JP6495787B2 - Method for producing crystalline scorodite - Google Patents
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- JP6495787B2 JP6495787B2 JP2015176022A JP2015176022A JP6495787B2 JP 6495787 B2 JP6495787 B2 JP 6495787B2 JP 2015176022 A JP2015176022 A JP 2015176022A JP 2015176022 A JP2015176022 A JP 2015176022A JP 6495787 B2 JP6495787 B2 JP 6495787B2
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- UYZMAFWCKGTUMA-UHFFFAOYSA-K iron(3+);trioxido(oxo)-$l^{5}-arsane;dihydrate Chemical compound O.O.[Fe+3].[O-][As]([O-])([O-])=O UYZMAFWCKGTUMA-UHFFFAOYSA-K 0.000 title claims description 119
- 238000004519 manufacturing process Methods 0.000 title claims description 21
- 239000007864 aqueous solution Substances 0.000 claims description 37
- 150000002500 ions Chemical class 0.000 claims description 37
- 238000006243 chemical reaction Methods 0.000 claims description 36
- 230000002378 acidificating effect Effects 0.000 claims description 35
- 238000000034 method Methods 0.000 claims description 32
- 238000007254 oxidation reaction Methods 0.000 claims description 26
- 230000003647 oxidation Effects 0.000 claims description 25
- 238000003756 stirring Methods 0.000 claims description 11
- 239000002253 acid Substances 0.000 claims description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 53
- 239000000243 solution Substances 0.000 description 35
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 34
- 238000012360 testing method Methods 0.000 description 34
- 238000003786 synthesis reaction Methods 0.000 description 23
- 230000015572 biosynthetic process Effects 0.000 description 19
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 17
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 15
- 239000001301 oxygen Substances 0.000 description 15
- 229910052760 oxygen Inorganic materials 0.000 description 15
- 229910052785 arsenic Inorganic materials 0.000 description 13
- 239000007789 gas Substances 0.000 description 13
- RQNWIZPPADIBDY-UHFFFAOYSA-N arsenic atom Chemical compound [As] RQNWIZPPADIBDY-UHFFFAOYSA-N 0.000 description 12
- 239000001257 hydrogen Substances 0.000 description 12
- 229910052739 hydrogen Inorganic materials 0.000 description 12
- 239000007788 liquid Substances 0.000 description 11
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 9
- 238000010438 heat treatment Methods 0.000 description 9
- 238000002848 electrochemical method Methods 0.000 description 8
- 239000000126 substance Substances 0.000 description 8
- 238000005868 electrolysis reaction Methods 0.000 description 7
- 238000001704 evaporation Methods 0.000 description 7
- 230000008020 evaporation Effects 0.000 description 7
- 238000005259 measurement Methods 0.000 description 7
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 6
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 description 6
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 description 6
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 6
- 238000002441 X-ray diffraction Methods 0.000 description 6
- 125000000223 arsonoyl group Chemical group [H][As](*)(*)=O 0.000 description 6
- 229910052802 copper Inorganic materials 0.000 description 6
- 239000010949 copper Substances 0.000 description 6
- 239000012153 distilled water Substances 0.000 description 6
- 238000001914 filtration Methods 0.000 description 6
- 229910052742 iron Inorganic materials 0.000 description 6
- 239000012528 membrane Substances 0.000 description 6
- 239000004810 polytetrafluoroethylene Substances 0.000 description 6
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 6
- 239000011148 porous material Substances 0.000 description 6
- 239000011734 sodium Substances 0.000 description 6
- 229910052938 sodium sulfate Inorganic materials 0.000 description 6
- 235000011152 sodium sulphate Nutrition 0.000 description 6
- 238000000967 suction filtration Methods 0.000 description 6
- DXXYTBCIXZGERI-UHFFFAOYSA-N O.O.O.O.O.O.O.[Fe] Chemical compound O.O.O.O.O.O.O.[Fe] DXXYTBCIXZGERI-UHFFFAOYSA-N 0.000 description 5
- 230000007423 decrease Effects 0.000 description 5
- 230000001965 increasing effect Effects 0.000 description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 4
- 238000003723 Smelting Methods 0.000 description 4
- RBFQJDQYXXHULB-UHFFFAOYSA-N arsane Chemical compound [AsH3] RBFQJDQYXXHULB-UHFFFAOYSA-N 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000007800 oxidant agent Substances 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- VETKVGYBAMGARK-UHFFFAOYSA-N arsanylidyneiron Chemical compound [As]#[Fe] VETKVGYBAMGARK-UHFFFAOYSA-N 0.000 description 3
- -1 arsenic acid disodium hydrogen heptahydrate Chemical class 0.000 description 3
- 238000007664 blowing Methods 0.000 description 3
- 239000012295 chemical reaction liquid Substances 0.000 description 3
- 238000000354 decomposition reaction Methods 0.000 description 3
- KOLXPEJIBITWIQ-UHFFFAOYSA-L disodium hydrogenarsenate heptahydrate Chemical compound O.O.O.O.O.O.O.[Na+].[Na+].O[As]([O-])([O-])=O KOLXPEJIBITWIQ-UHFFFAOYSA-L 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000010828 elution Methods 0.000 description 3
- 230000000977 initiatory effect Effects 0.000 description 3
- 235000014413 iron hydroxide Nutrition 0.000 description 3
- BMWMWYBEJWFCJI-UHFFFAOYSA-K iron(3+);trioxido(oxo)-$l^{5}-arsane Chemical compound [Fe+3].[O-][As]([O-])([O-])=O BMWMWYBEJWFCJI-UHFFFAOYSA-K 0.000 description 3
- NCNCGGDMXMBVIA-UHFFFAOYSA-L iron(ii) hydroxide Chemical compound [OH-].[OH-].[Fe+2] NCNCGGDMXMBVIA-UHFFFAOYSA-L 0.000 description 3
- 238000002386 leaching Methods 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 229910001220 stainless steel Inorganic materials 0.000 description 3
- 239000010935 stainless steel Substances 0.000 description 3
- DJHGAFSJWGLOIV-UHFFFAOYSA-N Arsenic acid Chemical compound O[As](O)(O)=O DJHGAFSJWGLOIV-UHFFFAOYSA-N 0.000 description 2
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 2
- 229940000488 arsenic acid Drugs 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 239000000919 ceramic Substances 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 238000000151 deposition Methods 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000004070 electrodeposition Methods 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 238000009434 installation Methods 0.000 description 2
- 239000000543 intermediate Substances 0.000 description 2
- 230000007774 longterm Effects 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 229910000510 noble metal Inorganic materials 0.000 description 2
- VLTRZXGMWDSKGL-UHFFFAOYSA-N perchloric acid Chemical compound OCl(=O)(=O)=O VLTRZXGMWDSKGL-UHFFFAOYSA-N 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- DJHGAFSJWGLOIV-UHFFFAOYSA-K Arsenate3- Chemical compound [O-][As]([O-])([O-])=O DJHGAFSJWGLOIV-UHFFFAOYSA-K 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 229910021607 Silver chloride Inorganic materials 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 239000008351 acetate buffer Substances 0.000 description 1
- 230000002411 adverse Effects 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
- 229940000489 arsenate Drugs 0.000 description 1
- 239000010425 asbestos Substances 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000003673 groundwater Substances 0.000 description 1
- 229940093920 gynecological arsenic compound Drugs 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 239000010842 industrial wastewater Substances 0.000 description 1
- 239000012212 insulator Substances 0.000 description 1
- FBAFATDZDUQKNH-UHFFFAOYSA-M iron chloride Chemical compound [Cl-].[Fe] FBAFATDZDUQKNH-UHFFFAOYSA-M 0.000 description 1
- 229910000358 iron sulfate Inorganic materials 0.000 description 1
- ZOUCGOUCHDLIRO-UHFFFAOYSA-N iron sulfuric acid heptahydrate Chemical compound O.O.O.O.O.O.O.[Fe].S(O)(O)(=O)=O ZOUCGOUCHDLIRO-UHFFFAOYSA-N 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
- 229910052745 lead Inorganic materials 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000006722 reduction reaction Methods 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 229910052895 riebeckite Inorganic materials 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- HKZLPVFGJNLROG-UHFFFAOYSA-M silver monochloride Chemical compound [Cl-].[Ag+] HKZLPVFGJNLROG-UHFFFAOYSA-M 0.000 description 1
- 239000000779 smoke Substances 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 231100000331 toxic Toxicity 0.000 description 1
- 230000002588 toxic effect Effects 0.000 description 1
- 231100000701 toxic element Toxicity 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Landscapes
- Compounds Of Iron (AREA)
- Manufacture And Refinement Of Metals (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
- Water Treatment By Electricity Or Magnetism (AREA)
Description
本発明は、結晶性スコロダイトの製造方法に関する。とりわけ、非鉄製錬工程で産出する中間物からの結晶性スコロダイトの製造方法に関する。 The present invention relates to a method of producing crystalline scorodite. In particular, it relates to a process for the production of crystalline scorodite from intermediates produced in non-ferrous smelting processes.
