JP3803858B2 - Electrochemical recovery of heavy metals from fly ash - Google Patents

Electrochemical recovery of heavy metals from fly ash Download PDF

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Publication number
JP3803858B2
JP3803858B2 JP2001037819A JP2001037819A JP3803858B2 JP 3803858 B2 JP3803858 B2 JP 3803858B2 JP 2001037819 A JP2001037819 A JP 2001037819A JP 2001037819 A JP2001037819 A JP 2001037819A JP 3803858 B2 JP3803858 B2 JP 3803858B2
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electrode
fly ash
lead
electrolysis
copper
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JP2002239553A (en
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近 稲住
雅芳 近藤
浩史 辰己
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Hitachi Zosen Corp
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Hitachi Zosen Corp
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00Technologies related to metal processing
    • Y02P10/20Recycling
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02WCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00Technologies for solid waste management
    • Y02W30/50Reuse, recycling or recovery technologies
    • Y02W30/82Recycling of waste of electrical or electronic equipment [WEEE]

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  • Water Treatment By Electricity Or Magnetism (AREA)
  • Electrolytic Production Of Metals (AREA)

Description

【0001】
【発明の属する技術分野】
本発明は、廃棄物の再資源化技術として焼却飛灰、溶融飛灰から金属類、とりわけ銅、鉛、カドミウム、亜鉛等の有害な金属類を電気化学的に回収する方法に関する。通常、廃自動車、廃家電製品などはシュレッダーにより破砕して金属を回収するが、その際残ったシュレッダーダストは焼却減容し、発生する焼却飛灰あるいは焼却飛灰をさらにプラズマなどで溶融処理する。本発明は、このようにシュレッダーダストの焼却の際に発生する焼却飛灰、あるいはこの焼却飛灰の溶融の際に発生する溶融飛灰から、各種金属を分離回収する方法に関する。
【0002】
【従来の技術】
ごみ焼却施設などから排出される飛灰中には有害な金属類類が高濃度で含有されている。そのため、飛灰は厚生省の定めるつぎの4方法▲1▼溶融法▲2▼セメント固化▲3▼薬剤処理▲4▼酸抽出のうちいずれかで中間処理することが定められている。中間処理された飛灰は最終処分地で埋め立て処分されるが、有害な金属類の除去、浸出水中の塩類による悪影響、最終処分量の減容化、あるいは金属類の再資源化の観点から、飛灰中の金属類を回収する技術の確立が望まれている。例えば、湿式処理によって金属を溶出し、次いで金属の種類ごとにこれを濃縮し、各金属を非鉄精錬用原料として使用できる程度の濃縮物として回収し、精錬する方法(特開平7−138630号公報参照)などが提案されている。
【0003】
しかし、この方法では、金属溶出用の液に高価な薬品を使用しなければならず、工程が複雑であり、加えて濃縮物が水酸化物や硫化物からなるスラッジであるため、容積が大きく、また有害物であることから運搬面上多くの問題を抱えている。
【0004】
