JP5326475B2 - Method for recovering chromium from chromium-containing slag - Google Patents
Method for recovering chromium from chromium-containing slag Download PDFInfo
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本発明は、酸化クロム含有スラグから金属クロムを回収するための方法に関する。 The present invention relates to a method for recovering metallic chromium from chromium oxide-containing slag.
含クロム鋼の製造プロセスを大別すると次の３つに分けられる。１つ目は、高炉溶銑を用いて、転炉でＦｅ−Ｃｒを投入しながら粗脱炭を行い、ＡＯＤまたはＶＯＤ等で脱炭精錬を行うプロセス。２つ目は、スクラップやＦｅ−Ｃｒ等の合金鉄を主原料として電気炉で溶解し、その後脱炭精錬を行うプロセス。３つ目は、Ｃｒ鉱石を溶融還元しながら粗溶鋼（溶銑）を溶製し、その後脱炭精錬を行うプロセスである。 The manufacturing process of chromium-containing steel can be roughly divided into the following three. The first is a process in which rough decarburization is performed using Fe-Cr in the converter using blast furnace hot metal, and decarburization and refining is performed using AOD or VOD. The second is a process in which scrap iron and alloy iron such as Fe-Cr are melted in an electric furnace as the main raw material and then decarburized and refined. The third is a process in which crude molten steel (molten metal) is melted while melting or reducing Cr ore, followed by decarburization refining.
いずれのプロセスにおいても、酸素を上吹きしながら、転炉やＡＯＤ、ＶＯＤ、真空精錬炉等で脱炭精錬を行うため、炭素の酸化と同時に一定量のクロムの酸化も余儀なくされ、酸化クロムを含有するスラグが生成される。現在は、この有価金属であるクロム分を回収するため、転炉やＡＯＤ、ＶＯＤ等の多量にクロムが酸化するプロセスにおいては、吹止後にＦｅ−Ｓｉ合金を添加して、Ｓｉによって酸化クロムを溶鉄中に還元回収してから出鋼する方法が主流である。 In any process, decarburization and refining is performed in a converter, AOD, VOD, vacuum refining furnace, etc. while blowing oxygen upward, so that a certain amount of chromium must be oxidized simultaneously with the oxidation of carbon. Containing slag is produced. At present, in order to recover chromium, which is a valuable metal, in processes where chromium is oxidized in large quantities such as converters, AOD, VOD, etc., Fe-Si alloy is added after blowing, and chromium oxide is removed by Si. The mainstream method is to recover and recover steel in molten iron and then to produce steel.
こうしたＳｉによる酸化クロムの還元回収においては、従来、高温であるほど平衡Ｃｒ2Ｏ3濃度が高くなるため、低温ほど還元に有利と考えられてきた（非特許文献１）。 In such reduction and recovery of chromium oxide by Si, conventionally, the higher the temperature, the higher the equilibrium Cr 2 O 3 concentration, and thus it has been considered that the lower the temperature, the more advantageous the reduction (Non-patent Document 1).
転炉内で酸化してスラグ中に移行したクロムを回収する方法としては、スラグを転炉内で還元することなく溶融状態のままスラグ用取鍋に取り出した後、電極加熱により溶融状態を保持したまま、電気炉に装入し、溶融金属中に含まれる珪素により還元回収する方法が提案されている（特許文献１）。 As a method of recovering chromium that has been oxidized in the converter and transferred into the slag, the slag is taken out into the slag ladle without being reduced in the converter, and then the molten state is maintained by heating the electrode. As it is, a method of charging in an electric furnace and reducing and recovering with silicon contained in the molten metal has been proposed (Patent Document 1).
また、種々の酸化クロム含有スラグを、処理プロセスの最後に還元することなく排出し、電気炉に装入して、付加的に炭素や珪素を添加し、スラグ中の酸化クロムを炭素と珪素によって電気炉内で還元回収する方法も提案されている（特許文献２）。 In addition, various chromium oxide-containing slag is discharged without reduction at the end of the treatment process, charged into an electric furnace, carbon and silicon are additionally added, and chromium oxide in the slag is added by carbon and silicon. A method of reducing and recovering in an electric furnace has also been proposed (Patent Document 2).
一方で、酸化クロム含有スラグを還元することが目的ではないが、溶解炉での精錬末期に行う還元期の効率向上のために、ＣａＯ源、ＳｉＯ2源、Ａｌ2Ｏ3源を装入して低融点スラグを形成する方法が提案されている（特許文献３）。 On the other hand, although the purpose is not to reduce chromium oxide-containing slag, in order to improve the efficiency of the reduction phase performed at the end of the refining in the melting furnace, a CaO source, a SiO 2 source, and an Al 2 O 3 source are charged. A method of forming a low melting point slag has been proposed (Patent Document 3).
現在主流である転炉やＡＯＤ、ＶＯＤ内でＦｅ−Ｓｉ合金を添加して、酸化クロムを還元回収してから出鋼する方法では、Ｆｅ−Ｓｉ合金が高価であるため、還元処理にコストがかかるという課題が大きい。また、還元処理時に炉内に空気を巻込むため、溶鉄中の窒素濃度が上昇し、加工性等の材質を悪化させるといった課題もあった。 In the current mainstream converter, AOD, and VOD, Fe—Si alloy is added to recover steel after reducing and recovering chromium oxide, and the Fe—Si alloy is expensive. This is a big problem. In addition, since air is entrained in the furnace during the reduction treatment, there is a problem that the nitrogen concentration in the molten iron increases and the material such as workability deteriorates.
還元処理を施さずに排出して電気炉内で還元回収処理を行う上記特許文献１や特許文献２の方法では、電気炉工程の後で脱炭精錬が施され、脱炭中に脱窒が進行するため、溶鉄の窒素濃度増加の課題は解決される。しかしながら、特許文献１の方法では、スラグを溶融状態に保持するための電極加熱に多大なコストがかかり、特許文献２の方法においては、電気炉内でスラグが固相状態のままではクロムの還元速度が極めて遅く、精錬が長時間に亘ること、スラグの溶解を促進して還元速度を増加するためには、環境問題から規制されているＦを含有する蛍石を使用せざるを得ないこと、という課題が生じていた。
In the methods of
また、特許文献３の方法においては、攪拌力が元々弱い電気炉内で、高濃度の酸化クロムを含むスラグを電気炉に装入した上で還元してクロム分を回収するには十分でなく、還元効率が低いという課題が生じていた。電気炉操業の場合、通常は底吹きガスによる攪拌がないため、スラグが殆ど攪拌されない。底吹きガスによる攪拌がある場合でも、電気炉操業では、メタル浴表面の面積に対して浴の深さが低い、いわゆるシャローバスであり、下記（３）式で定義される攪拌動力密度εが工業的に実用化されているレベルでは高々０．１ｋＷ／ｔ程度であり、複数の底吹き羽口を使用して、ガスが浴表面を突き抜ける限界まで吹き込んでも０．５〜１ｋＷ／ｔが限界であろうと推定され、通常の転炉の攪拌動力密度１〜５ｋＷ／ｔには遠く及ばない。
ε＝0.371ＱＴl／Ｗ×{ln(１＋9.8ρlｈ／Ｐa)＋η(１−Ｔn／Ｔl)} （ｋＷ／ｔ）（３）
ここで、Ｑ：底吹きガス流量（Ｎｍ3／ｓ）、Ｔl：溶鋼温度（Ｋ）、Ｔn：吹き込みガス温度（Ｋ）、ρl：溶鋼密度（ｋｇ／ｍ3）、ｈ：浴深（ｍ）、Ｐa：雰囲気圧力（Ｐａ）、η：温度膨張項の寄与度（＝０．０６）である。
Further, in the method of Patent Document 3, it is not sufficient to recover chromium by reducing slag containing high-concentration chromium oxide in an electric furnace in an electric furnace with originally weak stirring power. The problem of low reduction efficiency has arisen. In the case of electric furnace operation, since there is usually no stirring by the bottom blowing gas, the slag is hardly stirred. Even in the presence of stirring by bottom blowing gas, the electric furnace operation is a so-called shallow bath in which the bath depth is lower than the surface area of the metal bath, and the stirring power density ε defined by the following equation (3) is At the level that is practically used industrially, it is at most about 0.1 kW / t, and even if a plurality of bottom blowing tuyere is used and the gas is blown to the limit that penetrates the bath surface, 0.5 to 1 kW / t is the limit. It is estimated that this would be far from the stirring power density of 1-5 kW / t of a normal converter.
