JP3911538B2 - Heavy metal recovery from fly ash - Google Patents
Heavy metal recovery from fly ash Download PDFInfo
- Publication number
- JP3911538B2 JP3911538B2 JP2000170652A JP2000170652A JP3911538B2 JP 3911538 B2 JP3911538 B2 JP 3911538B2 JP 2000170652 A JP2000170652 A JP 2000170652A JP 2000170652 A JP2000170652 A JP 2000170652A JP 3911538 B2 JP3911538 B2 JP 3911538B2
- Authority
- JP
- Japan
- Prior art keywords
- alkali
- mineral acid
- fly ash
- solution
- leaching
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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- 229910001385 heavy metal Inorganic materials 0.000 title claims description 71
- 239000010881 fly ash Substances 0.000 title claims description 57
- 238000011084 recovery Methods 0.000 title claims description 9
- 238000002386 leaching Methods 0.000 claims description 86
- 239000002253 acid Substances 0.000 claims description 80
- 239000003513 alkali Substances 0.000 claims description 76
- 239000000243 solution Substances 0.000 claims description 72
- 229910052500 inorganic mineral Inorganic materials 0.000 claims description 71
- 239000011707 mineral Substances 0.000 claims description 71
- 238000000034 method Methods 0.000 claims description 43
- 238000006386 neutralization reaction Methods 0.000 claims description 39
- 239000011133 lead Substances 0.000 claims description 37
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 30
- 239000011737 fluorine Substances 0.000 claims description 28
- 229910052731 fluorine Inorganic materials 0.000 claims description 28
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 claims description 25
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 25
- 239000000460 chlorine Substances 0.000 claims description 25
- 229910052801 chlorine Inorganic materials 0.000 claims description 25
- 229910052725 zinc Inorganic materials 0.000 claims description 25
- 239000011701 zinc Substances 0.000 claims description 25
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 24
- 239000010949 copper Substances 0.000 claims description 24
- 229910052802 copper Inorganic materials 0.000 claims description 24
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 23
- 229910052782 aluminium Inorganic materials 0.000 claims description 20
- 239000003795 chemical substances by application Substances 0.000 claims description 17
- 239000007788 liquid Substances 0.000 claims description 14
- 239000000126 substance Substances 0.000 claims description 13
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 12
- 239000004568 cement Substances 0.000 claims description 12
- 238000002844 melting Methods 0.000 claims description 12
- 230000008018 melting Effects 0.000 claims description 12
- 230000003472 neutralizing effect Effects 0.000 claims description 12
- TVZPLCNGKSPOJA-UHFFFAOYSA-N copper zinc Chemical compound [Cu].[Zn] TVZPLCNGKSPOJA-UHFFFAOYSA-N 0.000 claims description 11
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 6
- -1 aluminum compound Chemical class 0.000 claims description 6
- 238000006115 defluorination reaction Methods 0.000 claims description 6
- 239000012670 alkaline solution Substances 0.000 claims description 4
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 3
- 239000002351 wastewater Substances 0.000 claims description 3
- 238000002156 mixing Methods 0.000 claims description 2
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 claims 3
- 235000010755 mineral Nutrition 0.000 description 58
- 239000000047 product Substances 0.000 description 33
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 28
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 25
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 16
- 235000002639 sodium chloride Nutrition 0.000 description 13
- 150000003839 salts Chemical class 0.000 description 12
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 11
- 238000003723 Smelting Methods 0.000 description 11
- 238000001914 filtration Methods 0.000 description 11
