On controllability of fluidized bed reduction of iron ore by CH4 for selective formation of magnetite

Bowen Ma , Zhanguo Zhang , Guangwen Xu
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引用次数: 0

Abstract

Magnetization roasting technology is one of the most representative ways to improve the magnetic separation efficiency and iron recovery of refractory weakly magnetic iron ores. However, utilization of CO-rich or H2-rich gas of strong reducibility as reducing agent for magnetization roasting would lead to over-reduction of Fe2O3 in the ore to non-magnetic FeO, which makes the magnetism of the roasted ore be lower than its maximum, and hence leads to a lower iron recovery than expected. To explore the possibility of using CH4 as reducing agent for controllable reduction of Fe2O3 in iron ores to selectively forming magnetic Fe3O4, i.e., for maximizing the magnetism of the reduced ore for efficient iron separation and recovery, a series of fluidized bed reduction tests in CH4 were carried out on two iron ores of 55 % and 33 % iron at different temperatures for different periods of time, and the resultant reduced ore particles were magnetically separated for recovery of iron concentrate. XRD and ICP analyses were performed on all recovered iron concentrates to identify the crystal forms of their iron species and to quantify their iron contents. The results have shown that the controllable reduction by CH4 of Fe2O3 in the iron ores to strongly magnetic Fe3O4 can be realized by controlling the reduction temperature and time condition applied. The resultant concentrates can be fully recovered by magnetic separation in a weak magnetic field of 60 kA/m to attain a maximum iron recovery of 98 % for the high-grade ore and that of 65 % for the low-grade ore. Besides, the results have also shown that the most critical factor affecting the controllability of the ore reduction process and the selectivity to the generation of magnetic Fe3O4-containing particles is the reduction temperature, and that the upper temperature threshold for the controllable reduction and selective generation of strongly magnetic iron concentrate is about 650℃.

Abstract Image

用 CH4 对铁矿石进行流化床还原以选择性形成磁铁矿的可控性
磁化焙烧技术是提高难选弱磁性铁矿石磁选效率和铁回收率最具代表性的方法之一。而利用富co或富h2强还原性气体作为磁化焙烧还原剂,会导致矿石中Fe2O3过度还原为非磁性FeO,使焙烧矿石的磁性低于其最大值,从而导致铁回收率低于预期。为探索利用CH4作为还原剂将铁矿石中Fe2O3可控还原为选择性形成磁性Fe3O4的可能性,即最大限度地发挥还原矿的磁性,实现铁的高效分离和回收,在不同温度和不同时间下,对铁含量分别为55%和33%的铁矿石进行了一系列CH4流化床还原试验。将得到的还原矿粒进行磁选,回收铁精矿。对所有回收铁精矿进行XRD和ICP分析,确定其铁种类的晶体形式,并量化其铁含量。结果表明,通过控制还原温度和还原时间条件,CH4可将铁矿石中的Fe2O3可控还原为强磁性Fe3O4。在60 kA/m的弱磁场条件下,磁选精矿可完全回收,高品位矿石铁回收率可达98%,低品位矿石铁回收率可达65%。此外,研究结果还表明,影响矿石还原过程可控性和磁性含fe3o4颗粒生成选择性的最关键因素是还原温度。强磁性铁精矿可控还原和选择性生成的温度上限约为650℃。
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