JP4373662B2 - Iron oxide particles and method for producing the same - Google Patents
Iron oxide particles and method for producing the same Download PDFInfo
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Description
【0001】
【発明の属する技術分野】
本発明は、マグネタイト粒子及びその製造方法に関し、詳しくはTiとFeの複合酸化鉄を粒子表面に被覆することにより、高流動性、低凝集、高電気抵抗、磁気特性のバランスが取れており、かつ耐酸性に優れ、汚染物質の磁気分離用途等に好適なマグネタイト粒子及びその製造方法に関する。
【0002】
【従来の技術及び発明が解決しようとする課題】
最近、電子複写機、プリンター等の磁性トナー用材料として、水溶液反応による酸化鉄粒子、殊にマグネタイト粒子が広く利用されている。磁性トナーとしては各種の一般的現像特性が要求されるが、近年、電子写真技術の発達により、特にデジタル技術を用いた複写機、プリンターが急速に発達し、要求特性がより高度なものになってきた。
【0003】
すなわち、従来の文字以外にもグラフィックや写真等の出力も要求されており、複写機、プリンターの中には1インチ当たり1200ドット以上の能力のものも現れ、感光体上の潜像はより緻密になってきている。そのため、個々の磁性トナー粒子や磁性キャリア粒子の有する各種特性のバラツキが少ないことが要求される。
【0004】
そのためには、これら粒子中に含有させる酸化鉄粒子が、バインダー中にできるだけ均一に分散していることが重要である。磁性トナー粒子や磁性キャリア粒子は、酸化鉄粒子とバインダーを乾式混合させた後、溶融、混練する工程を経るが、乾式混合時に用いる酸化鉄粒子が凝集し、流動性が不良であると、バインダー中への均一な分散に支障をきたす。この酸化鉄粒子の流動性の重要性については、例えば磁性トナーに関する特許文献1に開示がある。
【0005】
また、現像での細線再現性に優れ、かつ安定した画像を得るための磁性トナーや磁性キャリアを得る上で、酸化鉄粒子に要求される重要な特性としては、高電気抵抗であることが挙げられ、本出願人が先にそのような酸化鉄粒子に関する技術を開示している(特許文献2及び3)。同公報には、酸化鉄粒子の表面を、AlとFe、あるいはSiとFeの複合酸化物層にて被覆する技術が開示されており、同公報に開示の発明によれば、高電気抵抗の酸化鉄粒子が得られる。
【0006】
また、磁気特性のバランスが取れていること、殊に飽和磁化が高めであることも、静電複写用途において、安定した画像を得る上で、酸化鉄粒子に要求される特性として重要である。飽和磁化が高い酸化鉄粒子を用いた磁性キャリアは、二成分系現像の際の磁気ローラー上での安定した磁気ブラシ形成を実現できる。また、飽和磁化が高い酸化鉄粒子を用いた磁性トナーは、磁性トナーによるマグネットロール上での安定したトナー層形成に寄与するため、現像の際のカブリが抑制されるものと考えられる。
【0007】
また、トナー製造の一製法である懸濁重合法を採用した際の液中処理、黒色顔料として使用される際の耐候性、あるいは汚染物質の磁気分離用途として使用される液環境下での耐久性を考慮した場合、耐酸性に優れていることも重要である。
【0008】
上記した要求される各種特性、いわゆる高流動性、低凝集、高電気抵抗、磁気特性のバランス、耐酸性の個々の改善については従来技術での開示はあるものの、何れをも満足させ得る酸化鉄粒子、特にマグネタイト粒子は未だ提供されていない。
【0009】
従って、本発明の目的は、高流動性、低凝集、高電気抵抗、磁気特性のバランスが取れており、かつ耐酸性に優れた汚染物質の磁気分離用マグネタイト粒子及びその製造方法を提供することにある。
【0010】
【特許文献1】
特開平5−71801号公報
【特許文献2】
特開2000−239021号公報
【特許文献3】
特開2000−344527号公報
【0011】
【課題を解決するための手段】
本発明者らは、検討の結果、マグネタイトコア粒子の表面に、TiとFeの複合酸化物を被覆することにより、上記目的が達成し得ることを知見した。
【0012】
本発明は、上記知見に基づきなされたもので、マグネタイトコア粒子の表面がTiとFeの複合酸化鉄層にて被覆されたことを特徴とする汚染物質の磁気分離用マグネタイト粒子を提供するものである。
【0013】
また、本発明のマグネタイト粒子の好ましい製造方法として、本発明は、湿式法にて生成したマグネタイトコア粒子を含むスラリーに、水可溶性チタン塩と第一鉄塩とアルカリの水溶液を添加混合し、pH6〜10、温度60〜98℃にて酸化し、TiとFeの複合酸化鉄を粒子表面に存在させることを特徴とする汚染物質の磁気分離用マグネタイト粒子の製造方法を提供するものである。
