JP3568569B2 - Recycling of heavy metals by detoxifying incinerated ash or fly ash - Google Patents
Recycling of heavy metals by detoxifying incinerated ash or fly ash Download PDFInfo
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- JP3568569B2 JP3568569B2 JP2598994A JP2598994A JP3568569B2 JP 3568569 B2 JP3568569 B2 JP 3568569B2 JP 2598994 A JP2598994 A JP 2598994A JP 2598994 A JP2598994 A JP 2598994A JP 3568569 B2 JP3568569 B2 JP 3568569B2
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- 229910001385 heavy metal Inorganic materials 0.000 title claims description 70
- 239000010881 fly ash Substances 0.000 title claims description 50
- 239000002956 ash Substances 0.000 title claims description 22
- 238000004064 recycling Methods 0.000 title claims description 12
- 239000007788 liquid Substances 0.000 claims description 33
- 238000000034 method Methods 0.000 claims description 29
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- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 23
- 229910052725 zinc Inorganic materials 0.000 claims description 20
- 239000011701 zinc Substances 0.000 claims description 20
- 238000006386 neutralization reaction Methods 0.000 claims description 17
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims description 14
- 239000000706 filtrate Substances 0.000 claims description 14
- 239000002245 particle Substances 0.000 claims description 14
- 239000002351 wastewater Substances 0.000 claims description 10
- 150000002500 ions Chemical class 0.000 claims description 9
- 239000007787 solid Substances 0.000 claims description 9
- 229910052801 chlorine Inorganic materials 0.000 claims description 8
- 239000000460 chlorine Substances 0.000 claims description 8
- 239000013078 crystal Substances 0.000 claims description 8
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- 238000000926 separation method Methods 0.000 claims description 6
- 238000004062 sedimentation Methods 0.000 claims description 3
- 239000012141 concentrate Substances 0.000 claims description 2
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- 235000011121 sodium hydroxide Nutrition 0.000 description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical group O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 7
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- 229910052753 mercury Inorganic materials 0.000 description 5
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- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
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- 239000007858 starting material Substances 0.000 description 4
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- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 description 3
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- 238000004056 waste incineration Methods 0.000 description 3
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- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 2
- -1 and specifically Chemical compound 0.000 description 2
- 229910052785 arsenic Inorganic materials 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000003818 cinder Substances 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
