JP2004161544A - Method of manufacturing raw material for phosphate fertilizer - Google Patents
Method of manufacturing raw material for phosphate fertilizer Download PDFInfo
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- JP2004161544A JP2004161544A JP2002329833A JP2002329833A JP2004161544A JP 2004161544 A JP2004161544 A JP 2004161544A JP 2002329833 A JP2002329833 A JP 2002329833A JP 2002329833 A JP2002329833 A JP 2002329833A JP 2004161544 A JP2004161544 A JP 2004161544A
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、溶銑の予備脱燐処理工程で生成され、燐酸を含有するスラグからなる燐酸肥料用原料の製造方法の改良技術に関するもので、詳しくは、燐酸含有量が高く且つ優れた肥料特性を有する、燐酸肥料用原料としてのスラグを製造する方法に関するものである。
【０００２】
【従来の技術】
現在、燐酸肥料の多くは燐鉱石を原料として製造されているが、将来的には燐鉱石の枯渇が懸念されている。一方、環境問題の観点から、鉄鋼製造工程において溶鉄中の不純物を除去する際に発生するスラグを有効活用する要請は高く、鋼材特性を悪化させる燐を溶銑中から除去する際に発生する、燐酸を含有するスラグを、燐酸肥料用原料として用いることが、行われ且つ研究されてきた。
【０００３】
スラグを原料とする燐酸肥料として最も広く知られているのが、トーマス燐肥である。トーマス燐肥は、燐含有量の高い鉄鉱石を原料として製造される所謂トーマス溶銑（通常、溶銑中の燐濃度が２質量％前後）を、トーマス転炉を用いて精錬し、その際に発生するスラグを原料とするもので、燐酸濃度が１６〜２２質量％と高いことが特徴である。しかし、トーマス燐肥を製造するためには、トーマス転炉を用いると共に燐含有量の高い鉄鉱石を原料とする必要があり、しかも、トーマス転炉では、精錬された溶鋼の燐濃度が高いことやスラグの発生量が多いこと等の問題点が多く、そのため、トーマス転炉は、現在世界的に普及している純酸素を用いた所謂ＬＤ転炉に取って替わられ、現在、トーマス燐肥はほとんど製造されていない。
【０００４】
ところで、欧米で産出される鉄鉱石中の燐濃度よりも日本で輸入し使用される鉄鉱石中の燐濃度の方が高いため、日本では、溶銑を転炉で精錬する前に、脱燐反応に有利な低温域である溶銑の段階で脱燐処理する所謂予備脱燐処理が行われている。しかしながら、それでも高炉から出銑される溶銑中の燐濃度は０．１質量％程度であるため、従来の一般的な溶銑の予備脱燐処理で生成されるスラグ中のＰ２ Ｏ５ に換算した燐酸濃度は高々５質量％であり、燐酸肥料用の原料として利用できるほどの高濃度の燐酸を含有するスラグは生成されない。そのため、燐酸肥料用の原料として利用可能な、高濃度の燐酸を含有するスラグを、溶銑の予備脱燐処理工程において生成させる方法が幾つか提案されている。
【０００５】
例えば、特許文献１には、溶銑の予備脱燐処理を２段階で実施し、２回目の予備脱燐処理で生成したスラグを高炉原料の一部として使用して溶銑を製造することにより、高炉から出銑される溶銑の燐濃度を高め、１回目の予備脱燐処理によって生成されるスラグの燐酸濃度を高める方法が提案されており、又、特許文献２には、溶銑の予備脱燐処理後に行われる転炉精錬で生成した燐含有スラグを高炉原料の一部として使用することにより、高炉から出銑される溶銑の燐濃度を高め、溶銑の予備脱燐処理によって生成されるスラグの燐酸濃度を高める方法が提案されている。
【０００６】
【特許文献１】
特開平８−３６１２号公報
【０００７】
【特許文献２】
特開平８−３６１３号公報
【０００８】
【発明が解決しようとする課題】
しかしながら、これらの方法では、燐酸含有量の高いスラグを得るために、従来の工程に対して特別な工程を追加する必要があり、脱燐処理コストやスラグ回収コストが高くなると云う問題点がある。例えば、溶銑の予備脱燐処理を２回に分けて行う特許文献１の方法では、脱燐処理場が２基必要になり、仮に、１基の脱燐処理場で行った場合には、脱燐処理可能量が約半分になり、生産性が低下するのみならず、全ての溶銑に対して予備脱燐処理を施すことができなくなる恐れが発生する。又、溶銑を予備脱燐処理した後に転炉でも脱燐処理する特許文献２の方法では、転炉精錬を、生石灰等の脱燐用造滓剤を大量に使用した従来の精錬方法と大差ない方法で行う必要があり、溶銑を予備脱燐処理する利点が全く無くなってしまい、燐酸肥料の原料を製造するための特化したプロセスとなり、溶鋼の製造コストを上昇させてしまう。
【０００９】
更に、燐酸肥料として用いるには、スラグ中の燐酸は水溶性を有する必要があり、単にその濃度を上昇させるだけでは燐酸肥料として有効に利用することはできない。特許文献１及び特許文献２では、水溶性の燐酸を確保することに関しては何ら対策を講じておらず、肥料特性に優れたスラグ即ち水溶性の燐酸を確保したスラグが得られているとは必ずしも云い難い。
【００１０】
本発明は上記事情に鑑みてなされたもので、その目的とするところは、溶銑の脱燐処理を２回以上に分けて行う必要がなく、１回の予備脱燐処理だけで充分に転炉精錬後の溶鋼中燐濃度を製品規格以下まで低下させることが可能であり、溶鋼の製造コストを上昇させることなく、燐酸含有量が高く且つ優れた肥料特性を有する、燐酸肥料用原料としてのスラグを溶銑の予備脱燐処理によって製造する方法を提供することである。
【００１１】
【課題を解決するための手段】
本発明者等は、上記課題を解決するために鋭意検討を行った。以下に検討結果を説明する。