- 229910052793 cadmium Inorganic materials 0.000 description 9
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 description 9
- 238000000926 separation method Methods 0.000 description 9
- 239000000706 filtrate Substances 0.000 description 7
- 229910052742 iron Inorganic materials 0.000 description 5
- 239000002002 slurry Substances 0.000 description 5
- BUGBHKTXTAQXES-UHFFFAOYSA-N Selenium Chemical compound [Se] BUGBHKTXTAQXES-UHFFFAOYSA-N 0.000 description 4
- 230000004907 flux Effects 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 229910000000 metal hydroxide Inorganic materials 0.000 description 4
- 150000004692 metal hydroxides Chemical class 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- 229910052711 selenium Inorganic materials 0.000 description 4
- 239000011669 selenium Substances 0.000 description 4
- 239000002699 waste material Substances 0.000 description 4
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 239000011575 calcium Substances 0.000 description 3
- 229910052791 calcium Inorganic materials 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 3
- 229910052814 silicon oxide Inorganic materials 0.000 description 3
- 238000005406 washing Methods 0.000 description 3
- KLZUFWVZNOTSEM-UHFFFAOYSA-K Aluminium flouride Chemical compound F[Al](F)F KLZUFWVZNOTSEM-UHFFFAOYSA-K 0.000 description 2
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 2
- 230000002378 acidificating effect Effects 0.000 description 2
- 229910052787 antimony Inorganic materials 0.000 description 2
- WATWJIUSRGPENY-UHFFFAOYSA-N antimony atom Chemical compound [Sb] WATWJIUSRGPENY-UHFFFAOYSA-N 0.000 description 2
- 229910052785 arsenic Inorganic materials 0.000 description 2
- RQNWIZPPADIBDY-UHFFFAOYSA-N arsenic atom Chemical compound [As] RQNWIZPPADIBDY-UHFFFAOYSA-N 0.000 description 2
- 235000011148 calcium chloride Nutrition 0.000 description 2
- BRPQOXSCLDDYGP-UHFFFAOYSA-N calcium oxide Chemical compound [O-2].[Ca+2] BRPQOXSCLDDYGP-UHFFFAOYSA-N 0.000 description 2
- 239000000292 calcium oxide Substances 0.000 description 2
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium oxide Inorganic materials [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 2
- 150000004679 hydroxides Chemical class 0.000 description 2
- 239000002440 industrial waste Substances 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 230000001376 precipitating effect Effects 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000003672 processing method Methods 0.000 description 2
- 238000012958 reprocessing Methods 0.000 description 2
- 239000002893 slag Substances 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 229910052708 sodium Inorganic materials 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 150000004763 sulfides Chemical class 0.000 description 2
- 238000004065 wastewater treatment Methods 0.000 description 2
- IRPGOXJVTQTAAN-UHFFFAOYSA-N 2,2,3,3,3-pentafluoropropanal Chemical compound FC(F)(F)C(F)(F)C=O IRPGOXJVTQTAAN-UHFFFAOYSA-N 0.000 description 1
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical class [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 1
- 239000003929 acidic solution Substances 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 239000001110 calcium chloride Substances 0.000 description 1
- 229910001628 calcium chloride Inorganic materials 0.000 description 1
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 1
- 239000000920 calcium hydroxide Substances 0.000 description 1
- 235000011116 calcium hydroxide Nutrition 0.000 description 1
- 229910001861 calcium hydroxide Inorganic materials 0.000 description 1
- 239000013522 chelant Substances 0.000 description 1
- 150000001805 chlorine compounds Chemical class 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- LBJNMUFDOHXDFG-UHFFFAOYSA-N copper;hydrate Chemical compound O.[Cu].[Cu] LBJNMUFDOHXDFG-UHFFFAOYSA-N 0.000 description 1
- 238000011033 desalting Methods 0.000 description 1
