JP3911587B2 - Electrochemical recovery of heavy metals from fly ash - Google Patents
Electrochemical recovery of heavy metals from fly ash Download PDFInfo
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- JP3911587B2 JP3911587B2 JP2001273088A JP2001273088A JP3911587B2 JP 3911587 B2 JP3911587 B2 JP 3911587B2 JP 2001273088 A JP2001273088 A JP 2001273088A JP 2001273088 A JP2001273088 A JP 2001273088A JP 3911587 B2 JP3911587 B2 JP 3911587B2
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- fly ash
- zinc
- lead
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- electrolyzed
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- 239000010881 fly ash Substances 0.000 title claims description 39
- 229910001385 heavy metal Inorganic materials 0.000 title claims description 12
- 238000011084 recovery Methods 0.000 title claims description 10
- 239000011701 zinc Substances 0.000 claims description 31
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 30
- 229910052725 zinc Inorganic materials 0.000 claims description 29
- 238000000034 method Methods 0.000 claims description 28
- 239000000243 solution Substances 0.000 claims description 25
- 239000007864 aqueous solution Substances 0.000 claims description 18
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 15
- 239000010936 titanium Substances 0.000 claims description 15
- 229910052719 titanium Inorganic materials 0.000 claims description 15
- DHCDFWKWKRSZHF-UHFFFAOYSA-N sulfurothioic S-acid Chemical compound OS(O)(=O)=S DHCDFWKWKRSZHF-UHFFFAOYSA-N 0.000 claims description 12
- 229910052981 lead sulfide Inorganic materials 0.000 claims description 8
- 229940056932 lead sulfide Drugs 0.000 claims description 8
- 239000000126 substance Substances 0.000 claims description 8
- 229910052984 zinc sulfide Inorganic materials 0.000 claims description 8
- 239000005083 Zinc sulfide Substances 0.000 claims description 7
- DRDVZXDWVBGGMH-UHFFFAOYSA-N zinc;sulfide Chemical compound [S-2].[Zn+2] DRDVZXDWVBGGMH-UHFFFAOYSA-N 0.000 claims description 7
- 239000002956 ash Substances 0.000 claims 1
- 230000005611 electricity Effects 0.000 claims 1
- 239000011133 lead Substances 0.000 description 31
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 20
- 229910052751 metal Inorganic materials 0.000 description 17
- 239000002184 metal Substances 0.000 description 17
- 239000007788 liquid Substances 0.000 description 15
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 12
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 12
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 description 12
- 239000010949 copper Substances 0.000 description 12
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 12
- 229910052793 cadmium Inorganic materials 0.000 description 11
- 229910052802 copper Inorganic materials 0.000 description 11
- 238000005868 electrolysis reaction Methods 0.000 description 11
- 150000002739 metals Chemical class 0.000 description 11
- 239000002002 slurry Substances 0.000 description 9
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 6
