JP5903404B2 - Arsenic reducing material, arsenic reducing material manufacturing method, and arsenic reducing method - Google Patents
Arsenic reducing material, arsenic reducing material manufacturing method, and arsenic reducing method Download PDFInfo
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Description
本発明は、水、土壌、廃棄物等の処理対象物からヒ素を除去するヒ素低減材及びヒ素低減方法に関するものである。 The present invention relates to an arsenic reducing material and an arsenic reducing method for removing arsenic from an object to be treated such as water, soil, and waste.
近年、自然発生的要因及び／又は産業発生的要因によって発生した有害元素に起因する環境保全上の支障の除去の必要性が高まっている。このため、水質汚濁防止法では、排水中におけるヒ素（Ａｓ）の濃度が０．１ｍｇ／Ｌ以下に定められ、土壌汚染対策法では、環境省告示１３号及び４６号試験法での溶出液中におけるヒ素の濃度（土壌環境基準値（平６環庁告２５））が０．０１ｍｇ／Ｌ以下（農用地においては１５ｍｇ／Ｌ未満）に定められている。 In recent years, there has been an increasing need for removal of environmental conservation obstacles caused by harmful elements generated by natural and / or industrial factors. For this reason, in the Water Pollution Control Law, the concentration of arsenic (As) in the wastewater is set to 0.1 mg / L or less, and in the Soil Contamination Countermeasures Law, in the eluate in the Ministry of the Environment Notification Nos. 13 and 46 test methods. The concentration of arsenic (soil environmental standard value (Heisei 6 Ring Agency Notification 25)) is set to 0.01 mg / L or less (less than 15 mg / L in agricultural land).
水、土壌、廃棄物等の処理対象物からヒ素を除去する方法としては種々の方法が提案されている。例えば、特許文献１〜３には、鉄系化合物によるイオン交換反応や凝集沈殿分離処理を利用してヒ素を除去する方法が記載されている。特許文献４，５には、活性アルミナ等のアルミニウム化合物による化学吸着反応を利用してヒ素を除去する方法が記載されている。特許文献６には、第一鉄塩とＣａ（ＯＨ）２とを排水に添加してヒ素を凝集分離する方法が記載されている。特許文献７〜１１には、カルシウム源としてのカルシウムフェライトを提供する高炉徐冷スラグが記載されている。 Various methods have been proposed for removing arsenic from treatment objects such as water, soil, and waste. For example, Patent Documents 1 to 3 describe a method of removing arsenic using an ion exchange reaction or a coagulation precipitation separation process with an iron-based compound. Patent Documents 4 and 5 describe a method of removing arsenic using a chemisorption reaction by an aluminum compound such as activated alumina. Patent Document 6 describes a method of aggregating and separating arsenic by adding ferrous salt and Ca (OH) 2 to waste water. Patent Documents 7 to 11 describe a blast furnace annealed slag that provides calcium ferrite as a calcium source.
しかしながら、特許文献１〜３記載の方法は、鉄系化合物として還元性鉄粉を用いているために、処理対象物からヒ素を除去するまでに多くの時間を要する。特許文献２，３記載の方法は、鉄系化合物として硫酸第一鉄を用いているために、系に硫黄系の化合物を添加する必要があり、環境負荷の弊害が新たに発生するおそれがある。また、水酸化物としての凝集沈殿分離処理では、固液分離操作が煩雑であるのに加えてｐＨ等の調整が必要であり、またｐＨの変動によってヒ素の補集率が大幅に変動することがある。 However, since the methods described in Patent Documents 1 to 3 use reducing iron powder as the iron-based compound, it takes a long time to remove arsenic from the object to be treated. Since the methods described in Patent Documents 2 and 3 use ferrous sulfate as the iron-based compound, it is necessary to add a sulfur-based compound to the system, and there is a possibility that adverse environmental impacts may newly occur. . In addition, the coagulation-precipitation separation treatment as a hydroxide requires complicated adjustment of the solid-liquid separation, and also requires adjustment of pH and the like, and the arsenic collection rate fluctuates greatly due to pH fluctuation. There is.
