JP4567164B2 - Method for producing anhydrous gypsum for cement composition from waste gypsum - Google Patents
Method for producing anhydrous gypsum for cement composition from waste gypsum Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、石膏廃材からセメント組成物に適した無水石膏類を回収する方法に関する。詳しくは、石膏廃材をキルンで焼成する際に、炉内の燃焼環境を制御することにより、II型無水石膏の含有量が高く、かつ全炭素含有量が大幅に低いセメント組成物に適した無水石膏類を製造する方法に関する。
【０００２】
【従来の技術】
石膏ボード廃材の有効な用途としてセメント原料に使用することが考えられるが、石膏ボードには種々の紙類や有機混和剤が使用されており、石膏ボード廃材をそのまま石膏原料としてセメントに配合するとセメント強度の発現性を低下させるなどの問題を招く(特開平10-36149号公報)。従って、このような問題を生じないように、石膏ボード廃材からセメント組成物の原料に適する石膏を回収して利用する必要がある。
【０００３】
このような背景から、従来、石膏ボード廃材から石膏を回収する方法がいくつか提案されている。その一例は、石膏ボード廃材を概ね３００℃前後に加熱することによって半水石膏や可溶性のIII型無水石膏として回収する方法である(特開平06-142633号公報)。また、他の例は、これより高い加熱温度で石膏ボード廃材を焼成することによって主にII型無水石膏を回収する方法である(特開平10-36149号公報)。
【０００４】
【発明が解決しようとする課題】
しかし、前者の方法は焼成温度が低いために石膏ボード廃材に含まれている紙や有機混和剤が炭化して残留し易く、セメント組成物用の石膏として適さない。
一方、後者の方法は本出願人の提案に係るものであり、石膏ボード廃材をより高温で焼成するために紙や有機混和剤が燃焼して気化し、焼成物から除去されるのでセメント組成物に適したII型無水石膏を回収することができる。ただし、ロータリーキルンを用いた実操業においては、十分な温度や時間で焼成しても、廃材に含まれる紙の量などが異なることによって炭化物(無機炭素)が充分に除去されずに残留する場合が暫々ある。従って、単に加熱温度と時間を制御するだけではセメント組成物に適したII型無水石膏を回収するのは必ずしも容易ではない。
【０００５】
具体的には、例えば、無機炭素の除去を促進させるために１２００℃より高い温度で石膏廃材を焼成するとＩ型無水石膏や酸化カルシウム(生石灰：CaO)が生成する。Ｉ型無水石膏はセメントの凝結時間を調節する作用が殆どなく、ＣａＯの量が多いとセメントの凝結や強度発現性に悪影響を与えるので、これらの量が増すのは好ましくない。一方、焼成温度が１２００℃より低くてもキルン内の燃焼環境が適切でないと局部的な過熱や燃焼不足を生じて炭素が残留し、この場合にもセメント組成物に適する石膏を回収することができない。
【０００６】
【課題を解決するための手段】
本発明は、先に提案した石膏廃材からII型無水石膏を回収する方法を更に改善したものであり、ロータリーキルンを用いて石膏廃材を焼成する場合、単に窯内の温度や滞留時間を制御するだけではなく、石膏廃材の窯内充填率、燃焼ガス中の酸素濃度を制御することによって、さらに望ましくは炉内にリフターを設け、紙類や有機混和剤の好適な燃焼環境を整えてセメント原料に適した無水石膏類を安定的に製造できるようにしたものである。
【０００７】
すなわち、本発明は以下の構成からなる無水石膏類の製造方法に関する。
（１）石膏廃材をキルンで焼成することにより無水石膏類を製造する方法において、焼成温度６００〜１２００℃、焼成時間１０分以上、石膏廃材の窯内充填率１５体積％以下、キルン入口の燃焼ガス中の酸素濃度５体積％以上に制御することにより、II型無水石膏の含有量８０重量％以上、半水石膏とIII型無水石膏の合計含有量５重量％以下、ＣａＯの含有量５重量％以下、および炭素含有量０.３重量％以下の無水石膏類を石膏廃材から製造することを特徴とする方法。
（２）II型無水石膏の含有量９０重量％以上、半水石膏とIII型無水石膏およびＣａＯの合計含有量５重量％以下、および炭素含有量０.２重量％以下の無水石膏類を石膏廃材から製造する上記(1)の方法。
（３）キルン内にリフターを設けて焼成することにより、炭素含有量およびＣａＯ含有量を低減する上記(1)または(2)の製造方法。
【０００８】
本発明によって得られる無水石膏類は、II型無水石膏を８０重量％以上、好ましくは９０重量％以上含み、石膏廃材中に含まれる有機混和剤や紙などの有機炭素が充分に燃焼するので有機炭素が実質的に残留せず、しかも燃焼してガス化した炭素は系外に除去されるので無機炭素も大幅に少なく、炭素含有量０.３重量％以下、好ましくは０.２重量％以下であり、建築資材や土木資材の原料として好適である。特にセメント組成物に配合しても強度低下を生じないなどの利点を有する。また、一般にコンクリートに空気を連行するために空気連行剤(ＡＥ剤)を添加するが、フライアッシュ中に含まれる未燃炭素がそうであるように、無機炭素は空気連行剤を吸着し、結果的にコンクリートへの空気連行を阻害する。ところが本発明によって得られる無水石膏は無機炭素量が極めて少ないので、コンクリートに配合しても空気連行剤の性能を阻害しないという利点がある。
【０００９】
【発明の実施の形態】
以下、実施形態に即して本発明を詳細に説明する。
