのみで循環・再使用が可能である。更に水洗・回収された触媒層に含まれる貴金属を、王水または塩素を含んだ塩酸で溶解し、電気分解法で回収すれば溶媒も循環・再使用が可能となる。従って、この両プロセスを組み合わせれば、薬液所要量は触媒層剥離工程及び、貴金属溶解工程で消費される塩酸及び少量の王水等の補充分のみとなり、廃液処理量及びその処理設備費も著しく減少する。このため、塩酸による担体のステンレス箔ハニカム体の損傷費を考慮しても尚、貴金属回収工程全体の経済性を向上させ得る余地が考えられる。
【００１４】
その結果、貴金属含有触媒層を塩酸に浸漬した場合、塩酸がポーラスなアルミナ層に浸透してステンレス鋼の表面に接触すると、ステンレス鋼と反応して水素ガスが発生する。この際塩酸の濃度及び温度が一定の範囲以上に達すると、水素ガス発生量が急激に増加し、そのガス圧が高まるためアルミナ層の剥離が促進されることに着目した。塩酸濃度が５．０Ｎ以上で、且つ温度５０ ℃以上となると、ステンレス鋼の表面で発生した水素ガスによって、触媒層の剥離が促進されることが認められる。
【００１５】
一方、フェライト系ステンレス鋼の表面が塩酸で腐食された場合、表面各部の浸食程度が均一ではなく、その結果表面には不規則な凹凸形状が生成する。この現象はその他の耐酸性金属材料として化学装置に使用される、銅等が塩酸で腐食された場合表面が比較的均一に腐食されるのに較べて、ステンレス鋼の表面腐食の顕著な特徴である。しかしてステンレス鋼の浸食量に対する不均一性すなわち、部分的に生ずる浅深の度合は、浸食速度が速い程大きくなる。
【００１６】
このため塩酸の濃度及び温度が一定範囲以上に達すると、ステンレス鋼の表面に生成する凹凸の程度が益々激しくなり、そのため浸食度すなわち金属成分の溶解量が或る程度以上に達しても、尚部分的に未剥離の触媒層が残存する状態となる。その結果、触媒層を完全に剥離するために要する塩酸所要量が大幅に増加することに注目した。すなわち、貴金属含有触媒層を完全にステンレス鋼の表面から剥離して、貴金属を経済的に回収するためには、一定の範囲以下の塩酸濃度及び温度で処理する必要があることが分かった。
【００１７】
更にこの様な上限及び下限の範囲内で、貴金属含有触媒層と接触するステンレス鋼の表面を、一定範囲の時間内腐食・溶解させることによって、未剥離の触媒層が残存せずに、塩酸消費量を低下させ、且つ設備のコンパクト化が可能となり、経済性が向上できることが分かった。また、バッチ式で処理した場合には、反応時間と共に塩酸濃度が低下するため、反応の終末段階では反応速度が低下して、ステンレス鋼の表面に生成する凹凸のばらつきの生成が抑制される効果もあるため、更に塩酸所要量が減少して設備のコンパクト化も可能となる。これらの知見に基づいて詳細に貴金属含有触媒層の剥離率と塩酸所要量との関係及び、貴金属回収率について検討した結果本発明に到達した。
【００１８】
すなわち、貴金属含有触媒層を、濃度５．０Ｎ以上、１０．０Ｎ以下の塩酸に、温度５０℃以上、９０℃以下で、１０分以上、３０分以下の間浸漬して、該ステンレス鋼の表面を溶解する。これによるステンレス鋼表面の腐食と、水素ガスの発生によって貴金属を含む触媒層がステンレス鋼の表面より剥離され回収される。この触媒層に含まれる貴金属を塩素を含有する塩酸または王水で溶解し、得られた溶解液から貴金属を回収する方法である。
【００１９】
本発明にはまた貴金属含有触媒層を塩酸に浸漬する工程または／及び、浸漬後の洗浄工程において、触媒層に超音波照射を行う方法も含まれている。更に剥離された触媒層に含まれる貴金属を、塩素を含有する塩酸または王水で溶解して得られた溶解液から、電気分解法によって貴金属を回収する方法も含まれている。
【００２０】
貴金属含有触媒層をその表面にコートされた、フェライト系ステンレス鋼の箔からなる担体は、その構造的な特徴からハニカム状成形体と言われることもある。以下、本発明について詳しく説明する。
【００２１】
貴金属含有触媒層はポーラスなγ− アルミナからなり、その中に貴金属として白金、パラジウム及びロジウムの一種または複数種類が含まれている。貴金属含有触媒層の担体には、通常厚さ約５０〜６０μｍ程度の薄いフェライト系ステンレス鋼の箔が使用される。この平箔と波箔を交互に巻いたハニカム状成形体の表面に、貴金属含有触媒層がコートされている。このハニカム状成形体は通常更にフェライト系ステンレス鋼のケースに収納されて使用される。
【００２２】
使用済の貴金属含有触媒層を担持したハニカム状成形体から、本発明方法によって貴金属を回収する場合には、濃度５．０Ｎ以上、１０．０Ｎ以下の塩酸に、温度５０℃以上、９０℃以下で浸漬する必要がある。この際塩酸はポーラスなアルミナ層を浸透して、テンレス鋼の表面を浸食し水素ガスを発生させるが、塩酸濃度が５．０Ｎ以上で、且つ温度５０ ℃以上になると、水素ガス発生量が急激に増加してそのガス圧が高まり、そのため触媒層の剥離が促進されるからである。
【００２３】
塩酸濃度が５．０Ｎ以下或いは、温度５０ ℃以下では腐食速度が低下するため、水素ガス発生量が少なく、貴金属含有触媒層の剥離が不十分となるため、本発明には適用できない。尚、使用後鉄及びクロム等の金属塩化物が含まれている塩酸も、或いは他の金属精錬工程等から排出された廃塩酸でも、濃度が５．０Ｎ以上の塩酸であれば本発明に使用可能である。
【００２４】
一方、塩酸濃度が５．０Ｎ以上で、且つ温度５０ ℃以上となると、水素ガス発生量が増加する傾向は塩酸の濃度及び温度が高まる程促進される。しかし、塩酸濃度が１０．０Ｎ以上か、或いは温度９０ ℃以上となると、塩酸によるステンレス鋼表面の腐食速度が益々高まり、その結果、浸食されてステンレス鋼の表面に生成する凹凸の度合が益々激しくなる傾向が認められる。
【００２５】
更にこの腐食量のばらつきは、ステンレス鋼表面の腐食速度が高まる程増大する。このために腐食が進んでも尚部分的に未剥離の触媒層が残存するため、完全に触媒層を剥離するために要する塩酸所要量が大幅に増加する。従って、本発明に適用される塩酸濃度及びその温度は１０．０Ｎ以下で、且つ９０ ℃以下とする必要がある。尚、貴金属含有触媒層の剥離工程において、触媒層に含まれるアルミナも多少溶解されるが、触媒層を剥離する場合の障害にはならない。
【００２６】
また塩酸濃度が１０．０Ｎ以上になると、水素ガスの発生速度が更に急激となるため、突沸して危険があるので火傷・爆発等の危険防止の設備が必要となる。また、塩化水素ガスの発生量も増加するため、環境対策のための設備も必要となる。これらの点から塩酸濃度が１０．０Ｎ以上になると、経済性が一層低下するので本発明には不適当である。
【００２７】
前述の塩酸濃度及び浸漬温度が一定の範囲内において、貴金属含有触媒層を担体であるハニカム状成形体の表面から、完全に剥離するために要する時間は、塩酸濃度及び浸漬温度によって変化するが、浸漬時間を１０分以上、３０分以下の範囲内とする必要がある。浸漬時間が１０分以下となると、触媒層の剥離が不十分となる。また、浸漬時間が３０分以上となると、ステンレス鋼表面の浸食量が増大すると共に、溶液中の塩化鉄及び塩化クロムの含有量が増加し、系外に排出される薬液量が増加して、経済性が大幅に低下するため本発明には不適当である。
【００２８】
更に前述の貴金属含有触媒層を塩酸に浸漬して、担体のステンレス鋼の表面を腐食し触媒層を剥離・回収する工程おいて、触媒層に超音波照射をすることにより剥離を促進させることができる。これはポーラスなアルミナ層とハニカム状成形体との接触面への塩酸の浸透速度を高めると共に、ハニカム状成形体表面のステンレス鋼の腐食を促進するためである。この工程で照射される超音波の周波数は、工業的に用いられている周波数２８ＫＨｚ，４５ＫＨｚまたは１００ＫＨｚが好適である。また、ムラなく超音波を照射するためには、超音波発振子或いはハニカム成形体を移動させることがより好ましい。更に、剥離された触媒層を担体のハニカム状成形体から分離洗浄する工程においても、前記と同様に超音波照射をすることにより触媒層の担体からの分離を促進して、触媒層の回収率を高めるために有効である。
【００２９】
剥離後洗浄された触媒層に含まれる貴金属は、塩素を含有する塩酸または王水により溶解される。塩素を含有する塩酸の濃度は特に限定しないが、例えば３５％塩酸に塩素ガスを吸収させたものが好適である。また、王水は塩酸と硝酸との混合比率が多少変化しても使用可能である。
【００３０】
得られた溶解液から貴金属を回収するには、抽出分離法により貴金属を分離した後、化学還元法によって回収する方法或いは、電気分解法により貴金属を分離回収する方法等が適用可能である。電気分解法はコンパクト化が可能で、設備費及び運転コストが安価であり、また回収された貴金属を精製高純度化し易いため好適である。
【００３１】
【発明の実施の形態】
以下、実施例を挙げて本発明を更に詳しく説明する。
【００３２】
（実施例１）