銅鉱石などの非鉄製錬原料中には種々の不純物が混入しており、そのような不純物には砒素（Ａｓ）が含まれる。砒素は有毒元素であり周囲環境への影響を考えて、化学的に安定性の高い形態に変換した上で処分することが望まれる。この点、鉄砒素化合物であるスコロダイト（ＦｅＡｓＯ4・２Ｈ2Ｏ）の結晶は化学的に安定であることが知られており、長期保存にも適している。 Various impurities are mixed in non-ferrous smelting materials such as copper ore, and such impurities include arsenic (As). Arsenic is a toxic element, and in view of the influence on the surrounding environment, it is desirable to dispose it after converting it to a form that is chemically stable. In this regard, crystalline iron-arsenic compound scorodite (FeAsO 4 · 2H 2 O) is known to be chemically stable, it is also suitable for long-term storage.
従来、結晶性スコロダイトを製造する方法として一般に採用されてきたのは、５価の砒素溶液に２価又は３価の鉄を加え、酸性条件下、８０℃以上で熱処理を行い、結晶性スコロダイトを生成させる化学的な製造方法である。この技術は、例えば、特許第３７５６６８７号公報「砒素含有溶液からの砒素の除去および固定方法」、特開２００５−１６１１２３号公報「煙灰からの砒素除去方法」、特許第４１８５５４１号公報「結晶性の良い鉄砒素化合物の製法」に、その詳細が記載されている。 In the past, commonly used as a method for producing crystalline scorodite is the addition of divalent or trivalent iron to a pentavalent arsenic solution, and heat treatment at 80 ° C. or higher under acidic conditions to obtain crystalline scorodite. It is a chemical manufacturing method to produce. This technique is described, for example, in Japanese Patent No. 3756687, "Method of removing and fixing arsenic from arsenic-containing solution", Japanese Patent Application Laid-Open No. 2005-161123, "method of removing arsenic from smoke ash", Japanese Patent No. 4185541, "Crystalline The details are described in "Production of Good Iron Arsenic Compounds".
一方で、被処理水、特に地下水、工場排水等に含まれる砒素を、電気化学的な方法で鉄砒素化合物（砒酸鉄：ＦｅＡｓＯ4）を生成させて沈殿することにより、除去する方法も知られている（特開２００７−１６０２５７号公報「有害物の処理方法及び有害物処理装置」）。当該公報には、電気化学的手法により、オゾンや活性酸素を発生可能な陽極で対象物を酸化させる酸化物質を生成し、生成された当該酸化物質により、被処理水中のヒ素を酸化する酸化処理と、電気化学的手法により、鉄製の陽極から対象物と難溶性化合物を生成する金属を溶出させ、当該溶出した金属と前記酸化処理で酸化されたヒ素とを化学結合させて沈殿除去する沈殿処理とを含む方法が開示されている。 On the other hand, there is also known a method of removing arsenic contained in water to be treated, particularly groundwater, industrial waste water, etc. by forming an iron-arsenic compound (iron arsenate: FeAsO 4 ) by an electrochemical method and precipitating it. (Japanese Patent Application Laid-Open No. 2007-160257 “Method of treating harmful substances and harmful substance treatment apparatus”). In the publication, an oxidation treatment is performed to generate an oxidation substance that oxidizes an object with an anode capable of generating ozone or active oxygen by an electrochemical method, and oxidize the arsenic in the water to be treated with the generated oxidation substance. And an electrochemical method to elute the metal that produces the object and the sparingly soluble compound from the iron anode by an electrochemical method, and chemically combine the eluted metal with arsenic oxidized by the oxidation treatment to remove the precipitate. And methods are disclosed.
従来、スコロダイトは化学的な方法によって製造することが主流であり、電気化学的な方法は検討されてこなかった。特開２００７−１６０２５７号公報（特許文献４）に電気化学的手法により砒酸鉄を生成させることが記載されているのみである。しかしながら、当該公報には、生成する砒素と鉄の化合物が砒酸鉄（ＦｅＡｓＯ4）である旨の記載はあるものの、その結晶性についての議論は一切ない。また、特開２００７−１６０２５７号公報（特許文献４）には電解条件についての記述が乏しい。また、当該文献に記載の方法はオゾンや活性酸素を積極的に発生させる方法である。オゾンや活性酸素はそれ自体が有害及び／又は可燃性であるため、安全性の観点からは望ましいとは言えない。また、このようなガスを発生させるためには高電圧を必要とするところ、対極から可燃性の水素、更には有毒の高いアルシンガスが発生するポテンシャルを大きくする。 Conventionally, scorodite is mainly manufactured by a chemical method, and no electrochemical method has been considered. JP-A-2007-160257 (Patent Document 4) only describes that iron arsenate is produced by an electrochemical method. However, although the publication states that the compound of arsenic and iron to be formed is iron arsenate (FeAsO 4 ), there is no discussion about its crystallinity at all. Moreover, the description about electrolysis conditions is scarce in Unexamined-Japanese-Patent No. 2007-160257 (patent document 4). Further, the method described in the document is a method of positively generating ozone and active oxygen. Ozone and active oxygen are harmful and / or flammable per se, so they are not desirable from the viewpoint of safety. Also, in order to generate such a gas, a high voltage is required, and the potential to generate combustible hydrogen and further highly toxic arsine gas from the counter electrode is increased.
本発明は上記事情に鑑みてなされたものであり、砒素を含む溶液から電気化学的な手法を用いて結晶性の高いスコロダイトを製造する方法を提供することを課題の一つとする。 The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a highly crystalline scorodite from a solution containing arsenic by using an electrochemical method.
本発明者は上記課題を解決するために鋭意検討したところ、５価のＡｓイオンと２価のＦｅイオンとを含有し、該Ａｓイオンの初期濃度が５ｇ／Ｌ以上である酸性水溶液を調製し、当該酸性水溶液を陽極で電解酸化することにより、結晶性の良好なスコロダイトが製造できることを見出した。 The inventors of the present invention conducted intensive studies to solve the above problems, and prepared an acidic aqueous solution containing pentavalent As ions and divalent Fe ions and having an initial concentration of 5 g / L or more of the As ions. By electrolyzing the said acidic aqueous solution with an anode, it discovered that a favorable scorodite of crystallinity could be manufactured.
本発明は上記知見に基づいて完成したものであり、一側面において、５価のＡｓイオンと２価のＦｅイオンとを含有する酸性水溶液から、結晶性スコロダイトを製造する方法であって、酸性水溶液中の前記Ａｓイオンの初期濃度を５ｇ／Ｌ以上として、該酸性水溶液を陽極で電解酸化することを伴う方法である。 The present invention has been completed based on the above findings, and in one aspect, a method of producing crystalline scorodite from an acidic aqueous solution containing pentavalent As ions and divalent Fe ions, which is an acidic aqueous solution In this method, the acidic aqueous solution is electrolytically oxidized at the anode with an initial concentration of As ions of 5 g / L or more.
本発明に係る結晶性スコロダイトの製造方法の一実施形態においては、酸性水溶液中の前記Ａｓイオンの初期濃度を１５ｇ／Ｌ以上とする。 In one embodiment of the method for producing crystalline scorodite according to the present invention, the initial concentration of the As ion in the acidic aqueous solution is 15 g / L or more.
本発明に係る結晶性スコロダイトの製造方法の別の一実施形態においては、反応開始時点における前記酸性水溶液中の５価のＡｓイオンに対する２価のＦｅイオンのモル比が２以上である。 In another embodiment of the method for producing crystalline scorodite according to the present invention, the molar ratio of divalent Fe ions to pentavalent As ions in the acidic aqueous solution at the reaction initiation time is 2 or more.
本発明に係る結晶性スコロダイトの製造方法の更に別の一実施形態においては、前記酸性水溶液の温度を７０℃以上として電解酸化する。 In still another embodiment of the method for producing crystalline scorodite according to the present invention, the temperature of the acidic aqueous solution is set to 70 ° C. or higher for electrolytic oxidation.
本発明に係る結晶性スコロダイトの製造方法の更に別の一実施形態においては、前記酸性水溶液の反応開始時のｐＨが１〜２である。 In still another embodiment of the method for producing crystalline scorodite according to the present invention, the pH of the acidic aqueous solution at the start of the reaction is 1 to 2.
本発明に係る結晶性スコロダイトの製造方法の更に別の一実施形態においては、電解酸化は陽極電位を１．２Ｖ以下（ｖｓ．Ｓ．Ｈ．Ｅ．）にして行う。 In still another embodiment of the method for producing crystalline scorodite according to the present invention, the electrolytic oxidation is performed at an anode potential of 1.2 V or less (vs. S.H.E.).
本発明に係る結晶性スコロダイトの製造方法の更に別の一実施形態においては、電解酸化は陰極電位を−０．５Ｖ以上（ｖｓ．Ｓ．Ｈ．Ｅ．）にして行う。 In still another embodiment of the method for producing crystalline scorodite according to the present invention, the electrolytic oxidation is performed at a cathode potential of -0.5 V or more (vs. S.H.E.).
