Oxidation birnessite

Mn-Oxides Birnessite NaMn204-1.5H20 Resistant to dissolution... 

Reduction method was used to prepare potassium type manganese oxide birnessite K-OL-1. The solution of the mixture of ethanol and potassium hydroxide was added slowly to a beaker containing a solution of potassium permanganate with vigorous... 

In the present study the surface chemistry of birnessite and of birnessite following the interaction with aqueous solutions of cobalt(II) and cobalt(III) amine complexes as a function of pH has been investigated using two surface sensitive spectroscopic techniques. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The significant contribution that such an investigation can provide rests in the information obtained regarding the chemical nature of the neat metal oxide and of the metal oxide/metal ion adsorbate surfaces, within about the top 50 of the material surface. The chemical... 

The binding energy results at pH 7 and the Co 2p spectral features are similar to those obtained for CoOOH. If a distinct cobalt-containing phase is formed in the reactions of cobalt II) with birnessite, the XPS results are more consistent with those for CoOOH when compared with XPS data for other Co(III)-containing oxides, namely Co2°3 or Co3°4 The corr sponding results at pH 8... 

Surface characterization of birnessite following the sorption of Co(II) indicates the presence of oxidized cobalt (CoOOH) at pH values, 4-6, where precipitation of Co(0H>2 does not occur, and a... 

From a mineralogical perspective, Fe-Mn nodules are composed of layers of manganese oxides (vernadite, todorokite, and birnessite), hydrous Fe oxide FeOOH H2O), aluminosilicates, quartz, and feldspar. Like the rest of the Fe-Mn oxides, the nodules... 

Pizzigallo et al. (1998) investigated the reaction of 4-chloroaniline with ferric oxide and two forms of manganese dioxide [birnessite (5-Mn02) and pyrolusite (Mn02)] within the pH range of 4-8 at 25 °C. The reaction rate of 4-chloroaniline was in the order birnessite > pyrolusite > ferric oxide. At pH 4.0, the reaction with birnessite was so rapid that the reaction could not be determined. Half-lives for the reaction of 4-chloroaniline with pyrolusite and ferric oxide were 383 and 746 min, respectively. The reaction rate decreased as the pH was increased. The only oxidation compounds identified by GC/MS were 4,4 -dichloroazobenzene and 4-chloro-4 -hydroxydiphenylamine. 

Arsenic contaminants may be found in the aquatic and terrestrial environments as a result of anthropogenic inputs and weathering of primary materials. It is known (e.g., Oscarson et al. 1983 Tournassat et al. 2002) that in such environments, manganese oxides like birnessite (b-MnO ) directly and rapidly oxidize As(III) to As(V). However, As(III) oxidation can be inhibited in sediments when additional natural materials lead to coating of MnO by CaC03 (Oscarson et al. 1983). 

The extent and rate of As(III) oxidation on birnessite surfaces are affected strongly by sorbed or competitive metal ligands in solution. Figure 16.6 shows As(III) oxidation when Zn is preadsorbed or applied in solution. The abbreviations shown in the figure denote specific reaction conditions used. For example. 

Fig. 16.6 Effects of pre-adsorbed Zn(II) vs. Zn(lI)/As(III) simultaneous treatment on As(III) oxidation kinetics on birnessite surfaces (pH 4.5, suspension density = 0.1 g L , in 0.01 M NaCl, total Zn(II) concentration of 100pM, and atmosphere). Percent As(III) depletion, As(V) release, and total As adsorption are shown as a function of time (hours), (a) Initial As(III) concentrations [As(III)] = lOOpM (b) [As(III)]j = 300pM. Reprinted with permission from Power LE, Aral Y, Sparks DL (2005) Zinc adsorption effect on arsenite oxidation kinetics at the birnessite water interface. Environ Sci Technol 39 181-187. Copyright 2005 American Chemical Society...

Manning, B.A., Fendorf, S.E., Bostick, B. and Suarez, D.L. (2002) Arsenic(III) oxidation and arsenic(V) adsorption reactions on synthetic birnessite. Environmental Science and Technology, 36(5), 976-81. 

Following consumption of dissolved O2, the thermodynamically favored electron acceptor is nitrate (N03-). Nitrate reduction can be coupled to anaerobic oxidation of metal sulfides (Appelo and Postma, 1999), which may include arsenic-rich phases. The release of sorbed arsenic may also be coupled to the reduction of Mn(IV) (oxy)(hydr)oxides, such as birnessite CS-MnCb) (Scott and Morgan, 1995). The electrostatic bond between the sorbed arsenic and the host mineral is dramatically weakened by an overall decrease of net positive charge so that surface-complexed arsenic could dissolve. However, arsenic liberated by these redox reactions may reprecipitate as a mixed As(III)-Mn(II) solid phase (Toumassat et al., 2002) or resorb as surface complexes by iron (oxy)(hydr)oxides (McArthur et al., 2004). The most widespread arsenic occurrence in natural waters probably results from reduction of iron (oxy)(hydr)oxides under anoxic conditions, which are commonly associated with rapid sediment accumulation and burial (Smedley and Kinniburgh, 2002). In anoxic alluvial aquifers, iron is commonly the dominant redox-sensitive solute with concentrations as high as 30 mg L-1 (Smedley and Kinniburgh, 2002). However, the reduction of As(V) to As(III) may lag behind Fe(III) reduction (Islam et al., 2004). 

Scott, M.J. and Morgan, J.J. (1995) Reactions at oxide surfaces. 1. Oxidation of As(III) by synthetic birnessite. Environmental Science and Technology, 29, 1898-905. 

Tournassat, C., Charlet, L., Bosbach, D. and Manceau, A. (2002) Arsenic(III) oxidation by birnessite and precipitation of manganese(II) arsenate. Environmental Science and Technology, 36(3), 493-500. 

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