貴金属含有触媒層を担持した、厚さ５０μｍのフェライト系ステンレス鋼で形成されている、直径８９ｍｍ、高さ１３６ｍｍの使用済みのハニカム状成形体から、白金及びパラジウムの回収を行った。貴金属含有触媒層を担持したハニカム状成形体（外筒を含む）の重量は８８０ｇ、白金含有量０．８８ｇ、パラジウム含有量２．６４ｇ及び、アルミナ重量８８．０ｇである。このハニカム状成形体から次の方法によって白金及びパラジウムを回収した。
【００３３】
この触媒層を担持したハニカム状成形体を、濃度８．０Ｎの塩酸に、温度８０ ℃で２０分間浸漬した。この時のハニカム状成形体表面のステンレス鋼の金属成分溶解量は、その重量変化から２０．５％であった。ハニカム状成形体と外筒は容易に分離され、分離したハニカム状成形体を回収し、篩の上で成形体を洗浄し塩酸と洗浄液を濾過して、貴金属含有触媒層を回収した。触媒量は８７．１ｇであった。ここで、ステンレス鋼の腐食で生成した金属成分溶解量はこの工程における、塩酸消費量の指標ともなっている。また、この溶解された成分には白金及びパラジウム等の貴金属は含まれていない。
【００３４】
前記の様にして回収した貴金属含有触媒層を、濃度３５％塩酸（１１．２７Ｎ）に塩素をバブリングさせながら、温度１００℃に加熱して白金及びパラジウムを溶解した。得られた貴金属を含む溶解液の白金含有量は７．４３ｇ／ｌ、パラジウム含有量は２２．３ｇ／ｌであり、この溶解液から電気分解法によって白金及びパラジウムを回収した。この溶解液に含まれている白金及びパラジウムは剥離された触媒層に含まれていたものの他、剥離工程で塩酸中に懸濁し、洗浄・濾過工程で回収されたものも含まれている。この溶解液から電気分解法による白金及びパラジウムの回収率はほぼ１００％であり、その結果貴金属含有触媒層からの白金及びパラジウムの回収率は、それぞれ９８．９％及び９８．７％であった。
【００３５】
一方、前記の塩酸に塩素をバブリングさせながら溶解して得られた溶解液から、ＤＨＳ（ジ−ｎ− ヘキシルスルフィド）により、パラジウムを抽出した後、２８％アンモニア水で逆抽出し、得られた逆抽出液を水素で還元して白金及びパラジウムを回収した。その結果、貴金属含有触媒層からの白金及びパラジウムの回収率はそれぞれ９８．３％及び９７．９％であった。
【００３６】
更に、前記の塩酸に塩素をバブリングさせながら溶解して得られた溶解液の代わりに、王水で溶解した場合には電気分解法による回収率が９９．３％であり、貴金属含有触媒層からの白金及びパラジウムの回収率はそれぞれ９８．３％及び９８．２％であった。何れの方法でも回収率は良好であった。
【００３７】
（実施例２）
実施例１において、貴金属含有触媒層を担持したハニカム状成形体を、塩酸に浸漬した後濾過して得られた使用済塩酸の濃度を８．０Ｎに調整して、再度ハニカム状成形体から貴金属含有触媒層を剥離するために用いた以外は、実施例１と同様に処理して、貴金属含有触媒層を回収した。
【００３８】
その結果、回収した触媒層は８６．８ｇであり、回収した触媒層に含まれる白金及びパラジウムを王水で溶解した。得られた溶解液から電気分解法によって白金及びパラジウムを回収した結果、回収率はそれぞれ９８．１％及び９８．１％であった。使用済の塩酸を濃度調整した後再度使用したが、貴金属の回収率は良好であった。
【００３９】
（実施例３）
貴金属含有触媒層を担持したハニカム状成形体の塩酸浸漬時、触媒層に２８ＫＨｚの超音波を２分間照射した以外は実施例１と同様に処理して、触媒層をハニカム状成形体から剥離・回収した。その結果、回収した触媒層は８７．８ｇであり、触媒層に含まれる白金及びパラジウムを王水で溶解した。得られた白金及びパラジウムの溶解液から電気分解法によってこれらの貴金属を回収した。白金及びパラジウムの回収率はそれぞれ９９．４％及び９９．２％であった。超音波照射によって貴金属の回収率が、実施例１より更に向上したことが認められる。
【００４０】
（実施例４）
貴金属含有触媒層を担持したハニカム状成形体を、濃度６．０Ｎの塩酸に温度６０℃で、１２分間浸漬した以外は、実施例１と同様に処理して触媒層を剥離・回収した。その結果、ハニカム状成形体表面の金属成分溶解量は、その重量変化から１４．５％であり、回収した触媒層は８６．２ｇであった。回収した触媒層に含まれる白金及びパラジウムを王水で溶解した。得られた白金及びパラジウムの溶解液から電気分解法によって、これらの貴金属を回収した。白金及びパラジウムの回収率はそれぞれ９７．４％及び９７．２％であった。貴金属の回収率は良好であった。
【００４１】
（実施例５）
実施例４において、貴金属含有触媒層を担持したハニカム状成形体を、塩酸に浸漬した後濾過して得られた使用済塩酸の濃度を８．０Ｎに調整して、再度ハニカム状成形体から貴金属含有触媒層を剥離するために用いた以外は、実施例１と同様に処理して、貴金属含有触媒層を回収した。
【００４２】
その結果、回収した触媒層は８６．９ｇであり、回収した触媒層に含まれる白金及びパラジウムを王水で溶解した。得られた溶解液から電気分解法によって白金及びパラジウムを回収した結果、回収率はそれぞれ９８．３％及び９８．４％であった。使用済の塩酸を濃度調整した後再使用したが、貴金属の回収率は良好であった。
【００４３】
（実施例６）
貴金属含有触媒層を担持したハニカム状成形体を、濃度９．５Ｎの塩酸に温度８５ ℃で、２５分間浸漬した以外は、実施例１と同様に処理して触媒層を剥離・回収した。その結果、ハニカム状成形体の金属成分溶解量は、その重量変化から２５．１％であった。また、回収した触媒層は８７．２ｇであり、触媒層に含まれる白金及びパラジウムを王水で溶解した。得られた溶解液から電気分解法によって白金及びパラジウムを回収した結果、回収率はそれぞれ９８．１％及び９８．３％であった。貴金属の回収率は良好であった。
【００４４】
（実施例７）
実施例６において、貴金属含有触媒層を担持したハニカム状成形体を、塩酸に浸漬した後濾過して得られた使用済塩酸の濃度を８．０Ｎに調整して、再度ハニカム状成形体から貴金属含有触媒層を剥離するために用いた以外は、実施例１と同様に処理して、貴金属含有触媒層を回収した。
【００４５】
その結果、回収した触媒層は８６．７ｇであり、回収した触媒層に含まれる白金及びパラジウムを王水で溶解した。得られた溶解液から電気分解法によって白金及びパラジウムを回収した結果、回収率はそれぞれ９８．１％及び９８．０％であった。使用済の塩酸を濃度調整した後再使用したが、貴金属の回収率は良好であった。
【００４６】
（比較例１）
貴金属含有触媒層を担持したハニカム状成形体を、濃度３．０Ｎの塩酸に温度４０℃で、５分間浸漬した以外は、実施例１と同様に処理して触媒層を剥離・回収した。その結果、ハニカム状成形体表面の金属成分溶解量が５．６％であったが、尚、外筒とハニカム状成形体は分離できず、且つ触媒層も５０％しか回収できなかった。回収した触媒層に含まれる白金及びパラジウムを王水で溶解し、得られた溶解液から電気分解法によって白金及びパラジウムを回収した結果、回収率はそれぞれ４８．０％及び４８．０％であった。触媒層の剥離が不十分であり、そのため貴金属の回収率が低い結果となった。
【００４７】
（比較例２）
貴金属含有触媒層を担持したハニカム状成形体を、濃度１２．０Ｎの塩酸に温度１００℃で、４０分間浸漬した以外は、実施例１と同様に処理して触媒層を剥離・回収した。触媒層の塩酸浸漬時に溶液が突沸し危険であった。また、ハニカム状成形体表面の金属成分溶解量は、その重量変化から５１．１％であり、回収した触媒層は８６．８ｇであった。
【００４８】
回収した触媒層に含まれる白金及びパラジウムを王水で溶解し、得られた溶解液から電気分解法によって白金及びパラジウムを回収した。その結果、白金及びパラジウムの回収率は、それぞれ９８．０％及び９７．９％であった。貴金属回収率はほぼ良好であるが、金属成分溶解量が大きく塩酸所要量が大幅に増加することを示している。更に、廃液量の増加及びその処理費、設備等を考慮すれば、経済性が大幅に低下するので、本発明には不適当である。
【００４９】
（比較例３）
貴金属含有触媒層を担持したハニカム状成形体を、濃度６．０Ｎの塩酸に温度６０℃で、５分間浸漬した以外は、実施例１と同様に処理して触媒層を剥離・回収した。その結果、ハニカム状成形体表面の金属成分溶解量は７．４％であり、回収した触媒層は５６．４ｇであった。回収した触媒層に含まれる白金及びパラジウムを王水で溶解し、得られた溶解液から電気分解法によって白金及びパラジウムを回収した。その結果、回収率はそれぞれ６２．０％及び６２．１％であった。触媒層の剥離が不十分であり、そのため貴金属の回収率が低い結果となった。
【００５０】
（比較例４）
貴金属含有触媒層を担持したハニカム状成形体を、濃度１１．０Ｎの塩酸に温度６０℃で、１２分間浸漬した以外は、実施例１と同様に処理して触媒層を剥離・回収した。その結果、ハニカム状成形体表面の金属成分溶解量は２２．０％であり、回収した触媒層は８０．２ｇであった。回収した触媒層に含まれる白金及びパラジウムを王水で溶解し、得られた溶解液から電気分解法によって白金及びパラジウムを回収した。その結果、白金及びパラジウムの回収率はそれぞれ９１．２％及び９０．８％であった。
