【作者】 王鹏；

【导师】 刘桂华； 刘伟；

【作者基本信息】 中南大学 ， 冶金工程， 2014， 硕士

【摘要】 摘要：铝酸钠溶液晶种分解是氧化铝生产过程中的重要工序之一,也是氧化铝工业方面研究重点。提高溶液分解率可以有效地提高设备产能,降低能耗；而目前的研究表明,大幅度提高溶液分解率会导致产品严重细化。为了满足电解铝砂状化要求,溶液实际分解率较理论分解率低,由此导致大量Al(OH)3在溶液中循环,设备产能浪费严重,能耗较高。因此本文拟采用一段提高溶液分解率、二段制备粗颗粒一水软铝石的技术路线。重点研究了铝酸钠溶液体系中制备粗颗粒一水软铝石的工艺条件及反应机理,通过SEM、XRD、红外光谱、比表面积分析仪等分析了产品粒子的形貌、物相等。主要研究内容及结果如下：(1)提高温度、延长时间、原晶种加入一水软铝石有利于粒子物相转化。温度是影响其转化的主要因素,温度越高完全转化需要时间越短,140℃时需要11h以上,180℃需要2h,200℃需要40min,240℃仅需要5min。(2)提高温度、高温条件下增加苛性碱碱浓度、延长反应时间、减少搅拌强度、增加细粒子含量均有利于促进固体粒子的附聚长大。同时,只有在高温条件下粒子才能有效附聚,且温度越高,反应时间越短。(3)明确了高温下产品的形貌及其形成过程：氢氧化铝层状结构被破坏,形成薄片,薄片脱水变成一水软铝石,该过程从粒子表面由外向内扩散进行。最终形成疏松的具有大比表面的颗粒。(4)高温条件下溶液分解率呈现“W”起伏变化,产品总粒子数减少,其中0-30gm之间的粒子完全消失,而粗颗粒有小幅度增加。因此明确了产品粒子“溶解-析出-附聚”的长大机理。(5)本文通过调控反应条件,在温度大于180℃、苛性碱浓度PNa20小于50g/L时,产品不含30μm以下的粒子；将产品中AlOOH的含量提高到90%以上。产品最高比表面积达到141.05m2/g,孔容0.115cm3/g,平均孔径33A。更多还原

【Abstract】 Abstract:The seeded precipitation in sodium aluminate solution is one of the most important sub-processes in Bayer Process. It also has been the research priority in alumina industry. Promoting the precipitation ratio of gibbsite can improve equipment productivity and reduce energy cost but brings much fine gibbsite, and then it has to keep a very low precipitation ratio compared with the theoretical one to obtain sandy alumina in practical. Therefore, a large amount of alumina trihydrate is always cycling with the sodium aluminate solution, limiting the equipment productivity and increasing the energy cost. This paper adopted a new two-step technology, promoting firstly the precipitation ratio and then preparing the coarse boehmite from fine gibbsite. This paper mainly focuses on the preparation of coarse boehmite from fine gibbsite in the sodium aluminate solution. The morphology, the precipitation ratio particle size distribution and the formation of boehmite were analysed by SEM, XPD, FT-IR and BET. Results can be seen as follows:(1) The temperature, time and the seeds of boehmite benefit the formation of boehmite. Temperature is the main fact that affect the formation of boehmite. More than90%boehmite is formed at140℃for more than11h, at180℃for2h, at200℃for40min and at240℃for only5min.(2) The temperature, the time, the increase of alkali concentration at high temperature, increase of seed amount and weak stirring are favorable to the agglomeration of particles. Meanwhile, particles can agglomerate obviously at high temperature. Elevating the temperature can reduce the reaction time.(3) Layered structure of alumina trihydrade is destroyed from the surface of particles to inside, and boehmite is generated in the forms of nanoflakes, and then coarse, nanoflakes and porous boehmite is formed.(4)The precipitation ratio varies in the form of "W". Total population of particles decreases, among wich fine particles Between0μm and30μm disappear completely and the population of coarse particles increase. The agglomeration mechanism of "dissolution-precipitation-agglomeration" is then inferred.(5) Under T≥180℃and pNa2O≤50g/L, more than90%boehmite were prepared without fine particles below30μm and with the highest specific surface area of141.05m/g, pore volume of0.115cm3/g and average pore size of3.3nm.更多还原