JP3845893B2

JP3845893B2 - Metal iron manufacturing method

Info

Publication number: JP3845893B2
Application number: JP05980196A
Authority: JP
Inventors: 卓也根上; 和扶国井; 勲小林; 俊秀松村; 芳通竹中; 正賢清水; 晉一稲葉
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 1996-03-15
Filing date: 1996-03-15
Publication date: 2006-11-15
Anticipated expiration: 2016-03-15
Also published as: ZA972125B; JPH09256017A

Description

【０００１】
【発明の属する技術分野】
本発明は、鉄鉱石等の酸化鉄を炭材等の炭素質還元剤と共に加熱還元して金属鉄を得る方法の改良に技術に関し、より詳しくは、鉄鉱石等の酸化鉄を炭材などの炭素質還元剤と共に加熱還元して金属鉄を得る際に、酸化鉄を金属鉄にまで効率よく還元すると共に、鉄鉱石などの酸化鉄源中に脈石成分等として混入してくるスラグ成分をうまく溶融分離し、高純度の金属鉄を効率よく製造することのできる方法に関するものである。
【０００２】
【従来の技術】
鉄鉱石や酸化鉄ペレット等の酸化鉄を炭材や還元性ガスにより直接還元して還元鉄を得る直接製鉄法としては、従来よりミドレックス法に代表されるシャフト炉法が知られている。この種の直接製鉄法は、天然ガス等から製造される還元ガスをシャフト炉下部の羽口より吹き込み、その還元力を利用し酸化鉄を還元して還元鉄を得る方法である。また最近では、天然ガスに代わる還元剤として石炭等の炭材を使用する還元鉄製造プロセスが注目されており、具体的には、鉄鉱石等の焼成ペレットを石炭粉と共にロータリーキルンで加熱還元する、所謂ＳＬ／ＲＮ法がすでに実用化されている。
【０００３】
また他の還元鉄製造法として米国特許第３，４４３，９３１号公報には、炭材と粉状酸化鉄を混合して塊状化し、ロータリーハース上で加熱還元して還元鉄を製造するプロセスが開示されている。このプロセスは、粉鉱石と粉炭を混合して塊状化し、これを高温雰囲気下で加熱還元するものである。
【０００４】
これらの方法で製造された還元鉄は、そのまま或はブリケット状等に成形してから電気炉へ装入し、鉄源として用いられる。近年、鉄スクラップのリサイクルが活発化するにつれて、上記方法によって得られる還元鉄はスクラップ中に混入してくる不純物元素の希釈材として注目されている。
【０００５】
ところが従来の還元製鉄法によって得られる還元鉄には、原料として用いた酸化鉄（鉄鉱石など）や炭材（石炭など）に含まれるＳｉＯ₂ 、Ａｌ₂ Ｏ₃ 、ＣａＯ等のスラグ成分がそのまま混入してくるため、製品の鉄品位（金属鉄としての純度）は低くなる。実用に当たっては、次の精錬工程でこれらのスラグ成分は分離除去されるが、スラグ量の増加は精錬溶湯の歩留りを低下させるばかりでなく電気炉の操業コストにも大きな影響を及ぼすので、鉄品位が高くスラグ成分含有量の少ない還元鉄が求められているが、前述の如き従来の還元鉄の製法でこうした要求に応えるには、還元鉄製造原料として鉄品位の高い鉄鉱石を使用しなければならず、実用可能な製鉄原料の選択の幅を大幅に狭めることになる。
【０００６】
更に上記の様な従来法は、還元された固体製品を中間製品として得ることを最終の目的としており、実用化に当たっては、次の工程となる精練工程へ送るまでに搬送、貯蔵、ブリケット化あるいは冷却といった工程が必要であり、この間に大きなエネルギー損失が生じたり、ブリケット化のための余分のエネルギーや特殊な装置が必要になるといった欠点がある。
【０００７】
他方、酸化鉄を直接還元して還元鉄を得る方法としてＤＩＯＳ法等の溶融還元法も知られている。この方法は、酸化鉄を予め鉄純度で３０〜５０％程度にまで予備還元しておき、その後、鉄浴中で炭素との直接還元反応させることによって金属鉄にまで還元を行う方法であるが、この方法は予備還元と鉄浴中での最終還元の２工程が必須になるため作業が煩雑であるばかりでなくで、鉄浴中に存在する溶融酸化鉄（ＦｅＯ）と耐火物が直接接触するため、耐火物の損耗が激しいという問題も指摘される。
【０００８】
【発明が解決しようとする課題】
上記の様に、スラグ成分含有量の少ない金属鉄を製造する方法の実現は、製品金属鉄としての付加価値を高めるばかりでなく、電気炉を用いた製鉄コストの低減、更には金属鉄製造における使用原料の選択の柔軟性という観点から極めて重要になってくる。
【０００９】
本発明はこうした状況に着目してなされたものであって、その目的は、鉄成分含有量の高い酸化鉄はもとより鉄成分含有量の比較的低い鉄鉱石等からでも、耐火物の溶損などを生じることなく鉄純度の極めて高い金属鉄を、固形金属鉄もしくは溶融金属鉄として簡単な処理で効率よく得ることのできる方法を提供しようとするものである。
【００１０】
上記課題を解決することのできた本発明に係る金属鉄の製法とは、炭素質還元剤が存在する酸化鉄の成形物を加熱還元して金属鉄を製造する方法において、
▲１▼加熱還元により金属鉄外皮を生成且つ成長させ、内部に酸化鉄が実質的に存在しなくなるまで還元を進めると共に、内部に生成スラグの凝集物を形成し、
▲２▼加熱還元により金属鉄外皮を生成且つ成長させ、内部に酸化鉄が実質的に存在しなくなるまで還元を進め、更に加熱を続けて内部に生成するスラグを金属鉄外皮の外側へ流出させ、
▲３▼加熱還元により金属鉄外皮を生成且つ成長させ、内部に酸化鉄が実質的に存在しなくなるまで還元を進め、更に加熱を続けて金属鉄とスラグを溶融分離し、あるいは
▲４▼加熱還元により金属鉄外皮を生成且つ成長させ、内部に酸化鉄が実質的に存在しなくなるまで還元を進めると共に、内部に生成スラグの凝集物を形成させ、次いで生成スラグを金属鉄から分離する
ところに特徴を有している。
本発明をより具体的な製法として示すならば、
炭素質還元剤が存在する酸化鉄の成形物を加熱還元して金属鉄を製造する方法において、炭素質還元剤が存在する酸化鉄の成形物を加熱還元炉に装入し、加熱還元により金属鉄外皮を生成且つ成長させ、内部に酸化鉄が実質的に存在しなくなるまで還元を進めると共に、内部に生成スラグの凝集物を形成させ、更に加熱を続けて金属鉄外皮の一部を溶融させて内部に生成するスラグを外側へ流出させ、
あるいは、金属鉄外皮全部を溶融させて金属鉄とスラグを凝集させることにより、溶融状態で生成するスラグを金属鉄から分離し、若しくは
前記還元工程およびその後の工程で、金属鉄を固形状態に保ち、生成スラグのみを溶融させて両者を分離し、あるいは
炭素質還元剤が存在する酸化鉄の成形物を加熱還元して金属鉄を製造する方法において、原料酸化鉄粉粒体を炭素質還元剤粉末およびバインダーと共に混合し、次いで任意の形状に成形してから加熱還元炉内へ装入し、加熱還元を行なうことにより金属鉄外皮を生成且つ成長させ、内部に酸化鉄が実質的に存在しなくなるまで還元を進めると共に、内部にスラグ成分を溶融状態で凝集させ、溶融状態で生成するスラグを金属鉄から分離して金属鉄を得、或いは更にこれを冷却凝固させて金属鉄を得る方法が本発明に包含される。
【００１１】
上記方法を実施するに当たっては、金属鉄外皮の一部もしくは全部を溶融させることによって、内部の溶融スラグを金属鉄外皮外へ流出させればよい。この際、金属鉄外皮の一部もしくは全部を溶融させるには、還元反応の終了後さらに加熱温度を高めることによって行ない、或いは還元温度でそのまま加熱を続けることによって行なえばよい。このとき、金属外皮内に存在する炭素質還元剤による浸炭を進めて当該金属外皮の融点を降下させれば、金属鉄外皮の加熱溶融を一層容易に行なうことができるので好ましい。また、上記還元工程およびその後の工程で、金属鉄を固形状態に保ち、生成スラグのみを溶融させて分離することも可能である。
【００１２】
また上記本発明の製法を実施するに当たっては、加熱還元工程の最高加熱温度を、生成スラグの融点以上で且つ生成する金属鉄外皮の融点以下の温度に制御することによって、金属鉄生成反応をより効率よく進めることができ、この還元工程では、固相還元により酸化鉄を低減し、更に液相還元によりＦｅＯを主体とする酸化鉄が実質的に存在しなくなるまで還元すれば、得られる金属鉄の品位をより効率よく高めることが可能となる。そして本発明によれば、高品位の金属鉄を粒状物として容易に得ることも可能となる。
【００１３】
尚上記本発明において、「金属鉄外皮内部に酸化鉄が実質的に存在しなくなるまで還元を進める」ことの好ましい定量的基準としては、加熱還元工程で、「ＦｅＯを主体とする酸化鉄の含有率が５重量％以下、より好ましくは２重量％以下となるまで還元を進めること」が好ましく、また別の観点からすると、本発明によって金属鉄から分離される生成スラグ中のＦｅＯを主体とする酸化鉄の含有量が、５重量％以下、より好ましくは２重量％以下となるまで還元を進めることが望ましい。
【００１４】
上記方法によって得られる高純度の金属鉄および生成スラグは、加熱溶融して比重差により分離し、あるいは冷却凝固させてから破砕し磁選などによって高純度の金属鉄のみを選別回収すれば、金属化率で９５％程度以上、更には９８％以上といった非常に高純度の金属鉄を得ることが可能となる。
【００１５】
【発明の実施の形態】
上記の様に本発明では、第１の特徴点として、石炭等の炭素質還元剤と鉄鉱石等の酸化鉄の粉粒体を粒状、ペレット状など任意の形状に形成した成形物を加熱還元する際に、加熱還元により金属鉄外皮を生成且つ成長させ、内部に酸化鉄が実質的に存在しなくなるまで還元を進める点が挙げられる。
【００１６】
即ち本発明者らは、高炉を用いた製鉄法に代表される間接製鉄法や前記ＳＬ／ＲＮ法等に代表される直接製鉄法に代わる新たな金属鉄の製造技術の開発を期して種々研究を進めるうち、上記の様に、炭素質還元剤と酸化鉄の粉粒体を粒状、ペレット状など任意の形状に成形し、これを非酸化性雰囲気下で加熱すると、次の様な現象が起こることをつきとめた。即ち該成形物を加熱すると、該成形物中に含まれる炭素質還元剤によって酸化鉄が還元されて金属鉄が生成するが、当該還元は上記成形物の外周側から進行し、加熱還元の初期過程で生成する金属鉄が成形物の表面で拡散接合して上記成形物の外周側に金属鉄外皮を形成する。そしてその後、当該外皮内で炭素質還元剤による酸化鉄の還元が効率よく進行し、内部に残存する酸化鉄は、その後極く短時間のうちに実質的に酸化鉄が存在しなくなるまで速やかに還元され、生成する金属鉄は前記外皮の内面側に逐次付着して成長し、一方、鉄鉱石等の酸化鉄源中に含まれる脈石成分に由来して、あるいは炭素質還元剤に含まれる灰分に由来して副生するスラグの大部分は、該金属鉄外皮内に凝集（集合）し、外皮を構成する高純度の金属鉄とその内部に凝集するスラグとに効率よく分離することをつきとめた。
【００１７】
この還元時に生じる現象は、後述する実施例で実際の写真を示して説明するが、次の様な経緯を辿っていると考えられる。即ち図１は、本発明を実施する際に生じている現象を概念的に示す断面模式図であり、例えば図１（Ａ）に示す様な形状の、炭素質還元剤と酸化鉄の混合物よりなる成形物１を、非酸化性雰囲気中で例えば１４５０〜１５００℃程度に加熱すると、該成形物１の外側から炭素質還元剤による酸化鉄の還元が進み、生成する金属鉄は相互に拡散接合して金属鉄外皮１ａを形成する［図１（Ｂ）］。その後更に加熱を続けると、図１（Ｃ）に示す如く外皮１ａ内の酸化鉄は、内部に存在する炭素質還元剤による還元作用、更には当該炭素質還元剤と酸化鉄との反応によって生成するＣＯによる還元作用によって速やかに還元され、生成する金属鉄Ｆｅは上記外皮１Ａの内面側へ逐次付着して成長すると共に、前記脈石成分等に由来して副生するスラグＳｇの大部分は相互に付着・成長しつつ、図１（Ｄ）に示す如く上記外皮１ａ内に形成される空洞内で集合していく。
