不同pH环境下CMS改性纳米铁在异质多孔介质中的迁移

纳米铁在污染土壤和地下水的修复中受到广泛关注。为进一步探究其在多孔介质的迁移行为，本研究采用羧甲基淀粉钠（CMS）对纳米零价铁（nZVI）进行包覆，进行了改性纳米零价铁的沉降试验，测量zeta电位与粒径分布探究其分散性；进行了不同pH条件下改性纳米零价铁在酸洗砂与水洗砂的柱实验，分析了化学异质性与pH对纳米铁在多孔介质迁移的影响。结果表明，CMS包覆纳米铁不仅使纳米颗粒本身稳定，而且还减少其在多孔介质表面沉积，大大提高了迁移性。pH=6～8时，nZVI的zeta电位由18.3mV减小到2.9mV，有效粒径由685nm增大到880nm，稳定性变差；而CMS-nZVI的zeta电位值由-19.7mV增大到-53.5mV，颗粒间静电排斥力增强稳定性变好。经能量色散X射线光谱（EDS）分析，水洗砂表面存在碳、铝、铁等氧化物杂质，这些杂质带有正电荷，会增强与带负电的CMS-nZVI的吸附作用，不利于其迁移；而经过酸洗后的石英砂，其表面杂质大大减少，在pH=8时，CMS-nZVI在酸洗砂最大迁移率为77.0%要好于水洗砂的63.0%。此外较高pH环境有助于增加石英砂介质的表面负电荷，减少颗粒与介质的吸附，促进纳米颗粒的迁移。

Transport of CMS modified nano-iron in heterogeneous porous media under different pH environments

Nano-iron has received extensive attention in the repair of contaminated soil and groundwater. In order to further explore its migration behavior in porous media, nano-zero-valent iron (nZVI) was coated with sodium carboxymethyl starch (CMS), and the sedimentation test of modified nano-zero-valent iron was carried out. The zeta potential and particle size distribution were measured to explore its dispersion. The column experiments of modified nano-zero-valent iron in pickled sand and washed sand under different pH conditions were carried out. The effects of chemical heterogeneity and pH on the migration of nano-iron in porous media were analyzed. The results showed that CMS coated nano-iron not only stabilizes the nanoparticles themselves, but also reduces their deposition on the surface of porous media, which greatly improves the mobility. When pH=6 to 8, the zeta potential of nZVI was reduced from 18.3mV to 2.9mV, the effective particle size increased from 685nm to 880nm, and the stability was deteriorated. When the zeta potential of CMS-nZVI increased from -19.7mV to -53.5mV, the electrostatic repulsion between particles was enhanced and the stability was improved. According to energy dispersive spectroscopy (EDS) analysis, there were oxide impurities such as carbon, aluminum and iron on the surface of the washed sand. These impurities have a positive charge, which will enhance the adsorption of negatively charged CMS-nZVI, which is not conducive to its migration. After pickling quartz sand, the surface impurities were greatly reduced. At pH=8, the maximum mobility of CMS-nZVI in pickled sand was 77.0%, which is 63.0% better than that of washed sand. In addition, the higher pH environment helps to increase the surface negative charge of the quartz sand medium, reduce the adsorption of particles and the medium, and promote the migration of the nanoparticles.