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- 238000001784 detoxification Methods 0.000 description 2
- 150000002013 dioxins Chemical class 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- IHYNKGRWCDKNEG-UHFFFAOYSA-N n-(4-bromophenyl)-2,6-dihydroxybenzamide Chemical compound OC1=CC=CC(O)=C1C(=O)NC1=CC=C(Br)C=C1 IHYNKGRWCDKNEG-UHFFFAOYSA-N 0.000 description 2
- 229920001021 polysulfide Polymers 0.000 description 2
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- 150000004763 sulfides Chemical class 0.000 description 2
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- 239000005708 Sodium hypochlorite Substances 0.000 description 1
- RQNWIZPPADIBDY-UHFFFAOYSA-N arsenic atom Chemical compound [As] RQNWIZPPADIBDY-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 1
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- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 1
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- 229910052745 lead Inorganic materials 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
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- 239000007800 oxidant agent Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
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- 229910052700 potassium Inorganic materials 0.000 description 1
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- 239000002893 slag Substances 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 229910000029 sodium carbonate Inorganic materials 0.000 description 1
- SUKJFIGYRHOWBL-UHFFFAOYSA-N sodium hypochlorite Chemical compound [Na+].Cl[O-] SUKJFIGYRHOWBL-UHFFFAOYSA-N 0.000 description 1
- 229910052979 sodium sulfide Inorganic materials 0.000 description 1
- GRVFOGOEDUUMBP-UHFFFAOYSA-N sodium sulfide (anhydrous) Chemical compound [Na+].[Na+].[S-2] GRVFOGOEDUUMBP-UHFFFAOYSA-N 0.000 description 1
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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
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- Processing Of Solid Wastes (AREA)
- Manufacture And Refinement Of Metals (AREA)
Description
【０００１】
【産業上の利用分野】
本発明は、都市ごみ焼却工場や産業廃棄物焼却工場等における焼却炉および溶融炉から発生する有害物をも含めた各種重金属を含有する焼却灰または飛灰の無害化処理による重金属のリサイクル方法に関する。
【０００２】
【従来の技術】
一般に、事業場や一般家庭から排出されるゴミ（「都市ゴミ」または「一般廃棄物」と称されている）は、都市ゴミ焼却場に集められて焼却処分されるが、その際に焼却炉から発生する燃えがらや飛灰は最終処分場に堆積されていた。
【０００３】
しかしながら、近年、堆積場確保の困難性や、堆積される飛灰に含まれている水銀、鉛、亜鉛、カドミウム、砒素などの重金属やダイオキシン類の有害性が問題視されている。
【０００４】
そのため、上記有害物質の安定化を図るためセメント固化法や薬剤処理法等が開発され実用化されているが、セメント固化法等によると埋立容積を減らすことができないため、堆積場の確保に関する問題点は未解決のままであった。また、飛灰とセメントとの混練処理により、飛灰に含まれている重金属の溶出はなくなる（環境庁告示第１３号法による溶出試験）と報告されているが、酸性雨等の影響を考えた場合、セメントと混練した飛灰中の重金属類は必ずしも安定であるとはいいきれないものであった（菊池猛著「プラズマによるゴミ焼却灰の溶融処理による焼却残渣の無害化と生成スラグの資源化」ＰＰＭ１９９２／５）。
【０００５】
一方、焼却炉からの燃えがらや飛灰を溶融処理することにより、減容化やダイオキシン類の熱分解による無害化を図ることができるという報告がある（永田勝也著「都市ゴミ焼却炉におけるダイオキシン対策の現状と動向」廃棄物学会誌第３巻第３号）。
【０００６】
しかしながら、上記溶融処理によると、蒸気圧の大きい鉛やカドミウム等の重金属は、炉内で揮発して排ガス中に入り、排ガスに入った重金属は排ガス処理設備内で凝縮し、再び飛灰となってしまうという問題点があった。
【０００７】
【発明が解決しようとする課題】
そこで本発明は、上述従来の技術の問題点を解決し、飛灰中に含まれている重金属を安定な形で固定しながら積極的に分離回収し、環境汚染の問題を生じることなくリサイクルによる有価金属の有効利用が可能な焼却炉および溶融炉からの焼却灰または飛灰の処理方法を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明者等は、上記目的を達成するために鋭意研究した結果、焼却炉や溶融炉から発生する重金属を含有する焼却灰または飛灰を、塩素換算量で少なくとも２ｗｔ％ 以上、好ましくは３ｗｔ％ 以上の塩化物の存在下で加熱処理して重金属を塩化物として揮発させることによって重金属の塩化物を飛灰として濃縮させ、次いで該濃縮物から重金属を回収することによって前記重金属の有価金属としてのリサイクルをはかることが可能であることを見い出し、本発明方法を開発することができた。