【００５１】
金属成分溶解量よりみてステンレス鋼表面の腐食がかなり進んでいるにも拘わらず、尚、貴金属の回収率が低い結果となっている。これは未剥離の触媒層がかなり残存したためであり、貴金属の回収率が低いため本発明には不適当である。
【００５２】
（比較例５）
貴金属含有触媒層を担持したハニカム状成形体を、濃度９．５Ｎの塩酸に温度８５℃で、５分間浸漬した以外は、実施例１と同様に処理して触媒層を剥離・回収した。その結果、ハニカム状成形体の金属成分溶解量は８．１％であり、回収した触媒層は６４．３ｇであった。回収した触媒層に含まれる白金及びパラジウムを王水で溶解した。得られた溶解液から電気分解法によって白金及びパラジウムを回収した結果、回収率はそれぞれ７０．７％及び７１．３％であった。触媒層の剥離が不十分であり、そのため貴金属の回収率が低い結果となった。
【００５３】
（比較例６）
貴金属含有触媒層を担持したハニカム状成形体を、濃度１１．０Ｎの塩酸に温度８５℃で、２５分間浸漬した以外は、実施例１と同様に処理して触媒層を剥離・回収した。その結果、ハニカム状成形体表面の金属成分溶解量は３１．３％であり、回収した触媒層は８５．７ｇであった。回収した触媒層に含まれる白金及びパラジウムを王水で溶解した。得られた溶解液から電気分解法によって白金及びパラジウムを回収した結果、回収率はそれぞれ９７．０％及び９６．８％であった。
【００５４】
金属成分溶解量よりみてステンレス箔表面の腐食がかなり進んでいるにも拘わらず、尚、貴金属の回収率が低い結果となっている。これは未剥離の触媒層がかなり残存したためであり、貴金属の回収率が低いので本発明には不適当である。
【００５５】
（比較例７）
実施例１で用いた貴金属含有触媒層を担持したハニカム状成形体を、２０％水酸化ナトリウム水溶液に浸漬して、１２０ ℃で３時間加熱処理を行い、このハニカム状成形体を取り出した後に、水酸化ナトリウム水溶液を濾別して剥離された貴金属含有触媒層を回収した。その触媒層を水洗・粉砕した後粒径１〜５ｍｍに造粒し、６００ ℃で焼成した。ここで得られた粒子を王水に溶解し、この溶解液から電気分解法によって白金及びパラジウムを回収した。その結果、回収率はそれぞれ７２．３％及び６８．４％であった。貴金属の回収率が低い結果となっている。
【００５６】
（比較例８）
実施例１で用いた貴金属含有触媒層を担持したハニカム状成形体を、濃度３．０Ｎの硝酸に浸漬し、１２０ ℃で３時間加熱処理を行って貴金属含有触媒層を、担体のハニカム状成形体から剥離した。残存したハニカム状成形体を取り出した後、残存液に濃度１０．０Ｎの塩酸を加えて王水を調整し、１００ ℃で３時間加熱して触媒層に含まれる白金及びパラジウムを王水で溶解した。得られた溶解液から電気分解法によって白金及びパラジウムを回収した。その結果、回収率はそれぞれ９８．４％及び９８．１％であった。
【００５７】
貴金属の回収率は本発明とほぼ同程度であったが、回収後の残存液は王水であるため、貴金属含有触媒層を担体のハニカム状成形体からの剥離液としては再利用できない。廃棄する場合には中和等排出可能な成分となる様に再処理をする必要がある。一方、本発明方法では貴金属含有触媒層剥離用の塩酸は、一部ステンレス鋼の金属成分の溶解による濃度低下分を補充すれば、循環使用が可能であり、また王水も、電解によって白金及びパラジウムを回収した後、循環使用が可能であるため薬液所要量が少なく、経済性が高い。
【００５８】
しかし、前述の硝酸による触媒層の剥離方法では電解後多量の王水が廃棄されるが、その他で王水を利用できる分野は限定されている。このため廃棄する場合には本発明方法と較べて、薬液所要量及び廃棄のための再処理費用が大幅に増加する。従って、経済性低下が著しく低下することは避けられない。
【００５９】
（比較例９）
実施例１で使用した貴金属含有触媒層を担持したハニカム状成形体を、常圧で加熱炉にて１０００ ℃に加熱した後、炉から取り出し、圧力１０Ｋｇ／ｃｍ^２Ｇ、流量５０リットル／分・ｃｍ^２の高圧水を、このハニカム状成形体のガス流路を通過して排出される様に、成形体が冷却される迄注入した。この操作を３回繰り返し、ハニカム状成形体から剥離された触媒層を回収した。回収された触媒層に含まれる白金及びパラジウムを王水で溶解した。得られた溶解液から電気分解法によって白金及びパラジウムを回収した結果、回収率はそれぞれ９４．７％及び９３．１％であった。
【００６０】
この方法は貴金属含有触媒層の剥離・回収に薬液を使用しない点では優れているが、ハニカム状成形体の加熱炉、高圧水が噴射可能な設備、ハニカム状成形体に高圧水を噴射して貴金属含有触媒層の剥離・回収するための設備更に、高圧水の循環設備が必要となるため、設備の複雑化・大型化が避けられず、設備のコンパクト化は望めない。更に水蒸気爆発の危険性を考慮すれば、保安設備等が必要となり、更に設置場所も制約される。従って、設備費が高額となるため経済性が大幅に低下することは避けられない。
【００６１】
【発明の効果】
貴金属含有触媒層を担持したハニカム状成形体を塩酸に浸漬し、ステンレス鋼表面を腐食させ、触媒層を剥離・回収する工程で、塩酸を補充することにより浸漬液の循環使用が可能となる。更に、回収した触媒層に含まれる白金及びパラジウムを、王水等で溶解後電気分解法による貴金属回収工程でも、電解液を循環使用することによって、薬液所要量を低下させ、且つ廃液を減少させることができる。これらの薬液所要量等の減少による経済性の向上と、電気分解法による装置のコンパクト化が可能であり、また高純度の貴金属が得られる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for recovering a noble metal from a catalyst layer in which an alumina layer containing a platinum group noble metal is supported on the surface of a used ferritic stainless steel. More specifically, the catalyst layer is immersed in hydrochloric acid of a specific range of concentration and temperature, so that the surface of the stainless steel supporting the catalyst layer is corroded and the generated hydrogen gas separates and recovers the catalyst layer. Is dissolved in hydrochloric acid containing chlorine or the like, and the noble metal is recovered by an electrolysis method or the like.
[0002]
[Prior art]
At present, noble metal-containing catalysts are widely used in the chemical industry, automobile exhaust gas treatment and the like. Precious metals are expensive and finite, and recovery of precious metals from spent catalysts and the like is an important issue from the viewpoint of resource conservation. For this reason, many recovery methods have been previously studied and disclosed.
[0003]
Catalysts used in automobile exhaust gas treatment include catalysts supported on ceramic bases and catalysts supported on metal bases. The carrier of the catalyst supported on the metal base is mainly composed of a cylindrical honeycomb structure in which corrugated and flat foils of ferritic stainless steel (mainly Fe-Cr) are alternately wound, and a noble metal is coated on the surface thereof. The contained alumina is coated. The honeycomb body is further used by being inserted into a cylindrical outer cylinder made of metal.