【００１２】
溶銑の予備脱燐処理工程においては、転炉における脱炭精錬に比較して処理時の溶湯温度が低いので、脱燐剤として使用するＣａＯの滓化を促進させるために、通常、蛍石（ＣａＦ２ ）が用いられている。ＣａＯは螢石と反応することによってその融点が低下し、滓化が促進される。しかしながら、フッ素がスラグ中に存在すると、フッ素は燐酸及びＣａＯと結合してフルオアパタイトを形成させるため、燐酸の水溶性が阻害され、このスラグを燐酸肥料用原料として用いた場合に十分な燐酸溶解性が確保されないと云う問題が発生する。
【００１３】
この問題を解決すべく、本発明者等は、スラグ中に含まれるフッ素量と燐酸の溶解性との関係を解明した。その結果、溶解性の燐酸をスラグ中に確保するためには、スラグ中のＰ２ Ｏ５ に換算した燐酸濃度（質量％）を、少なくともスラグ中のフッ素濃度（質量％）の５．６倍以上確保する必要があるとの知見を得た。即ち、スラグ中のＰ２ Ｏ５ に換算した燐酸濃度がフッ素濃度の５．６倍未満の場合には、スラグ中の燐酸のほとんどはフルオアパタイトの形態で存在し、水溶性を有する燐酸を得ることができないとの知見を得た。
【００１４】
そこで、この知見並びにスラグが燐酸肥料用の原料であることに基づいて、スラグ中のＰ２ Ｏ５ に換算した燐酸濃度（質量％）とフッ素濃度（質量％）との関係を下記（１）式の範囲内に定めた。下記（１）式の範囲を満足することにより、少なくとも１０質量％以上の溶解性燐酸がスラグ中に確保され、燐酸肥料として優れた効果を発揮することができる。
【００１５】
【数１】
そして、又、上記（１）式を満足させるためには、予備脱燐処理前の溶銑中の燐濃度を０．１５質量％から０．２５質量％の範囲に調整する必要があるとの知見を得た。この理由は、溶銑の燐濃度が０．１５質量％未満の場合には、予備脱燐処理においてスラグ中に移行する燐量が少ないため、スラグ中の燐酸濃度が十分に高くならず、一方、溶銑の燐濃度が０．２５質量％を越える場合には、予備脱燐処理工程で脱燐処理を行っても、脱燐処理後の燐濃度が製品の規格値以下まで低減せず、次工程の転炉精錬工程でも脱燐処理を実施しなければならず、製造コストの上昇を招くためである。
【００１７】
本発明は上記知見に基づきなされたもので、第１の発明に係る燐酸肥料用原料の製造方法は、高炉で製造された溶銑の予備脱燐処理工程で生成する燐含有スラグであり、スラグ中のＰ２ Ｏ５ に換算した燐酸濃度（質量％）がスラグ中のフッ素濃度（質量％）に対して上記の（１）式を満足する燐含有スラグからなる燐酸肥料用原料の製造方法であって、予備脱燐処理工程で脱燐処理される前の溶銑の燐濃度を０．１５質量％から０．２５質量％の範囲内に調整し、該溶銑を予備脱燐処理工程で脱燐処理することを特徴とするものである。
【００１８】
第２の発明に係る燐酸肥料用原料の製造方法は、第１の発明において、溶銑の予備脱燐処理工程で生成する燐含有スラグは、実質的にフッ素を含有しないことを特徴とするものである。
【００１９】
第３の発明に係る燐酸肥料用原料の製造方法は、第１又は第２の発明において、溶銑の予備脱燐処理工程で生成する燐含有スラグを、溶銑の予備脱燐処理工程よりも前の工程で装入原料の一部として使用することを特徴とするものである。
【００２０】
第４の発明に係る燐酸肥料用原料の製造方法は、第３の発明において、溶銑の予備脱燐処理工程で生成する燐含有スラグの５０％以上の量を、溶銑の予備脱燐処理工程よりも前の工程で装入原料の一部として使用することを特徴とするものである。
【００２１】
第５の発明に係る燐酸肥料用原料の製造方法は、第３又は第４の発明において、高炉工程又は鉄鉱石を焼結する焼結炉工程若しくはその双方の工程で、前記燐含有スラグを装入原料の一部として使用することを特徴とするものである。
【００２２】
第６の発明に係る燐酸肥料用原料の製造方法は、第３又は第４の発明において、予備脱燐処理工程の前工程である溶銑の脱珪処理工程で、前記燐含有スラグを装入原料の一部として使用することを特徴とするものである。
【００２３】
第７の発明に係る燐酸肥料用原料の製造方法は、第１又は第２の発明において、高炉で製造された溶銑は、燐含有量と鉄含有量との質量比が０．００１５以上である鉄鉱石を全量若しくは一部分使用して製造された溶銑であることを特徴とするものである。
【００２４】
第８の発明に係る燐酸肥料用原料の製造方法は、第１ないし第７の発明の何れかにおいて、予備脱燐処理後の溶銑中の燐濃度が製品の規格以下であり、予備脱燐処理工程の後工程である転炉精錬工程では、実質的に脱燐処理しないことを特徴とするものである。
【００２５】
第９の発明に係る燐酸肥料用原料の製造方法は、第１ないし第８の発明の何れかにおいて、前記燐含有スラグは、ＣａＯ源と酸素源とを脱燐処理容器内の浴面又は浴中の同一位置に供給することにより行われる脱燐処理によって生成したスラグであることを特徴とするものである。
【００２６】
第１０の発明に係る燐酸肥料用原料の製造方法は、第１ないし第８の発明の何れかにおいて、前記燐含有スラグは、ＣａＯ源と酸素源とを脱燐処理容器の浴面上方から浴面に投射することにより行われる脱燐処理によって生成したスラグであることを特徴とするものである。
【００２７】
【発明の実施の形態】
以下、本発明の実施の形態を説明する。
【００２８】
本発明では、溶銑の予備脱燐処理工程で生成される燐含有スラグを燐酸肥料用原料として利用する。但し、スラグ中のＰ２ Ｏ５ に換算した燐酸濃度（質量％）が、スラグ中のフッ素濃度（質量％）に対して上記（１）式の範囲内となる燐含有スラグを燐酸肥料用原料として利用する。そして、本発明においては、スラグ中のＰ２ Ｏ５ に換算した燐酸濃度が上記（１）式を満足するための必要条件として、予備脱燐処理前の溶銑中の燐濃度を、０．１５質量％から０．２５質量％の範囲に調整する。
【００２９】
