Medium-low temperature reduction of high-iron Bayer process red mud using biomass pine sawdust
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摘要: 對生物質松木鋸末和煙煤還原焙燒高鐵拜耳法赤泥進行對比試驗研究,包括還原溫度、還原時間、還原劑用量對還原效果的影響.生物質松木鋸末還原高鐵拜耳法赤泥所需還原溫度低而且還原時間短最終還原效果較好.試驗通過熱分析和X射線衍射、動力學研究結果揭示出生物質松木鋸末中低溫還原高鐵拜耳法赤泥機理.同時確定了生物質松木鋸末中低溫還原的最佳還原條件.研究表明生物質松木鋸末為赤泥質量分數的20%,還原溫度為650℃,還原時間為30 min可將赤泥完全磁化.生物質松木鋸末熱重試驗分析表明250~375℃溫度區間為鋸末熱解的主要階段,350℃左右熱解速率達到最大,450℃后熱解反應趨于平緩;煙煤熱重試驗表明300~700℃溫度區間為煙煤熱解的主要階段,450℃左右熱解速率達到最大,650℃后熱解反應趨于平緩.動力學研究表明鋸末在300~400℃區間熱解表觀活化能比煙煤熱解表觀活化能要低很多,說明在此溫度范圍內鋸末比煙煤更加容易發生熱解反應.生物質能夠中低溫還原高鐵拜耳法赤泥,還原溫度比煤基還原的還原溫度低200℃左右.Abstract: An experiment was conducted to determine the difference between using biomass pine sawdust and pulverized coal in the reduction roasting of high-iron Bayer process red mud from the perspective of reduction temperature, reduction time, and reducing agent dosage. Experimental results show that biomass pine sawdust reduction roasting is quicker, occurs at a lower temperature, and is a superior process to pulverized coal reduction roasting. The mechanism of using biomass pine sawdust in reduction roasting of high-iron Bayer process red mud at a low temperature was investigated using thermal analysis, X-ray diffraction, and dynamic analysis. In addition, the optimum conditions involved in reducing high-iron Bayer process red mud were determined using biomass pine sawdust at medium and low temperatures. It is found that when using 20% biomass pine sawdust in mass at a reduction temperature of 650℃ and a reduction time of 30 min, the high-iron red mud in the Bayer process can be completely magnetized. A thermogravimetric experiment conducted on biomass pine sawdust indicates that the main stage of sawdust pyrolysis occurs within a temperature range of 250-375℃. The pyrolysis rate reaches a maximum at about 350℃, but tends to be gentle at 450℃. The main stage of pulverized coal pyrolysis occurs at 300-700℃; the pyrolysis rate is at its maximum at 450℃ but it tends to be gentle at 650℃. The kinetic study shows that at a temperature of 300-400℃, the apparent pyrolysis activation energy of the sawdust is much lower than that of pulverized coal, indicating that sawdust is more prone to pyrolysis than pulverized coal at this temperature range. In summary, biomass reduces high-iron Bayer red mud at a lower temperature, which is about 200℃ lower than that of coal-based reduction.
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Key words:
- biomass /
- pulverized coal /
- high-iron Bayer process red mud /
- roasting /
- pyrolysis
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參考文獻
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