特許文献４，５記載の方法では、アルミニウム化合物として用いられるハイドロタルサイトや酸化アルミニウム等の材料が高価であるのに加えて、アルミニウム摂取とアルツハイマー病との関連が指摘される等、安全性が十分に検証されていない。特許文献６記載の方法では、固液分離操作が煩雑であるのに加えて、ｐＨ等の調整が必要である。特許文献８記載の方法は、カルシウムフェライトと高炉水砕スラグとの混合物を用いてＣｒ（６価），Ａｓ，Ｓｅを固定化する方法であるが、これは特許文献７に記載された高炉水砕スラグによるＣｒ（６価）固定化の方法を発展させた方法であり、５〜９０％のカルシウムフェライトが必要であるため、高価である。 In the methods described in Patent Documents 4 and 5, in addition to the expensive materials such as hydrotalcite and aluminum oxide used as the aluminum compound, the safety of aluminum intake and Alzheimer's disease is pointed out. Not fully verified. In the method described in Patent Document 6, in addition to the complicated solid-liquid separation operation, it is necessary to adjust pH and the like. The method described in Patent Document 8 is a method of immobilizing Cr (hexavalent), As, Se using a mixture of calcium ferrite and blast furnace granulated slag, which is a blast furnace water described in Patent Document 7. This is a method developed from the method of fixing Cr (hexavalent) with crushed slag, and requires 5 to 90% of calcium ferrite, which is expensive.
特許文献９，１０記載の方法は、Ｓ，Ｆｅを含有する高炉徐冷スラグをヒ素低減材として用いるものであるが、Ｓの混入は新たな環境負荷の要因となりうるため好ましくない。特許文献１１記載の方法は、高炉徐冷スラグと製鋼スラグとからなるヒ素低減材を用いるものであるが、ヒ素低減材がＳを０．３％以上含有しているために、Ｓの混入が新たな環境負荷の要因となりうるため好ましくない。また、ヒ素低減材を添加混合した際の水又は土壌のｐＨが７以下であることが規定されており、ｐＨが７を超えるような処理対象物には適用できない、若しくは、ｐＨを７以下に調整するための煩雑な処理が必要になる。特許文献８〜１１記載の方法では、水質検液５０ｍＬに対して１０ｇと非常に多くのヒ素低減材が必要な上に、非常に長い処理日数（実施例では２８日）が必要になる。 The methods described in Patent Documents 9 and 10 use blast furnace slow-cooled slag containing S and Fe as an arsenic-reducing material, but mixing of S is not preferable because it may cause a new environmental load. The method described in Patent Document 11 uses an arsenic reducing material composed of blast furnace slow-cooled slag and steelmaking slag. However, since the arsenic reducing material contains 0.3% or more of S, mixing of S is not possible. This is not preferable because it may cause a new environmental load. Moreover, it is prescribed that the pH of water or soil when an arsenic reducing material is added and mixed is specified to be 7 or less, and cannot be applied to an object to be processed whose pH exceeds 7, or the pH is set to 7 or less. A complicated process for adjustment is required. In the methods described in Patent Documents 8 to 11, an extremely large amount of arsenic reducing material of 10 g per 50 mL of the water quality test solution is required, and a very long processing day (28 days in the embodiment) is required.
処理が求められる汚染土壌等には通常０．１μｇ／ｋｇ〜数１０００ｍｇ／ｋｇのヒ素が含まれている。このため、このような土壌に対して、同程度若しくは同程度以下の量のヒ素低減材を用いてｐＨを７以下に調整することなく、ヒ素を低減できる方法の提供が望まれている。 Contaminated soil or the like that requires treatment usually contains 0.1 μg / kg to several thousand mg / kg of arsenic. For this reason, it is desired to provide a method that can reduce arsenic without adjusting the pH to 7 or less by using an arsenic reducing material of the same level or lower than that of such soil.
本発明は、上記課題に鑑みてなされたものであって、その目的は、処理対象物からヒ素を簡単、迅速、且つ、安価に除去可能なヒ素低減材及びヒ素低減方法を提供することにある。 The present invention has been made in view of the above problems, and an object thereof is to provide an arsenic reducing material and an arsenic reducing method capable of removing arsenic from an object to be processed easily, quickly, and inexpensively. .
本発明に係るヒ素低減材は、鉄塩含有高温高圧水を接触させることによって表層が改質された高炉スラグにより形成されていることを特徴とする。 The arsenic-reducing material according to the present invention is characterized by being formed of blast furnace slag whose surface layer is modified by bringing iron salt-containing high-temperature and high-pressure water into contact therewith.