【０００９】
すなわち本発明者等の開発した第１の発明は、重金属を含有する焼却灰または飛灰を、塩素換算量で少なくとも１２ｗｔ％の塩化物となるように調整した後加熱処理して重金属分を塩化物として揮発させることにより重金属を飛灰中に濃縮する第１工程、得られた飛灰をそのまままたは鉱酸とともに水性液中に添加し、ｐＨ３以下において溶解することによって鉛以外の重金属を液中に溶出せしめ、鉛を含む残渣を沈降分離または濾別して液から分離し資源としての有価物として回収する第２工程、上記第２工程において得られた上澄液または濾液を中和槽内で中和して亜鉛を主とする重金属の水酸化殿物を生成させた後、該水酸化殿物を種結晶として一定時間中和槽内で滞留循環させて粒子径の大きい水酸化殿物とする第３工程、および第３工程液に少量の硫化剤を添加することによって液中に含まれる水酸化殿物表面の重金属および液中の微量重金属イオンを硫化物とした後固液分離して重金属を含む固形殿物から重金属を資源としての有価物として回収する第４工程からなることを特徴とする焼却灰または飛灰の無害化処理による重金属のリサイクル方法であり；第２の発明は、前記重金属は鉛および亜鉛を含む、第１記載の焼却灰または飛灰の無害化処理による重金属のリサイクル方法であり；第３の発明は、前記固液分離によって得られる液分が直接放流される排水である、第１または２に記載の焼却灰または飛灰の無害化処理による重金属のリサイクル方法である。上記本発明方法において第１工程で使用する塩化物とは重金属を塩化物として揮発させるための塩素源となり得る化合物を意味し、具体的にはＮａＣｌ、ＣａＣｌ2、ＫＣｌ、ＭｇＣｌ2等である。
【００１０】
【作用】
本発明法を、都市ゴミ焼却工場において焼却灰の溶融処理の際に発生する飛灰の処理方法を中心に例にあげて具体的に説明する。
【００１１】
なお、明細書の実施例では、焼却灰として都市ゴミ焼却工場で発生したものを用いたが、この他下水処理工場や産業廃棄物処理工場からのものでも重金属を含有するものは、全て本発明法の対象原料となり得る。
【００１２】
これらの焼却灰または飛灰を処理原料として用いる場合、重金属分を揮発させて飛灰として濃縮する手段として、電気炉、アーク炉、バーナー炉、プラズマ炉、低周波炉あるいは高周波炉等公知の溶融炉を用いて９００℃以上の温度で原料中の重金属を揮発させ、生じた飛灰はＥＰやバッグフィルターあるいはベンチュリースクラバー等の捕集装置を用いて捕集する。
【００１３】
上記飛灰を捕集する場合、原料中に塩素換算量で少なくとも２ｗｔ％ 、好ましくは３ｗｔ％ 以上の塩化物の存在が必要である。この理由として、一般に、塩化物が不存在の原料を溶融する場合、１２００〜１４００℃位の温度で重金属分が溶融するが、塩化物が２ｗｔ％ 以上存在すると約９００℃前後の温度で原料中の重金属分がより多く揮発することが、本発明者等の試験により確認することができた（第１工程）。
【００１４】
この場合、出発原料によっては塩化物の存在しないものもあるが、この時はＮａＣｌ、ＣａＣｌ２ 等の塩化物を適量添加するか、飛灰のように重金属の他、塩化物を多量に含有する原料を併せて溶融してもよい。
【００１５】
次いで、得られた飛灰を液中に溶解して中和処理後、重金属分を固形殿物中に集め、固液分離して、これら固形殿物中の重金属を有価物として回収することにより有価金属をリサイクルする（第２工程）。
【００１６】
上記重金属分の回収手段としては、まず、飛灰を水あるいは水性液に溶解させてスラリーとし、このスラリーを攪拌しながら塩酸または硫酸等の鉱酸（無機酸）を添加してｐＨを３以下に調整する。なお、飛灰のｐＨはその組成によって異なるため、鉱酸の添加量は飛灰のｐＨに応じて調整する必要がある。すなわち、スラリーのｐＨは低いほうが後に得られる鉛残渣の鉛品位が高くなる傾向を示すため、飛灰の品位等に応じて最適ｐＨを設定し、そのｐＨを得るべく鉱酸の添加量を調整すればよいのである。また、上記スラリーのｐＨがすでに最適ｐＨである場合には鉱酸を加える必要はない。さらに、上記ｐＨを維持しての攪拌時間は少なくとも１０分あればよく、その時の温度は室温でもよい。
【００１７】
次いで、上記スラリーを沈降分離または濾過し、鉛を含有する残渣と鉛以外の重金属を含む水溶液とに分離する。なお、上記濾過において残渣に付着する浸出液を除去するためには、十分に水洗を行う必要があり、この作業は特に得られた残渣を資源として活用する場合に重要となる。
【００１８】
上記のようにして得た濾液には、一般に亜鉛のほかにカドミウム、銅、鉄、水銀等が含まれているが、飛灰に鉄が多く含まれている場合には、後工程で得られる亜鉛を主とする重金属の沈殿物における亜鉛品位が低くなるため、鉄を選択的に分離する必要がある。
【００１９】
この場合、上記濾液中に酸化剤（過酸化水素水、次亜塩素酸ナトリウムおよび塩素ガスなどからなる群より選ばれる少なくとも１種）を添加し、液中に溶解している第一鉄イオンを第二鉄イオンに酸化し、その後苛性ソーダ等の中和剤を添加して中和することによって第二鉄イオンを水酸化物として沈殿させ、この沈殿物を濾別することによって鉄を選択的に分離している。
【００２０】
次に、鉛および鉄が除かれた濾液に、水酸化ナトリウム、炭酸ナトリウムまたは水酸化カルシウムなどの中和剤を添加してそのｐＨを６以上に調整することにより、亜鉛を主とする重金属の水酸化殿物を生成させる。
【００２１】
この場合、生成する水酸化殿物の粒子は小さいため、後工程において添加する硫化剤の消費量が多くなることから、本発明法の一態様においては中和槽内で生成した水酸化殿物を種結晶として一定時間槽内に滞留循環させ、結晶粒子の大きい水酸化殿物が得られるようにした。
【００２２】
次いで、中和槽からのオーバーフロー液すなわち第２工程液を、硫化反応槽に導き硫化ナトリウム、水硫化ナトリウムまたは硫化水素などの硫化剤を少量添加することにより、水酸化殿物表面の重金属分のみを硫化物化させる他、液中の微量の重金属イオンを硫化物として沈殿させ、この溶液を濾過して亜鉛殿物と中和濾液を得る。
【００２３】
従来法の硫化物法では、非常に細かい結晶が生成するため沈降速度が遅く脱水性の悪い欠点を有するとともに、硫化剤が不足であれば液中の重金属イオンは十分低くならず、反対に過剰であれば、重金属が多硫化物イオンとなって液中に再び溶解し、排水の重金属イオンレベルが低くならなかった。
【００２４】
これに対し、本発明法は水酸化殿物粒子の表面のみを硫化物化する方法であり、先ず大きな水酸化殿物粒子に結晶を生成せしめてから硫化するので、生成する結晶は大きく沈降速度も大きく脱水性も極めて良好な殿物を得ることができる。
【００２５】
また、硫化剤も水酸化殿物粒子表面のみを十分に硫化するだけの量を添加すればよいため、硫化剤は従来法の１／５〜１／６程度あるいはそれ以下で済み、従来法のように多硫化物を生成させることなく液中に重金属イオンの非常に低い排水を安定して得ることができ、特に重金属イオンの中でも水銀、カドミウム濃度の低下に関しては顕著な効果があることがわかった。
【００２６】
以下、実施例により本発明をさらに詳細に説明する。しかし本発明の範囲は以下の実施例により制限されるものではない。
【００２７】
【実施例１】
