仇山酸化钙基膨润土的^(27)Al和^(29)Si魔角旋转核磁共振谱及脱色率研究

^(27)Al and ^(29)Si MAS NMR spectroscopy and bleaching capacity of acid activated Ca bentonite from Qiushan, China

对用不同酸度处理的仇山钙基膨润土进行了化学分析、X射线衍射(XRD)、27Al和29Si魔角旋转核磁共振(MASNMR)、吡啶吸附样品的红外光谱(IR)、比表面积、阳离子交换容量(CEC)和脱色率等测定。结果表明,随着处理酸度的增加和蒙脱石中阳离子的溶出,它的d(00l)的衍射强度降低,同时其Si和Al原子局域结构环境发生了显著的改变,Al原子由AlⅥ变成AlⅣ,Si原子由Q3Si(0Al)结构向Q4Si(0Al)和Q3Si(1OH)结构转变。八面体片阳离子的溶出和Si、Al原子局域结构环境的改变,显著地增加了比表面积和孔结构;AlⅥ向AlⅣ的转变形成了Lewis酸中心,而Si原子局域结构环境的改变形成了Brnsted酸中心。膨润土脱色率随处理酸度增加的本质原因是在Si和Al原子局域环境的变化过程中,在其表面分别形成了Brnsted酸中心和Lewis酸中心。

Ca bentonites, treated with H2SO4 at various acidic concentrations, are studied by chemical analysis, X ray diffraction, 29Si and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR), infrared spectrum (IR) and measurement of surface area, capacity of exchangeable cations (CEC) and bleaching capacity, to investigate the microstructural characteristics of the activated bentonites and their relation with the bleaching capacity. The results show that with the increase of the concentration of the acid, there are more and more cations dissolved and the diffraction strength of (001) decrease. Also, 6 coordinated aluminum transformed into 4 coordinated aluminum while Q3Si(0Al) into Q4Si(0Al) and Q3Si(1OH). The surface area and bleaching capacity are obviously increased as the result of the dissolution of the octahedral cations and the microstructural change of Si and Al atoms. The transformation from AlⅥto AlⅣresults in the formation of Lewis centers while Brnsted centers result from the microstructural change of Si atoms. It is concluded that the formation of Lewis and Brnsted centers is the main contribution for increase of bleaching capacity of acid activated bentonite.