【００１８】
この間に生じる加熱還元反応は下記式に示す通りであり、
ＦｅＯ_X ＋ｘＣ→Ｆｅ＋ｘＣＯ（１）
ＦｅＯ_X ＋（ｘ／２）Ｃ→Ｆｅ＋（ｘ／２）ＣＯ₂ （２）
Ｙ＝ｙ₁ ＋ｙ₂ （３）
但し、Ｙ：還元に必要な炭素の化学等量（ｍｏｌ）
ｙ₁ ：（１）式の反応に必要な炭素量（ｍｏｌ）
ｙ₂ ：（２）式の反応に必要な炭素量（ｍｏｌ）
成形物を製造する際の酸化鉄に対する炭素質還元剤の配合量が、上記（３）式で示される理論当量以上となる様に両者の配合比率を調整することによって、加熱還元反応を効率よく進めることが可能となる。
【００１９】
この様に本発明では、加熱還元の初期過程で成形物外周側に金属鉄外皮１ａを形成し、該外皮１ａで囲まれた内部で更に還元反応を進めることによって、還元効率を飛躍的に高めることができるのである。更に好ましくは、加熱還元の最高到達温度を、生成する金属鉄外皮１ａの溶融温度未満で且つ生成するスラグの溶融温度以上に設定する。該最高到達温度が金属外皮１ａの溶融温度以上になると、生成する金属鉄は直ちに溶融して相互に融着し、前述の様な金属鉄外皮１ａが形成されなくなり、その後の還元反応が効率よく進行しなくなる。また内部の未還元の酸化鉄が溶融して流出すると、耐火物が損傷する可能性も高まる。上記最高到達温度が生成スラグの溶融温度以上では、加熱還元に伴って副生するスラグが溶融してスラグ同士の融着・集合が進み、金属鉄同士の拡散接合も促進されて図１（Ｃ），（Ｄ）に示す様な金属鉄外皮１ａの成長とスラグＳｇ分離が進むからである。
【００２０】
上記の様に本発明では、従来の間接製鉄法や直接製鉄法では全く採用されたことのない「金属鉄外皮の形成とその内部での還元反応の効率的進行」を活用して加熱還元反応を飛躍的に高めるところに最大の特徴を有するものであり、金属鉄外皮１ａの形成は成形物中に含まれる炭素質還元剤による還元反応によって進行し、金属鉄外皮１ａの形成後は、外皮１ａ内での炭素質還元剤と生成したＣＯによる還元によって進行するので、加熱還元雰囲気を還元性雰囲気とする必要はなく、例えば窒素ガスの如き非酸化性ガス雰囲気とすればよい点でも、従来法とは顕著な違いを有している。
【００２１】
尚上記の加熱還元反応は、基本的に金属鉄外皮１ａが溶融しない固相還元によって進行するが、前記の説明からも明らかである様に金属鉄外皮１ａ内は炭素質還元剤およびその還元反応によって生成するＣＯの存在によって高度の還元性雰囲気に保たれ、これが還元効率の飛躍的上昇に繋がっているものと考えられるが、内部に生成する金属鉄はこの様な高い還元性の内部雰囲気下で浸炭を受け、次第に融点が低下してくる。そのため、還元反応の末期ないし後半期では原料の一部が溶融し液相還元により酸化鉄の最終還元が進行していることも考えられる。還元温度を低めに設定してやれば、すべてを固相還元によって進めることも可能であるが、還元反応速度は高温になるほど早くなるので、より短時間で還元反応を完結させるうえでは、反応温度を高めに設定する方が有利であり、そうなると、前述の如く還元反応の末期では液相還元によって還元反応が完結する様にする方が望ましいと言える。
【００２２】
尚、上記還元反応が終了したかどうかの簡便な確認法としては、加熱還元雰囲気ガス中のＣＯまたはＣＯ₂ 濃度によって確認する方法が例示される。即ち加熱還元工程では、前述の如く炭素質還元剤自体による還元反応および該還元剤と酸化鉄との反応によって生成するＣＯガスによる還元反応が進行し、酸化鉄の全てが還元された後は、ＣＯおよびＣＯ₂ は生成しなくなるので、還元反応炉内の生成ガスを逐次抜き出し、ＣＯおよびＣＯ₂ ガスが生成しなくなった時点で還元反応が完了したことを知ることができるのである。
【００２３】
但し、実用化に当たってはＣＯやＣＯ₂ ガスが完全に放出されなくなるまで反応を行なはなければならない訳ではなく、本発明者らが確認したところによると、反応炉の空間容積等にもよるが、炉内ガス中のＣＯおよびＣＯ₂ ガス濃度が２体積％程度以下にまで減少した時点で、酸化鉄の９５重量％以上が還元され、同ガス濃度が１体積％程度以下にまで減少した時点では、酸化鉄の９８重量％以上が還元されていることを確認している。
【００２４】
上記図１（Ｄ）に示した状態では、成形物中のＦｅＯを主体とする酸化鉄は実質的に全てが還元されて金属鉄に変化し（通常は、酸化鉄含有率で５重量％以下、実験で確認したところでは２重量％以下、あるいは１重量％以下にまで還元されている）、内部に凝集した溶融スラグＳｇ内に一部溶け込んだＦｅＯを主体とする酸化鉄もその殆んどが還元されている（通常は、スラグ中のＦｅＯを主体とする酸化鉄の含有率で５重量％以下、実験で確認したところでは２重量％以下、あるいは１重量％以下）。従って、この状態で冷却して取り出し、破砕機等によって金属鉄外皮１ａを破砕し、磁選などによって金属鉄のみを選別して取り出せば、凝集したスラグ成分の全てが除去され、高純度の金属鉄を効率よく得ることができる。また、その後同温度に保って更に加熱を続け、あるいは温度を高めて更に加熱を続け、以下に示す様に金属鉄外皮１ａの一部もしくは全部を溶融させて生成スラグと金属鉄を分離する方法を採用することも好ましい。
【００２５】
即ち、前記図１（Ｄ）の状態から、必要により温度を若干高めて更に加熱を続けると、例えば図１（Ｅ）に示す如く金属鉄外皮１ａの一部が溶融し、内部の生成スラグＳｇが外皮１ａ外へ流出するので、その後の分離を一層容易にすることができる。あるいはその後更に加熱を続けると、例えば図１（Ｆ）に示す如く金属鉄外皮の全てが溶融して凝集し、先に溶融して凝集したスラグＳｇと分離する。従って、この様な状態としてから冷却凝固させて取り出し、破砕機などにかけると、脆弱なスラグのみが破砕され金属鉄は塊として残るので、これを適度の篩目のスクリーンに通し或は磁選すると、高純度の金属鉄を簡単に選別することができる。金属鉄と生成スラグの他の分離法としては、前述の如く加熱溶融した金属鉄とスラグを溶融状態のままで比重差によって分離することが勿論可能である。
【００２６】
上記において金属鉄外皮の加熱溶融は、還元反応の終了後更に加熱温度を高めて加熱することによって行なうこともできるが、金属鉄外皮内での還元末期には、前述の如く内部の強い還元性雰囲気により還元鉄が浸炭を受けてその融点はかなり降下してくるので、還元温度でそのまま加熱を続けるだけでも、浸炭の進行に伴う融点降下によって金属鉄外皮を溶融させることも可能である。
【００２７】
上記本発明を実施する際に使用される炭素質還元剤としては、採掘後、粉砕・篩い分け等の処理を加えただけの石炭粉、乾留等の熱処理に付した例えばコークスを粉砕したもの、石油コークス等、その種類の如何は一切問わず、例えば炭素質を含む廃棄物として回収される高炉ダスト等であっても勿論構わない。ただし本発明で使用する炭素質還元剤は、加熱還元反応を効率よく進行させるため炭素含有量が７０重量％以上、より好ましくは８０重量％以上のものを選択し、且つ比表面積を高めるため粒径が２ｍｍ以下、望ましくは１ｍｍ以下の粉状のものを使用することが望ましい。また鉄鉱石等の酸化鉄についても、同様に比表面積を大きくして還元反応効率を高めるため、粒径が２ｍｍ以下、望ましくは１ｍｍ以下の粉状のものを使用するのがよい。
【００２８】
本発明では、これらの炭素質還元剤と酸化鉄を均一に混合し、必要により適当なバインダーを併用して塊状、粒状、ブリケット状、ペレット状、棒状など任意の形状に成形して前述の加熱還元に供されるが、このとき配合される炭素質還元剤の量は、併用される酸化鉄中の酸素量に応じて、前記式（１）〜（３）で示した様に還元反応に必要な化学量論量以上、好ましくは金属鉄外皮の融点降下に必要な浸炭量も加味してやや過剰量配合するのが良い。
【００２９】
また、加熱還元時の最高到達温度を生成スラグの融点以上で且つ金属鉄外皮の融点以下にすることが望ましいことは先に述べた通りであるが、生成スラグの温度は使用する鉄鉱石等の酸化鉄源中に含まれる脈石成分や酸化鉄の混入等によって変わり、また還元鉄外皮の融点も浸炭量によってかなり変わってくるので、上記最高到達温度を絶対値として規定することは必ずしも適当とは言えない。しかしながら、標準的な好適還元温度としては１４００〜１５４０℃、より好ましくは１４３０〜１５００℃の範囲が推奨され、この様な温度条件を採用することによって、金属化率で少なくとも９５重量％以上、通常は９８重量％以上、更には９９重量％以上といった極めて高純度の金属鉄を得ることが可能となる。
【００３０】
また、副生するスラグについても、前述の如くその中に含まれるＦｅＯを主体とする酸化鉄の含有率で５重量％以下、通常は２重量％以下、加熱還元条件をより適正に制御すれば１重量％以下にまで低減することができ、これは処理炉の耐火壁の溶損防止に極めて有利となる。即ち前述の様な従来の還元製鉄法では、鉄鉱石等の酸化鉄を炭材によって加熱還元し、あるいは還元により生成した金属鉄を生成スラグと分離するに際に、スラグ中にかなり多量のＦｅＯを主体とする酸化鉄が未還元状態で混在しており、これが処理炉の耐火物を溶損するといった問題を引き起こすが、本発明では上記の様にスラグ中のＦｅＯを主体とする酸化鉄についてもその殆んど全てが還元され、スラグ中に酸化鉄は殆んど存在せず、残っているとしてもその量は極く少量であるので、還元工程はもとよりその後のスラグ分離工程でも処理炉耐火物の溶損といった問題を生じることもなくなる。
【００３１】
かくして得られる金属鉄は、上記の様に鉄純度の高いものであり、スラグ成分も含まれていないので、製鋼時の希釈材等として使用する限りそのままで支障なく用いることができるが、該金属鉄の中には不純物元素として相当量のＳ，Ｐなどが含まれているので、これらの不純物が障害となる場合は、必要に応じて精錬処理を行ってこれらの不純物元素の低減を図り、あるいは炭素量の調整を行うことも勿論可能である。
【００３２】
尚、本発明を実施する際に、成長した金属鉄外皮を溶融させないで溶融スラグを凝集させる方法を採用し、その後も金属鉄を溶融させることなくスラグを分離除去する方法を採用すれば、得られる金属鉄中のＳやＰ量も可及的に少なく抑えることができるので好ましい。即ち還元後にスラグと共に金属鉄を溶融させると、溶融スラグ中に取り込まれたＳやＰの一部が溶融金属鉄中に溶け込む復硫・復燐に似た現象を起こす可能性があるが、還元工程およびその後の工程で金属鉄を固形状態に保ち、生成スラグのみを溶融させて分離する方法を採用すると、石炭分などの炭素質還元剤中に混入しているＳやＰは溶融スラグ中に溶け込んで生成スラグと共に分離除去され、金属鉄への混入が可及的に抑えられるからである。
【００３３】
【実施例】
次に、具体的な実施例を示して本発明をより詳細に説明するが、本発明はもとより下記実施例によって制限を受けるものではなく、前後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも勿論可能であり、それらはいずれも本発明の技術的範囲に含まれる。
【００３４】
実施例
表１に示した組成の炭素質還元剤（石炭粉）と酸化鉄（鉄鉱石）およびバインダーとしてベントナイト（いずれも平均粒子径４５μｍ以下のものを使用）を、表１に示す比率で混合してから略球形のペレット状に予備成形し、これを非酸化性雰囲気（窒素ガス雰囲気）中１４００℃、１４５０℃および１５００℃で２０分間加熱還元した後冷却し、ペレットの断面状態を観察した。そのうち代表的な断面写真を図２に示す。
【００３５】
【表１】

