Regenerated Manganese-Oxide Coated Sands: The Role of Mineral Phase in Organic Contaminant Reactivity

Abstract

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, KMnO4, 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. KMnO4-regenerated geomedia also had less Mn­(III), but it exhibited less reactivity with bisphenol A because regeneration produced a structure with characteristics of δ-MnO2. 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.

Atomic-Level Structural Differences between Fe(III) Coprecipitates Generated by the Addition of Fe(III) Coagulants and by the Oxidation of Fe(II) Coagulants Determine Their Coagulation Behavior in Phosphate and DOM Removal

“…The addition of KMnO 4 to the coagulation system produced many short-range ordered and nondirectional lattice fringes in amorphous spheres due to the formation of nanoscale manganese dioxide. With lattice fringes, the structure was judged to be birnessite (δ-MnO 2 ) . Despite the formation of larger crystalline manganese dioxide nanoparticles with increasing KMnO 4 concentration, amorphous Fe-phosphate coprecipitates always encapsulated them, resulting in no obvious peaks in the XRD results.…”

High yield and isolation of 2,5-furandicarboxylic acid from HMF and sugars in ionic liquids, a new prospective for the establishment of a scalable and efficient catalytic route

“…13,29,30 Different regeneration methodologies are reported to restore the manganese activity based on the treatment with stoichiometric oxidants at high pH. 31…”

“…13,29,30 Different regeneration methodologies are reported to restore the manganese activity based on the treatment with stoichiometric oxidants at high pH. 31 Further analysis of the liquor by ICP showed a consistent leaching of manganese into the solvent (12 ± 4%). This amount could be recovered by diluting the ionic liquid solution and adjusting the pH of the solution to 10 through addition of [bmim]OH, followed by neutralization with HCl and water evaporation.…”

An electrochemical advanced oxidation process for the treatment of urban stormwater

“…Infiltration rates are also limited by the need to achieve adequate contact times between the engineered geomedia and the contaminants ( Grebel et al., 2016 ; Shimabuku et al., 2016 ). In addition, geomedia eventually will clog or be exhausted, which necessitates replacement or regeneration to assure continued operation ( Charbonnet et al., 2018 , 2021 ). As a result, infiltration-based techniques that employ geomedia are often unable to treat large volumes of stormwater in urban areas.…”