溶銑中の燐濃度がこの範囲にあれば、この溶銑に対して予備脱燐処理を施すことにより、脱燐剤であるＣａＯの使用量を減じることなく、即ち高い脱燐率を維持しつつ、（１）式を満足する組成の燐含有スラグを得ることができる。但し、予備脱燐処理を施した後の溶銑中燐濃度は０．０１〜０．０２質量％程度であるので、予備脱燐処理工程における脱燐量に応じて脱燐剤であるＣａＯ源の使用量を決めることが重要である。即ち、ＣａＯ源の過剰の使用は、スラグ中の燐酸濃度を低下させるので好ましくない。具体的には、ＣａＯ源の添加上限を、溶銑の燐濃度にも依るが、溶銑トン当たり２０ｋｇ（以下「ｋｇ／ｔ」と記す）程度としておけばよい。
【００３０】
予備脱燐処理工程前の溶銑中の燐濃度を０．１５〜０．２５質量％の範囲に調整する手段の１つとして、本発明においては、溶銑の予備脱燐処理工程で生成したスラグを、予備脱燐処理工程よりも前の工程で装入原料即ち副原料の一部として使用する。使用する工程は、例えば、溶銑を製造する高炉工程、粉鉄鉱石を焼結して高炉装入用の塊状原料とする焼結炉工程、予備脱燐処理工程前に予め溶銑中の珪素を除去する脱珪処理工程等が適当である。これらの工程ではＣａＯ源を造滓剤として使用しており、一方、予備脱燐処理工程で生成されるスラグはＣａＯを主成分としており、これら工程の造滓剤として十分に使用可能である。この場合、これら工程の何れかで使用しても、又、これら工程の２以上の工程で併用しても、どちらでも構わない。
【００３１】
予備脱燐処理工程で生成するスラグ中では、燐は酸化物の形態で存在するが、高炉内及び脱珪処理反応中においては酸化物として安定的に存在できなくなり、還元されて溶銑中に移行する。現在、日本に輸入される鉄鉱石を用いて溶銑を製造した場合には、前述したように、溶銑中の燐濃度は０．１質量％程度であるが、スラグ中の燐が還元されて溶銑中に移行することで、燐濃度の高い溶銑を製造することができる。
【００３２】
この場合、予備脱燐処理工程よりも前の工程で、予備脱燐処理工程で発生するスラグの５０％以上の量を使用することが好ましい。これにより、燐濃度が０．１５〜０．２５質量％の溶銑を安定して得ることができる。予備脱燐処理工程よりも前工程におけるスラグの使用量が発生量の５０％未満の場合には、燐のマスバランスの関係上から、溶銑中の燐濃度が所望する値まで十分に高くならず、前工程におけるスラグの使用量が発生量の５０％を超えた辺りから、溶銑中の燐濃度が（１）式の範囲を満足する程度に高くなってくるためである。このように、再使用するスラグ量を限定することで、所定の値の燐濃度を有する溶銑を安定して得ることができる。
【００３３】
一方、予備脱燐処理工程で発生する燐含有スラグを利用しなくても、予備脱燐処理工程前の溶銑中の燐濃度を０．１５〜０．２５質量％の範囲に調整することができる。例えば、燐含有量の多い鉄鉱石を用いて溶銑を製造する方法であり、燐含有量と鉄含有量との質量比が０．００１５以上である鉄鉱石を、１００％配合するか若しくは一部分配合して高炉に装入し、当該鉄鉱石から溶銑を製造すれば、燐濃度が０．１５〜０．２５質量％の範囲の溶銑を製造することができる。従って、このような鉄鉱石を用いて溶銑を製造してもよい。
【００３４】
予備脱燐処理の方法は特に限定するものではなく、通常の溶銑脱燐処理方法を適用すればよい。即ち、溶銑鍋やトーピードカー等の溶銑搬送容器或いは転炉等の収納容器に収納された溶銑に、酸素ガスや酸素含有ガス等の気体酸素源又は鉄鉱石やミルスケール等の固体酸素源を溶銑に吹き付け若しくは吹き込みつつ、窒素ガス等の攪拌ガスを溶銑に吹き込んで溶銑を攪拌しながら、脱燐剤である生石灰等のＣａＯ源を溶銑に吹き付け若しくは吹き込んで脱燐処理する。
【００３５】
但し、上記の（１）式からも明らかなように、水溶性燐酸の含有量を高めるためには、スラグ中のフッ素含有量は可能な限り少ないことが好ましく、特に実質的にフッ素を含有しないこと、即ち、不可避的に混入するフッ素以外のフッ素を含有しないことが好ましい。換言すれば、予備脱燐処理工程のみならず、予備脱燐処理工程よりも前の工程でも、蛍石等のフッ素含有物質を使用しないて製錬及び精錬することが好ましい。
【００３６】
蛍石等のフッ素含有物質を使用せずに高い脱燐率を維持しつつ溶銑を脱燐するためには、ＣａＯ源及び酸素源を溶銑中の燐と効率良く反応させる必要があり、従って、ＣａＯ源と酸素源とを浴中や浴面に同時に添加する、或いは、ＣａＯ源と酸素源とを浴面上方から浴面に投射することによって、溶銑を脱燐する方法が好適である。又、このような方法で脱燐することにより、溶銑中の燐濃度を製品の規格以下まで安定して低減することができると共に、ＣａＯ源の融解が促進されて反応効率が上昇するため、少ないＣａＯ源の使用量で脱燐処理することができる。
【００３７】
予備脱燐処理工程で溶銑中の燐濃度を製品の規格以下まで下げた場合には、予備脱燐処理工程後の転炉精錬工程では実質的に脱燐処理する必要がなくなるため、鉄歩留まりの向上や生石灰等の媒溶剤原単位の低減が可能となり、更に、炉内にスラグがほとんどないために、安価なＭｎ源として転炉内に添加されるＭｎ鉱石の還元歩留まりを向上させることができる。
【００３８】
以上説明したように、本発明によれば、転炉精錬工程では脱燐処理を施すことなく、１回の溶銑の予備脱燐処理だけで充分に転炉精錬後の溶鋼中燐濃度を製品の規格以下にまで低下させることが可能であり、従って、溶鋼の製造コストを上昇させることなく、溶銑に予備脱燐処理を施すことによって、燐酸含有量が高く且つ優れた肥料特性を有する、燐酸肥料用原料としてのスラグを製造することが可能となる。又、予備脱燐処理工程で発生するスラグを前工程で使用した場合には、前工程における媒溶剤の原単位を削減することもできる。
【００３９】
【実施例】
以下、本発明を実施例に基づき説明する。図１に示す製造フロー図に基づき溶銑から溶鋼を溶製する試験を実施した。即ち、通常の鉄鉱石を用いて高炉で溶銑を製造し、この溶銑を、容量が３００トンの転炉に装入して予備脱燐処理を施した。予備脱燐処理は、脱燐剤であるＣａＯ源として生石灰を用い、生石灰及び酸素源を溶銑中の燐と効率良く反応させるために、生石灰粉体を酸素ガスと共に浴面に同時に吹き付ける方法（投射法）を採用した。そして、当該予備脱燐処理工程で発生した燐含有スラグの５０％の量を高炉用造滓剤として高炉でリサイクル使用した。この場合に、予備脱燐処理工程のみならず、予備脱燐処理工程よりも前の工程では蛍石等のフッ素含有物質を使用せずに製錬及び精錬した。