ε = 0.371 QT 1 /W×{ln(1+9.8ρ 1 h / P a ) + η (1−T n / T 1 )} (kW / t) (3)
Where, Q: bottom blowing gas flow rate (Nm 3 / s), T l : molten steel temperature (K), T n : blowing gas temperature (K), ρ l : molten steel density (kg / m 3 ), h: bath Depth (m), P a : Atmospheric pressure (Pa), η: Contribution of temperature expansion term (= 0.06).
また、非特許文献１では平衡Ｃｒ2Ｏ3濃度から低温ほどクロム還元に有利であるとしており、特許文献３でも１２５０〜１４００℃という比較的低い温度範囲での操業について述べられているが、上述のような実機の攪拌力では工業的に実施可能な処理時間内で反応を平衡に到達させることは困難であり、むしろ低温であるほどスラグの粘性が上昇するため反応速度が低下し処理効率が悪化する、という課題があった。
本発明は、酸化クロムを高濃度で含有するスラグでも、上記のように攪拌力の弱い電気炉内で低濃度まで効率良くクロムの還元処理を行うと同時に、付加的に添加するフラックスに蛍石等のＦ含有物を用いないことによってスラグの資源化を可能にし、安価にクロムを回収する方法を提供することを課題とする。 In the present invention, even when slag containing a high concentration of chromium oxide is used, the reduction treatment of chromium is efficiently performed to a low concentration in an electric furnace having a weak stirring force as described above, and at the same time, fluorite is added to the flux to be additionally added. It is an object of the present invention to provide a method for recovering chromium at a low cost by making it possible to recycle slag by not using such F-containing materials.
かかる課題を解決するため、本発明の要旨とするところは、以下の通りである。
（１）酸化クロムを５質量％以上含むスラグを電気炉に添加して、溶鉄中あるいは付加的に添加される合金に含まれる珪素と炭素によりスラグ中の酸化クロムを還元してクロムを溶鉄中に還元回収する方法において、還元処理後の溶鉄温度が１５００℃以上であって、かつ、還元処理後の溶鉄中の炭素濃度（質量％）と珪素濃度（質量％）が式（１）を満たすように炭素源と珪素源を添加し、還元処理後のスラグ中ＣａＯ濃度（質量％）とＳｉＯ2濃度（質量％）とＡｌ2Ｏ3濃度（質量％）の関係が下記（２）式を満たすように、アルミナ源や生石灰および／または石灰石を添加することを特徴とするクロム含有スラグからのクロム回収方法。
Ｃ≧−29.4＋0.015×（Ｔ＋273）−0.003×（Ｔ＋273）×logＳｉ （１）
１．８≧ＣａＯ／（ＳｉＯ2＋Ａｌ2Ｏ3）≧０．８ （２）
ここで、Ｃ、Ｓｉはそれぞれ還元処理後の溶鉄中の炭素、珪素濃度（質量％）、ＣａＯ、ＳｉＯ2、Ａｌ2Ｏ3は還元処理後のスラグ中のＣａＯ、ＳｉＯ2、Ａｌ2Ｏ3濃度（質量％）、Ｔは還元処理後の溶鉄温度（℃）を意味する。
（２）還元処理後のスラグ中Ａｌ2Ｏ3濃度が５質量％以上３０質量％以下となるようにアルミナ源を添加し、実質的にフッ素を使用しないことを特徴とする、上記（１）記載のクロム含有スラグからのクロム回収方法。
（３）電気炉操業時の攪拌動力密度が０．０１ｋＷ／ｔ以上１ｋＷ／ｔ以下であることを特徴とする、上記（１）又は（２）記載のクロム含有スラグからのクロム回収方法。
（４）還元処理後の溶鉄中Ｃｒ濃度（質量％）が２０％以上６０％以下であることを特徴とする、上記（１）、（２）又は（３）記載のクロム含有スラグからのクロム回収方法。
In order to solve this problem, the gist of the present invention is as follows.
(1) Add slag containing 5% by mass or more of chromium oxide to the electric furnace, reduce chromium oxide in the slag with silicon and carbon contained in the molten iron or additionally added alloy, and add chromium in the molten iron In the method of reducing and recovering, the molten iron temperature after the reduction treatment is 1500 ° C. or more, and the carbon concentration (mass%) and the silicon concentration (mass%) in the molten iron after the reduction treatment satisfy the formula (1). Thus, the relationship between the CaO concentration (% by mass), the SiO 2 concentration (% by mass) and the Al 2 O 3 concentration (% by mass) in the slag after the reduction treatment is added by the following formula (2): A method for recovering chromium from chromium-containing slag, characterized by adding an alumina source and quicklime and / or limestone so as to satisfy.
C ≧ −29.4 + 0.015 × (T + 273) −0.003 × (T + 273) × logSi (1)
1.8 ≧ CaO / (SiO 2 + Al 2 O 3 ) ≧ 0.8 (2)
Here, C, carbon in the molten iron after Si each reduction treatment, the silicon concentration (mass%), CaO, SiO 2, Al 2 O 3 is CaO in the slag after reduction treatment, SiO 2, Al 2 O 3 The concentration (% by mass) and T mean the molten iron temperature (° C.) after the reduction treatment.
(2) The above (1), wherein the alumina source is added so that the Al 2 O 3 concentration in the slag after the reduction treatment is 5% by mass or more and 30% by mass or less, and substantially no fluorine is used. A method for recovering chromium from the chromium-containing slag as described.
(3) The method for recovering chromium from the chromium-containing slag as described in (1) or (2) above, wherein the stirring power density during operation of the electric furnace is 0.01 kW / t or more and 1 kW / t or less.
(4) Cr from the chromium-containing slag as described in (1), (2) or (3) above, wherein the Cr concentration (mass%) in the molten iron after the reduction treatment is 20% or more and 60% or less Collection method.
