JP2007044606A - Chelating agent for scavenging heavy metal - Google Patents
Chelating agent for scavenging heavy metal Download PDFInfo
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- JP2007044606A JP2007044606A JP2005230345A JP2005230345A JP2007044606A JP 2007044606 A JP2007044606 A JP 2007044606A JP 2005230345 A JP2005230345 A JP 2005230345A JP 2005230345 A JP2005230345 A JP 2005230345A JP 2007044606 A JP2007044606 A JP 2007044606A
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- 239000002738 chelating agent Substances 0.000 title claims abstract description 94
- 229910001385 heavy metal Inorganic materials 0.000 title claims abstract description 62
- 230000002000 scavenging effect Effects 0.000 title abstract 4
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- 239000003446 ligand Substances 0.000 claims abstract description 29
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- 235000010413 sodium alginate Nutrition 0.000 claims description 5
- 239000000661 sodium alginate Substances 0.000 claims description 5
- 229940005550 sodium alginate Drugs 0.000 claims description 5
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 abstract description 36
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 abstract description 12
- 238000001035 drying Methods 0.000 abstract description 8
- 229910052757 nitrogen Inorganic materials 0.000 abstract description 8
- 239000001301 oxygen Substances 0.000 abstract description 7
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 abstract description 5
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- JOPOVCBBYLSVDA-UHFFFAOYSA-N chromium(6+) Chemical compound [Cr+6] JOPOVCBBYLSVDA-UHFFFAOYSA-N 0.000 description 38
- 229910052804 chromium Inorganic materials 0.000 description 37
- 238000002474 experimental method Methods 0.000 description 33
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- 239000000648 calcium alginate Substances 0.000 description 24
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- FHVDTGUDJYJELY-UHFFFAOYSA-N 6-{[2-carboxy-4,5-dihydroxy-6-(phosphanyloxy)oxan-3-yl]oxy}-4,5-dihydroxy-3-phosphanyloxane-2-carboxylic acid Chemical compound O1C(C(O)=O)C(P)C(O)C(O)C1OC1C(C(O)=O)OC(OP)C(O)C1O FHVDTGUDJYJELY-UHFFFAOYSA-N 0.000 description 1
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- Treatment Of Water By Ion Exchange (AREA)
- Treatment Of Sludge (AREA)
- Compositions Of Macromolecular Compounds (AREA)
Abstract
Description
本発明は、重金属捕捉用のキレート剤に関する。より詳しくは、底泥や土壌中の重金属除去処理に適するキレート剤に関する。 The present invention relates to a chelating agent for capturing heavy metals. More specifically, the present invention relates to a chelating agent suitable for removing heavy metal from bottom mud and soil.
河川、湖沼、内湾などの水域における底泥の浚渫工事は、水質浄化や水深確保などの目的で行われることが多い。当該工事の過程で発生する浚渫土は、従来、凝集剤処理を行って脱水した後、遊休地や埋め立て地に廃棄されることが多かったが、近年では、浚渫土の廃棄用地の確保が困難となっていることや地下水汚染の問題が顕在化しているため、浚渫土を資源として再利用することが検討されている。 The dredging work of bottom mud in water areas such as rivers, lakes, and inner bays is often performed for the purpose of purifying water quality and securing water depth. In the past, dredged soil generated during the construction process was often disposed of in idle land or landfill after being dehydrated by coagulant treatment. However, in recent years, it has been difficult to secure land for disposal of dredged soil. Therefore, the reuse of dredged soil as a resource is under consideration.
浚渫土などの底泥には、水銀(Hg)、砒素(As)、カドミニューム(Cd)、クロム(Cr)などの有害重金属が底泥中の鉱物や腐植物質と結合等して底泥粒子に捕捉された状態で含まれている。従って、浚渫土などの底泥を資源として再利用するためには、これらの有害物質を底泥粒子から溶離させて、確実に回収することが必要である。 In the bottom mud such as dredged soil, toxic heavy metals such as mercury (Hg), arsenic (As), cadmium (Cd), chromium (Cr) combine with minerals and humic substances in the bottom mud, etc. Is included in the captured state. Therefore, in order to reuse the bottom mud such as dredged soil as a resource, it is necessary to elute these harmful substances from the bottom mud particles and reliably collect them.
浚渫土などの土壌中に含まれる有害重金属を除去する技術として、キレート剤を用いた洗浄方法が提案されている(非特許文献1、特許文献1〜5)。キレート剤は、溶出した重金属と錯体を形成して吸着する。このキレート剤を用いた重金属処理方法は、中性付近での抽出が可能で土壌損傷が少ないという利点があるが、既存の合成キレート剤が高価であり、生分解性も低いので、大量の汚染土壌を処理する場合への適用は難しい。
近年、浚渫された底泥などの土壌を再利用(資源化)するために、当該対象土壌を酸化焼成処理することによってセラミックスやゼオライトを製造する方法が注目されている。 In recent years, in order to recycle (recycle) soil such as dredged bottom mud, a method for producing ceramics and zeolite by subjecting the target soil to oxidation and firing has attracted attention.