本発明は、石膏廃材をキルンで焼成することにより無水石膏類を製造(回収)する方法において、焼成環境を制御することによりセメント組成物に適する無水石膏類を製造する方法に関する。具体的には、焼成温度６００〜１２００℃、焼成時間１０分以上、石膏廃材の窯内充填率１５体積％以下、キルン入口の燃焼ガス中の酸素濃度５体積％以上に制御することにより、II型無水石膏の含有量８０重量％以上、半水石膏とIII型無水石膏の合計含有量５重量％以下、ＣａＯの含有量５重量％以下、および炭素含有量０.３重量％以下の無水石膏類を石膏廃材から製造することを特徴とする方法であり、好ましくは、炭素含有量およびＣａＯ含有量をさらに低減し、II型無水石膏の含有量９０重量％以上、半水石膏とIII型無水石膏およびＣａＯの合計含有量５重量％以下、および炭素含有量０.２重量％以下の無水石膏類を石膏廃材から製造する方法である。
【００１０】
本発明において、石膏廃材とは石膏を主体とする廃材を云い、石膏ボード廃材やその他の石膏製品の廃材等を含む。特に発生量の多い石膏ボード廃材が例示され、その発生場所や石膏廃材の形態は問わない。石膏ボード原紙や塩化ビニル樹脂等の化粧材を有するものでも良く、板状や塊状または粉粒状のものでも良い。
さらに、石膏廃材に含まれる石膏の形態や含水量等も制限されず、二水石膏、半水石膏もしくは無水石膏またはこれらの混合物からなるものでも良い。
【００１１】
本発明において、無水石膏類とはII型無水石膏を主体とするものを云い、少量の半水石膏やＣａＯ、灰分、炭分等を含むものでも良い。本発明の製造方法は、II型無水石膏の含有量８０重量％以上であって、半水石膏とIII型無水石膏の合計含有量５重量％以下、ＣａＯの含有量５重量％以下、および炭素含有量０.３重量％以下の無水石膏類を石膏廃材から製造する方法であり、好ましくはII型無水石膏の含有量９０重量％以上、半水石膏とIII型無水石膏およびＣａＯの合計含有量５重量％以下、および炭素含有量０.２重量％以下の無水石膏類を石膏廃材から製造する方法である。なお、この炭素含有量は無水石膏類を１２５０℃で２分間加熱し、生成した二酸化炭素を赤外線吸収法で定量して得た値を炭素(Ｃ)量に換算し、この炭素(Ｃ)量が測定に供した無水石膏類の重量中に占める値を重量％で示したものであり、有機炭素および無機炭素を合わせた換算量である。
【００１２】
II型無水石膏はモルタルやコンクリートなどのセメント組成物に配合したときに、その瞬結防止に効果的に作用する。一方、半水石膏やIII型無水石膏の量が多いと偽凝結を生じやすい。また、ＣａＯの含有量が多いと凝結時間(始発、終結)の短縮化を起こしやすく、有機炭素は強度発現性の低下をきたし、無機炭素はＡＥ剤、減水剤等のコンクリート用混和剤を吸着してコンクリートの空気量および流動性の低下等を招く。Ｉ型無水石膏は凝結調整作用が殆どない。従って、本発明においては、II型無水石膏の含有量を８０重量％以上、半水石膏とIII型無水石膏の合計含有量を５重量％以下、ＣａＯの含有量を５重量％以下、および炭素含有量を０.３重量％以下とする。好ましくは、II型無水石膏の含有量を９０重量％以上、半水石膏とIII型無水石膏およびＣａＯの合計含有量を５重量％以下、および炭素含有量を０.２重量％以下とする。
【００１３】
本発明の製造方法は、キルン等を用いて石膏廃材を焼成して無水石膏類を製造する際に、焼成温度を６００〜１２００℃、焼成時間(キルン内滞留時間)を１０分以上とし、石膏廃材の窯内充填率１５体積％以下、キルン入口(窯尻)の燃焼ガス中の酸素濃度を５体積％以上に制御することによって上記組成の無水石膏類を製造する方法である。
【００１４】
炉内の焼成温度が６００℃未満では焼成時間を延長しても石膏廃材が焼成不足になり、無水石膏類の炭素含有量を０.３重量％以下に低減するのが難しい。焼成温度が１２００℃より高いと炭素含有量は０.３％以下に低減するが、一方で石膏が熱分解して三酸化イオウ(SO3)と生石灰(CaO)が生成し、またII型無水石膏からＩ型無水石膏への転移が起るので好ましくない。なお、上記焼成温度の範囲において、上限側の焼成温度で操業する場合には出来る限り焼成時間を上記範囲内で短くし、下限側の焼成温度で操業する場合には焼成時間を長くすることが望ましい。
【００１５】
焼成時間(キルン内滞留時間)は１０分以上が好ましい。焼成時間が１０分未満であると、焼成温度が上記範囲内でも石膏廃材の焼成が不十分となり、石膏ボード廃材等に含まれる原紙や有機混和剤が完全に燃焼せず、この炭素分が無水石膏中に残留して、炭素含有量が０.３重量％を上回るようになる。さらには半水石膏やIII型無水石膏が残留する場合もある。
【００１６】
さらに、キルンを用いた実操業において上記組成の無水石膏類を安定に回収するためには、単に窯内温度や焼成時間を制御するだけではなく、炭素を十分に系外に除去し、かつII型無水石膏の含有量を高めるように焼成環境を整える必要がある。すなわち、石膏廃材の窯内充填率１５体積％以下、キルン入口(窯尻)の燃焼ガス中の酸素濃度を５体積％以上に制御することが好ましい。石膏廃材の窯内充填率が１５体積％より多く、また燃焼ガス中の酸素濃度が５体積％より少ないと石膏廃材の燃焼が不十分になり、無水石膏類の炭素含有量が０.３重量％を上回るようになる。一方、焼成温度と時間、石膏廃材の窯内充填率、燃焼ガス中の酸素濃度を上記本発明の範囲内に制御することにより無水石膏類の炭素含有量が０.３重量％以下、好ましくは０.２重量％以下に低減することができる。因みに、後述の実施例に示すように、本発明の焼成条件下で焼成したもの(No.3,6,11,14,17,20,23,26)は回収した無水石膏に含まれる炭素含有量は何れも０.３重量％以下であり、一部(No.14,20,23,26)の炭素含有量は０.２重量％以下である。