本発明者らは、飛灰中の金属類の分離回収を行うために鋭意研究を進めた結果、各種飛灰中の金属類を鉱酸の水溶液で抽出した後、この抽出液を電解浴とし、各金属の間に電気化学的析出電位に差異がある点を利用し、陰極電位を貴な電位から卑な電位へ段階的にもしくは徐々に低下させ、各段階で電解を行うことにより、銅、鉛、カドミウム、亜鉛等の金属類を金属インゴットの形態で分別して析出させることが可能であることを知見し、先に特許出願を行った(特願2000−370877号)。
【0005】
また、その改良発明として、pH1以上の水溶液で飛灰中の銅、カドミウム、亜鉛などの重金属を抽出した後に、各種金属の電気化学的析出電位に差異がある点を利用し、陰極電位を貴な電位から卑な電位へ段階的に移行させ、銅、カドミウム、亜鉛を電解析出後、pHを1以下にして鉛を抽出後に電気分解で鉛を析出させる方法を見出し、これも特許出願した(特願2001−3384号)。
【0006】
飛灰中の重金属の内で廃棄規制の観点から特に重要なものは鉛とカドミウムであり(金属等を含む産業廃棄物に係わる判定基準を定める総理府令環告13号)、その中でも飛灰中の含有量の大きさから鉛の処理が重要である。上記2件の電解析出法により、鉛を金属インゴットの形で析出させることができる。
【0007】
しかし、上記2件の電解析出法において、標準電極電位は銅では0.340V、鉛では−0.126V、カドミウムでは−0.403V、亜鉛では−0.763Vであるので、上記1件目の方法では、電解液の中に銅と鉛が共存し、また2件目の方法でも最初の工程で未反応の銅が鉛の電解時に残存し、そのために、電解析出した鉛はいずれも銅元素を含有するいわゆる合金めっきの形態をとることになる。従って、回収した鉛金属は不純物の銅を含み、鉛金属の資源的な価値が低下する。
【0008】
【発明が解決しようとする課題】
本発明の課題は、上記の実状に鑑み、シュレッダーダスト等の廃棄物を焼却した際に発生する焼却飛灰、あるいは焼却飛灰をさらにプラズマなどで溶融した際に発生する溶融飛灰から、各種金属を効率よくかつ簡単に分離回収することができる方法を提供することである。
【0009】
【課題を解決するための手段】
本発明は、飛灰をpH12以上の水溶液で抽出して鉛と亜鉛を含む抽出液を得、この抽出液の電気分解を行い、この前段電気分解において陰極電位を徐々にもしくは段階的に負の方向に変化させることにより陰極に鉛と亜鉛を分別して電解析出させ、その後、上記抽出で残った残査をpH1〜5の水溶液で抽出して銅とカドミウムを含む抽出液を得、この抽出液の電気分解を行い、この後段電気分解において陰極電位を徐々にもしくは段階的に負の方向に変化させることにより陰極に銅とカドミウムを分別して電解析出させることを特徴とする飛灰からの重金属の電気化学的回収方法を提供する。
【0010】
本発明の方法において、前段電気分解後の電解浴および後段電気分解後の電解浴を、別々に、新たな飛灰の処理における上記pH12以上の水溶液および上記pH1〜5の水溶液として再使用することが好ましい。
【0011】
本発明においては、また、前段電気分解の陽極電極として、チタン電極あるいは白金めっきしたチタン電極を、後段電気分解の陽極電極として、酸化イリジウム被覆したチタン上に二酸化マンガンと酸化モリブデンを析出させた電極あるいは白金めっきしたチタン電極をそれぞれ使用し、陰極電極として、鉛の電解析出時には鉛電極あるいは鉛めっきした鋼電極を、亜鉛の電解析出時にはチタン電極を、銅の電解析出時には銅電極を、カドミウムの電解析出時にはチタン電極あるいはアルミニウム電極を、順次取り替えて使用することが好ましい。
【0012】
本発明においては、鉛の抽出にpH12以上の水溶液を使用するために、抽出液には銅が含まれず前段電気分解で析出した鉛は銅を含まない。
【0013】
このような電解析出を行うと、反応が進行するにつれて電解浴中の金属イオンの濃度が低下し、析出に関する電流効率が低くなる。この問題を解決するために、電解析出により浴中の金属を析出させることができる金属イオン濃度の目安を10−4〜10−2mol/l程度の範囲に置き、あまり低い濃度まで反応をさせないで、低濃度の浴を抽出用の水溶液としてそのまま再利用し、新たな飛灰に対し上記方法により複数種の金属の抽出および分別析出を行う。この方法によると、析出に関する電流効率を下げずに効率よく電解析出を行うことができる。
【0014】
第1工程で、抽出槽で飛灰を水に溶解してスラリーとし、このスラリーを攪拌しながらNaOH、KOHなどの強アルカリを添加してpHを12以上にする。ここで、pHを12以上にするのは、液中に鉛と亜鉛を溶解させて、他の重金属である銅とカドミウムを溶解させないためである。上記pH値を維持しての攪拌時間は30分以上行なうのが好ましい。抽出液の温度は室温でもよいが、溶解速度を促進するために50℃以上にするのが望ましい。
【0015】
次いで、上記スラリーを濾過槽やフィルタープレスなどの固液分離装置を用いて固液分離する。
【0016】