なお、還元処理後スラグに含まれる金属Ａｌは、Ａｌ2Ｏ3に換算して上記（２）式のＡｌ2Ｏ3に含まれる。 The metal Al contained in the slag after the reduction treatment is contained in Al 2 O 3 of the above formula (2) in terms of Al 2 O 3 .
本発明により、酸化クロムを高濃度で含有するスラグでも、攪拌力の弱い電気炉内で低濃度まで効率良くクロムの還元処理を行うと同時に、付加的に添加するフラックスに蛍石等のＦ含有物を用いないことによってスラグの資源化を可能にし、安価にクロムを回収することが可能となった。 According to the present invention, even in a slag containing a high concentration of chromium oxide, chromium is efficiently reduced to a low concentration in an electric furnace having a weak stirring force, and at the same time, F is added to the flux to be additionally added. By not using materials, slag can be recycled and chromium can be recovered at low cost.
以下、本発明の詳細と好ましい実施形態について説明する。 Hereinafter, details and preferred embodiments of the present invention will be described.
電気炉に、スクラップやＦｅ−Ｃｒ合金鉄等の鉄やクロムの原料、必要に応じて、種湯となる溶銑や、炭材、付加的に添加されるＳｉ含有合金等の副原料を装入し、アーク加熱により電気炉溶解する際に、酸化クロムを含有するスラグを添加する。添加方法としては、溶解開始前の前装入でも溶解中の上方添加でも良い。 Raw materials for iron and chromium such as scrap and Fe-Cr alloy iron are added to the electric furnace, and hot metal used as seed hot water, charcoal, and additional materials such as Si-containing alloys that are added as needed. Then, when the electric furnace is melted by arc heating, slag containing chromium oxide is added. As an addition method, pre-charging before the start of dissolution or upward addition during dissolution may be used.
添加されたスラグに含まれる酸化クロムは、溶鉄中や添加された原料、副原料中の珪素や炭素が溶鉄中に溶け込み、下記（４）式のように溶鉄中Ｓｉにより還元され、溶鉄中に回収される。
２Ｃｒ2Ｏ3＋３Ｓｉ→４Ｃｒ＋３ＳｉＯ2 （４）
ここで、Ｓｉ、Ｃｒはそれぞれ溶鉄中の珪素、クロム成分、ＳｉＯ2、Ｃｒ2Ｏ3はスラグ中のＳｉＯ2、Ｃｒ2Ｏ3成分を意味する。
Chromium oxide contained in the added slag is dissolved in the molten iron, silicon and carbon in the added raw material and auxiliary materials, and is reduced by Si in the molten iron as shown in the following formula (4). Collected.
2Cr 2 O 3 + 3Si → 4Cr + 3SiO 2 (4)
Here, Si and Cr mean silicon and chromium components in the molten iron, and SiO 2 and Cr 2 O 3 mean SiO 2 and Cr 2 O 3 components in the slag, respectively.
本発明者らは、１トンの溶鉄を溶製できる試験電気炉を用いて、以下に示すクロムを含有する溶鉄上での転炉未還元スラグの還元処理実験を行い、熱力学計算による検討を行った。その結果、酸化クロムの還元が十分進行するために必要な炭素濃度と珪素濃度を特定した。 The present inventors conducted a reduction treatment experiment of unreduced converter slag on molten iron containing chromium shown below using a test electric furnace capable of producing 1 ton of molten iron, and studied by thermodynamic calculation. went. As a result, the carbon concentration and the silicon concentration necessary for the reduction of chromium oxide to proceed sufficiently were specified.
実験では溶解後の溶鉄成分がＣｒ濃度２０〜４０質量％、炭素濃度０．１〜４．５質量％、珪素濃度０．０５〜０．６５質量％となるように、スクラップ、Ｆｅ−Ｃｒ合金、炭材を配合した。これらの材料を黒鉛電極からのアーク加熱により溶解する際に、Ｃｒ2Ｏ3濃度３０〜４０質量％の転炉未還元スラグを生成溶鉄１トンに対して１４０ｋｇ添加し、通電開始から４０分の還元処理を行った。実験中の溶鉄温度は１５００〜１７００℃とした。還元処理後のスラグ組成は、ＣａＯ濃度３０〜５０質量％、ＳｉＯ2濃度２０〜４０質量％、Ａｌ2Ｏ3濃度５〜２０質量％であり、ＣａＯ／（ＳｉＯ2＋Ａｌ2Ｏ3）は１．０以上１．５以下であった。なお、還元条件の良否判定としては、還元処理後のＣｒ2Ｏ3濃度が１０質量％以下の場合を良、１０質量％超の場合を不良とした。 In the experiment, scrap, Fe-Cr alloy were prepared so that the molten iron component after melting was 20 to 40% by mass of Cr, 0.1 to 4.5% by mass of carbon, and 0.05 to 0.65% by mass of silicon. The charcoal was blended. When these materials are melted by arc heating from a graphite electrode, 140 kg of unreduced converter slag having a Cr 2 O 3 concentration of 30 to 40% by mass is added to 1 ton of molten iron, and 40 minutes from the start of energization. Reduction treatment was performed. The molten iron temperature during the experiment was 1500-1700 ° C. The slag composition after the reduction treatment is CaO concentration 30-50% by mass, SiO 2 concentration 20-40% by mass, Al 2 O 3 concentration 5-20% by mass, and CaO / (SiO 2 + Al 2 O 3 ) is 1. 0.0 or more and 1.5 or less. As the quality determination of the reducing conditions, the case where Cr 2 O 3 concentration after reduction treatment is 10 wt% or less good and bad in the case of 10 mass percent.
図１（ａ）に溶鉄温度１６００℃での実験結果を、図１（ｂ）に溶鉄温度１５００℃での結果を示す。このように、溶鉄中珪素濃度を増加させることで還元反応が促進されると同時に、同一珪素濃度において炭素濃度を増加させることで還元反応が促進されることを見出した。これは酸化クロムの還元反応が、メタル側の平衡論的特性により支配されることによる。すなわち（４）式に示される溶鉄中珪素による酸化クロム還元に際して、溶鉄中炭素が溶鉄中クロムの活量係数を減少、または溶鉄中珪素の活量係数を上昇させる効果があるためと考えられる。ここで、クロムの活量＝クロムの活量係数×クロム濃度、クロムの活量係数は溶鋼中珪素や溶鋼中炭素の関数、と前提をおいている。さらに、図１（ａ）と図１（ｂ）とを対比すると、溶鉄温度が低いほど、還元が良好に行われる珪素と炭素の成分領域が広がることが明らかである。 FIG. 1A shows the experimental results at a molten iron temperature of 1600 ° C., and FIG. 1B shows the results at a molten iron temperature of 1500 ° C. Thus, it has been found that the reduction reaction is promoted by increasing the silicon concentration in molten iron, and at the same time the reduction reaction is promoted by increasing the carbon concentration at the same silicon concentration. This is because the reduction reaction of chromium oxide is governed by the equilibrium properties on the metal side. That is, it is considered that, in the reduction of chromium oxide by silicon in molten iron represented by the formula (4), carbon in molten iron has an effect of decreasing the activity coefficient of chromium in molten iron or increasing the activity coefficient of silicon in molten iron. Here, it is assumed that the activity of chromium = the activity coefficient of chromium × the chromium concentration and the activity coefficient of chromium are functions of silicon in molten steel and carbon in molten steel. Further, when FIG. 1A is compared with FIG. 1B, it is clear that the lower the molten iron temperature, the wider the component region of silicon and carbon where the reduction is performed better.