【００３６】
これらの図からも明らかである様に、１４００℃および１４５０℃で加熱還元したものでは、ペレット表面に金属鉄外皮が形成されその内側に金属鉄が付着成長すると共に、内部空間に生成スラグが固まり合った状態で分離している状態が観察される。また１５００℃で加熱還元を行なったものでは、一旦形成された金属鉄外皮が還元反応の後で溶融し、溶融スラグと分離した状態で凝固したものと思われ、金属光沢を呈する金属鉄と黒色のガラス状スラグに分離している（写真は、破砕後スラグを除去して選別された金属鉄のみを示している）。このときの還元後ペレットの化学組成を表２に、ガラス状スラグの化学組成を表３に示す。
【００３７】
【表２】

【００３８】
【表３】

【００３９】
表２より、還元温度を１５００℃に高めたものでは、楕円形状に固まった金属光沢を有する金属鉄（図２参照）にはスラグ成分が殆んど含まれておらず、還元によって生成した金属化率９９重量％以上の金属鉄とスラグをほぼ完全に分離し得ることが分かる。一方、還元温度を１４００℃または１４５０℃にしたものでは、金属鉄外皮がまだ残っており、還元後のペレットの化学組成を見ると酸化鉄の還元はやや不十分に見えるが、図２によっても確認できる様に、ペレット内部では外皮を構成する金属鉄と内部に凝集したスラグとの分離が既に起こっている。従って、これを粉砕し磁選などによって選別し、或は温度を高めて更に加熱を続け金属鉄外皮の一部を溶融させてスラグを金属鉄外皮外に流出させ、あるいは金属鉄外皮の全てを溶融させて金属鉄とスラグを凝集させてから分離すると、高純度の粒状金属鉄が得られることが分かる。
【００４０】
次に、加熱還元温度を１５００℃に設定し、処理時間を３分から１５分の間で変化させたときに見られるペレットの外観変化を図３に、また各還元後ペレットの化学組成を表４に、更に各処理時間における金属化率、スラグ成分含有量、酸化鉄含有量、炭素量を夫々図４〜図７に示す。
【００４１】
【表４】