【００４０】
スラグをリサイクル使用することにより、高炉から出銑される溶銑中燐濃度は、スラグのリサイクルを開始する当初の０．１質量％から除々に増加し、最大で０．２５質量％まで増加した。そこで、燐濃度が０．１５〜０．２５質量％の範囲の高燐溶銑を３００トン転炉に装入して、上記と同一方法によって予備脱燐処理を施した。その結果、全ての試験操業において、予備脱燐処理後の溶銑中燐濃度は、製品規格（Ｐ≦０．０１５質量％）以下である０．０１２質量％まで低下し、スラグ中のＰ２ Ｏ５ に換算した燐酸濃度（以下、単に「Ｐ２ Ｏ５ 濃度」と記す）は、予備脱燐処理により発生したスラグ量が２５ｋｇ／ｔの場合で１２．３質量％となった（試験Ｎｏ．２参照）。発生したスラグの一部を燐酸肥料用原料として供した。
【００４１】
又、比較のために、図２に示す従来法によって溶銑から溶鋼を溶製する試験も実施した。この場合、使用した鉄鉱石は上記と同様の通常の鉄鉱石である。高炉で出銑した溶銑を３００トン転炉に装入して予備脱燐処理を施した。予備脱燐処理は、溶銑を転炉内へ装入した後、所定量の生石灰を上置き添加し、上吹きランスから酸素吹錬を実施して行った。
【００４２】
高炉から出銑した溶銑の燐濃度は０．１質量％であり、予備脱燐処理によって燐濃度は０．０２質量％まで低下した。予備脱燐処理により発生したスラグ中のＰ２ Ｏ５ 濃度は、スラグ発生量が４５ｋｇ／ｔの場合に４．６質量％となった（試験Ｎｏ．９参照）。そして、この予備脱燐処理を施した溶銑を脱炭精錬用転炉に装入して脱炭精錬して、炭素を除去すると共に、燐を製品規格（Ｐ≦０．０１５質量％）以下の燐濃度である０．０１２質量％まで低減させた。この場合、転炉内には脱燐剤としてＣａＯ源即ち生石灰を添加した。尚、従来法においても蛍石等のフッ素含有物質は使用しないで製錬及び精錬した。
【００４３】
表１に、これらの試験操業における予備脱燐処理条件及びスラグ中のＰ２ Ｏ５ 濃度等の操業結果を示す。又、図３に、予備脱燐処理で生成したスラグ中のＰ２ Ｏ５ 濃度とスラグ発生量との関係を示す。尚、表１の備考欄には、本発明の範囲内の試験操業には本発明例と表示し、それ以外の試験操業は従来例と表示した。
【００４４】
【表１】
表１に示すように、本発明方法によって溶銑を予備脱燐処理することにより、Ｐ２ Ｏ５ 濃度が１０質量％以上のスラグ即ち上記（１）式を満足するスラグを安定して製造することが可能であることが分かった。又、表１及び図３に示すように、スラグ発生量が増加するほど、即ち、脱燐剤添加量の増加に伴ってスラグ中のＰ２ Ｏ５ 濃度は低下しており、従って、スラグ中のＰ２ Ｏ５ 濃度を高位に維持するには、脱燐率を低下させない範囲で脱燐剤の添加量を少なくすることが好ましいことが分かった。
【００４６】
【発明の効果】
本発明によれば、転炉精錬工程では脱燐処理を施すことなく、１回の溶銑の予備脱燐処理だけで充分に転炉精錬後の溶鋼中燐濃度を製品の規格以下にまで低下させることが可能であり、従って、溶鋼の製造コストを上昇させることなく、溶銑の予備脱燐処理により、燐酸含有量が高く且つ優れた肥料特性を有する、燐酸肥料用原料としてのスラグを製造することが可能となる。
【図面の簡単な説明】
【図１】本発明方法の１つの例を示す製造フロー図である。
【図２】従来方法の製造フロー図である。
【図３】予備脱燐処理で生成したスラグ中のＰ２ Ｏ５ 濃度とスラグ発生量との関係を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improved technology of a method for producing a raw material for a phosphate fertilizer formed of a slag containing phosphoric acid, which is generated in a preliminary dephosphorization treatment process of hot metal, and specifically, has a high phosphoric acid content and excellent fertilizer characteristics. The present invention relates to a method for producing slag as a raw material for a phosphate fertilizer.
[0002]
[Prior art]
At present, most phosphate fertilizers are manufactured using phosphate rock as a raw material, but there is a concern that phosphate rock will be depleted in the future. On the other hand, from the viewpoint of environmental issues, there is a high demand for effective use of slag generated when removing impurities in molten iron in the steel making process, and phosphoric acid generated when removing phosphorus, which deteriorates steel material properties, from molten iron is high. The use of slag containing as a raw material for phosphate fertilizer has been practiced and studied.