第2工程では、得られた分離液すなわち抽出液を電解槽内に入れ、同槽内に陽極と陰極を配し、これらの間に一定電流を流して電解を行う。その時、陰極電位を段階的にもしくは徐々に負の方向に変化させる。この電解により、各段階で電解浴中の銅と鉛が分別して析出される。陽極としては、チタンあるいは白金めっきしたチタンを使用し、陰極としては、鉛あるいは鉛めっき鋼板を使用するのが好ましい。電気分解により亜鉛を析出する際には、陽極にチタンあるいは白金めっきしたチタン、陰極にはチタンを使用するのが好ましい。なぜなら、アルカリ溶液で鉛あるいは亜鉛をめっきすると、陽極上に二酸化鉛が析出するから酸化イリジウム被覆したチタン上に二酸化マンガンと酸化モリブデンを析出させた電極を使用しても本来の機能(塩素発生を起こさない)を発揮しないからである。この場合には、発生した塩素を苛性ソーダに吸収させることにより、次亜塩素酸ソーダとして回収する。
【0017】
さらに、電解析出により溶液中の金属イオン濃度を減少させる際の目安として、10−4〜10−2mol/l程度に置き、あまり低い濃度まで反応をさせないようにする。なぜなら、溶液中の金属イオン濃度が10−4mol/l以下になると、電流効率が20%以下と小さくなるからである。
【0018】
第3工程では、上記抽出で残った残査、すなわち第1工程で固液分離した後の残査をpH1〜5の水溶液で抽出して銅とカドミウムを含む抽出液を得る。pH1〜5の水溶液は、塩酸、硫酸などの鉱酸の水溶液であってよい。
【0019】
第4工程では、第3工程で得られた抽出液の電気分解を行う。この後段電気分解において陰極電位を徐々にもしくは段階的に負の方向に変化させることにより陰極に銅とカドミウムを分別して電解析出させる。その際、塩素が発生しないようにするために、陽極には酸化イリジウム被覆したチタン上に二酸化マンガンと酸化モリブデンを析出させた電極を使用するか、あるいは発生塩素を苛性ソーダで吸収して次亜塩素酸ソーダとして回収する。陰極には回収と電流効率を考慮して銅の析出時には銅板を、カドミウムの析出時にはアルミニウム板を使用するのが望ましい。
【0020】
第5工程では、前段電気分解後の電解浴および後段電気分解後の電解浴(銅、鉛、カドミウム、亜鉛の各イオン濃度が10−4mol/l以下になった電解浴)を、別々に、新たな飛灰の処理における上記pH12以上の水溶液および上記pH1〜5の水溶液として再使用する。
【0021】
なお、このような操作を繰り返し行うと、アルミニウム、カリウム、ナトリウムなどは次第に濃縮してそれ自身の溶解度にまで達して、第4工程において自然に溶解しなくなる。また、鉄、クロムはカドミウムめっき時に合金めっきとして析出する。
【0022】
【発明の実施の形態】
つぎに、本発明方法を実施例に基づいて具体的に説明する。
【0023】
第1工程
先ず、500mlビーカーに飛灰10gを入れ、その中に1N−NaOHを200ml加え、全体を50℃で1時間攪拌し、その後に固液分離した。その時、抽出液のpHは13であった。
【0024】
第2工程
得られた抽出液中に、陽極として面積10cm の白金めっきしたチタン電極を、陰極として面積10cm の鉛板電極をそれぞれ配し、0.05Aの一定電流で両極間で電気分解を行った。その時、陰極電位は−0.92V(標準水素電位に対し)から−1.29V(標準水素電位に対し)まで徐々に低下し、鉛の濃度は表1に示すように1.48(g/l)から0.21(g/l)まで減少した。
【0025】
その後、陰極を面積10cm のチタン電極に変えて同じく0.05Aの一定電流で電気分解を行った。その時、陰極電位は−1.29V(標準水素電位に対し)から−1.38V(標準水素電位に対し)まで徐々に低下し、亜鉛の濃度は表1に示すように3.45(g/l)から0.048(g/l)まで減少した。
【0026】
第3工程
第1工程で固液分離した後の残査7.8gを500mlビーカーに入れ、その中に1N−HClを170ml加え、全体を50℃で1時間攪拌し、その後に固液分離した。その時、抽出液のpHは3であった。固液分離後の残査は廃棄した。
【0027】
第4工程
得られた抽出液中に、陽極として面積10cm の酸化イリジウム被覆したチタン上に二酸化マンガンと酸化モリブデンを析出させた電極を、陰極として面積10cm の銅板電極をそれぞれ配し、0.05Aの一定電流で電気分解を行った。その時、陰極電位は−0.23V(標準水素電位に対し)から−0.30V(標準水素電位に対し)まで徐々に低下し、銅の濃度は表1に示すように0.17(g/l)から0.012(g/l)まで減少した。
【0028】
第5工程