【0014】
【発明の実施の形態】
以下、本発明の実施の形態を説明する。
本発明でいう酸化鉄粒子とは、好ましくはマグネタイトを主成分とするものであり、コアとなるマグネタイトを主成分とする酸化鉄粒子にはケイ素、アルミニウム等の各種の有効元素を含有するものも包含される。以下の説明では、酸化鉄粒子としてその代表的なものであるマグネタイト粒子について説明する。また、酸化鉄粒子又はマグネタイト粒子という時には、その内容によって個々の粒子またはその集合のいずれも意味する。
【0015】
本発明のマグネタイト粒子は、その表面にTiとFeの複合酸化鉄が存在する。ここでTiとFeの複合酸化鉄が存在するとは、芯材(コア材)となるマグネタイトコア粒子の表面にTiとFeの複合酸化鉄の微粒子が分散又は被覆している状態をいう。さらに、被覆している状態は、緻密な形成層でも、多量の微粒子による固着や付着による形成層のどちらも意味する。本発明では、マグネタイトコア粒子の表面にTiとFeの複合酸化鉄の微粒子が層状に被覆している状態が最も好ましい。また、ここでいうTiとFeの複合酸化鉄とは、鉄成分がチタン成分存在下で酸化することにより、チタンを取り込む又は結合した酸化鉄をいう。マグネタイトコア粒子は、通常は湿式法で製造されるが、乾式法で製造されたものでもよい。また、このマグネタイトコア粒子中には、上記のように、粒子内部にチタン、ケイ素、アルミニウム等の各種の有効元素を含有していてもよい。
【0016】
マグネタイトコア粒子の表面にTiの中和処理やTi化合物を機械的な処理で固着したようなものは、被覆や被着物のコア粒子への密着性が不十分であったり、疎らであったりして、本発明の目的を十分満足する特性が得られない。
【0017】
また、本発明のマグネタイト粒子においては、複合酸化鉄中のTi成分の存在量が、マグネタイト粒子全体に対してTiに換算して好ましくは0.05〜5重量%、より好ましくは0.5〜4重量%である。Tiの存在量が0.05重量%未満の場合には目的とする効果が少なく、5重量%を超えると、更なる効果の向上が期待できないばかりか、飽和磁化が低くなる等、磁気特性のバランスが崩れるおそれがある。
【0018】
また、本発明のマグネタイト粒子においては、複合酸化鉄を形成するTiとFeのモル比が、好ましくはTi:Fe=1:100〜100:1、さらに好ましくは5:100〜75:25である。TiがFeに対して1/100未満の場合には目的とする効果が少なく、TiがFeに対して100倍を超える場合、磁気特性のバランスの崩れや色相の低下のおそれがある。
【0019】
また、本発明のマグネタイト粒子においては、電気抵抗が1×104Ω・cm以上であると、現像での細線再現性に優れ、かつ安定した画像を得るための磁性トナーや磁性キャリア用途において好ましい。
【0020】
また、本発明のマグネタイト粒子においては、負荷磁場796kA/mにおける飽和磁化が75Am2/kg以上であると、静電複写用途において、安定した画像を得る上で好ましい。
【0021】
また、本発明のマグネタイト粒子においては、凝集度が30以下であることが好ましい。凝集度が30を超えると取り扱い性、樹脂への混合性、トナー製造設備への供給安定性が悪く、ひいてはトナー自身の流動性に影響を及ぼす恐れがある。
【0022】
また、本発明のマグネタイト粒子においては、安息角が40°以下であることが好ましい。安息角が40°より大きい場合、取り扱い性、樹脂への混合性、トナー製造設備への供給安定性が悪く、ひいてはトナー自身の流動性に影響を及ぼすおそれがある。
【0023】
本発明のマグネタイト粒子は、TiとFeの複合酸化鉄を粒子表面に被覆することにより、Ti等の化合物が単体で存在するのではなく、複合酸化鉄中に存在し、しかも粒子表面層に制御されたことにより、Ti化合物が単体で不安定に存在するのではなく、密着性の高い安定した状態で存在することにより、各種特性に優れているものと推測される。
【0024】
また、TiとFeの複合酸化鉄の微粒子の存在により、電気伝導を妨げ、少量のTiの添加にて高抵抗であり、表面の磁気凝集が抑えられたこと等により、目的とする効果が得られたのでないかと推測される。
【0025】
本発明のマグネタイト粒子の好適な製造方法は、湿式法にて生成した酸化鉄粒子を含むスラリーに、水可溶性チタン塩と第一鉄塩とアルカリの水溶液を添加混合し、pH6〜10、温度60〜98℃にて酸化し、TiとFeの複合酸化鉄を粒子表面に存在させるものである。
【0026】
この時に使用されるマグネタイトコア粒子は、その形状が八面体、六面体、球形等であり、何ら限定されるものではない。第一鉄塩としては硫酸第一鉄、塩化第一鉄等が挙げられる。アルカリとしては水酸化ナトリウム、炭酸ナトリウム、水酸化カリウム等が用いられる。