[0003]
Thomas phosphorus fertilizer is most widely known as a phosphate fertilizer made from slag. Thomas Phosphorus fertilizes so-called Thomas hot metal (usually, the concentration of phosphorus in the hot metal is around 2% by mass), which is produced from iron ore with a high phosphorus content, using a Thomas converter to refine it. The slag is used as a raw material, and is characterized by a high phosphoric acid concentration of 16 to 22% by mass. However, in order to produce Thomas phosphorus fertilizer, it is necessary to use a Thomas converter and to use iron ore having a high phosphorus content as a raw material, and in the Thomas converter, the phosphorus concentration of refined molten steel is high. There are many problems such as the large amount of slag and slag generated. Therefore, the Thomas converter has been replaced by the so-called LD converter using pure oxygen, which is now widely used worldwide. Is hardly manufactured.
[0004]
By the way, the phosphorus concentration in iron ore imported and used in Japan is higher than that in iron ore produced in Europe and the United States. A so-called preliminary dephosphorization treatment is performed in which the dephosphorization is performed at the stage of the hot metal, which is a low temperature region that is advantageous to the above. However, since the concentration of phosphorus in the hot metal that is tapped from the blast furnace is still about 0.1% by mass, it was converted to P 2 O 5 in the slag generated by the conventional general hot metal preliminary dephosphorization treatment. The concentration of phosphoric acid is at most 5% by mass, and slag containing phosphoric acid at such a high concentration that it can be used as a raw material for phosphate fertilizer is not produced. Therefore, several methods have been proposed for producing slag containing high concentration of phosphoric acid, which can be used as a raw material for a phosphate fertilizer, in a pre-phosphorus removal process of hot metal.
[0005]
For example, in Patent Literature 1, a preliminary dephosphorization treatment of hot metal is performed in two stages, and slag generated in the second preliminary dephosphorization treatment is used as a part of the blast furnace raw material to produce hot metal, whereby blast furnace There has been proposed a method of increasing the phosphorus concentration of hot metal from tapping and increasing the phosphoric acid concentration of slag generated by the first preliminary dephosphorization treatment. By using the phosphorus-containing slag generated in the converter refining performed later as a part of the blast furnace raw material, the phosphorus concentration of the hot metal discharged from the blast furnace is increased, and the phosphoric acid in the slag generated by the pre-phosphorus treatment of the hot metal is reduced. Methods for increasing the concentration have been proposed.
[0006]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 8-3612
[Patent Document 2]
JP-A-8-3613
[Problems to be solved by the invention]
However, in these methods, in order to obtain a slag having a high phosphoric acid content, it is necessary to add a special process to the conventional process, and there is a problem that a dephosphorization treatment cost and a slag recovery cost increase. . For example, in the method of Patent Document 1 in which the preliminary dephosphorization treatment of hot metal is divided into two, two dephosphorization treatment plants are required. The amount of phosphorus that can be treated is reduced by about half, and not only productivity is reduced, but also there is a risk that all the hot metal cannot be subjected to the preliminary dephosphorization treatment. Further, in the method of Patent Document 2 in which dephosphorization is performed in a converter after preliminarily dephosphorizing hot metal, converter refining is not much different from a conventional refining method using a large amount of a dephosphorizing slagging agent such as quicklime. It is necessary to carry out the method, and the advantage of preliminarily dephosphorizing the hot metal is completely lost, so that the process becomes a specialized process for producing a raw material of a phosphate fertilizer, and increases the production cost of molten steel.
[0009]
Furthermore, in order to use it as a phosphate fertilizer, phosphoric acid in slag needs to be water-soluble, and it cannot be effectively used as a phosphate fertilizer simply by increasing its concentration. In Patent Literature 1 and Patent Literature 2, no measures are taken with respect to securing water-soluble phosphoric acid, and slag excellent in fertilizer properties, that is, slag securing water-soluble phosphoric acid is not necessarily obtained. It is hard to say.
[0010]
The present invention has been made in view of the above circumstances, and it is an object of the present invention to eliminate the need for performing hot metal dephosphorization treatment in two or more steps, and to perform a sufficient converter with only one preliminary dephosphorization treatment. A slag as a raw material for phosphate fertilizer, which has a high phosphoric acid content and excellent fertilizer properties without increasing the production cost of molten steel, capable of lowering the phosphorus concentration in molten steel after refining to a product standard or less. Is to provide a method for producing a hot metal by a preliminary dephosphorization treatment of hot metal.
[0011]
[Means for Solving the Problems]
The present inventors have conducted intensive studies in order to solve the above problems. The results of the study are described below.
[0012]
In the hot metal preliminary dephosphorization treatment step, since the temperature of the molten metal during the treatment is lower than that in the decarburization refining in the converter, the fluorite is usually used to promote the slagging of CaO used as a dephosphorizer. CaF 2 ) is used. CaO reacts with fluorite to lower its melting point and promote slagging. However, when fluorine is present in the slag, the fluorine binds to phosphoric acid and CaO to form fluorapatite, which inhibits the water solubility of phosphoric acid. The problem that the performance is not ensured occurs.
[0013]
In order to solve this problem, the present inventors have clarified the relationship between the amount of fluorine contained in slag and the solubility of phosphoric acid. As a result, in order to secure soluble phosphoric acid in the slag, the phosphoric acid concentration (% by mass) calculated as P 2 O 5 in the slag is at least 5.6 times the fluorine concentration (% by mass) in the slag. We have learned that it is necessary to secure the above. That is, when the phosphoric acid concentration in terms of P 2 O 5 in the slag is less than 5.6 times the fluorine concentration, most of the phosphoric acid in the slag exists in the form of fluorapatite, and water-soluble phosphoric acid is obtained. I learned that I can't do that.
[0014]
Therefore, based on this finding and the fact that slag is a raw material for phosphate fertilizer, the relationship between the phosphoric acid concentration (% by mass) converted to P 2 O 5 in the slag and the fluorine concentration (% by mass) is shown in the following (1). Specified within the range of the formula. By satisfying the range of the following formula (1), at least 10% by mass or more of soluble phosphoric acid is ensured in the slag, and an excellent effect as a phosphate fertilizer can be exerted.