【００１７】
さらに、無水石膏類の炭素含有量を低減するには、石膏廃材に含まれる紙や可燃物の燃焼および無機炭素の除去を促進することが必要であり、特に無機炭素をガス化して系外に除去する必要がある。そこで、窯内壁にリフターを設け、キルンの回転によって炉内の石膏廃材を十分に攪拌することにより、炉内の石膏廃材に対する燃焼ガスおよび炭酸ガスなどの通気性を高めると良い。これにより石膏廃材の全体に燃焼ガスが供給されて均一に燃焼し、炭素源はガス化して系外に除去されるので、無水石膏類の炭素含有量を大幅に低減することができる。また、炉内にリフターを設けて石膏廃材の攪拌を促すことにより、リフターを設けない場合よりも低い温度で焼成しても無水石膏類の炭素含有量を低減することができる。従って、高温焼成によるＣａＯの副生も少なく、セメント組成物用として好適な無水石膏類を得ることができる。
【００１８】
以上のようにして得た本発明の無水石膏類はセメント組成物に配合する無水石膏原料として好適である。なお、ここでセメント組成物とは、セメントを主体とした水硬性組成物を云い、例えば、普通ポルトランドセメント、早強セメント、低熱セメント、フライアッシュセメント、高炉セメント等の混合セメント、およびアーウィン(3CaO・3Al2O3・CaSO4)系セメント、カルシウムフルオロアルミネート(11CaO・7Al2O3・CaF2)系セメント、膨張セメントなどを主体とし、固化材、注入材、裏込材、地盤改良材等の各種用途に用いられるものを含む。本発明の無水石膏類はこれらのモルタルやコンクリートなどに用いるセメント組成物に配合する無水石膏原料として好適である。
【００１９】
【実施例】
以下、本発明を実施例によって具体的に示す。なお、これらは例示であり、本発明の適用範囲を限定するものではない。
【００２０】
〔実施例１〕
石膏ボード廃材(厚さ21mm、紙含有量７〜25wt％)をロールクラッシャーで粗砕し、振動篩を使用して直径100mm以下に篩い分けした。この石膏ボード廃材の粗砕物(原紙付着)をロータリーキルン(直径1.3m、長さ20m)に投入し、表１に示す条件下で焼成した。得られた無水石膏類の形態を粉末X線回折によって同定・定量し、ＣａＯの含有量を規格試験(CAJS I 01:セメント協会標準試験方法)に準じて測定した。また、炭素含有量をカーボン分析計によって測定した。その結果を表１にまとめて示した。
【００２１】
焼成温度が５００℃では、炉内の酸素濃度や石膏廃材の充填率を適切な範囲に整えても、石膏廃材の紙量および焼成時間にかかわらず、回収した無水石膏類の炭素含有量は０.３重量％を上回る(No.1,2)。また、焼成温度が６００℃では、紙の量が多い石膏廃材を用いた場合において、充填率１５体積％以下および酸素濃度５体積％以上に制御したもののみ炭素含有量を０.３重量％以下とすることができた(No.3,6)。この場合、焼成時間を長くしても大きな効果はなかった(No.10)。焼成温度が７００℃〜１０００℃に上昇すると無水石膏類に含まれる炭素含有量は次第に減少するが、炉内の酸素濃度と石膏廃材充填率については同様の傾向が認められ、酸素濃度が少なく、石膏廃材の充填率が高いものは炭素含有量が０.３重量％を上回る(No.12,13,15,16,18,19,21,22)。
【００２２】
また、１１００℃の焼成温度では酸素濃度が比較的少なくても無水石膏類の炭素含有量は０.３重量％以下に低減されるが、焼成時間が１５分より長いとII型無水石膏の量が減少してＣａＯ量が多くなる(No.24)。また、焼成温度が１２５０℃では炭素含有量は０.３重量％以下に低減するが、焼成時間が１０分でもII型無水石膏の量が減少してＣａＯ量が増加する(No.29)。キルンによる焼成において焼成時間を１０分未満とすると安定操業が極めて困難である。以上のことから、II型無水石膏の含有量８０重量％以上、半水石膏とIII型無水石膏の合計含有量５重量％以下、ＣａＯの含有量５重量％以下、および炭素含有量０.３重量％以下の無水石膏類を得るには、焼成温度６００〜１２００℃、石膏廃材の充填率１５体積％以下、燃焼ガス中の酸素濃度５体積％以上の焼成条件が適当である(No.3,6,11,14,17,20,23,26)。
【００２３】
【表１】
〔実施例２〕
図１に示すように、実施例１で用いたキルン１にリフター２を取り付け、その他は実施例１と同様の条件下で石膏廃材を焼成して無水石膏類を回収した。この結果を表２に示した(リフター距離４ｍの場合)。なお、リフターの有無以外は焼成条件がほぼ同様な実施例１の結果を対比して表２に示した(No.41に対してNo.6、No.42に対してNo.3、No.43に対してNo.10)。
本例に示すように、回収した無水石膏類に含まれる炭素含有量はリフターを設置して石膏廃材の窯内における攪拌を高めたものが相対的に低い。このことから、キルンにリフターを設けることにより、石膏の分解などの問題を生じない、より低い温度で焼成しても十分な焼成効果が得られ、無水石膏類に含まれる炭素含有量を効率的に低減できることがかわる。
【００２５】
【表２】
〔実施例３〕
実施例１で得た無水石膏類(No.9,11,14,17,20,28)をセメント中のＳＯ3量が２.０重量％になるように、普通ポルトランドセメントクリンカー粗砕物(粒径1.2mm以下)に混合し、これをボールミルでブレーン比表面積３２５０cm2/gまで粉砕してセメントを製造した。なお、比較のため、天然二水石膏を単独に用い(以下、標準石膏)、上記と同様にしてセメントを製造した。これらのセメントを用い、表３に示す示方配合でコンクリートを練り混ぜ、各種コンクリート試験を行った。その結果を表４に示した。なお、コンクリートの調製時に、セメントに対して０.０２％の空気量調整剤(ＡＥ助剤:商品名ポゾリス303A,ＮＭＢ社製品)を混練水に溶解して加えた。スランプ、空気量、凝結および強度試験は各々規格(JIS A1101、JIS A1116、JIS A6204、JIS A1108)で定める方法に準拠した。