[0004]
As a method of recovering the noble metal from the noble metal catalyst supported on the metal base, this catalyst is heat-treated in an alkaline solution, the alumina supporting the noble metal is peeled off, and after collecting, the alumina layer is treated with a strong acid to recover the noble metal. (For example, see Patent Document 1).
[0005]
Also disclosed is a method of heating and dissolving a noble metal catalyst supported on a metal base in nitric acid, peeling the alumina layer supporting the noble metal from the metal carrier, and further adding hydrochloric acid to nitric acid to dissolve and recover the noble metal. (For example, see Patent Document 2).
[0006]
Alternatively, the heating and water cooling of the noble metal catalyst supported on the metal base are repeated, and by utilizing the difference in the coefficient of thermal expansion between the metal base and the alumina layer, the alumina layer supporting the noble metal is separated and recovered, and then the recovered alumina layer is removed. A method of recovering a noble metal by a strong acid treatment is disclosed (for example, see Patent Document 3).
[0007]
[Patent Document 1]
Japanese Patent Publication No. 6-55277 (page 2)
[Patent Document 2]
JP-A-3-154640 (page 2)
[Patent Document 3]
JP-A-11-158563 (pages 2-3)
[0008]
[Problems to be solved by the invention]
As described above, many methods have been disclosed for recovering a noble metal from a catalyst layer in which an alumina layer containing a platinum group noble metal is supported on the surface of a used ferritic stainless steel. However, all of these methods have problems in that the steps are complicated, the amount of the chemical solution required is large, the waste liquid treatment is not easy, or the recovery device is large and its structure is complicated and it is difficult to make it compact. . An object of the present invention is to provide a recovery method which is more economical by reducing the required amount of a chemical solution and the amount of waste liquid to be treated and by downsizing the apparatus.
[0009]
[Means for Solving the Problems]
One of the methods for recovering a noble metal from a catalyst layer in which an alumina layer containing a platinum group noble metal is supported on the surface of a ferritic stainless steel (hereinafter, referred to as a noble metal-containing catalyst layer) is disclosed in the above-mentioned Japanese Patent Publication No. 6-55277. Is disclosed. However, in this method, in order to dissolve the noble metal with a strong acid after exfoliating the noble metal-containing catalyst layer, it is necessary to neutralize the alkali and add an acid to dissolve the noble metal. For this reason, the process becomes complicated, the required amount of the chemical solution and the amount of the waste liquid to be treated increase, and the recovery rate of the noble metal is low as shown in Comparative Example 7 described later.
[0010]
In the method disclosed in Japanese Patent Application Laid-Open No. 3-154640, after dissolving and stripping the catalyst layer with nitric acid, hydrochloric acid is added to nitric acid to dissolve the noble metal. Since the chemical solution having such a composition cannot be used, and the use of the chemical solution having such a composition is limited in other fields, the required amount of the chemical solution and the disposal amount of the waste solution are increased.
[0011]
Furthermore, in the method disclosed in Japanese Patent Application Laid-Open No. 11-158563, there is a danger of steam explosion, and 10 to 50 liters / minute · cm ² Complicated and large-sized equipment for injection is required, and equipment cost is increased, so that cost increase is inevitable.