第2工程と第4工程を終えた電解浴(銅、鉛、カドミウム、亜鉛の各イオン濃度が10−4mol/l以下になった電解浴)を、新たな飛灰の処理における上記pH12以上の水溶液および上記pH1〜5の水溶液として再使用した。こうして新しい飛灰に対し、第1工程〜第4工程を行った。その場合にも、1回目と同様に抽出、電解析出ができた。このような操作を繰り返し行ったところ5回目以降では、抽出液中のカドミウム濃度が高くなり、カドミウムの電解が可能となったので、銅の電解時に−0.42V(標準水素電位に対し)になった時点で陰極を面積10cm のアルミニウム板電極に変更して−1.03V(標準水素電位に対し)になるまで0.05Aの電流で電気分解を行った。各々の浸出操作時の収率は90%以上、電解操作時の効率は60%以上であり、飛灰から効率的に重金属を回収できることが明らかになった。
【0029】
【発明の効果】
本発明方法により、シュレッダーダスト等の廃棄物を焼却した際に発生する焼却飛灰、あるいは焼却飛灰をさらにプラズマなどで溶融した際に発生する溶融飛灰から、各種金属、とりわけ鉛、カドミウムを効率よくかつ簡単に分離回収することができる。
【0030】
本発明方法では、鉛の抽出にpH12以上の水溶液を使用するために、抽出液には銅が含まれず、前段電気分解で析出した鉛は銅を含まない。こうして高純度の鉛金属を得ることができる。
【0031】
【表1】

Figure 0003803858

【図面の簡単な説明】
【図1】本発明の実施例を示すフローシートである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for electrochemically recovering metals, particularly harmful metals such as copper, lead, cadmium and zinc, from incinerated fly ash and molten fly ash as a waste recycling technology. Usually, scrapped automobiles and waste home appliances are shredded with a shredder to recover the metal, but the remaining shredder dust is incinerated and reduced, and the generated incinerated fly ash or incinerated fly ash is further melted with plasma. . The present invention relates to a method for separating and recovering various metals from incinerated fly ash generated during incineration of shredder dust or from molten fly ash generated during melting of the incinerated fly ash.
[0002]
[Prior art]
The fly ash discharged from garbage incineration facilities, etc. contains high concentrations of harmful metals. For this reason, fly ash is determined to be intermediately treated by any one of the following four methods (1) melting method (2) cement solidification (3) chemical treatment (4) acid extraction determined by the Ministry of Health and Welfare. Intermediate fly ash is landfilled at the final disposal site, but from the viewpoints of removing harmful metals, adverse effects of salts in leachate, reducing the volume of final disposal, or recycling metals. Establishment of technology to recover metals in fly ash is desired. For example, a method of eluting a metal by wet processing, then concentrating it for each type of metal, recovering and refining each metal as a concentrate that can be used as a raw material for nonferrous refining (Japanese Patent Laid-Open No. 7-138630) Have been proposed).