- 150000002500 ions Chemical class 0.000 description 6
- 229910052697 platinum Inorganic materials 0.000 description 6
- 238000000926 separation method Methods 0.000 description 6
- 238000000605 extraction Methods 0.000 description 5
- PTFCDOFLOPIGGS-UHFFFAOYSA-N Zinc dication Chemical compound [Zn+2] PTFCDOFLOPIGGS-UHFFFAOYSA-N 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 4
- 230000003247 decreasing effect Effects 0.000 description 4
- 238000000151 deposition Methods 0.000 description 4
- 239000000428 dust Substances 0.000 description 4
- 235000011121 sodium hydroxide Nutrition 0.000 description 4
- 238000003756 stirring Methods 0.000 description 4
- 239000002699 waste material Substances 0.000 description 4
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 3
- 230000008021 deposition Effects 0.000 description 3
- 238000007747 plating Methods 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- 239000011593 sulfur Substances 0.000 description 3
- 229910052717 sulfur Inorganic materials 0.000 description 3
- KZBUYRJDOAKODT-UHFFFAOYSA-N Chlorine Chemical compound ClCl KZBUYRJDOAKODT-UHFFFAOYSA-N 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- IOVCWXUNBOPUCH-UHFFFAOYSA-N Nitrous acid Chemical compound ON=O IOVCWXUNBOPUCH-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 239000002585 base Substances 0.000 description 2
- 239000012141 concentrate Substances 0.000 description 2
- FGRVOLIFQGXPCT-UHFFFAOYSA-L dipotassium;dioxido-oxo-sulfanylidene-$l^{6}-sulfane Chemical compound [K+].[K+].[O-]S([O-])(=O)=S FGRVOLIFQGXPCT-UHFFFAOYSA-L 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000004070 electrodeposition Methods 0.000 description 2
- 238000010828 elution Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- PIJPYDMVFNTHIP-UHFFFAOYSA-L lead sulfate Chemical compound [PbH4+2].[O-]S([O-])(=O)=O PIJPYDMVFNTHIP-UHFFFAOYSA-L 0.000 description 2
- RVPVRDXYQKGNMQ-UHFFFAOYSA-N lead(2+) Chemical compound [Pb+2] RVPVRDXYQKGNMQ-UHFFFAOYSA-N 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- 230000001376 precipitating effect Effects 0.000 description 2
- 238000004064 recycling Methods 0.000 description 2
- 238000007670 refining Methods 0.000 description 2
- AKHNMLFCWUSKQB-UHFFFAOYSA-L sodium thiosulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=S AKHNMLFCWUSKQB-UHFFFAOYSA-L 0.000 description 2
- 235000019345 sodium thiosulphate Nutrition 0.000 description 2
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- 229910000978 Pb alloy Inorganic materials 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 229910001297 Zn alloy Inorganic materials 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- CXKCTMHTOKXKQT-UHFFFAOYSA-N cadmium oxide Inorganic materials [Cd]=O CXKCTMHTOKXKQT-UHFFFAOYSA-N 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- 239000004568 cement Substances 0.000 description 1
- 229910001956 copper hydroxide Inorganic materials 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 150000004679 hydroxides Chemical class 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- -1 lead and zinc Chemical class 0.000 description 1
