Manganese oxides have been proposed as promising geomedia to remove trace organic contaminants in both natural soils and artificial infiltration systems. Although MnO_x-based redox processes have been largely investigated, little is known on the effects of water flow and dissolved Mn^II on manganese-mediated redox reactions in saturated porous media. Here, we have demonstrated that the reactive transport of a widely used quinolone antibiotic, pipemidic acid (PIP), in MnO₂-coated sand (MCS) columns is altered by the presence of dissolved Mn^II, generated in situ as reduced ions or present in inflow solution. Decreasing the flow rate or flow interruption facilitated oxidation reactions and generated redox byproducts (Mn^II and PIP_ox). However, preloading of MCS columns with dissolved Mn^II led to suppressed reactivity with PIP. When PIP and Mn^II are simultaneously injected, competition between PIP and Mn^II for binding at the edge sites takes place during the initial kinetic phase of reaction, while at a later breakthrough time Mn^II will occupy both edge and vacancy sites due to the continuous supply of Mn^II. We also developed a reactive transport model that accounts for adsorption kinetics to predict changes in transport behavior of antibiotics in the presence of different doses of dissolved Mn^II. This work has strong implications for an accurate assessment of the reactivity of manganese oxides used as engineered geomedia for quinolone remediation and in developing transport models of antibiotics in natural systems.

中文翻译：

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水流量和溶解的MnII改变氧化锰对哌啶酸的转化。

锰氧化物已被提出作为有前途的地理介质，以去除天然土壤和人工渗透系统中的痕量有机污染物。尽管已经大量研究了基于MnO _x的氧化还原过程，但对于水流量和溶解的Mn ^II对饱和多孔介质中锰介导的氧化还原反应的影响知之甚少。在这里，我们已经证明，原位生成的溶解的Mn ^II改变了广泛使用的喹诺酮抗生素哌啶酸（PIP）在MnO ₂涂层砂（MCS）色谱柱中的反应性运输作为还原离子或存在于流入溶液中。降低流速或中断流动有助于氧化反应并产生氧化还原副产物（Mn ^II和PIP _ox）。但是，用溶解的Mn ^II预加载MCS色谱柱会导致与PIP的反应性降低。当PIP和Mn ^II被同时注入，PIP和Mn之间的竞争^II在边缘部位结合在反应的初始动能阶段发生，而在稍后的突破时间锰^II将占据两个边缘和空位位点由于连续Mn ^II的供应。我们还开发了一种反应转运模型，该模型解释了吸附动力学以预测在不同剂量的溶解的Mn ^II存在下抗生素的转运行为的变化。这项工作对准确评估用作喹诺酮修复工程土工材料的锰氧化物的反应性以及开发天然系统中抗生素的运输模型具有重要意义。