Ａ都市ゴミ焼却工場からの焼却灰を出発原料として塩素量が約１２ｗｔ％ になるように調整したものを電気炉中に入れ、温度を１３００℃一定で３時間溶融して重金属分を塩化物として揮発させ、飛灰として濃縮したものをバグフィルターで捕集した（第１工程）。
【００２８】
次いで得られた飛灰を、図１に示す前工程６中に設けられた溶解槽（図示せず）に入れ、硫酸酸性侵出液中の固形殿物の割合が５０ｇ／ｌ となるように調整してスラリー化した。溶解槽からのオーバーフロー液を中和槽１および２に導き中和剤としてＮａＯＨを加えｐＨ６．０まで中和した。本実施例に用いた装置は、図１に示すような円筒形状の寸法が１５０ｍｍφ×２１０ｍｍＨの槽で上方にオーバーフロー口を要する２つの中和反応槽１および２と硫化反応槽３である。これら槽間の液の移動は、電磁定量ポンプを用いて行なったが、この場合、電磁定量ポンプによる流量の設定は浸出液の移動が５２〜３．５ｍｌ／ｍｉｎの流量、中和剤の添加が２２．６〜０．３６ｍｌ／ｍｉｎの流量となるようにした。
【００２９】
溶解槽内で得られた飛灰のスラリー液は液温２０℃、ｐＨ１．０であった。このスラリーを濾別して鉛を主体とする残渣を得た。
【００３０】
次いで上記濾別によって得られた濾液を中和反応槽１および２に送って、２００ｇ／ｌ に濃度を調整した水酸化ナトリウム水溶液を添加してｐＨ６以上に中和して水酸化殿物を生成させ、中和反応槽１および２内の滞留時間が合計で２時間となるように反応時間を調節して液を循環させ、水酸化殿物の粒径が大きくなるようにした。
【００３１】
次いで、上記水酸化殿物含有液を硫化反応槽３に導き、１０ｇ／ｌ に濃度調製した水硫化ナトリウム水溶液を酸化還元電位で−１００ｍＶまで添加し、亜鉛を主とする重金属の水酸化物および他の重金属の硫化殿物を生成させた。この場合の水硫化ナトリウムの添加量は硫化反応槽内の液中濃度で０．７ｇ／ｌ であり、水酸化殿物の凝集粒子は、凝集粒子の表面のみが硫化物となっているのが確認できた。
【００３２】
次に、上記沈殿物が生成した溶液を濾過し、亜鉛殿物と中和濾液とに分けた。このようにして得た残渣、沈殿物（亜鉛殿物）、中和濾液および飛灰におけるＣｕ、Ｐｂ、Ｚｎ、Ｆｅ、Ｃｄ、Ａｓ、Ｎａ、Ｋ、Ｃａ、Ｍｇ、ＳｉＯ２ 、Ａｌ２ Ｏ３ 、Ｃｌ、Ｓ、Ｈｇ等の含有量を調べ、その結果を表１および表２に示した。
【００３３】
【表１】
原料と各産物の化学組成
【表２】
原料と各産物の化学組成
（単位：固形物％・排水およびＨｇはｐｐｍ ）
このとき処理した灰の約１０％に当たる量が溶融飛灰として回収された。
【００３６】
表１および表２からわかるように、飛灰に含まれている鉛、亜鉛等の重金属は安定な形でほぼ完全に分離されていた。また、残渣中の鉛品位は３５．６０％、沈殿物中の亜鉛品位は３８．３５％であり、これらは資源として非鉄製錬所で処理できる品位のものであった。さらに、中和排水は排水基準を下回っており、直接、河川や海に放流できるものであった。
【００３７】
【実施例２】
実施例１の第１工程で得られた飛灰を、図１に示す中和反応槽１の前工程６中に設けた溶解槽において浸出してスラリーを得、このスラリーを中和反応槽１、２に送った後中和剤として２００ｇ／ｌ に濃度調整した水酸化ナトリウム水溶液を添加してｐＨ６以上になるように中和して水酸化殿物を生成させ、中和反応槽１および２内の滞留時間が合計で２時間となるように反応時間を調節して中和槽反応２のオーバーフロー液の一部を中和反応槽１に戻すことにより液を循環させて、水酸化殿物の粒径が大きくなるようにした。
【００３８】
次いで、該水酸化殿物含有液を硫化反応槽３に導き、１０ｇ／ｌ に濃度調整した水硫化ナトリウム水溶液を酸化還元電位で−１００ｍＶまで添加して、鉛および亜鉛を主とする重金属の水酸化殿物と他の重金属の硫化殿物を生成させた。この場合の水硫化ナトリウムの添加量は硫化反応槽内の液中濃度で０．８ｇ／ｌ であり、水酸化殿物の凝集粒子は凝集粒子の表面のみが硫化物となっていることが確認できた。
【００３９】
次に、上記沈殿物が生成した溶液を濾過し、亜鉛殿物と中和濾液とに分けた。このようにして得た沈殿物（鉛・亜鉛殿物）、中和濾液および飛灰における化学組成を調べ、その結果を表３および表４に示した。
【００４０】
【表３】
原料と各産物の化学組成
【表４】
原料と各産物の化学組成
（単位：固形物％・排水およびＨｇはｐｐｍ ）
表３および表４からもわかるように、飛灰に含まれている鉛・亜鉛等の重金属は安定な形でほぼ完全に分離されていた。この時の沈殿物中の鉛は１２．８９％、亜鉛は２４．１４％であり、この殿物を資源として非鉄製錬所で処理できる品位のものであった。さらに中和排水も実施例１と同様に排水基準を下回っており、直接、河川や海に放流できるものであった。
【００４３】
【比較例１】
焼却灰として塩化物含有量が、塩素として１．３ｗｔ％ しかないものを出発原料として実施例１に示す電気炉中で１２５０℃で溶融して、飛灰としてバグフィルターで捕集した。
【００４４】
次いで得られた飛灰を、中和反応槽において浸出してスラリー化して固液分離し、鉛を主とする残渣を得た。
【００４５】
次いで濾液には２００ｇ／ｌ に濃度調整した水酸化ナトリウム水溶液を添加してｐＨ８以上に中和して水酸化殿物を生成したものを循環することなく、次工程の硫化反応槽に導き、１０ｇ／ｌ に調整した水酸化ナトリウム水溶液を酸化還元電位で−１００ｍＶまで添加し、亜鉛を主とする重金属および他の重金属の硫化殿物を生成させた。
【００４６】
次に、上記沈殿物が生成した溶液を濾過し、亜鉛殿物と中和濾液とに分けた。このようにして得た残渣、沈殿物（亜鉛殿物）、中和濾液および飛灰における化学組成を調べ、その結果を表５および表６に示した。
【００４７】
【表５】
原料と各産物の化学組成
【表６】
原料と各産物の化学組成
（単位：固形物％・排水およびＨｇはｐｐｍ ）
このとき処理した灰の約３％に当たる量が溶融飛灰として回収された。
【００５０】
表５および表６からわかるように、重金属の回収率は本発明法に比べて相当悪く、その上中和反応時において生成する水酸化殿物の粒子が小さいため、硫化剤を多量に入れなければならず、その添加量は５〜６倍量を要した。さらに亜鉛殿物の脱水性が悪く、水分は８３％であった。これは本発明の方法による場合は水分が６４％であったのに比し、極めて脱水性が劣ることを示している。さらに排水の亜鉛、カドミウムおよび水銀の重金属イオン濃度も本発明の場合に比べて高く、排水基準を満たすことはできなかった。
【００５１】
【発明の効果】
上述のように本発明法によれば、出発原料である焼却灰からの重金属の回収を効率よく行なえるとともに、分離回収工程の中和剤や硫化剤の添加量も従来法に比し相当量減らすことができるため、処理コストを安価にできる効果を有する。
【図面の簡単な説明】
【図１】本発明法に用いた処理装置の断面概略図である。
【符号の説明】
１，２ 中和反応槽
３ 硫化反応槽
４ 攪拌棒
５ 種結晶を含む循環液
６ 前工程
７ 次工程[0001]
[Industrial applications]
The present invention relates to a method for recycling heavy metals by detoxifying incinerated ash or fly ash containing various heavy metals including harmful substances generated from incinerators and melting furnaces in municipal waste incineration plants, industrial waste incineration plants, and the like. .