- 238000011038 discontinuous diafiltration by volume reduction Methods 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 229940079593 drug Drugs 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000011790 ferrous sulphate Substances 0.000 description 1
- 235000003891 ferrous sulphate Nutrition 0.000 description 1
- 150000002222 fluorine compounds Chemical class 0.000 description 1
- 229910000041 hydrogen chloride Inorganic materials 0.000 description 1
- IXCSERBJSXMMFS-UHFFFAOYSA-N hydrogen chloride Substances Cl.Cl IXCSERBJSXMMFS-UHFFFAOYSA-N 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
- 235000014413 iron hydroxide Nutrition 0.000 description 1
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 description 1
- 229910000359 iron(II) sulfate Inorganic materials 0.000 description 1
- NCNCGGDMXMBVIA-UHFFFAOYSA-L iron(ii) hydroxide Chemical compound [OH-].[OH-].[Fe+2] NCNCGGDMXMBVIA-UHFFFAOYSA-L 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 1
- 229910052753 mercury Inorganic materials 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 238000010979 pH adjustment Methods 0.000 description 1
- 235000021395 porridge Nutrition 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 239000010802 sludge Substances 0.000 description 1
- HYHCSLBZRBJJCH-UHFFFAOYSA-M sodium hydrosulfide Chemical compound [Na+].[SH-] HYHCSLBZRBJJCH-UHFFFAOYSA-M 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 238000004056 waste incineration Methods 0.000 description 1
Images
Classifications
-
- 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
Landscapes
- Processing Of Solid Wastes (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
- Manufacture And Refinement Of Metals (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、都市ごみ焼却場や産業廃棄物焼却場等のおける焼却炉や溶融炉あるいは汚泥を処理するセメントキルン等から発生する銅、鉛、亜鉛等の重金属及び多量のカルシウムやナトリウムおよび塩素やフッ素の化合物等塩類を含有する飛灰の処理方法に関する。
【０００２】
【従来の方法】
通常、「都市ごみ」または「一般廃棄物」と称されている一般家庭や一般事業所から排出されるごみは都市ごみ焼却場や産業廃棄物焼却場等に集められ、焼却処分されている。その焼却処理を行う焼却炉等からの排ガス中には、塩化水素ガス等有害酸性ガスが多く含まれているため、多量の消石灰等中和剤が投入され、無害化が図られている。このため、焼却炉等からの飛灰は、一般に、鉄、銅、鉛、亜鉛及びカドミウム等の重金属の他、多量のカルシウム、ナトリウム等の塩化物や酸化物等の塩類を含む高アルカリ性飛灰となっている。
このような飛灰については、含有重金属が有害視され、硫酸による中和処理、セメント固化処理あるいは溶融炉によるスラグ化処理が施され、安定化され減容化された後、最終堆積処分場に堆積されるようにされている。
【０００３】
しかしながら、硫酸中和処理においては硫酸の使用量が多く、また、セメント固化処理においては重金属不溶化のための薬剤使用量が多く、さらにそのセメント固形物が長期に亘る放置で脆くなり、露出した重金属が再反応によって有害化するという問題があり、溶融スラグ化処理の場合では、熔融時、蒸気圧の高い鉛、亜鉛およびカドミウム等の重金属やカルシウム等の塩類が炉内で再ガス化し、排ガス処理過程で凝縮して再び飛灰となり、飛灰処理が繰り返されるという問題があった。すなわち、いずれの飛灰処理手段においても、不溶化や減容化のための中間処理費用が多く、堆積処分費の手当てを必要とし、さらに含まれている有用重金属の資源化は望めない状況にある。
【０００４】
一方、このような飛灰を対象として、その減容化と共に含有重金属の回収を目的とした提案も種々なされている。例えば、特開平７−１０９５３３号公報には、飛灰を槽内の水に懸濁し、この懸濁液を酸またはアルカリの添加により、アルカリ域の適当値にｐＨ調整することにより飛灰中の重金属を水酸化物として沈殿させ、この沈殿を回収する方法について開示している。また、本出願人も、湿式処理方式による重金属の回収についていくつか提案している。例えば、特開平８−１１７７２４号公報において、飛灰を水でスラリー化し、ｐＨ調整して、固液分離する第１工程と、該第１工程からの残渣を酸液でリパルプし、ｐＨ３以下に調整した後、固液分離して鉛残渣を得る第２工程と、前記の両工程からの酸性濾液に中和剤またさらに水硫化ソーダを加えて亜鉛、銅を含む残渣を分別し、濾過水を排水液とする第３工程とからなる方法を提案している。
【０００５】
さらに、特開平１０−５７３６号公報には飛灰の減容化と共に、重金属の回収を図る湿式処理法として、飛灰をアルカリ浸出して重金属の回収を図る手段が提案されている。この方法は、スラリー状態のアルカリ性飛灰に水酸化ナトリウム又は水酸化カリウムの水溶液を添加し、ｐＨが、１２．５以上のアルカリ域として含有されている鉛、亜鉛および銅を液相中に浸出して分離する方法であり、また、前記の溶出重金属を硫化物として回収する方法である。
【０００６】
【発明が解決しようとする課題】
しかしながら、前記の特開平７−１０９５３３号の方法は、回収した重金属殿物中に塩化カルシウム等の塩類が多量に入り込み、重金属の分別回収を妨げる塩素分が製錬工程に持ち込まれるという問題があり、また、特開平８−１１７７２４号の方法は、酸に難溶の鉛分を不溶解残渣側に集めて回収するようにしており、不溶解残渣に含有される酸化珪素や酸化アルミ等フラックス成分と混合状態で回収されるため、鉛品位が低く回収率については問題があるといえる。さらに特開平１０−５７３６号の方法においては、本来高アルカリ液に難溶の銅分が高アルカリ浸出により回収されるとする点に疑問があり、重金属の回収率に問題がある。また、高アルカリ浸出液から硫化剤の使用で重金属硫化物を回収しているが、浸出液中に多量に存在する塩素さらにはフッ素が回収物に混入することについての配慮がなく、回収重金属はそのままでは製錬工程に供給できないという問題がある。
【０００７】
すなわち、上記の状況に鑑み、本発明の目的とするところは、飛灰を処理して、製錬工程で有害な塩素とフッ素を低減した有用重金属を製錬原料として効率的に回収すると共に、飛灰処理における使用薬剤の節減等処理費の低減が図れる経済的な飛灰からの重金属回収方法の提供にある。
【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べく、鋭意研究の結果、飛灰のアルカリ浸出と、その浸出液の鉱酸中和により、効果的に塩素とフッ素を重金属から分離することができること、さらに、飛灰のリパルプにおいて、パルプ濃度をできるだけ高くすることによりアルカリ浸出におけるアルカリ薬剤の原単位の低減が図れ、中和液からの脱フッ素には飛灰中に含まれているアルミ分が利用でき、また、アルカリ浸出液の中和にアルカリ不溶解残渣の鉱酸浸出液を利用するようにすれば、飛灰処理時の薬剤の節減が図れると共に工程の簡易化にも繋がることを見出し、本発明に到達した。
【０００９】