次に、上記実験結果をもとに熱力学的に検討することを試みた。以下の説明で、ｘ（たとえばＳｉ、Ｃ）は成分ｘの含有量（質量％）、ａxは成分ｘの活量、ｆxは成分ｘの活量係数、ｅx yは成分ｘの活量係数に対する成分ｙの影響を表す相互作用助係数、Ｔ'は絶対温度である。 Next, an attempt was made to study thermodynamically based on the above experimental results. In the following description, x (e.g. Si, C) the content of component x (mass%), the activity of a x component x, utilization of f x activity coefficient of component x, e x y component x An interaction assistant coefficient T ′ representing the influence of the component y on the quantity coefficient is an absolute temperature.
上記（４）式の反応が還元方向に進むとき、
ΔＧ0≦ＲＴ'ln(ａSi・ａCr2O3／ａCr・ａSiO2)＝2.303ＲＴ'log(ａSi・ａCr2O3／ａCr・ａSiO2) （５−１）
と表現できる。この式の左辺について一般的に、
ΔＧ0＝ｃ1＋ｃ2・Ｔ' （ｃ1、ｃ2は定数） （５−２）
と表すことができる。また右辺についてたとえばメタル成分Ｓｉの活量ａSi、メタル成分Ｃｒの活量ａCrは、
logａSi＝log(ｆSi・Ｓｉ)＝logｆSi＋logＳｉ
logａCr＝log(ｆCr・Ｃｒ)＝logｆCr＋logＣｒ （５−３）
と記載することができる。ここで上記図１に示す実験結果から、溶鉄中炭素が溶鉄中クロムの活量係数を減少、または溶鉄中珪素の活量係数を上昇させる効果があると考えられるので、
ｆSi＝ｅSi C・Ｃ、 ｆCr＝ｅCr C・Ｃ （５−４）
と表現することができる。この結果、
logａSi＝ｅSi C・Ｃ＋logＳｉ
logａCr＝ｅCr C・Ｃ＋logＣｒ （５−５）
が得られる。また、相互作用助係数ｅSi C、ｅCr Cは、操業温度の範囲内では温度Ｔ'に反比例する。
When the reaction of the above formula (4) proceeds in the reduction direction,
ΔG 0 ≦ RT'ln (a Si · a Cr2O3 / a Cr · a SiO2) = 2.303RT'log (a Si · a Cr2O3 / a Cr · a SiO2) (5-1)
Can be expressed. In general for the left side of this equation,
ΔG 0 = c 1 + c 2 · T ′ (c 1 and c 2 are constants) (5-2)
It can be expressed as. For the right side, for example, the activity a Si of the metal component Si and the activity a Cr of the metal component Cr are:
loga Si = log (f Si · Si) = logf Si + logSi
loga Cr = log (f Cr · Cr) = log f Cr + log Cr (5-3)
Can be described. From the experimental results shown in FIG. 1 above, it is considered that carbon in molten iron has an effect of decreasing the activity coefficient of chromium in molten iron or increasing the activity coefficient of silicon in molten iron.
f Si = e Si C · C, f Cr = e Cr C · C (5-4)
It can be expressed as As a result,
loga Si = e Si C・ C + logSi
loga Cr = e Cr C · C + logCr (5-5)
Is obtained. Further, the interaction assistant coefficients e Si C and e Cr C are inversely proportional to the temperature T ′ within the operating temperature range.
一方、スラグ成分の活量については、本発明が対象とするスラグ組成の範囲内では、平衡到達Ｃｒへの影響は軽微であり、無視することができた。 On the other hand, regarding the activity of the slag component, the influence on the equilibrium reached Cr was negligible within the range of the slag composition targeted by the present invention, and could be ignored.
以上より、（５−１）式に（５−２）式、（５−５）式を代入し、ａCr2O3、ａSiO2を無視し、ｅSi C、ｅCr Cは温度Ｔ'に反比例するとの仮定をおくことにより、
ΔＧ0／2.303ＲＴ'≦logａSi−logａCr
＝（ｅSi C−ｅCr C）・Ｃ＋logＳｉ−logＣｒ
＝ｃ3・Ｃ／Ｔ'＋logＳｉ−logＣｒ （ｃ3は定数）
が得られる。これから、Ｃｒ還元を進行させるためのメタル成分と温度との関係については、
Ｃ≧ｃ4＋ｃ5・Ｔ'＋ｃ6・Ｔ' (logＳｉ−logＣｒ) （ｃ4、ｃ5、ｃ6は定数）
といった式の形となることが予想された。
From the above, (5-1) formula (5-2) below, by substituting (5-5) equation, ignoring a Cr2O3, a SiO2, e Si C, e Cr C is the inversely proportional to the temperature T ' By making the assumption
ΔG 0 /2.303RT'≦loga Si -loga Cr
= (E Si C -e Cr C ) · C + logSi-logCr
= C 3 · C / T ′ + log Si−log Cr (c 3 is a constant)
Is obtained. From now on, regarding the relationship between the metal component and the temperature for advancing Cr reduction,
C ≧ c 4 + c 5 · T ′ + c 6 · T ′ (logSi−logCr) (c 4 , c 5 and c 6 are constants)
It was expected to take the form of
そこで、図１（ａ）、（ｂ）の実績と合致するように定数ｃ4、ｃ5、ｃ6を定めたところ、下記（１）式を得ることができた。なお、メタル成分Ｃｒの影響については軽微であり、無視することができた。この（１）式は、酸化クロムの還元反応が十分進行するために必要な溶鉄中炭素濃度と溶鉄温度の関係を意味している。なお、温度Ｔ'は絶対温度、温度Ｔは摂氏温度を意味する。
Ｃ≧−29.4＋0.015×（Ｔ＋273）−0.003×（Ｔ＋273）×logＳｉ （１）
ここで、Ｃ、Ｓｉはそれぞれ還元処理後の溶鉄中の炭素、珪素濃度（質量％）、Ｔは還元処理後の溶鉄温度（℃）を意味する。
Therefore, when constants c 4 , c 5 , and c 6 were determined so as to match the results of FIGS. 1A and 1B, the following expression (1) could be obtained. The influence of the metal component Cr was negligible and could be ignored. This equation (1) means the relationship between the concentration of carbon in molten iron and the temperature of molten iron necessary for the reduction reaction of chromium oxide to proceed sufficiently. The temperature T ′ means an absolute temperature, and the temperature T means a Celsius temperature.
C ≧ −29.4 + 0.015 × (T + 273) −0.003 × (T + 273) × logSi (1)
Here, C and Si respectively represent carbon and silicon concentration (mass%) in the molten iron after the reduction treatment, and T means the molten iron temperature (° C.) after the reduction treatment.