[0003]
However, in this method, an expensive chemical must be used for the metal elution liquid, the process is complicated, and the concentrate is a sludge composed of hydroxide and sulfide. Also, because it is a harmful substance, it has many problems on the transportation surface.
[0004]
As a result of diligent research to separate and recover metals in fly ash, the present inventors have extracted metals in various fly ash with an aqueous solution of mineral acid, and then used this extract as an electrolytic bath. Taking advantage of the difference in electrochemical deposition potential between each metal, the cathode potential is lowered stepwise or gradually from a noble potential to a base potential, and electrolysis is carried out at each step to produce copper. It was discovered that metals such as lead, cadmium and zinc can be separated and deposited in the form of metal ingots, and a patent application was filed first (Japanese Patent Application No. 2000-370877).
[0005]
In addition, as an improved invention, after extracting heavy metals such as copper, cadmium, and zinc in fly ash with an aqueous solution having a pH of 1 or higher, the cathode potential can be increased by utilizing the difference in electrochemical deposition potential of various metals. A method of gradually shifting from a low potential to a base potential, electrolytically depositing copper, cadmium, and zinc, and then extracting lead after extracting the pH to 1 or less, and also applying for a patent. (Japanese Patent Application No. 2001-3384).
[0006]
Among the heavy metals in fly ash, those that are particularly important from the viewpoint of disposal regulations are lead and cadmium (the Prime Minister's Ordinance Notification No. 13 that establishes criteria for industrial waste containing metals, etc.), among which in fly ash It is important to treat lead due to its large content. Lead can be deposited in the form of a metal ingot by the above two electrolytic deposition methods.
[0007]
However, in the above two electrolytic deposition methods, the standard electrode potential is 0.340V for copper, -0.126V for lead, -0.403V for cadmium, and -0.763V for zinc. In this method, copper and lead coexist in the electrolyte, and in the second method, unreacted copper remains in the electrolysis of lead in the first step. It will take the form of so-called alloy plating containing copper element. Therefore, the recovered lead metal contains impurity copper, and the resource value of the lead metal is reduced.
[0008]
[Problems to be solved by the invention]
In view of the above situation, the problem of the present invention is that various kinds of incineration fly ash generated when incineration of waste such as shredder dust, or molten fly ash generated when the incineration fly ash is further melted with plasma, etc. The object is to provide a method capable of efficiently and easily separating and recovering metals.
[0009]
[Means for Solving the Problems]
In the present invention, fly ash is extracted with an aqueous solution having a pH of 12 or more to obtain an extract containing lead and zinc. The extract is electrolyzed, and the cathode potential is gradually or stepwise negative in the preceding electrolysis. By changing the direction, lead and zinc are separated and electrolytically deposited on the cathode, and then the residue remaining in the extraction is extracted with an aqueous solution of pH 1 to 5 to obtain an extract containing copper and cadmium. Electrolysis of liquid, and in this latter stage electrolysis, the cathode potential is gradually or stepwise changed in the negative direction to separate copper and cadmium on the cathode and electrolytically deposit them. A method for electrochemical recovery of heavy metals is provided.
[0010]
In the method of the present invention, the electrolytic bath after the first-stage electrolysis and the electrolytic bath after the second-stage electrolysis are separately reused as the aqueous solution having a pH of 12 or more and the aqueous solution having the pH of 1 to 5 in the treatment of fresh fly ash. Is preferred.
