JP3962855B2 - Recovery method of heavy metals from fly ash - Google Patents
Recovery method of heavy metals from fly ash Download PDFInfo
- Publication number
- JP3962855B2 JP3962855B2 JP2001219256A JP2001219256A JP3962855B2 JP 3962855 B2 JP3962855 B2 JP 3962855B2 JP 2001219256 A JP2001219256 A JP 2001219256A JP 2001219256 A JP2001219256 A JP 2001219256A JP 3962855 B2 JP3962855 B2 JP 3962855B2
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- Prior art keywords
- lead
- copper
- cadmium
- zinc
- fly ash
- Prior art date
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- 239000010881 fly ash Substances 0.000 title claims description 36
- 238000000034 method Methods 0.000 title claims description 29
- 229910001385 heavy metal Inorganic materials 0.000 title claims description 14
- 238000011084 recovery Methods 0.000 title claims description 9
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 41
- 239000010949 copper Substances 0.000 claims description 41
- 229910052802 copper Inorganic materials 0.000 claims description 39
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 claims description 38
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 36
- 229910052793 cadmium Inorganic materials 0.000 claims description 36
- 239000011701 zinc Substances 0.000 claims description 36
- 229910052725 zinc Inorganic materials 0.000 claims description 35
- 239000000243 solution Substances 0.000 claims description 33
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- 239000007864 aqueous solution Substances 0.000 claims description 18
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 16
- 239000002244 precipitate Substances 0.000 claims description 16
- 230000008021 deposition Effects 0.000 claims description 14
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- 239000007788 liquid Substances 0.000 claims description 13
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- 239000011575 calcium Substances 0.000 claims description 12
- 238000005868 electrolysis reaction Methods 0.000 claims description 12
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- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 6
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- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 5
- 239000002253 acid Substances 0.000 claims description 5
- 229910052782 aluminium Inorganic materials 0.000 claims description 5
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 5
- 150000004679 hydroxides Chemical class 0.000 claims description 5
- 229910017604 nitric acid Inorganic materials 0.000 claims description 5
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 4
- 238000000926 separation method Methods 0.000 claims description 4