[0012]
In any of these methods, the catalyst layer is peeled and collected without damaging the stainless steel of the carrier. Among them, the chemical liquid cannot be circulated and reused by the chemical liquid peeling method. Processing is required. It is thought that the cost of waste liquid treatment and the equipment cost will increase further in consideration of the environment. The present inventor believes that even if the stainless steel of the carrier is damaged, if the required amount of the chemical solution and the amount of waste are significantly reduced, it is possible to improve the economic efficiency on the contrary. The method of peeling and collecting the catalyst layer by corroding the surface of the catalyst was studied.
[0013]
As a result, circulation and reuse are possible only by replenishing hydrochloric acid used for dissolving the surface of the stainless steel on which the catalyst layer is carried. Further, if the noble metal contained in the washed and recovered catalyst layer is dissolved in aqua regia or hydrochloric acid containing chlorine and recovered by an electrolysis method, the solvent can be circulated and reused. Therefore, if these two processes are combined, the required amount of the chemical solution is only the replenishment of hydrochloric acid and a small amount of aqua regia consumed in the catalyst layer peeling step and the noble metal dissolving step, and the amount of waste liquid treatment and the cost of the treatment equipment are also remarkable. Decrease. For this reason, there is still room for improving the economics of the entire precious metal recovery step even when considering the cost of damaging the stainless steel honeycomb body of the carrier due to hydrochloric acid.
[0014]
As a result, when the noble metal-containing catalyst layer is immersed in hydrochloric acid, when the hydrochloric acid permeates the porous alumina layer and comes into contact with the surface of the stainless steel, it reacts with the stainless steel to generate hydrogen gas. At this time, when the concentration and temperature of hydrochloric acid reached a certain range or more, attention was paid to the fact that the amount of generated hydrogen gas sharply increased, and the gas pressure was increased, thereby promoting the separation of the alumina layer. When the hydrochloric acid concentration is 5.0 N or more and the temperature is 50 ° C. or more, it is recognized that the separation of the catalyst layer is promoted by the hydrogen gas generated on the surface of the stainless steel.
[0015]
On the other hand, when the surface of the ferritic stainless steel is corroded with hydrochloric acid, the degree of erosion of each part of the surface is not uniform, and as a result, irregular irregular shapes are generated on the surface. This phenomenon is a remarkable feature of surface corrosion of stainless steel, compared to the fact that the surface is relatively uniformly corroded when copper or the like is corroded with hydrochloric acid, which is used in chemical equipment as another acid-resistant metal material. is there. Thus, the non-uniformity with respect to the amount of erosion of stainless steel, that is, the degree of partially occurring shallow depth increases as the erosion rate increases.
[0016]
For this reason, when the concentration and temperature of hydrochloric acid reach a certain range or more, the degree of unevenness generated on the surface of stainless steel becomes more and more intense. Therefore, even if the erosion degree, that is, the dissolved amount of the metal component, reaches a certain level or more, A state in which an unstripped catalyst layer partially remains is obtained. As a result, it was noted that the required amount of hydrochloric acid required for completely removing the catalyst layer was greatly increased. That is, in order to completely remove the noble metal-containing catalyst layer from the surface of the stainless steel and economically recover the noble metal, it was found that it was necessary to perform treatment at a hydrochloric acid concentration and temperature within a certain range or less.
[0017]
Further, within such a range of the upper limit and the lower limit, the surface of the stainless steel in contact with the noble metal-containing catalyst layer is corroded and dissolved for a certain range of time, so that the unexfoliated catalyst layer does not remain and hydrochloric acid is consumed. It has been found that the amount can be reduced, the equipment can be made compact, and the economy can be improved. In addition, when the treatment is performed in a batch system, the hydrochloric acid concentration decreases with the reaction time, so that the reaction speed decreases at the final stage of the reaction, thereby suppressing the generation of unevenness generated on the surface of stainless steel. Therefore, the required amount of hydrochloric acid is further reduced, and the equipment can be made more compact. Based on these findings, a detailed study was made on the relationship between the peeling rate of the noble metal-containing catalyst layer and the required amount of hydrochloric acid and the noble metal recovery rate, and as a result, the present invention was reached.
[0018]
That is, the noble metal-containing catalyst layer is immersed in hydrochloric acid having a concentration of 5.0 N or more and 10.0 N or less at a temperature of 50 ° C. or more and 90 ° C. or less for 10 minutes or more and 30 minutes or less. Dissolve the surface. This causes corrosion of the stainless steel surface and generation of hydrogen gas, whereby the catalyst layer containing the noble metal is separated from the stainless steel surface and collected. This is a method of dissolving the noble metal contained in the catalyst layer with hydrochloric acid or aqua regia containing chlorine and recovering the noble metal from the obtained solution.
[0019]
The present invention also includes a method of irradiating the catalyst layer with ultrasonic waves in the step of immersing the noble metal-containing catalyst layer in hydrochloric acid and / or the washing step after immersion. Further, there is also included a method of recovering the noble metal contained in the separated catalyst layer with a hydrochloric acid containing chlorine or aqua regia from a solution obtained by dissolving the noble metal by electrolysis.
[0020]
A support made of a ferritic stainless steel foil coated on its surface with a noble metal-containing catalyst layer is sometimes referred to as a honeycomb-shaped formed body due to its structural characteristics. Hereinafter, the present invention will be described in detail.
[0021]
The noble metal-containing catalyst layer is made of porous γ-alumina and contains one or more of platinum, palladium and rhodium as noble metals. As the support of the noble metal-containing catalyst layer, a thin ferrite stainless steel foil having a thickness of about 50 to 60 μm is usually used. A noble metal-containing catalyst layer is coated on the surface of the honeycomb formed body in which the flat foil and the corrugated foil are alternately wound. The honeycomb formed body is usually used by being housed in a ferritic stainless steel case.
[0022]
When the noble metal is recovered from the honeycomb-shaped formed body supporting the used noble metal-containing catalyst layer by the method of the present invention, hydrochloric acid having a concentration of 5.0 N or more and 10.0 N or less, a temperature of 50 N or more and 90 N or less. It is necessary to immerse at below ℃. At this time, the hydrochloric acid penetrates the porous alumina layer and erodes the surface of the stainless steel to generate hydrogen gas. However, when the hydrochloric acid concentration is 5.0 N or more and the temperature is 50 ° C. or more, the amount of hydrogen gas generated rapidly increases. This is because the gas pressure increases and the separation of the catalyst layer is accelerated.
[0023]
If the concentration of hydrochloric acid is 5.0 N or less or the temperature is 50 ° C. or less, the corrosion rate is reduced, the amount of hydrogen gas generated is small, and the noble metal-containing catalyst layer is insufficiently peeled off. It should be noted that hydrochloric acid containing metal chlorides such as iron and chromium after use, or waste hydrochloric acid discharged from other metal refining processes, etc., can be used in the present invention if the concentration of hydrochloric acid is 5.0N or more. It is possible.
[0024]
On the other hand, when the concentration of hydrochloric acid is 5.0 N or more and the temperature is 50 ° C. or more, the tendency of increasing the amount of generated hydrogen gas is accelerated as the concentration and temperature of hydrochloric acid increase. However, when the hydrochloric acid concentration is 10.0 N or more or the temperature is 90 ° C. or more, the corrosion rate of the stainless steel surface due to hydrochloric acid is further increased, and as a result, the degree of unevenness formed on the stainless steel surface due to erosion is further increased. There is a tendency to become severe.