本発明に係る結晶性スコロダイトの製造方法の更に別の一実施形態においては、前記酸性水溶液を攪拌しながら電解酸化を行う。 In still another embodiment of the method for producing crystalline scorodite according to the present invention, electrolytic oxidation is performed while stirring the acidic aqueous solution.
本発明に係る結晶性スコロダイトの製造方法の更に別の一実施形態においては、電解酸化は電流密度を５０〜５００Ａ／ｍ2として行う。 In still another embodiment of the method for producing crystalline scorodite according to the present invention, the electrolytic oxidation is performed at a current density of 50 to 500 A / m 2 .
本発明によれば、酸素や空気等の酸化剤を液中に吹き込むことなく、電気化学的な方法によって結晶性の高いスコロダイトを製造可能となる。酸素や空気を吹き込む場合、酸素利用効率は最大でも２０％程度と低い。また、ガスを吹き込んで酸化する場合、吹き込みガスが溶液から放出される際に溶液の熱を奪うためエネルギーロスが発生する。この点、本発明にかかるスコロダイトの製造方法によれば、酸素や空気を吹き込んで酸化する化学的な方法に比べて吹き込みガスが持ち去る熱量を抑えることができるメリットがある。そのうえ、電気分解時に発生する熱は溶液の加熱に使われるため、溶液の温度維持に必要な加熱設備の能力を抑えることができる。 According to the present invention, a highly crystalline scorodite can be produced by an electrochemical method without blowing an oxidizing agent such as oxygen or air into the solution. When oxygen or air is blown, the oxygen utilization efficiency is as low as at most 20%. In addition, when gas is blown to oxidize, energy loss occurs because the heat of the solution is removed when the blown gas is released from the solution. In this respect, according to the method of manufacturing scorodite according to the present invention, there is an advantage that the amount of heat carried by the blowing gas can be suppressed as compared with a chemical method of blowing oxygen or air to oxidize. Moreover, since the heat generated during the electrolysis is used to heat the solution, the capacity of the heating equipment required to maintain the temperature of the solution can be reduced.
また、諸般の事情により、空気や酸素等の酸化剤の供給設備が設置できないが、電解設備は確保できるというような場合には、本発明に係る結晶性スコロダイトの製造方法は特に有利である。貯蔵安定性の高い結晶性スコロダイトの製造方法のバリエーションを増やしておくことは、現場環境に応じた砒素処理設備の柔軟な設計を可能とすることに寄与するであろう。 Moreover, although the supply installation of oxidizing agents, such as air and oxygen, can not be installed by various circumstances, when an electrolytic installation can be ensured, the manufacturing method of the crystalline scorodite based on this invention is especially advantageous. Increasing variations in the method of producing storage-stable crystalline scorodite will contribute to enabling flexible design of arsenic processing equipment according to the on-site environment.
本発明に係る結晶性スコロダイトの製造方法の一実施形態においては、５価のＡｓイオンと２価のＦｅイオンとを含有する酸性水溶液を陽極で電解酸化することを伴う。電解酸化を実施する際、酸性水溶液中へ空気や酸素等の酸化剤を吹き込む必要はない。 One embodiment of the method for producing crystalline scorodite according to the present invention involves electrolytic oxidation of an acidic aqueous solution containing pentavalent As ions and divalent Fe ions at the anode. When the electrolytic oxidation is carried out, it is not necessary to blow an oxidizing agent such as air or oxygen into the acidic aqueous solution.
５価のＡｓは例示的には砒酸（Ｈ3ＡｓＯ4）等の形態で与えることができる。砒酸は銅製錬工程で産出する中間物である電解沈殿銅を硫酸浸出した後の硫酸浸出液中に含まれる。そのため、当該硫酸浸出液を原料とすることもできる。５価のＡｓを使用することにより、低電圧でスコロダイトを合成可能であり、安全性も高い。３価以下のＡｓを使用する場合は、スコロダイトを合成するのに高電圧が必要となるため、電解酸化中にアノードからは酸素及び／又はオゾンの発生リスク、カソードからは水素及び／又はアルシンガスの発生リスクが高まる。これらのガスは可燃性ガスや人体に悪影響のあるガスであるため、安全性の観点からは発生させないほうが好ましい。 Pentavalent As can be exemplarily given in the form of arsenate (H 3 AsO 4 ) or the like. Arsenic acid is contained in a sulfuric acid leaching solution after sulfuric acid leaching of electrolytically precipitated copper, which is an intermediate produced in the copper smelting process. Therefore, the said sulfuric acid leaching solution can also be used as a raw material. By using pentavalent As, scorodite can be synthesized at low voltage and safety is high. When using trivalent or less As, since a high voltage is required to synthesize scorodite, the risk of generation of oxygen and / or ozone from the anode during electrolytic oxidation, hydrogen and / or arsine gas from the cathode Risk of occurrence increases. Since these gases are flammable gases and gases that adversely affect the human body, it is preferable not to generate them from the viewpoint of safety.
２価のＦｅは例示的には酸化鉄、硫酸鉄、塩化鉄及び水酸化鉄等の形態で与えることができる。また、鉄、酸化鉄及び水酸化鉄を塩酸、硫酸等の酸で溶解した液も使用可能である。スコロダイト中のＦｅの価数は３価であることから、当初から３価のＦｅを使用することも考えられるが、３価のＦｅを使用するとスコロダイトの合成反応が過度に早く進行するため、高い結晶性を得るのが困難となる。 The divalent Fe can be provided illustratively in the form of iron oxide, iron sulfate, iron chloride, iron hydroxide and the like. Further, a solution in which iron, iron oxide and iron hydroxide are dissolved in an acid such as hydrochloric acid or sulfuric acid can also be used. Since the valence of Fe in scorodite is trivalent, it is conceivable to use trivalent Fe from the beginning, but if trivalent Fe is used, the synthesis reaction of scorodite proceeds too fast, so it is high. It becomes difficult to obtain crystallinity.
酸性水溶液は例示的には塩酸酸性、硫酸酸性、硝酸酸性、過塩素酸酸性等の水溶液として与えることができる。銅製錬工程で発生する電解沈殿銅中に含まれる砒酸中のＡｓからスコロダイトを製造する場合、スコロダイトの合成後液を銅電解槽に戻すことができるため、硫酸酸性の水溶液が好ましい。 The acidic aqueous solution can be, for example, provided as an aqueous solution of hydrochloric acid, sulfuric acid, nitric acid, perchloric acid and the like. In the case of producing scorodite from As in arsenic acid contained in electrolytically precipitated copper generated in the copper smelting process, the aqueous solution of sulfuric acid acid is preferable because the solution after synthesis of scorodite can be returned to the copper electrolytic cell.
本発明においては、結晶性スコロダイトは陽極（以下、「アノード」ともいう。）において該酸性水溶液を陽極で電解酸化することにより製造可能である。理論によって本発明が限定されることを意図するものではないが、例示的には以下の反応（１）及び（２）が陽極で進行すると考えられる。
Ｆｅ2+→Ｆｅ3+＋ｅ- ・・・（１）
Ｆｅ3+＋Ｈ3ＡｓＯ4＋２Ｈ2Ｏ→ＦｅＡｓＯ4・２Ｈ2Ｏ＋３Ｈ+ ・・・（２）
In the present invention, crystalline scorodite can be produced by electrolytic oxidation of the acidic aqueous solution at the anode (hereinafter also referred to as "anode") at the anode. While it is not intended that the present invention be limited by theory, it is believed that the following reactions (1) and (2) will proceed at the anode as an example.
Fe 2+ → Fe 3+ + e - ··· (1)
Fe 3+ + H 3 AsO 4 + 2H 2 O → FeAsO 4 · 2H 2 O + 3H + ··· (2)
結晶性の高いスコロダイトを製造するためには、酸性水溶液中の前記Ａｓイオンの初期濃度を高くすることが有効である。スコロダイトは結晶性が高まるにつれて形状の規則性及び平滑性が高くなり、特に高い結晶性をもつスコロダイトは多面体形状となり得る。また、多面体形状の中でも球形に近い形状であることが比表面積を低下させる観点から好ましい。多面体形状であると、各面は平滑であるので凹凸の多いスコロダイトに比べて比表面積が小さくなり、Ａｓ溶出リスクの低減効果があると考えられる。また、凹凸が少なくなることで、スコロダイト表面に付着した未反応Ａｓ成分を洗浄除去しやすくなる。 In order to produce highly crystalline scorodite, it is effective to increase the initial concentration of the As ion in the acidic aqueous solution. As the crystallinity of the scorodite increases, the regularity and smoothness of the shape increase, and in particular, scorodite having high crystallinity can be in the shape of a polyhedron. Moreover, it is preferable from a viewpoint of reducing a specific surface area that it is a shape close | similar to spherical shape among polyhedron shape. If it is polyhedral shape, each surface is smooth, so the specific surface area is smaller than scorodite with many irregularities, and it is considered that the As elution risk is reduced. In addition, since the unevenness is reduced, the unreacted As component adhering to the surface of the scorodite can be easily removed by washing.