すなわち、本発明は、第１に、焼却炉、溶融炉またはセメントキルンから発生し、銅、亜鉛または鉛のうちの少なくとも１種の重金属を含み、かつ塩素とフッ素のうちの１種以上を含む飛灰からの重金属回収方法であって、飛灰に水およびアルカリ性薬剤を添加してｐＨ１３以上とし、アルカリ浸出液とアルカリ不溶解残渣を得るアルカリ浸出工程と、該アルカリ浸出工程から濾別されたアルカリ不溶解残渣を水でリパルプした後、鉱酸を添加してｐＨ２〜５に調整し、鉱酸浸出液と鉱酸不溶解残渣を得る鉱酸浸出工程と、前記アルカリ浸出工程からのアルカリ浸出液に前記鉱酸浸出工程からの鉱酸浸出液を混合してｐＨ１０〜１３のｐＨ域において中和し、銅、亜鉛または鉛のうちの少なくとも１種の重金属を含む重金属含有産物とアルカリ中和液を得るアルカリ中和工程とからなることを特徴とする飛灰からの重金属回収方法であり、第２に、焼却炉、溶融炉またはセメントキルンから発生し、銅、亜鉛または鉛のうちの少なくとも１種の重金属を含み、かつ塩素とフッ素のうちの１種以上を含む飛灰からの重金属回収方法であって、飛灰に水およびアルカリ性薬剤を添加してｐＨ１３以上とし、アルカリ浸出液とアルカリ不溶解残渣を得るアルカリ浸出工程と、該アルカリ浸出工程から濾別されたアルカリ不溶解残渣を水でリパルプした後、鉱酸を添加してｐＨ２〜５に調整し、鉱酸浸出液と鉱酸不溶解残渣を得る鉱酸浸出工程と、該鉱酸浸出工程からの鉱酸浸出液にアルカリ性薬剤を添加してｐＨ１０〜１３に調整して銅、亜鉛のうちの少なくとも１種の重金属を含む銅亜鉛産物と中和液を得る酸中和工程と、前記アルカリ浸出工程からのアルカリ浸出液に鉱酸を添加してｐＨ１０〜１３のｐＨ域において中和して鉛を主体とする重金属を含む鉛産物とアルカリ中和液を得るアルカリ中和工程とを備えることを特徴とする飛灰からの重金属回収方法であり、第３に、前記アルカリ中和工程からのアルカリ中和液をｐＨ５〜８のｐＨ域に調整することにより含有フッ素をアルミニウム化合物として除去する脱フッ素工程を有することを特徴とする前記第１または第２に記載の飛灰からの重金属回収方法であり、第４に、前記アルカリ浸出工程において、アルカリ性薬剤添加前のパルプ濃度を４０重量％以上とすることを特徴とする前記第１〜第３のいずれかに記載の飛灰からの重金属回収方法であり、第５に、前記アルカリ性薬剤は水酸化ナトリウム、水酸化カリウム、炭酸ナトリウムの１種又は２種以上のアルカリ溶液であることを特徴とする前記第１〜第４のいずれかに記載の飛灰からの重金属回収方法であり、第６に、前記鉱酸不溶解残渣を、焼却炉、溶融炉またはセメントキルンに戻すことを特徴とする前記第１〜第５のいずれかに記載の飛灰からの重金属回収方法である。
【００１０】
【発明の実施の形態】
本発明を、実施例による図１のフロー図を参照して説明する。
本発明は、まず、飛灰を水と混合して懸濁させた後、水酸化ナトリウム等アルカリ性薬剤を添加してアルカリ浸出を行う（アルカリ浸出工程）。懸濁時、パルプ濃度はできるだけ高くするが、好ましくは４０wt％以上とする。このことによって水酸化ナトリウム等アルカリ薬剤の原単位を低減でき、また用水量の節減も図れる。これは、飛灰を直接酸浸出する場合、脱塩のためできるだけパルプ濃度を薄くしなければならないのとは対称的な利点でもある。アルカリ性薬剤としては水酸化ナトリウム、水酸化カリウム、炭酸ナトリウムのいずれであってもよい。アルカリ浸出時のｐＨは１３以上、好ましくは１４以上とすることにより、飛灰中の鉛、亜鉛、アルミニウム、セレン、塩素、フッ素をアルカリ溶液中に溶出させることができる。
【００１１】
このアルカリ浸出工程後、固液分離により、飛灰中の鉛、亜鉛、アルミニウム、セレン、フッ素が各５０％以上溶出し、かつ、ナトリウム、カリウム等の塩素化合物を主体とする塩類が殆ど溶出しているアルカリ浸出液と、アルカリ浸出で溶出しなかった銅をはじめ、鉛、亜鉛、カドミウムを含み、酸化珪素、酸化カルシウム、酸化アルミニウム等フラックス成分を含むアルカリ不溶解残渣とに分別することができる。
【００１２】
このアルカリ不溶解残渣は、再度水と混合してリパルプ化した後、鉱酸液添加によりｐＨ２〜５程度で鉱酸浸出を行い（鉱酸浸出工程）、固液分離することにより、アルカリ不溶解残渣中の銅、亜鉛、カドミウム等重金属を溶出させた鉱酸浸出液と、鉱酸不溶解残渣とに分別することができる。鉱酸としては、硫酸、塩酸、硝酸またはそれらの混酸を用いることができるが、硫酸を用いることがコスト面等で好ましい。カドミウムはこの鉱酸浸出で８５％以上が鉱酸浸出液に分配され、その全量が中和処理により銅産物と共に系外に抽出される。アルカリ不溶解残渣をリパルプした際の液のパルプ濃度は、できるだけ高くすることにより鉱酸浸出工程の鉱酸および用水の使用量を節減できる。
【００１３】
鉱酸浸出工程から固液分離して得られた鉱酸不溶解残渣には、重金属が含まれず、酸化珪素、酸化アルミニウム、酸化カルシウム等のフラックス成分が多く、この鉱酸不溶解残渣は溶融炉あるいはセメントキルンに循環的に戻すことにより、残渣のスラグ化が図れる。
【００１４】
一方、前記鉱酸浸出工程からの鉱酸浸出液はアルカリ浸出で溶出しなかった銅等重金属を含み、この鉱酸浸出液は、鉱酸酸性液であってそのまま前記アルカリ中和工程の中和用鉱酸液として利用することができる。すなわち、アルカリ浸出工程からのアルカリ浸出液に、前記鉱酸浸出工程からの鉱酸浸出液を添加し、さらに鉱酸液を補充的に添加してｐＨ１０〜１３のｐＨ域に調整して中和させることにより（アルカリ中和工程）、アルカリ浸出液中の鉛、亜鉛等と鉱酸浸出液中の銅、亜鉛等による重金属を水酸化物態で殿物化させることができ、固液分離してアルミニウム、塩素およびフッ素を含むアルカリ中和液を分別することにより、塩素とフッ素の少ない重金属含有産物を得ることができる。
【００１５】
通常、塩素が多量に含まれている液を中和処理して金属水酸化物を生成させると、塩素が金属水酸化物中に吸着的にあるいは化合物態で取り込まれることが多いが、前記アルカリ浸出液の場合のように、ｐＨ１３以上の高アルカリ域からｐＨを下げてｐＨ１０〜１３で中和させるようにすると、液中の塩素は、生成する金属水酸化物に取り込まれることなく溶存状態を保持する。また、アルカリ液に対してフッ素は溶存状態を保持して金属水酸化物（銅亜鉛・鉛産物）への取り込みが抑制される。したがって、得られた銅・鉛産物は、水洗浄により付着塩類が除かれた後、有害なフッ素、塩素が少ない重金属含有産物として製錬工程に供給することができる。
【００１６】
本発明の方法によれば、鉛を一旦アルカリ溶液に浸出してから抽出するようにしたので、従来、飛灰を酸溶解処理して酸に難溶の鉛をフラックス成分と共にその不溶解残渣として回収していたのに較べ、鉛品位の高い鉛産物を得ることができる。さらに、このアルカリ中和工程において、前記のように、中和剤として代替的に鉱酸浸出液を用いることにより、中和剤としての鉱酸液の使用量を節減できることになる。また、この鉱酸浸出液を単独で中和処理する場合に比較すると、中和設備や濾過設備が一元化するという利点が得られる。
【００１７】
アルカリ中和工程から重金属含有産物と分別されたアルカリ中和液については、ｐＨを５〜８、好ましくは５〜６にｐＨ調整することにより（脱フッ素工程）、液中の溶存アルミニウムは水酸化物態（Al(OH)3）で殿物化すると共に溶存フ ッ素を吸着して、またはフッ化アルミニウム（AlF3）を生成して共沈するので、固液分離によりフッ素を含むアルミニウム殿物を回収することができる。このアルミニウム殿物は、例えば、溶融炉あるいはセメントキルンに戻して再処理に供する。
【００１８】
アルカリ中和工程からのアルカリ中和液中にアルミニウムが含有されていない場合、脱フッ素剤としてアルミニウム化合物等アルミニウム剤を添加する必要があるが、本発明では、アルカリ浸出により、飛灰中のアルミニウムをそのままアルカリ浸出液に移行させ、ｐＨ調整のみで脱フッ素剤として作用させるようにしたので、新たなアルミニウム化合物を必要とせず、工程が簡易化される。
【００１９】
アルミニウム殿物と分離された脱フッ素濾液は塩類を含むが、一般的な排水処理に供することが可能で、例えば、図１のように、硫酸第一鉄や鉄粉等を添加し鉄還元処理を行って、残存塩類を水酸化鉄を主体とした鉄殿物と共に除去することができる。また、この脱フッ素濾液は高塩濃度のため、排水基準値を上回る鉛、亜鉛、銅、水銀、砒素、アンチモン、カドミウム等重金属が残留している場合があるが、これらの重金属もまた鉄殿物と共に還元または共沈除去される。セレンも鉄殿物に吸着されて共沈除去される。鉄殿物を除去した濾液はｐＨ調整した後、清浄水として放流することができる。排水基準が厳しければ、前記濾液をキレート樹脂塔を経由させるようにしてもよい。鉄殿物はまた、溶融炉等での再処理に供することができる。
【００２０】
図１のフロー図では、アルカリ中和工程の中和剤として新たな鉱酸は補充的に使用することとして鉱酸浸出工程からの鉱酸浸出液を利用したが、この鉱酸浸出液は、図２のフロー図のように、単独で処理することもできる。