【0027】
この際の溶液のpHは6〜10である。pHが6未満だと、酸化する工程において反応スピードが遅く工業的ではなく、pHが10を超えるとコストがかかり、経済的ではない。また、溶液の温度は60〜98℃であり、温度が60℃未満だとFeOOH等が混在し、色味、飽和磁化、粒子の均一性等の問題点が生じる。温度が98℃超では工業的ではない。酸化する方法としては、酸素を含有するガスを通気すればよく、経済的にも好ましくは空気を使用する。また、液体の酸化剤を使用してもよい。
【0028】
【実施例】
以下、実施例等に基づいて本発明を具体的に説明する。
【0029】
(実施例1)
表1に示すように、Fe2+1.8mol/lを含む硫酸第一鉄水溶液50リットルと、3.6mol/lの水酸化ナトリウム水溶液50リットルを混合撹拌した。このスラリーをpH5〜7、温度85℃を維持しながら30リットル/minの空気を吹き込み反応を終了させた(マグネタイトコア粒子の製造)。
【0030】
上記スラリーに、硫酸チタニル水溶液と硫酸第一鉄水溶液の混合水溶液(pH0.9に調整、Ti4 +2.4mol/l、Fe2+1.3mol/l)10リットルを混合した。このスラリーをpH8〜8.5、温度85℃を維持しながら10リットル/minの空気を吹き込み再度酸化し反応を終了させた(複合酸化鉄被覆の形成)。
【0031】
得られた生成粒子は、通常の濾過洗浄、乾燥、粉砕工程により処理しマグネタイト粒子を得た。また、下記に示す方法にて、各種特性を評価した。結果を表2に示す。
【0032】
(測定方法)
▲1▼Ti含有量分析
サンプルを溶解し、ICPにて測定した。
▲2▼粒子形状と粒径測定
走査型電子顕微鏡を用い、倍率20000倍にて粒子形状観察及び200個の粒子についてフェレ径の測定を行い、平均粒径を求めた。
▲3▼比表面積
島津−マイクロメリティックス製2200型BET計にて測定した。
▲4▼磁気特性
東英工業製振動試料型磁力計VSM−P7を使用し、負荷磁場796kA/mにて測定した。
▲5▼凝集度
Hosokawa Micron製「Powder Tester TypePT−R」(商品名)を用いて、振動時間65secにて測定した。測定結果を所定の計算式にて凝集度を求めた。
▲6▼電気抵抗
試料10gをホルダーに入れ600kg/cm2 の圧力を加えて、25mmφの錠剤型に成形後、電極を取り付け、150kg/cm2 の加圧状態で測定した。測定に使用した試料の厚さ、及び断面積と抵抗値から算出してマグネタイト粒子の電気抵抗値を求めた。
▲7▼安息角
Hosokawa Micron製「Powder Tester TypePT−R」(商品名)を用い、本体付属のマニュアルに従って測定した。
▲8▼耐酸性
pH2.5、60℃の希硝酸水溶液0.6リットルを用意し、試料3gを添加して、pH、温度を維持しながら2時間撹拌した。撹拌後、濾過、洗浄、乾燥した試料の重量を測定し、減量値を元試料重量で除し、百分率を溶出率とした。
【0033】
(実施例2及び3)
表1に示すように、表面の複合酸化鉄層の被覆条件を変えた以外は、実施例1と同様にマグネタイト粒子を製造した。このマグネタイト粒子の製造条件を表1に示す。また、実施例1と同様に各種性状及び特性を評価した結果を表2に示す。
【0034】
(比較例1)
表1に示すように、マグネタイトコア粒子の製造の際に、硫酸チタニルを添加した硫酸第一鉄水溶液を用い、マグネタイト粒子を製造した。このマグネタイト粒子の製造条件を表1に示す。また、実施例1と同様に各種性状及び特性を評価した結果を表2に示す。
【0035】
(比較例2)
表1に示すように、硫酸第一鉄水溶液を用いない等、表面の複合酸化鉄層の被覆条件を変えた以外は、実施例1と同様にマグネタイト粒子を製造した。このマグネタイト粒子の製造条件を表1に示す。また、実施例1と同様に各種性状及び特性を評価した結果を表2に示す。
【0036】
【表1】
【0037】
【表2】
【0038】
表2からも明らかなように、実施例1〜3のマグネタイト粒子は、流動性に優れ、低凝集(低凝集度、小安息角)、高電気抵抗、磁気特性のバランスが取れており、かつ耐酸性(溶出度少)に優れている。
【0039】
これに対し、比較例1は、Tiがマグネタイト粒子中にドープされているため、実施例に比べ、溶出度以外の特性は全て劣るものであった。
【0040】
また、比較例2は、Feを含まないTi化合物で表面処理を行ったものであるが、実施例に比べ、磁気特性は良好であるが、流動性や抵抗、溶出度に劣るものであった。
【0041】
【発明の効果】