[0025]
Further, this variation in the amount of corrosion increases as the corrosion rate of the stainless steel surface increases. For this reason, even if the corrosion progresses, the catalyst layer which has not been peeled still remains partially, so that the required amount of hydrochloric acid required for completely peeling the catalyst layer is greatly increased. Therefore, the concentration of hydrochloric acid and the temperature applied to the present invention must be 10.0 N or less and 90 ° C. or less. In the step of removing the noble metal-containing catalyst layer, alumina contained in the catalyst layer is also slightly dissolved, but this does not hinder the separation of the catalyst layer.
[0026]
When the concentration of hydrochloric acid is 10.0 N or more, the rate of generation of hydrogen gas is further increased, and there is a danger of bumping. Therefore, equipment for preventing danger such as burns and explosions is required. Further, since the amount of generated hydrogen chloride gas increases, equipment for environmental measures is also required. From these points, if the hydrochloric acid concentration is 10.0 N or more, the economic efficiency is further reduced, and therefore, it is not suitable for the present invention.
[0027]
While the above-mentioned hydrochloric acid concentration and the immersion temperature are within a certain range, the time required for completely separating the noble metal-containing catalyst layer from the surface of the honeycomb formed body as the carrier varies depending on the hydrochloric acid concentration and the immersion temperature, The immersion time needs to be within a range of 10 minutes or more and 30 minutes or less. When the immersion time is 10 minutes or less, the peeling of the catalyst layer becomes insufficient. In addition, when the immersion time is 30 minutes or more, the amount of erosion on the stainless steel surface increases, the content of iron chloride and chromium chloride in the solution increases, and the amount of the chemical solution discharged out of the system increases, This is unsuitable for the present invention because the economic efficiency is greatly reduced.
[0028]
Further, in the step of immersing the above-mentioned noble metal-containing catalyst layer in hydrochloric acid to corrode the surface of the stainless steel of the carrier and to separate and recover the catalyst layer, it is possible to promote the separation by irradiating the catalyst layer with ultrasonic waves. it can. This is to increase the permeation rate of hydrochloric acid to the contact surface between the porous alumina layer and the honeycomb formed body and to promote the corrosion of stainless steel on the surface of the honeycomb formed body. The frequency of the ultrasonic wave applied in this step is preferably an industrially used frequency of 28 KHz, 45 KHz or 100 KHz. Further, in order to irradiate the ultrasonic waves without unevenness, it is more preferable to move the ultrasonic oscillator or the honeycomb formed body. Further, in the step of separating and washing the separated catalyst layer from the honeycomb formed body of the carrier, the separation of the catalyst layer from the carrier is promoted by irradiating ultrasonic waves in the same manner as described above, and the recovery rate of the catalyst layer is improved. It is effective to enhance.
[0029]
The noble metal contained in the washed catalyst layer after stripping is dissolved by hydrochloric acid containing chlorine or aqua regia. The concentration of the hydrochloric acid containing chlorine is not particularly limited, but for example, 35% hydrochloric acid in which chlorine gas is absorbed is preferable. Also, aqua regia can be used even if the mixing ratio of hydrochloric acid and nitric acid slightly changes.
[0030]
In order to recover the noble metal from the obtained solution, a method in which the noble metal is separated by an extraction separation method and then recovered by a chemical reduction method or a method in which the noble metal is separated and recovered by an electrolysis method can be applied. The electrolysis method is suitable because it can be made compact, the equipment cost and the operating cost are low, and the recovered noble metal can be easily purified and highly purified.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to examples.
[0032]
(Example 1)
Platinum and palladium were recovered from a used honeycomb shaped body having a diameter of 89 mm and a height of 136 mm formed of a 50 μm-thick ferritic stainless steel carrying a noble metal-containing catalyst layer. The weight of the honeycomb formed body (including the outer cylinder) supporting the noble metal-containing catalyst layer is 880 g, the platinum content is 0.88 g, the palladium content is 2.64 g, and the alumina weight is 88. 0 g. Platinum and palladium were recovered from the honeycomb formed body by the following method.
[0033]
The honeycomb formed body carrying the catalyst layer was immersed in 8.0N hydrochloric acid at a temperature of 80 ° C. for 20 minutes. At this time, the dissolution amount of the metal component of the stainless steel on the surface of the honeycomb formed body was 20.5% from the change in weight. The honeycomb-shaped formed body and the outer cylinder were easily separated, the separated honeycomb-shaped formed body was collected, the formed body was washed on a sieve, and hydrochloric acid and a washing liquid were filtered to collect a noble metal-containing catalyst layer. The amount of the catalyst was 87.1 g. Here, the dissolved amount of the metal component generated by the corrosion of the stainless steel is also an index of the hydrochloric acid consumption in this step. The dissolved components do not contain noble metals such as platinum and palladium.
[0034]
The noble metal-containing catalyst layer recovered as described above was heated to a temperature of 100 ° C. while bubbling chlorine into 35% hydrochloric acid (11.27 N) to dissolve platinum and palladium. The platinum solution and the palladium content of the obtained solution containing noble metal were 7.43 g / l and 22.3 g / l, respectively, and platinum and palladium were recovered from the solution by electrolysis. Platinum and palladium contained in the solution include those contained in the peeled catalyst layer and those suspended in hydrochloric acid in the peeling step and recovered in the washing / filtration step. The recovery of platinum and palladium from this solution by electrolysis was almost 100%. As a result, the recovery of platinum and palladium from the noble metal-containing catalyst layer was 98.9% and 98.7%, respectively. .
[0035]
On the other hand, palladium was extracted with DHS (di-n-hexyl sulfide) from a solution obtained by dissolving chlorine in the above hydrochloric acid while bubbling chlorine, and then back-extracted with 28% aqueous ammonia. The back extract was reduced with hydrogen to recover platinum and palladium. As a result, the recovery rates of platinum and palladium from the noble metal-containing catalyst layer were 98.3% and 97.9%, respectively.
[0036]
Furthermore, in the case of dissolving with aqua regia instead of the solution obtained by dissolving chlorine in the hydrochloric acid while bubbling chlorine, the recovery rate by electrolysis is 99.3%, and the noble metal-containing catalyst layer The recovery of platinum and palladium was 98.3% and 98.2%, respectively. The recovery rate was good in any of the methods.
[0037]
(Example 2)
In Example 1, the concentration of the used hydrochloric acid obtained by immersing the honeycomb-shaped molded body carrying the noble metal-containing catalyst layer in hydrochloric acid and then filtering the same was adjusted to 8.0 N, and the noble metal was again removed from the honeycomb-shaped molded body. The same treatment as in Example 1 was carried out except that the noble metal-containing catalyst layer was used for removing the noble metal-containing catalyst layer.
[0038]
As a result, the recovered catalyst layer weighed 86.8 g, and platinum and palladium contained in the recovered catalyst layer were dissolved in aqua regia. As a result of recovering platinum and palladium from the obtained solution by electrolysis, the recovery rates were 98.1% and 98.1%, respectively. After adjusting the concentration of the used hydrochloric acid, it was used again, but the recovery rate of the noble metal was good.
[0039]
(Example 3)
The catalyst layer was peeled off from the honeycomb formed body by performing the same treatment as in Example 1 except that the catalyst layer was irradiated with ultrasonic waves of 28 KHz for 2 minutes when the honeycomb formed body carrying the noble metal-containing catalyst layer was immersed in hydrochloric acid.・ Recovered. As a result, the recovered catalyst layer weighed 87.8 g, and platinum and palladium contained in the catalyst layer were dissolved in aqua regia. These noble metals were recovered by electrolysis from the obtained solution of platinum and palladium. The recovery of platinum and palladium was 99.4% and 99.2%, respectively. It is recognized that the recovery rate of the noble metal was further improved by the ultrasonic irradiation as compared with Example 1.