- 229910021514 lead(II) hydroxide Inorganic materials 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 239000010802 sludge Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- UGZADUVQMDAIAO-UHFFFAOYSA-L zinc hydroxide Chemical compound [OH-].[OH-].[Zn+2] UGZADUVQMDAIAO-UHFFFAOYSA-L 0.000 description 1
- 229910021511 zinc hydroxide Inorganic materials 0.000 description 1
- 229940007718 zinc hydroxide Drugs 0.000 description 1
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
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- 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、とりわけ鉛、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重金属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】
請求項１記載の発明は、ｐＨ７〜１２のチオ硫酸塩水溶液で飛灰から鉛を溶出させ、この溶出液を電解して鉛を硫化鉛として析出回収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である。
【０００６】
請求項２記載の発明は、請求項１記載の方法により溶出および電解を終えたチオ硫酸塩水溶液のｐＨを４〜６．５にして飛灰から亜鉛を溶出させ、この溶出液を電解して亜鉛を硫化亜鉛として析出回収することを特徴とする、請求項１記載の電気化学的回収方法である。
【０００７】
請求項３記載の発明は、請求項２記載の方法により溶出および電解を終えたチオ硫酸塩水溶液のｐＨを７〜１２にし、この液を請求項１の方法に循環再使用することを特徴とする、請求項１記載の電気化学的回収方法である。
【０００８】
請求項４記載の発明は、ｐＨ４〜６．５のチオ硫酸塩水溶液で飛灰から鉛と亜鉛を溶出させ、この溶出液を電解して鉛を硫化鉛として、および亜鉛を硫化亜鉛として析出回収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である。
【０００９】
請求項５記載の発明は、陽極としてはチタン電極あるいは白金めっきしたチタン電極を、陰極としてはチタン電極を使用することを特徴とする、請求項１〜４のいずれかに記載の電気化学的重金属の回収方法である。
【００１０】
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）。
【００１１】
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肝要である。
【００１２】
そこで、本発明者らは、飛灰をｐＨ４以下の硫酸水溶液で抽出処理して同液に銅、カドミウムおよび亜鉛を溶出させ、生じた飛灰含有スラリーの固液分離により得られた分離液中で陽極と陰極の間で電気分解を行い、その後、上記固液分離で残った残渣を苛性ソーダ等の抽出薬液で抽出処理して同液に鉛を溶出させ、生じた残渣含有スラリーの固液分離により得られた分離液から鉛を電解析出させる方法（特願２００１−２１９２５１号明細書）、および、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、得られた銅、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、得られた銅、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う方法（特願２００１−２１９２５６号明細書）を見出した、
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。
【００１３】
四番目と五番目の発明においては、ｐＨ４以下の硫酸水溶液を使用するので、抽出液は鉛を含まず、電解析出した亜鉛は鉛を含まない。また、電解を硫酸水溶液で行うので、電解中には有害な塩素ガスや亜硝酸ガスが発生しない。さらに、硫酸抽出後の残渣にはＰｂＳＯ４、ＣａＳＯ４、アルミナ、シリカしか残っていないので、鉛を抽出する場合の薬剤使用量が少なくてすむ。
【００１４】
ところが、四番目と五番目の発明においても、電解析出では、電解の進行により溶液中の金属イオンが低下していって１０−４ｍｏｌ／ｌ以下になると、電流効率が低下するという課題が残った。そこで、本発明者らは、鉛と亜鉛の電解をチオ硫酸ソーダあるいはチオ硫酸カリウムの水溶液中で行った際に、錯体の形態で溶解していた鉛イオンと亜鉛イオンがチオ硫酸中のイオウと非常に高い効率で反応を起こして硫化鉛を生じること、およびこの反応が水溶液中の鉛イオン濃度と亜鉛イオン濃度が１０−５ｍｏｌ／ｌ以下まで高い効率で進行することを見出し、この点に着目して本発明を完成した。
【００１５】
【発明の実施の形態】
鉛と亜鉛を分離回収する場合には次のプロセスを利用する。即ち、溶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チオ硫酸ソーダ、チオ硫酸カリウムと苛性ソーダを添加してｐＨを７〜１２にする。ここで、ｐＨを７以上にするのは、鉛を溶解させて亜鉛を溶解させないためである。上記ｐＨを維持しての攪拌時間は、好ましくは３０分以上であり、温度は室温でもよいが溶解速度を促進するために５０℃以上にしても良い。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し、溶出液と残渣を得る（第一工程）。
【００１６】
第二工程では、第一工程で得られた溶出液において、陽極と陰極の間に直流電圧をかけて溶液中の鉛とイオウを反応させて、硫化鉛を析出させる。陽極と陰極との間で電気分解により硫化鉛として鉛を析出させるにあたり、陽極としては、チタン電極あるいは白金めっきしたチタン電極を使用し、陰極としては、チタン電極を使用する。本反応は、錯イオンであるＰｂ（Ｓ２ Ｏ３ ）３ ４＋イオンが陰極上で分解反応してＰｂＳに変化するものと考えられる。
【００１７】
第三工程では、第二工程で電解を行った後の残液に硫酸を添加することにより、ｐＨを４〜６．５にして、この液へ、第一工程で生じた残渣から亜鉛を溶出させる。
【００１８】