以上説明したように、本発明のマグネタイト粒子は、TiとFeの複合酸化鉄をマグネタイトコア粒子表面に被覆することにより、高流動性、低凝集、高電気抵抗、磁気特性のバランスが取れており、かつ耐酸性に優れていることから、汚染物質の磁気分離用途等に好適である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to magnetite particles and a method for producing the same, and in particular, by coating the particle surface with composite iron oxide of Ti and Fe, a balance between high fluidity, low aggregation, high electrical resistance, and magnetic properties is achieved. In addition, the present invention relates to magnetite particles excellent in acid resistance and suitable for use in magnetic separation of pollutants and a method for producing the same.
[0002]
[Prior art and problems to be solved by the invention]
In recent years, iron oxide particles, particularly magnetite particles, produced by an aqueous solution reaction have been widely used as materials for magnetic toners for electronic copying machines and printers. Various general development characteristics are required for magnetic toners, but in recent years, due to the development of electrophotographic technology, especially copiers and printers using digital technology have rapidly developed, and the required characteristics have become more advanced. I came.
[0003]
In other words, in addition to conventional characters, output of graphics, photographs, etc. is also required, and some copiers and printers have a capacity of 1200 dots or more per inch, and the latent image on the photoconductor is more precise. It is becoming. For this reason, it is required that there is little variation in various properties of individual magnetic toner particles and magnetic carrier particles.
[0004]
For that purpose, it is important that the iron oxide particles contained in these particles are dispersed as uniformly as possible in the binder. Magnetic toner particles and magnetic carrier particles are subjected to a process of dry mixing iron oxide particles and a binder, followed by melting and kneading. The iron oxide particles used at the time of dry mixing aggregate and the fluidity is poor. Impairs uniform dispersion inside. The importance of the fluidity of the iron oxide particles is disclosed in, for example, Patent Document 1 relating to magnetic toner.
