天然蒙脱石的结构与带电性

Study on the Relationship between Charge and Structure of Montmorillonite

选择了我国不同产地、有相当储量的12种蒙脱石,用化学组成结构分析法、阳离子交换容量法和直链烷基铵法对其电荷密度的来源、大小、分布进行了研究,发现所有双八面体蒙脱石的总电荷密度值在0.40～0.45eq/犤(Al,Si)4O10犦之间,其中永久负电荷和端面可变负电荷由于受八面体位Al与Mg占位数间差异的影响而差别悬殊,八面体位Al占位数1.5以上,Mg占位数0.3～0.4的是低层电荷(0.28～0.33eq/犤(Al,Si)4O10犦)、高端面可变负电荷(>0.16mmol·g-1)的蒙脱石;八面体位Al占位数1.3～1.4,Mg占位数0.30左右的是高层电荷(0.40～0.45eq/犤(Al,Si)4O10犦)、低端面可变负电荷(<0.07mmol·g-1)的蒙脱石.多数天然蒙脱石八面体片中Mg与Al的占位数介于这二者之间,层电荷密度和可变端面负电荷也介于二者之间,大部分蒙脱石的负电荷主要来自八面体位,但也有个别主要来自于四面体位中Al对Si的同晶取代.文中还讨论了影响可变端面电荷的因素和八面体片中铁对电性的影响.

Chemical composition analysis, CEC method, and alkylammonium method were used to study the charge density and distribution of 12 montmorillonite samples coming from different sources. The results show hat the total charge of all dioctahedron montmorillonites is between 0.40 to 0.45 eq/ [ (Al, Si)(4)O-10], but the layer charge and the variable surface charge vary with the ratio of Al/Mg in octahedron. For the montmorillonites with lower layer charge and higher variable surface charge, the occupancy of Al and Mg in the octahedron site is above 1.5 and 0.3 similar to 0.4 respectively, while for the montmorillonites with higher layer charge and lower variable surface charge, the occupancy of that is 1.3 similar to 1.4 and about 0.3 respectively. Charge that mostly origin from Mg2+ substituting Al3+ in octahedron and Al3+ substituting Si4+ in tetrahedron is mainly related to Mg content and Al/Mg ratio in montmorillonites. Generally, montmorillonites with higher Mg content have higher charge. The difference of Al/Mg ratio and Fe content accounts for the structural variety, charge and physicochemical property of montmorillonites.