[0040]
(Example 4)
The honeycomb-shaped formed body carrying the noble metal-containing catalyst layer was treated and treated in the same manner as in Example 1 except that it was immersed in 6.0 N hydrochloric acid at a temperature of 60 ° C. for 12 minutes, and the catalyst layer was peeled and collected. As a result, the amount of metal component dissolved on the surface of the honeycomb formed body was 14.5% from the change in weight, and the recovered catalyst layer was 86.2 g. Platinum and palladium contained in the recovered catalyst layer were dissolved in aqua regia. These noble metals were recovered from the obtained solution of platinum and palladium by electrolysis. The recovery of platinum and palladium was 97.4% and 97.2%, respectively. The recovery of precious metals was good.
[0041]
(Example 5)
In Example 4, the concentration of the used hydrochloric acid obtained by immersing the honeycomb-shaped formed body carrying the noble metal-containing catalyst layer in hydrochloric acid and then filtering was adjusted to 8.0 N, and the noble metal was again removed from the honeycomb-shaped formed body. The same treatment as in Example 1 was carried out except that the noble metal-containing catalyst layer was used for removing the noble metal-containing catalyst layer.
[0042]
As a result, the recovered catalyst layer weighed 86.9 g, and platinum and palladium contained in the recovered catalyst layer were dissolved in aqua regia. As a result of recovering platinum and palladium from the obtained solution by electrolysis, the recovery rates were 98.3% and 98.4%, respectively. The concentration of the used hydrochloric acid was adjusted and then reused, but the recovery rate of the noble metal was good.
[0043]
(Example 6)
The honeycomb-shaped formed body carrying the noble metal-containing catalyst layer was treated and treated in the same manner as in Example 1 except that it was immersed in 9.5N hydrochloric acid at a temperature of 85 ° C. for 25 minutes, and the catalyst layer was peeled and collected. As a result, the amount of metal component dissolved in the honeycomb formed body was 25.1% from the weight change. The recovered catalyst layer weighed 87.2 g, and platinum and palladium contained in the catalyst layer were dissolved in aqua regia. As a result of recovering platinum and palladium from the obtained solution by electrolysis, the recovery rates were 98.1% and 98.3%, respectively. The recovery of precious metals was good.
[0044]
(Example 7)
In Example 6, the concentration of the used hydrochloric acid obtained by immersing the honeycomb-shaped formed body carrying the noble metal-containing catalyst layer in hydrochloric acid and then filtering the same was adjusted to 8.0 N, and the noble metal was again removed from the honeycomb-shaped formed body. The same treatment as in Example 1 was carried out except that the noble metal-containing catalyst layer was used for removing the noble metal-containing catalyst layer.
[0045]
As a result, the recovered catalyst layer weighed 86.7 g, and platinum and palladium contained in the recovered catalyst layer were dissolved in aqua regia. As a result of recovering platinum and palladium from the obtained solution by electrolysis, the recovery rates were 98.1% and 98.0%, respectively. The concentration of the used hydrochloric acid was adjusted and then reused, but the recovery rate of the noble metal was good.
[0046]
(Comparative Example 1)
The honeycomb-shaped formed body carrying the noble metal-containing catalyst layer was treated and treated in the same manner as in Example 1 except that the catalyst layer was peeled off and collected in hydrochloric acid having a concentration of 3.0 N at a temperature of 40 ° C. for 5 minutes. As a result, the dissolution amount of the metal component on the surface of the honeycomb formed body was 5.6%. However, the outer cylinder and the honeycomb formed body could not be separated, and only 50% of the catalyst layer could be recovered. Platinum and palladium contained in the recovered catalyst layer were dissolved in aqua regia, and platinum and palladium were recovered from the resulting solution by electrolysis. The recovery rates were 48.0% and 48.0%, respectively. Was. The peeling of the catalyst layer was insufficient, resulting in a low recovery rate of the noble metal.
[0047]
(Comparative Example 2)
The honeycomb-shaped formed body carrying the noble metal-containing catalyst layer was treated and treated in the same manner as in Example 1 except that it was immersed in hydrochloric acid having a concentration of 12.0 N at a temperature of 100 ° C. for 40 minutes to peel and collect the catalyst layer. When the catalyst layer was immersed in hydrochloric acid, the solution bumped and was dangerous. The amount of metal component dissolved on the surface of the honeycomb formed body was 51.1% from the change in weight, and the recovered catalyst layer was 86.8 g.
[0048]
Platinum and palladium contained in the recovered catalyst layer were dissolved in aqua regia, and platinum and palladium were recovered from the resulting solution by electrolysis. As a result, the recovery rates of platinum and palladium were 98.0% and 97.9%, respectively. Although the recovery rate of precious metals is almost good, the amount of dissolved metal components is large and the required amount of hydrochloric acid is greatly increased. Furthermore, considering the increase in the amount of waste liquid, the processing cost thereof, the equipment, etc., the economic efficiency is greatly reduced, and thus the present invention is not suitable for the present invention.
[0049]
(Comparative Example 3)
The honeycomb-shaped formed body carrying the noble metal-containing catalyst layer was treated and treated in the same manner as in Example 1 except that the catalyst layer was peeled and recovered, except that it was immersed in 6.0N hydrochloric acid at a temperature of 60 ° C. for 5 minutes. As a result, the dissolved amount of metal components on the surface of the honeycomb formed body was 7.4%, and the recovered catalyst layer was 56.4 g. Platinum and palladium contained in the recovered catalyst layer were dissolved in aqua regia, and platinum and palladium were recovered from the resulting solution by electrolysis. As a result, the recovery rates were 62.0% and 62.1%, respectively. The peeling of the catalyst layer was insufficient, resulting in a low recovery rate of the noble metal.
[0050]
(Comparative Example 4)
The honeycomb-shaped formed body carrying the noble metal-containing catalyst layer was treated and treated in the same manner as in Example 1 except that it was immersed in hydrochloric acid having a concentration of 11.0 N at a temperature of 60 ° C. for 12 minutes, thereby removing and collecting the catalyst layer. As a result, the dissolved amount of the metal component on the surface of the honeycomb formed body was 22.0%, and the recovered catalyst layer was 80.2 g. Platinum and palladium contained in the recovered catalyst layer were dissolved in aqua regia, and platinum and palladium were recovered from the resulting solution by electrolysis. As a result, the recovery rates of platinum and palladium were 91.2% and 90.8%, respectively.
[0051]
In spite of the fact that the corrosion of the stainless steel surface has progressed considerably from the viewpoint of the dissolution amount of the metal component, the recovery rate of the noble metal is still low. This is because a considerable amount of the unexfoliated catalyst layer remained, which was unsuitable for the present invention because the recovery rate of the noble metal was low.
[0052]
(Comparative Example 5)
The honeycomb-shaped formed body carrying the noble metal-containing catalyst layer was treated in the same manner as in Example 1 except that it was immersed in 9.5N hydrochloric acid at a temperature of 85 ° C. for 5 minutes, and the catalyst layer was peeled and collected. As a result, the dissolved amount of the metal component of the honeycomb formed body was 8.1%, and the recovered catalyst layer was 64.3 g. Platinum and palladium contained in the recovered catalyst layer were dissolved in aqua regia. As a result of recovering platinum and palladium from the obtained solution by electrolysis, the recovery rates were 70.7% and 71.3%, respectively. The peeling of the catalyst layer was insufficient, resulting in a low recovery rate of the noble metal.