[0015]
(Equation 1)
Further, in order to satisfy the above expression (1), the knowledge that it is necessary to adjust the phosphorus concentration in the hot metal before the preliminary dephosphorization treatment in the range of 0.15% by mass to 0.25% by mass. Got. The reason is that when the phosphorus concentration of the hot metal is less than 0.15% by mass, the amount of phosphorus transferred into the slag in the preliminary dephosphorization treatment is small, so that the phosphoric acid concentration in the slag does not become sufficiently high. When the phosphorus concentration of the hot metal exceeds 0.25% by mass, the phosphorus concentration after the dephosphorization treatment does not decrease to below the specification value of the product even if the dephosphorization treatment is performed in the preliminary dephosphorization treatment step. This is because the dephosphorization process must be performed in the converter refining process described above, which leads to an increase in production cost.
[0017]
The present invention has been made based on the above findings, and the method for producing a raw material for a phosphate fertilizer according to the first invention is a phosphorus-containing slag generated in a preliminary dephosphorization step of hot metal produced in a blast furnace, wherein the slag contains A method for producing a raw material for a phosphate fertilizer comprising a phosphorus-containing slag that satisfies the above formula (1) with respect to the concentration of phosphoric acid (% by mass) converted to P 2 O 5 with respect to the concentration of fluorine (% by mass) in slag. Then, the phosphorus concentration of the hot metal before the dephosphorization treatment in the preliminary dephosphorization treatment process is adjusted within a range of 0.15% by mass to 0.25% by mass, and the hot metal is dephosphorized in the preliminary dephosphorization treatment process. It is characterized by doing.
[0018]
The method for producing a raw material for phosphate fertilizer according to the second invention is characterized in that, in the first invention, the phosphorus-containing slag generated in the preliminary dephosphorization step of hot metal does not substantially contain fluorine. is there.
[0019]
The method for producing a raw material for a phosphate fertilizer according to a third invention is the method of the first or second invention, wherein the phosphorus-containing slag generated in the preliminary dephosphorization process of the hot metal is subjected to a process prior to the preliminary dephosphorization process of the hot metal. It is characterized in that it is used as a part of the charged material in the process.
[0020]
The method for producing a raw material for a phosphate fertilizer according to a fourth invention is the method for producing a raw material for phosphate fertilizer according to the third invention, wherein at least 50% of the phosphorus-containing slag generated in the preliminary dephosphorization process of the hot metal is subjected to the preliminary dephosphorization process of the hot metal. Is also used as a part of the charged raw material in the previous step.
[0021]
The method for producing a raw material for phosphate fertilizer according to a fifth invention is the method according to the third or fourth invention, wherein the phosphorus-containing slag is loaded in a blast furnace step or a sintering furnace step for sintering iron ore. It is characterized in that it is used as a part of a raw material.
[0022]
The method for producing a raw material for a phosphate fertilizer according to a sixth invention is the method according to the third or fourth invention, wherein the phosphorus-containing slag is charged in a de-siliconization process of hot metal which is a process preceding the preliminary de-phosphorization process. It is characterized in that it is used as a part of.
[0023]
In the method for producing a raw material for phosphate fertilizer according to the seventh invention, in the first or second invention, the hot metal produced in the blast furnace has a mass ratio between the phosphorus content and the iron content of 0.0015 or more. It is characterized by being hot metal produced by using all or a part of iron ore.
[0024]
The method for producing a raw material for a phosphate fertilizer according to an eighth invention is the method according to any one of the first to seventh inventions, wherein the phosphorus concentration in the hot metal after the preliminary dephosphorization treatment is equal to or less than the product specification. In the converter refining step, which is a post-step of the step, substantially no dephosphorization treatment is performed.
[0025]
The method for producing a raw material for a phosphate fertilizer according to a ninth invention is the method according to any one of the first to eighth inventions, wherein the phosphorus-containing slag is obtained by mixing a CaO source and an oxygen source with a bath surface or bath in a dephosphorization vessel. The slag is characterized by being a slag generated by a dephosphorization treatment performed by supplying the slag to the same position inside.
[0026]
In the method for producing a raw material for a phosphate fertilizer according to a tenth aspect of the present invention, in any one of the first to eighth aspects, the phosphorus-containing slag is obtained by bathing a CaO source and an oxygen source from above a bath surface of a dephosphorization treatment vessel. The slag is characterized by being a slag generated by a dephosphorization treatment performed by projecting on a surface.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0028]
In the present invention, the phosphorus-containing slag generated in the preliminary dephosphorization step of hot metal is used as a raw material for phosphate fertilizer. However, the phosphorus-containing slag in which the phosphoric acid concentration (mass%) in terms of P 2 O 5 in the slag is within the range of the above formula (1) with respect to the fluorine concentration (mass%) in the slag is used as a raw material for phosphate fertilizer. Use as In the present invention, as a necessary condition for the phosphoric acid concentration in terms of P 2 O 5 in the slag to satisfy the above formula (1), the phosphorus concentration in the hot metal before the preliminary dephosphorization treatment is 0.15. It is adjusted in the range from mass% to 0.25 mass%.
[0029]
If the phosphorus concentration in the hot metal is in this range, by performing a preliminary dephosphorization treatment on the hot metal, without reducing the amount of CaO used as a dephosphorizing agent, that is, while maintaining a high dephosphorization rate, A phosphorus-containing slag having a composition satisfying the formula (1) can be obtained. However, since the phosphorus concentration in the hot metal after the preliminary dephosphorization treatment is about 0.01 to 0.02% by mass, the CaO source which is a dephosphorizing agent in accordance with the amount of dephosphorization in the preliminary dephosphorization treatment step. It is important to determine the amount used. That is, excessive use of the CaO source is not preferable because it lowers the phosphoric acid concentration in the slag. Specifically, the upper limit of the addition of the CaO source may be set to about 20 kg per ton of hot metal (hereinafter referred to as “kg / t”), although it depends on the phosphorus concentration of the hot metal.