【００２７】
【表３】
【表４】
表４に示すように、本発明の組成範囲を有する無水石膏(No.11,14,17,20)を配合したセメントを用いて調製したコンクリートは、天然二水石膏(標準石膏)を用いたセメントを用いた場合とほぼ同等の試験結果を示しており、セメント用石膏原料として十分な効果を有するものであった。一方、II型無水石膏の含有量が少なく、ＣａＯ含有量が高い無水石膏(No.28)を配合したセメントを用いて調製したコンクリートは凝結時間が始発および終結の何れもが大幅に短縮され、圧縮強度も低い。また、炭素含有量の多い無水石膏(No.9)を用いたコンクリートでは、所定の空気量調整剤の添加にもかかわらず十分な空気量を確保することができず、セメント用無水石膏として望ましくないことがわかる。空気量はコンクリートの凍結融解抵抗性確保などの目的から、規格(JIS A5308)において許容量が４.５±１.５％に規定されている。従って、空気量がセメントによって変化することはコンクリートの品質管理を極めて困難にするので好ましくない。また、無水石膏に含まれる炭素含有量が多いとコンクリート表面に炭素粉が浮き上がり色斑の原因になる。
【００３０】
〔実施例４〕
実施例１で得た無水石膏類(No.14)をセメント系固化材用の添加剤として使用した場合の性能を評価した。具体的には、普通ポルトランドセメントクリンカーに固化材中のＳＯ3量が７.５重量％となるように上記無水石膏類を添加してボールミルによりブレーン比表面積４５００cm2/ｇに粉砕してセメント系固化材を調製した。この固化材を粘性土（含水比87.3重量％）、ローム土（含水比86.4重量％）および有機質土（含水比87.3重量％）に使用した。
試験方法は、固化材と対象土の合量１ｍ3に対して固化材１００kgを添加し、５分間攪拌した後、これを鋼製モールド(直径5cm、高さ10cm)に充填して成形し、規格(JIS A 1216)に従い、一軸圧縮強さ試験を行った。この結果を表５に示した。この結果から明らかなように、本発明の組成の範囲内に属する無水石膏類は固化材の添加材として使用した場合、いずれの対象土に対しても標準石膏を使用した場合と比べてほぼ同等の圧縮強さを示し、固化材の添加材としても十分に使用可能であることを示している。
【００３１】
【表５】
【発明の効果】
本発明の製造方法によれば、石膏廃材を原料として、II型無水石膏の含有量８０重量％以上、半水石膏とIII型無水石膏の合計含有量５重量％以下、ＣａＯの含有量５重量％以下、および炭素含有量０.３重量％以下の無水石膏類、好ましくは、II型無水石膏の含有量９０重量％以上、半水石膏とIII型無水石膏およびＣａＯの合計含有量５重量％以下、および炭素含有量０.２重量％以下の無水石膏類を得ることができる。この無水石膏類は半水石膏とIII型無水石膏の合計含有量、ＣａＯの含有量および炭素含有量が大幅に少なく、セメント組成物の石膏原料として好適である。また、本発明によれば、石膏廃材の有効な処理方法が提供されると共に石膏廃材の有効利用も併せて図ることができる。
【図面の簡単な説明】
【図１】 実施例２におけるリフターの設置状態を示す説明図。
【符号の説明】
１−キルン、２−リフター[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for recovering anhydrous gypsum suitable for a cement composition from gypsum waste. Specifically, when calcining gypsum waste in a kiln, by controlling the combustion environment in the furnace, the anhydrous type suitable for cement compositions with a high content of type II anhydrous gypsum and a significantly lower total carbon content The present invention relates to a method for producing gypsum.
[0002]
[Prior art]
As an effective use of gypsum board waste, it is conceivable to use it as a cement raw material, but various papers and organic admixtures are used in gypsum board. This causes problems such as a decrease in strength (Japanese Patent Laid-Open No. 10-36149). Therefore, it is necessary to collect and use gypsum suitable for the raw material of the cement composition from the gypsum board waste material so as not to cause such problems.