[0002]
[Prior art]
Generally, garbage (known as “municipal garbage” or “general waste”) discharged from business establishments and households is collected at municipal waste incineration plants and incinerated. Cinders and fly ash generated from the river had been deposited at the final disposal site.
[0003]
However, in recent years, problems have been raised about difficulties in securing a deposition site and the harmful effects of heavy metals such as mercury, lead, zinc, cadmium, and arsenic and dioxins contained in fly ash to be deposited.
[0004]
Therefore, cement solidification methods and chemical treatment methods have been developed and put into practical use in order to stabilize the above harmful substances. The points remained unresolved. In addition, it has been reported that the elution of heavy metals contained in fly ash is eliminated by the kneading treatment of fly ash and cement (dissolution test according to the Environment Agency Notification No. 13 method). Heavy metals in fly ash kneaded with cement were not always stable (Takeshi Kikuchi, "Detoxification of incineration residues by melting treatment of garbage incineration ash by plasma and generation of slag Recycling "PPM 1992/5).
[0005]
On the other hand, there is a report that melting and treatment of cinders and fly ash from incinerators can reduce the volume and render them harmless due to the thermal decomposition of dioxins (Katsuya Nagata, "Dioxin countermeasures in municipal waste incinerators" Current Status and Trends, Journal of the Society of Waste Management, Vol.
[0006]
However, according to the above melting treatment, heavy metals such as lead and cadmium having a high vapor pressure are volatilized in the furnace and enter the exhaust gas, and the heavy metals entering the exhaust gas are condensed in the exhaust gas treatment facility and fly ash again. There was a problem that would.
[0007]
[Problems to be solved by the invention]
Accordingly, the present invention solves the above-mentioned problems of the conventional technology, and actively separates and collects heavy metals contained in fly ash while fixing the same in a stable manner, thereby recycling without causing environmental pollution problems. It is an object of the present invention to provide a method for treating incinerated ash or fly ash from an incinerator and a melting furnace, in which valuable metals can be effectively used.
[0008]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to achieve the above object. As a result, the incinerated ash or fly ash containing heavy metals generated from an incinerator or melting furnace was reduced to at least 2 wt% or more, preferably 3 wt% in terms of chlorine. The heavy metal chloride is concentrated as fly ash by heat treatment in the presence of the above chloride to volatilize the heavy metal as chloride, and then the heavy metal is recovered as valuable metal by recovering the heavy metal from the concentrate. It was found that recycling was possible, and the method of the present invention could be developed.