[0005]
In addition, an important characteristic required for iron oxide particles in obtaining a magnetic toner or a magnetic carrier that is excellent in fine line reproducibility in development and for obtaining a stable image is high electrical resistance. The present applicant has previously disclosed a technique relating to such iron oxide particles (Patent Documents 2 and 3). In this publication, a technique for coating the surface of iron oxide particles with a composite oxide layer of Al and Fe or Si and Fe is disclosed. According to the invention disclosed in the publication, a high electric resistance is disclosed. Iron oxide particles are obtained.
[0006]
In addition, the balance of magnetic properties, particularly the high saturation magnetization, is also important as a property required for iron oxide particles in order to obtain a stable image in electrostatic copying applications. A magnetic carrier using iron oxide particles having high saturation magnetization can realize stable magnetic brush formation on a magnetic roller during two-component development. Further, the magnetic toner using iron oxide particles having a high saturation magnetization contributes to the stable toner layer formation on the magnet roll by the magnetic toner, so that it is considered that fogging during development is suppressed.
[0007]
In addition, liquid processing when using the suspension polymerization method, which is a manufacturing method of toner, weather resistance when used as a black pigment, or durability in a liquid environment used for magnetic separation of contaminants In view of the properties, it is also important that the acid resistance is excellent.
[0008]
Although there are disclosures in the prior art regarding the various required properties described above, so-called high fluidity, low agglomeration, high electrical resistance, balance of magnetic properties, and individual improvements in acid resistance, iron oxide that can satisfy any of them is disclosed. Particles, in particular magnetite particles, have not yet been provided.
[0009]
Accordingly, an object of the present invention is to provide a magnetite particle for magnetic separation of contaminants having a good balance of high fluidity, low aggregation, high electrical resistance, and magnetic properties and excellent in acid resistance, and a method for producing the same. It is in.
[0010]
[Patent Document 1]
JP-A-5-71801 [Patent Document 2]
JP 2000-239021 A [Patent Document 3]
Japanese Patent Laid-Open No. 2000-344527
[Means for Solving the Problems]
As a result of the study, the present inventors have found that the above object can be achieved by coating the surface of the magnetite core particles with a composite oxide of Ti and Fe.
[0012]
The present invention has been made based on the above knowledge, and provides magnetite particles for magnetic separation of contaminants characterized in that the surface of magnetite core particles is coated with a composite iron oxide layer of Ti and Fe. is there.
[0013]
Further, as a preferred method for producing the magnetite particles of the present invention, the present invention comprises adding a water-soluble titanium salt, a ferrous salt, and an alkaline aqueous solution to a slurry containing magnetite core particles produced by a wet method, and adding pH 6 The present invention provides a method for producing magnetite particles for magnetic separation of pollutants , characterized in that the composite iron oxide of Ti and Fe is present on the particle surface by oxidation at a temperature of 10 to 10 ° C. and a temperature of 60 to 98 ° C.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
The iron oxide particles referred to in the present invention are preferably composed mainly of magnetite, and the iron oxide particles mainly composed of magnetite as a core also contain various effective elements such as silicon and aluminum. Is included. In the following description, magnetite particles that are typical examples of iron oxide particles will be described. The term “iron oxide particles” or “magnetite particles” means either individual particles or aggregates depending on the content.
[0015]
The magnetite particles of the present invention have a composite iron oxide of Ti and Fe on the surface. Here, the presence of composite iron oxide of Ti and Fe means a state in which fine particles of composite iron oxide of Ti and Fe are dispersed or coated on the surface of magnetite core particles serving as a core material (core material). Further, the covering state means both a dense formed layer and a formed layer formed by adhering or adhering with a large amount of fine particles. In the present invention, it is most preferable that the surface of the magnetite core particle is coated with fine particles of composite iron oxide of Ti and Fe in a layered manner. Moreover, the composite iron oxide of Ti and Fe here means the iron oxide which took in or couple | bonded titanium, when an iron component oxidizes in titanium presence presence. The magnetite core particles are usually produced by a wet method, but may be produced by a dry method. The magnetite core particles may contain various effective elements such as titanium, silicon, and aluminum inside the particles as described above.
[0016]
The surface of the magnetite core particles with Ti neutralized or Ti compounds fixed by mechanical treatment may have insufficient or poor adhesion to the core particles of the coating or adherend. Therefore, the characteristics that sufficiently satisfy the object of the present invention cannot be obtained.