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- 229910021511 zinc hydroxide Inorganic materials 0.000 claims description 3
- 229940007718 zinc hydroxide Drugs 0.000 claims description 3
- CXKCTMHTOKXKQT-UHFFFAOYSA-N cadmium oxide Inorganic materials [Cd]=O CXKCTMHTOKXKQT-UHFFFAOYSA-N 0.000 claims description 2
- 229910001956 copper hydroxide Inorganic materials 0.000 claims description 2
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 2
- AKHNMLFCWUSKQB-UHFFFAOYSA-L sodium thiosulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=S AKHNMLFCWUSKQB-UHFFFAOYSA-L 0.000 claims description 2
- 235000019345 sodium thiosulphate Nutrition 0.000 claims description 2
- 229910052751 metal Inorganic materials 0.000 description 19
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- 238000000151 deposition Methods 0.000 description 11
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 8
- 239000001257 hydrogen Substances 0.000 description 8
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- 229910021645 metal ion Inorganic materials 0.000 description 7
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Images
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/82—Recycling of waste of electrical or electronic equipment [WEEE]
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- Removal Of Specific Substances (AREA)
- Extraction Or Liquid Replacement (AREA)
- Water Treatment By Electricity Or Magnetism (AREA)
- Manufacture And Refinement Of Metals (AREA)
- Electrolytic Production Of Metals (AREA)
- Processing Of Solid Wastes (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、飛灰は厚生労働省の定めるつぎの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】
【発明が解決しようとする課題】
本発明の課題は、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。
【０００５】
【課題を解決するための手段】
本発明は、飛灰をｐＨ４以下の塩酸水溶液あるいは硝酸水溶液で抽出処理して同液に銅、鉛、カドミウム、亜鉛およびカルシウムを溶出させ、生じた飛灰含有スラリーの固液分離により得られた抽出液にアルカリをｐＨ７〜９まで添加し、銅、鉛、カドミウムおよび亜鉛を水酸化物として沈殿させ、生じた沈殿物を分離し、カルシウムを含む液を除去し、次いで、銅、鉛、カドミウムおよび亜鉛の水酸化物を含む沈殿物に硫酸水溶液を添加して銅、カドミウムおよび亜鉛を溶解させ、鉛を硫酸鉛として沈殿させ、生じた沈殿物を分離し、次いで、銅、カドミウムおよび亜鉛の硫酸溶液中で陽極と陰極の間で電気分解を行い、陰極電位を徐々にまたは段階的に負の方向に変化させることにより、陰極に銅、カドミウムおよび亜鉛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回収方法である。
【０００６】
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、先に、各種飛灰中の重金属を塩酸酸性水溶液などで溶出した後、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徐々にまたは段階的に変化させ、銅、鉛、カドミウム、亜鉛等の重金属を金属インゴットの形態で析出させることが可能であることを知見した（特願２０００−３７０８７７号明細書）。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、カドミウムおよび亜鉛を電解析出させた後、ｐＨを１以下にして鉛を抽出し、抽出液の電気分解で鉛を析出させる方法を見出した（特願２００１−００３３８４号明細書）。さらに、その改良発明として、飛灰からｐＨ１２以上の水溶液で鉛と亜鉛を抽出した後に、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、鉛、亜鉛を電解析出させた後、ｐＨ１２以上で抽出できなかった銅、カドミウムを含む残渣をｐＨ１〜５にして銅、カドミウムを抽出させ、貴な電位から卑な電位へ電位を段階的に移行させ、銅、カドミウムを電解析出させる方法を見出した（特願２００１−０３７８１９号明細書）。