図２において、鉱酸浸出工程からの鉱酸浸出液は、銅を主体として亜鉛、カドミウム等の重金属を含んでおり、さらに水酸化ナトリウムの添加によりｐＨ１０〜１３において中和処理して水酸化物態殿物（銅亜鉛産物）として析出させ（酸中和工程）、固液分離することにより、塩素とフッ素の少ない銅亜鉛産物と塩素その他塩類を含む中和液とに分別することができる。得られた銅亜鉛産物は洗浄して付着塩類を除去した後、製錬工程に供給することができ、また、得られた中和液は、排水処理工程に供給してもよいが、系内のリパルプ用リサイクル水、あるいは稀釈水として使用することができる。
【００２１】
この鉱酸浸出液の単独処理により、前記アルカリ浸出液のアルカリ中和工程は、新たな鉱酸液による中和処理となる。得られた鉛産物は、水洗浄により、付着塩類を除去した後、製錬工程へ供給することにより重金属の回収を行うことができる。
【００２２】
前記鉱酸浸出液は、塩素とフッ素を含まず銅を主体に亜鉛、カドミウム等を含む溶液であり、これらの重金属はｐＨ１０〜１３域で水酸化物態殿物として析出し、また、アルカリ浸出液は鉛を主体に亜鉛等重金属を含み、ｐＨ１０〜１３域でアルカリ中和工程で塩素とフッ素を分別して水酸化物態殿物を生成するので、回収重金属の品位が高く、塩素とフッ素の品位の低い産物が得られるという利点がある。
重金属すなわち産物の回収を一元的に行うか、二元的に並行して行うかは、飛灰の性状や操業目的等により選択することができる。
【００２３】
【実施例】
以下、図面を参照して本発明の実施例を示す。
［実施例１］
Ａ工場からの飛灰８００ｇを水１ｌに溶かしてパルプ濃度が４４．４重量％のスラリーにした後、４０％の水酸化ナトリウムを２００ｃｃ添加して（ｐＨ＝１４．３）３０分浸出した。
次いで濾過装置を用いて濾過し、アルカリ不溶解残渣とアルカリ浸出液を回収した。
次ぎに、得られたアルカリ不溶解残渣を水に溶かしてスラリーとし、さらに、鉱酸として硫酸を添加し、ｐＨ＝２に調整して６０分間浸出してから濾過装置にかけ、硫酸不溶解残渣と硫酸浸出液を分離回収した。
そして、前記の回収アルカリ浸出液にこの硫酸浸出液を添加して、さらに硫酸を添加し、ｐＨ＝１２になるように調整して３０分間保持して中和させた。中和反応の終了後、濾別して重金属含有産物とアルカリ中和液とに分別した。
得られたアルカリ中和液をｐＨ６に調整した後、アルミ殿物と脱フッ素濾液とに分別濾過した。
飛灰の品位および得られたアルカリ不溶解残渣と硫酸不溶解残渣と重金属含有産物（銅亜鉛・鉛産物）の品位を表１に示した。
この結果、銅亜鉛・鉛産物には塩素およびフッ素が殆ど含まれず、製錬用原料として使用できることがわかった。
なお、アルカリ中和液の脱フッ素処理により、元液のフッ素 45mg/l は 2.6mg/l に低減し、アルミニウム 304mg/l は 2.3mg/l に低減した。
【００２４】
【表１】
［実施例２］
実施例１の場合と同一の飛灰を使用し、この飛灰８００ｇを水１ｌに懸濁してパルプ濃度が４４．４重量％のスラリーにした後、４０％水酸化ナトリウムを２００ｃｃ添加して（ｐＨ＝１４．２）３０分浸出した。
次いで濾過装置を用いて濾過し、アルカリ不溶解残渣とアルカリ浸出液を回収した。
次ぎに、得られたアルカリ不溶解残渣を水でリパルプしてスラリーとし、さらに、鉱酸として硫酸を添加し、ｐＨ＝２に調整して６０分間浸出してから濾過装置にかけ、硫酸不溶解残渣と硫酸浸出液を分離回収した。
ついで、硫酸浸出液に水酸化ナトリウムを添加してｐＨを１３に調整して中和させた。ついで濾過分離により銅亜鉛産物と中和液を回収した。
一方、アルカリ浸出液に鉱酸として硫酸を添加してｐＨが１２になるように調整して中和させた後、濾過分離し、鉛産物とアルカリ中和液を得た。
ついで、得られたアルカリ中和液に硫酸を添加し、ｐＨ６に調整した後、アルミ殿物と脱フッ素濾液とに分別濾過した。
【００２６】
得られたアルカリ不溶解残渣と硫酸不溶解残渣と銅亜鉛産物と鉛産物の品位を表２に示した。
この結果から、塩素とフッ素を殆ど含まず、製錬用原料として使用できる銅亜鉛産物および鉛産物が回収できることがわかる。また、処理工程が増すが、回収産物の銅・鉛品位の点からは、銅亜鉛産物と鉛産物は並行的に回収したほうが良好であることもわかる。
なお、アルカリ中和液の脱フッ素処理により、元液のフッ素 34mg/l は 2.0mg/l に低減し、アルミニウム 140mg/l は 0.05mg/l 以下に低減した。
【００２７】
【表２】
【発明の効果】
飛灰をアルカリ浸出し、アルカリ浸出液を中和処理することによって、塩素とフッ素の少ない鉛等重金属含有殿物を得ることができる。また、アルカリ不溶解残渣を鉱酸浸出し、その鉱酸浸出液を中和処理することにより、塩素とフッ素の少ない銅、亜鉛等の有用重金属の回収が図れ、製錬工程に供給できる有用重金属を効率的に回収できる。また、前記アルカリ浸出液と前記鉱酸浸出液を混合することにより、一元的な有用重金属産物の回収が図れる。
【００２９】
アルカリ不溶解残渣の鉱酸浸出により、溶融炉等への返戻時に問題となるセレン、カドミウム、アンチモン、砒素等も回収でき、フラックス成分を含む酸不溶解残渣を溶融炉等に戻すことにより、品位の高い重金属含有殿物のみを製錬原料として回収することができる。
アルカリ中和液から、フッ素をフッ化アルミニウムとして除去する際に、飛灰に含まれているアルミニウムを利用できるようにしたので、脱フッ素剤の添加を必要とせず、さらに、飛灰のアルカリ浸出に先立つリパルプにおいて、パルプ濃度を高くしたので、アルカリ薬剤の添加量を低減でき、また、アルカリ浸出液の中和に際し、アルカリ浸出残渣の鉱酸浸出液を中和剤として用いることができ、この場合、中和剤としての鉱酸液を節減できる等、飛灰処理時の使用薬剤の節減を図ることができる。
【図面の簡単な説明】
【図１】本発明の実施例による飛灰からの重金属回収方法を示すフロー図である。
【図２】本発明の別の実施例による飛灰からの重金属回収方法を示すフロー図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to heavy metals such as copper, lead, and zinc generated in incinerators, melting furnaces, cement kilns for treating sludge, etc. in municipal waste incinerators and industrial waste incinerators, and a large amount of calcium, sodium and chlorine, The present invention relates to a method for treating fly ash containing salts such as fluorine compounds.
[0002]
Conventional method
Generally, waste discharged from ordinary households and general business establishments called “urban waste” or “general waste” is collected in an incineration plant, an industrial waste incineration plant or the like and incinerated. Since exhaust gas from an incinerator or the like that performs the incineration process contains a large amount of harmful acidic gas such as hydrogen chloride gas, a large amount of neutralizing agent such as slaked lime is introduced to make it harmless. For this reason, fly ash from incinerators is generally highly alkaline fly ash containing heavy metals such as iron, copper, lead, zinc and cadmium, as well as large amounts of salts such as calcium and sodium chlorides and oxides. It has become.
For such fly ash, the heavy metals contained in it are considered harmful, neutralized with sulfuric acid, cement solidified or slagged with a melting furnace, stabilized and reduced in volume, and then put into the final deposit disposal site. It is supposed to be deposited.