結晶性を高める上では、酸性水溶液中の前記Ａｓイオンの初期濃度は５ｇ／Ｌ以上であることが好ましく、１０ｇ／Ｌ以上であることがより好ましく、１５ｇ／Ｌ以上であることが更により好ましく、２０ｇ／Ｌ以上であることが更により好ましく、２５ｇ／Ｌ以上であることが更により好ましく、３０ｇ／Ｌ以上であることが更により好ましい。前記Ａｓイオンの初期濃度の上限は特に設定されないが、Ｆｅ／Ａｓモル比を高くするために、７０ｇ／Ｌ以下であることが好ましく、６０ｇ／Ｌ以下であることがより好ましく、５０ｇ／Ｌ以下であることが更により好ましい。当該Ａｓイオン濃度は反応の進行に従って減少していくが、反応開始時点のみならず、反応終了時にも上記範囲を満たしていることが望ましい。Ａｓイオン濃度を維持するために、反応液中にＡｓイオンを断続的又は連続的に添加してもよいし、反応液中の水分量を蒸発等によって調整してもよい。 In order to enhance the crystallinity, the initial concentration of the As ion in the acidic aqueous solution is preferably 5 g / L or more, more preferably 10 g / L or more, and still more preferably 15 g / L or more. 20 g / L or more is more preferable, 25 g / L or more is even more preferable, and 30 g / L or more is even more preferable. The upper limit of the initial concentration of the As ion is not particularly set, but is preferably 70 g / L or less, more preferably 60 g / L or less, and 50 g / L or less in order to increase the Fe / As molar ratio. It is even more preferred that The As ion concentration decreases as the reaction proceeds, but it is desirable that the above range be satisfied not only at the reaction initiation time but also at the reaction completion time. In order to maintain the As ion concentration, As ions may be added intermittently or continuously to the reaction solution, or the water content in the reaction solution may be adjusted by evaporation or the like.
反応開始時点において、酸性水溶液中の５価のＡｓイオンに対する２価のＦｅイオンのモル比（Ｆｅ／Ａｓモル比）は高くするほうが、電流効率が高くなる傾向にあるため好ましい。また、未反応のＡｓを減らすという観点からも、Ｆｅ／Ａｓモル比が高いほうが好ましい。具体的には、反応開始時点において、酸性水溶液中のＦｅ／Ａｓモル比を１．０以上に設定することが好ましく、１．２以上に設定することがより好ましく、１．５以上に設定することが更により好ましく、２．０以上に設定することが更により好ましく、２．５以上に設定することが更により好ましく、３．０以上に設定することが更により好ましく、５．０以上に設定することが更により好ましい。また、Ｆｅに係る無駄なコストを省くという観点からは、酸性水溶液中の初期のＦｅ／Ａｓモル比を８．０以下に設定することが好ましく、７．０以下に設定することがより好ましい。当該Ｆｅ／Ａｓモル比は反応初期のみならず、反応終了時にも上記範囲を満たしていることが望ましい。 It is preferable to increase the molar ratio (Fe / As molar ratio) of divalent Fe ions to pentavalent As ions in the acidic aqueous solution at the start of the reaction because current efficiency tends to be high. Also, from the viewpoint of reducing unreacted As, it is preferable that the Fe / As molar ratio be high. Specifically, at the reaction initiation time, the Fe / As molar ratio in the acidic aqueous solution is preferably set to 1.0 or more, more preferably 1.2 or more, and 1.5 or more. Is more preferably set to 2.0 or more, still more preferably set to 2.5 or more, still more preferably set to 3.0 or more, to 5.0 or more It is even more preferable to set. Further, from the viewpoint of eliminating the waste cost of Fe, it is preferable to set the initial Fe / As molar ratio in the acidic aqueous solution to 8.0 or less, and more preferably to 7.0 or less. It is desirable that the Fe / As molar ratio satisfies the above range not only at the initial stage of the reaction but also at the end of the reaction.
結晶性スコロダイトの溶解度はｐＨ０．３未満で急速に増大するため、反応開始時の酸性水溶液のｐＨを０．３以上に設定することが好ましく、０．６以上に設定することがより好ましく、１．０以上に設定することが更により好ましく、１．２以上に設定することが更により好ましい。また、酸性水溶液のｐＨが２．２を超えると添加した鉄が水酸化鉄となって沈殿してしまい、鉄が有効にスコロダイトの合成に使われないことから、反応開始時の酸性水溶液のｐＨを２．２以下に設定することが好ましく、２．０以下に設定することがより好ましく、１．６以下に設定することが更により好ましい。当該ｐＨの範囲は反応開始時のみならず、反応終了時まで継続的に満たされていることが望ましい。 Since the solubility of crystalline scorodite rapidly increases at a pH of less than 0.3, the pH of the acidic aqueous solution at the start of the reaction is preferably set at 0.3 or more, more preferably 0.6 or more, and 1 It is further more preferable to set to .0 or more, and still more preferable to set to 1.2 or more. In addition, if the pH of the acidic aqueous solution exceeds 2.2, the added iron precipitates as iron hydroxide and the iron is not effectively used for synthesizing scorodite, so the pH of the acidic aqueous solution at the start of the reaction Is preferably set to 2.2 or less, more preferably 2.0 or less, and still more preferably 1.6 or less. It is desirable that the pH range is continuously satisfied not only at the start of the reaction but also at the end of the reaction.
スコロダイトは上記酸性水溶液を例えば大気条件下で６０〜９５℃に加熱することにより生成させることができる。当該酸性水溶液は７０℃以上に加熱することが好ましく、８０℃以上に加熱することがより好ましく、９０℃以上に加熱することが更により好ましい。 The scorodite can be produced, for example, by heating the above acidic aqueous solution to 60 to 95 ° C. under atmospheric conditions. The acidic aqueous solution is preferably heated to 70 ° C. or higher, more preferably heated to 80 ° C. or higher, and still more preferably heated to 90 ° C. or higher.
電解酸化を実施中の陽極電位は、高い方がスコロダイトの合成反応が進行しやすいが、高すぎると酸素及び／又はオゾンが生成し得る。先述したように、これらのガスは安全性の観点から発生させないことが好ましいことから、電解酸化は酸素及びオゾンの何れも発生しない陽極電位の条件とすることが望まれる。具体的には、基準電極を標準水素電極（ＳＨＥ）としたときに、陽極電位を１．２Ｖ以下とすることが好ましく、１．０Ｖ以下とすることがより好ましく、０．８Ｖ以下とすることが更により好ましい。但し、陽極電位が低すぎるとスコロダイト合成反応の進行が遅くなるため、基準電極を標準水素電極（ＳＨＥ）としたときに、陽極電位を０．４Ｖ以上とすることが好ましく、０．５Ｖ以上とすることがより好ましく、０．６Ｖ以上とすることが更により好ましい。 The higher the anodic potential during electrolytic oxidation, the easier the scorodite synthesis reaction proceeds, but if it is too high oxygen and / or ozone may be generated. As described above, since it is preferable that these gases not be generated from the viewpoint of safety, it is desirable that the electrolytic oxidation be performed under conditions of an anodic potential which does not generate either oxygen or ozone. Specifically, when the reference electrode is a standard hydrogen electrode (SHE), the anode potential is preferably 1.2 V or less, more preferably 1.0 V or less, and 0.8 V or less Is even more preferred. However, if the anode potential is too low, the progress of the scorodite synthesis reaction will be delayed, so when the standard electrode is a standard hydrogen electrode (SHE), it is preferable to set the anode potential to 0.4 V or more. Is more preferable, and it is even more preferable to set it to 0.6 V or more.
電解酸化を実施中の陰極電位は、スコロダイトの合成反応自体には関係しないが、低くなるにつれて水素及び／又はアルシンガスの発生ポテンシャルが高まる。先述したように、これらのガスは安全性の観点から発生させないことが好ましいことから、電解酸化は水素及びアルシンガスの何れも発生しない陰極電位の条件とすることが望まれる。具体的には、基準電極を標準水素電極（ＳＨＥ）としたときに、陰極電位を−０．５Ｖ以上とすることが好ましく、−０．４Ｖ以上とすることがより好ましく、−０．３Ｖ以上とすることが更により好ましい。但し、陰極電位を高く保とうとすると電気が流れなくなる為、基準電極を標準水素電極（ＳＨＥ）としたときに、陰極電位を０．２Ｖ以下とすることが好ましく、０．１Ｖ以下とすることがより好ましく、０．０Ｖ以下とすることが更により好ましい。 The cathodic potential during the electrolytic oxidation is not related to the scorodite synthesis reaction itself, but as it decreases, the generation potential of hydrogen and / or arsine gas increases. As described above, since it is preferable that these gases not be generated from the viewpoint of safety, it is desirable that the electrolytic oxidation be performed under conditions of a cathode potential in which neither hydrogen nor arsine gas is generated. Specifically, when the reference electrode is a standard hydrogen electrode (SHE), the cathode potential is preferably -0.5 V or more, more preferably -0.4 V or more, -0.3 V or more It is even more preferable to However, when the cathode potential is kept high, electricity does not flow, so when the reference electrode is a standard hydrogen electrode (SHE), the cathode potential is preferably 0.2 V or less, preferably 0.1 V or less. It is more preferable that the voltage be 0.0 V or less.