[0030]
As one of means for adjusting the phosphorus concentration in the hot metal before the preliminary dephosphorization step to a range of 0.15 to 0.25% by mass, in the present invention, the slag generated in the preliminary dephosphorization processing of the hot metal is used. It is used as a part of the charged raw material, that is, a part of the auxiliary raw material in the step before the preliminary dephosphorization treatment step. The steps to be used include, for example, a blast furnace process for producing hot metal, a sintering furnace process for sintering fine iron ore into a bulk material for charging the blast furnace, and removing silicon in the hot metal before the preliminary dephosphorization process step The desiliconization treatment step is appropriate. In these steps, a CaO source is used as a slag-making agent, while the slag produced in the preliminary dephosphorization step contains CaO as a main component and can be sufficiently used as a slag-making agent in these steps. In this case, either one of these steps may be used, or two or more of these steps may be used in combination.
[0031]
Phosphorus exists in the form of oxides in the slag generated in the preliminary dephosphorization process, but cannot be stably present as oxides in the blast furnace and during the desiliconization reaction, and is reduced and transferred to the hot metal. I do. At present, when hot metal is manufactured using iron ore imported to Japan, the phosphorus concentration in the hot metal is about 0.1% by mass as described above, but the phosphorus in the slag is reduced and the hot metal is reduced. By moving to the inside, hot metal having a high phosphorus concentration can be produced.
[0032]
In this case, it is preferable to use 50% or more of the slag generated in the preliminary dephosphorization step in the step before the preliminary dephosphorization step. This makes it possible to stably obtain hot metal having a phosphorus concentration of 0.15 to 0.25 mass%. If the amount of slag used in the process preceding the preliminary dephosphorization process is less than 50% of the generated amount, the phosphorus concentration in the hot metal will not be sufficiently increased to a desired value due to the mass balance of phosphorus. The reason is that the phosphorus concentration in the hot metal becomes high enough to satisfy the range of the expression (1) when the amount of slag used in the previous step exceeds 50% of the generated amount. In this way, by limiting the amount of slag to be reused, hot metal having a predetermined phosphorus concentration can be stably obtained.
[0033]
On the other hand, even without using the phosphorus-containing slag generated in the preliminary dephosphorization step, the phosphorus concentration in the hot metal before the preliminary phosphorus removal step can be adjusted to the range of 0.15 to 0.25% by mass. . For example, a method for producing hot metal using iron ore having a high phosphorus content is to mix 100% or a part of iron ore having a mass ratio of phosphorus content to iron content of 0.0015 or more. Then, if the molten iron is charged into a blast furnace and hot metal is produced from the iron ore, hot metal having a phosphorus concentration in the range of 0.15 to 0.25 mass% can be produced. Therefore, hot metal may be manufactured using such iron ore.
[0034]
The method of the preliminary dephosphorization treatment is not particularly limited, and an ordinary method for dephosphorization of hot metal may be applied. That is, a hot metal source such as an oxygen gas or an oxygen-containing gas or a solid oxygen source such as iron ore or a mill scale is added to a hot metal stored in a hot metal transfer container such as a hot metal pot or a torpedo car or a storage container such as a converter. While blowing or blowing, a stirring gas such as nitrogen gas is blown into the hot metal to stir the hot metal, and a CaO source such as quick lime as a dephosphorizing agent is blown or blown into the hot metal to perform a dephosphorization treatment.
[0035]
However, as is apparent from the above formula (1), in order to increase the content of water-soluble phosphoric acid, the fluorine content in the slag is preferably as small as possible, and in particular, it does not substantially contain fluorine. That is, it is preferable not to contain fluorine other than fluorine inevitably mixed. In other words, it is preferable to perform smelting and smelting without using a fluorine-containing substance such as fluorite not only in the preliminary dephosphorization step but also in a step before the preliminary dephosphorization step.
[0036]
In order to dephosphorize hot metal while maintaining a high dephosphorization rate without using a fluorine-containing substance such as fluorite, it is necessary to efficiently react a CaO source and an oxygen source with phosphorus in the hot metal, A method of dephosphorizing hot metal by simultaneously adding a CaO source and an oxygen source to a bath or a bath surface or by projecting a CaO source and an oxygen source onto a bath surface from above the bath surface is preferable. Further, by performing the dephosphorization by such a method, the phosphorus concentration in the hot metal can be stably reduced to below the product specification, and the melting efficiency of the CaO source is promoted to increase the reaction efficiency. Dephosphorization can be performed using the amount of the CaO source.
[0037]
If the phosphorus concentration in the hot metal is reduced to below the product specification in the preliminary dephosphorization process, the dephosphorization process will not be necessary in the converter refining process after the preliminary dephosphorization process, and the iron yield will be reduced. It is possible to improve and reduce the basic unit of solvent such as quicklime, and furthermore, because there is almost no slag in the furnace, it is possible to improve the reduction yield of Mn ore added in the converter as an inexpensive Mn source. .
[0038]
As described above, according to the present invention, in the converter refining process, the phosphorus concentration in the molten steel after the converter refining can be sufficiently increased by only one preliminary dephosphorization treatment of the hot metal without performing the dephosphorization process. A phosphate fertilizer having a high phosphoric acid content and excellent fertilizer properties by preliminarily dephosphorizing hot metal without increasing the production cost of molten steel, and thus it is possible to reduce the production cost of molten steel. It is possible to manufacture slag as a raw material. Further, when slag generated in the preliminary dephosphorization step is used in the previous step, it is possible to reduce the basic unit of the solvent in the previous step.
[0039]
【Example】
Hereinafter, the present invention will be described based on examples. A test for producing molten steel from hot metal was carried out based on the production flow diagram shown in FIG. That is, hot metal was manufactured in a blast furnace using ordinary iron ore, and the hot metal was charged into a converter having a capacity of 300 tons to perform a preliminary dephosphorization treatment. The preliminary dephosphorization treatment uses a method in which quicklime is simultaneously blown together with oxygen gas onto a bath surface in order to use quicklime as a CaO source as a dephosphorizing agent and to cause quicklime and an oxygen source to efficiently react with phosphorus in hot metal (projection). Law) was adopted. Then, 50% of the phosphorus-containing slag generated in the preliminary dephosphorization step was recycled in a blast furnace as a blast furnace slag-making agent. In this case, smelting and smelting were performed without using a fluorine-containing substance such as fluorite in the pre-phosphorus removal step as well as in the steps before the preliminary dephosphorization step.
