不带层电荷的层状硅酸盐粘土矿物表面的酸位数量

NUMBER OF ACID SITES ON THE CLAY MINERALS SURFACES OF LAYER SILICATES WITHOUT LAYER CHARGE

非极性溶剂中的有机碱 (偶氮苯指示剂 )主要吸附在粘土矿物的表面酸位上 ,粘土的表面酸位数量可用有机碱的吸附量大小进行评价。测定了四种理想晶格中不带电荷的“中性”层状硅酸盐粘土矿物 (即 1∶1型的高岭石 ,板状蛇纹石和 2∶1型的叶蜡石及滑石 )对二硫化碳溶液中甲基红和N ,N -二甲基 -4 -亚硝基苯胺的吸附等温线。根据单分子层最大吸附量 ,矿物的比表面积及非垂直定向时一分子有机碱的有效占有面积 ,计算了四种粘土矿物表面甲基红和N ,N -二甲基 -4 -亚硝基苯胺的覆盖率。结果表明 :不带层电荷的粘土矿物的几乎整个外表面 (即不仅仅是结晶边缘或极少数交换性阳离子的周围 )

The number of acid sites on 1∶1 and 2∶1 type layer silicates ideally without layer charge (kaolinite, lizardite, pyrophyllite, and talc) was determined by the adsorption of methyl red(p K a =5.0) and p-nitroso-N, N-dimethyl aniline (p-NDMA) from carbon disulfide solutions.By using the monolayer adsorption maxima of methyl red and p-NDMA, the specific surface area of the minerals and the effective adsorption area per molecule, the external surface coverages of the four minerals by the two organic bases were calculated.The results suggest that acid sites are distributed on almost all of the external surfaces of the minerals, i.e ., not only crystal edges and/or small amounts of exchangeable cations on basal surfaces.