本発明に係るヒ素低減材は、上記発明において、前記高炉スラグの表層が、温度７０℃以上、圧力０．１５ＭＰａ以上の鉄塩含有高温高圧水を接触させることによって改質されていることを特徴とする。 The arsenic reducing material according to the present invention is characterized in that, in the above invention, the surface layer of the blast furnace slag is modified by contacting iron salt-containing high-temperature high-pressure water at a temperature of 70 ° C. or higher and a pressure of 0.15 MPa or higher. And
本発明に係るヒ素低減方法は、鉄塩含有高温高圧水を接触させることによって表層が改質された高炉スラグを処理対象物に接触させることによって、該処理対象物のヒ素含有量を低減させるステップを含むことを特徴とする。 In the arsenic reduction method according to the present invention, the step of reducing the arsenic content of the object to be treated by bringing the blast furnace slag whose surface layer has been modified by contacting the iron salt-containing high-temperature and high-pressure water with the object to be treated. It is characterized by including.
本発明に係るヒ素低減材及びヒ素低減方法によれば、処理対象物からヒ素を簡単、迅速、且つ、安価に除去することができる。 According to the arsenic reducing material and the arsenic reducing method according to the present invention, arsenic can be easily and quickly removed from a processing object at low cost.
本発明の発明者らは、鋭意研究を重ねてきた結果、（１）鉄水酸化物がヒ素のオキソ酸イオンに対して高い親和性を示すこと、及び（２）Ｃａ酸化物を多く含む高炉スラグがＣａＯによるｐＨ調整作用を発揮して高炉スラグ表層への鉄水酸化物の凝集作用を促進することに着目し、高炉スラグ表層に鉄水酸化物層を形成することにより、水及び固体から溶出するヒ素を捕集する能力に優れたヒ素低減材を製造できることを見出した。 As a result of extensive research, the inventors of the present invention have found that (1) iron hydroxide has a high affinity for arsenic oxoacid ions, and (2) a blast furnace containing a large amount of Ca oxide. Paying attention to the fact that slag promotes the coagulation action of iron hydroxide on the surface of blast furnace slag by exerting pH adjustment effect by CaO, by forming an iron hydroxide layer on the surface of blast furnace slag, It was found that an arsenic-reducing material excellent in the ability to collect eluting arsenic can be produced.
さらに、本発明の発明者らは、高炉スラグは多孔性物質であることから、高い浸透性及びイオン積を有する鉄塩含有高温高圧水を高炉スラグに作用させる鉄塩亜臨界水処理を施すことによって、高炉スラグの孔内面の改質及び孔内面への鉄水酸化物層の形成が可能になり、ヒ素の捕集に関与する有効捕集表面積を増大させて、ヒ素の捕集率及び捕集容量を増加できることを見出した。 Furthermore, since the blast furnace slag is a porous material, the inventors of the present invention perform iron salt subcritical water treatment that causes iron salt-containing high-temperature high-pressure water having high permeability and ionic product to act on the blast furnace slag. This makes it possible to modify the inner surface of the hole in the blast furnace slag and form an iron hydroxide layer on the inner surface of the hole, increase the effective collection surface area involved in arsenic collection, and increase the arsenic collection rate and collection rate. We found that the collection capacity can be increased.
ここで、高炉スラグとは、高炉で鉄鉱石を溶融・還元する際に発生するスラグであって、鉄鉱石に含まれるシリカ等の鉄以外の成分や還元剤として使われるコークスの灰分が副原料の石灰石と結合したものである。高炉スラグは冷却方法によって徐冷スラグと水砕スラグとに大別されるが、本発明に用いられるスラグとしては高炉徐冷スラグが好適である。高炉徐冷スラグの主要鉱物相は、ゲーレナイト（２ＣａＯ・Ａｌ２Ｏ３・ＳｉＯ２）とオケルマナイト（２ＣａＯ・ＭｇＯ・２ＳｉＯ２）とを端成分とする固溶体であるメリライト及びダイカルシウムシリケート（２ＣａＯ・ＳｉＯ２）であり、主な組成は、Ｆｅ０．１〜５質量％、Ｓｉ１０〜２０質量％、Ａｌ２〜１０質量％、Ｃａ２０〜５０質量％である。 Here, blast furnace slag is slag generated when iron ore is melted and reduced in the blast furnace. Components other than iron, such as silica, contained in iron ore and coke ash used as a reducing agent are secondary materials. It is combined with limestone. Blast furnace slag is roughly classified into slowly cooled slag and granulated slag depending on the cooling method. As the slag used in the present invention, blast furnace slowly cooled slag is suitable. Major mineral phase of slowly cooled blast furnace slag, gehlenite (2CaO · Al 2 O 3 · SiO 2) and akermanite a solid solution to (2CaO · MgO · 2SiO 2) and the end component melilite and Dicalcium silicate (2CaO · SiO 2 ) and the main composition is Fe 0.1-5 mass%, Si 10-20 mass%, Al 2-10 mass%, Ca 20-50 mass%.