[0017]
Further, in the magnetite particles of the present invention, the amount of Ti component in the composite iron oxide is preferably 0.05 to 5% by weight, more preferably 0.5 to 5% in terms of Ti with respect to the whole magnetite particles. 4% by weight. When the amount of Ti present is less than 0.05% by weight, the intended effect is small, and when it exceeds 5% by weight, further improvement in the effect cannot be expected, and saturation magnetization is lowered. Balance may be lost.
[0018]
In the magnetite particles of the present invention, the molar ratio of Ti and Fe forming the composite iron oxide is preferably Ti: Fe = 1: 100 to 100: 1, more preferably 5: 100 to 75:25. . When Ti is less than 1/100 of Fe, the intended effect is small, and when Ti exceeds 100 times with respect to Fe, the balance of magnetic properties may be lost or the hue may be lowered.
[0019]
In the magnetite particles of the present invention, if the electric resistance is 1 × 10 4 Ω · cm or more, it is excellent in reproducibility of fine lines in development and preferable for magnetic toners and magnetic carriers for obtaining stable images. .
[0020]
In the magnetite particles of the present invention, it is preferable that the saturation magnetization at a load magnetic field of 796 kA / m is 75 Am 2 / kg or more for obtaining a stable image in electrostatic copying applications.
[0021]
In the magnetite particles of the present invention, the degree of aggregation is preferably 30 or less. When the cohesion degree exceeds 30, the handling property, the mixing property with the resin, and the supply stability to the toner production facility are poor, and as a result, the fluidity of the toner itself may be affected.
[0022]
Moreover, in the magnetite particle | grains of this invention, it is preferable that an angle of repose is 40 degrees or less. When the angle of repose is larger than 40 °, the handling property, the mixing property with the resin, and the supply stability to the toner production facility are poor, and the flowability of the toner itself may be affected.
[0023]
In the magnetite particles of the present invention, the composite iron oxide of Ti and Fe is coated on the particle surface, so that a compound such as Ti does not exist alone but is present in the composite iron oxide and is controlled in the particle surface layer. As a result, it is presumed that the Ti compound is excellent in various properties because it does not exist in an unstable state alone but exists in a stable state with high adhesion.
[0024]
In addition, the presence of fine particles of composite iron oxide of Ti and Fe hinders electrical conduction, high resistance is achieved with the addition of a small amount of Ti, and the intended effect is obtained by suppressing surface magnetic aggregation. It is speculated that it was done.
[0025]
A preferred method for producing the magnetite particles of the present invention is to add a water-soluble titanium salt, a ferrous salt and an aqueous solution of alkali to a slurry containing iron oxide particles produced by a wet method, pH 6 to 10, temperature 60. It is oxidized at ˜98 ° C., and composite iron oxide of Ti and Fe is present on the particle surface.
[0026]
The magnetite core particles used at this time are octahedral, hexahedral, spherical, etc., and are not limited at all. Examples of ferrous salts include ferrous sulfate and ferrous chloride. As the alkali, sodium hydroxide, sodium carbonate, potassium hydroxide or the like is used.
[0027]
The pH of the solution at this time is 6-10. If the pH is less than 6, the reaction speed in the oxidation step is slow and not industrial, and if the pH exceeds 10, it is costly and not economical. Moreover, the temperature of a solution is 60-98 degreeC, and when temperature is less than 60 degreeC, FeOOH etc. will coexist and problems, such as a color tone, saturation magnetization, and the uniformity of particle | grains, will arise. If the temperature exceeds 98 ° C, it is not industrial. As an oxidation method, a gas containing oxygen may be vented, and air is preferably used economically. A liquid oxidant may be used.
[0028]
【Example】
Hereinafter, the present invention will be specifically described based on examples and the like.
[0029]
(Example 1)
As shown in Table 1, 50 liters of a ferrous sulfate aqueous solution containing Fe 2+ 1.8 mol / l and 50 liters of a 3.6 mol / l sodium hydroxide aqueous solution were mixed and stirred. The slurry was blown with 30 liter / min of air while maintaining the pH at 5-7 and the temperature of 85 ° C. to complete the reaction (production of magnetite core particles).