【０００７】
ここで、飛灰中の重金属の内で廃棄規制の観点から重要なものは、鉛と亜鉛の回収であり、これらを分別して回収することが重要である。
【０００８】
一番目と二番目の発明では、いずれも酸性水溶液で抽出を行うが、薬剤として硫酸を使用すると不溶性の硫酸鉛が析出するため、これを以後の電解析出へ供することができない。従ってこの場合には必然的に塩酸あるいは硝酸を使用することになるが、この場合は抽出液を電解すると有害な塩素ガスや、亜硝酸ガスが発生する問題が生ずる。また、三番目の発明では、ｐＨ１２以上の水溶液で抽出をする場合に、苛性ソーダなどの薬剤がアルミニウムや鉄の抽出のためにも多量に消費されてしまいコスト高を招く上に、抽出した鉛と亜鉛を電解する場合に、陰極電圧を制御しても一部は鉛と亜鉛の合金として電解析出し、析出物の資源価値が落ちるという問題があった。
【０００９】
本発明方法は、ｐＨ７〜９以下では鉛の水酸化物が析出するがカルシウムは析出せず、カルシウムはｐＨ９〜１３において消石灰として析出するという現象を利用したものである。
【００１０】
また、銅、鉛、カドミウムおよび亜鉛の水酸化物を含む沈殿物に硫酸水溶液を添加して生じた硫酸鉛はカルシウムを含まないので、硫酸鉛を溶解する溶解薬液の使用量が少なくてすむ。
【００１１】
電解析出反応が進行するにつれて水溶液中の金属イオンの濃度が薄くなり、析出に関する電流効率が低下するので、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を１０−４〜１０−２ｍｏｌ／ｌ程度に置き、あまり低い濃度まで反応を行わないで、低濃度の金属イオンを含有する水溶液を循環再利用する。本方法によると、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。
【００１２】
【発明の実施の形態】
第１工程で、抽出槽で飛灰を水の添加によりスラリーとし、このスラリーを攪拌しながら塩酸水溶液または硝酸水溶液を添加してｐＨを４以下にする。ここで、塩酸水溶液または硝酸水溶液の添加でｐＨを４以下にするのは、銅、鉛、カドミウムおよび亜鉛を溶解させるためである。上記ｐＨを維持しての攪拌時間は、３０分以上であればよく、温度は室温でもよいが溶解速度を促進するためには５０℃以上にするのが望ましい。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濾過装置で濾過して固液分離する。
【００１３】
第２工程では、塩酸抽出液に苛性ソーダ、苛性カリ等のアルカリまたはその水溶液をｐＨ７〜９まで添加し、カルシウム以外の金属すなわち銅、鉛、カドミウムおよび亜鉛を水酸化物として沈殿させ、生じた沈殿物を分離し、カルシウムを含む排水を除去する。
【００１４】
第３工程では、第２工程で生じたカルシウム以外の金属すなわち銅、鉛、カドミウムおよび亜鉛の水酸化物に硫酸水溶液を添加して銅、カドミウムおよび亜鉛を溶解させ、鉛を硫酸鉛として沈殿させ、生じた沈殿物を分離する。
【００１５】
第４工程では、銅、カドミウムおよび亜鉛の硫酸溶液中で陽極と陰極の間で電気分解を行い、陰極電位を徐々にまたは段階的に負の方向に変化させることにより、陰極に銅、カドミウムおよび亜鉛を分別して電解析出させる。ここで陽極としては、チタンあるいは白金めっきしたチタンからなる電極を使用し、陰極としては、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アルミニウム電極を、亜鉛の電解析出時にはチタン電極を使用する。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を１０−４〜１０−２ｍｏｌ／ｌ程度に置き、あまり低い濃度まで反応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。
【００１６】
第５工程では、第３工程で分離した硫酸鉛を溶解薬液に溶解させ、得られた鉛溶解液から鉛を電解析出させる。鉛を溶解する溶解薬液として好ましくは苛性ソーダ、炭酸ソーダおよび／またはチオ硫酸ソーダを含む液を用いる。
【００１７】
第６工程では、第５工程で抽出した溶液から鉛を電解析出するが、陽極にはチタンあるいは白金めっきしたチタンからなる電極を使用し、陰極には鉛あるいはチタンからなる電極を使用するのが望ましい。
【００１８】
第７工程では、第４工程により銅、カドミウムおよび亜鉛の回収を終えこれら金属イオン濃度が１０−４ｍｏｌ／ｌ以下になった液を第１工程の酸含有液として循環再使用し、第６工程により鉛の回収を終えそのイオン濃度が１０−４ｍｏｌ／ｌ以下になった液を第５工程で硫酸鉛を溶解する溶液として循環再使用する。こうして、第１〜第６工程を行う。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これら自身の溶解度まで達して、第７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鍍金として析出する。
【００１９】
つぎに、本発明を実施例に基づいて具体的に説明する。
【００２０】
実施例
（第１工程）
まず、５００ｍｌビーカーに溶融飛灰２０ｇを入れ、その中に１Ｎ塩酸水溶液を２００ｍｌ入れて全体を５０℃で１時間攪拌し、同液に銅、鉛、カドミウム、亜鉛およびカルシウムを溶出させ、生じた飛灰含有スラリーを固液分離した。得られた分離液のｐＨは１．０であった。
【００２１】
（第２工程）
その後、分離液中に、１Ｎ苛性ソーダ水溶液をｐＨ９まで添加し、銅、鉛、カドミウムおよび亜鉛を水酸化物として沈殿させ、生じた沈殿物を分離し、カルシウムを含む排水を除去した。
【００２２】
（第３工程）
第２工程で析出した水酸化物を含む沈殿物に１Ｎ硫酸２００ｍｌを添加して銅、カドミウムおよび亜鉛を溶解させ、鉛を硫酸鉛として沈殿させ、生じた沈殿物を分離した。
【００２３】
（第４工程）
第３工程で分離した硫酸溶液中に、陽極として面積５０ｃｍ２ の白金めっきしたチタン電極を、陰極として面積５０ｃｍ２ の銅板を入れて、２．５Ａの一定電流で電解を行った。その時、陰極電位は−０．２３Ｖ（ｖｓ．標準水素電位）から−０．３０Ｖ（ｖｓ．標準水素電位）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。