この方法では、土壌中のセラミックスやゼオライトの有効成分となるケイ素やアルミニウムなどの溶出を極力抑制しながら有害重金属を溶出させることができることが重要である。特に、クロム(Cr)を大量に含有する土壌に酸化焼成処理を施して資源化する場合は、この酸化焼成の過程で三価クロム(Cr(III))からより毒性の強い六価クロム(Cr(VI))へ変化するという問題が起こる。加えて、このような三価クロム(Cr(III))から六価クロム(Cr(VI))への変化は、地上に置かれた浚渫土の酸化還元電位が上昇するときにも発生する問題である。従って、三価、六価を問わずクロム(Cr)の除去は、浚渫土の資源化における重要な技術的課題となっている。さらに、浚渫土の重金属除去に用いるキレート剤は、処理対象の浚渫土の量に照らし、大量使用が見込まれため、安価であることが望まれている。 In this method, it is important that toxic heavy metals can be eluted while suppressing elution of silicon and aluminum, which are active ingredients of ceramics and zeolite in the soil, as much as possible. In particular, when oxidizing and firing a soil containing a large amount of chromium (Cr) to produce resources, trivalent chromium (Cr (III)) is more toxic to hexavalent chromium (Cr The problem of changing to (VI)) occurs. In addition, such a change from trivalent chromium (Cr (III)) to hexavalent chromium (Cr (VI)) also occurs when the redox potential of dredged soil placed on the ground rises. It is. Therefore, the removal of chromium (Cr), whether trivalent or hexavalent, is an important technical issue in the recycling of dredged soil. Furthermore, the chelating agent used for removing heavy metals from the clay is expected to be inexpensive because it is expected to be used in large quantities in light of the amount of the clay to be treated.
そこで、本発明は、底泥や土壌に含まれている重金属、特にクロム(Cr)を効率よく捕捉できる安価なキレート剤を提供することを主な目的とする。 Therefore, the main object of the present invention is to provide an inexpensive chelating agent capable of efficiently capturing heavy metals contained in bottom mud and soil, particularly chromium (Cr).
本発明では、まず、窒素型リガンドを有する第1高分子と、酸素型リガンドを有し、かつ、ゲル化可能な第2高分子と、を備え、不溶性担体に固定化された重金属捕捉用キレート剤を提供する。なお、本発明において「窒素型リガンド」とは、重金属とキレート錯体(chelate complex)を形成し得る窒素原子含有基(例えば、アミノ基、イミンなど)を広く意味し、「酸素型リガンド」とは、重金属とキレート錯体(chelate complex)を形成し得る酸素原子含有基(例えば、イミノジアセテート、カルボキシル基など)を広く意味する。 In the present invention, first, a chelate for capturing a heavy metal, comprising a first polymer having a nitrogen-type ligand and a second polymer having an oxygen-type ligand and capable of being gelled, is immobilized on an insoluble carrier. Provide the agent. In the present invention, the “nitrogen type ligand” widely means a nitrogen atom-containing group (for example, amino group, imine, etc.) capable of forming a chelate complex with a heavy metal, and the “oxygen type ligand” And oxygen atom-containing groups that can form chelate complexes with heavy metals (eg iminodiacetate, carboxyl groups, etc.).
本発明に係る重金属捕捉用キレート剤は、窒素型リガンド(第1高分子由来)と酸素型リガンド(第2高分子由来)の両方を有するハイブリッド型キレート剤であることが第一の特徴であって、この構成によって特にクロム(Cr)の捕捉に有効である。 The first feature of the chelating agent for capturing heavy metals according to the present invention is that it is a hybrid chelating agent having both a nitrogen-type ligand (derived from the first polymer) and an oxygen-type ligand (derived from the second polymer). Thus, this configuration is particularly effective for capturing chromium (Cr).
より詳しくは、pH領域に応じた各リガンドの帯電状態に基づいて、三価クロム(Cr(III))や六価クロム(Cr(VI))の捕捉を行う。例えば、pH>3の領域では、窒素型リガンドのキレート作用により、また負に帯電した酸素型リガンド(例えば、−O−)はキレート作用と共に陽イオンである三価クロム(Cr(III)をイオン結合によって捕捉し、pH<2の領域では、窒素型リガンドがプロトン化(正帯電)することによって、陰イオンであるCr2O7 2-(即ち、六価クロムの陰イオン状態)をイオン結合によって有効に捕捉する。従って、本発明に係る重金属捕捉用キレート剤は、処理対象の重金属含有土壌のpHおよび酸化還元電位の変化に応じて、三価クロム(Cr(III))や六価クロム(Cr(VI))を有効に捕捉することができる。 More specifically, trivalent chromium (Cr (III)) or hexavalent chromium (Cr (VI)) is captured based on the charged state of each ligand according to the pH range. For example, in the region of pH> 3, the chelating action of a nitrogen-type ligand, and the negatively charged oxygen-type ligand (for example, —O − ) ionizes trivalent chromium (Cr (III), which is a cation, together with the chelating action. In the region of pH <2, the nitrogen-type ligand is protonated (positively charged), and the anion Cr 2 O 7 2− (that is, the anion state of hexavalent chromium) is ionically bound. Therefore, the chelating agent for capturing heavy metals according to the present invention is trivalent chromium (Cr (III)) or hexavalent chromium depending on changes in the pH and redox potential of the heavy metal-containing soil to be treated. (Cr (VI)) can be captured effectively.
また、本発明に係る重金属捕捉用キレート剤は、不溶性担体に固定化されているため、該キレート剤に捕捉された重金属を水溶液中から回収することが容易である。さらには、重金属捕捉用キレート剤を乾燥処理することによって、カラム容器(充填塔)への充填量を増加させ、重金属捕捉効率を高めることができる。 In addition, since the chelating agent for capturing heavy metals according to the present invention is immobilized on an insoluble carrier, it is easy to recover the heavy metal captured by the chelating agent from an aqueous solution. Furthermore, by drying the chelating agent for capturing heavy metals, the amount of packing in the column container (packing tower) can be increased, and the heavy metal capturing efficiency can be increased.
ここで、前記第1高分子は、窒素型リガンドを備える高分子であればよいが、例えば、ポリエチレンイミン(PEI)やキトサンを採用でき、前記第2高分子は、酸素型リガンドを備える化合物であればよいが、例えば、アルギン酸ナトリウム、カラギーナン、ジュランガムなどを採用することができる。不溶性担体は、採用された第1高分子や第2高分子と結合等することによって、キレート剤の固定化に適した物質であれば特に限定されないが、一例を挙げると、塩化カルシウムをゲル化剤として調整したアルギン酸カルシウムなどを採用できる。 Here, the first polymer may be a polymer having a nitrogen-type ligand. For example, polyethyleneimine (PEI) or chitosan can be used, and the second polymer is a compound having an oxygen-type ligand. For example, sodium alginate, carrageenan, dulan gum and the like can be employed. The insoluble carrier is not particularly limited as long as it is a substance suitable for immobilization of the chelating agent by binding to the first polymer or the second polymer adopted. For example, calcium chloride is gelled. Calcium alginate prepared as an agent can be used.