上述のとおり、（１）式は、（４）式に示される反応式の平衡関係式をもとに、溶鉄中珪素による酸化クロム還元に際して溶鉄中炭素が溶鉄中クロムの活量係数を減少、または溶鉄中珪素の活量係数を上昇させる効果を加味したものであり、係数は実験測定値を元に決定した。なお、本発明の範囲内では溶鉄中Ｃｒ濃度による酸化クロム還元結果（クロムの活量の増加）に対する影響は小さく、またスラグ成分についても必要な溶鉄中炭素濃度に与える影響は小さいことが実験により明らかとなったため、これらの項を（１）式に含める必要はなかった。 As described above, the formula (1) is based on the equilibrium relational expression of the reaction formula shown in the formula (4), and the carbon in the molten iron reduces the activity coefficient of chromium in the molten iron when chromium oxide is reduced by silicon in the molten iron. Alternatively, the effect of increasing the activity coefficient of silicon in molten iron is taken into account, and the coefficient is determined based on experimental measurement values. Within the scope of the present invention, the effect of Cr concentration in molten iron on chromium oxide reduction results (increase in chromium activity) is small, and the effect of slag components on the necessary carbon concentration in molten iron is also small by experiment. Since it became clear, it was not necessary to include these terms in equation (1).
（１）式で規定される酸化クロムを還元するために適正な範囲は、図１の実線以上の範囲で示される。溶鉄中炭素濃度、珪素濃度を（１）式に従って設定することで、スラグ中酸化クロムが適切に還元されることがわかる。また、図２に示すように、必要な溶鉄中Ｃ濃度を決定する際には溶鉄温度も考慮する必要がある。 An appropriate range for reducing chromium oxide defined by the formula (1) is shown in a range beyond the solid line in FIG. It can be seen that the chromium oxide in the slag is appropriately reduced by setting the carbon concentration and silicon concentration in the molten iron according to the formula (1). In addition, as shown in FIG. 2, the molten iron temperature needs to be taken into consideration when determining the necessary molten iron C concentration.
上記（１）式の条件は、Ｃｒ還元が進行するための平衡論的な条件である。さらに、適正な時間内において還元を進行させるためには、速度論的に十分な速度で還元反応が進行することが必要である。即ち、平衡論的条件である（１）式と、速度論的な好適条件をともに満たしていることが必要である。 The condition of the above formula (1) is an equilibrium condition for the Cr reduction to proceed. Furthermore, in order to proceed the reduction within an appropriate time, it is necessary that the reduction reaction proceeds at a kinetically sufficient rate. That is, it is necessary to satisfy both the equation (1) which is an equilibrium condition and a favorable kinetic condition.
本発明者らは、酸化クロムを含有するスラグの種々の還元実験を行い、スラグに蛍石等のＦ含有物を添加しない場合には、還元処理後の溶鉄温度を１６００℃以上の高温にしてもスラグの溶解が進行せず、スラグ中酸化クロムの充分な還元速度が得られないため、還元処理後のスラグ中Ｃｒ2Ｏ3濃度を１０質量％以下にできないことを知見した。 The present inventors conducted various reduction experiments on slag containing chromium oxide, and when no F-containing material such as fluorite was added to the slag, the molten iron temperature after the reduction treatment was set to a high temperature of 1600 ° C. or higher. Furthermore, it was found that the dissolution of slag does not proceed and a sufficient reduction rate of chromium oxide in the slag cannot be obtained, so that the Cr 2 O 3 concentration in the slag after the reduction treatment cannot be reduced to 10% by mass or less.
即ち、本発明者らは、攪拌力の弱い電気炉内で高濃度の酸化クロムを含むスラグを還元してクロム分を回収する場合には還元速度や還元効率が低下する場合があること、スラグの攪拌が弱い場合にはスラグの粘度がクロムの還元速度や還元効率に大きな影響を及ぼすこと、塩基性成分であるＣａＯを含む生石灰や石灰石を添加することでスラグの粘度を低下でき、還元速度や還元効率を向上できることを初めて知見した。そこで、スラグの溶解促進と同時に粘度も低下させて、より酸化クロムの還元速度を向上する方法を詳細に調査した。 That is, the present inventors have found that reduction of slag containing high concentration of chromium oxide in an electric furnace with weak stirring force and recovery of chromium content may reduce the reduction rate and reduction efficiency, When the stirring of the slag is weak, the viscosity of the slag has a great influence on the reduction rate and efficiency of chromium, and the addition of quick lime and limestone containing CaO, which is a basic component, can reduce the viscosity of the slag, and the reduction rate For the first time that it can improve the reduction efficiency. Therefore, a method for further improving the reduction rate of chromium oxide by reducing the viscosity at the same time as promoting the dissolution of slag was investigated in detail.
スラグの粘度は、スラグの塩基度すなわち塩基性成分であるＣａＯ濃度（質量％）と酸性成分であるＳｉＯ2濃度（質量％）とＡｌ2Ｏ3濃度（質量％）の和との比ＣａＯ／（ＳｉＯ2＋Ａｌ2Ｏ3）が増加するに伴い低下できる。図３に、実験で得られた還元処理後のスラグ塩基度とスラグ中Ｃｒ2Ｏ3濃度の関係を示すが、ＣａＯ／（ＳｉＯ2＋Ａｌ2Ｏ3）≧０．８、好ましくはＣａＯ／（ＳｉＯ2＋Ａｌ2Ｏ3）≧１．０とすることで、還元処理後のスラグ中Ｃｒ2Ｏ3濃度を１０質量％未満まで、特に溶鉄温度を１６００℃とした場合には５質量％未満まで還元できることを知見した。 The viscosity of the slag is the ratio of the basicity of the slag, that is, the CaO concentration (% by mass) which is a basic component, and the sum of the SiO 2 concentration (% by mass) and the Al 2 O 3 concentration (% by mass), which are acidic components. It can be lowered as (SiO 2 + Al 2 O 3 ) increases. FIG. 3 shows the relationship between the slag basicity after reduction treatment obtained in the experiment and the Cr 2 O 3 concentration in the slag. CaO / (SiO 2 + Al 2 O 3 ) ≧ 0.8, preferably CaO / ( By making SiO 2 + Al 2 O 3 ) ≧ 1.0, the Cr 2 O 3 concentration in the slag after the reduction treatment is less than 10% by mass, especially when the molten iron temperature is 1600 ° C., to less than 5% by mass. It was found that it can be reduced.
一方、ＣａＯ／（ＳｉＯ2＋Ａｌ2Ｏ3）が１．８超となった場合には、スラグの融点が著しく増加してスラグの溶解が阻害され、クロムの還元速度が大きく低下することも知見した。よって、クロムの還元速度を確保するためにはＣａＯ／（ＳｉＯ2＋Ａｌ2Ｏ3）≦１．８、好ましくはＣａＯ／（ＳｉＯ2＋Ａｌ2Ｏ3）≦１．６、更に好ましくはＣａＯ／（ＳｉＯ2＋Ａｌ2Ｏ3）≦１．４とすることが望ましい。 On the other hand, it is also found that when CaO / (SiO 2 + Al 2 O 3 ) exceeds 1.8, the melting point of slag is remarkably increased to inhibit dissolution of slag, and the reduction rate of chromium is greatly reduced. did. Therefore, in order to ensure the reduction rate of chromium, CaO / (SiO 2 + Al 2 O 3 ) ≦ 1.8, preferably CaO / (SiO 2 + Al 2 O 3 ) ≦ 1.6, more preferably CaO / ( It is desirable that SiO 2 + Al 2 O 3 ) ≦ 1.4.