【００２４】
その後、陰極を面積５０ｃｍ２ のチタン電極に代えて同じく２．５Ａの一定電流で電解を行った。その時、陰極電位は−１．２９Ｖ（ｖｓ．標準水素電位）から−１．３８Ｖ（ｖｓ．標準水素電位）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。
【００２５】
（第５工程）
第３工程で分離した硫酸鉛０．２ｇを５００ｍｌのビーカーに入れ、その中に、１Ｎ苛性ソーダ水溶液を７０ｍｌを加え５０℃で１時間攪拌し、鉛を鉛酸ナトリウムとして溶解させた。この溶液のｐＨは１３．８であった。
【００２６】
（第６工程）
第５工程で得た溶液中に、陽極として面積５０ｃｍ２ の白金めっきしたチタン電極を、陰極として面積５０ｃｍ２ の銅板を入れて、２．５Ａの一定電流で電解を行った。その時、陰極電位は−０．９２Ｖ（ｖｓ．標準水素電位）から−１．２９Ｖ（ｖｓ．標準水素電位）まで徐々に低下し、鉛の濃度は表１に示すように３．５９（ｇ／ｌ）から０．２１（ｇ／ｌ）まで減少した。
【００２７】
（第７工程）
第４工程により銅、カドミウムおよび亜鉛の回収を終えこれら金属イオン濃度が１０−４ｍｏｌ／ｌ以下になった液を第１工程の酸含有液として循環再使用し、第６工程により鉛の回収を終えそのイオン濃度が１０−４ｍｏｌ／ｌ以下になった液を第５工程で硫酸鉛を溶解する溶液として循環再使用した。こうして、第１〜第６工程を行った。その場合、２回目抽出液、２回目電解後液も１回目と同様に抽出および電解ができた。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（ｖｓ．標準水素電位）になった時点で陰極を面積５０ｃｍ２ のアルミニウム板に変更して−１．０３Ｖ（ｖｓ．標準水素電位）になるまで２．５Ａの電流で電解を行った。この後は４回目までと同様に陰極を亜鉛めっき鋼板に変更し、亜鉛のめっきを行った。各々の抽出操作時の収率は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。
【００２８】
【表１】
【発明の効果】
本発明の方法によれば、飛灰から銅、カドミウム、亜鉛、鉛等の重金属を効率的に回収することができる。
【図面の簡単な説明】
【図１】実施例による飛灰からの重金属回収方法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 subjected to intermediate treatment 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, Labor 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]
[Problems to be solved by the invention]
An object of the present invention is to efficiently and easily make various metals from incineration fly ash generated when incineration of wastes such as shredder dust, or molten fly ash generated when incineration fly ash is further melted with plasma or the like. It is to provide a method that can be separated and recovered.
[0005]
[Means for Solving the Problems]
The present invention was obtained by subjecting fly ash to extraction with a hydrochloric acid aqueous solution or a nitric acid aqueous solution having a pH of 4 or less to elute copper, lead, cadmium, zinc and calcium into the same solution, and solid-liquid separation of the resulting fly ash-containing slurry. Alkali is added to the extract to pH 7-9, copper, lead, cadmium and zinc are precipitated as hydroxides, the resulting precipitate is separated, the liquid containing calcium is removed , then copper, lead, cadmium And an aqueous solution of sulfuric acid to a precipitate containing zinc hydroxide to dissolve copper, cadmium and zinc, precipitate lead as lead sulfate, isolate the resulting precipitate, and then separate copper, cadmium and zinc Electrolysis is performed between the anode and cathode in a sulfuric acid solution, and the cathode potential is gradually or stepwise changed in the negative direction, so that copper, cadmium and zinc are separated and electrolyzed at the cathode. A method for recovering heavy metals from fly ash, characterized in that to out.