本発明に係る重金属捕捉用キレート剤は、底泥や土壌中の重金属の捕捉に有効であり、特にクロム(Cr)については、処理水のpH領域に応じて三価クロム(Cr(III))とCr2O7 2-(即ち、六価クロム)をそれぞれ捕捉することができる。また、本キレート剤は、不溶性担体に固定化されているので、重金属を捕捉させた後に水溶液中から容易に回収することができる。さらに、本キレート剤は安価であるので、浚渫土の重金属処理などの大量土壌処理に適している。 The chelating agent for capturing heavy metals according to the present invention is effective for capturing heavy metals in bottom mud and soil. Especially for chromium (Cr), trivalent chromium (Cr (III)) depending on the pH range of the treated water. And Cr 2 O 7 2− (that is, hexavalent chromium) can be captured respectively. Further, since the chelating agent is immobilized on an insoluble carrier, it can be easily recovered from the aqueous solution after capturing the heavy metal. Furthermore, since this chelating agent is inexpensive, it is suitable for large-scale soil treatment such as heavy metal treatment of dredged soil.
以下、本発明に係る重金属捕捉用キレート剤の好適な実施形態について説明する。 Hereinafter, preferred embodiments of the chelating agent for capturing heavy metals according to the present invention will be described.
本発明に係る重金属捕捉用キレート剤(以下、単に「キレート剤」)は、二種類の高分子(第1高分子と、第2高分子)から構成され、かつ不溶性担体に固定化された構成を備えている。不溶性担体に固定する理由は、水溶液中からのキレート剤の回収を容易化するためである。 The chelating agent for capturing heavy metals according to the present invention (hereinafter simply referred to as “chelating agent”) is composed of two types of polymers (first polymer and second polymer) and is immobilized on an insoluble carrier. It has. The reason for fixing to the insoluble carrier is to facilitate the recovery of the chelating agent from the aqueous solution.
第1高分子は、重金属とキレート錯体(chelate complex)を形成し得る「窒素型リガンド」を備えており、一方の第2高分子は、同様に、重金属とキレート錯体(chelate complex)を形成し得る「酸素型リガンド」を備え、かつゲル化可能なものである。 The first polymer has a “nitrogen-type ligand” that can form a chelate complex with a heavy metal, while the second polymer similarly forms a chelate complex with a heavy metal. It has a “oxygen-type ligand” to be obtained and can be gelled.
第1高分子の「窒素型リガンド」は、重金属とキレート錯体(chelate complex)を形成し得るアミノ基、イミン基のような窒素原子含有基であり、第2高分子の「酸素型リガンド」は、重金属とキレート錯体(chelate complex)を形成し得るイミノジアセテート、カルボキシル基のような酸素原子含有基である。 The “nitrogen type ligand” of the first polymer is a nitrogen atom-containing group such as an amino group or an imine group capable of forming a chelate complex with a heavy metal, and the “oxygen type ligand” of the second polymer is An iminodiacetate capable of forming a chelate complex with a heavy metal, or an oxygen atom-containing group such as a carboxyl group.
第1高分子は、例えば、次の化学式1で示すポリエチレンイミンやキトサン、などを採用することができる。第2高分子は、例えば、アルギン酸ナトリウム、カラギーナン、ジュランガムなどを採用することができる。
As the first polymer, for example, polyethyleneimine or chitosan represented by the following
不溶性担体は、第1高分子、あるいは第2高分子に結合等してキレート剤を固定化、とりわけこれら高分子の官能基が自由に反応活性を発揮できる包括固定化が可能な物質が望ましい。例えば、アルギン酸カルシウムゲルなどを利用できる。このアルギン酸カルシウムゲルは、ポリエチレンイミン(第1高分子)のイミン基やアルギン酸のカルボキシル基が重金属と反応する場を提供すると共に、アルギン酸のゲル化特性による包括固定作用によって、キレート剤の固定化担体としても機能する。本発明に係るキレート剤は、不溶性担体に固定化されているため、該キレート剤に捕捉された重金属を水溶液中から回収することが容易である。 The insoluble carrier is preferably a substance capable of immobilizing a chelating agent by binding to the first polymer or the second polymer, and in particular capable of comprehensive immobilization in which the functional groups of these polymers can freely exhibit reaction activity. For example, calcium alginate gel can be used. This calcium alginate gel provides a place where the imine group of polyethyleneimine (first polymer) or the carboxyl group of alginic acid reacts with a heavy metal. Also works. Since the chelating agent according to the present invention is immobilized on an insoluble carrier, it is easy to recover the heavy metal captured by the chelating agent from the aqueous solution.
固定化担体としてアルギン酸カルシウム(CA)ゲルを採用し、第1高分子にポリエチレンイミン(PEI)を採用した場合は、アルギン酸カルシウムゲルに対するポリエチレンイミンの固定化率を高めるために、2万ダルトン以上、より好ましくは7万ダルトン以上の分子量のポリエチレンイミンを用いることが望ましい。 When calcium alginate (CA) gel is adopted as the immobilization carrier and polyethyleneimine (PEI) is adopted as the first polymer, in order to increase the immobilization ratio of polyethyleneimine to the calcium alginate gel, 20,000 daltons or more, More preferably, it is desirable to use polyethyleneimine having a molecular weight of 70,000 daltons or more.