電解酸化を実施中の電流密度は小さすぎると生産効率が悪いことから、電流密度は５０Ａ／ｍ2以上することが好ましく、６０Ａ／ｍ2以上とすることがより好ましく、７０Ａ／ｍ2以上とすることが更により好ましい。一方で、高くなるにつれて結晶性スコロダイトの平滑性が損なわれ、更には電流効率が低下する傾向にあることから、電流密度は５００Ａ／ｍ2以下とすることが好ましく、３００Ａ／ｍ2以下とすることがより好ましく、２００Ａ／ｍ2以下とすることが更により好ましく、１００Ａ／ｍ2以下とすることが更により好ましい。 The current density is preferably 50 A / m 2 or more, more preferably 60 A / m 2 or more, and more preferably 70 A / m 2 or more, because the production efficiency is poor if the current density during electrolytic oxidation is too small. It is even more preferable to do. On the other hand, the smoothness of the crystalline scorodite is impaired as the temperature increases, and the current efficiency tends to decrease. Therefore, the current density is preferably 500 A / m 2 or less, and 300 A / m 2 or less More preferably, it is more preferably 200 A / m 2 or less, and still more preferably 100 A / m 2 or less.
電解酸化は酸性水溶液を攪拌しながら実施することが好ましい。酸化反応が進むことで電極表面近傍の２価のＦｅ濃度が減少するが、撹拌によって沖合の２価のＦｅを供給する事で反応効率を向上させるためである。また攪拌により、生成したスコロダイトを陽極から離脱して新たなスコロダイトの合成を促すという効果もある。 It is preferable to carry out the electrolytic oxidation while stirring the acidic aqueous solution. Although the concentration of divalent Fe in the vicinity of the electrode surface decreases as the oxidation reaction proceeds, the reaction efficiency is improved by supplying offshore divalent Fe by stirring. The stirring also has the effect of separating the generated scorodite from the anode and promoting the synthesis of new scorodite.
電解酸化によって陽極で生成したスコロダイト（ＦｅＡｓＯ4・２Ｈ2Ｏ）は、電流効率を高める観点から、陰極（以下、「カソード」ともいう。）に接触させないことが好ましい。理論によって本発明が限定されることを意図しないが、これは、スコロダイトが陰極に接触すると還元反応が生じて分解する場合があるためであると考えられる。このため、陰極にスコロダイトが接触しないようにするために電解隔膜を使用することが好ましい。電解隔膜としては、隔膜電解法に採用される一般的なもので構わない。電解隔膜は電気抵抗（隔膜自体は絶縁体であるが、低い方が好ましい。）、透水性能（陽極側と陰極側では酸化還元電位の違いにより液組成が異なり、目的に応じて液を分けるため、低い方が好ましい。例えば、陰極側でＦｅＡｓの電着を抑制しようとした場合、陽極側：本発明に係る酸性水溶液、陰極側：芒硝溶液とする事で、陰極側でのＦｅＡｓの電着を防止できる。）及び耐薬品性（高い方が好ましい。）などを考慮して適宜選択すればよい。電解隔膜としては例えば、石綿、セラミックス系及び樹脂系が挙げられる。なお、電解隔膜の材質として金属を用いると電解隔膜が陰極と同じ働きをして接触したスコロダイトの分解が生じるため好ましくない。 It is preferable that scorodite (FeAsO 4 .2H 2 O) generated at the anode by electrolytic oxidation is not in contact with a cathode (hereinafter also referred to as “cathode”) from the viewpoint of enhancing current efficiency. While the present invention is not intended to be limited by theory, it is believed that when scorodite comes in contact with the cathode, a reduction reaction may occur to cause decomposition. For this reason, it is preferable to use an electrolytic diaphragm to prevent scorodite from contacting the cathode. As an electrolysis diaphragm, the general thing employ | adopted by diaphragm electrolysis method may be used. In the electrolytic diaphragm, the electric resistance (the diaphragm itself is an insulator, but the lower one is preferable) and the water permeability (the anode side and the cathode side differ in liquid composition due to the difference of redox potential, and the liquid is separated according to the purpose. For example, when it is intended to suppress the electrodeposition of FeAs on the cathode side, the anode side: the acidic aqueous solution according to the present invention, the cathode side: the electrodeposition of FeAs on the cathode side And the chemical resistance (the higher the better), etc., may be selected appropriately. Examples of the electrolytic diaphragm include asbestos, ceramics and resins. The use of metal as the material of the electrolytic diaphragm is not preferable because the electrolytic diaphragm functions in the same way as the cathode to cause decomposition of the contacted scorodite.
電解隔膜の設置方法としては、陽極で生成したスコロダイトが陰極に接触するのを防止できれば特に制限はないが、例えば陰極の周囲を覆うように箱状又は筒状に設置する方法、陽極の周囲を覆うように箱状又は筒状に設置する方法、及び、陰極と陽極の間に壁状に設置する方法が挙げられる。 The method of installing the electrolytic diaphragm is not particularly limited as long as it can prevent the scorodite formed by the anode from coming into contact with the cathode. For example, a method of installing in a box or cylinder so as to cover the periphery of the cathode, around the anode The method of installing in a box shape or cylinder shape so that it may cover, and the method of installing in wall shape between a cathode and an anode are mentioned.
陽極及び陰極の材質としては、特に制限はなく、電解に使用される一般的な材質を採用すればよい。陽極及び陰極としては例えばＰｂ及びＰｔ等の貴金属電極、Ｐｔめっきチタン等の貴金属めっき電極、カーボン電極、ステンレス電極、及びセラミックス等の酸化物電極等の不溶性電極を使用することができる。可溶性電極を使用してもよいが、溶け出した電極成分によって酸性水溶液の組成が変化してスコロダイトの性状が予期せず変化する可能性があり、また、電極の交換が必要となって電解設備の維持管理が複雑化するため、不溶性電極が好ましい。 There is no restriction | limiting in particular as a material of an anode and a cathode, What is necessary is just to employ | adopt the general material used for electrolysis. As the anode and the cathode, for example, insoluble electrodes such as noble metal electrodes such as Pb and Pt, noble metal plated electrodes such as Pt plated titanium, carbon electrodes, stainless steel electrodes, and oxide electrodes such as ceramics can be used. Although a soluble electrode may be used, the composition of the acidic aqueous solution may be changed by the dissolved electrode component to change the properties of the scorodite unexpectedly, and it is necessary to replace the electrode, resulting in an electrolytic plant Insoluble electrodes are preferred because they complicate maintenance of the
結晶性のスコロダイトは化学的に安定であり、長期保存にも適している。得られたスコロダイトを含有する残渣と脱砒後液とに固液分離すれば、スコロダイトを回収することができる。 Crystalline scorodite is chemically stable and suitable for long-term storage. If solid-liquid separation is performed on the obtained scorodite-containing residue and the liquid after de-arsenic, scorodite can be recovered.
以下、本発明の実施例を示すが、これらの実施例は本発明及びその利点をより良く理解するために提示するものであり、本発明が限定されることを意図するものではない。 The following examples illustrate the present invention, but these examples are presented to better understand the present invention and its advantages, and are not intended to limit the present invention.
（電解装置）
図１に、実験に用いた電解装置１００の構成を示す。電解装置１００は、電解槽１０１、ホットスターラー１０２、整流器１０３、縦６５ｍｍ×横４０ｍｍのカーボン製のアノード１０４、ステンレス（ＳＵＳ３０４）製のカソード１０５、撹拌子（図示せず）を備える。電解槽１０１はホットスターラー１０２上に載置されており、反応液１０７は電解槽１０１内に入れた撹拌子によって撹拌可能となっている。アノード１０４及びカソード１０５は電解槽１０１中の反応液１０７に浸漬する。アノード１０４及びカソード１０５はそれぞれ整流器１０３に接続されている。表１中に、隔膜「有」と表示されている例では、カソード１０５の周囲にアルミナ製の箱形の電解隔膜１０６を配置した。なお、電解装置１００は、空気や酸素等の酸化剤を導入するための機器は備えていない。
(Electrolyzer)
FIG. 1 shows the configuration of the electrolytic device 100 used in the experiment. The electrolytic device 100 includes an electrolytic cell 101, a hot stirrer 102, a rectifier 103, a carbon-made anode 104 of 65 mm × 40 mm, a cathode 105 made of stainless steel (SUS304), and a stirrer (not shown). The electrolytic cell 101 is placed on the hot stirrer 102, and the reaction liquid 107 can be stirred by a stirrer placed in the electrolytic cell 101. The anode 104 and the cathode 105 are immersed in the reaction solution 107 in the electrolytic cell 101. The anode 104 and the cathode 105 are connected to the rectifier 103, respectively. In the example shown in Table 1 where the diaphragm is "present", a box-shaped electrolytic diaphragm 106 made of alumina was placed around the cathode 105. The electrolysis apparatus 100 is not equipped with a device for introducing an oxidant such as air or oxygen.