したがって、本発明では、アルミナ源の添加と併せて、電気炉での溶解開始前もしくは溶解中の上方投入により、生石灰および／または石灰石を添加することで、還元処理後のＣａＯ／（ＳｉＯ2＋Ａｌ2Ｏ3）が下記（２）式の範囲になるように制御することが必要である。
１．８≧ＣａＯ／（ＳｉＯ2＋Ａｌ2Ｏ3）≧０．８ （２）
Therefore, in the present invention, by adding quick lime and / or limestone before starting melting in the electric furnace or during upward melting in addition to the addition of the alumina source, CaO / (SiO 2 + Al after reduction treatment is added. It is necessary to control so that 2 O 3 ) falls within the range of the following formula (2).
1.8 ≧ CaO / (SiO 2 + Al 2 O 3 ) ≧ 0.8 (2)
生石灰および／または石灰石の添加量を調整して、ＣａＯ／（ＳｉＯ2＋Ａｌ2Ｏ3）を１．０〜１．４の範囲内に制御することが、酸化クロムの還元効率を向上するのに更に望ましい実施の形態である。 Adjusting the amount of quicklime and / or limestone to control CaO / (SiO 2 + Al 2 O 3 ) within the range of 1.0 to 1.4 improves the reduction efficiency of chromium oxide. This is a more desirable embodiment.
また、酸化クロムの還元速度と還元処理後の到達Ｃｒ2Ｏ3濃度は、溶鉄の温度にも依存する。図４に、実験で得られた還元処理後の温度と到達Ｃｒ2Ｏ3濃度の関係を示す。 Further, the reduction rate of chromium oxide and the reached Cr 2 O 3 concentration after the reduction treatment also depend on the temperature of the molten iron. FIG. 4 shows the relationship between the temperature after reduction treatment and the ultimate Cr 2 O 3 concentration obtained in the experiment.
従来、（４）式に示される酸化クロムのＳｉ還元反応については、高温となるほど平衡Ｃｒ2Ｏ3濃度は高くなるため、低温ほど還元に有利と考えられてきた（非特許文献１参照）。平衡論的には、図１に示す実績及びその実績から導いた（１）式からも、クロムの還元が進行するＳｉとＣの成分範囲は、高温になるほど狭まることが明らかである。しかし今回、（１）式を満足するという条件の下で、還元処理後の溶鉄温度が１５００℃でも１０質量％未満まではＣｒ2Ｏ3濃度を低減でき、クロム回収効果を享受できるが、１６００℃以上とすることで、５質量％未満と更に低濃度の領域まで効率良く酸化クロムが還元可能となることを知見した。これは、本発明で想定される操業範囲では反応は平衡まで到達し難く、むしろ高温であることがスラグの粘性を低下させ、還元反応に有利に寄与するためである。したがって、還元処理後の溶鉄温度を１５００℃以上とすることが望ましい実施の形態であり、好ましくは溶鉄温度を１５５０℃以上、更に好ましくは１６００℃以上とすると更に望ましい。 Conventionally, the Si reduction reaction of chromium oxide represented by the formula (4) has been considered to be advantageous for reduction at lower temperatures because the equilibrium Cr 2 O 3 concentration increases as the temperature increases (see Non-Patent Document 1). In equilibrium, it is clear from the results shown in FIG. 1 and the formula (1) derived from the results that the component range of Si and C in which the reduction of chromium progresses becomes narrower as the temperature increases. However, under the condition that the expression (1) is satisfied, the Cr 2 O 3 concentration can be reduced to less than 10% by mass even when the molten iron temperature after the reduction treatment is 1500 ° C., and the chromium recovery effect can be enjoyed. It has been found that chromium oxide can be efficiently reduced to a lower concentration region of less than 5 mass% by setting the temperature to higher than or equal to 5 ° C. This is because the reaction hardly reaches equilibrium in the operating range assumed in the present invention, but rather the high temperature lowers the viscosity of the slag and contributes advantageously to the reduction reaction. Therefore, it is desirable to set the molten iron temperature after the reduction treatment to 1500 ° C. or higher, preferably 1550 ° C. or higher, more preferably 1600 ° C. or higher.
ここで、アルミナ源の添加については、還元処理後のスラグ中Ａｌ2Ｏ3濃度を５質量％以上となるようにアルミナ源の添加量を調整すると、スラグの融点が下がり、酸化クロムの還元速度向上において望ましい。スラグ中Ａｌ2Ｏ3濃度が１０質量％以上であれば更に望ましい。しかしながら、Ａｌ2Ｏ3濃度が３０質量％超では、もはやスラグの溶解促進による酸化クロムの還元速度の向上効果は小さく、アルミナ源の副材コストがかかるだけでクロム回収の経済効果がないことも知見した。よって、スラグ中Ａｌ2Ｏ3濃度は３０質量％以下であることが望ましい。 Here, regarding the addition of the alumina source, when the addition amount of the alumina source is adjusted so that the Al 2 O 3 concentration in the slag after the reduction treatment is 5% by mass or more, the melting point of the slag is lowered, and the reduction rate of chromium oxide Desirable in improvement. It is more desirable if the Al 2 O 3 concentration in the slag is 10% by mass or more. However, when the Al 2 O 3 concentration exceeds 30% by mass, the effect of improving the reduction rate of chromium oxide by promoting the dissolution of slag is small, and the cost of recovering chromium may not be obtained only by the cost of the secondary material of the alumina source. I found out. Therefore, the Al 2 O 3 concentration in the slag is desirably 30% by mass or less.
以上のとおり、電気炉での溶解開始前もしくは溶解中の上方投入により、アルミナ源を添加することで、スラグの融点が下がり、酸化クロムの還元速度が向上する。一般に、スラグ中のＡｌ2Ｏ3濃度を増加させることでスラグの融点が低下して溶解が促進される一方でスラグの粘度も増加する。これに対し本発明では、前述のとおり（２）式を満たすように生石灰および／または石灰石を添加しており、これによってスラグの粘度が低下している。従って、スラグのＡｌ2Ｏ3濃度を増加しても粘度増加の悪影響は発生しない。 As described above, by adding the alumina source before starting the melting in the electric furnace or during the melting, the melting point of the slag is lowered and the reduction rate of the chromium oxide is improved. In general, increasing the Al 2 O 3 concentration in the slag decreases the melting point of the slag and promotes dissolution, while increasing the viscosity of the slag. On the other hand, in the present invention, quick lime and / or limestone is added so as to satisfy the formula (2) as described above, and this reduces the viscosity of the slag. Accordingly, even if the Al 2 O 3 concentration of the slag is increased, the adverse effect of increasing the viscosity does not occur.