[0053]
(Comparative Example 6)
The honeycomb-shaped formed body carrying the noble metal-containing catalyst layer was treated in the same manner as in Example 1 except that it was immersed in hydrochloric acid having a concentration of 11.0 N at a temperature of 85 ° C. for 25 minutes, and the catalyst layer was peeled and collected. As a result, the dissolved amount of the metal component on the surface of the honeycomb formed body was 31.3%, and the recovered catalyst layer was 85.7 g. Platinum and palladium contained in the recovered catalyst layer were dissolved in aqua regia. As a result of recovering platinum and palladium from the obtained solution by electrolysis, the recovery rates were 97.0% and 96.8%, respectively.
[0054]
In spite of the fact that the corrosion of the stainless steel foil surface has considerably progressed from the viewpoint of the dissolved amount of the metal component, the recovery rate of the noble metal is still low. This is because a considerable amount of the unexfoliated catalyst layer remained, and the recovery rate of the noble metal was low.
[0055]
(Comparative Example 7)
The honeycomb-shaped formed body carrying the noble metal-containing catalyst layer used in Example 1 was immersed in a 20% aqueous sodium hydroxide solution and subjected to a heat treatment at 120 ° C. for 3 hours. The sodium hydroxide aqueous solution was separated by filtration, and the separated noble metal-containing catalyst layer was recovered. The catalyst layer was washed and pulverized, granulated to a particle size of 1 to 5 mm, and fired at 600 ° C. The particles obtained here were dissolved in aqua regia, and platinum and palladium were recovered from the solution by electrolysis. As a result, the recovery rates were 72.3% and 68.4%, respectively. The result is a low precious metal recovery rate.
[0056]
(Comparative Example 8)
The honeycomb-shaped formed body supporting the noble metal-containing catalyst layer used in Example 1 was immersed in nitric acid having a concentration of 3.0 N and subjected to a heat treatment at 120 ° C. for 3 hours to form the noble metal-containing catalyst layer into a honeycomb-shaped support. Peeled from the body. After taking out the remaining honeycomb-shaped formed body, hydrochloric acid having a concentration of 10.0 N was added to the remaining liquid to adjust aqua regia, and the mixture was heated at 100 ° C. for 3 hours to dissolve platinum and palladium contained in the catalyst layer with aqua regia. did. Platinum and palladium were recovered from the resulting solution by electrolysis. As a result, the recovery rates were 98.4% and 98.1%, respectively.
[0057]
Although the recovery rate of the noble metal was almost the same as that of the present invention, since the residual liquid after the recovery was aqua regia, the noble metal-containing catalyst layer could not be reused as a stripping liquid from the honeycomb formed body of the carrier. In the case of disposal, it is necessary to reprocess such components as neutralizable components. On the other hand, in the method of the present invention, hydrochloric acid for peeling the noble metal-containing catalyst layer can be recycled if part of the concentration decrease due to dissolution of the metal component of stainless steel can be used. After the palladium is recovered, it can be recycled and used, so the amount of chemical solution required is small and economical.
[0058]
However, a large amount of aqua regia is discarded after electrolysis in the above-described method of stripping the catalyst layer using nitric acid, but other fields in which aqua regia can be used are limited. Therefore, in the case of disposal, the required amount of the chemical solution and the cost of reprocessing for disposal are greatly increased as compared with the method of the present invention. Therefore, it is inevitable that economical decline will be significantly reduced.
[0059]
(Comparative Example 9)
The honeycomb-shaped formed body carrying the noble metal-containing catalyst layer used in Example 1 was heated to 1000 ° C. in a heating furnace at normal pressure, taken out of the furnace, and pressured at 10 kg / cm. ² G, flow rate 50 liter / min.cm ² Of high-pressure water was injected until the molded body was cooled so as to be discharged through the gas flow path of the honeycomb molded body. This operation was repeated three times, and the catalyst layer separated from the honeycomb formed body was recovered. Platinum and palladium contained in the recovered catalyst layer were dissolved in aqua regia. As a result of recovering platinum and palladium from the obtained solution by electrolysis, the recovery rates were 94.7% and 93.1%, respectively.
[0060]
This method is excellent in that no chemical solution is used for stripping and recovering the noble metal-containing catalyst layer.However, a heating furnace for the honeycomb formed body, equipment capable of injecting high-pressure water, and high-pressure water injected into the honeycomb formed body are sprayed. Equipment for stripping and recovering the noble metal-containing catalyst layer and a high-pressure water circulation equipment are required, so that the equipment is inevitably complicated and large, and the equipment cannot be downsized. Further, considering the danger of steam explosion, security equipment and the like are required, and the installation place is further restricted. Therefore, it is unavoidable that the facility cost becomes high and the economic efficiency is greatly reduced.
[0061]
【The invention's effect】
The honeycomb-shaped formed body supporting the noble metal-containing catalyst layer is immersed in hydrochloric acid to corrode the stainless steel surface, and in the step of peeling and recovering the catalyst layer, replenishment of hydrochloric acid enables the circulating use of the immersion liquid. Furthermore, platinum and palladium contained in the recovered catalyst layer are dissolved in aqua regia and the like, and also in a noble metal recovery step by electrolysis, by circulating and using the electrolytic solution, the required amount of the chemical solution is reduced, and the waste liquid is reduced. be able to. It is possible to improve the economic efficiency by reducing the required amount of the chemical solution and the like, to make the apparatus compact by the electrolysis method, and to obtain a high-purity noble metal.

Claims

フェライト系ステンレス鋼の表面に、白金族の貴金属を含むアルミナ層を担持せしめた触媒層を、濃度５．０Ｎ以上、１０．０Ｎ以下の塩酸に、温度５０℃以上、９０℃以下で、１０分以上、３０分以下の間浸漬して、該ステンレス鋼の表面部分を溶解し、該触媒層を該ステンレス鋼の表面より剥離回収した後、該触媒層に含まれる貴金属を塩素を含有する塩酸または王水で溶解し、得られた溶解液から貴金属を回収することを特徴とする、白金族の貴金属回収方法。A catalyst layer in which an alumina layer containing a platinum group noble metal is supported on the surface of a ferritic stainless steel is coated with hydrochloric acid having a concentration of 5.0 N or more and 10.0 N or less at a temperature of 50 ° C. or more and 90 ° C. or less. After being immersed for 10 minutes or more and 30 minutes or less, the surface portion of the stainless steel is dissolved, and the catalyst layer is separated and recovered from the surface of the stainless steel, and then the noble metal contained in the catalyst layer contains chlorine. A method for recovering a platinum group noble metal, comprising dissolving with hydrochloric acid or aqua regia and recovering the noble metal from the resulting solution.

フェライト系ステンレス鋼の表面に、白金族の貴金属を含むアルミナ層を担持せしめた触媒層を、塩酸に浸漬する工程または／及び、浸漬後の洗浄工程において、該触媒層に超音波照射を行う、請求項１記載の白金族の貴金属回収方法。In a step of immersing the catalyst layer in which an alumina layer containing a platinum group noble metal is supported on the surface of a ferritic stainless steel in hydrochloric acid or / and a washing step after immersion, the catalyst layer is irradiated with ultrasonic waves. The method for recovering a platinum group noble metal according to claim 1.

剥離された該触媒層に含まれる貴金属を、塩素を含有する塩酸または王水で溶解して得られた溶解液から、電気分解法によって白金族の貴金属を回収する、請求項１または２に記載の白金族の貴金属回収方法。The platinum group noble metal is recovered by electrolysis from a solution obtained by dissolving the noble metal contained in the separated catalyst layer with hydrochloric acid or aqua regia containing chlorine by electrolysis. Recovery method of platinum group noble metals.