[0009]
That is, the first invention developed by the present inventors is to adjust the incinerated ash or fly ash containing a heavy metal to chloride of at least 12 wt% in terms of chlorine, and then heat-treat the heavy ash to remove the heavy metal component. The first step of concentrating heavy metals in fly ash by volatilizing it as a substance, adding the obtained fly ash as it is or adding it to an aqueous liquid together with a mineral acid and dissolving it at a pH of 3 or less to remove heavy metals other than lead in the liquid A second step in which the residue containing lead is settled or separated by filtration and separated from the liquid to recover as valuable resources as resources. The supernatant or filtrate obtained in the second step is neutralized in a neutralization tank. After summing to form a hydroxide precipitate of a heavy metal mainly composed of zinc, the hydroxide residue is used as a seed crystal to be retained and circulated in a neutralization tank for a certain period of time to form a hydroxide particle having a large particle diameter. Third step, and By adding a small amount of a sulfurizing agent to the process liquid, heavy metals on the surface of the hydroxide precipitate contained in the liquid and trace heavy metal ions in the liquid are converted into sulfides, and then separated into solids and liquids to remove heavy metals from solid precipitates containing heavy metals. A method of recycling heavy metals by detoxifying incinerated ash or fly ash, comprising a fourth step of recovering as resources as valuable resources; the second invention is characterized in that the heavy metals include lead and zinc , be a method for recycling heavy metal by detoxification of incineration ash or fly ash of the first described; third invention, the liquid fraction obtained by solid-liquid separation is wastewater discharged directly, first or 2 And a method for recycling heavy metals by detoxifying incinerated ash or fly ash. In the method of the present invention, the chloride used in the first step means a compound which can be a chlorine source for volatilizing heavy metals as chloride, and specifically, NaCl, CaCl 2 , KCl, MgCl 2 and the like.
[0010]
[Action]
The method of the present invention will be specifically described with reference to an example of a method of treating fly ash generated during melting treatment of incinerated ash in an incineration plant for municipal waste.
[0011]
In the examples of the specification, the incineration ash generated at the municipal garbage incineration plant was used. It can be a target material of the law.
[0012]
When these incinerated ash or fly ash are used as processing raw materials, as a means for volatilizing heavy metal components and concentrating it as fly ash, a known melting method such as an electric furnace, an arc furnace, a burner furnace, a plasma furnace, a low-frequency furnace or a high-frequency furnace is used. The heavy metals in the raw materials are volatilized at a temperature of 900 ° C. or higher using a furnace, and the generated fly ash is collected using a collecting device such as an EP, a bag filter, or a venturi scrubber.
[0013]
When collecting the fly ash, it is necessary that at least 2 wt%, preferably 3 wt% or more of chloride is present in the raw material in terms of chlorine. As a reason for this, in general, when a raw material in which chloride is not present is melted, a heavy metal component is melted at a temperature of about 1200 to 1400 ° C. It was confirmed by a test by the present inventors that the heavy metal component of (1) volatilized more (first step).
[0014]
In this case, depending on the starting material, there is a case where no chloride is present. In this case, an appropriate amount of chloride such as NaCl or CaCl 2 is added, or a large amount of chloride is contained in addition to heavy metals such as fly ash. The raw materials may be melted together.
[0015]
Next, the obtained fly ash is dissolved in the liquid, neutralized, and then the heavy metals are collected in a solid deposit, separated by solid-liquid separation, and the heavy metals in these solid deposits are collected as valuable resources. Recycling valuable metals (second step).
[0016]
As a means for recovering the heavy metals, first, fly ash is dissolved in water or an aqueous liquid to form a slurry, and a mineral acid (inorganic acid) such as hydrochloric acid or sulfuric acid is added to the slurry while stirring to adjust the pH to 3 or less. Adjust to Since the pH of fly ash varies depending on its composition, the amount of mineral acid added needs to be adjusted according to the pH of fly ash. In other words, the lower the pH of the slurry, the higher the lead quality of the lead residue obtained later tends to be. Therefore, the optimum pH is set according to the grade of fly ash, etc., and the amount of the mineral acid added is adjusted to obtain the pH. You just have to do it. Further, when the pH of the slurry is already at the optimum pH, it is not necessary to add a mineral acid. Further, the stirring time for maintaining the above pH may be at least 10 minutes, and the temperature at that time may be room temperature.
[0017]
Next, the slurry is settled or separated by filtration to separate a residue containing lead and an aqueous solution containing heavy metals other than lead. In order to remove the leachate adhering to the residue in the above-mentioned filtration, it is necessary to sufficiently wash with water, and this operation is particularly important when the obtained residue is used as a resource.
[0018]
The filtrate obtained as described above generally contains cadmium, copper, iron, mercury, etc. in addition to zinc, but when fly ash contains a large amount of iron, it is obtained in a later step. It is necessary to selectively separate iron because the zinc quality in the sediment of heavy metals, mainly zinc, is low.