＜試験例１：Ａｓ濃度の影響（Ｆｅ／Ａｓモル比＝２）＞
表１に記載の試験番号に応じた２価のＦｅイオン濃度、５価のＡｓイオン濃度、硫酸イオン濃度及びｐＨの反応液が得られるように、電解槽中に硫酸、硫酸ナトリウム、硫酸第一鉄七水和物（ＦｅＳＯ4・７Ｈ2Ｏ）及びヒ酸水素二ナトリウム七水和物（Ｎａ2ＨＡｓＯ4・７Ｈ2Ｏ）を添加した（反応開始時のＦｅ／Ａｓモル比＝２）。その後、大気条件下で、当該反応液を表１に記載の液温に加熱し、表１に記載の電解条件にて、攪拌しながらスコロダイトの合成を行った。表中、「電流密度」は電流［Ａ］／陽極表面積［ｍ2］によって算出した値である。なお、加熱中、蒸発によって液量が減らないように、適宜水を追加した。
<Test Example 1: Effect of As concentration (Fe / As molar ratio = 2)>
Sulfuric acid, sodium sulfate, sulfuric acid first in the electrolytic cell so that a reaction solution of divalent Fe ion concentration, pentavalent As ion concentration, sulfate ion concentration and pH according to the test numbers described in Table 1 is obtained. Iron heptahydrate (FeSO 4 · 7H 2 O) and disodium hydrogen arsenate heptahydrate (Na 2 HAsO 4 · 7H 2 O) were added (Fe / As molar ratio at the start of the reaction = 2). Thereafter, the reaction solution was heated to the solution temperature described in Table 1 under atmospheric conditions, and scorodite synthesis was performed while stirring under the electrolytic conditions described in Table 1. In the table, “current density” is a value calculated by current [A] / anode surface area [m 2 ]. During the heating, water was appropriately added so as not to reduce the liquid amount by evaporation.
スコロダイトの合成終了後は孔径１μｍのＰＴＦＥ製メンブレンフィルターを使用して吸引ろ過した。次いで、ろ過後のスコロダイトは蒸留水で洗浄して同様の方法で吸引ろ過した。その後、６０℃の乾燥器で２４ｈ以上乾燥した。各スコロダイトのＳＥＭ写真（倍率：３万倍）を図２にそれぞれ示す。ＳＥＭ写真から分かるように、５価のＡｓ濃度が上昇するにつれて結晶性スコロダイトの表面形状の平滑性及び規則性が高くなっており、Ｎｏ．１−３の結晶性スコロダイトは多面体の形状となっていることが分かる。これは、５価のＡｓ濃度が上昇するにつれて結晶性が高まっていることを示唆している。実際、得られたスコロダイトをＸ線回折により分析したところ、何れの試験例も結晶性スコロダイトに特徴的なパターンが確認されたが、表面形状の平滑性及び規則性が高いスコロダイトほど、当該パターンのピーク強度が大きかった。 After completion of scorodite synthesis, suction filtration was performed using a PTFE membrane filter with a pore size of 1 μm. Then, the scorodite after filtration was washed with distilled water and suction filtered in the same manner. Thereafter, it was dried in a drier at 60 ° C. for 24 hours or more. The SEM photograph (magnification: 30,000 times) of each scorodite is shown in FIG. 2, respectively. As can be seen from the SEM photographs, the smoothness and regularity of the surface shape of the crystalline scorodite are increased as the concentration of As5 increases. It can be seen that the crystalline scorodite of 1-3 has a polyhedral shape. This suggests that the crystallinity increases as the concentration of As pentavalent increases. In fact, when the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed in all the test examples, but the scorodite having the higher smoothness and regularity of the surface shape indicates the pattern The peak intensity was large.
また、スコロダイト合成の電流効率を以下の式により計算した。結果を表１に示す。
電流効率（％）＝回収残渣量（ｇ）／理論スコロダイト電析量（ｇ）×１００
理論スコロダイト電析量（ｇ）＝電流（Ａ）×時間（ｓｅｃ）／９６５００（Ｃ／ｍｏｌ）×２３０．７７（ｇ／ｍｏｌ）
式中、２３０．７７ｇ／ｍｏｌはスコロダイトの分子量である。
In addition, the current efficiency of scorodite synthesis was calculated by the following equation. The results are shown in Table 1.
Current efficiency (%) = amount of recovered residue (g) / theoretical scorodite deposition amount (g) x 100
Theoretical scorodite deposition amount (g) = current (A) × time (sec) / 96500 (C / mol) × 230.77 (g / mol)
In the formula, 230.77 g / mol is the molecular weight of scorodite.
＜試験例２：Ａｓ濃度の影響（Ｆｅ／Ａｓモル比＝３）＞
表２に記載の試験番号に応じた２価のＦｅイオン濃度、５価のＡｓイオン濃度、硫酸イオン濃度及びｐＨの反応液が得られるように、電解槽中に硫酸、硫酸ナトリウム、硫酸第一鉄七水和物（ＦｅＳＯ4・７Ｈ2Ｏ）及びヒ酸水素二ナトリウム七水和物（Ｎａ2ＨＡｓＯ4・７Ｈ2Ｏ）を添加した（反応開始時のＦｅ／Ａｓモル比＝３）。その後、大気条件下で、当該反応液を表２に記載の液温に加熱し、表２に記載の電解条件にて、攪拌しながらスコロダイトの合成を行った。なお、加熱中、蒸発によって液量が減らないように、適宜水を追加した。
<Test Example 2: Effect of As concentration (Fe / As molar ratio = 3)>
Sulfuric acid, sodium sulfate, sulfuric acid first in the electrolytic cell so that a reaction solution of divalent Fe ion concentration, pentavalent As ion concentration, sulfate ion concentration and pH according to the test numbers described in Table 2 is obtained. Iron heptahydrate (FeSO 4 · 7H 2 O) and disodium hydrogen arsenate heptahydrate (Na 2 HAsO 4 · 7H 2 O) were added (Fe / As molar ratio at the start of the reaction = 3). Thereafter, the reaction solution was heated to the solution temperature described in Table 2 under atmospheric conditions, and scorodite synthesis was performed while stirring under the electrolytic conditions described in Table 2. During the heating, water was appropriately added so as not to reduce the liquid amount by evaporation.
スコロダイトの合成終了後は孔径１μｍのＰＴＦＥ製メンブレンフィルターを使用して吸引ろ過した。次いで、ろ過後のスコロダイトは蒸留水で洗浄して同様の方法で吸引ろ過した。その後、６０℃の乾燥器で２４ｈ以上乾燥した。得られたスコロダイトをＸ線回折により分析したところ、何れも結晶性スコロダイトに特徴的なパターンが確認された。各スコロダイトのＳＥＭ写真（倍率：３万倍）を図３にそれぞれ示す。ＳＥＭ写真から分かるように、５価のＡｓ濃度が上昇するにつれて結晶性スコロダイトの表面形状が平滑で規則性が高く、結晶性が高まっていることが分かる。Ｎｏ．２−３及び２−４の結晶性スコロダイトは多面体の形状となっていた。Ｎｏ．２−１はＳＥＭ写真からみて、非晶質部分を含んだ結晶性スコロダイトであると考えられる。 After completion of scorodite synthesis, suction filtration was performed using a PTFE membrane filter with a pore size of 1 μm. Then, the scorodite after filtration was washed with distilled water and suction filtered in the same manner. Thereafter, it was dried in a drier at 60 ° C. for 24 hours or more. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed in each case. The SEM photograph (magnification: 30,000 times) of each scorodite is shown in FIG. 3, respectively. As can be seen from the SEM photograph, it can be seen that the surface shape of the crystalline scorodite is smooth and highly ordered, and the crystallinity is enhanced as the concentration of As in the pentavalent As increases. No. The crystalline scorodite of 2-3 and 2-4 was in the shape of a polyhedron. No. 2-1 is considered to be a crystalline scorodite containing an amorphous part in view of the SEM photograph.
スコロダイト合成の電流効率を試験例１と同様に計算した結果を表２に示す。 The current efficiency of scorodite synthesis was calculated in the same manner as in Test Example 1 and the results are shown in Table 2.