[0006]
As a result of diligent research for separating and recovering metals in fly ash, the present inventors first eluted heavy metals in various fly ash with hydrochloric acid aqueous solution, etc. Utilizing the point that there is a difference in mechanical deposition potential, the cathode potential is gradually or stepwise changed from a noble potential to a base potential to deposit heavy metals such as copper, lead, cadmium, and zinc in the form of metal ingots. (Japanese Patent Application No. 2000-370877). 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 low potential, electrolytically depositing copper, cadmium and zinc, extracting the lead at a pH of 1 or less, and precipitating the lead by electrolysis of the extract (Japanese Patent Application No. 2001-003384). Further, as an improved invention, after extracting lead and zinc from fly ash with an aqueous solution having a pH of 12 or more, the cathode potential is changed from a noble potential to a base potential by utilizing the difference in electrochemical deposition potential of various metals. After the lead and zinc are electrolytically deposited, the residue containing copper and cadmium that could not be extracted at pH 12 or higher is adjusted to
[0007]
Here, among the heavy metals in fly ash, what is important from the viewpoint of disposal regulation is the recovery of lead and zinc, and it is important to separate and recover these.
[0008]
In both the first and second inventions, extraction is carried out with an acidic aqueous solution. However, when sulfuric acid is used as a chemical, insoluble lead sulfate is deposited, and this cannot be used for subsequent electrolytic deposition. Therefore, in this case, hydrochloric acid or nitric acid is inevitably used. In this case, however, electrolysis of the extract causes a problem of generating harmful chlorine gas or nitrous acid gas. In addition, in the third invention, when extracting with an aqueous solution having a pH of 12 or more, a chemical such as caustic soda is consumed in a large amount for the extraction of aluminum and iron, and the cost is increased. In the case of electrolyzing zinc, there is a problem that even if the cathode voltage is controlled, a part of it is electrolytically deposited as an alloy of lead and zinc, and the resource value of the deposit is lowered.
[0009]
The method of the present invention utilizes the phenomenon that lead hydroxide precipitates at pH 7-9 or less, but calcium does not precipitate, and calcium precipitates as slaked lime at pH 9-13.
[0010]
Moreover, since the lead sulfate produced by adding an aqueous sulfuric acid solution to a precipitate containing copper, lead, cadmium and zinc hydroxide does not contain calcium, the amount of a dissolved chemical solution for dissolving lead sulfate can be reduced.
[0011]
As the electrolytic deposition reaction proceeds, the concentration of metal ions in the aqueous solution decreases, and the current efficiency related to the precipitation decreases. Therefore, the standard for reducing the metal ion concentration in the solution by electrolytic deposition is 10 −4 to 10. -2 It is placed at about mol / l, and an aqueous solution containing a low concentration of metal ions is circulated and reused without performing the reaction to a very low concentration. According to this method, electrolytic deposition can be performed efficiently without reducing the current efficiency related to deposition.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
In the first step, fly ash is made into a slurry by adding water in an extraction tank, and a hydrochloric acid aqueous solution or a nitric acid aqueous solution is added while stirring the slurry to make the pH 4 or less. Here, the reason why the pH is lowered to 4 or less by adding an aqueous hydrochloric acid solution or an aqueous nitric acid solution is to dissolve copper, lead, cadmium and zinc. The stirring time for maintaining the pH may be 30 minutes or more, and the temperature may be room temperature, but it is desirable to set the stirring temperature to 50 ° C. or more in order to promote the dissolution rate. Next, the slurry is filtered by a filtration device such as a filtration tank or a filter press to separate into solid and liquid.
[0013]
In the second step, an alkali such as caustic soda and caustic potash or an aqueous solution thereof is added to the hydrochloric acid extract until pH 7-9, and metals other than calcium, that is, copper, lead, cadmium and zinc are precipitated as hydroxides, and the resulting precipitate The waste water containing calcium is removed.
