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随着我国矿业得到更多重视和发展,采矿业发展必然带来大量的尾矿产生[1]。2019年我国铁尾矿产生量 5.36×108 t,综合利用量 1.16×108 t,铁尾矿综合利用率不足30%造成其堆积[2],而尾矿堆积引起的环境问题如累积潜在有毒元素等已成为全球性问题[3-4]。铁尾矿的铅、锌、镉、铜、镍、铬和锰等重金属,受到风化和沥滤等自然环境作用时,会产生具有毒性的酸性重金属废水污染地表水和地下水,而产生不可忽视地经济损失[5]。随着国家人民健康发展需求的日益增长,铁尾矿安全处置已引起广大关注。
目前,学者对铁尾矿资源化利用研究已有报道,如烧结固化技术[6-7]、制备改性材料[8]和磁化回收铁资源等。在烧结固化技术中,WANG等[5]在铁尾矿中添加高岭土和飞灰制备烧结砖,满足重金属浸出和抗压标准;在制备改性材料中,LI等[8]以铁尾矿和粉煤灰制备高比表面积(1.185 m2·g−1)和高孔隙率(62%)的多孔人工陶粒滤料。但以上两种途径对铁尾矿资源化回收方式没利用铁尾矿中赋存价值高的矿物,或是存在高能耗低价值等缺点[5, 8]。因而高效利用铁尾矿中赋存价值较高的铁元素显得格外重要。
中国因高品质铁矿石产量少,而成为高度依赖高品质铁矿石进口大国[1]。我国政协十三届全国委员会第四次会议也将铁矿列为战略性矿产,并大力加强铁矿石理论研究及其创新。可见,通过回收国内铁尾矿的铁以补充国内高品质铁矿石需求符合当代提倡的内循环模式。目前,学者通过磁化焙烧,对铁矿中的铁进行还原回收。按照还原剂不同,LI等[9]采用50% H2磁化焙烧铁尾矿获品位65.30%,回收率39.79%的铁精矿;YUAN等[10]采用20% CO磁化焙烧铁尾矿获品位68.31%,回收率96.34%的铁精矿;HUANG等[11]采用15%木屑磁化焙烧铁尾矿获品位62.84%,回收率94.58%的铁精矿。按照焙烧方式不同,其中YUAN等[10]采用悬浮磁化焙烧铁尾矿;HUANG等[11]采用固定床磁化焙烧铁尾矿。新颖的悬浮磁化焙烧法具有传热传质效率高等优点[12],但目前使用的还原剂多为单一还原剂或为理想性比例混气为主[9-10]。若采用还原性废气如高炉尾气和生物质造气等,按其主要成分为CO、H2、CO2和N2进行模拟还原混气研究[13-14],可寻找到一种低成本、节能、环保的工艺解决铁尾矿堆存资源浪费问题。
本研究以CO、H2、CO2和N2混气作为还原混气,研究不同温度、时间、混气H2和CO占比对铁尾矿磁化焙烧后铁品位和回收率的影响。利用X射线衍射(XRD)和扫描电子显微镜(SEM)研究焙烧前后铁尾矿基本特性和晶相结构,利用振动样品磁强计(VSM)测试样品磁性变化,利用光电子能谱仪(XPS)测试元素价态变化,利用N2吸脱附等温仪(BET)测试样品孔隙变化。本研究结果可为铁尾矿的资源化利用提供参考。
混气悬浮磁化焙烧铁尾矿及其磁分选效果
Recycling Fe3O4 from iron tailings via suspension magnetized roasting by mixed gas and magnetic separation
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摘要: 为实现铁尾矿资源化回收利用,以H2、CO、CO2和N2模拟还原混气对铁尾矿进行悬浮磁化焙烧,通过磁选获得铁精矿。探究温度、时间、H2和CO占比对铁精矿铁品位和回收率的影响,采用X射线衍射、振动样品强磁计、X射线光电子能谱、BET表面分析和扫描电子显微镜X光微区分析方法,探究悬浮磁化焙烧磁选过程中晶相结构变化和反应机理。结果表明,铁尾矿在温度、时间和H2∶CO∶CO2∶N2(体积比)分别为600 ℃、10 min和20∶15∶15∶50时,铁精矿铁品位和回收率最优分别为62.06%和98.03%。铁精矿饱和磁化强度由0.77 Am2·kg−1提升到59.43 Am2·kg-1。悬浮磁化焙烧能有效将赤铁矿针铁矿还原为磁铁矿,且BET表面积提升了13.1676 m2·g−1,并能通过磁选有效分离Fe3O4和SiO2等脉石。本研究可为从铁尾矿中回收铁资源提供参考。Abstract: For recycling Fe3O4 from iron tailing, iron tailing was reduced by mixed gas of H2, CO, CO2 and N2, and then magnetic separated. In this study, the effects of temperature, time, proportion of H2 and CO on iron grade and recovery ratio were investigated. XRD, VSM, XPS, BET and SEM-EDS methods were used to reveal the diversification of crystal structure and reaction mechanisms in the process of suspension magnetized roasting and magnetic separation. The optimal iron grade of 62.06% and recovery ratio of 98.03% was obtained via suspension magnetized roasted at 600 ℃, 10 min, and H2: CO: CO2: N2 of 20: 15: 15: 50. The saturation magnetization of iron concentrate had been increased from 0.77 to 59.43 Am2·kg−1. The suspension magnetized roasting can effectively reduce the hematite goethite into magnetite, and the BET surface area of tailing was increased by 13.1676 m2·g−1. Finally, magnetic separation was used for effectively separating Fe3O4 and SiO2 form reduced iron tailing. This study provided an effective method to recovery iron form the disposed iron tailing for sustainable development of the mine environment.
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表 1 铁尾矿元素质量分数
Table 1. Element content of iron tailings %
Fe2O3 SiO2 Al2O3 SO3 K2O ZnO CuO 其他 46.78 27.90 19.59 4.11 0.54 0.20 0.17 0.71 表 2 样品及纯物质磁性参数
Table 2. Magnetic parameters of samples and pure substances Am2·kg-1
样品 饱和磁化强度 剩磁 原矿 0.77 0.05 焙烧矿 52.31 10.82 铁精矿 59.43 13.72 纯赤铁矿 0.40 - 纯磁铁矿 92.00 - 表 4 原矿焙烧矿EDS分析Fe、O元素占比
Table 4. EDS analysis of raw ore roasted ore Fe and O elements account wt%
样品 Fe O 铁尾矿 61.98 33.71 焙烧矿 66.01 24.02 表 3 BET分析的相关参数
Table 3. Relevant parameters of bet analysis
供试样品 BET表面积/
(m2·g−1)朗缪尔表面积/
(m2·g−1)孔隙体积/
(cm3·g−1)孔径/
nm铁尾矿 8.122 6 81.491 1 0.018681 9.199 4 焙烧矿 21.290 2 356.333 3 0.0628 02 11.799 2 -
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