ヒ素低減材を製造する際には、高炉スラグを数ｍｍ程度以下に粉砕し、粉砕された高炉スラグを液体状態の鉄塩含有高温高圧水に接触させることによって、高炉スラグの表層を改質する。具体的には、粉砕された高炉スラグと鉄塩含有水溶液とを耐圧密閉容器に入れて加温、加圧することによって、高炉スラグの表層を改質する。加温、加圧の好適な範囲は７０℃以上、２５０℃以下、０．１５ＭＰａ以上、４．０ＭＰａ以下である。温度や圧力がこの範囲より低いと有効な処理ができず、また、この範囲より高いと効果はさほど変わらないにもかかわらずコストが上がる等の問題がある。また、さらに好ましくは、温度９０℃以上、圧力０．２０ＭＰａ以上とすることによって捕集効率のよいヒ素低減材を製造できる。処理時間は、高炉スラグの粒径、処理温度、圧力、鉄塩濃度等によって変動するが、１〜３時間程度で十分な改質効果が得られる。高炉スラグは、放冷後、処理液から分離、乾燥してヒ素低減材として用いる。但し、乾燥工程を経ずに高炉スラグを直接処理対象物に接触させてヒ素の低減処理に用いることもできる。 When manufacturing the arsenic reducing material, the surface layer of the blast furnace slag is modified by pulverizing the blast furnace slag to about several millimeters or less and bringing the pulverized blast furnace slag into contact with liquid iron salt-containing high-temperature high-pressure water. . Specifically, the ground layer of the blast furnace slag is modified by putting the pulverized blast furnace slag and the iron salt-containing aqueous solution in a pressure-resistant airtight container and heating and pressurizing. Suitable ranges for heating and pressurization are 70 ° C. or more, 250 ° C. or less, 0.15 MPa or more and 4.0 MPa or less. If the temperature and pressure are lower than this range, effective treatment cannot be performed. If the temperature and pressure are higher than this range, there is a problem that the cost increases despite the fact that the effect does not change much. More preferably, an arsenic-reducing material with good collection efficiency can be produced by setting the temperature to 90 ° C. or higher and the pressure to 0.20 MPa or higher. The treatment time varies depending on the particle size of the blast furnace slag, the treatment temperature, the pressure, the iron salt concentration, etc., but a sufficient reforming effect can be obtained in about 1 to 3 hours. The blast furnace slag is allowed to cool and then separated from the treatment liquid and dried to be used as an arsenic reducing material. However, the blast furnace slag can be directly brought into contact with the object to be processed without passing through the drying step and used for the arsenic reduction process.
鉄塩含有高温高圧水で処理した高炉スラグの表層には微細な水酸化鉄の積層が形成され、これらがヒ素低減材として有効に作用する。 A fine layer of iron hydroxide is formed on the surface layer of blast furnace slag treated with iron salt-containing high-temperature and high-pressure water, and these effectively act as an arsenic reducing material.
