National Science Foundation Engineering Research Center for Reinventing the Nation's Urban Water Infrastructure (ReNUWIt) and Department of Civil & Environmental Engineering, University of California, Berkeley, California United States.
Geochemistry Department of the Geological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark.
Environ Sci Technol. 2021 Apr 20;55(8):5282-5290. doi: 10.1021/acs.est.0c05745. Epub 2021 Mar 22.
Manganese oxide-coated sand can oxidize electron-rich organic contaminants, but after extended exposure to contaminated water its reactivity decreases. To assess the potential for regenerating geomedia, we measured the ability of passivated manganese-oxide coated sand to oxidize bisphenol A after treatment with oxidants, acid, or methanol. Among the regenerants studied, KMnO, HOCl, HOBr, and pH 2 or 3 HCl solutions raised the average oxidation state of the Mn, but only HOCl and HOBr restored the reactivity of passivated geomedia to levels comparable to those of the virgin manganese-oxide coated sand. Treatment with HCl restored about one third of the reactivity of the material, likely due to dissolution of reduced Mn. Mn K-edge X-ray absorption spectroscopy data indicated that the reactive manganese oxide phases present in virgin geomedia and geomedia regenerated with HOCl or HOBr had nanocrystalline cryptomelane-like structures and diminished Mn(III) abundance relative to the passivated geomedia. KMnO-regenerated geomedia also had less Mn(III), but it exhibited less reactivity with bisphenol A because regeneration produced a structure with characteristics of δ-MnO. The results imply that manganese oxide reactivity depends on both oxidation state and crystal structure; the most effective chemical regenerants oxidize Mn(III) to Mn(IV) oxides exhibiting nanocrystalline, cryptomelane-like forms.
氧化锰涂层砂可以氧化富电子的有机污染物，但在长时间接触受污染的水后，其反应活性会降低。为了评估地质介质再生的潜力，我们测量了经过氧化剂、酸或甲醇处理后，钝化氧化锰涂层砂氧化双酚 A 的能力。在所研究的再生剂中，KMnO4、HOCl、HOBr 和 pH 为 2 或 3 的 HCl 溶液提高了 Mn 的平均氧化态，但只有 HOCl 和 HOBr 恢复了钝化地质介质的反应活性，使其与原始氧化锰涂层砂的水平相当。用 HCl 处理可恢复约三分之一的材料活性，这可能是由于还原 Mn 的溶解。Mn K 边 X 射线吸收光谱数据表明，原始地质介质和用 HOCl 或 HOBr 再生的地质介质中存在的反应性氧化锰相具有纳米晶隐钾锰矿样结构，且 Mn(III)丰度相对于钝化地质介质降低。KMnO4 再生的地质介质中 Mn(III)也较少，但与双酚 A 的反应性较低，因为再生产生了具有 δ-MnO 特征的结构。结果表明，氧化锰的反应活性既取决于氧化态又取决于晶体结构；最有效的化学再生剂将 Mn(III)氧化为具有纳米晶、隐钾锰矿样形态的 Mn(IV)氧化物。