[0003]
However, in sulfuric acid neutralization treatment, the amount of sulfuric acid used is large. In cement solidification treatment, the amount of chemical used for insolubilizing heavy metals is large. Further, the cement solids become brittle when left for a long period of time, and exposed heavy metals. In the case of molten slag treatment, during melting, heavy metals such as lead, zinc and cadmium with high vapor pressure, and salts such as calcium are regasified in the furnace, and exhaust gas treatment is performed. There was a problem that it condensed in the process and became fly ash again, and the fly ash treatment was repeated. That is, in any fly ash treatment means, there is a lot of intermediate treatment costs for insolubilization and volume reduction, it is necessary to pay for the disposal costs of the deposits, and it is not possible to recycle the contained useful heavy metals .
[0004]
On the other hand, for such fly ash, various proposals have been made for the purpose of reducing the volume and recovering contained heavy metals. For example, in JP-A-7-109533, fly ash is suspended in water in a tank, and the pH of the suspension is adjusted to an appropriate value in the alkali range by adding acid or alkali. A method for precipitating heavy metals as hydroxides and recovering the precipitates is disclosed. The present applicant has also proposed a number of heavy metal recovery methods by a wet processing method. For example, in JP-A-8-117724, fly ash is slurried with water, pH adjusted, solid-liquid separation is performed, and the residue from the first step is repulped with an acid solution to a pH of 3 or lower. After the adjustment, the second step to obtain a lead residue by solid-liquid separation, the neutralized agent or further sodium hydrosulfide is added to the acidic filtrate from both of the above steps to separate the residue containing zinc and copper, and the filtered water Has proposed a method comprising a third step in which effluent is used as waste water.
[0005]
Furthermore, Japanese Patent Application Laid-Open No. 10-5736 proposes means for recovering heavy metals by alkaline leaching of fly ash as a wet processing method for reducing the volume of fly ash and for recovering heavy metals. In this method, an aqueous solution of sodium hydroxide or potassium hydroxide is added to alkaline fly ash in a slurry state, and lead, zinc and copper contained as an alkaline region having a pH of 12.5 or more are leached into the liquid phase. And the aforementioned eluted heavy metals are recovered as sulfides.
[0006]
[Problems to be solved by the invention]
However, the above-mentioned method of JP-A-7-109533 has a problem that a large amount of salts such as calcium chloride enter the recovered heavy metal deposits, and chlorine components that impede the separation and recovery of heavy metals are brought into the smelting process. In addition, the method disclosed in Japanese Patent Laid-Open No. 8-117724 collects and collects a lead content hardly soluble in an acid on the insoluble residue side, and flux components such as silicon oxide and aluminum oxide contained in the insoluble residue. Since it is recovered in a mixed state, the lead quality is low and it can be said that there is a problem with the recovery rate. Further, in the method disclosed in JP-A-10-5736, there is a question that a copper component which is originally hardly soluble in a high alkali solution is recovered by high alkali leaching, and there is a problem in the recovery rate of heavy metals. In addition, heavy metal sulfides are recovered from the highly alkaline leachate by using a sulfiding agent, but there is no consideration for the presence of a large amount of chlorine or fluorine in the leachate, and the recovered heavy metals are left as they are. There is a problem that it cannot be supplied to the smelting process.
[0007]
That is, in view of the above situation, the object of the present invention is to treat fly ash and efficiently recover useful heavy metals that have reduced harmful chlorine and fluorine in the smelting process as smelting raw materials, The object is to provide an economical method for recovering heavy metals from fly ash that can reduce processing costs such as reducing the amount of chemicals used in fly ash treatment.
[0008]
[Means for Solving the Problems]
As a result of earnest research, the present inventors have been able to effectively separate chlorine and fluorine from heavy metals by alkali leaching of fly ash and neutralizing the mineral acid of the leaching solution, in order to achieve the above object. In fly ash repulp, by increasing the pulp concentration as much as possible, the basic unit of alkali chemicals in alkali leaching can be reduced, and aluminum contained in fly ash can be used for defluorination from the neutralized solution. In addition, it has been found that if a mineral acid leachate of an alkali-insoluble residue is used for neutralization of the alkali leachate, the chemical during fly ash treatment can be saved and the process can be simplified. Reached.
[0009]
That is, the present invention firstly generates from an incinerator, a melting furnace or a cement kiln, includes at least one heavy metal of copper, zinc or lead, and includes one or more of chlorine and fluorine. A method for recovering heavy metals from fly ash, which comprises adding alkali and alkaline chemicals to fly ash to a pH of 13 or higher to obtain an alkaline leachate and an alkali-insoluble residue, and an alkali separated by filtration from the alkali leaching step After repulping the insoluble residue with water, the mineral acid is added to adjust the pH to 2 to 5, the mineral acid leaching step to obtain the mineral acid leaching solution and the mineral acid insoluble residue, and the alkali leaching solution from the alkali leaching step A mineral acid leaching solution from the mineral acid leaching step is mixed and neutralized in a pH range of pH 10 to 13, and a heavy metal-containing product containing at least one heavy metal of copper, zinc or lead and an alkali A method for recovering heavy metals from fly ash characterized by comprising an alkali neutralization step for obtaining a neutralization solution, and secondly, it is generated from an incinerator, a melting furnace or a cement kiln and is made of copper, zinc or lead A method for recovering heavy metal from fly ash containing at least one kind of heavy metal and containing one or more of chlorine and fluorine, wherein water and an alkaline chemical are added to the fly ash to a pH of 13 or more, An alkali leaching step for obtaining an alkali-insoluble residue, and after repulping the alkali-insoluble residue filtered from the alkali leaching step with water, adjusting the pH to 2 to 5 by adding a mineral acid, a mineral acid leaching solution and a mineral acid A mineral acid leaching step for obtaining an insoluble residue, and a copper suboxide containing at least one heavy metal of copper and zinc by adding an alkaline agent to the mineral acid leaching solution from the mineral acid leaching step and adjusting the pH to 10-13. An acid neutralization step for obtaining a product and a neutralization solution; and a lead product containing a heavy metal mainly composed of lead by adding a mineral acid to the alkali leaching solution from the alkali leaching step and neutralizing in a pH range of pH 10-13. An alkali neutralization step for obtaining an alkali neutralization solution, and a method for recovering heavy metals from fly ash, and thirdly, the alkali neutralization solution from the alkali neutralization step is in a pH range of pH 5-8. The method for recovering heavy metals from fly ash according to the first or second aspect, further comprising a defluorination step of removing contained fluorine as an aluminum compound by adjusting to 4th, and fourth, the alkali leaching step In the method for recovering heavy metals from fly ash according to any one of the first to third aspects, wherein the pulp concentration before addition of the alkaline agent is 40% by weight or more. The method for recovering heavy metals from fly ash according to any one of the first to fourth aspects, characterized in that the Lucari drug is one or more alkaline solutions of sodium hydroxide, potassium hydroxide, and sodium carbonate. Sixth, the method for recovering heavy metals from fly ash according to any one of the first to fifth aspects, wherein the mineral acid insoluble residue is returned to an incinerator, a melting furnace or a cement kiln. is there.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described with reference to the flow diagram of FIG. 1 according to an embodiment.