ここで、上記構成のキレート剤は、好適には、該キレート剤を固定したビーズ(例えば、アルギン酸カルシウムビーズ)群をカラム容器(又はカラム塔)に詰めた状態で使用する。より具体的には、重金属を含む底泥や土壌について、該重金属を水溶液に溶出させる前処理(例えば、酸処理)を行なった後、この処理水溶液を前記カラム容器に流し入れることによって、キレート剤で重金属を捕捉するという方法が採用される。 Here, the chelating agent having the above-described configuration is preferably used in a state where a group of beads (for example, calcium alginate beads) to which the chelating agent is fixed is packed in a column container (or column tower). More specifically, the bottom mud and soil containing heavy metal are subjected to pretreatment (for example, acid treatment) for eluting the heavy metal into an aqueous solution, and then the treated aqueous solution is poured into the column container to thereby add a chelating agent. A method of capturing heavy metals is employed.
また、本発明では、キレート剤を乾燥処理することによって、該キレート剤中の水分容積を減少させることにより、カラム容器に対するキレート剤充填量を増加させて、重金属捕捉の能力又は効率を高めるように工夫することができる。 Further, in the present invention, the chelating agent is dried to reduce the water volume in the chelating agent, thereby increasing the amount of the chelating agent packed in the column container and increasing the capability or efficiency of heavy metal capture. Can be devised.
ここで、本発明に係るキレート剤は、クロム、カドミウム、銅、ニッケル、鉛、亜鉛などの有害重金属の捕捉に有効であるが、処理対象の重金属含有水溶液の pH 領域に応じた各リガンドの帯電状態に基づいて、三価クロム(Cr(III))や六価クロム(Cr(VI))の捕捉を行うことができるという特徴を有している。 Here, the chelating agent according to the present invention is effective in capturing harmful heavy metals such as chromium, cadmium, copper, nickel, lead, zinc, etc., but charging of each ligand according to the pH region of the heavy metal-containing aqueous solution to be treated. Based on the state, trivalent chromium (Cr (III)) and hexavalent chromium (Cr (VI)) can be captured.
例えば、pH2を超える領域では、窒素型リガンドのキレート作用と、負に帯電した酸素型リガンド(例えば、−O−)がキレート作用と共に陽イオンである三価クロム(Cr(III))をイオン結合で捕捉し、pH2以下の領域では、窒素型リガンドがプロトン化(正帯電)することによって、陰イオンである Cr2O7 2-(即ち、六価クロムの陰イオン状態)を有効にイオン結合で捕捉することができる。
For example, in the
本発明に係るキレート剤の三価クロム(Cr(III))捕捉(吸着)効果検証試験を実施した。比較例として、ポリエチレンイミン(PEI)を含まないアルギン酸カルシウム(CA)ビーズを用いた。本発明で使用したキレート剤の調整方法は、次の通りである。 A test for verifying the effect of capturing (adsorbing) trivalent chromium (Cr (III)) of the chelating agent according to the present invention was conducted. As a comparative example, calcium alginate (CA) beads not containing polyethyleneimine (PEI) were used. The method for adjusting the chelating agent used in the present invention is as follows.
(1)アルギン酸カルシュームビーズ(CA)の調整:3%アルギン酸ナトリウムを蒸留水で調整し、これを20%のCaCl2溶液にペリスターポンプによって滴下させ、一昼夜放置させてゲル化させた。形成されたビーズは蒸留水中で保存した。 (1) Preparation of calcium alginate beads (CA): 3% sodium alginate was adjusted with distilled water, and this was dropped into a 20% CaCl 2 solution with a peristaltic pump and allowed to stand overnight for gelation. The formed beads were stored in distilled water.
(2)本発明に係るキレート剤(CA-PEI)の調整:3%アルギン酸ナトリウム水溶液に分子量70,000のポリエチレンイミンを1%の濃度になるように添加して混合溶液を作製し、これを20%CaCl2溶液に滴下し、一昼夜放置してゲル化させた。形成されたCA-PEIビーズは蒸留水中で保存した。 (2) Preparation of chelating agent (CA-PEI) according to the present invention: A polyethyleneimine having a molecular weight of 70,000 is added to a 3% sodium alginate aqueous solution so as to have a concentration of 1%, and a mixed solution is prepared. The solution was added dropwise to the CaCl 2 solution and left to stand overnight for gelation. The formed CA-PEI beads were stored in distilled water.
実験方法:80mg/Lの三価クロム水溶液20mLに、上記アルギン酸カルシウムビーズとCA-PEIビーズをそれぞれ、0〜2g添加し、30時間振とう機に掛けて吸着させた。吸着剤への吸着量は、三価クロム水溶液の初期濃度と吸着終了後の濃度差より算出した。なお、三価クロムはpH>4において沈殿を生じるため、三価クロム水溶液の調整には燐酸アンモニウム緩衝液(pH4.0)を用いた。 Experimental method: 0 to 2 g of the above-mentioned calcium alginate beads and CA-PEI beads were added to 20 mL of 80 mg / L trivalent chromium aqueous solution and adsorbed by shaking for 30 hours. The amount of adsorption to the adsorbent was calculated from the initial concentration of the trivalent chromium aqueous solution and the concentration difference after completion of adsorption. Since trivalent chromium precipitates at pH> 4, an ammonium phosphate buffer (pH 4.0) was used to adjust the trivalent chromium aqueous solution.
本実験の結果を図1に示した。この図1の三価クロム(Cr(III))に対する吸着等温曲線に示されているように、本発明に係るキレート剤(図1中、CA-PEI)は、カルシウム-アルギン酸ビーズ(図1中、Ca-Alginate)と比較して、低濃度領域の三価クロム(Cr(III))を効率良く捕捉(吸着)できることを検証することができた。また、窒素型リガンド、酸素型リガンド共に三価クロム(Cr(III))の捕捉能力を有していることも明らかである。 The results of this experiment are shown in FIG. As shown in the adsorption isotherm curve for trivalent chromium (Cr (III)) in FIG. 1, the chelating agent according to the present invention (CA-PEI in FIG. 1) is composed of calcium-alginate beads (in FIG. 1). As compared with Ca-Alginate), it was verified that trivalent chromium (Cr (III)) in a low concentration region can be efficiently captured (adsorbed). It is also clear that both nitrogen-type and oxygen-type ligands have the ability to capture trivalent chromium (Cr (III)).
