悬浮颗粒形状对其在多孔介质中迁移和沉积特性的影响

Influence of particle shape on the suspended particle transport and deposition in porous media

悬浮颗粒在多孔介质中迁移的研究在地下水回灌、地下污染物扩散、核废料处置、石油开采等领域有重要的理论意义和应用价值。为了研究形状对颗粒迁移的影响,对1组球状颗粒(10?m中位粒径)和2组杆状颗粒(长径比为3:1和6:1)进行了三阶段室内土柱试验,得到了不同形状颗粒在多种溶液离子强度条件下的穿透曲线。结合DLVO理论分析了悬浮颗粒沉积和释放机制,阐释了形状对颗粒迁移行为的影响。试验结果表明,颗粒形状对迁移特性有重要影响,当离子强度较低时(6 mmol/L),DLVO势能曲线展现较高能量壁垒,各种形状颗粒沉积主要为次级势阱沉积;当离子强度较高时(150 mmol/L),球状颗粒因能量壁垒较高,其滞留机制仍以次级势阱沉积为主,但长径比为6:1的杆状颗粒在次级势阱和初级势阱都有沉积,这和杆状颗粒的静电性能和优先方向有关。对于杆状颗粒,边位沉积比端位沉积具有更深的次级势阱和更大的影响距离,边位沉积是更加稳定的沉积方式和沉积的优先方向。基于Derjaguin近似方法的DLVO理论计算显示,DLVO理论预测结果和土柱试验结果吻合较好。

The study on transport and deposition of suspended particles in porous media is important to groundwater recharge, underground pollutant diffusion, nuclear waste disposal and oil exploitation. Most natural suspended particles are non-spherical. To study the effect of shape on particle migration, soil column tests with three-phases were carried out on spherical particles（10 ？m in median particle diameter） and rod-shaped particles（aspect ratios of 3：1 and 6：1）. The breakthrough curves of different shape particles under different ionic intensities were obtained. The mechanism of the deposition and release of suspended particles was analyzed by DLVO theory, and the effect of shape on particle migration behavior was explained. When the ionic strength is low（6 mmol/L）, the DLVO interaction energy profile shows higher energy barriers. So particles of various shapes is mainly retained in secondary minimum. When the ionic strength is high（150 mmol/L）, the retention mechanism of spherical particles is the secondary minimum retention due to high energy barriers. The 6：1 rod-like particles are retained in the secondary minimum and the primary minimum, relating to the electrostatic properties and the preferential orientation of the rod-like particles. For rod-like particles, a side-on orientation provides a deeper attractive well and larger influential distance than an end-on orientation. A side-on configuration is a more stable deposition method and preferred orientation for particle deposition. The Derjaguin approximation method is used in the DLVO calculation. The results show that the theoretical prediction agrees well with the soil test results.