[0003]
Against this background, several methods for recovering gypsum from gypsum board waste have been proposed. One example is a method of recovering gypsum board waste material as hemihydrate gypsum or soluble type III anhydrous gypsum by heating to about 300 ° C. (Japanese Patent Laid-Open No. 06-142633). Another example is a method of mainly recovering type II anhydrous gypsum by firing gypsum board waste at a higher heating temperature (Japanese Patent Laid-Open No. 10-36149).
[0004]
[Problems to be solved by the invention]
However, the former method is not suitable as a gypsum for a cement composition because the firing temperature is low and the paper and the organic admixture contained in the gypsum board waste are easily carbonized and remain.
On the other hand, the latter method is based on the proposal of the present applicant, and in order to fire the gypsum board waste at a higher temperature, the paper and the organic admixture are burned and vaporized, and are removed from the fired product. Type II anhydrous gypsum suitable for use can be recovered. However, in actual operation using a rotary kiln, even if baked at a sufficient temperature and time, carbide (inorganic carbon) may remain without being removed sufficiently due to differences in the amount of paper contained in the waste material. There is for a while. Therefore, it is not always easy to recover type II anhydrous gypsum suitable for a cement composition simply by controlling the heating temperature and time.
[0005]
Specifically, for example, when gypsum waste is fired at a temperature higher than 1200 ° C. in order to promote removal of inorganic carbon, type I anhydrous gypsum and calcium oxide (quick lime: CaO) are generated. Type I anhydrous gypsum has almost no effect of adjusting the setting time of cement, and a large amount of CaO adversely affects the setting and strength development properties of cement, so it is not preferable to increase these amounts. On the other hand, even if the firing temperature is lower than 1200 ° C., if the combustion environment in the kiln is not appropriate, local overheating and combustion shortage occur, and carbon remains. In this case, gypsum suitable for the cement composition can be recovered. Can not.
[0006]
[Means for Solving the Problems]
The present invention is a further improvement of the previously proposed method for recovering type II anhydrous gypsum from gypsum waste, and when firing gypsum waste using a rotary kiln, simply controlling the temperature and residence time in the kiln. Instead, by controlling the filling rate of gypsum waste in the kiln and the oxygen concentration in the combustion gas, it is more desirable to install a lifter in the furnace to prepare a suitable combustion environment for papers and organic admixtures as a cement raw material. A suitable anhydrous gypsum can be stably produced.
[0007]
That is, this invention relates to the manufacturing method of the anhydrous gypsum which consists of the following structures.
(1) In a method for producing anhydrous gypsum by firing gypsum waste in a kiln, a firing temperature of 600 to 1200 ° C., a firing time of 10 minutes or more, a filling rate of gypsum waste in a kiln of 15% by volume or less, combustion at the kiln inlet By controlling the oxygen concentration in the gas to 5% by volume or more, the content of type II anhydrous gypsum is 80% by weight or more, the total content of hemihydrate gypsum and type III anhydrous gypsum is 5% by weight or less, and the content of CaO is 5% by weight. %, And an anhydrous gypsum having a carbon content of 0.3% by weight or less is produced from gypsum waste.
(2) Gypsum with an anhydrous gypsum content of Type II anhydrous gypsum of 90 wt% or more, hemihydrate gypsum, type III anhydrous gypsum and CaO total content of 5 wt% or less, and carbon content of 0.2 wt% or less The method of (1) above, wherein the method is produced from waste materials.
(3) The production method of (1) or (2) above, wherein the carbon content and the CaO content are reduced by providing a lifter in the kiln and firing.
[0008]
The anhydrous gypsum obtained by the present invention contains 80% by weight or more, preferably 90% by weight or more of type II anhydrous gypsum, and organic carbon such as organic admixture and paper contained in the gypsum waste material is sufficiently burned. Carbon does not substantially remain, and the carbon that is burned and gasified is removed from the system, so the amount of inorganic carbon is greatly reduced, and the carbon content is 0.3% by weight or less, preferably 0.2% by weight or less. It is suitable as a raw material for building materials and civil engineering materials. In particular, there is an advantage that even if it is blended in a cement composition, the strength is not lowered. Also, in general, an air entraining agent (AE agent) is added to entrain air in concrete, but as with unburned carbon contained in fly ash, inorganic carbon adsorbs the air entraining agent and results. Impedes air entrainment to concrete. However, since the anhydrous gypsum obtained by the present invention has an extremely small amount of inorganic carbon, there is an advantage that the performance of the air entraining agent is not hindered even when blended with concrete.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail according to embodiments.
The present invention relates to a method for producing anhydrous gypsum suitable for a cement composition by controlling a firing environment in a method for producing (collecting) anhydrous gypsum by calcining gypsum waste in a kiln. Specifically, by controlling the firing temperature to 600 to 1200 ° C., the firing time of 10 minutes or more, the filling rate in the kiln of the gypsum waste material to 15% by volume or less, and the oxygen concentration in the combustion gas at the kiln inlet of 5% by volume or more, II Anhydrous gypsum with a content of 80% by weight or more of type anhydrous gypsum, a total content of hemihydrate gypsum and type III anhydrous gypsum of 5% by weight or less, a CaO content of 5% by weight or less, and a carbon content of 0.3% by weight or less In which the carbon content and CaO content are further reduced, the content of type II anhydrous gypsum is 90% by weight or more, hemihydrate gypsum and type III anhydrous In this method, anhydrous gypsum having a total content of gypsum and CaO of 5% by weight or less and a carbon content of 0.2% by weight or less is produced from gypsum waste.