＜試験例３：Ａｓ濃度の影響（Ｆｅ／Ａｓモル比＝１．３）＞
表３に記載の試験番号に応じた２価のＦｅイオン濃度、５価のＡｓイオン濃度、硫酸イオン濃度及びｐＨの反応液が得られるように、電解槽中に硫酸、硫酸ナトリウム、硫酸第一鉄七水和物（ＦｅＳＯ4・７Ｈ2Ｏ）及びヒ酸水素二ナトリウム七水和物（Ｎａ2ＨＡｓＯ4・７Ｈ2Ｏ）を添加した（反応開始時のＦｅ／Ａｓモル比＝１．３）。その後、大気条件下で、当該反応液を表３に記載の液温に加熱し、表３に記載の電解条件にて、攪拌しながらスコロダイトの合成を行った。なお、加熱中、蒸発によって液量が減らないように、適宜水を追加した。
<Test Example 3: Influence of As concentration (Fe / As molar ratio = 1.3)>
Sulfuric acid, sodium sulfate, sulfuric acid first in the electrolytic cell to obtain a reaction solution of divalent Fe ion concentration, pentavalent As ion concentration, sulfate ion concentration and pH according to the test numbers described in Table 3. Iron heptahydrate (FeSO 4 · 7H 2 O) and disodium hydrogen arsenate heptahydrate (Na 2 HAsO 4 · 7H 2 O) were added (Fe / As molar ratio at the start of reaction = 1.3) ). Thereafter, the reaction solution was heated to the solution temperature described in Table 3 under atmospheric conditions, and scorodite synthesis was performed while stirring under the electrolytic conditions described in Table 3. During the heating, water was appropriately added so as not to reduce the liquid amount by evaporation.
スコロダイトの合成終了後は孔径１μｍのＰＴＦＥ製メンブレンフィルターを使用して吸引ろ過した。次いで、ろ過後のスコロダイトは蒸留水で洗浄して同様の方法で吸引ろ過した。その後、６０℃の乾燥器で２４ｈ以上乾燥した。得られたスコロダイトをＸ線回折により分析したところ、何れも結晶性スコロダイトに特徴的なパターンが確認された。Ｎｏ．３−１のスコロダイトのＳＥＭ写真（倍率：３万倍）を図４に示す。試験例１及び試験例２と同様に、５価のＡｓ濃度が高い試験例のほうが結晶性スコロダイトの表面形状が平滑で規則性が高かった。また、Ｎｏ．３−１と３−２を比較すると、液温が高いＮｏ．３−１のほうが結晶性スコロダイトの表面形状の平滑性及び規則性が高かった。 After completion of scorodite synthesis, suction filtration was performed using a PTFE membrane filter with a pore size of 1 μm. Then, the scorodite after filtration was washed with distilled water and suction filtered in the same manner. Thereafter, it was dried in a drier at 60 ° C. for 24 hours or more. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed in each case. No. The SEM photograph (magnification: 30,000 times) of 3-1 scorodite is shown in FIG. As in Test Example 1 and Test Example 2, the surface shape of the crystalline scorodite was smoother and the regularity was higher in the test example with a higher pentavalent As concentration. Also, no. When 3-1 and 3-2 are compared, No. 1 with a high liquid temperature. The smoothness and regularity of the surface shape of crystalline scorodite were higher in the case of 3-1.
スコロダイト合成の電流効率を試験例１と同様に計算した結果を表３に示す。 The current efficiency of scorodite synthesis was calculated in the same manner as in Test Example 1 and the results are shown in Table 3.
ここで、試験例１〜３を対比すると、これらはＦｅ／Ａｓモル比が異なる。試験例１ではＦｅ／Ａｓモル比＝２、試験例２ではＦｅ／Ａｓモル比＝３、試験例３ではＦｅ／Ａｓモル比＝１．３とした。Ａｓ濃度が同程度の試験例同士を比較することにより、Ｆｅ／Ａｓモル比が高くなるにつれて電流効率が上昇する傾向にあることが理解できる。 Here, when testing examples 1 to 3 are compared, they have different Fe / As molar ratios. In Test Example 1, Fe / As molar ratio = 2, in Test Example 2, Fe / As molar ratio = 3, and in Test Example 3, Fe / As molar ratio = 1.3. It can be understood that the current efficiency tends to increase as the Fe / As molar ratio increases, by comparing the test examples with the same As concentration.
＜試験例４：隔膜の有無による電流効率への影響＞
表４に記載の試験番号に応じた２価のＦｅイオン濃度、５価のＡｓイオン濃度、硫酸イオン濃度及びｐＨの反応液が得られるように、電解槽中に硫酸、硫酸ナトリウム、硫酸第一鉄七水和物（ＦｅＳＯ4・７Ｈ2Ｏ）及びヒ酸水素二ナトリウム七水和物（Ｎａ2ＨＡｓＯ4・７Ｈ2Ｏ）を添加した。その後、大気条件下で、当該反応液を表４に記載の液温に加熱し、表４に記載の電解条件にて、攪拌しながらスコロダイトの合成を行った。なお、加熱中、蒸発によって液量が減らないように、適宜水を追加した。
<Test Example 4: Influence on the current efficiency by the presence or absence of the diaphragm>
Sulfuric acid, sodium sulfate, sulfuric acid first in the electrolytic cell to obtain a reaction solution of divalent Fe ion concentration, pentavalent As ion concentration, sulfate ion concentration and pH according to the test numbers described in Table 4. iron heptahydrate (FeSO 4 · 7H 2 O) and arsenic acid disodium hydrogen heptahydrate of (Na 2 HAsO 4 · 7H 2 O) was added. Thereafter, the reaction solution was heated to the solution temperature described in Table 4 under atmospheric conditions, and scorodite synthesis was performed while stirring under the electrolytic conditions described in Table 4. During the heating, water was appropriately added so as not to reduce the liquid amount by evaporation.
スコロダイトの合成終了後は孔径１μｍのＰＴＦＥ製メンブレンフィルターを使用して吸引ろ過した。次いで、ろ過後のスコロダイトは蒸留水で洗浄して同様の方法で吸引ろ過した。その後、６０℃の乾燥器で２４ｈ以上乾燥した。得られたスコロダイトをＸ線回折により分析したところ、Ｎｏ．４−１は結晶性スコロダイトに特徴的なパターンが確認されず、Ｎｏ．４−２には結晶性スコロダイトに特徴的なパターンが確認された。各スコロダイトのＳＥＭ写真（倍率：３万倍）を図５に示す。Ｎｏ．４−２は結晶性スコロダイトではあるが、隔膜を設置しなかったために、角が欠けているものが多かった。これはカソードに接触した部分が分解したことに由来すると考えられる。 After completion of scorodite synthesis, suction filtration was performed using a PTFE membrane filter with a pore size of 1 μm. Then, the scorodite after filtration was washed with distilled water and suction filtered in the same manner. Thereafter, it was dried in a drier at 60 ° C. for 24 hours or more. The obtained scorodite was analyzed by X-ray diffraction. In No. 4-1, no pattern characteristic of crystalline scorodite was confirmed. A characteristic pattern of crystalline scorodite was confirmed in 4-2. The SEM photograph (magnification: 30,000 times) of each scorodite is shown in FIG. No. Although 4-2 is a crystalline scorodite, there were many cases where corners were missing because no diaphragm was installed. This is considered to be derived from the decomposition of the portion in contact with the cathode.
スコロダイト合成の電流効率を試験例１と同様に計算した結果を表４に示す。Ｎｏ．２−４とＮｏ．４−２の対比により、隔膜を設置しなかったことで、電流効率が顕著に低下していることが分かる。 The current efficiency of scorodite synthesis was calculated in the same manner as in Test Example 1 and the results are shown in Table 4. No. No. 2-4 and no. By comparison of 4-2, it turns out that current efficiency is falling notably by not having installed a diaphragm.
なお、Ｎｏ．４−２については、スコロダイト製造中の陽極電位及び陰極電位を確認した。陽極電位及び陰極電位の測定手順は以下の通りである。図８に測定に用いた電解装置２００の構成を示す。電解装置２００は、電解槽２０１、ホットスターラー２０２、整流器２０３、カーボン製のアノード２０４、ステンレス（ＳＵＳ３０４）製のカソード２０５、撹拌子（図示せず）を備える。電解槽２０１はホットスターラー２０２上に載置されており、反応液２０７は電解槽２０１内に入れた撹拌子によって撹拌可能となっている。アノード２０４及びカソード２０５は電解槽２０１中の反応液２０７に浸漬する。アノード２０４及びカソード２０５はそれぞれ整流器２０３に接続されている。電極電位の測定には、ルギン管２０９の先端を電位を測定したい電極表面（図８では陽極表面）へ付け、テスター２０８で電位を測定する。
陽極電位の測定においては、そのまま測定を実施すると陽極表面に付着したスコロダイトが抵抗となり、陽極電位が過大な値を示す為、付着したスコロダイトを掻き落としてから測定を実施した。
測定に用いた電極はＡｇ／ＡｇＣｌ電極の為、標準水素電極（ＳＨＥ）に換算して評価を実施した。
No. Regarding 4-2, the anode potential and the cathode potential during scorodite production were confirmed. The measurement procedures of the anode potential and the cathode potential are as follows. The structure of the electrolyzer 200 used for the measurement at FIG. 8 is shown. The electrolytic device 200 includes an electrolytic cell 201, a hot stirrer 202, a rectifier 203, an anode 204 made of carbon, a cathode 205 made of stainless steel (SUS304), and a stirrer (not shown). The electrolytic cell 201 is placed on the hot stirrer 202, and the reaction liquid 207 can be stirred by a stirrer placed in the electrolytic cell 201. The anode 204 and the cathode 205 are immersed in the reaction solution 207 in the electrolytic cell 201. The anode 204 and the cathode 205 are connected to the rectifier 203, respectively. To measure the electrode potential, the tip of the Lugin tube 209 is attached to the electrode surface (the anode surface in FIG. 8) whose potential is to be measured, and the potential is measured by the tester 208.