本発明に係るキレート剤の低pH領域(<pH2)における六価クロム(Cr(VI))捕捉(吸着)効果検証試験を実施した。比較例として、カルシウム-アルギン酸ビーズを用いた。なお、本実験で使用したキレート剤は、実施例1と同様である。 The hexavalent chromium (Cr (VI)) trapping (adsorption) effect verification test was conducted in the low pH region (<pH 2) of the chelating agent according to the present invention. As a comparative example, calcium-alginate beads were used. The chelating agent used in this experiment is the same as in Example 1.
実験方法:重クロム酸カリを用いて六価クロム(Cr(VI))濃度を10mg/Lに調整した水溶液(pH<2)に、実施例1と同様の方法で調整したアルギン酸カルシウムビーズおよびCA-PEIビーズを添加し、吸着に伴う水溶液中の六価クロム(Cr(VI))の濃度変化を測定した。 Experimental method: calcium alginate beads and CA prepared by the same method as in Example 1 in an aqueous solution (pH <2) in which hexavalent chromium (Cr (VI)) concentration was adjusted to 10 mg / L using potassium dichromate. -PEI beads were added, and the concentration change of hexavalent chromium (Cr (VI)) in the aqueous solution accompanying adsorption was measured.
本実験の結果を図2に示した。この図2の吸着経時曲線に示されているように、本発明に係るキレート剤(図2中、CA-PEI)は、六価クロム(Cr(VI))を短時間で効率良く捕捉(吸着)できることを検証できた。一方、カルシウム-アルギン酸ビーズ(図2中、Ca-Alginate)にはこの捕捉能力の無いことが明らかになった。 The results of this experiment are shown in FIG. As shown in the adsorption time curve of FIG. 2, the chelating agent according to the present invention (CA-PEI in FIG. 2) captures (adsorbs) hexavalent chromium (Cr (VI)) efficiently in a short time. ) I was able to verify what I could do. On the other hand, it was revealed that the calcium-alginate beads (Ca-Alginate in FIG. 2) do not have this capturing ability.
これは、低pH領域においてポリエチレンイミンのアミノ基(窒素リガンド)はプロトン化して、陰イオンである六価クロムイオン(Cr2O7 2−)をイオン結合で捕捉するが、一方のカルシウム-アルギン酸の酸素リガンドは負に帯電しているため六価クロムイオン(Cr2O7 2−)を捕捉できなかったものと推定できる。 This is because the amino group (nitrogen ligand) of polyethyleneimine is protonated in a low pH region, and the hexavalent chromium ion (Cr 2 O 7 2− ), which is an anion, is captured by an ionic bond. It can be presumed that this oxygen ligand was negatively charged, so that hexavalent chromium ions (Cr 2 O 7 2− ) could not be captured.
このような吸着機構を模式的に図3に示す。この図3に示すように、キレート剤(CA-PEI)は、低いpH領域(pH<2)ではイオン結合によって六価クロム(Cr(VI))を吸着し、またpH2以上のpH領域では三価クロム(Cr(III))をキレート結合によって吸着する。
Such an adsorption mechanism is schematically shown in FIG. As shown in FIG. 3, the chelating agent (CA-PEI) adsorbs hexavalent chromium (Cr (VI)) by ionic bonding in the low pH region (pH <2), and three in the pH region above
本発明に係るキレート剤の各種重金属に対する捕捉(吸着)効果検証試験を実施した。比較例として、カルシウム-アルギン酸ビーズを用いた。 The capture (adsorption) effect verification test for various heavy metals of the chelating agent according to the present invention was conducted. As a comparative example, calcium-alginate beads were used.
実験方法:本発明に係るキレート剤およびカルシウム-アルギン酸ビーズの調整方法は前述のとおりである。重炭酸ソーダー緩衝液(pH4)を用いてクロム(Cr)、カドミウム(Cd)、銅(Cu)、鉄(Fe)、ニッケル(Ni)、鉛(Pb)、亜鉛(Zn)がほぼ10mg/Lになるように試料液を調整した。80mg/Lの試料液20mLに、アルギン酸カルシウムビーズおよびCA-PEIビーズをそれぞれ2g添加し、30時間振とう機に掛けて吸着させた。吸着剤への吸着量は、試料液中の各種重金属の初期濃度と吸着終了後の濃度差より算出した。 Experimental method: The preparation method of the chelating agent and calcium-alginate beads according to the present invention is as described above. Using sodium bicarbonate buffer (pH 4), chromium (Cr), cadmium (Cd), copper (Cu), iron (Fe), nickel (Ni), lead (Pb), zinc (Zn) is approximately 10 mg / L The sample solution was adjusted so that 2 g of calcium alginate beads and CA-PEI beads were added to 20 mL of 80 mg / L sample solution, respectively, and adsorbed by shaking for 30 hours. The amount of adsorption to the adsorbent was calculated from the initial concentration of various heavy metals in the sample solution and the concentration difference after completion of adsorption.
本実験の結果を図4に示した。この図4のグラフに示された結果から明らかなように、本発明に係るキレート剤(CA-PEI)は、クロム(Cr)、カドミウム(Cd)、銅(Cu)、鉄(Fe)、ニッケル(Ni)、鉛(Pb)、亜鉛(Zn)に対する広範な捕捉(吸着)能力を発揮することが明らかになった。 The results of this experiment are shown in FIG. As is clear from the results shown in the graph of FIG. 4, the chelating agent (CA-PEI) according to the present invention includes chromium (Cr), cadmium (Cd), copper (Cu), iron (Fe), nickel. It has become clear that it exhibits a wide range of capture (adsorption) ability for (Ni), lead (Pb), and zinc (Zn).