In the present invention, first, fly ash is mixed with water and suspended, and then alkaline leaching is performed by adding an alkaline chemical such as sodium hydroxide (alkali leaching step). When suspended, the pulp concentration is as high as possible, but preferably 40 wt% or more. As a result, the basic unit of alkali chemicals such as sodium hydroxide can be reduced, and the amount of water used can be reduced. This is also a symmetric advantage when the fly ash is directly acid leached and the pulp concentration must be as thin as possible for desalting. As an alkaline chemical | medical agent, any of sodium hydroxide, potassium hydroxide, and sodium carbonate may be sufficient. By setting the pH during alkali leaching to 13 or more, preferably 14 or more, lead, zinc, aluminum, selenium, chlorine and fluorine in fly ash can be eluted into the alkaline solution.
[0011]
After this alkali leaching process, lead, zinc, aluminum, selenium, and fluorine in the fly ash are eluted by 50% or more by solid-liquid separation, and salts mainly composed of chlorine compounds such as sodium and potassium are eluted. The alkaline leaching solution can be separated into an alkali-insoluble residue containing flux components such as silicon oxide, calcium oxide, and aluminum oxide containing lead, zinc, and cadmium as well as copper that has not been eluted by alkali leaching.
[0012]
This alkali-insoluble residue is mixed with water again and repulped, and then mineral acid leaching is performed at a pH of about 2 to 5 by adding a mineral acid solution (mineral acid leaching step). A mineral acid leaching solution from which heavy metals such as copper, zinc, and cadmium in the residue are eluted can be separated into a mineral acid insoluble residue. As the mineral acid, sulfuric acid, hydrochloric acid, nitric acid or a mixed acid thereof can be used, but it is preferable to use sulfuric acid in terms of cost. In this mineral acid leaching, 85% or more of cadmium is distributed to the mineral acid leaching solution, and the entire amount is extracted out of the system together with the copper product by the neutralization treatment. The amount of mineral acid and water used in the mineral acid leaching process can be reduced by increasing the pulp concentration of the liquid when repulping the alkali-insoluble residue as much as possible.
[0013]
The mineral acid insoluble residue obtained by solid-liquid separation from the mineral acid leaching process does not contain heavy metals and has many flux components such as silicon oxide, aluminum oxide, calcium oxide, etc. Alternatively, the residue can be made into slag by returning to the cement kiln cyclically.
[0014]
On the other hand, the mineral acid leaching solution from the mineral acid leaching step contains a heavy metal such as copper that has not been eluted by alkali leaching. This mineral acid leaching solution is a mineral acid acidic solution and is used as it is as a neutralization mineral in the alkali neutralization step. It can be used as an acid solution. That is, the mineral acid leaching solution from the mineral acid leaching step is added to the alkali leaching solution from the alkali leaching step, and the mineral acid solution is supplementally added to adjust to the pH range of pH 10 to 13 and neutralize. (Alkali neutralization step), lead, zinc, etc. in the alkaline leaching solution and copper, zinc, etc. in the mineral acid leaching solution can be hydrated in a hydroxide state and separated into solid, liquid, aluminum, chlorine and By separating the alkali neutralized solution containing fluorine, a heavy metal-containing product with less chlorine and fluorine can be obtained.
[0015]
Usually, when a metal hydroxide is produced by neutralizing a liquid containing a large amount of chlorine, chlorine is often taken into the metal hydroxide adsorbably or in a compound state. As in the case of the leachate, when the pH is lowered from a high alkali range of
[0016]
According to the method of the present invention, since lead is once extracted in an alkaline solution and extracted, conventionally, fly ash is acid-dissolved to make lead insoluble in acid as an insoluble residue together with a flux component. Compared to the recovery, lead products with higher lead quality can be obtained. Further, in this alkali neutralization step, as described above, the use of the mineral acid leaching solution as a neutralizing agent can be used to reduce the amount of the mineral acid used as the neutralizing agent. Moreover, compared with the case where this mineral acid leaching solution is neutralized alone, there is an advantage that the neutralization equipment and the filtration equipment are unified.
[0017]
About the alkali neutralization liquid separated from the heavy metal-containing product from the alkali neutralization process, the dissolved aluminum in the liquid is hydroxylated by adjusting the pH to 5 to 8, preferably 5 to 6 (defluorination process). Aluminum deposits that contain fluorine by solid-liquid separation because they are deposited in the physical state (Al (OH) 3 ) and adsorb dissolved fluorine, or produce aluminum fluoride (AlF 3 ) and coprecipitate. Can be recovered. This aluminum article is returned to a melting furnace or a cement kiln, for example, and subjected to reprocessing.
[0018]
When aluminum is not contained in the alkali neutralization solution from the alkali neutralization step, it is necessary to add an aluminum agent such as an aluminum compound as a defluorinating agent. In the present invention, aluminum in fly ash is obtained by alkali leaching. Is transferred to the alkaline leaching solution as it is and allowed to act as a defluorinating agent only by adjusting the pH, so that a new aluminum compound is not required and the process is simplified.
[0019]
The defluorinated filtrate separated from the aluminum deposit contains salts, but can be used for general wastewater treatment. For example, as shown in FIG. 1, ferrous sulfate or iron powder is added to reduce iron. The residual salts can be removed together with the iron deposit mainly composed of iron hydroxide. In addition, due to the high salt concentration of this defluorinated filtrate, heavy metals such as lead, zinc, copper, mercury, arsenic, antimony, and cadmium that may exceed the wastewater standards may remain. Reduced or co-precipitated with the product. Selenium is also adsorbed and removed by iron deposits. The filtrate from which the iron deposit has been removed can be discharged as clean water after pH adjustment. If the drainage standard is strict, the filtrate may be passed through a chelate resin tower. The ironware can also be subjected to reprocessing in a melting furnace or the like.
[0020]
In the flow diagram of FIG. 1, the mineral acid leaching solution from the mineral acid leaching step was used as a supplementary use of new mineral acid as a neutralizing agent in the alkali neutralization step. As shown in the flowchart of FIG.