【００４２】
図３から見ると、加熱開始後３分では極端な外観変化は認められないが、表４からも明らかである様にペレット中の酸化鉄の還元は既にかなり進んでおり、加熱開始から５分後にはペレット表面が明らかな金属光沢を呈しており金属鉄外皮が形成されていること、しかもその時点で金属鉄中のＴ．Ｆｅ量は９０重量％を超えており、６分後の金属鉄のＴ．Ｆｅは９８重量％以上にまで高まっていることが分かる。
【００４３】
この時点で、金属鉄外皮の一部が溶融して外皮外へのスラグの流出が認められ、９分後には金属鉄外皮の殆んど全てが溶融・凝集し、目玉焼き状となって黄身に対応する位置に金属鉄が固まると共に、白身に対応する外側にガラス状の生成スラグが凝集している。この時点以降、金属鉄とスラグの形状は若干変化するが、表４によっても確認できる様に金属鉄中のＴ．Ｆｅ濃度の上昇はそれ以上殆んど進んでおらず、このことからペレット中の酸化鉄の還元反応は、金属鉄外皮が形成されるまでの間と、外皮が形成された後その内部での強化された還元条件下で速やかに且つほぼ完全に進行し、その後は時間の経過と共に金属鉄とスラグの分離が進行している。また、表４および図４〜図７からも分かる様に、加熱還元開始後６分で、生成する金属鉄に含まれるスラグ含有量およびＦｅＯ含有量は非常に低いレベルまで低減し、金属化率９９％以上の非常に高品質の金属鉄が得られることが分かる。
【００４４】
以上の結果からも明らかである様に、鉄原料となる酸化鉄に対し当量比以上の炭素質還元剤を混合し成形した成形物を、１４００℃程度以上の温度で加熱すると、成形物の外周側に初期段階で金属鉄外皮が形成され、その後金属鉄外皮内で酸化鉄の還元が速やかに進行すると共に、生成するスラグ成分は溶融状態で金属鉄から分離する。そして処理温度を１５００℃にまで高めると、還元反応および金属鉄と生成スラグの分離が非常に短い時間で進行し、鉄分純度の非常に高い金属鉄を高い収率で得ることができる。
【００４５】
図８は、本発明を実施する際の代表的なフロー図を示したものであり、原料酸化鉄粉粒体を炭素質還元剤粉末およびバインダーと共に混合し、次いでペレット状など任意の形状に成形してから加熱還元炉内へ装入し、１４００℃以上の温度で加熱還元を行なう。還元工程では、初期段階で金属鉄外皮が形成された後、その内部で還元反応が進行し、生成したスラグ成分は外皮の内側に溶融状態で凝集する。これから鉄分を選別するに当たっては、一旦冷却凝固させてから破砕し磁選等によって金属鉄のみを収集し、或は更に加熱を続けこれらを金属鉄の融点以上の温度にまで昇温して比重差によって金属鉄のみを収集すればよい。また必要によっては、収集された該金属鉄を精錬処理することによってＳ，Ｐ等の不純物を除去し、更には炭素量を調整することも勿論可能である。
【００４６】
【発明の効果】
以上の様に本発明によれば、炭素質還元剤を含む酸化鉄の成形物を加熱還元しし、初期段階で金属鉄外皮を形成させ、該外皮内に形成される強化された還元条件下で酸化鉄の還元を進めることによって還元反応を極めて効率よく速やかに進めることができ、金属化率が９５重量％、更には９８重量％以上といった、従来の直接製鉄法では到底得ることのできない高純度の金属鉄を極めて短時間の加熱還元で効率よく製造することができる。得られる高品位の金属鉄は、その後冷却して破砕し磁選等によって、あるいは溶融した後比重差によってスラグと簡単に選別することができる。
【００４７】
また本発明によれば、生成スラグ中の酸化鉄含有量を可及的に少なくすることができるので、酸化鉄に起因する処理炉耐火物の溶損も起こらず、設備保全の観点からしても極めて実用性の高い技術と言える。
【図面の簡単な説明】
【図１】本発明を実施する際の還元反応の進行状況を模式的に示す断面説明図である。
【図２】本発明により温度を変えて加熱還元したときの還元ペレットの断面形状を示す図面代用写真である。
【図３】加熱還元温度を１５００℃に設定し、同温度での保持時間を変えた時の還元ぺレットの外観変化を示す図面代用写真である。
【図４】加熱還元温度を１５００℃に設定し、同温度での保持時間を変えた時の還元ぺレットの金属化率変化を示すグラフである。
【図５】加熱還元温度を１５００℃に設定し、同温度での保持時間を変えた時の還元ぺレット中のスラグ含有量変化を示すグラフである。
【図６】加熱還元温度を１５００℃に設定し、同温度での保持時間を変えた時の還元ぺレット中のＦｅＯ含有量変化を示すグラフである。
【図７】加熱還元温度を１５００℃に設定し、同温度での保持時間を変えた時の還元ぺレット中の炭素量変化を示すグラフである。
【図８】本発明の実施例を示す還元鉄製造プロセスの概略フロー図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for improving a method of obtaining metallic iron by heating and reducing iron oxide such as iron ore together with a carbonaceous reducing agent such as carbonaceous material, and more specifically, iron oxide such as iron ore or the like such as carbonaceous material. When metallic iron is obtained by heat reduction with a carbonaceous reducing agent, iron oxide is efficiently reduced to metallic iron, and slag components mixed as gangue components in iron oxide sources such as iron ore are added. The present invention relates to a method that can be successfully melted and separated to efficiently produce high-purity metallic iron.
[0002]
[Prior art]
As a direct iron manufacturing method for obtaining reduced iron by directly reducing iron oxide such as iron ore and iron oxide pellets with a carbonaceous material or a reducing gas, a shaft furnace method represented by the Midrex method has been known. This type of direct iron manufacturing method is a method in which reducing gas produced from natural gas or the like is blown from the tuyere at the bottom of the shaft furnace, and the reducing power is used to reduce iron oxide to obtain reduced iron. Recently, a reduced iron production process using a coal material such as coal as a reducing agent in place of natural gas has been attracting attention. Specifically, a calcined pellet of iron ore or the like is heated and reduced with coal powder in a rotary kiln. The so-called SL / RN method has already been put into practical use.
[0003]
As another method for producing reduced iron, U.S. Pat. No. 3,443,931 discloses a process for producing reduced iron by mixing a carbonaceous material and powdered iron oxide and agglomerating and reducing heat on a rotary hearth. It is disclosed. In this process, pulverized ore and pulverized coal are mixed and agglomerated, and this is heated and reduced in a high-temperature atmosphere.
[0004]
Reduced iron produced by these methods is used as an iron source after being formed into a briquette or the like as it is and then charged into an electric furnace. In recent years, as iron scrap recycling has become active, reduced iron obtained by the above method has attracted attention as a diluent for impurity elements mixed in scrap.
[0005]
However, the reduced iron obtained by the conventional reduced iron manufacturing method includes SiO contained in iron oxide (iron ore etc.) and carbonaceous materials (coal etc.) used as raw materials. ₂ , Al ₂ O _Three Since slag components such as CaO are mixed as they are, the iron quality (purity as metallic iron) of the product is lowered. In practical use, these slag components are separated and removed in the next refining process, but an increase in the amount of slag not only reduces the yield of the refining melt, but also greatly affects the operating cost of the electric furnace. However, in order to meet these demands with the conventional methods for producing reduced iron as described above, high-quality iron ore must be used as a raw material for producing reduced iron. In other words, the range of selection of practical steelmaking raw materials will be greatly narrowed.
[0006]
Further, the conventional method as described above has the final purpose of obtaining a reduced solid product as an intermediate product. For practical use, it is transported, stored, briquetted or sent to the next scouring step. There is a disadvantage that a process such as cooling is necessary, and a large energy loss occurs during this period, and extra energy and special equipment are required for briquetting.
[0007]
On the other hand, a smelting reduction method such as the DIOS method is also known as a method for obtaining reduced iron by directly reducing iron oxide. In this method, iron oxide is preliminarily reduced to about 30 to 50% in terms of iron purity, and then reduced to metallic iron by direct reduction reaction with carbon in an iron bath. In this method, two steps of preliminary reduction and final reduction in an iron bath are indispensable, so the work is not only complicated, but the molten iron oxide (FeO) present in the iron bath is in direct contact with the refractory. Therefore, the problem that the wear of the refractory is severe is also pointed out.
[0008]
[Problems to be solved by the invention]
As described above, the realization of a method for producing metallic iron with a low slag component content not only increases the added value as product metallic iron, but also reduces the cost of iron making using an electric furnace, and further in producing metallic iron. It becomes extremely important from the viewpoint of flexibility in selection of raw materials used.
[0009]
The present invention has been made by paying attention to such a situation, and its purpose is not only iron oxide having a high iron component content but also iron ore having a relatively low iron component content, etc. It is an object of the present invention to provide a method capable of efficiently obtaining metallic iron having an extremely high iron purity as solid metallic iron or molten metallic iron without causing any problems.
[0010]
The method for producing metallic iron according to the present invention, which was able to solve the above problems, is a method for producing metallic iron by heating and reducing a molded product of iron oxide in which a carbonaceous reducing agent is present.
(1) A metallic iron shell is generated and grown by heat reduction, and the reduction is advanced until iron oxide is substantially absent inside, and aggregates of the generated slag are formed inside.
(2) Generate and grow metallic iron skin by heat reduction, proceed reduction until iron oxide is substantially absent inside, and continue heating to allow the slag produced inside to flow outside the metallic iron skin. ,
(3) Generate and grow a metallic iron shell by heat reduction, proceed with the reduction until iron oxide is substantially absent, and further heat and melt and separate the metallic iron and slag, or
(4) Formation and growth of metallic iron shell by heat reduction, proceeding with reduction until iron oxide is substantially absent inside, and forming aggregates of produced slag inside, and then producing the produced slag from metallic iron To separate
However, it has the characteristics.
If the present invention is shown as a more specific production method,
In a method for producing metallic iron by heat reduction of a molded product of iron oxide in which a carbonaceous reducing agent is present, the molded product of iron oxide in which a carbonaceous reducing agent is present is charged into a heating reduction furnace, and the metal is obtained by thermal reduction. Produce and grow an iron skin, proceed with reduction until iron oxide is substantially absent inside, form aggregates of the produced slag inside, and further heat to melt part of the metal iron skin The slag that forms inside flows out to the outside,
Alternatively, by melting the entire metal iron shell and aggregating the metal iron and slag, the slag produced in the molten state is separated from the metal iron, or
In the reduction step and the subsequent step, keep the metallic iron in a solid state, melt only the generated slag, and separate both, or
In a method for producing metallic iron by heat reduction of a molded product of iron oxide containing a carbonaceous reducing agent, raw iron oxide powder particles are mixed with a carbonaceous reducing agent powder and a binder, and then formed into an arbitrary shape. After that, it is charged into a heat reduction furnace, and heat reduction is performed to produce and grow a metallic iron shell, and the reduction is continued until iron oxide is substantially absent, and the slag component is melted inside. The present invention includes a method of aggregating and separating slag formed in a molten state from metallic iron to obtain metallic iron, or further cooling and solidifying this to obtain metallic iron.
[0011]