[0040]
By using the slag by recycling, the phosphorus concentration in the hot metal tapping from the blast furnace gradually increased from the initial 0.1% by mass when the slag was recycled, and increased to a maximum of 0.25% by mass. Therefore, high phosphorus hot metal having a phosphorus concentration in the range of 0.15 to 0.25% by mass was charged into a 300-ton converter and subjected to preliminary dephosphorization by the same method as described above. As a result, in all the test operations, the phosphorus concentration in the hot metal after the preliminary dephosphorization treatment was reduced to 0.012% by mass, which is below the product specification (P ≦ 0.015% by mass), and P 2 O in the slag was reduced. The phosphoric acid concentration converted to 5 (hereinafter simply referred to as “P 2 O 5 concentration”) was 12.3% by mass when the amount of slag generated by the preliminary dephosphorization treatment was 25 kg / t (Test No. 5). 2). Part of the generated slag was used as a raw material for phosphate fertilizer.
[0041]
For comparison, a test for smelting molten steel from hot metal by the conventional method shown in FIG. 2 was also performed. In this case, the iron ore used is a normal iron ore similar to the above. The hot metal spiked in the blast furnace was charged into a 300-ton converter to perform a preliminary dephosphorization treatment. The preliminary dephosphorization treatment was performed by charging hot metal into a converter, placing a predetermined amount of quicklime thereon, and performing oxygen blowing from an upper blowing lance.
[0042]
The phosphorus concentration of the hot metal spiked from the blast furnace was 0.1% by mass, and the phosphorus concentration was reduced to 0.02% by mass by the preliminary dephosphorization treatment. The P 2 O 5 concentration in the slag generated by the preliminary dephosphorization treatment was 4.6% by mass when the amount of slag generated was 45 kg / t (see Test No. 9). Then, the hot metal that has been subjected to the preliminary dephosphorization treatment is charged into a converter for decarburization refining and decarburization refining to remove carbon and to reduce phosphorus to a product standard (P ≦ 0.015 mass%) or less. The phosphorus concentration was reduced to 0.012% by mass. In this case, a CaO source, that is, quicklime was added as a dephosphorizing agent in the converter. In the conventional method, smelting and refining were performed without using a fluorine-containing substance such as fluorite.
[0043]
Table 1 shows the operation results such as the pre-phosphorus removal treatment conditions and the P 2 O 5 concentration in the slag in these test operations. FIG. 3 shows the relationship between the P 2 O 5 concentration in the slag generated by the preliminary dephosphorization treatment and the amount of slag generated. In the remarks column of Table 1, test operations within the scope of the present invention are indicated as examples of the present invention, and other test operations are indicated as conventional examples.
[0044]
[Table 1]
As shown in Table 1, the slag having a P 2 O 5 concentration of 10% by mass or more, that is, a slag satisfying the above formula (1), is stably produced by preliminarily dephosphorizing hot metal by the method of the present invention. Turned out to be possible. Further, as shown in Table 1 and FIG. 3, as the amount of slag generated increases, that is, the P 2 O 5 concentration in the slag decreases with an increase in the amount of the dephosphorizing agent added. In order to maintain the P 2 O 5 concentration at a high level, it was found that it is preferable to reduce the amount of the dephosphorizing agent as long as the dephosphorization rate is not reduced.
[0046]
【The invention's effect】
According to the present invention, in the converter refining process, the phosphorus concentration in the molten steel after the converter refining is sufficiently reduced to a level below the product specification by only one preliminary dephosphorization treatment of the hot metal without performing the dephosphorization treatment. Therefore, it is possible to produce slag as a raw material for phosphate fertilizer having a high phosphoric acid content and excellent fertilizer properties by preliminarily dephosphorizing hot metal without increasing the production cost of molten steel. Becomes possible.
[Brief description of the drawings]
FIG. 1 is a manufacturing flowchart showing one example of the method of the present invention.
FIG. 2 is a manufacturing flowchart of a conventional method.
FIG. 3 is a diagram showing the relationship between the concentration of P 2 O 5 in slag generated by preliminary dephosphorization and the amount of slag generated.
Claims (10)
燐酸濃度≧ ５．６×フッ素濃度＋１０…（１）Phosphorus-containing slag produced in the preliminary dephosphorization process of hot metal produced in a blast furnace, in which the concentration of phosphoric acid (% by mass) converted to P 2 O 5 in the slag is relative to the concentration of fluorine (% by mass) in the slag. A method for producing a raw material for a phosphate fertilizer comprising a phosphorus-containing slag satisfying the following formula (1), wherein the phosphorus concentration of hot metal before dephosphorization in a preliminary dephosphorization step is from 0.15% by mass to 0%. A method for producing a raw material for phosphate fertilizer, comprising adjusting the hot metal to a concentration of 25% by mass and dephosphorizing the hot metal in a preliminary dephosphorization step.
Phosphoric acid concentration ≧ 5.6 × fluorine concentration + 10 (1)
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| JP2002329833A JP2004161544A (en) | 2002-11-13 | 2002-11-13 | Method of manufacturing raw material for phosphate fertilizer |
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| JP2002329833A JP2004161544A (en) | 2002-11-13 | 2002-11-13 | Method of manufacturing raw material for phosphate fertilizer |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2016056075A (en) * | 2014-09-12 | 2016-04-21 | Ｊｆｅスチール株式会社 | Raw material for silicate phosphate fertilizer and method for manufacturing the same |
| CN115093253A (en) * | 2022-06-06 | 2022-09-23 | 中国恩菲工程技术有限公司 | Method and device for preparing calcium magnesium phosphate fertilizer by smelting |
-
2002
- 2002-11-13 JP JP2002329833A patent/JP2004161544A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2016056075A (en) * | 2014-09-12 | 2016-04-21 | Ｊｆｅスチール株式会社 | Raw material for silicate phosphate fertilizer and method for manufacturing the same |
| CN115093253A (en) * | 2022-06-06 | 2022-09-23 | 中国恩菲工程技术有限公司 | Method and device for preparing calcium magnesium phosphate fertilizer by smelting |
| CN115093253B (en) * | 2022-06-06 | 2024-04-09 | 中国恩菲工程技术有限公司 | Method and device for preparing calcium magnesium phosphate fertilizer by smelting |
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