In FIG. 2, the mineral acid leaching solution from the mineral acid leaching step contains copper and heavy metals such as zinc and cadmium, and further neutralized at pH 10 to 13 by addition of sodium hydroxide to form a hydroxide state. By precipitating as a porridge (copper zinc product) (acid neutralization step) and solid-liquid separation, it can be separated into a copper zinc product containing less chlorine and fluorine and a neutralized solution containing chlorine and other salts. The obtained copper-zinc product can be supplied to the smelting process after washing and removing attached salts, and the obtained neutralized solution may be supplied to the wastewater treatment process. It can be used as recycled water for repulp or diluted water.
[0021]
By the single treatment of the mineral acid leaching solution, the alkali neutralization step of the alkali leaching solution becomes a neutralization treatment with a new mineral acid solution. The obtained lead product can recover heavy metals by removing the attached salts by water washing and then supplying it to the smelting process.
[0022]
The mineral acid leaching solution is a solution that does not contain chlorine and fluorine but mainly contains copper, zinc, cadmium, etc., and these heavy metals are precipitated as hydroxides at pH 10-13, and the alkaline leaching solution is It contains heavy metals such as zinc, mainly zinc, and produces hydroxide-type deposits by separating chlorine and fluorine in the alkali neutralization process at pH 10-13, so the quality of recovered heavy metals is high and the quality of chlorine and fluorine is high. There is an advantage that a low product can be obtained.
Whether to collect heavy metals, that is, products in a centralized manner or in parallel in a dual manner, can be selected depending on the properties of fly ash, the purpose of operation, and the like.
[0023]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[Example 1]
800 g of fly ash from factory A was dissolved in 1 liter of water to make a slurry having a pulp concentration of 44.4% by weight, and then 200 cc of 40% sodium hydroxide was added (pH = 14.3) and leached for 30 minutes.
Subsequently, it filtered using the filtration apparatus and collect | recovered the alkali insoluble residue and the alkali leaching solution.
Next, the obtained alkali-insoluble residue is dissolved in water to form a slurry, and sulfuric acid is further added as a mineral acid, adjusted to pH = 2, leached for 60 minutes, and then applied to a filtration device to obtain a sulfuric acid-insoluble residue. The sulfuric acid leachate was separated and recovered.
Then, this sulfuric acid leaching solution was added to the recovered alkaline leaching solution, and further sulfuric acid was added, and the pH was adjusted to 12 and maintained for 30 minutes for neutralization. After completion of the neutralization reaction, the product was separated by filtration and separated into a heavy metal-containing product and an alkali neutralized solution.
The obtained alkali neutralized solution was adjusted to pH 6 and then subjected to fractional filtration into an aluminum precipitate and a defluorinated filtrate.
Table 1 shows the quality of the fly ash and the quality of the resulting alkali-insoluble residue, sulfuric acid-insoluble residue, and heavy metal-containing product (copper zinc / lead product).
As a result, it was found that the copper zinc / lead product contains almost no chlorine and fluorine and can be used as a raw material for smelting.
As a result of the defluorination treatment of the alkali neutralization solution, the original solution fluorine 45 mg / l was reduced to 2.6 mg / l, and the aluminum 304 mg / l was reduced to 2.3 mg / l.
[0024]
[Table 1]
[Example 2]
Using the same fly ash as in Example 1, 800 g of this fly ash was suspended in 1 liter of water to make a slurry with a pulp concentration of 44.4% by weight, and then 200 cc of 40% sodium hydroxide was added ( pH = 14.2) Leached for 30 minutes.
Subsequently, it filtered using the filtration apparatus and collect | recovered the alkali insoluble residue and the alkali leaching solution.
Next, the obtained alkali-insoluble residue is repulped with water to make a slurry. Further, sulfuric acid is added as a mineral acid, adjusted to pH = 2, leached for 60 minutes, and then applied to a filtration device. And the sulfuric acid leachate were separated and recovered.
Subsequently, sodium hydroxide was added to the sulfuric acid leaching solution to adjust the pH to 13 for neutralization. Subsequently, the copper zinc product and the neutralized solution were recovered by filtration separation.
On the other hand, sulfuric acid was added to the alkaline leachate as a mineral acid to adjust the pH to 12 and neutralize, followed by filtration and separation to obtain a lead product and an alkali neutralization solution.
Subsequently, sulfuric acid was added to the obtained alkali neutralized solution to adjust to pH 6, and then subjected to fractional filtration into an aluminum product and a defluorinated filtrate.
[0026]
Table 2 shows the grades of the obtained alkali-insoluble residue, sulfuric acid-insoluble residue, copper zinc product, and lead product.
From this result, it can be seen that a copper zinc product and a lead product which hardly contain chlorine and fluorine and can be used as a raw material for smelting can be recovered. Although the number of processing steps increases, it can be seen that it is better to collect the copper zinc product and the lead product in parallel from the viewpoint of the copper and lead quality of the recovered product.
By defluorination of the alkali neutralization solution, the original solution fluorine 34 mg / l was reduced to 2.0 mg / l, and aluminum 140 mg / l was reduced to 0.05 mg / l or less.
[0027]
[Table 2]
【The invention's effect】
By carrying out alkaline leaching of fly ash and neutralizing the alkaline leaching solution, a heavy metal containing residue such as lead with less chlorine and fluorine can be obtained. In addition, alkaline insoluble residue is leached with mineral acid, and the mineral acid leaching solution is neutralized to recover useful heavy metals such as copper and zinc with less chlorine and fluorine, which can be supplied to the smelting process. It can be recovered efficiently. Further, by mixing the alkaline leaching solution and the mineral acid leaching solution, it is possible to collect a unified useful heavy metal product.
[0029]
Selenium, cadmium, antimony, arsenic, etc., which are problematic when returning to the melting furnace, etc. can be recovered by leaching the mineral insoluble residue with mineral acid. Only high-heavy metal-containing temples can be recovered as smelting raw materials.
When removing fluorine from the alkali neutralization solution as aluminum fluoride, aluminum contained in the fly ash can be used, so there is no need to add a defluorinating agent. In the repulp prior to, the pulp concentration was increased, so that the amount of alkali chemicals added could be reduced, and when neutralizing the alkaline leachate, the mineral acid leachate of the alkaline leach residue could be used as the neutralizer, It is possible to reduce the amount of chemicals used during fly ash treatment, such as saving the mineral acid solution as a neutralizing agent.
[Brief description of the drawings]
FIG. 1 is a flow diagram showing a method for recovering heavy metals from fly ash according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a method for recovering heavy metals from fly ash according to another embodiment of the present invention.
Claims (6)
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