In carrying out the above method, the molten slag inside may be discharged out of the metal iron shell by melting part or all of the metal iron shell. At this time, in order to melt part or all of the metallic iron shell, it may be carried out by further increasing the heating temperature after completion of the reduction reaction, or by continuing heating as it is at the reduction temperature. At this time, it is preferable to advance the carburization with the carbonaceous reducing agent present in the metal shell to lower the melting point of the metal shell because the metal iron shell can be heated and melted more easily. In the reduction step and the subsequent steps, it is also possible to keep the metallic iron in a solid state and melt and separate only the generated slag.
[0012]
In carrying out the production method of the present invention, the maximum heating temperature in the heat reduction step is controlled to a temperature not lower than the melting point of the generated slag and not higher than the melting point of the generated metal iron shell, thereby further improving the metal iron generation reaction. In this reduction process, if the iron oxide is reduced by solid-phase reduction and further reduced by liquid phase reduction until there is substantially no FeO-based iron oxide, the resulting metallic iron It is possible to improve the quality of the product more efficiently. According to the present invention, high-grade metallic iron can be easily obtained as a granular material.
[0013]
In the present invention, as a preferable quantitative standard for “progressing the reduction until iron oxide is substantially absent in the metallic iron shell”, in the heat reduction step, “the inclusion of iron oxide mainly composed of FeO” It is preferable to proceed the reduction until the rate is 5% by weight or less, more preferably 2% by weight or less. From another viewpoint, the present invention mainly comprises FeO in the generated slag separated from metallic iron. It is desirable to proceed the reduction until the iron oxide content is 5% by weight or less, more preferably 2% by weight or less.
[0014]
The high-purity metallic iron and produced slag obtained by the above method can be converted into metallized by heating and melting and separating by specific gravity difference, or by cooling and solidifying and then crushing and collecting only high-purity metallic iron by magnetic separation or the like. It becomes possible to obtain metallic iron of very high purity such as about 95% or more and further 98% or more.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
As described above, in the present invention, as a first feature point, a molded product formed by granulating a carbonaceous reducing agent such as coal and iron oxide powder such as iron ore into an arbitrary shape such as granular or pellet is reduced by heating. In this case, a metal iron skin is generated and grown by heat reduction, and the reduction is advanced until iron oxide is substantially absent.
[0016]
That is, the present inventors have made various researches for the development of a new metallic iron production technology that can replace the indirect iron making method represented by the iron making method using a blast furnace and the direct iron making method represented by the SL / RN method. As described above, when the carbonaceous reductant and iron oxide powder are formed into any shape such as granules or pellets and heated in a non-oxidizing atmosphere, the following phenomenon occurs: I figured out what happened. That is, when the molded product is heated, iron oxide is reduced by the carbonaceous reducing agent contained in the molded product to produce metallic iron, but the reduction proceeds from the outer peripheral side of the molded product, and the initial stage of the heating reduction is performed. Metallic iron produced in the process is diffusion bonded on the surface of the molded product to form a metallic iron skin on the outer peripheral side of the molded product. After that, the reduction of iron oxide by the carbonaceous reducing agent proceeds efficiently in the outer skin, and the iron oxide remaining in the inside is then promptly rapidly until there is substantially no iron oxide in a very short time. The reduced and produced metallic iron grows by sequentially adhering to the inner surface side of the outer skin, while it is derived from the gangue component contained in the iron oxide source such as iron ore or contained in the carbonaceous reducing agent Most of the slag derived from ash is agglomerated (aggregated) in the metallic iron outer shell, and efficiently separated into high-purity metallic iron constituting the outer shell and slag aggregated in the inner shell. I caught it.
[0017]
The phenomenon that occurs at the time of reduction will be described with reference to an actual photograph in an example that will be described later, and is considered to follow the following process. That is, FIG. 1 is a schematic cross-sectional view conceptually showing a phenomenon occurring when the present invention is carried out. For example, from a mixture of a carbonaceous reducing agent and iron oxide having a shape as shown in FIG. When the molded product 1 is heated to, for example, about 1450 to 1500 ° C. in a non-oxidizing atmosphere, the reduction of iron oxide by the carbonaceous reducing agent proceeds from the outside of the molded product 1, and the produced metallic iron is diffusion-bonded to each other. As a result, the metallic iron shell 1a is formed [FIG. 1 (B)]. When the heating is further continued, iron oxide in the outer skin 1a is generated by the reduction action by the carbonaceous reducing agent present inside, and further by the reaction between the carbonaceous reducing agent and iron oxide as shown in FIG. 1 (C). The metallic iron Fe that is rapidly reduced by the reducing action by the CO that grows adheres to the inner surface side of the outer skin 1A and grows, and most of the slag Sg that is by-produced from the gangue component is While adhering to each other and growing, they gather in a cavity formed in the outer skin 1a as shown in FIG.
[0018]
The thermal reduction reaction that occurs during this time is as shown in the following formula,
FeO _X + XC → Fe + xCO (1)
FeO _X + (X / 2) C → Fe + (x / 2) CO ₂ (2)
Y = y ₁ + Y ₂ (3)
Y: chemical equivalent of carbon required for reduction (mol)
y ₁ : Carbon amount required for reaction of formula (1) (mol)
y ₂ : Carbon amount required for reaction of formula (2) (mol)
By adjusting the blending ratio of the two so that the blending amount of the carbonaceous reducing agent with respect to the iron oxide in producing the molded product is equal to or more than the theoretical equivalent represented by the above formula (3), the heat reduction reaction is efficiently performed. It is possible to proceed.
[0019]
As described above, in the present invention, the metal iron skin 1a is formed on the outer peripheral side of the molded product in the initial stage of the heat reduction, and the reduction reaction is further advanced in the interior surrounded by the skin 1a, thereby greatly improving the reduction efficiency. It can be done. More preferably, the maximum temperature reached in the heat reduction is set to be lower than the melting temperature of the generated metal iron skin 1a and higher than the melting temperature of the generated slag. When the maximum temperature reaches or exceeds the melting temperature of the metal shell 1a, the produced metal iron immediately melts and fuses with each other, and the metal iron shell 1a as described above is not formed, and the subsequent reduction reaction is efficiently performed. It will not progress. In addition, when the internal unreduced iron oxide melts and flows out, the possibility that the refractory is damaged increases. When the above-mentioned maximum attained temperature is equal to or higher than the melting temperature of the generated slag, the slag produced as a by-product in the heat reduction is melted and fusion / aggregation between the slags progresses, and diffusion bonding between the metal irons is promoted, and FIG. This is because the growth of the metal iron shell 1a and the separation of the slag Sg as shown in FIGS.
[0020]
As described above, in the present invention, the heat reduction reaction utilizing the “formation of metal iron skin and efficient progress of the reduction reaction therein”, which has never been adopted in the conventional indirect iron production method or direct iron production method. The formation of the metallic iron skin 1a proceeds by a reduction reaction with a carbonaceous reducing agent contained in the molded product, and after the formation of the metallic iron skin 1a, the outer skin 1a has the greatest feature. Since it progresses by the reduction | restoration by the carbonaceous reducing agent and produced | generated CO in 1a, it is not necessary to make a heating reduction atmosphere into a reducing atmosphere, for example, what is necessary is just to make non-oxidizing gas atmosphere like nitrogen gas, for example. There is a significant difference from the law.
[0021]
The heating reduction reaction basically proceeds by solid-phase reduction in which the metal iron shell 1a does not melt, but as is apparent from the above description, the inside of the metal iron shell 1a has a carbonaceous reducing agent and its reduction reaction. It is considered that the presence of CO produced by the above is maintained in a highly reducing atmosphere, which is thought to lead to a dramatic increase in the reduction efficiency, but the metallic iron produced inside is in such a highly reducing internal atmosphere. As the carburizing process begins, the melting point gradually decreases. Therefore, it may be considered that a part of the raw material is melted in the final stage or the latter half of the reduction reaction, and the final reduction of iron oxide proceeds by liquid phase reduction. If the reduction temperature is set to a low value, it is possible to proceed with solid-phase reduction. However, the higher the temperature, the higher the reduction reaction rate. In order to complete the reduction reaction in a shorter time, the reaction temperature must be increased. Therefore, it can be said that it is desirable to complete the reduction reaction by liquid phase reduction at the end of the reduction reaction as described above.