[0010]
In the present invention, the gypsum waste material refers to a waste material mainly composed of gypsum, and includes gypsum board waste materials and other gypsum product waste materials. In particular, a large amount of gypsum board waste is generated, and the location of the gypsum board and the form of the gypsum waste are not limited. It may have a decorative material such as gypsum board base paper or vinyl chloride resin, and may be a plate, block or powder.
Furthermore, the form and water content of the gypsum contained in the gypsum waste material are not limited, and it may be composed of dihydrate gypsum, hemihydrate gypsum, anhydrous gypsum or a mixture thereof.
[0011]
In the present invention, anhydrous gypsum refers to those mainly composed of type II anhydrous gypsum, and may include a small amount of hemihydrate gypsum, CaO, ash, charcoal and the like. The production method of the present invention comprises a type II anhydrous gypsum content of 80 wt% or more, a total content of hemihydrate gypsum and type III anhydrite of 5 wt% or less, a CaO content of 5 wt% or less, and carbon. A method for producing anhydrous gypsum with a content of 0.3% by weight or less from waste gypsum, preferably a type II anhydrous gypsum content of 90% by weight or more, a total content of hemihydrate gypsum, type III anhydrous gypsum and CaO This is a method for producing anhydrous gypsum having a carbon content of 5% by weight or less and a carbon content of 0.2% by weight or less from gypsum waste. In addition, this carbon content is calculated by converting the value obtained by heating anhydrous gypsum at 1250 ° C. for 2 minutes and quantifying the generated carbon dioxide by the infrared absorption method into the amount of carbon (C). Indicates the value in weight% of the anhydrous gypsum used for the measurement, and is an equivalent amount of organic carbon and inorganic carbon combined.
[0012]
Type II anhydrous gypsum works effectively to prevent its instantaneous setting when it is added to cement compositions such as mortar and concrete. On the other hand, if the amount of hemihydrate gypsum or type III anhydrous gypsum is large, false condensation is likely to occur. In addition, if the content of CaO is large, the setting time (starting and closing) is likely to be shortened, organic carbon has reduced strength development, and inorganic carbon adsorbs concrete admixtures such as AE and water reducing agents. As a result, the air volume and fluidity of the concrete are reduced. Type I anhydrous gypsum has almost no setting control effect. Therefore, in the present invention, the content of type II anhydrous gypsum is 80% by weight or more, the total content of hemihydrate gypsum and type III anhydrous gypsum is 5% by weight or less, the content of CaO is 5% by weight or less, and carbon The content is set to 0.3% by weight or less. Preferably, the content of type II anhydrous gypsum is 90% by weight or more, the total content of hemihydrate gypsum, type III anhydrous gypsum and CaO is 5% by weight or less, and the carbon content is 0.2% by weight or less.
[0013]
In the production method of the present invention, when gypsum waste is fired using a kiln or the like to produce anhydrous gypsum, the firing temperature is 600 to 1200 ° C., the firing time (retention time in the kiln) is 10 minutes or more, This is a method for producing anhydrous gypsum having the above composition by controlling the waste material filling rate in the kiln to 15% by volume or less and the oxygen concentration in the combustion gas at the kiln inlet (kiln bottom) to 5% by volume or more.
[0014]
When the firing temperature in the furnace is less than 600 ° C., the gypsum waste material becomes insufficiently fired even if the firing time is extended, and it is difficult to reduce the carbon content of anhydrous gypsum to 0.3% by weight or less. When the calcination temperature is higher than 1200 ° C, the carbon content is reduced to 0.3% or less, while gypsum is pyrolyzed to produce sulfur trioxide (SO 3 ) and quicklime (CaO), and type II anhydrous This is not preferable because a transition from gypsum to type I anhydrous gypsum occurs. In the above firing temperature range, when operating at the upper firing temperature, the firing time should be as short as possible within the above range, and when operating at the lower firing temperature, the firing time may be lengthened. desirable.
[0015]
The firing time (retention time in the kiln) is preferably 10 minutes or longer. When the firing time is less than 10 minutes, even if the firing temperature is within the above range, the firing of the gypsum waste material becomes insufficient, the base paper and the organic admixture contained in the gypsum board waste material etc. do not burn completely, and this carbon content is anhydrous. It remains in the gypsum and the carbon content exceeds 0.3% by weight. Furthermore, hemihydrate gypsum and type III anhydrous gypsum may remain.
[0016]
Furthermore, in order to stably recover the anhydrous gypsum having the above composition in the actual operation using the kiln, not only simply controlling the temperature in the kiln and the firing time, but also sufficiently removing carbon out of the system and II It is necessary to arrange the firing environment so as to increase the content of type anhydrous gypsum. That is, it is preferable to control the filling rate of the gypsum waste material in the kiln to 15% by volume or less and the oxygen concentration in the combustion gas at the kiln inlet (kiln bottom) to 5% by volume or more. If the filling rate of gypsum waste in the kiln is more than 15% by volume and the oxygen concentration in the combustion gas is less than 5% by volume, the gypsum waste will not be burned sufficiently, and the carbon content of anhydrous gypsum will be 0.3% by weight. % Will be exceeded. On the other hand, by controlling the firing temperature and time, the filling rate of the gypsum waste material in the kiln, and the oxygen concentration in the combustion gas within the range of the present invention, the carbon content of the anhydrous gypsum is 0.3 wt% or less, preferably It can be reduced to 0.2% by weight or less. Incidentally, as shown in the examples described later, those calcined under the calcining conditions of the present invention (No. 3, 6, 11, 14, 17, 20, 23, 26) contain carbon contained in the recovered anhydrous gypsum. In any case, the carbon content is 0.3 wt% or less, and the carbon content of some (No. 14, 20, 23, 26) is 0.2 wt% or less.