In the measurement of the anode potential, when the measurement was carried out as it was, the scorodite attached to the surface of the anode became a resistance, and the anode potential showed an excessive value.
Since the electrode used for the measurement was an Ag / AgCl electrode, the evaluation was carried out by converting it to a standard hydrogen electrode (SHE).
陽極電位は０．６０〜０．６５Ｖ（ＳＨＥ）、陰極電位は−０．４〜−０．３Ｖ（ＳＨＥ）であった。陽極電位についは酸素発生電位よりも電位が低い事から（ｐＨ１．５ではおおよそ１．６Ｖ（ＳＨＥ）程度）、水の電気分解によって発生した酸素によって２価のＦｅが酸化されているのではなく、電気的に２価のＦｅが３価のＦｅに酸化され、スコロダイトが生成している事を確認した。その他の試験例については電極電位を測定しなかったが、ルギン管を用いた測定では、隔膜の有無は電位にほとんど影響を与えないので、その他の試験例についても同程度の電位であると考えられる。 The anode potential was 0.60 to 0.65 V (SHE), and the cathode potential was -0.4 to -0.3 V (SHE). Since the anodic potential is lower than the oxygen generation potential (about 1.6 V (SHE) at pH 1.5), the divalent Fe is not oxidized by the oxygen generated by the electrolysis of water. It was confirmed that electrically divalent Fe is oxidized to trivalent Fe to form scorodite. Although the electrode potential was not measured for the other test examples, in the measurement using a Luggin tube, the presence or absence of the diaphragm hardly affects the potential, so the same potential is considered for the other test examples. Be
（試験例５：Ａｓ濃度が溶出性に与える影響）
表５に記載の試験番号に応じた２価のＦｅイオン濃度、５価のＡｓイオン濃度、硫酸イオン濃度及びｐＨの反応液が得られるように、電解槽中に硫酸、硫酸ナトリウム、硫酸第一鉄七水和物（ＦｅＳＯ4・７Ｈ2Ｏ）及びヒ酸水素二ナトリウム七水和物（Ｎａ2ＨＡｓＯ4・７Ｈ2Ｏ）を添加した。その後、大気条件下で、当該反応液を表５に記載の液温に加熱し、表５に記載の電解条件にて、攪拌しながらスコロダイトの合成を行った。なお、加熱中、蒸発によって液量が減らないように、適宜水を追加した。
(Test Example 5: Influence of As concentration on dissolution)
Sulfuric acid, sodium sulfate, sulfuric acid first in the electrolytic cell so that a reaction solution of divalent Fe ion concentration, pentavalent As ion concentration, sulfate ion concentration and pH according to the test numbers described in Table 5 is obtained. iron heptahydrate (FeSO 4 · 7H 2 O) and arsenic acid disodium hydrogen heptahydrate of (Na 2 HAsO 4 · 7H 2 O) was added. Thereafter, the reaction solution was heated to the solution temperature described in Table 5 under atmospheric conditions, and scorodite synthesis was performed while stirring under the electrolytic conditions described in Table 5. During the heating, water was appropriately added so as not to reduce the liquid amount by evaporation.
スコロダイトの合成終了後は孔径１μｍのＰＴＦＥ製メンブレンフィルターを使用して吸引ろ過した。次いで、ろ過後のスコロダイトは蒸留水で洗浄して同様の方法で吸引ろ過した。その後、６０℃の乾燥器で２４ｈ以上乾燥した。得られたスコロダイトをＸ線回折により分析したところ、何れも結晶性スコロダイトに特徴的なパターンが確認された。各スコロダイトのＳＥＭ写真（倍率：３万倍）を図６にそれぞれ示す。ＳＥＭ写真から分かるように、５価のＡｓ濃度が上昇するにつれて結晶性スコロダイトの表面形状が平滑で規則性が高く、結晶性が高まっていることが分かる。 After completion of scorodite synthesis, suction filtration was performed using a PTFE membrane filter with a pore size of 1 μm. Then, the scorodite after filtration was washed with distilled water and suction filtered in the same manner. Thereafter, it was dried in a drier at 60 ° C. for 24 hours or more. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed in each case. The SEM photograph (magnification: 30,000 times) of each scorodite is shown in FIG. 6, respectively. As can be seen from the SEM photograph, it can be seen that the surface shape of the crystalline scorodite is smooth and highly ordered, and the crystallinity is enhanced as the concentration of As in the pentavalent As increases.
これらの結晶性スコロダイトのＡｓ溶出性試験（ＴＣＬＰ ｐＨ４．９３の酢酸緩衝溶液使用）を行った。その結果、製造時のＡｓ濃度が高く、表面形状が平滑なＮｏ．５−２の方が低い溶出特性を示した。結果を表５に示す。 As elution test (using a acetate buffer solution of TCLP pH 4.93) of these crystalline scorodites was conducted. As a result, No. 1 having a high As concentration at the time of manufacture and a smooth surface shape. 5-2 showed lower elution characteristics. The results are shown in Table 5.
（試験例６：電流密度が電流効率に与える影響）
表６に記載の試験番号に応じた２価のＦｅイオン濃度、５価のＡｓイオン濃度、硫酸イオン濃度及びｐＨの反応液が得られるように、電解槽中に硫酸、硫酸ナトリウム、硫酸第一鉄七水和物（ＦｅＳＯ4・７Ｈ2Ｏ）及びヒ酸水素二ナトリウム七水和物（Ｎａ2ＨＡｓＯ4・７Ｈ2Ｏ）を添加した。その後、大気条件下で、当該反応液を表６に記載の液温に加熱し、表６に記載の電解条件にて、攪拌しながらスコロダイトの合成を行った。なお、加熱中、蒸発によって液量が減らないように、適宜水を追加した。
(Test example 6: Influence of current density on current efficiency)
In order to obtain a reaction solution of divalent Fe ion concentration, pentavalent As ion concentration, sulfate ion concentration and pH according to the test numbers described in Table 6, sulfuric acid, sodium sulfate, sulfuric acid iron heptahydrate (FeSO 4 · 7H 2 O) and arsenic acid disodium hydrogen heptahydrate of (Na 2 HAsO 4 · 7H 2 O) was added. Thereafter, the reaction solution was heated to the solution temperature described in Table 6 under atmospheric conditions, and scorodite synthesis was performed while stirring under the electrolytic conditions described in Table 6. During the heating, water was appropriately added so as not to reduce the liquid amount by evaporation.
スコロダイトの合成終了後は孔径１μｍのＰＴＦＥ製メンブレンフィルターを使用して吸引ろ過した。次いで、ろ過後のスコロダイトは蒸留水で洗浄して同様の方法で吸引ろ過した。その後、６０℃の乾燥器で２４ｈ以上乾燥した。得られたスコロダイトをＸ線回折により分析したところ、何れも結晶性スコロダイトに特徴的なパターンが確認された。各スコロダイトのＳＥＭ写真（倍率：３万倍）を図７に示す。電流密度が上昇するにつれて、結晶性スコロダイトの表面形状の平滑性が失われることが分かる。 After completion of scorodite synthesis, suction filtration was performed using a PTFE membrane filter with a pore size of 1 μm. Then, the scorodite after filtration was washed with distilled water and suction filtered in the same manner. Thereafter, it was dried in a drier at 60 ° C. for 24 hours or more. When the obtained scorodite was analyzed by X-ray diffraction, a pattern characteristic of crystalline scorodite was confirmed in each case. The SEM photograph (magnification: 30,000 times) of each scorodite is shown in FIG. It can be seen that as the current density is increased, the smoothness of the surface profile of crystalline scorodite is lost.
スコロダイト合成の電流効率を試験例１と同様に計算した結果を表６に示す。電流密度を高くしていくにつれて、電流効率が低下することが分かる。 The current efficiency of scorodite synthesis was calculated in the same manner as in Test Example 1 and the results are shown in Table 6. It can be seen that the current efficiency decreases as the current density is increased.
１００、２００ 電解装置
１０１、２０１ 電解槽
１０２、２０２ ホットスターラー
１０３、２０３ 整流器
１０４、２０４ アノード
１０５、２０５ カソード
１０６、２０６ 電解隔膜
１０７、２０７ 反応液
２０８ テスター
２０９ ルギン管
DESCRIPTION OF SYMBOLS 100, 200 Electrolyzer 101, 201 Electrolyzer 102, 202 Hot stirrer 103, 203 Rectifier 104, 204 Anode 105, 205 Cathode 106, 206 Electrolytic diaphragm 107, 207 Reaction liquid 208 Tester 209 Lugin tube
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