[0019]
In this case, an oxidizing agent (at least one selected from the group consisting of aqueous hydrogen peroxide, sodium hypochlorite, and chlorine gas) is added to the filtrate, and ferrous ions dissolved in the liquid are added. The ferric ion is oxidized to ferric ion and then neutralized by adding a neutralizing agent such as caustic soda to precipitate the ferric ion as a hydroxide, and the precipitate is separated by filtration to selectively remove iron. Are separated.
[0020]
Next, a neutralizing agent such as sodium hydroxide, sodium carbonate or calcium hydroxide is added to the filtrate from which lead and iron have been removed to adjust the pH thereof to 6 or more, whereby zinc-based heavy metals are removed. A hydroxide deposit is formed.
[0021]
In this case, since the particles of the hydroxide precipitate generated are small, the consumption amount of the sulfurizing agent added in the subsequent step increases, and therefore, in one embodiment of the method of the present invention, the hydroxide precipitate generated in the neutralization tank is used. Was circulated as a seed crystal in a tank for a certain period of time so that a hydroxide having a large crystal particle was obtained.
[0022]
Next, the overflow liquid from the neutralization tank, that is, the second process liquid, is introduced into the sulfurization reaction tank, and a small amount of a sulfurizing agent such as sodium sulfide, sodium hydrosulfide, or hydrogen sulfide is added, so that only heavy metal on the surface of the hydroxide precipitate is added. In addition to the sulfide conversion, a trace amount of heavy metal ions in the solution is precipitated as sulfide, and the solution is filtered to obtain a zinc residue and a neutralized filtrate.
[0023]
The conventional sulfide method has the disadvantage that the sedimentation rate is slow due to the formation of very fine crystals and the dehydration is poor.If the sulfide agent is insufficient, the heavy metal ions in the liquid will not be low enough, and In this case, the heavy metal was converted into polysulfide ions and dissolved again in the liquid, and the level of heavy metal ions in the wastewater did not decrease.
[0024]
On the other hand, the method of the present invention is a method of sulphidizing only the surface of the hydroxide precipitate particles.Since the crystals are first formed on the large hydroxide precipitate particles and then sulfided, the generated crystals are large and the sedimentation speed is large. It is possible to obtain a deposit with great dehydration properties and very good dehydration properties.
[0025]
Also, the sulphidating agent may be added in an amount sufficient to sufficiently sulphide only the surface of the hydroxide precipitate particles. It is possible to stably obtain a very low drainage of heavy metal ions in the liquid without generating polysulfides as described above, and it is clear that there is a remarkable effect especially on the reduction of mercury and cadmium concentrations among heavy metal ions. Was.
[0026]
Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited by the following examples.
[0027]
Embodiment 1
A Incinerated ash from the municipal garbage incineration plant was used as a starting material, and adjusted into an electric furnace with the amount of chlorine adjusted to about 12 wt%, melted at a constant temperature of 1300 ° C for 3 hours to convert heavy metal components into chlorides. What was volatilized and concentrated as fly ash was collected by a bag filter (first step).
[0028]
Next, the obtained fly ash is put into a dissolving tank (not shown) provided in the pre-process 6 shown in FIG. 1 so that the ratio of solid deposits in the sulfuric acid leaching solution is 50 g / l. The slurry was adjusted and slurried. The overflow solution from the dissolution tank was introduced into
[0029]
The fly ash slurry obtained in the dissolution tank had a liquid temperature of 20 ° C. and a pH of 1.0. The slurry was separated by filtration to obtain a residue mainly composed of lead.
[0030]
Next, the filtrate obtained by the above-mentioned filtration is sent to
[0031]
Next, the solution containing the hydroxide precipitate was introduced into the
[0032]
Next, the solution in which the precipitate was formed was filtered, and separated into a zinc residue and a neutralized filtrate. Cu, Pb, Zn, Fe, Cd, As, Na, K, Ca, Mg, SiO 2 , Al 2 O 3 in the residue, precipitate (zinc deposit), neutralized filtrate and fly ash thus obtained , Cl, S, Hg and the like were examined, and the results are shown in Tables 1 and 2.
[0033]
[Table 1]
Raw material and chemical composition of each product
[Table 2]
Raw material and chemical composition of each product
(Unit:% solids, wastewater and Hg are ppm)
At this time, about 10% of the treated ash was recovered as molten fly ash.
[0036]
As can be seen from Tables 1 and 2, heavy metals such as lead and zinc contained in fly ash were almost completely separated in a stable form. Further, the lead grade in the residue was 35.60%, and the zinc grade in the precipitate was 38.35%, and these were grades that could be treated as a resource in a non-ferrous smelter. Furthermore, the neutralized effluent was below the effluent standard and could be discharged directly into rivers and the sea.
[0037]
The fly ash obtained in the first step of Example 1 is leached in a dissolving tank provided in the
[0038]
Next, the hydroxide-containing solution is introduced into the
[0039]
Next, the solution in which the precipitate was formed was filtered, and separated into a zinc residue and a neutralized filtrate. The precipitates (lead / zinc deposits), neutralized filtrate and fly ash thus obtained were examined for their chemical compositions. The results are shown in Tables 3 and 4.