充填塔における重金属吸着実験。 Heavy metal adsorption experiment in packed tower.
(1)試料の調整:茨城県霞ヶ浦の底泥を酸処理によって重金属を溶出して重金属分析を実施し、濃度の低い重金属については添加してそれぞれの初濃度をほぼ10mg/Lになるように調整した。なお、この水溶液のpHは1.8であった。 (1) Preparation of sample: Heavy metal is eluted by acid treatment of the bottom mud of Kasumigaura, Ibaraki Prefecture, and heavy metal analysis is performed. For heavy metals with low concentrations, the initial concentration of each is about 10 mg / L. It was adjusted. The pH of this aqueous solution was 1.8.
(2)吸着カラムの調整:本発明に係るキレート剤(CA-PEI)20gを充填した3本のカラムを直列に連結し、カラム最上部より試料液を流速0.5ml/minの下降流で供給した。各カラムの容積は20mLであり、1カラム当たりの液滞留時間は40である。また、各カラムの連結部分には試料採取部を設けて、吸着実験時の濃度変化を求めた。 (2) Adjustment of adsorption column: Three columns packed with 20 g of the chelating agent (CA-PEI) according to the present invention are connected in series, and the sample solution is flowed downward from the top of the column at a flow rate of 0.5 ml / min. Supplied. The volume of each column is 20 mL, and the liquid residence time per column is 40. In addition, a sample collection part was provided at the connection part of each column, and the change in concentration during the adsorption experiment was determined.
この実験で得られた各重金属 (Cr, Cd, Cu, Ni, Pb, Zn)の破過曲線を図5〜図10にそれぞれ示した。なお、図5〜10の横軸は破過時間、縦軸はカラム出口濃度と入り口濃度の比(cf/Ci)である。破過時間を、カラム出口濃度と入り口濃度の比(cf/Ci)が0.1に達した時間とすると、おおむね10〜12時間である。なお、底泥から大量に溶出するアルミニウム(Al)、鉄(Fe)の初濃度はそれぞれ317,263mg/Lであったが、これらの破過時間はそれぞれ13時間、16時間以上と良好に吸着された。 The breakthrough curves of heavy metals (Cr, Cd, Cu, Ni, Pb, Zn) obtained in this experiment are shown in FIGS. 5 to 10, the horizontal axis represents the breakthrough time, and the vertical axis represents the ratio of the column outlet concentration to the inlet concentration (cf / Ci). If the breakthrough time is defined as the time when the ratio of the column outlet concentration to the inlet concentration (cf / Ci) reaches 0.1, it is approximately 10 to 12 hours. The initial concentrations of aluminum (A1) and iron (Fe) eluted in large quantities from the bottom mud were 317 and 263 mg / L, respectively, but these breakthrough times were 13 hours and 16 hours or more, respectively. It was done.
比較例であるキトサンを基材とした重金属キレート剤との六価クロム(Cr(VI))吸着性能の比較(回分実験)。 Comparison of hexavalent chromium (Cr (VI)) adsorption performance with a heavy metal chelating agent based on chitosan as a comparative example (batch experiment).
比較対象のキトサンを基材とした重金属キレート剤(以下、「比較例キレート剤」と称する。)として、市販のキレート剤キトパールCS-03を選択した。なお、このキトパールCS-03は、キトサンを基材とした優れた重金属キレート剤として知られている。この市販キレート剤と本発明に係るCA-PEIキレート剤の六価クロム(Cr(VI))吸着性能を比較検討することにより、本発明に係るCA-PEIキレート剤の特徴をさらに明らかにした。 A commercially available chelating agent chitopearl CS-03 was selected as a heavy metal chelating agent based on chitosan as a comparison target (hereinafter referred to as “comparative chelating agent”). This chitopearl CS-03 is known as an excellent heavy metal chelating agent based on chitosan. The characteristics of the CA-PEI chelating agent according to the present invention were further clarified by comparing the hexavalent chromium (Cr (VI)) adsorption performance of this commercially available chelating agent and the CA-PEI chelating agent according to the present invention.
CA-PEIキレート剤と比較例キレート剤0.15gをそれぞれpH2、初濃度 10mg/Lの六価クロム(Cr(VI))水溶液150mLに添加し、振とう機にかけて回分吸着実験を行い、ICP分析によって全クロム(Cr)を、またdiphenyl carbazide法によって六価クロム(Cr(VI))の経時変化を測定した。CA-PEIキレート剤の調整に際しては、アルギン酸の濃度を1.5,2.0,2.5,3.0%と変え、滴下法によって直径2〜3mmのゲルビーズと、2%アルギン酸でスプレイ法によって直径0.5mm程度の微小ゲルビーズを作製した。
Add 0.15 g of CA-PEI chelating agent and comparative example chelating agent to 150 mL of hexavalent chromium (Cr (VI)) aqueous solution with
両キレート剤の実験結果を図11に示した。この図11から明らかなように、滴下法で調整したCA-PEIキレート剤の吸着速度は、アルギン酸濃度の影響を顕著に受け、1.5%アルギン酸の場合にキトパールの吸着速度と同等の値を示した。アルギン酸濃度の減少に伴ってゲルビーズの孔径が大きくなり、内部拡散抵抗が減少するためと考えられる。 The experimental results of both chelating agents are shown in FIG. As is apparent from FIG. 11, the adsorption rate of the CA-PEI chelating agent adjusted by the dropping method is significantly affected by the concentration of alginic acid, and in the case of 1.5% alginic acid, a value equivalent to the adsorption rate of chitopearl. Indicated. This is probably because the pore size of the gel beads increases with decreasing alginic acid concentration, and the internal diffusion resistance decreases.
