To shorten the ripening period of filter sand, iron–manganese co-oxide filter film (MeOx) was formed quickly on the virgin quartz sand surface by oxidizing Mn2+ and Fe2+ from groundwater using KMnO4 continuously. After the start-up period, we found that Mn2+ could be removed efficiently by MeOx, even if the dissolved oxygen (DO) concentration in the influent was only about 1.0–1.5 mg/L. This means that the removal process of Mn2+ does not need to consume DO. The kinetic experiments for Mn2+ indicated that the adsorption and oxidation kinetics followed pseudo-first-order kinetics. The film (MeOx) was characterized by X-ray photoelectron spectroscopy (XPS). All manganese adsorbed on the surface of the sand was the oxidized form, and the manganese oxide coated onto the sand effectively oxidized Mn2+ to Mn3+ or Mn4+. The binding energy of the observed photoelectron peaks of O(1s) showed the existence of [≡Mn-OH] on the surface of the film by XPS, which might be a key intermediate in the mechanism of Mn2+ oxidation. Finally, a chemical catalytic oxidation mechanism for Mn2+ removal was proposed by the analysis of the oxidation process.
The chemical adsorption of dissolved oxygen (DO) by co-oxide filter film-coated sands, formed through the filtration of ground water containing high concentrations of ammonia, manganese and iron, were studied. The results showed that the filter film consisted of silicates, carbonates, manganese and iron oxides and was constructed in a three-layer porous structure. The specific area of film-coated sands was 6.5 m2/g. The chemical adsorption sites of DO are composed of silicates, iron and manganese atoms, and the adsorption was a weak chemical effect. The O2− is the adsorbed species of DO.
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