第四工程では、第三工程で得られた溶出液において、陽極と陰極の間に直流電圧をかけて溶液中の亜鉛とイオウを反応させて、硫化亜鉛を析出させる。直流電圧をかける際に、陽極にはチタン電極あるいは白金めっきしたチタン電極を使用し、陰極にはチタン電極を使用するのが望ましい。本反応は、錯イオンであるＺｎ（Ｓ２ Ｏ３ ）３ ４＋イオンが陰極上で分解反応してＺｎＳに変化するものと考えられる。
【００１９】
第五工程では、第四工程で溶出および電解を終えたチオ硫酸塩水溶液のｐＨを７〜１２にし、この液を第１工程へ循環し再使用する。
【００２０】
一方、鉛と亜鉛を分離せずに回収する場合には、チオ硫酸塩水溶液のｐＨを４〜６．５にし、この水溶液を用いて一段で飛灰から鉛と亜鉛を溶出させ、陽極と陰極との間でこの溶出液を電気分解することにより硫化鉛と硫化亜鉛を同時に析出回収する。
【００２１】
【発明の実施の形態】
実施例１
（第一工程） 先ず、５００ｍｌビーカーに焼却飛灰２０ｇを入れ、その中に１Ｎ−チオ硫酸ソーダ水溶液を２００ｍｌ加えた後に、苛性ソーダによりｐＨを１０に調整し、得られたスラリーを３０℃で１時間攪拌後に固液分離して、溶出液と残渣を得た。
【００２２】
（第二工程） その後、この溶出液中に、陽極として面積５０ｃｍ２ の白金めっきしたチタン電極、陰極として面積５０ｃｍ２ のチタン電極板を入れて、両極間に２．５Ａの一定電流を流して溶出液を電解した。その時、液中の鉛イオン濃度は６８０ｍｇ／ｌから１ｍｇ／ｌ以下に低下した。
【００２３】
（第三工程） 第一工程で得られた残渣１５．８ｇを５００ｍｌのビーカーに入れ、その中に、第二工程における電解後の残液である１Ｎ−チオ硫酸ソーダ水溶液に硫酸を添加してｐＨを４に調整したものを２００ｍｌ入れて、得られたスラリーを５０℃で１時間攪拌後に固液分離して、溶出液と残渣を得た。
【００２４】
（第四工程） 第三工程で得た溶出液中に、陽極として面積５０ｃｍ２ の白金めっきしたチタン電極、陰極として面積５０ｃｍ２ のチタン電極を入れて、両極間に２．５Ａの一定電流を流して溶出液を電解した。その時、液中の亜鉛イオンの濃度は、２，８００（ｍｇ／ｌ）から５（ｍｇ／ｌ）まで低下した。
【００２５】
（第五工程） 第四工程で電解を終えたチオ硫酸塩水溶液のｐＨを７〜１２にし、この液を第一工程へ循環して再使用し、新しい飛灰を対象として第一工程〜第四工程を行った。
【００２６】
実施例２
（第一工程） 先ず、５００ｍｌビーカーに焼却飛灰２０ｇを入れ、その中に１Ｎ−チオ硫酸ソーダ水溶液を２００ｍｌ加えた後に、硫酸によりｐＨを４〜６．５に調整し、得られたスラリーを３０℃で１時間攪拌後に固液分離して、溶出液と残渣を得た。
【００２７】
（第二工程） その後、この溶出液中に、陽極として面積５０ｃｍ２ の白金めっきしたチタン電極、陰極として面積５０ｃｍ２ のチタン電極板を入れて、両極間に２．５Ａの一定電流を流して溶出液を電解した。その時、液中の鉛イオン濃度は６８０ｍｇ／ｌから１ｍｇ／ｌ以下に、亜鉛イオン濃度は２，８００（ｍｇ／ｌ）から５（ｍｇ／ｌ）まで低下した。
【００２８】
【発明の効果】
本発明によれば、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。
【図面の簡単な説明】
【図１】 実施例１を示すフローシートである。
【図２】 実施例２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, in particular harmful metals such as lead 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]
Harmful heavy metals are contained in high concentration in the fly ash discharged from garbage incineration facilities. 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 invention according to claim 1 is characterized in that lead is eluted from fly ash with an aqueous thiosulfate solution having a pH of 7 to 12, and this eluate is electrolyzed to precipitate and recover lead as lead sulfide. This is an electrochemical recovery method for heavy metals.
[0006]
The invention according to claim 2 is to elute zinc from fly ash by adjusting the pH of the aqueous thiosulfate solution that has been eluted and electrolyzed by the method according to claim 1 to 4 to 6.5, and electrolyzing the eluate. 2. The electrochemical recovery method according to claim 1, wherein zinc is precipitated and recovered as zinc sulfide.
[0007]
The invention according to claim 3 is characterized in that the pH of the thiosulfate aqueous solution that has been eluted and electrolyzed by the method according to claim 2 is adjusted to 7 to 12, and this solution is circulated and reused in the method of claim 1. The electrochemical recovery method according to claim 1.
[0008]
In the invention according to
[0009]
The invention according to claim 5 is characterized in that a titanium electrode or a platinum-plated titanium electrode is used as the anode, and a titanium electrode is used as the cathode. Electrochemical heavy metal according to any one of claims 1 to 4 This is a recovery method.