[0017]
Furthermore, in order to reduce the carbon content of anhydrous gypsum, it is necessary to promote the combustion of paper and combustible materials contained in gypsum waste materials and the removal of inorganic carbon. Need to be removed. Therefore, it is preferable to provide a lifter on the inner wall of the kiln and sufficiently stir the gypsum waste material in the furnace by rotating the kiln, thereby improving the breathability of combustion gas and carbon dioxide gas to the gypsum waste material in the furnace. As a result, combustion gas is supplied to the entire gypsum waste material and uniformly burned, and the carbon source is gasified and removed out of the system, so that the carbon content of anhydrous gypsum can be greatly reduced. In addition, by providing a lifter in the furnace to promote stirring of the gypsum waste material, the carbon content of anhydrous gypsum can be reduced even when firing at a lower temperature than when no lifter is provided. Therefore, there are few by-products of CaO by high-temperature baking, and anhydrous gypsum suitable for cement compositions can be obtained.
[0018]
The anhydrous gypsum of the present invention obtained as described above is suitable as an anhydrous gypsum raw material to be blended in the cement composition. Here, the cement composition refers to a hydraulic composition mainly composed of cement.・ 3Al 2 O 3・ CaSO 4 ) -based cement, calcium fluoroaluminate (11CaO ・ 7Al 2 O 3・ CaF 2 ) -based cement, expanded cement, etc., mainly solidifying material, injecting material, backing material, ground improvement material Including those used for various purposes. The anhydrous gypsum of the present invention is suitable as an anhydrous gypsum raw material to be blended in a cement composition used for these mortars and concretes.
[0019]
【Example】
Hereinafter, the present invention will be specifically described by way of examples. Note that these are examples and do not limit the scope of the present invention.
[0020]
[Example 1]
Gypsum board waste (thickness 21 mm, paper content 7-25 wt%) was coarsely crushed with a roll crusher and sieved to a diameter of 100 mm or less using a vibrating sieve. The coarsely crushed gypsum board waste (base paper adhered) was put into a rotary kiln (diameter 1.3 m, length 20 m) and fired under the conditions shown in Table 1. The form of the obtained anhydrous gypsum was identified and quantified by powder X-ray diffraction, and the CaO content was measured according to a standard test (CAJS I 01: Cement Association Standard Test Method). The carbon content was measured with a carbon analyzer. The results are summarized in Table 1.
[0021]
When the firing temperature is 500 ° C., the carbon content of the collected anhydrous gypsum is 0 regardless of the paper amount and firing time of the gypsum waste material even if the oxygen concentration in the furnace and the filling rate of the gypsum waste material are adjusted to an appropriate range. More than 3 wt% (No.1,2). Also, when the firing temperature is 600 ° C., when the gypsum waste material with a large amount of paper is used, the carbon content is only 0.3% by weight or less when the filling rate is controlled to 15% by volume or less and the oxygen concentration is 5% by volume or more. (No.3, 6). In this case, even if the firing time was increased, there was no significant effect (No. 10). When the firing temperature rises to 700 ° C to 1000 ° C, the carbon content contained in anhydrous gypsum gradually decreases, but the same tendency is observed for the oxygen concentration in the furnace and the gypsum waste material filling rate, and the oxygen concentration is low. Those with a high filling rate of gypsum waste have a carbon content of more than 0.3% by weight (No. 12, 13, 15, 16, 18, 19, 21, 22).
[0022]
In addition, even if the oxygen concentration is relatively low, the carbon content of anhydrous gypsum is reduced to 0.3% by weight or less at a firing temperature of 1100 ° C., but if the firing time is longer than 15 minutes, the amount of type II anhydrous gypsum Decreases and the amount of CaO increases (No. 24). Further, when the firing temperature is 1250 ° C., the carbon content is reduced to 0.3% by weight or less, but even when the firing time is 10 minutes, the amount of type II anhydrous gypsum decreases and the amount of CaO increases (No. 29). If the firing time is less than 10 minutes in the kiln firing, stable operation is extremely difficult. From the above, the content of type II anhydrous gypsum is 80% by weight or more, the total content of hemihydrate gypsum and type III anhydrous gypsum is 5% by weight or less, the content of CaO is 5% by weight or less, and the carbon content is 0.3. In order to obtain anhydrous gypsum having a weight percentage of less than 5%, a firing temperature of 600 to 1200 ° C., a filling rate of gypsum waste material of 15% by volume or less, and an oxygen concentration in combustion gas of 5% by volume or more are suitable (No. 3 , 6,11,14,17,20,23,26).
[0023]
[Table 1]
[Example 2]
As shown in FIG. 1, the lifter 2 was attached to the kiln 1 used in Example 1, and the other gypsum waste was fired under the same conditions as in Example 1 to recover anhydrous gypsum. The results are shown in Table 2 (when the lifter distance is 4 m). The results of Example 1 with substantially the same firing conditions except for the presence or absence of a lifter are shown in Table 2 (No. 41 for No. 41, No. 3 for No. 42, No. 3). No. 10 against 43).
As shown in this example, the carbon content contained in the recovered anhydrous gypsum is relatively low when a lifter is installed to increase the stirring of the gypsum waste material in the kiln. For this reason, by providing a lifter in the kiln, there is no problem such as decomposition of gypsum, a sufficient firing effect can be obtained even at a lower temperature, and the carbon content contained in anhydrous gypsum is efficiently increased. It can be reduced.