[0022]
As a simple method for confirming whether or not the above reduction reaction has been completed, CO or CO in the heated reducing atmosphere gas is used. ₂ A method for confirming the concentration is exemplified. That is, in the heat reduction process, as described above, after the reduction reaction by the carbonaceous reducing agent itself and the reduction reaction by the CO gas generated by the reaction between the reducing agent and iron oxide proceed, and after all of the iron oxide has been reduced, CO and CO ₂ Is no longer produced, so the produced gas in the reduction reactor is withdrawn sequentially, and CO and CO ₂ When the gas is no longer generated, it can be known that the reduction reaction has been completed.
[0023]
However, for practical use, CO and CO ₂ The reaction does not have to be performed until the gas is not completely released, and according to the present inventors, it has been confirmed that the CO and CO in the furnace gas depend on the space volume of the reactor. ₂ When the gas concentration is reduced to about 2% by volume or less, 95% by weight or more of iron oxide is reduced, and when the gas concentration is reduced to about 1% by volume or less, 98% by weight or more of iron oxide is reduced. It is confirmed that it has been reduced.
[0024]
In the state shown in FIG. 1 (D), the iron oxide mainly composed of FeO in the molded product is substantially all reduced to change into metallic iron (usually, the iron oxide content is not more than 5% by weight). In the experiments, it has been reduced to 2% by weight or less, or 1% by weight or less), and most of the iron oxide mainly composed of FeO partially dissolved in the molten slag Sg agglomerated inside. (Normally, the content of iron oxide mainly composed of FeO in the slag is 5% by weight or less, and 2% by weight or less or 1% by weight or less as confirmed by experiments). Therefore, cooling and taking out in this state, crushing the metal iron shell 1a with a crusher or the like, and selecting and taking out only the metal iron by magnetic separation or the like, all of the aggregated slag components are removed, and high purity metal iron Can be obtained efficiently. Further, after that, the heating is continued at the same temperature, or the heating is continued at a higher temperature, and a part or all of the metallic iron shell 1a is melted as shown below to separate the generated slag from the metallic iron. It is also preferable to adopt.
[0025]
That is, from the state of FIG. 1 (D), if the temperature is slightly raised as necessary and heating is continued, for example, as shown in FIG. 1 (E), a part of the metal iron outer shell 1a is melted, and the internally generated slag Sg Flows out of the outer skin 1a, so that the subsequent separation can be further facilitated. Alternatively, when the heating is further continued thereafter, for example, as shown in FIG. 1 (F), all of the metallic iron shell is melted and aggregated, and separated from the previously melted and aggregated slag Sg. Therefore, when it is cooled and solidified after being in such a state, when it is applied to a crushing machine etc., only fragile slag is crushed and metal iron remains as a lump. High-purity metallic iron can be easily selected. As another method for separating metallic iron and produced slag, it is of course possible to separate metallic iron and slag which have been heated and melted as described above by their specific gravity difference in the molten state.
[0026]
In the above, the metal iron shell can be heated and melted by heating at a higher heating temperature after completion of the reduction reaction, but at the end of reduction in the metal iron shell, as described above, the strong internal reducibility is reduced. Since the reduced iron undergoes carburization due to the atmosphere and its melting point drops considerably, it is also possible to melt the metallic iron skin by simply lowering the melting point as carburization proceeds even if heating is continued at the reduction temperature.
[0027]
As the carbonaceous reducing agent used in carrying out the present invention, after mining, coal powder just subjected to treatment such as pulverization and sieving, crushed coke, for example, subjected to heat treatment such as dry distillation, Any kind of petroleum coke or the like may of course be used, for example, blast furnace dust recovered as a waste containing carbonaceous matter. However, the carbonaceous reducing agent used in the present invention is selected to have a carbon content of 70% by weight or more, more preferably 80% by weight or more in order to allow the heat reduction reaction to proceed efficiently, and to increase the specific surface area. It is desirable to use a powdery material having a diameter of 2 mm or less, preferably 1 mm or less. Similarly, iron oxide such as iron ore is preferably used in the form of powder having a particle size of 2 mm or less, preferably 1 mm or less in order to increase the specific surface area and increase the reduction reaction efficiency.
[0028]
In the present invention, these carbonaceous reducing agents and iron oxide are uniformly mixed, and if necessary, an appropriate binder is used in combination to form an arbitrary shape such as a lump, granule, briquette, pellet, rod, etc. The amount of the carbonaceous reducing agent blended at this time depends on the amount of oxygen in the iron oxide used together, as shown in the above formulas (1) to (3). More than the required stoichiometric amount, preferably a slightly excessive amount may be added in consideration of the amount of carburization necessary for lowering the melting point of the metallic iron shell.
[0029]
In addition, as described above, it is desirable that the maximum temperature achieved during the heating reduction is not less than the melting point of the generated slag and not more than the melting point of the metallic iron shell. It varies depending on the gangue components contained in the iron oxide source, iron oxide contamination, etc., and the melting point of the reduced iron shell also varies considerably depending on the amount of carburization, so it is not always appropriate to specify the maximum temperature as an absolute value. I can't say that. However, the standard preferred reduction temperature is recommended to be in the range of 1400 to 1540 ° C., more preferably in the range of 1430 to 1500 ° C. By adopting such a temperature condition, the metallization rate is usually at least 95% by weight, usually It is possible to obtain extremely high purity metallic iron such as 98 wt% or more, and further 99 wt% or more.
[0030]
As for by-product slag, as described above, the content of iron oxide mainly composed of FeO is 5% by weight or less, usually 2% by weight or less. It can be reduced to 1% by weight or less, which is extremely advantageous for preventing the refractory wall of the processing furnace from being melted. That is, in the conventional reduction iron manufacturing method as described above, when iron oxide such as iron ore is reduced by heating with a carbonaceous material, or when metallic iron produced by reduction is separated from the produced slag, a considerably large amount of FeO is contained in the slag. This causes the problem that the refractory of the processing furnace is melted, but in the present invention, the iron oxide mainly composed of FeO in the slag is also present as described above. Almost all of this is reduced, and there is almost no iron oxide in the slag, and even if it remains, the amount is very small. Therefore, in the slag separation process as well as in the subsequent slag separation process, There is no longer a problem of melting of objects.
[0031]
The metal iron thus obtained has a high iron purity as described above and does not contain slag components, so that it can be used as it is as long as it is used as a diluent during steelmaking. Since iron contains a considerable amount of S, P, etc. as impurity elements, if these impurities become obstacles, refining treatment is performed as necessary to reduce these impurity elements, It is of course possible to adjust the carbon amount.
[0032]
In carrying out the present invention, if a method of aggregating molten slag without melting the grown metal iron shell is adopted, and then a method of separating and removing slag without melting the metal iron is obtained. The amount of S and P in the metallic iron to be produced is preferable because it can be suppressed as much as possible. In other words, when metallic iron is melted together with slag after reduction, there is a possibility that a part of S or P taken in the molten slag may cause a phenomenon similar to sulfurization / rephosphorus, which dissolves in molten metallic iron. In the process and subsequent processes, when the method of keeping the metallic iron in a solid state and melting and separating only the generated slag, S and P mixed in the carbonaceous reducing agent such as coal are contained in the molten slag. It is because it melts and is separated and removed together with the generated slag, and mixing into metallic iron is suppressed as much as possible.
[0033]
【Example】
Next, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited by the following examples as a matter of course, and appropriate modifications are made within a range that can meet the gist of the preceding and following descriptions. In addition, it is of course possible to carry out them, and they are all included in the technical scope of the present invention.
[0034]
Example
A carbonaceous reducing agent (coal powder) having the composition shown in Table 1, iron oxide (iron ore), and bentonite (both having an average particle diameter of 45 μm or less) are mixed at a ratio shown in Table 1. From this, it was preformed into a substantially spherical pellet shape, and this was heated and reduced at 1400 ° C., 1450 ° C. and 1500 ° C. for 20 minutes in a non-oxidizing atmosphere (nitrogen gas atmosphere) and then cooled, and the cross-sectional state of the pellet was observed. A typical cross-sectional photograph is shown in FIG.
[0035]
[Table 1]