このような微細な水酸化鉄の積層を形成するために添加する鉄塩としては、塩化鉄、硫酸鉄等の水溶性化合物を用いることができる。また、クエン酸鉄やシュウ酸鉄等の有機塩を用いることもできる。実際に有効に作用するのは３価の鉄塩であるが、高温高圧水中では２価の鉄は容易に３価になるので、２価の鉄塩を添加しても有効である。鉄塩の高炉スラグへの担持量は鉄の量の質量比で高炉スラグの１〜２０％程度が好適である。この範囲以下の担持量では鉄塩付与の効果が発現しにくく、この範囲以上の割合で鉄塩を担持させてもヒ素の捕集率の大幅な向上は発現されない。通常、上記の条件により処理することによって、鉄の担持量は、質量比で１〜２０％程度となる。担持量の質量比は、高炉スラグの処理前後での処理液中の鉄濃度をＩＣＰ発光分析法等で求め、この差から処理により処理液中から消失した鉄量を求め、消失した鉄量の高炉スラグの重さに対する質量比を求めることにより得られる。 As the iron salt added to form such a fine iron hydroxide laminate, water-soluble compounds such as iron chloride and iron sulfate can be used. Organic salts such as iron citrate and iron oxalate can also be used. Although the trivalent iron salt actually works effectively, divalent iron easily becomes trivalent in high-temperature and high-pressure water, so it is effective even if a divalent iron salt is added. The loading amount of iron salt on the blast furnace slag is preferably about 1 to 20% of the blast furnace slag by mass ratio of the amount of iron. If the loading amount is less than this range, the effect of imparting iron salt is hardly exhibited, and even if the iron salt is loaded at a rate exceeding this range, the arsenic collection rate is not significantly improved. Usually, by carrying out the treatment under the above conditions, the amount of iron supported is about 1 to 20% by mass ratio. The mass ratio of the supported amount is obtained by calculating the iron concentration in the treatment liquid before and after the treatment of the blast furnace slag by ICP emission spectrometry, etc., and obtaining the amount of iron lost from the treatment liquid by this difference. It is obtained by determining the mass ratio with respect to the weight of the blast furnace slag.
ヒ素低減材を水質の処理に用いる場合、試料水にヒ素低減材を添加、攪拌後、ろ過等によってヒ素低減材を除くことにより、試料水中のヒ素はヒ素低減材に捕集されて固相に移動し、試料水中のヒ素量を低減することができる。ヒ素低減材をカラムに充填又は所定形状に成型し、これに対象の試料水を通液することによっても試料水中のヒ素量を低減することができる。 When using the arsenic reducing material for water quality treatment, after adding the arsenic reducing material to the sample water, stirring, and removing the arsenic reducing material by filtration, the arsenic in the sample water is collected by the arsenic reducing material and becomes a solid phase. It can move and the amount of arsenic in sample water can be reduced. The amount of arsenic in the sample water can also be reduced by filling the column with an arsenic reducing material or molding the arsenic reducing material into a predetermined shape and passing the sample water through the column.
処理する際の試料のｐＨは２〜３程度の酸性領域から１２程度の強アルカリ領域まで広範に対応できる。 The pH of the sample at the time of treatment can correspond widely from an acidic region of about 2 to 3 to a strong alkali region of about 12.
〔実験例１〕
２ｍｍ目のふるいを通過するように粉砕した高炉徐冷スラグ（Ｆｅ０．６％、Ｓｉ１５．８％、Ａｌ７．２％、Ｃａ２８．４％）(ここで％は質量％を表す)２０ｇに（１）水６０ｍｌ又は（２）塩化鉄（III）（Ｆｅ１．５ｇ含有）と水６０ｍｌとを添加し、それぞれ内容量１２０ｍｌの耐圧容器中に密閉し、２００℃で２時間加熱した。この時容器内の内圧は１．７３ＭＰａであった。放冷後、高炉徐冷スラグを処理液から分離して風乾した。（２）の方法で処理した高炉徐冷スラグの鉄担持量を求めるために、処理液中に残存する鉄量をＩＣＰ発光分析法で定量したところ、高炉徐冷スラグ１ｇ当たり０．１３ｇの鉄が担持されていることが確認できた。
[Experimental Example 1]
Blast furnace slow-cooled slag (0.6% Fe, 15.8% Si, 7.2% Al, 28.4% Ca) crushed so as to pass through a 2 mm screen (where% represents mass%) ) 60 ml of water or (2) iron (III) chloride (containing 1.5 g of Fe) and 60 ml of water were added, each was sealed in a pressure-resistant container having an internal volume of 120 ml, and heated at 200 ° C. for 2 hours. At this time, the internal pressure in the container was 1.73 MPa. After standing to cool, the blast furnace slow cooling slag was separated from the treatment liquid and air-dried. In order to determine the amount of iron supported in the blast furnace annealed slag treated by the method (2), the amount of iron remaining in the treatment liquid was quantified by ICP emission spectrometry. It was confirmed that was supported.