[0025]
[Table 2]
Example 3
Anhydrous gypsum (No. 9, 11, 14, 17, 20, 28) obtained in Example 1 was mixed with ordinary Portland cement clinker crushed material (grains) so that the amount of SO 3 in the cement was 2.0% by weight. The mixture was mixed to a diameter of 1.2 mm or less, and pulverized with a ball mill to a Blaine specific surface area of 3250 cm 2 / g to produce a cement. For comparison, natural dihydrate gypsum was used alone (hereinafter, standard gypsum), and cement was produced in the same manner as described above. Using these cements, concrete was kneaded according to the formulation shown in Table 3, and various concrete tests were conducted. The results are shown in Table 4. At the time of preparing the concrete, 0.02% of an air amount adjusting agent (AE auxiliary agent: trade name POZORIS 303A, product of NMB) was added to the cement after being dissolved in the kneaded water. The slump, air volume, condensation, and strength tests were in accordance with the methods specified by the standards (JIS A1101, JIS A1116, JIS A6204, JIS A1108).
[0027]
[Table 3]
[Table 4]
As shown in Table 4, natural dihydrate gypsum (standard gypsum) was used as the concrete prepared using cement containing anhydrous gypsum (No. 11, 14, 17, 20) having the composition range of the present invention. The test results were almost the same as when cement was used, and it had a sufficient effect as a raw material for gypsum for cement. On the other hand, concrete prepared with cement containing anhydrous gypsum (No. 28) with low content of type II anhydrous gypsum and high CaO content has significantly reduced both the initial and final setting times. Compressive strength is also low. In addition, in concrete using anhydrous gypsum (No. 9) with a high carbon content, it is not possible to secure a sufficient amount of air despite the addition of a predetermined air amount adjusting agent, which is desirable as anhydrous gypsum for cement. I understand that there is no. For the purpose of ensuring the freeze-thaw resistance of concrete and the like, the allowable amount is defined as 4.5 ± 1.5% in the standard (JIS A5308). Therefore, it is not preferable that the amount of air varies depending on the cement because quality control of the concrete becomes extremely difficult. Moreover, when the carbon content contained in anhydrous gypsum is large, carbon powder floats on the concrete surface and causes color spots.
[0030]
Example 4
The performance when the anhydrous gypsum (No. 14) obtained in Example 1 was used as an additive for a cement-based solidifying material was evaluated. Specifically, the above anhydrous gypsum was added to ordinary Portland cement clinker so that the SO 3 content in the solidified material was 7.5% by weight, and the resulting mixture was pulverized to a Blaine specific surface area of 4500 cm 2 / g by a ball mill. A solidified material was prepared. This solidified material was used for clay soil (water content ratio 87.3% by weight), loam soil (water content ratio 86.4% by weight) and organic soil (water content ratio 87.3% by weight).
Test method, the addition of solidifying material 100kg against the total amount 1 m 3 of the solidifying material and the target soil, after stirring for 5 minutes, which was molded and filled into a steel mold (diameter 5 cm, height 10 cm), A uniaxial compressive strength test was performed in accordance with the standard (JIS A 1216). The results are shown in Table 5. As is apparent from these results, anhydrous gypsum belonging to the composition range of the present invention is almost the same as the case of using standard gypsum for any target soil when used as an additive for a solidifying material. It shows that it can be used sufficiently as an additive for a solidifying material.
[0031]
[Table 5]
【The invention's effect】
According to the production method of the present invention, using gypsum waste as a raw material, the content of type II anhydrous gypsum is 80% by weight or more, the total content of hemihydrate gypsum and type III anhydrous gypsum is 5% by weight or less, and the content of CaO is 5% by weight. % Or less, and an anhydrous gypsum having a carbon content of 0.3% by weight or less, preferably a type II anhydrous gypsum content of 90% by weight or more, a total content of hemihydrate gypsum, type III anhydrous gypsum and CaO 5% by weight Anhydrous gypsum having a carbon content of 0.2% by weight or less can be obtained below. The anhydrous gypsum has a significantly low total content of hemihydrate gypsum and type III anhydrous gypsum, CaO content and carbon content, and is suitable as a gypsum raw material for cement compositions. Moreover, according to this invention, while the effective processing method of gypsum waste material is provided, the effective utilization of gypsum waste material can also be aimed at.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an installation state of a lifter according to a second embodiment.
[Explanation of symbols]
1-kiln, 2-lifter
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| JP5270370B2 (en) * | 2006-12-05 | 2013-08-21 | 太平洋セメント株式会社 | Cement manufacturing apparatus and manufacturing method |
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| JP4590447B2 (en) * | 2007-10-25 | 2010-12-01 | 祥貴 中筋 | Method for producing recycled gypsum and recycled gypsum |
| JP4982332B2 (en) * | 2007-11-06 | 2012-07-25 | 太平洋マテリアル株式会社 | Quick-hardening cement composition admixture, quick-hardening cement composition containing the same, quick-hardening cement kneaded material and spraying material |
| JP4999179B2 (en) * | 2007-12-28 | 2012-08-15 | 太平洋マテリアル株式会社 | Admixture for high-strength cement composition and high-strength cement composition using the same |
| CN105060748B (en) * | 2015-07-22 | 2018-02-09 | 湖南省小尹无忌环境能源科技开发有限公司 | With the method for rotary kiln factory and office reason ardealite special type anhydrite matured slag |
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