Experimental study and micro-mechanism analysis on chemico-osmotic membrane behavior of kaolin-bentonite
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摘要: 黏土类材料固有的半透膜特性能够显著延缓污染物扩散，对各类堆场防渗屏障服役性能的高效评估具有重要的意义。采用自制的刚性壁膜效应试验装置，开展了不同膨润土掺量的高岭土-膨润土（K-B）防渗材料的化学渗透膜性能试验及SEM电镜扫描试验，确定了5%~60%膨润土掺量的K-B试样化学渗透效率系数的变化规律，从微观角度定量研究并揭示了膜效应行为的影响机理。结果表明：随着膨润土掺量的增加，化学渗透效率系数的变化趋势呈现分阶段性规律，即缓慢增加（< 30%）、急剧增加（30%~40%）和稳定（> 40%）3个阶段，膨润土掺量从5%增到60%时，相应的化学渗透效率系数由0.002提高至0.197。通过电镜扫描发现，膨润土掺量的增加导致K-B试样孔隙结构变化，大孔数量减小，小孔数量逐渐增加，孔隙周长增大，表明孔隙数量和孔隙周长的改变是导致K-B化学渗透膜效应随膨润土掺量而变化的微观原因。Abstract: The semipermeable membrane behavior of clay materials can significantly delay contaminant diffusion, which is of great importance to evaluating the service performance of barriers in various landfills effectively. Using the self-made rigid wall test device, a series of chemico-osmotic tests on the kaolin-bentonite (K-B) mixtures with bentonite content (5%~60%) are carried out, and the variation trends of chemico-osmotic efficiency coefficients of K-B specimens are determined. Meanwhile, the influence mechanism of membrane effect behavior is revealed through the scanning electron microscope. The results show that the change process of chemico-osmotic efficiency coefficient can be divided into three stages, slow increase (< 30%), sharp increase (30%~40%) and steady condition (> 40%). When the content of bentonite increases from 5% to 60%, the corresponding chemico-osmotic efficiency coefficient increases from 0.002 to 0.197. In addition, the increase of bentonite content causes the pore structure change of K-B specimens, the number of large holes decreases, and the number of small holes gradually increases. Furthermore, the aperture perimeter of holes increases, indicating that the variation of pore number and aperture perimeter is the internal reason for leading to the change of chemico-osmotic membrane behavior with bentonite content.
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图 3 化学渗透效率系数与膨润土掺量的关系
Figure 3. Relationship between chemico-osmotic efficiency coefficient and bentonite content
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图 5 化学渗透效率系数、孔隙率与膨润土掺量的关系
Figure 5. Relationship among chemico-osmotic efficiency coefficient, porosity and bentonite content
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图 6 孔隙周长、化学渗透效率系数与膨润土掺量的关系
Figure 6. Relationship among perimeter of pore size, chemico- osmotic efficiency coefficient and bentonite content
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图 7 化学渗透效率系数与膨润土掺量的关系
Figure 7. Relationship between chemico-osmotic coefficient and bentonite content
表 1 高岭土和膨润土基本参数
Table 1 Parameters of kaolin and bentonite
指标 高岭土 膨润土 含水率/% 0.15 6.7 液限/% 60.4 234 塑限/% 9.8 194 Gs 2.84 2.87 pH 7.14 10.52 膨胀指数/(mL·2g-1) 1.5 25.0 阳离子交换量meq/(100 g-1) 0.91 62.84 
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表 2 K-B试样孔隙率
Table 2 Porosities of K-B specimens
膨润土掺量/% SEM定量化孔隙率/% 5 61.6 10 61.1 15 59.8 20 56.4 30 51.3 40 48.5 50 48.5 60 48.3
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