尿素法合成镁铁水滑石的制备机理  

Preparation Mechanism of the Mg–Fe Hydrotalcite with Urea Method

作　　者：黄炎[1] 曾虹燕[1] 王亚举[1] 杨永杰[1] 魏英民[1] 赵策[1] 

机构地区：[1]湘潭大学化工学院,湖南湘潭411105

出　　处：《硅酸盐学报》2011年第2期365-370,共6页Journal of The Chinese Ceramic Society

基　　金：国家重大科技专项(2009ZX07212–001–03);湖南省研究生科研创新项目(CX2010B268);湖南省高校科技创新团队项目资助

摘　　要：采用改进尿素法制备了分布均匀、高结晶度的镁铁水滑石。通过X射线衍射、扫描电子显微镜和能谱仪分析了镁铁水滑石结构、形貌及其组成,研究了镁铁水滑石的制备机理,探讨了尿素与Fe3+摩尔比对镁铁水滑石制备的影响。结果表明:当pH为8.48～9.35时,Mg2+与Fe3+开始发生共沉淀形成镁铁水滑石晶体。其形成机理为:Fe3+形成Keggin结构Fe13聚集体(多氧络合阳离子,[Fe13O4(OH)24(OH2)12]7+),Mg2+形成无定型态Mg(OH)2,Fe13聚集体吸附在无定型Mg(OH)2上,形成带正电荷的镁铁水滑石层板主体,反应液中的CO32?通过Coulomb力被带正电荷层板吸引进入层间以平衡电荷,从而形成电中性的镁铁水滑石晶核。当尿素与Fe3+摩尔比为12时,可得到最佳相对产率、结晶状况理想的镁铁水滑石。Mg–Fe hydrotalcite with uniform and high crystallinity was prepared using an improved urea method.The structure,mor-phology and composition of Mg–Fe hydrotalcite were analyzed by X-ray diffraction,scanning electron microscopy and energy dis-persive spectrometer.The preparation mechanism is discussed,and the effect of mole ratio of urea to Fe3＋ in the reaction system on the precipitation of the Mg–Fe hydrotalcite was investigated.The results show that the coprecipitation of Mg2＋ and Fe3＋ to form the Mg–Fe hydrotalcite crystal could occur when the pH value is between 8.48 and 9.35.The nucleation mechanism of the Mg–Fe hy-drotalcite is as follows： Fe3＋ formed Keggin structure Fe13 cluster（polyoxocation [Fe13O4（OH）24（OH2）12]7＋）,and Mg2＋ formed amor-phous Mg（OH）2 in the reaction system.On one hand,the brucite-like sheets of Mg–Fe hydrotalcite with positive charges are formed after the Fe13 cluster was adsorbed rapidly on the surface of amorphous Mg（OH）2.On the other hand,this net positive charge can be compensated by CO32？ anions through coulomb forces,which lay in the interlayer region between brucite-like sheets for the balance of the potential valence.At last,the nucleation of Mg–Fe hydrotalcite with electrical neutrality is quickly finished.When the mole ratio of urea to Fe3＋ is 12,the optimal relative yield of the Mg–Fe hydrotalcite that possessed well-crystalline structures is obtained.

关 键 词：镁铁水滑石 尿素 制备机理 PH值 

分 类 号：TQ132.2[化学工程—无机化工] TQ138.1