[0010]
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 pH 1 to 5, and copper and cadmium are extracted. The present inventors have found a method in which the potential is gradually transferred to the potential and copper and cadmium are electrolytically deposited (Japanese Patent Application No. 2001-037819).
[0011]
Here, among the heavy metals in fly ash, what is important from the viewpoint of disposal regulations is the recovery of lead and zinc, and it is important to separate and recover these.
[0012]
Therefore, the present inventors extracted fly ash with a sulfuric acid aqueous solution having a pH of 4 or less to elute copper, cadmium and zinc in the same solution, and in the separated liquid obtained by solid-liquid separation of the resulting fly ash-containing slurry. Electrolysis is performed between the anode and the cathode, and then the residue remaining in the solid-liquid separation is extracted with an extraction chemical solution such as caustic soda to elute lead into the same solution, and the resulting slurry containing the residue is solid-liquid separated. And a method of electrolytically precipitating lead from the separated solution obtained by the above (Japanese Patent Application No. 2001-219251), and the fly ash is extracted with a hydrochloric acid aqueous solution or a nitric acid aqueous solution having a pH of 4 or less, and copper, lead, Cadmium, zinc and calcium are eluted, and alkali is added to pH 7-9 to the extract obtained by solid-liquid separation of the resulting fly ash-containing slurry, and copper, lead, cadmium and zinc are precipitated as hydroxides. The resulting precipitate is separated, and an aqueous sulfuric acid solution is added to the resulting precipitate containing copper, lead, cadmium and zinc hydroxide to dissolve copper, cadmium and zinc, and lead is precipitated as lead sulfate. The resulting precipitate was separated, and a method for electrolysis between the anode and the cathode in the obtained sulfuric acid solution of copper, cadmium and zinc was found (Japanese Patent Application No. 2001-219256),
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.
[0013]
In the fourth and fifth inventions, since an aqueous sulfuric acid solution having a pH of 4 or less is used, the extract solution does not contain lead, and zinc that has been electrolytically deposited does not contain lead. Further, since electrolysis is performed with a sulfuric acid aqueous solution, no harmful chlorine gas or nitrous acid gas is generated during electrolysis. Furthermore, since only PbSO 4 , CaSO 4 , alumina, and silica remain in the residue after the sulfuric acid extraction, the amount of chemical used when extracting lead can be reduced.
[0014]
However, even in the fourth and fifth inventions, in the electrolytic deposition, when the metal ions in the solution are lowered by the progress of electrolysis and become 10 −4 mol / l or less, the problem that the current efficiency is lowered. The remaining. Therefore, the present inventors conducted the electrolysis of lead and zinc in an aqueous solution of sodium thiosulfate or potassium thiosulfate, and lead ions and zinc ions dissolved in the form of a complex were converted to sulfur in thiosulfate. It has been found that the reaction occurs with very high efficiency to produce lead sulfide, and that this reaction proceeds with high efficiency up to a concentration of lead ions and zinc ions in the aqueous solution of 10 −5 mol / l or less. The present invention was completed with attention.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The following process is used to separate and recover lead and zinc. That is, fly ash is dissolved in water in an elution tank to form a slurry, and while stirring the slurry, sodium thiosulfate, potassium thiosulfate and caustic soda are added to adjust the pH to 7-12. Here, the reason why the pH is set to 7 or more is to dissolve lead but not zinc. The stirring time while maintaining the pH is preferably 30 minutes or more, and the temperature may be room temperature, but may be 50 ° C. or more in order to accelerate the dissolution rate. Next, the slurry is filtered through a filtration device such as a filtration tank or a filter press to separate into solid and liquid to obtain an eluate and a residue (first step).
[0016]
In the second step, in the eluate obtained in the first step, a direct current voltage is applied between the anode and the cathode to cause the lead and sulfur in the solution to react to precipitate lead sulfide. When lead is deposited as lead sulfide by electrolysis between the anode and the cathode, a titanium electrode or a platinum-plated titanium electrode is used as the anode, and a titanium electrode is used as the cathode. In this reaction, it is considered that Pb (S 2 O 3 ) 3 4+ ions, which are complex ions, are decomposed on the cathode and changed to PbS.
