Fe(II) reduction of pyrolusite (β-MnO2) and secondary mineral evolution

Abstract Iron (Fe) and manganese (Mn) are the two most common redox-active elements in the Earth’s crust and are well known to influence mineral formation and dissolution, trace metal sequestration, and contaminant transformations in soils and sediments. Here, we characterized the reaction of aqueous Fe(II) with pyrolusite (β-MnO2) using electron microscopy, X-ray diffraction, aqueous Fe and Mn analyses, and 57Fe Mössbauer spectroscopy. We reacted pyrolusite solids repeatedly with 3 mM Fe(II) at pH 7.5 to evaluate whether electron transfer occurs and to track the evolving reactivity of the Mn/Fe solids. We used Fe isotopes (56 and 57) in conjunction with 57Fe Mössbauer spectroscopy to isolate oxidation of Fe(II) by Fe(III) precipitates or pyrolusite. Using these complementary techniques, we determined that Fe(II) is initially oxidized by pyrolusite and that lepidocrocite is the dominant Fe oxidation product. Additional Fe(II) exposures result in an increasing proportion of magnetite on the pyrolusite surface. Over a series of nine 3 mM Fe(II) additions, Fe(II) continued to be oxidized by the Mn/Fe particles suggesting that Mn/Fe phases are not fully passivated and remain redox active even after extensive surface coverage by Fe(III) oxides. Interestingly, the initial Fe(III) oxide precipitates became further reduced as Fe(II) was added and additional Mn was released into solution suggesting that both the Fe oxide coating and underlying Mn phase continue to participate in redox reactions when freshly exposed to Fe(II). Our findings indicate that Fe and Mn chemistry is influenced by sustained reactions of Fe(II) with Mn/Fe oxides

Two sides of a coin: targets and by-products of water and wastewater treatment

With time new methods/technique developed for clean/portable as same, it is essential to authenticate them. In this chapter the discussion on what is the disadvantage of tertiary treatment including harmful disinfection by-products (DBP). The details of Trihalomethanes, Haloacetic acid, Nitrosamine and Perfluorinated compounds, its necessary condition like precursors for formation the in treatment. As well as how to get rid of these compounds and their pathways are also summarized. Chlorination is the cheapest, realistic and most effective method in comparison to ozonation and UV radiations. Among all the methods mentioned above, chlorination is the cheapest, realistic and most effective method for achieving the best results. However, its results in harmful disinfection by-products, which need to understand the critical situation.by Bhagwana Ram, Divya Sharma and Manish Kuma