Characterization and manipulation of montmorillonite properties towards technological and environmental applications

ABSTRACT The combination of pillarization and charge neutralization with Li+ can make montmorillonite an important support material for industry and decontamination of pollutants in soil and water. Montmorillonite characterization techniques were described in detail, and pillarization procedures were used, after Li+ saturation, to modify and manipulate the chemical and mineralogical surface properties of this montmorillonite. Eight samples were produced: 1) natural montmorillonite (Chisholm Mine - MMT); 2) Li+ saturated montmorillonite (MMTLi); 3) polyethylene glycol (PEG) Al-pillared montmorillonite (AlPEG); 4) PEG Al-pillared montmorillonite saturated with Li (AlPEGLi); 5) Al-pillared montmorillonite with 14 h contact time (Al14h); 6) Al-pillared montmorillonite Al14h saturated with Li (Al14hLi); 7) Al-pillared montmorillonite with 0 h contact time (Al0h); and 8) Al-pillared montmorillonite Al0h saturated with Li (Al0hLi). The natural sample was identified as interlayered montmorillonite composed of chlorite layers or with a high degree of Al-hydroxy filling. Concerning the total permanent charges, 70 % occurred by isomorphic substitution of Al3+ by Mg2+ in octahedral layer and 30 % of Si4+ by Al3+ in tetrahedral layer. The pillarization method using the PEG produced a small number of stable pillars. The new milder pillarization method (Al0h) did not cause damage in the formation of Al-hydroxy. In this method, the resulting pillars were more homogeneous in size. Thereby, the Al0h Li method has been shown to produce a supporting material with a constant interlayer spacing, increased of the specific surface area (SSA), and drastic reduction of the cation exchange capacity (CEC) as compared to MMT. This modified mineral can be used in, for example, decontamination of polluted water with nonionic organic pollutants.

摘要 将柱撑改性与锂离子（Li+）电荷中和相结合，可使蒙脱石（montmorillonite）成为工业领域的重要载体材料，并可用于土壤与水体中污染物的净化修复。本文详细阐述了蒙脱石的表征手段，并在锂离子饱和改性后通过柱撑工艺对该蒙脱石的化学与矿物学表面性质进行调控修饰。本次实验共制备8组样品：1) 天然蒙脱石（奇泽姆矿——MMT）；2) 锂离子饱和蒙脱石（MMTLi）；3) 聚乙二醇（polyethylene glycol, PEG）铝柱撑蒙脱石（AlPEG）；4) 经锂离子饱和的聚乙二醇铝柱撑蒙脱石（AlPEGLi）；5) 接触时长14小时的铝柱撑蒙脱石（Al14h）；6) 经锂离子饱和的接触时长14小时的铝柱撑蒙脱石（Al14hLi）；7) 接触时长0小时的铝柱撑蒙脱石（Al0h）；8) 经锂离子饱和的接触时长0小时的铝柱撑蒙脱石（Al0hLi）。天然样品被鉴定为含绿泥石层或羟基铝填充度较高的夹层状蒙脱石。就总永久电荷而言，70%源自八面体层中Mg2+对Al3+的同晶置换，剩余30%源自四面体层中Al3+对Si4+的同晶置换。采用聚乙二醇的柱撑工艺仅能生成少量稳定柱体。新型温和柱撑工艺（Al0h）未对羟基铝的形成造成破坏，该工艺所得柱体的尺寸更为均一。由此可见，相较于天然蒙脱石（MMT），经Al0h锂改性工艺制得的载体材料具有恒定的层间距、更高的比表面积（specific surface area, SSA），且阳离子交换容量（cation exchange capacity, CEC）大幅降低。该改性矿物可用于非离子型有机污染物污染水体的净化修复。