未処理の高炉徐冷スラグと（１），（２）の方法で処理した高炉徐冷スラグ各５ｇにヒ素１μｇ／ｍＬを含有する溶液１００ｍＬを添加し１０分間攪拌後、溶液中に残存するヒ素濃度をＩＣＰ質量分析法で定量し、各高炉徐冷スラグのヒ素捕集率を調べた。捕集時のｐＨの影響を明確化するためにヒ素を含有する溶液に種々のｐＨ緩衝液を添加することにより溶液のｐＨを２．０から１２．２まで変化させてヒ素捕集率を調査した結果を表１及び図１に示す。 Arsenic remaining in the solution after adding 100 mL of a solution containing 1 μg / mL arsenic to 5 g each of untreated blast furnace annealed slag and 5 g of blast furnace annealed slag treated by the methods of (1) and (2) The concentration was quantified by ICP mass spectrometry, and the arsenic collection rate of each blast furnace annealed slag was examined. In order to clarify the effect of pH at the time of collection, the pH of the solution was changed from 2.0 to 12.2 by adding various pH buffers to the solution containing arsenic, and the arsenic collection rate was investigated. The results are shown in Table 1 and FIG.
表１及び図１に示すように、未処理の高炉徐冷スラグでは、検討したｐＨ領域ではヒ素はほとんど捕集されず、（１）で処理した高炉徐冷スラグ（亜臨界水処理スラグ）でも、ｐＨが４〜８の範囲内で２０〜４０％のヒ素捕集率が得られたに過ぎなかった。これに対し、（２）の方法で処理した高炉徐冷スラグ（鉄塩亜臨界水処理スラグ）では、ｐＨが２〜約１２の広範囲で５０％以上、ｐＨ５〜８の範囲内では８０％以上の高い捕集率が得られた。 As shown in Table 1 and FIG. 1, in the untreated blast furnace chilled slag, arsenic is hardly collected in the examined pH region, and even in the blast furnace chilled slag (subcritical water treated slag) treated in (1). Only an arsenic collection rate of 20 to 40% was obtained within a pH range of 4 to 8. On the other hand, in the blast furnace slow cooling slag (iron salt subcritical water treatment slag) treated by the method of (2), the pH ranges from 2 to about 12 over a range of 50% or more, and within the range of pH 5 to 8 over 80%. A high collection rate was obtained.
以上のことから、高炉徐冷スラグを鉄塩含有高温高圧水に接触させる鉄塩亜臨界水処理によって高炉徐冷スラグが優れたヒ素捕集材となりうること、及びヒ素捕集材をヒ素含有水に添加して攪拌するだけで、ヒ素が高い効率で簡単に除去できることが確認できた。 From the above, the blast furnace slow-cooled slag can be an excellent arsenic collector by the iron salt subcritical water treatment in which the blast furnace slow-cooled slag is brought into contact with iron salt-containing high-temperature and high-pressure water, and the arsenic collector is treated with arsenic-containing water. It was confirmed that arsenic could be easily removed with high efficiency simply by adding to and stirring.
〔実験例２〕
２ｍｍ目のふるいを通過するように粉砕した高炉徐冷スラグ（Ｆｅ０．６％、Ｓｉ１５．８％、Ａｌ７．２％、Ｃａ２８．４％）(ここで％は質量％を表す)２０ｇに（１）水６０ｍｌ、又は（２）塩化鉄（III）（Ｆｅ１．５ｇ含有）と水６０ｍｌとを添加し、それぞれ内容量１２０ｍｌの耐圧容器中に密閉し、７０、７５、９０、１００、１５０、２００℃で２時間加熱した。放冷後、高炉徐冷スラグを処理液から分離し、風乾した。
[Experimental example 2]
Blast furnace slow-cooled slag (0.6% Fe, 15.8% Si, 7.2% Al, 28.4% Ca) crushed so as to pass through a 2 mm screen (where% represents mass%) ) 60 ml of water, or (2) iron (III) chloride (containing 1.5 g of Fe) and 60 ml of water are added and sealed in a pressure-resistant container having an inner volume of 120 ml, respectively. 70, 75, 90, 100, 150, 200 Heated at 0 ° C. for 2 hours. After standing to cool, the blast furnace slow cooling slag was separated from the treatment liquid and air-dried.