[0014]
In the third step, an aqueous sulfuric acid solution is added to the metal other than calcium generated in the second step, that is, hydroxides of copper, lead, cadmium and zinc to dissolve copper, cadmium and zinc, and lead is precipitated as lead sulfate. The resulting precipitate is separated.
[0015]
In the fourth step, electrolysis is performed between the anode and the cathode in a sulfuric acid solution of copper, cadmium and zinc, and the cathode potential is gradually or stepwise changed in the negative direction, whereby copper, cadmium and Zinc is fractionated and electrolytically deposited. Here, as the anode, an electrode made of titanium or platinum-plated titanium is used. As the cathode, a copper electrode is used for electrolytic deposition of copper, an aluminum electrode is used for electrolytic deposition of cadmium, and a titanium electrode is used for electrolytic deposition of zinc. Use electrodes. Furthermore, the standard at the time of reducing the metal ion concentration in the solution by electrolytic deposition is set to about 10 −4 to 10 −2 mol / l so as not to react 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.
[0016]
In the fifth step, the lead sulfate separated in the third step is dissolved in a dissolving chemical solution, and lead is electrolytically deposited from the obtained lead dissolving solution. A solution containing caustic soda, sodium carbonate and / or sodium thiosulfate is preferably used as a dissolving chemical for dissolving lead.
[0017]
In the sixth step, lead is electrolytically deposited from the solution extracted in the fifth step. An electrode made of titanium or platinum plated titanium is used for the anode, and an electrode made of lead or titanium is used for the cathode. Is desirable.
[0018]
In the seventh step, the recovery of copper, cadmium, and zinc in the fourth step is completed and the liquid in which the metal ion concentration is 10 −4 mol / l or less is circulated and reused as the acid-containing liquid in the first step. The liquid whose lead concentration is 10 −4 mol / l or less after the recovery of lead in the process is recycled and reused as a solution for dissolving lead sulfate in the fifth process. Thus, the first to sixth steps are performed. 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 seventh step. Iron and chromium are deposited as alloy plating during cadmium plating.
[0019]
Next, the present invention will be specifically described based on examples.
[0020]
Example (first step)
First, 20 g of molten fly ash was put into a 500 ml beaker, 200 ml of 1N hydrochloric acid aqueous solution was put therein, the whole was stirred at 50 ° C. for 1 hour, and copper, lead, cadmium, zinc and calcium were eluted in the same solution. The fly ash-containing slurry was subjected to solid-liquid separation. The pH of the obtained separation liquid was 1.0.
[0021]
(Second step)
Thereafter, a 1N aqueous solution of sodium hydroxide was added to the separated solution until pH 9, and copper, lead, cadmium and zinc were precipitated as hydroxides. The resulting precipitate was separated and the waste water containing calcium was removed.
[0022]
(Third step)
To the precipitate containing hydroxide precipitated in the second step, 200 ml of 1N sulfuric acid was added to dissolve copper, cadmium and zinc, and lead was precipitated as lead sulfate, and the resulting precipitate was separated.
[0023]
(4th process)
The sulfuric acid solution separated in the third step, a platinum plated titanium electrode with an area of 50 cm 2 as the anode, put the copper plate of area 50 cm 2 as a cathode, subjected to electrolysis at a constant current of 2.5A. At that time, the cathode potential gradually decreased from −0.23 V (vs. standard hydrogen potential) to −0.30 V (vs. standard hydrogen potential), and the copper concentration was 0.17 (g / kg) as shown in Table 1. from 1) to 0.012 (g / l).
[0024]
Thereafter, the cathode was replaced with a titanium electrode having an area of 50 cm 2 and electrolysis was performed at a constant current of 2.5 A. At that time, the cathode potential gradually decreased from -1.29 V (vs. standard hydrogen potential) to -1.38 V (vs. standard hydrogen potential), and the zinc concentration was 3.45 (g / g) as shown in Table 1. from 1) to 0.048 (g / l).