また、スプレイ法で調整した2%アルギン酸CA-PEIキレート剤の吸着速度もキトパールと同等の吸着速度を示し、微小化の効果の大きいことを示している。CA-PEIキレート剤の吸着速度は、アルギン酸濃度とビーズの粒子径を選択することによって、市販の比較例キレート剤に匹敵するものを調整できることが明らかである。 Moreover, the adsorption rate of the 2% alginate CA-PEI chelating agent adjusted by the spray method also shows an adsorption rate equivalent to that of chitopearl, indicating that the effect of miniaturization is great. It is clear that the adsorption rate of the CA-PEI chelating agent can be adjusted to be comparable to a commercially available comparative chelating agent by selecting the alginic acid concentration and the bead particle size.
一方、この図11より、本発明に係るCA-PEIキレート剤は、市販の比較例キレート剤に無い機能を有することも明らかとなった。市販の比較例キレート剤を用いた場合、吸着によって全クロム(Cr)の濃度は急激に減少するが、時間の経過に伴って再び増加している。一方、本発明に係るCA-PEIキレート剤では、このような“より戻し現象”は見られず、吸着された六価クロム(Cr(VI))は確実に捕捉されている。 On the other hand, FIG. 11 also revealed that the CA-PEI chelating agent according to the present invention has a function that is not found in commercially available comparative chelating agents. When a commercially available comparative chelating agent is used, the total chromium (Cr) concentration rapidly decreases due to adsorption, but increases again with the passage of time. On the other hand, in the CA-PEI chelating agent according to the present invention, such a “return phenomenon” is not observed, and the adsorbed hexavalent chromium (Cr (VI)) is reliably captured.
この“より戻し現象”は、比較例キレート剤(キトパールCS-03)に吸着された六価クロム(Cr(VI))が三価クロム(Cr(III))に還元されて溶出したことに起因している。“より戻り”後の水中には、六価クロム(Cr(VI))は存在せず、全クロム(Cr)は三価クロム(Cr(III))であること、またこの吸着実験中における比較例キレート剤(キトパールCS-03)の色の変化からもこのことが容易に推定される。 This “more return phenomenon” is due to the elution of hexavalent chromium (Cr (VI)) adsorbed on the comparative chelating agent (Chitopearl CS-03) to trivalent chromium (Cr (III)). is doing. There is no hexavalent chromium (Cr (VI)) in the water after “return”, and the total chromium (Cr) is trivalent chromium (Cr (III)). This is easily deduced from the color change of the chelating agent (Chitopearl CS-03).
即ち、未使用の比較例キレート剤(キトパールCS-03)は白色であるが、六価クロム(Cr(VI))の吸着によって黄色に変化し、時間の経過によって色が消失した。一方、本発明に係るCA-PEIキレート剤においても吸着した六価クロム(Cr(VI))の三価クロム(Cr(III))への変化は起こるが、この陽イオンである三価クロム(Cr(III))はアルギン酸のカルボキシル基によって捕捉され、水中に溶出することは無い。 That is, the unused comparative chelating agent (Chitopearl CS-03) was white, but turned yellow due to adsorption of hexavalent chromium (Cr (VI)), and the color disappeared over time. On the other hand, in the CA-PEI chelating agent according to the present invention, the adsorbed hexavalent chromium (Cr (VI)) is changed to trivalent chromium (Cr (III)). Cr (III)) is captured by the carboxyl group of alginic acid and does not elute in water.
これらの様子はゲルビーズの色の変化によっても観察できる。即ち、六価クロム(Cr(VI))の吸着によって一旦は黄色に変化し、ついで三価クロム(Cr(III))の緑色に変わる。これらの事実は、アミノ基を有する窒素型キレート剤は、低pH領域ではアミノ基がプロトン化されており陰イオンの六価クロム(Cr(VI))をイオン結合で捕捉するが、還元によって生じる陽イオンの三価クロム(Cr(III))に対しては全く無力である。窒素型―酸素型ハイブリッド型の本発明に係るキレート剤では、酸素型リガンドが低pH領域においても陽イオンの捕捉能力を保持しており、窒素型リガンドの欠点を補っている。 These states can also be observed by a change in the color of the gel beads. That is, it turns yellow once by the adsorption of hexavalent chromium (Cr (VI)) and then turns green of trivalent chromium (Cr (III)). These facts indicate that nitrogen-type chelating agents having amino groups are protonated in the low pH region and capture the anionic hexavalent chromium (Cr (VI)) by ionic bonds, but are caused by reduction. It is completely ineffective against the cationic trivalent chromium (Cr (III)). In the chelating agent according to the present invention of the nitrogen type-oxygen type hybrid type, the oxygen type ligand retains the ability to capture cations even in a low pH region, and compensates for the disadvantages of the nitrogen type ligand.
市販の比較例キレート剤(キトパールCS-03)との六価クロム(Cr(VI))性能の比較実験(カラム吸着実験)。 Comparative experiment (column adsorption experiment) of hexavalent chromium (Cr (VI)) performance with a commercially available comparative chelating agent (Chitopearl CS-03).