本発明ではまた、フッ素を実質的に添加しなくても十分に高いスラグからのクロムの還元回収効率が得られることを特徴としている。実質的に添加しないこととは、脱硫精錬後のスラグからフッ素（Ｆ）の溶出が顕著には認められないことを指すもので、本発明者らの知見では精錬後のスラグ組成においてＦが０．５質量％以下となる場合を指す。Ｆが０．３質量％以下であれば更に好ましい。 The present invention is also characterized in that sufficiently high reduction and recovery efficiency of chromium from slag can be obtained without substantially adding fluorine. The fact that it is not substantially added means that the elution of fluorine (F) is not recognized remarkably from the slag after desulfurization refining. According to the knowledge of the present inventors, F is 0 in the slag composition after refining. .5% by mass or less. More preferably, F is 0.3% by mass or less.
本発明において、電気炉操業時に底吹きガスによる溶湯の攪拌を行うと好ましい。この際の底吹きガスによる攪拌動力密度に好適範囲がある。電気炉で底吹きガスによって溶湯の攪拌を行うに際し、攪拌動力密度εは下記（３）式で表される。
ε＝0.371ＱＴl／Ｗ×{ln(１＋9.8ρlｈ／Ｐa)＋η(１−Ｔn／Ｔl)} （３）
ここで、ε：攪拌動力密度（ｋＷ／ｔ）、Ｑ：底吹きガス流量（Ｎｍ3／ｓ）、Ｔl：溶鋼温度（Ｋ）、Ｔn：吹き込みガス温度（Ｋ）、ρl：溶鋼密度（ｋｇ／ｍ3）、ｈ：浴深（ｍ）、Ｐa：雰囲気圧力（Ｐａ）、η：温度膨張項の寄与度（＝０．０６）である。
In the present invention, it is preferable to stir the molten metal with a bottom blowing gas during operation of the electric furnace. At this time, there is a preferred range for the stirring power density by the bottom blowing gas. When the molten metal is stirred by the bottom blowing gas in the electric furnace, the stirring power density ε is expressed by the following equation (3).
ε = 0.371QT 1 /W×{ln(1+9.8ρ 1 h / P a ) + η (1−T n / T 1 )} (3)
Here, ε: stirring power density (kW / t), Q: bottom blowing gas flow rate (Nm 3 / s), T l : molten steel temperature (K), T n : blowing gas temperature (K), ρ l : molten steel Density (kg / m 3 ), h: bath depth (m), P a : atmospheric pressure (Pa), η: contribution of temperature expansion term (= 0.06).
電気炉操業時の攪拌動力密度εが低すぎると攪拌の効果が十分には得られないが、攪拌動力密度εが０．０１ｋＷ／ｔ以上であれば、底吹きガスによる攪拌の効果でスラグ中の酸化クロムの還元を促進することができる。一方、攪拌動力密度εが高すぎると底吹きガスが浴表面を突き抜けて攪拌の意味をなさなかったり、揺動浴面と電極間の距離が変動し、投入電力が不安定になる。しかし、攪拌動力密度εが１ｋＷ／ｔ以下であればこのような問題が発生することがない。 If the stirring power density ε during operation of the electric furnace is too low, the effect of stirring cannot be sufficiently obtained. However, if the stirring power density ε is 0.01 kW / t or more, the effect of stirring by the bottom blowing gas causes slag Can reduce the reduction of chromium oxide. On the other hand, if the stirring power density ε is too high, the bottom blowing gas penetrates the bath surface and does not make any sense of stirring, or the distance between the rocking bath surface and the electrode fluctuates, and the input power becomes unstable. However, if the stirring power density ε is 1 kW / t or less, such a problem does not occur.
また、溶鉄中Ｃｒ濃度の影響ついても検討した。溶鉄中Ｃｒ濃度が低いほど、（４）式に示される酸化クロムの還元反応が起こりやすくなるため、スラグ中Ｃｒ2Ｏ3濃度の低減に有利である。図５に、実験で得られた還元処理後の溶鉄中Ｃｒ濃度［％Ｃｒ］（質量％）と到達Ｃｒ2Ｏ3濃度（％Ｃｒ2Ｏ3）（質量％）の関係を示すが、溶鉄中Ｃｒ濃度を６０質量％以下、好ましくは５０質量％以下とすることで、還元処理後のスラグ中Ｃｒ2Ｏ3濃度を１０質量％未満まで還元できることを知見した。なお、還元反応は平衡まで達していないため、Ｃｒ濃度６０質量％以下であればＣｒ濃度に関係なく、酸化クロムは十分に還元されていた。 The influence of Cr concentration in molten iron was also examined. As the Cr concentration in the molten iron is lower, the reduction reaction of chromium oxide represented by the formula (4) is more likely to occur, which is advantageous in reducing the Cr 2 O 3 concentration in the slag. FIG. 5 shows the relationship between the Cr concentration [% Cr] (% by mass) in the molten iron after the reduction treatment obtained in the experiment and the ultimate Cr 2 O 3 concentration (% Cr 2 O 3 ) (% by mass). It was found that the Cr 2 O 3 concentration in the slag after the reduction treatment can be reduced to less than 10% by mass by setting the intermediate Cr concentration to 60% by mass or less, preferably 50% by mass or less. Since the reduction reaction did not reach equilibrium, the chromium oxide was sufficiently reduced regardless of the Cr concentration when the Cr concentration was 60% by mass or less.
一方、溶鉄中Ｃｒ濃度がより高い条件で、到達Ｃｒ2Ｏ3濃度をより低くまで還元できれば、効率良く還元プロセスが進行したこととなり経済的に有利である。そこで、還元処理後の溶鉄中Ｃｒ濃度に対する到達Ｃｒ2Ｏ3濃度の比を指標として図６に示すが、Ｃｒ濃度２０質量％未満では還元後の到達Ｃｒ2Ｏ3濃度が同等である事から、溶鉄中Ｃｒ濃度を２０質量％以上とすることで、Ｃｒ濃度２０質量％未満の場合よりも効率的にＣｒ2Ｏ3の還元を進められることがわかる。よって、還元処理後の溶鉄中Ｃｒ濃度を２０質量％以上とすることが望ましい。 On the other hand, if the ultimate Cr 2 O 3 concentration can be reduced to a lower level under a condition where the Cr concentration in the molten iron is higher, the reduction process has proceeded efficiently, which is economically advantageous. Therefore, the ratio of the reached Cr 2 O 3 concentration to the Cr concentration in the molten iron after the reduction treatment is shown in FIG. 6 as an index. However, when the Cr concentration is less than 20% by mass, the reached Cr 2 O 3 concentration after the reduction is equivalent. , by the Cr concentration in molten iron and 20% by mass or more, it can be seen that proceed the reduction of efficiently Cr 2 O 3 than in the case of less than Cr concentration of 20 mass%. Therefore, it is desirable that the Cr concentration in the molten iron after the reduction treatment is 20% by mass or more.
１トンの溶鉄を溶製できる試験電気炉を用いて、以下に示す転炉未還元スラグの還元処理を行った。還元処理条件を表１に示す。 Using a test electric furnace capable of producing 1 ton of molten iron, the reduction treatment of the unreduced converter slag shown below was performed. Table 1 shows the reduction treatment conditions.