[0036]
As is apparent from these figures, in the case of heat reduction at 1400 ° C. and 1450 ° C., a metallic iron skin is formed on the pellet surface, and metallic iron adheres and grows inside, and the generated slag is solidified in the internal space. A state of separation in the combined state is observed. In the case of heat reduction at 1500 ° C., the metallic iron shell once formed is melted after the reduction reaction and solidified in a state separated from the molten slag. (The photo shows only metallic iron selected by removing the slag after crushing). Table 2 shows the chemical composition of the pellet after reduction, and Table 3 shows the chemical composition of the glassy slag.
[0037]
[Table 2]

[0038]
[Table 3]

[0039]
From Table 2, when the reduction temperature was increased to 1500 ° C., the metal iron (see FIG. 2) having a metallic luster solidified into an elliptical shape contained almost no slag component, and the metal produced by the reduction. It can be seen that metallic iron and slag having a conversion rate of 99% by weight or more can be almost completely separated. On the other hand, when the reduction temperature is 1400 ° C. or 1450 ° C., the metallic iron shell still remains, and when the chemical composition of the pellet after reduction is seen, the reduction of iron oxide seems somewhat insufficient, but also according to FIG. As can be confirmed, separation of the metallic iron constituting the outer shell and the slag aggregated inside has already occurred inside the pellet. Therefore, this is crushed and sorted by magnetic separation or the like, or the temperature is increased and further heating is continued to melt a part of the metal iron outer shell and the slag flows out of the metal iron outer shell, or all of the metal iron outer shell is melted. It can be seen that high-purity granular metallic iron can be obtained by separating the metallic iron and slag after aggregation.
[0040]
Next, FIG. 3 shows changes in the appearance of pellets when the heating reduction temperature is set to 1500 ° C. and the treatment time is changed between 3 minutes and 15 minutes, and the chemical composition of each pellet after reduction is shown in Table 4. Furthermore, the metallization rate, slag component content, iron oxide content, and carbon content in each treatment time are shown in FIGS.
[0041]
[Table 4]