[0011]
In the present invention, a titanium electrode or a platinum-plated titanium electrode is used as the anode electrode for the first-stage electrolysis, and an electrode in which manganese dioxide and molybdenum oxide are deposited on titanium coated with iridium oxide as the anode electrode for the second-stage electrolysis. Alternatively, platinum-plated titanium electrodes are used respectively, and the cathode electrode is a lead electrode or a lead-plated steel electrode when lead is electrodeposited, a titanium electrode when zinc is electrodeposited, and a copper electrode when copper is electrodeposited. It is preferable that the titanium electrode or the aluminum electrode be sequentially replaced when cadmium is electrodeposited.
[0012]
In the present invention, since an aqueous solution having a pH of 12 or more is used for lead extraction, the extract does not contain copper and the lead deposited by the previous electrolysis does not contain copper.
[0013]
When such electrolytic deposition is performed, the concentration of metal ions in the electrolytic bath decreases as the reaction proceeds, and the current efficiency related to deposition decreases. In order to solve this problem, the standard of the metal ion concentration capable of depositing the metal in the bath by electrolytic deposition is set in the range of about 10 −4 to 10 −2 mol / l, and the reaction is carried out to a very low concentration. Instead, the low-concentration bath is reused as it is as an aqueous solution for extraction, and a plurality of types of metals are extracted and fractionated by the above method with respect to fresh fly ash. According to this method, electrolytic deposition can be performed efficiently without lowering the current efficiency related to deposition.
[0014]
In the first step, fly ash is dissolved in water in an extraction tank to form a slurry, and a strong alkali such as NaOH or KOH is added to the slurry while stirring the slurry to adjust the pH to 12 or more. Here, the pH is set to 12 or more because lead and zinc are dissolved in the liquid and copper and cadmium, which are other heavy metals, are not dissolved. The stirring time while maintaining the pH value is preferably 30 minutes or longer. The temperature of the extract may be room temperature, but is preferably 50 ° C. or higher in order to accelerate the dissolution rate.
[0015]
Next, the slurry is subjected to solid-liquid separation using a solid-liquid separation device such as a filtration tank or a filter press.
[0016]
In the second step, the obtained separated liquid, that is, the extracted liquid is put in an electrolytic cell, an anode and a cathode are arranged in the electrolytic cell, and a constant current is passed between them to perform electrolysis. At that time, the cathode potential is changed stepwise or gradually in the negative direction. By this electrolysis, copper and lead in the electrolytic bath are separated and deposited at each stage. Titanium or platinum-plated titanium is preferably used as the anode, and lead or lead-plated steel plate is preferably used as the cathode. When depositing zinc by electrolysis, it is preferable to use titanium or platinum-plated titanium for the anode and titanium for the cathode. This is because when lead or zinc is plated with an alkaline solution, lead dioxide is deposited on the anode. This is because it does not show up. In this case, the generated chlorine is absorbed by caustic soda and recovered as sodium hypochlorite.
[0017]
Further, as a guideline for reducing the metal ion concentration in the solution by electrolytic deposition, it is placed at about 10 −4 to 10 −2 mol / l so as not to cause the reaction to a very low concentration. This is because when the metal ion concentration in the solution is 10 −4 mol / l or less, the current efficiency is as small as 20% or less.
[0018]
In the third step, the residue remaining after the extraction, that is, the residue after solid-liquid separation in the first step is extracted with an aqueous solution having a pH of 1 to 5 to obtain an extract containing copper and cadmium. The aqueous solution having a pH of 1 to 5 may be an aqueous solution of a mineral acid such as hydrochloric acid or sulfuric acid.
[0019]
In the fourth step, the extract obtained in the third step is electrolyzed. In this post-stage electrolysis, the cathode potential is gradually or stepwise changed in the negative direction, whereby copper and cadmium are separated and electrolytically deposited on the cathode. At that time, in order to prevent chlorine from being generated, an electrode in which manganese dioxide and molybdenum oxide are deposited on iridium oxide-coated titanium is used for the anode, or the generated chlorine is absorbed by caustic soda and hypochlorous acid is used. Collect as acid soda. In consideration of recovery and current efficiency, it is desirable to use a copper plate for the deposition of copper and an aluminum plate for the deposition of cadmium.