溶解後の溶鉄成分がＣｒ濃度１０〜７０質量％、炭素濃度０．１〜４．５質量％、珪素濃度０．４〜０．５質量％となるように配合したスクラップ、Ｆｅ−Ｃｒ合金、炭材を黒鉛電極からのアーク加熱により溶解する際に、Ｃｒ2Ｏ3濃度３０〜４０質量％の転炉未還元スラグを生成溶鉄１トンに対して１４０ｋｇ添加し、通電開始から４０分の還元処理を行った。溶鉄温度を１４０５〜１６８８℃の範囲で調整した。 Scrap, Fe-Cr alloy blended so that the molten iron component after melting has a Cr concentration of 10 to 70 mass%, a carbon concentration of 0.1 to 4.5 mass%, and a silicon concentration of 0.4 to 0.5 mass%, When melting a carbonaceous material by arc heating from a graphite electrode, 140 kg of unreduced converter slag having a Cr 2 O 3 concentration of 30 to 40% by mass is added to 1 ton of molten iron, and reduction is performed for 40 minutes from the start of energization. Processed. The molten iron temperature was adjusted in the range of 1405 to 1688 ° C.
アルミナ源を添加するに際してはアルミ灰を通電開始前に添加し、石灰源を添加するに際しては溶解中に上方ホッパーより生石灰を添加した。溶湯の攪拌を行うために底吹きＡｒガスを吹き込み、攪拌動力密度を（３）式に基づいて算出した。底吹きガスを吹き込まない水準については攪拌動力密度を「０」と表示した。表１の本発明例５についてはホタル石を添加し、それ以外の水準についてはホタル石を添加しなかった。 When adding the alumina source, aluminum ash was added before the start of energization, and when adding the lime source, quick lime was added from the upper hopper during melting. In order to stir the molten metal, bottom-blown Ar gas was blown, and the stirring power density was calculated based on the equation (3). The stirring power density was indicated as “0” for the level at which the bottom blowing gas was not blown. Fluorite was added for Invention Example 5 in Table 1, and fluorite was not added for other levels.
還元処理の結果を表１に示す。還元処理後の電気炉の耐火物損耗状況を目視で評価し、スラグ接触面の凹みが確認されなければ「○」と評価し、凹みの存在が確認できれば「×」と評価した。 The results of the reduction treatment are shown in Table 1. The refractory wear situation of the electric furnace after the reduction treatment was visually evaluated. If no dent of the slag contact surface was confirmed, it was evaluated as “◯”, and if the presence of the dent was confirmed, it was evaluated as “x”.
本発明例１〜１２においては全て還元処理後のＣｒ2Ｏ3濃度が１０質量％未満まで酸化クロムの還元が進行していることがわかる。特に、還元処理後のスラグ中Ａｌ2Ｏ3濃度を５〜３０質量％の好適範囲とし、攪拌動力密度を０．０１ｋＷ／ｔ以上の好適範囲とし、溶解後の溶鉄中クロム濃度を６０％以下の好適範囲とした本発明例１、２、７〜１１については、Ｃｒ2Ｏ3濃度が５質量％未満となっており、低濃度域まで効率良く酸化クロムの還元回収ができていることがわかる。 In Examples 1 to 12 of the present invention, it can be seen that the reduction of chromium oxide proceeds until the Cr 2 O 3 concentration after the reduction treatment is less than 10% by mass. In particular, the Al 2 O 3 concentration in the slag after the reduction treatment is in a preferred range of 5 to 30% by mass, the stirring power density is in a preferred range of 0.01 kW / t or more, and the chromium concentration in the molten iron after melting is 60% or less. In the present invention examples 1, 2 , and 7 to 11 in the preferred range, the Cr 2 O 3 concentration is less than 5% by mass, and the reduction and recovery of chromium oxide can be efficiently performed up to a low concentration range. Recognize.
本発明例３はスラグ中Ａｌ2Ｏ3濃度が好適範囲を上限に外れ、本発明例５はホタル石を用いたためにスラグ中ＣａＦ2濃度が高く、いずれも還元処理後のＣｒ2Ｏ3濃度は１０質量％以下を実現したものの、耐火物評価が「×」であった。 In Invention Example 3, the Al 2 O 3 concentration in the slag deviates from the preferred range, and in Example 5 of the present invention, fluorite was used, so the CaF 2 concentration in the slag was high, both of which were Cr 2 O 3 concentration after reduction treatment. Was 10% by mass or less, but the refractory evaluation was “x”.
一方、比較例１３は溶鉄温度が低く、比較例１４、１５は（２）式の範囲を外れ、比較例１６、１７は溶鉄温度が低いとともに（２）式の範囲を外れ、比較例１８は溶鉄温度が低いとともに攪拌動力密度が好適範囲を外れ、比較例１９は（１）式の範囲を外れ、いずれも還元後Ｃｒ2Ｏ3濃度が１０質量％を超えていた。比較例１５、１７は（２）式の下限を外れていたため、耐火物評価も「×」であった。 On the other hand, Comparative Example 13 has a low molten iron temperature, Comparative Examples 14 and 15 are out of the range of Equation (2), Comparative Examples 16 and 17 are out of the range of Equation (2) with a low molten iron temperature, and Comparative Example 18 is While the molten iron temperature was low and the stirring power density was out of the preferred range, Comparative Example 19 was out of the range of the formula (1), and in all cases, the Cr 2 O 3 concentration after reduction exceeded 10 mass%. Since Comparative Examples 15 and 17 deviated from the lower limit of the expression (2), the refractory evaluation was also “x”.
Claims (4)
Ｃ≧−29.4＋0.015×（Ｔ＋273）−0.003×（Ｔ＋273）×logＳｉ （１）
１．８≧ＣａＯ／（ＳｉＯ2＋Ａｌ2Ｏ3）≧０．８ （２）
ここで、Ｃ、Ｓｉはそれぞれ還元処理後の溶鉄中の炭素、珪素濃度（質量％）、ＣａＯ、ＳｉＯ2、Ａｌ2Ｏ3は還元処理後のスラグ中のＣａＯ、ＳｉＯ2、Ａｌ2Ｏ3濃度（質量％）、Ｔは還元処理後の溶鉄温度（℃）を意味する。 Add slag containing 5% by mass or more of chromium oxide to the electric furnace, reduce chromium oxide in the molten iron by reducing the chromium oxide in the slag with silicon and carbon contained in the molten iron or additionally added alloy. In such a method, the molten iron temperature after the reduction treatment is 1500 ° C. or more, and the carbon concentration (mass%) and the silicon concentration (mass%) in the molten iron after the reduction treatment satisfy the formula (1). Source and silicon source are added so that the relationship between the CaO concentration (% by mass), the SiO 2 concentration (% by mass) and the Al 2 O 3 concentration (% by mass) in the slag after the reduction treatment satisfies the following formula (2) A method for recovering chromium from chromium-containing slag, comprising adding one or both of an alumina source and quick lime and / or limestone.
C ≧ −29.4 + 0.015 × (T + 273) −0.003 × (T + 273) × logSi (1)
1.8 ≧ CaO / (SiO 2 + Al 2 O 3 ) ≧ 0.8 (2)
Here, C, carbon in the molten iron after Si each reduction treatment, the silicon concentration (mass%), CaO, SiO 2, Al 2 O 3 is CaO in the slag after reduction treatment, SiO 2, Al 2 O 3 The concentration (% by mass) and T mean the molten iron temperature (° C.) after the reduction treatment.
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