[0030]
To the slurry, 10 liters of a mixed aqueous solution of titanyl sulfate aqueous solution and ferrous sulfate aqueous solution (adjusted to pH 0.9, Ti 4 + 2.4 mol / l, Fe 2+ 1.3 mol / l) was mixed. While maintaining the pH of 8 to 8.5 and the temperature of 85 ° C., 10 l / min of air was blown into the slurry to oxidize again to complete the reaction (formation of composite iron oxide coating).
[0031]
The resulting product particles were processed by ordinary filtration washing, drying, and pulverization processes to obtain magnetite particles. Moreover, various characteristics were evaluated by the method shown below. The results are shown in Table 2.
[0032]
(Measuring method)
(1) A Ti content analysis sample was dissolved and measured by ICP.
(2) Particle shape and particle size measurement Using a scanning electron microscope, the particle shape was observed at a magnification of 20000 and the ferret diameter was measured for 200 particles, and the average particle size was determined.
(3) Specific surface area Measured with a 2200 type BET meter made by Shimadzu-Micromeritics.
{Circle around (4)} Magnetic properties Using a vibrating sample magnetometer VSM-P7 manufactured by Toei Industry Co., Ltd., measurement was performed with a load magnetic field of 796 kA / m.
(5) Aggregation degree Using “Powder Tester Type PT-R” (trade name) manufactured by Hosokawa Micron, the aggregation time was measured at 65 sec. The degree of aggregation was determined from the measurement result using a predetermined calculation formula.
(6) An electric resistance sample (10 g) was put in a holder, and a pressure of 600 kg / cm 2 was applied to form a 25 mmφ tablet mold. Then, an electrode was attached and the measurement was performed under a pressure of 150 kg / cm 2 . The electric resistance value of the magnetite particles was obtained by calculating from the thickness, cross-sectional area and resistance value of the sample used for the measurement.
(7) Angle of repose Measured according to a manual attached to the main body using “Powder Tester Type PT-R” (trade name) manufactured by Hosokawa Micron.
(8) Acid resistant pH 2.5, 0.6 liter of dilute nitric acid aqueous solution at 60 ° C. was prepared, 3 g of sample was added, and the mixture was stirred for 2 hours while maintaining pH and temperature. After stirring, the weight of the filtered, washed and dried sample was measured, the weight loss value was divided by the original sample weight, and the percentage was taken as the elution rate.
[0033]
(Examples 2 and 3)
As shown in Table 1, magnetite particles were produced in the same manner as in Example 1 except that the coating conditions of the composite iron oxide layer on the surface were changed. The production conditions for the magnetite particles are shown in Table 1. Table 2 shows the results of evaluating various properties and characteristics in the same manner as in Example 1.
[0034]
(Comparative Example 1)
As shown in Table 1, magnetite particles were produced using a ferrous sulfate aqueous solution to which titanyl sulfate was added during the production of magnetite core particles. The production conditions for the magnetite particles are shown in Table 1. Table 2 shows the results of evaluating various properties and characteristics in the same manner as in Example 1.
[0035]
(Comparative Example 2)
As shown in Table 1, magnetite particles were produced in the same manner as in Example 1 except that the coating conditions of the composite iron oxide layer on the surface were changed, such as not using a ferrous sulfate aqueous solution. The production conditions for the magnetite particles are shown in Table 1. Table 2 shows the results of evaluating various properties and characteristics in the same manner as in Example 1.
[0036]
[Table 1]
[0037]
[Table 2]
[0038]
As is apparent from Table 2, the magnetite particles of Examples 1 to 3 are excellent in fluidity, have low agglomeration (low agglomeration degree, small angle of repose), high electrical resistance, and balance of magnetic properties, and Excellent acid resistance (low elution).
[0039]
On the other hand, in Comparative Example 1, since Ti was doped in the magnetite particles, all the characteristics other than the elution degree were inferior to those in Examples.
[0040]
In Comparative Example 2, the surface treatment was performed with a Ti compound not containing Fe, but the magnetic properties were better than those of the Examples, but the flowability, resistance, and elution degree were inferior. .
[0041]
【The invention's effect】
As described above, the magnetite particles of the present invention have a balance of high fluidity, low aggregation, high electrical resistance, and magnetic properties by covering the surface of the magnetite core particles with composite iron oxide of Ti and Fe. And excellent in acid resistance, it is suitable for magnetic separation of pollutants.
Claims (8)
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