湿潤タイプの比較例キレート剤(キトパールCS-03)と本発明に係るCA-PEIキレート剤20gをそれぞれ内径16mm、充填容積5mLのカラム3本に充填し、六価クロム(Cr(VI))水溶液(濃度5mg/L、pH2)を15mL/h(滞留時間1時間)で流入させ、カラム出口での全クロム(Cr)、六価クロム(Cr(VI))を測定した。なお、420mLを供給した後(28時間後)から、供給速度を30mL/h(滞留時間30分)に増加させた。
Wet type comparative chelating agent (Chitopearl CS-03) and CA-PEI chelating agent 20g according to the present invention were packed in 3 columns each having an inner diameter of 16 mm and a packing volume of 5 mL, and a hexavalent chromium (Cr (VI)) aqueous solution. (
これらの破過曲線を図12に示した。回分実験(実施例5)で明らかになった本発明に係るキレート剤(CA-PEI)の優位性は、この破過曲線にも顕著に現れている。本発明に係るキレート剤は、キレート剤容積の100倍の六価クロム(Cr(VI))水溶液を処理しても未だ破過には至らず、市販の比較例キレート剤よりも優れた性能を示した。
These breakthrough curves are shown in FIG. The superiority of the chelating agent (CA-PEI) according to the present invention, which has been clarified in the batch experiment (Example 5), also appears remarkably in this breakthrough curve. The chelating agent according to the present invention does not yet break through even when a hexavalent chromium (Cr (VI))
本発明に係るキレート剤が充填塔で利用されることを想定して、乾燥処理を施した本発明に係るキレート剤の重金属捕捉能力が向上するか否かについての検証実験を行った。 Assuming that the chelating agent according to the present invention is used in a packed tower, a verification experiment was conducted as to whether or not the heavy metal capturing ability of the chelating agent according to the present invention that had been subjected to the drying treatment was improved.
当該キレート吸着剤の実際的な利用は、一般は充填塔で行われる。この充填塔の単位容積あたりの吸着能力を高めるためには、吸着剤の容積を下げることが極めて有効であると考えられる。そこで、ポリエチレンイミン(PEI)をアルギン酸カルシウム(CA)で固定化したビーズ容積の大半は水であるため、これを乾燥させることによって充填塔単位容積あたりの吸着能を高めることを試みた。その結果、減圧乾燥によって前記ビーズ容積は87.5%に、質量では90%の減少が達成された。 The practical use of the chelate adsorbent is generally carried out in a packed tower. In order to increase the adsorption capacity per unit volume of the packed tower, it is considered extremely effective to reduce the volume of the adsorbent. Therefore, since most of the volume of beads immobilizing polyethyleneimine (PEI) with calcium alginate (CA) is water, an attempt was made to increase the adsorption capacity per packed column unit volume by drying it. As a result, the bead volume was reduced to 87.5% and reduced by 90% in mass by drying under reduced pressure.
続いで、乾燥させたキレート剤(PEI-CA)の吸着量および吸着速度特性を明らかにするため下記の実験をさらに実施した。六価クロム(Cr(VI))10.4mg/L、pH1.8の水溶液を25℃、50℃に調整し、これに湿潤基準で0.1、0.25、0.5gの湿潤CA-PEI及び乾燥CA-PEIを添加して、2時間の懸濁吸着処理を行った。その結果を図13に示した。 Subsequently, the following experiment was further performed to clarify the adsorption amount and adsorption rate characteristics of the dried chelating agent (PEI-CA). An aqueous solution of hexavalent chromium (Cr (VI)) 10.4 mg / L, pH 1.8 was adjusted to 25 ° C. and 50 ° C., and 0.1, 0.25, and 0.5 g of wet CA − on a wet basis. PEI and dry CA-PEI were added to carry out suspension adsorption treatment for 2 hours. The results are shown in FIG.
この図13(表)に示された結果から、乾燥CA-PEIは、湿潤 CA-PEIと同等の吸着能を有しており、さらに50℃においても膨潤することなく安定した形状を維持した。このことから、乾燥CA-PEIを充填したカラムの吸着容量は、湿潤CA-PEIを充填した場合に比して8倍に増大される。また、吸着速度は、図14で示されるように、乾燥によって担体内部の拡散抵抗が増加して若干の低下は見られたが実用的に大きな問題ではないものと考えられる。 From the results shown in FIG. 13 (table), dry CA-PEI had an adsorption capacity equivalent to that of wet CA-PEI, and maintained a stable shape without swelling even at 50 ° C. From this, the adsorption capacity of the column packed with dry CA-PEI is increased by a factor of 8 compared to when packed with wet CA-PEI. Further, as shown in FIG. 14, the adsorption rate is considered to be not a big problem in practice although the diffusion resistance inside the carrier is increased by drying and slightly decreased.
本発明に係る重金属捕捉用キレート剤は、大量の土壌(例えば、浚渫土)の重金属処理に特に適している。特に、乾燥処理を施したものは、カラム充填塔における利用に好適である。 The chelating agent for capturing heavy metals according to the present invention is particularly suitable for heavy metal treatment of a large amount of soil (for example, dredged soil). In particular, those subjected to a drying treatment are suitable for use in a column packed column.
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JP2008200651A (en) * | 2007-02-22 | 2008-09-04 | Kyushu Univ | Method for recovering harmful ion |
JP2012515083A (en) * | 2009-01-15 | 2012-07-05 | ダウ グローバル テクノロジーズ エルエルシー | Ion exchange resins containing interpenetrating polymer networks and their use for chromium removal |
JP2013227553A (en) * | 2012-03-30 | 2013-11-07 | Yoshino Gypsum Co Ltd | Insolubilizing and solidifying agent for specific toxic substance containing gypsum and soil improvement method using the same |
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JP2008200651A (en) * | 2007-02-22 | 2008-09-04 | Kyushu Univ | Method for recovering harmful ion |
JP2012515083A (en) * | 2009-01-15 | 2012-07-05 | ダウ グローバル テクノロジーズ エルエルシー | Ion exchange resins containing interpenetrating polymer networks and their use for chromium removal |
JP2013227553A (en) * | 2012-03-30 | 2013-11-07 | Yoshino Gypsum Co Ltd | Insolubilizing and solidifying agent for specific toxic substance containing gypsum and soil improvement method using the same |
US10850256B2 (en) | 2012-03-30 | 2020-12-01 | Yoshino Gypsum Co., Ltd. | Insolubilizing agent for specific toxic substances, method for insolubilizing specific toxic substances using same, and soil improving method |
CN116143973A (en) * | 2022-11-29 | 2023-05-23 | 嘉兴沃特泰科环保科技股份有限公司 | Chelating agent with heavy metal capturing function and preparation method and application thereof |
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