[0020]
In the fifth step, the electrolytic bath after the first-stage electrolysis and the electrolytic bath after the second-stage electrolysis (electrolytic bath in which each ion concentration of copper, lead, cadmium, and zinc is 10 −4 mol / l or less) are separately used. The aqueous solution having a pH of 12 or higher and the aqueous solution having a pH of 1 to 5 are reused in the treatment of fresh fly ash.
[0021]
When such an operation is repeated, aluminum, potassium, sodium and the like are gradually concentrated to reach their own solubility and are not naturally dissolved in the fourth step. Iron and chromium are deposited as alloy plating during cadmium plating.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Next, the method of the present invention will be specifically described based on examples.
[0023]
First Step First, 10 g of fly ash was put into a 500 ml beaker, 200 ml of 1N-NaOH was added thereto, the whole was stirred at 50 ° C. for 1 hour, and then solid-liquid separation was performed. At that time, the pH of the extract was 13.
[0024]
In the extract obtained second step, the platinum-plated titanium electrode with an area of 10 cm 2 as the anode, arranged respectively lead plate electrode with an area of 10 cm 2 as a cathode, electrolysis between the two electrodes at a constant current of 0.05A Went. At that time, the cathode potential gradually decreases from -0.92 V (relative to the standard hydrogen potential) to -1.29 V (relative to the standard hydrogen potential), and the lead concentration is 1.48 (g / g) as shown in Table 1. from 1) to 0.21 (g / l).
[0025]
Thereafter, the cathode was changed to a titanium electrode having an area of 10 cm 2 and electrolysis was performed at a constant current of 0.05 A. At that time, the cathode potential gradually decreases from −1.29 V (relative to the standard hydrogen potential) to −1.38 V (relative to the standard hydrogen potential), and the zinc concentration is 3.45 (g / g) as shown in Table 1. from 1) to 0.048 (g / l).
[0026]
Third Step 7.8 g of the residue after solid-liquid separation in the first step was put in a 500 ml beaker, 170 ml of 1N HCl was added thereto, the whole was stirred at 50 ° C. for 1 hour, and then solid-liquid separation was performed. . At that time, the pH of the extract was 3. The residue after solid-liquid separation was discarded.
[0027]
The fourth step obtained extract, arranged electrodes to deposit a molybdenum oxide and manganese dioxide on titanium and iridium oxide-coated area 10 cm 2 as the anode, a copper plate electrode with an area of 10 cm 2 as a cathode, respectively, 0 Electrolysis was performed at a constant current of .05A. At that time, the cathode potential gradually decreases from −0.23 V (relative to the standard hydrogen potential) to −0.30 V (relative to the standard hydrogen potential), and the copper concentration is 0.17 (g / kg) as shown in Table 1. from 1) to 0.012 (g / l).
[0028]
5th step The electrolytic bath (electrolytic bath in which each ion concentration of copper, lead, cadmium, and zinc becomes 10 −4 mol / l or less) after finishing the second step and the fourth step is used in a new fly ash treatment. It was reused as an aqueous solution having a pH of 12 or more and an aqueous solution having the pH of 1 to 5. Thus, the first to fourth steps were performed on the new fly ash. Even in that case, extraction and electrolytic deposition were possible as in the first time. When such an operation was repeated, the cadmium concentration in the extract became higher and the cadmium electrolysis became possible after the fifth time, so that it was -0.42 V (relative to the standard hydrogen potential) during copper electrolysis. At that time, the cathode was changed to an aluminum plate electrode having an area of 10 cm 2 , and electrolysis was performed at a current of 0.05 A until it became −1.03 V (relative to the standard hydrogen potential). The yield during each leaching operation was 90% or more, and the efficiency during the electrolysis operation was 60% or more. It was revealed that heavy metals can be efficiently recovered from fly ash.
