The environmental fate and risks of ciprofloxacin (CIP) in the subsurface have raised intensive concerns. Herein, the transport behaviors of CIP in both saturated quartz sand and sand/multi-walled carbon nanotubes (MWCNTs) mixtures under different solution ionic strength of the solution and coexisting cation types were investigated. Batch adsorption experiments highlighted growing adsorptive capacity for CIP with the increasing content of MWCNTs in the MWCNTs-quartz sand mixtures (from 0.5% to 1.5%, w/w). Breakthrough curves (BTCs) of CIP in the MWCNTs-quartz sand mixtures were well fitted by the two-site chemical nonequilibrium model (R² > 0.833). The estimated retardation factors for CIP increased from 9.68 to 282 with growing content of MWCNTs in the sand column, suggesting the presence of MWCNTs significantly inhibited the transport of CIP in saturated porous media. Moreover, the values of retardation factors are negatively correlated with the ionic strength and higher ionic strength could facilitate the transport of CIP in the saturated porous media. Compared with monovalent cations (Na⁺), the presence of divalent cations (Ca²⁺) significantly facilitated the transport of CIP in the columns due to the complexation between CIP and Ca²⁺ as well as deposition of MWCNTs aggregates on the sand surface. Results regarding CIP retention in columns indicated that MWCNTs could enhance the accumulation of CIP in the layers close to the influent of sand columns, while they could hinder upward transport of CIP to the effluent. This study improves our understanding for transport behaviors and environmental risk assessments of CIP in the saturated porous media with MWCNTs.

环丙沙星 (CIP) 在地下的环境归宿和风险引起了人们的强烈关注。在此，研究了在不同溶液离子强度和共存阳离子类型下，CIP 在饱和石英砂和砂/多壁碳纳米管 (MWCNT) 混合物中的传输行为。批量吸附实验强调，随着 MWCNT-石英砂混合物中 MWCNT 含量的增加（从 0.5% 到 1.5%，w/w），CIP 的吸附能力不断增强。多壁碳纳米管-石英砂混合物中 CIP 的突破曲线 (BTC) 通过两位点化学非平衡模型很好地拟合（R ²  > 0.833）。随着砂柱中 MWCNT 含量的增加，CIP 的估计延迟因子从 9.68 增加到 282，这表明 MWCNT 的存在显着抑制了 CIP 在饱和多孔介质中的传输。此外，延迟因子的值与离子强度呈负相关，较高的离子强度有利于CIP在饱和多孔介质中的传输。与一价阳离子 (Na ⁺ )相比，二价阳离子 (Ca ²⁺ )的存在显着促进了 CIP 在柱中的传输，这是由于 CIP 和 Ca ²⁺之间的络合以及 MWCNT 聚集体在砂表面上的沉积。关于 CIP 在柱中保留的结果表明，多壁碳纳米管可以增强 CIP 在靠近砂柱进水层的积累，同时它们可以阻碍 CIP 向上传输到流出物。这项研究提高了我们对多壁碳纳米管饱和多孔介质中 CIP 的传输行为和环境风险评估的理解。