[0025]
(5th process)
Into a 500 ml beaker, 0.2 g of lead sulfate separated in the third step was added, and 70 ml of 1N sodium hydroxide aqueous solution was added and stirred at 50 ° C. for 1 hour to dissolve lead as sodium lead acid. The pH of this solution was 13.8.
[0026]
(6th process)
In the solution obtained in the fifth step, the platinum-plated titanium electrode with an area of 50 cm 2 as the anode, put the copper plate of area 50 cm 2 as a cathode, subjected to electrolysis at a constant current of 2.5A. At that time, the cathode potential gradually decreased from −0.92 V (vs. standard hydrogen potential) to −1.29 V (vs. standard hydrogen potential), and the lead concentration was 3.59 g / g as shown in Table 1. from 1) to 0.21 (g / l).
[0027]
(Seventh step)
After the recovery of copper, cadmium and zinc in the fourth step, the solution in which the metal ion concentration is 10 −4 mol / l or less is recycled and used as the acid-containing solution in the first step, and the recovery of lead is performed in the sixth step. Then, the solution whose ion concentration became 10 −4 mol / l or less was recycled and reused as a solution for dissolving lead sulfate in the fifth step. Thus, the first to sixth steps were performed. In that case, the second extract and the second electrolyzed solution were extracted and electrolyzed in the same manner as in the first. When such an operation was repeated, the cadmium concentration in the extract became high and the cadmium electrolysis became possible after the fifth time, so that -0.42 V (vs. standard hydrogen potential) during copper electrolysis. At that time, the cathode was changed to an aluminum plate with an area of 50 cm 2 and electrolysis was performed at a current of 2.5 A until it reached −1.03 V (vs. standard hydrogen potential). After this, the cathode was changed to a galvanized steel sheet in the same manner up to the fourth time, and zinc plating was performed. The yield during each extraction 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.
[0028]
[Table 1]
【The invention's effect】
According to the method of the present invention, heavy metals such as copper, cadmium, zinc and lead can be efficiently recovered from fly ash.
[Brief description of the drawings]
FIG. 1 is a flow sheet showing a heavy metal recovery method from fly ash according to an embodiment.
Claims (5)
次いで、銅、鉛、カドミウムおよび亜鉛の水酸化物を含む沈殿物に硫酸水溶液を添加して銅、カドミウムおよび亜鉛を溶解させ、鉛を硫酸鉛として沈殿させ、生じた沈殿物を分離し、
次いで、銅、カドミウムおよび亜鉛の硫酸溶液中で陽極と陰極の間で電気分解を行い、陰極電位を徐々にまたは段階的に負の方向に変化させることにより、陰極に銅、カドミウムおよび亜鉛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回収方法。The fly ash is extracted with a hydrochloric acid aqueous solution or a nitric acid aqueous solution having a pH of 4 or less to elute copper, lead, cadmium, zinc and calcium into the same solution, and the extract obtained by solid-liquid separation of the resulting fly ash-containing slurry is alkaline. Is added to pH 7-9, copper, lead, cadmium and zinc are precipitated as hydroxides, the resulting precipitate is separated, the liquid containing calcium is removed ,
Next, an aqueous sulfuric acid solution is added to the precipitate containing copper, lead, cadmium and zinc hydroxide to dissolve copper, cadmium and zinc, lead is precipitated as lead sulfate, and the resulting precipitate is separated,
Next, electrolysis is performed between the anode and the cathode in a sulfuric acid solution of copper, cadmium and zinc, and the cathode potential is gradually or stepwise changed in the negative direction to separate copper, cadmium and zinc into the cathode. A method for recovering heavy metals from fly ash, which is separately electrolytically deposited .
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2001
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2024147160A1 (en) * | 2023-01-03 | 2024-07-11 | Kaushik Palicha | Method of conversion of combustion wastes and refuse derived fuel into value-added products |
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