未処理の高炉徐冷スラグと（１）、（２）の方法で処理した高炉徐冷スラグ各５ｇとにヒ素１μｇ／ｍＬを含有するｐＨ緩衝液（ｐＨ＝６）、及びｐＨ緩衝液（ｐＨ＝３）１００ｍＬをそれぞれ添加し１０分間攪拌後、ｐＨ緩衝液中のヒ素濃度をＩＣＰ質量分析法で定量し、各高炉徐冷スラグのヒ素捕集率を評価した。評価結果を以下の表２に示す。 PH buffer solution (pH = 6) containing arsenic 1 μg / mL in untreated blast furnace annealed slag and 5 g each of blast furnace annealed slag treated by the method of (1) and (2), and pH buffer solution (pH = 3) After 100 mL was added and stirred for 10 minutes, the arsenic concentration in the pH buffer solution was quantified by ICP mass spectrometry, and the arsenic collection rate of each blast furnace annealed slag was evaluated. The evaluation results are shown in Table 2 below.
表２に示すように、（１）の方法で処理した高炉徐冷スラグ（亜臨界水処理スラグ）に比較して、（２）の方法で処理した高炉徐冷スラグ（鉄塩亜臨界水処理スラグ）は、処理液のｐＨに関わらず、処理温度７０℃以上２００℃以下であれば非常に高いヒ素捕集率が得られた。特に、処理温度７５℃以上の（２）の方法で処理した高炉徐冷スラグでは、処理液のｐＨが３でもヒ素捕集率が４０％以上と非常に高いものであった。 As shown in Table 2, compared to the blast furnace slow cooling slag (subcritical water treatment slag) treated by the method (1), the blast furnace slow cooling slag (iron salt subcritical water treatment) treated by the method (2) Regardless of the pH of the treatment liquid, a very high arsenic collection rate was obtained when the treatment temperature was 70 ° C. or higher and 200 ° C. or lower. In particular, in the blast furnace slow-cooled slag treated by the method (2) having a treatment temperature of 75 ° C. or higher, the arsenic collection rate was 40% or higher even when the pH of the treatment liquid was 3.
（２）の方法で処理した高炉徐冷スラグの表層を走査電子顕微鏡（ＳＥＭ）を用いて観察したところ、処理温度７５℃及び２００℃の高炉徐冷スラグの表層には水酸化鉄層がスラグ表層に沿って積層して形成されていた。これに対して、処理温度７０℃の高炉徐冷スラグでは、スラグ表層に水酸化鉄が積層している部分と積層していない部分とが共存していることが確認された。以上のことから、ｐＨ緩衝液のｐＨが３以下になるとヒ素捕集率が１０％程度に低下した理由は、緩衝液のｐＨが３以下になると水酸化鉄が溶解するためと推測される。このことから広いｐＨ領域で高いヒ素捕集能を発現するためには、積層した水酸化鉄層の低ｐＨ領域でも水酸化鉄が溶解しないような強固な水酸化鉄層を形成する方が有利になり、その結果、高炉徐冷スラグを７５℃以上の温度で処理したものが特に有効であったと考えられる。 When the surface layer of the blast furnace annealed slag treated by the method (2) was observed using a scanning electron microscope (SEM), an iron hydroxide layer was formed on the surface layer of the blast furnace annealed slag at a treatment temperature of 75 ° C and 200 ° C. It was formed by laminating along the surface layer. On the other hand, in the blast furnace slow-cooled slag having a treatment temperature of 70 ° C., it was confirmed that a portion where iron hydroxide was laminated and a portion where iron hydroxide was not laminated coexisted on the slag surface layer. From the above, it is estimated that the reason why the arsenic collection rate was reduced to about 10% when the pH of the pH buffer solution was 3 or less was that iron hydroxide was dissolved when the pH of the buffer solution was 3 or less. Therefore, in order to express high arsenic collection ability in a wide pH range, it is advantageous to form a strong iron hydroxide layer that does not dissolve iron hydroxide even in the low pH range of the laminated iron hydroxide layer. As a result, it was considered that the blast furnace slow cooling slag treated at a temperature of 75 ° C. or more was particularly effective.
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