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.     

原位合成方镁石-铁铝尖晶石材料的烧结工艺及性能研究

以镁砂细粉、Fe粉、Fe2O3粉和α-Al2O3粉为原料,采用原位合成法制备方镁石-铁铝尖晶石材料。不同气氛下烧成试验显示N2气氛是合成铁铝尖晶石的最佳气氛。通过XRD和SEM分析在N2气氛中不同热处理温度制备铁铝尖晶石材料的相组成及其显微结构,研究了烧结温度和铁加入量对试样烧结性能的影响。结果表明,试样在N2气氛中于1450、1500、1550℃下保温3h处理后都能原位合成出方镁石-铁铝尖晶石材料;烧结温度的提高有利于铁铝尖晶石的发育和试样烧结性能的提高;铁加入量为10％时烧结性能最佳。     

消失模涂料防渗与自剥离机理的研究

为研究消失模涂料的防渗与剥离情况,分别配制了以石英粉与高铝矾土为骨料的两种涂料,并在相同浇注条件下浇注铸件.采用扫描电镜及X射线衍射分别观察涂料断面微观组织及分析铸件上涂料层的物相.结果表明,浇注后以石英粉为骨料的涂料仅仅轻度烧结,而以高铝矾土为骨料的涂料生成了比骨料耐火度更高的新物质,阻挡了钢液的侵入且不与钢液发生反应.生成的新物相提高了高铝矾土涂料的防渗性并促使涂料自动剥离.     

等离子体反应合成铁铝尖晶石基复合材料

用喷雾造粒工艺制备了Fe2O3–Al复合粉体,通过等离子喷涂工艺制备出FeAl2O4基复合材料。对Fe2O3–Al复合粉颗粒在等离子体焰流内的状态变化、反应动力学、反应产物和急冷后材料的组织结构进行研究。结果表明：Fe2O3–Al复合粉颗粒在沉积前的温度为3 274.5℃,速率为179 m/s,主要反应产物为Fe–Al...     

板状刚玉粒度和加入量对高铁镁砂-烧结刚玉复合材料性能的影响

以粒度为3~1、≤1、≤0.088 mm的高铁镁砂,≤0.088 mm的高纯镁砂为主要原料,分别研究了不同加入量(质量分数分别为3%、6%、9%、12%、15%)和不同粒度(3~2、2~1、≤1 mm)的烧结板状刚玉对试样性能的影响,并分析其物相组成和显微结构。结果表明:当烧结板状刚玉细粉加入量为6%(w)时,试样的显气孔率16%,体积密度2.99 g·cm-3,常温耐压强度80.9 MPa,荷重软化温度1 609℃,抗热震性达到20次,综合性能最好;改变加入刚玉的粒度,可以控制刚玉反应速度,同时影响高铁镁砂中Fe的扩散;铁在方镁石中固溶度大,高铁镁砂的引入可以起到方镁石改性的作用;由于铁氧化物的存在,高铁镁砂-刚玉体系在高温下易于促进镁铝尖晶石和铁铝尖晶石固溶体的形成。     

铁铝尖晶石的合成及应用研究进展

较系统地介绍了铁铝尖晶石的合成机制,并对铁铝尖晶石的合成方法特点进行了对比,同时还对比了以铁铝尖晶石为原料制备的氧化镁-铁铝尖晶石砖与其他水泥回转窑烧成带常用砖的基本性能与特点,指出铁铝尖晶石是一种非常有使用前景的水泥回转窑衬砖用耐火原料。     

Study on Properties of Magnesia-Hercynite Brick

Using magnesia and hercynite as materials, we researched the magnesia-hercynite brick in order to solve the problem of chrome-free brick used in the burning zone of cement rotary kiln. Effect of different firing temperature and different content of hercynite on properties of the brick were studied. The results show that the magnesiahercynite specimen fired at 1600℃ was densified and when the hercynite content is 7%, the cold crushing strength and the adhesive strength of rupture of the specimen have the highest value.     

回转窑烧成带用镁铁铝尖晶石砖的研制与应用

以新理论、新工艺合成出了结晶完好、质地均匀的铁铝尖晶石,并以合成的铁铝尖晶石为原料制备了镁铁铝尖晶石砖。大量应用结果表明,研制的镁铁铝尖晶石砖具有窑皮形成迅速、稳定、导热率小及使用寿命长等优点,总体性能超过了镁铬砖,满足了大型回转窑烧成带的无铬化要求。     

铁铝尖晶石的组成和结构

采用X射线、荧光光谱化学分析XRF、场发射扫描电镜FESEM、能谱分析EDS、X射线衍射XRD以及KMnO4溶液滴定等方法,对一种市售电熔铁铝尖晶石原料进行了分析。结果显示:该原料并不是纯的FeAl2O4,其主晶相为Fe(Al,Fe)2O4型固溶体,与磁铁矿型固溶体共生;次晶相为β-Al2O3,由氧化铝原料中的Na2O所致。