Reaction behavior of kaolinite with ferric oxide during reduction roasting

The pre-separation of silica and alumina in aluminosilicates is of great significance for efficiently treating alumina-/silica-bearing minerals for alumina production. In this work, the reaction behavior of kaolinite with ferric oxide during reduction roasting was investigated. The results of thermodynamic analyses and reduction roasting experiments show that ferrous oxide obtained from ferric oxide reduction preferentially reacts with alumina in kaolinite to form hercynite, meanwhile the silica in kaolinite is transformed into quartz solid solution and/or cristobalite solid solution. With increasing roasting temperature, fayalite formed by reaction of surplus ferrous oxide with silica at low temperature is reduced to silica and metallic iron in the presence of sufficient carbon dosage. However, increasing roasting temperature and decreasing Fe₂O₃/Al₂O₃ molar ratio favor mullite formation. The complete conversion of kaolinte into free silica and hercynite can be obtained by roasting raw meal of kaolin, ferric oxide and coal powder with Fe₂O₃/Al₂O₃/C molar ratio of 1.2:2.0:1.2 at 1373 K for 60 min. This work may facilitate the development of a technique for comprehensively utilizing silica and alumina in aluminosilicates.     

隧道窑反应烧结合成铁铝尖晶石

以工业氧化铝、铁磷铝钙石、石墨粉为原料,隧道窑内反应烧结合成铁铝尖晶石。研究了窑炉气氛、煅烧温度、保温时间对合成铁铝尖晶石的影响。利用X射线衍射(XRD)表征合成试样的物相,采用扫描电子显微镜（SEM）观察和分析合成试样的形貌和分布。结果表明：隧道窑内反应烧结合成高纯度铁铝尖晶石的最佳条件是窑炉气氛V(O2)∶V(CO)为0.3,煅烧温度为1540℃,保温时间为5 h。在最佳条件下合成的铁铝尖晶石结晶性好、外形规则,粒径约为6μm,含量可达到98.26%。     

煤熔渣对镁铝尖晶石质耐火材料的侵蚀机制

为了实现水煤浆气化炉炉衬材料的无铬化,研究开发合适的耐火材料代替水煤浆气化炉用高铬砖,以尖晶石骨料及细粉、α-Al_2O_3微粉和轻烧Mg O微粉为原料,于1 600℃保温5 h烧成,制备了φ50 mm×40 mm、内孔为φ25 mm×25 mm的镁铝尖晶石质坩埚试样。采用静态坩埚法,借助XRD、SEM+EDS研究了高温煤熔渣对试样的侵蚀行为。结果表明:1)侵蚀后的镁铝尖晶石材料结构疏松,出现较明显的裂纹,煤熔渣完全渗入试样内部。2)经煤熔渣侵蚀后的镁铝尖晶石材料,物相组成发生变化,除原有的镁铝尖晶石外,还有新物相镁铁铝复合尖晶石相存在。3)煤熔渣对镁铝尖晶石材料的侵蚀机制是物理渗透为主,化学熔蚀为辅。     

原位合成方镁石-铁铝尖晶石材料

通过对铁铝尖晶石合成过程反应机理及MgO-Al_2O_3-FeOn三元体系中可能发生的高温反应进行热力学分析,尝试采用原位合成法制备方镁石-铁铝尖晶石材料,并用XRD、SEM等测试方法对材料进行了表征.结果表明:控制气氛10(-27117.9/T+11.54)＜Po_2＜10(-32625/T+18.09),经过1400, 1550 ℃高温处理后,能够成功合成出方镁石-铁铝尖晶石材料;同一温度下铁铝尖晶石的生成量随着金属铁加入量的增大而逐渐增多,1550 ℃处理后的试样FeAl_2O_4晶体发育更加良好.     

粉煤灰中铝硅高效分离的动态扩大试验

为缓解我国氧化铝工业存在的铝土矿需求量大与国内铝土矿供应严重不足间的矛盾和粉煤灰大量堆积造成的环境问题,基于粉煤灰还原?氧化焙烧?碱浸实现铝硅分离的全新工艺路线,在已有静态小实验基础上,开展了实验室回转窑动态扩大试验研究.结果表明:在1100℃、配料比n(Fe):n(Al):n(C)=1.2:2:1.2、进料量75 g...     

反应烧结法合成铁铝尖晶石中二氧化硅的赋存状态

以Fe2O3、Al2O3和Si O2为原料,按照Fe O和Al2O3质量比为40.8:59.2配料,并在合成体系中引入质量分数为1%的二氧化硅,在高纯氮气下于1 600℃保温4 h。用X射线衍射、扫描电子显微镜、能谱和透射电子显微镜等对试样进行了表征,利用Fe O-Al2O3-Si O2三元相图对二氧化硅的存在状态进行了分析。结果表明:引入的二氧化硅没有进入铁铝尖晶石晶格,而是以Fe O-Al2O3-Si O2三元组分的非晶态形式存在于铁铝尖晶石晶粒间。在二氧化硅质量分数为1%时,含Si O2组分的非晶相呈不连续状态分布,未改变铁铝尖晶石晶粒间的直接接触。     

铁铝尖晶石的制备

以铁鳞、Fe2O3粉及Al2O3粉为原料,分别采用烧结法、电熔法,进行铁铝尖晶石的合成.利用X射线衍射(XRD)检测了合成试样的物相组成,采用扫描电子显微镜(SEM)观察和分析了合成试样的物相的形貌和分布.研究结果表明:采用在配料中加入石墨和埋炭的方法均能营造弱还原性气氛,合成出铁铝尖晶石,但是铁铝尖晶石的含量仅为20%左右,采用合适的原料并利用电熔法能够合成铁铝尖晶石,含量在97%以上.     

Efficient separation of alumina and silica in reduction-roasted kaolin by alkali leaching

Alkali leaching was employed to investigate the separation of alumina and silica in roasted kaolin obtained by roasting kaolin alone in air at 1273 K for 60 min and in clinker prepared by roasting the mixed raw meal of kaolin, ferric oxide and coal powder with Fe₂O₃/Al₂O₃/C molar ratio of 1.2:2.0:1.2 in reducing atmosphere at 1373 K for 60 min. The thermodynamic analyses and alkali leaching results show that the composition of the Al?Si spinel in roasted kaolin is close to that of 3Al₂O₃·2SiO₂ and the spinel is dissolved with increasing leaching time, resulting in difficulty in deeply separating alumina and silica in kaolin by the traditional roasting?leaching process. On the contrary, the efficient separation of alumina and silica in kaolin can be reached by fully converting kaolinite into insoluble hercynite and soluble free silica, namely quartz solid solution and cristobalite solid solution, during reduction roasting, followed by alkali leaching of the obtained clinker. Furthermore, experimental results from treating high-silica diasporic bauxite indicate that the reduction roasting?alkali leaching process is potential to separate silica and alumina in aluminosilicates.     

Characteristics of Hercynite and Its Application in Refractories

The characteristics of hercynite including crystal structure,chemical compositions and physical properties, R D background of hercynite,synthesis problems of hercynite,and roles of hercynite in refractories were reviewed. The application of hercynite in refractories was introduced with emphasis. The practical applications in cement rotary kiln showed the prepared magnesia hercynite brick had better performance than the original magnesia chrome brick obviously.