[0040]
[Table 3]
Raw material and chemical composition of each product
[Table 4]
Raw material and chemical composition of each product
(Unit:% solids, wastewater and Hg are ppm)
As can be seen from Tables 3 and 4, heavy metals such as lead and zinc contained in fly ash were almost completely separated in a stable form. At this time, the lead in the precipitate was 12.89% and the zinc was 24.14%, and the deposit was of a grade that could be processed at a nonferrous smelter as a resource. Further, the neutralized wastewater was below the wastewater standard similarly to Example 1, and could be discharged directly to rivers and the sea.
[0043]
[Comparative Example 1]
The incinerated ash having a chloride content of only 1.3 wt% as chlorine was melted at 1250 ° C. in the electric furnace shown in Example 1 as a starting material, and was collected as fly ash by a bag filter.
[0044]
Next, the obtained fly ash was leached in a neutralization reaction tank to form a slurry, which was subjected to solid-liquid separation to obtain a residue mainly containing lead.
[0045]
Next, an aqueous solution of sodium hydroxide adjusted to a concentration of 200 g / l was added to the filtrate to neutralize the solution to a pH of 8 or more to form a hydroxide precipitate. An aqueous sodium hydroxide solution adjusted to / l was added to an oxidation-reduction potential of up to -100 mV to produce zinc-mainly heavy metal and sulfide of other heavy metals.
[0046]
Next, the solution in which the precipitate was formed was filtered, and separated into a zinc residue and a neutralized filtrate. The chemical compositions of the residue, precipitate (zinc deposit), neutralized filtrate and fly ash thus obtained were examined. The results are shown in Tables 5 and 6.
[0047]
[Table 5]
Raw material and chemical composition of each product
[Table 6]
Raw material and chemical composition of each product
(Unit:% solids, wastewater and Hg are ppm)
At this time, about 3% of the treated ash was recovered as molten fly ash.
[0050]
As can be seen from Tables 5 and 6, the recovery rate of heavy metals is considerably worse than that of the method of the present invention. In addition, since the particles of hydroxide precipitate generated during the neutralization reaction are small, a large amount of sulphidating agent must be added. It had to be added 5 to 6 times. Further, the dehydration property of the zinc deposit was poor, and the water content was 83%. This indicates that the method according to the present invention is extremely inferior in dehydration properties as compared with a water content of 64%. Furthermore, the heavy metal ion concentrations of zinc, cadmium and mercury in the wastewater were higher than in the case of the present invention, and the wastewater standards could not be satisfied.
[0051]
【The invention's effect】
As described above, according to the method of the present invention, it is possible to efficiently recover heavy metals from incineration ash, which is a starting material, and the amount of a neutralizing agent and a sulphidating agent added in the separation and recovery process is considerably larger than in the conventional method. Since it can be reduced, there is an effect that the processing cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a processing apparatus used in the method of the present invention.
[Explanation of symbols]
1, 2
Claims (3)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2598994A JP3568569B2 (en) | 1994-01-28 | 1994-01-28 | Recycling of heavy metals by detoxifying incinerated ash or fly ash |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2598994A JP3568569B2 (en) | 1994-01-28 | 1994-01-28 | Recycling of heavy metals by detoxifying incinerated ash or fly ash |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH07214029A JPH07214029A (en) | 1995-08-15 |
| JP3568569B2 true JP3568569B2 (en) | 2004-09-22 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2598994A Expired - Lifetime JP3568569B2 (en) | 1994-01-28 | 1994-01-28 | Recycling of heavy metals by detoxifying incinerated ash or fly ash |
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Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR970069157A (en) * | 1996-04-30 | 1997-11-07 | 이대원 | Stabilization Method of Municipal Waste Incineration Ash using Waste Desulfurization Slag |
| JP4567544B2 (en) * | 2005-07-25 | 2010-10-20 | 株式会社神鋼環境ソリューション | Detoxification treatment method and detoxification treatment apparatus for composite heavy metal contaminated soil |
| JP5016929B2 (en) * | 2007-01-15 | 2012-09-05 | Ｄｏｗａメタルマイン株式会社 | Arsenic solution purification method |
| JP5570106B2 (en) * | 2008-09-26 | 2014-08-13 | 太平洋セメント株式会社 | Cement kiln exhaust gas treatment apparatus and treatment method |
| JP6724433B2 (en) * | 2016-03-10 | 2020-07-15 | 住友金属鉱山株式会社 | Wastewater treatment method |
| CN106378352B (en) * | 2016-11-18 | 2018-10-16 | 华中科技大学 | A kind of incineration of refuse flyash fused salt heat treatment method |
| JP6809915B2 (en) * | 2017-01-27 | 2021-01-06 | 太平洋セメント株式会社 | Heavy metal recovery method for incineration ash and heavy metal recovery processing system for incineration ash |
| CN113943011A (en) * | 2021-09-17 | 2022-01-18 | 光大环保技术研究院（深圳）有限公司 | Method for resource utilization of secondary fly ash after melting of hazardous waste plasma |
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1994
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| Publication number | Publication date |
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| JPH07214029A (en) | 1995-08-15 |
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