[0042]
As can be seen from FIG. 3, no extreme change in appearance was observed 3 minutes after the start of heating, but as is apparent from Table 4, the reduction of iron oxide in the pellets has already progressed considerably, and 5 minutes after the start of heating. After that, the pellet surface has a clear metallic luster and a metallic iron shell is formed. The amount of Fe exceeds 90% by weight, and the T.O. It can be seen that Fe is increased to 98% by weight or more.
[0043]
At this point, a part of the metal iron hull melts and slag flows out of the hull, and after 9 minutes, almost all of the metal iron hull melts and agglomerates to form a fried egg. Metallic iron is solidified at the corresponding position, and glassy generated slag is agglomerated on the outside corresponding to the white meat. From this point on, although the shapes of metallic iron and slag slightly change, as shown in Table 4, T.O. The increase in the Fe concentration has hardly progressed any further, and from this, the reduction reaction of iron oxide in the pellets takes place until the metallic iron skin is formed, and after the outer skin is formed. It progresses rapidly and almost completely under the enhanced reducing conditions, and thereafter, separation of metallic iron and slag progresses with time. Further, as can be seen from Table 4 and FIGS. 4 to 7, the slag content and FeO content contained in the produced metal iron are reduced to a very low level 6 minutes after the start of the heating reduction, and the metallization rate It can be seen that 99% or more of very high quality metallic iron can be obtained.
[0044]
As is clear from the above results, when a molded product formed by mixing a carbonaceous reducing agent having an equivalent ratio or more with respect to iron oxide as an iron raw material is heated at a temperature of about 1400 ° C. or more, At the initial stage, a metallic iron shell is formed on the side, and thereafter, the reduction of iron oxide proceeds rapidly in the metallic iron shell, and the slag component produced is separated from the metallic iron in a molten state. When the treatment temperature is increased to 1500 ° C., the reduction reaction and separation of metallic iron and produced slag proceed in a very short time, and metallic iron having a very high iron purity can be obtained in a high yield.
[0045]
FIG. 8 shows a typical flow chart for carrying out the present invention. The raw iron oxide particles are mixed with the carbonaceous reducing agent powder and the binder, and then formed into an arbitrary shape such as a pellet. Then, it is charged into a heating reduction furnace and subjected to heating reduction at a temperature of 1400 ° C. or higher. In the reduction process, after the metallic iron skin is formed in the initial stage, the reduction reaction proceeds inside thereof, and the generated slag component is aggregated in the molten state inside the skin. In order to select iron from now, it is cooled and solidified and then crushed and collected only by metallic separation, etc., or it is further heated to raise the temperature to a temperature above the melting point of metallic iron and the difference in specific gravity. Only metallic iron needs to be collected. If necessary, it is of course possible to remove impurities such as S and P by refining the collected metallic iron and further adjust the carbon content.
[0046]
【The invention's effect】
As described above, according to the present invention, an iron oxide molded product containing a carbonaceous reducing agent is heated and reduced to form a metallic iron skin at an initial stage, and the enhanced reducing conditions formed in the skin are reduced. In this case, the reduction reaction can be carried out very efficiently and rapidly by proceeding with the reduction of the iron oxide, and the metallization rate is 95% by weight, and more than 98% by weight. Purity metallic iron can be efficiently produced by heating and reducing in a very short time. The resulting high-grade metallic iron can then be easily separated from slag by cooling, crushing, magnetic separation, etc., or after melting and by specific gravity difference.
[0047]
Further, according to the present invention, the iron oxide content in the generated slag can be reduced as much as possible, so that the refractory of the processing furnace caused by iron oxide does not melt, and from the viewpoint of equipment maintenance. It can be said that this is an extremely practical technology.
[Brief description of the drawings]
FIG. 1 is an explanatory cross-sectional view schematically showing the progress of a reduction reaction when carrying out the present invention.
FIG. 2 is a drawing-substituting photograph showing a cross-sectional shape of a reducing pellet when the temperature is changed and reduced by heating according to the present invention.
FIG. 3 is a drawing-substituting photograph showing a change in appearance of a reducing pellet when the heating reduction temperature is set to 1500 ° C. and the holding time at the same temperature is changed.
FIG. 4 is a graph showing a change in metallization rate of a reduced pellet when the heating reduction temperature is set to 1500 ° C. and the holding time at the same temperature is changed.
FIG. 5 is a graph showing changes in slag content in a reduced pellet when the heating reduction temperature is set to 1500 ° C. and the holding time at the same temperature is changed.
FIG. 6 is a graph showing a change in FeO content in a reduced pellet when the heating reduction temperature is set to 1500 ° C. and the holding time at the same temperature is changed.
FIG. 7 is a graph showing the carbon content change in the reduced pellet when the heating reduction temperature is set to 1500 ° C. and the holding time at the same temperature is changed.
FIG. 8 is a schematic flow diagram of a reduced iron production process showing an embodiment of the present invention.

Claims

In a method for producing metallic iron by heat reduction of a molded iron oxide containing a carbonaceous reducing agent, a metallic iron skin is formed and grown by heat reduction until the iron oxide is substantially absent. A process for producing metallic iron, characterized by advancing reduction and forming aggregates of produced slag inside.

In a method of producing metallic iron by heat reduction of a molded iron oxide containing a carbonaceous reducing agent, a metallic iron skin is generated and grown by heat reduction, and reduced until iron oxide is substantially absent inside. The method for producing metallic iron is characterized in that the slag produced inside is further flowed out to the outside of the metallic iron skin.

The manufacturing method of Claim 2 which fuse | melts a part of metallic iron outer skin and isolate | separates metallic iron and molten slag.

The manufacturing method according to claim 3, wherein the melting point of the metallic iron shell is lowered by carburizing to melt a part of the metallic iron shell.

The manufacturing method according to claim 1 or 2, wherein in the reduction step and the subsequent step, metallic iron is kept in a solid state and only the generated slag is melted and separated.

In a method for producing metallic iron by heat reduction of a molded iron oxide containing a carbonaceous reducing agent, a metallic iron skin is formed and grown by heat reduction until the iron oxide is substantially absent. A method for producing metallic iron, characterized by proceeding reduction and further heating and melting and separating metallic iron and slag.

The process according to claim 6 , wherein the melting point of the metallic iron shell is lowered by carburizing, and the metallic iron shell is melted and melted and separated from the slag.

In a method for producing metallic iron by heat reduction of a molded iron oxide containing a carbonaceous reducing agent, a metallic iron skin is formed and grown by heat reduction until the iron oxide is substantially absent. A process for producing metallic iron, characterized by advancing reduction, forming aggregates of produced slag inside, and then separating produced slag from metallic iron.

Heat reduction of iron oxide moldings with carbonaceous reducing agent in a method for producing metallic iron by heating reduction of iron oxide moldings with carbonaceous reducing agent It is charged into the furnace, and the metallic iron skin is generated and grown by heat reduction, and the reduction is continued until iron oxide is substantially not present inside, and aggregates of the generated slag are formed inside, and further heating is continued. The slag generated in the molten state is melted by melting part of the metal iron outer shell and flowing out the slag generated inside, or by melting the entire metal iron outer shell and aggregating the metal iron and slag. A process for producing metallic iron characterized by separation from iron.

The process according to claim 9, wherein the melting of the metallic iron shell is carried out by further increasing the heating temperature after completion of the reduction reaction, or by continuing the heating as it is at the reduction temperature.

In a method for producing metallic iron by heat reduction of a molded product of iron oxide containing a carbonaceous reducing agent, raw iron oxide powder particles are mixed with a carbonaceous reducing agent powder and a binder, and then formed into an arbitrary shape. After that, it is charged into a heat reduction furnace, and heat reduction is performed to produce and grow a metallic iron shell, and the reduction is continued until iron oxide is substantially absent, and the slag component is melted inside. A method for producing metallic iron, characterized in that the slag that is agglomerated in a molten state is separated from metallic iron.

The manufacturing method in any one of Claims 9-11 which isolate | separate the slag produced | generated in a molten state from metallic iron, and then make it cool and solidify, and obtain metallic iron.

The manufacturing method of Claim 12 which obtains metallic iron as granular metallic iron.

The manufacturing method according to any one of claims 1 to 13 , wherein the maximum heating temperature in the heat reduction step is not less than the melting point of the produced slag and not more than the melting point of the produced metal iron shell.

The process according to any one of claims 1 to 14 , wherein iron oxide is reduced by solid-phase reduction in the heat reduction step, and further reduced by liquid phase reduction until iron oxide mainly composed of FeO is substantially absent.

The process according to any one of claims 1 to 15 , wherein the reduction is performed until the content of iron oxide mainly composed of FeO is 5 wt% or less in the heat reduction step.

The process according to claim 16 , wherein the reduction is carried out until the content of iron oxide mainly composed of FeO is 2% by weight or less in the heat reduction step.

The process according to any one of claims 1 to 17 , wherein the content of iron oxide mainly composed of FeO in the generated slag is 5% by weight or less.

The process according to claim 18 , wherein the content of iron oxide mainly composed of FeO in the generated slag is 2% by weight or less.