[0029]
【The invention's effect】
According to the method of the present invention, various metals, especially lead and cadmium, are produced from incinerated fly ash generated when incineration of waste such as shredder dust, or from molten fly ash generated when incinerated fly ash is further melted with plasma or the like. It can be separated and recovered efficiently and easily.
[0030]
In the method of the present invention, since an aqueous solution having a pH of 12 or more is used for lead extraction, the extract does not contain copper, and the lead deposited by the previous electrolysis does not contain copper. In this way, high purity lead metal can be obtained.
[0031]
[Table 1]
Figure 0003803858

[Brief description of the drawings]
FIG. 1 is a flow sheet showing an embodiment of the present invention.

Claims (3)

飛灰をpH12以上の水溶液で抽出して鉛と亜鉛を含む抽出液を得、この抽出液の電気分解を行い、この前段電気分解において陰極電位を徐々にもしくは段階的に負の方向に変化させることにより陰極に鉛と亜鉛を分別して電解析出させ、その後、上記抽出で残った残査をpH1〜5の水溶液で抽出して銅とカドミウムを含む抽出液を得、この抽出液の電気分解を行い、この後段電気分解において陰極電位を徐々にもしくは段階的に負の方向に変化させることにより陰極に銅とカドミウムを分別して電解析出させることを特徴とする飛灰からの重金属の電気化学的回収方法。The fly ash is extracted with an aqueous solution having a pH of 12 or more to obtain an extract containing lead and zinc, the extract is electrolyzed, and the cathode potential is gradually or stepwise changed in the negative direction in the preceding electrolysis. Thus, lead and zinc are separated and electrolytically deposited on the cathode, and then the residue remaining in the above extraction is extracted with an aqueous solution having a pH of 1 to 5 to obtain an extract containing copper and cadmium. Electrolysis of heavy metals from fly ash, characterized in that in the latter-stage electrolysis, the cathode potential is gradually or stepwise changed in the negative direction to separate copper and cadmium on the cathode and electrolytically deposit them. Recovery method. 請求項1記載の方法において、前段電気分解後の電解浴および後段電気分解後の電解浴を、別々に、新たな飛灰の処理における上記pH12以上の水溶液および上記pH1〜5の水溶液として再使用することを特徴とする、飛灰からの重金属の電気化学的回収方法。2. The method according to claim 1, wherein the electrolytic bath after the first-stage electrolysis and the electrolytic bath after the second-stage electrolysis are separately reused as the aqueous solution having the pH of 12 or more and the aqueous solution having the pH of 1 to 5 in the treatment of fresh fly ash. A method for electrochemical recovery of heavy metals from fly ash. 請求項1または2記載の方法において、前段電気分解の陽極電極として、チタン電極あるいは白金めっきしたチタン電極を、後段電気分解の陽極電極として、酸化イリジウム被覆したチタン上に二酸化マンガンと酸化モリブデンを析出させた電極あるいは白金めっきしたチタン電極をそれぞれ使用し、陰極電極として、鉛の電解析出時には鉛電極あるいは鉛めっきした鋼電極を、亜鉛の電解析出時にはチタン電極を、銅の電解析出時には銅電極を、カドミウムの電解析出時にはチタン電極あるいはアルミニウム電極を、順次取り替えて使用することを特徴とすることを特徴とする、飛灰からの重金属の電気化学的回収方法。3. The method according to claim 1, wherein a titanium electrode or a platinum-plated titanium electrode is used as an anode electrode for pre-stage electrolysis, and manganese dioxide and molybdenum oxide are deposited on iridium oxide-coated titanium as an anode electrode for post-stage electrolysis. Electrode or platinum-plated titanium electrode, respectively, and as cathode electrode, lead electrode or lead-plated steel electrode when lead is electrodeposited, titanium electrode when zinc is electrodeposited, and electrode when copper is electrodeposited A method for electrochemical recovery of heavy metals from fly ash, wherein a copper electrode is used by sequentially replacing a titanium electrode or an aluminum electrode when cadmium is electrolytically deposited.
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