[0017]
In the third step, by adding sulfuric acid to the remaining liquid after electrolysis in the second step, the pH is adjusted to 4 to 6.5, and zinc is eluted from the residue generated in the first step into this liquid. Let
[0018]
In the fourth step, in the eluate obtained in the third step, a direct current voltage is applied between the anode and the cathode to react zinc and sulfur in the solution to precipitate zinc sulfide. When applying a DC voltage, it is desirable to use a titanium electrode or a platinum-plated titanium electrode for the anode and a titanium electrode for the cathode. In this reaction, it is considered that Zn (S 2 O 3 ) 3 4+ ions, which are complex ions, are decomposed on the cathode to change to ZnS.
[0019]
In the fifth step, the pH of the aqueous thiosulfate solution that has been eluted and electrolyzed in the fourth step is set to 7 to 12, and this solution is circulated to the first step and reused.
[0020]
On the other hand, when recovering lead and zinc without separating them, the pH of the aqueous thiosulfate solution is set to 4 to 6.5, and the aqueous solution is used to elute lead and zinc from fly ash in one step, and the anode and cathode The eluate is electrolyzed between the lead and zinc sulfide and zinc sulfide are simultaneously deposited and recovered.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
(First Step) First, 20 g of incinerated fly ash was put into a 500 ml beaker, 200 ml of 1N-sodium thiosulfate aqueous solution was added thereto, pH was adjusted to 10 with caustic soda, and the resulting slurry was 1 at 30 ° C. After stirring for a period of time, solid-liquid separation was performed to obtain an eluate and a residue.
[0022]
(Second step) Thereafter, a platinum electrode having a platinum plating area of 50 cm 2 as an anode and a titanium electrode plate having an area of 50 cm 2 as a cathode were put in the eluate, and a constant current of 2.5 A was passed between both electrodes. The eluate was electrolyzed. At that time, the lead ion concentration in the liquid decreased from 680 mg / l to 1 mg / l or less.
[0023]
(Third Step) 15.8 g of the residue obtained in the first step is put in a 500 ml beaker, and sulfuric acid is added to the 1N-sodium thiosulfate aqueous solution that is the residual solution after the electrolysis in the second step. 200 ml of a solution adjusted to
[0024]
(Fourth step) In the eluate obtained in the third step, a platinum electrode having a platinum plating area of 50 cm 2 as an anode and a titanium electrode having an area of 50 cm 2 as a cathode are put, and a constant current of 2.5 A is applied between both electrodes. The eluate was electrolyzed by flowing. At that time, the concentration of zinc ions in the liquid decreased from 2,800 (mg / l) to 5 (mg / l).
[0025]
(Fifth step) The pH of the thiosulfate aqueous solution that has been electrolyzed in the fourth step is adjusted to 7 to 12, and this solution is circulated and reused in the first step. Four steps were performed.
[0026]
Example 2
(First step) First, 20 g of incinerated fly ash was put into a 500 ml beaker, 200 ml of 1N-sodium thiosulfate aqueous solution was added thereto, pH was adjusted to 4 to 6.5 with sulfuric acid, and the resulting slurry was obtained. After stirring for 1 hour at 30 ° C., solid-liquid separation was performed to obtain an eluate and a residue.
[0027]
(Second step) Thereafter, a platinum electrode having a platinum plating area of 50 cm 2 as an anode and a titanium electrode plate having an area of 50 cm 2 as a cathode were put in the eluate, and a constant current of 2.5 A was passed between both electrodes. The eluate was electrolyzed. At that time, the lead ion concentration in the liquid decreased from 680 mg / l to 1 mg / l or less, and the zinc ion concentration decreased from 2,800 (mg / l) to 5 (mg / l).
[0028]
【The invention's effect】
According to the present invention, various metals can be efficiently and easily produced from 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 or the like. Can be separated and recovered.
[Brief description of the drawings]
1 is a flow sheet showing Example 1. FIG.
2 is a flow sheet showing Example 2. FIG.
Claims (5)
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