超声波对铝酸钠溶液分解影响的探索

【作者】 张俊；

【导师】 张平民； 李洁；

【作者基本信息】 中南大学 ， 物理化学， 2004， 硕士

【摘要】 种分过程是拜耳法生产氧化铝的关键工序之一，也是拜耳法生产中耗时最长的一个工序。铝酸钠溶液分解速率缓慢，种分分解率远低于理论分解率，因此铝酸钠溶液强化分解研究成为铝酸钠种分过程研究的热点方向。本文研究了超声波对铝酸钠溶液分解的强化作用，并通过自发分解实验、晶体生长实验和拉曼光谱测定探索了超声波强化铝酸钠溶液分解的作用机理。 通过种分分解率分析、粒度分析、扫描电镜分析及x-射线衍射分析，研究了不同频率、不同温度条件下，超声波对工业生产条件的铝酸钠溶液分解的强化作用。结果表明超声波作用促进大量晶核的形成和大颗粒氢氧化铝的附聚，提高铝酸钠溶液的分解速率，但超声波作用并不改变分解产物的晶体结构。铝酸钠溶液自发分解实验结果表明，超声波缩短铝酸钠溶液成核诱导期，促进铝酸钠溶液自发成核过程及晶粒长大过程。通过分析铝酸钠溶液加晶种分解过程中固相产物的粒度分布情况，提出用（dN／dt）_成核，（dN／dt）_附聚和（dr／dt）_径向长大来分别表示出二次成核，附聚长大和晶粒径向长大的速率，并分别得到了其速率表达式。采用自行设计的微分反应器研究了三水铝石晶体生长，结果表明在超声与未超声作用的情况下，三水铝石晶体线形生长速率都遵从与晶体尺寸无关的△L—McCake规则。70℃的高种分温度条件下，超声波对三水铝石晶体线性生长速率没有影响。通过对比超声前后铝酸钠溶液拉曼光谱，发现超声作用改变了铝酸钠溶液结构，影响了铝酸根阴离子之间的平衡。结合超声波对铝酸钠溶液种分过程和自发分解过程的影响，认为超声波促进铝酸钠溶液中的铝酸根离子向有利生长基元[Al₆（OH）₁₈（H₂O）₆]的转化，从而强化了铝酸钠溶液的分解，提高反应速率。更多还原

【Abstract】 An important step in the production of aluminate from bauxite by the Bayer process is the crystallization of alumina trihydrate from caustic aluminate solution, which takes up most of the residence time. Because of the low precipitation rate and lower precipitation yield than theroretical precipitation ratios, study on promoting Gibbsite particles precipitating from caustic aluminate solutions is always hotspot in aluminum industry. In this paper, precipitation of A1(OH)3 from supersaturated sodium aluminate solution processed by ultrasound was investigated, and the mechanism of ultrasound action was explored by the experiment of unseeded precipitation crystal growth , Raman spectrum.The precipitation of A1(OH)3 from supersaturated sodium aluminate solution processed by ultrasound is researched in the difference frenquency and temperature condition.The results indicate that the nucleation,agglomeration of large grain and precipitation rate are promoted by ultrasound, but the A1(OH)3 structure is not changed whether ultrasound or not. The experiment of unseeded precipitation show that the induction time is shorten, the nucleation and crystal growth are promoted by ultrasound. According to the particle size distribution information on sodium aluminate seeded precipitation,the rate expression of each basic process ,which is secondary nucleation, agglomeration or crystal growth on seeded precipitation ,is obtained. Differential reactor is adopted to study the radial growth of crystal. The results appear that the line growth rate of A1(OH)3 obey the rule of A L-McCake whether ultrasound or not.The Raman spectrum analysis show that ultrasound changed the equilibrium of aluminate anion ,thereby affecting the structure of sodium aluminate. Combined with the effect of seeded precipitation and unseeded precipitation with ultrasound ,it can be concluded that the formation of growth unit [A16(OH)|8(H2O)6] was promoted by ultrasound,then the precipitation rate was improved.更多还原