Manganese Hydr oxides

Properties Structure confirmed by XRD, BET specific surface area 20.4 m7g [82]. 

Properties Hausmannite, XRD and IR spectra, particle size histogram, and 

PZC/IEP of Groutite Obtained by Hydrolysis of Mn II Acetate Electrolyte T Method Instrument pH Reference 

Recipe from 11693] 1 drn of 0.06 M MnSO4 was mixed with 20 cm of 30% H2O2 and 300 cm of 0.2 M ammonia. The mixture was stirred at 95°C for 6 h, then washed and dried at room temperature. 

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Nelson, Y.M. et al., Effect of oxide formation mechanisms on lead adsorption by biogenic manganese (hydr)oxides, iron (hydr)oxides, and their mix lures, Environ. Sci. Technol., 36, 421, 2002. 

K. Ndung u, S. Friedrich, A. R. Gonzalez, A. R. Flegal (2010) Chromium oxidation by manganese (hydr)oxides in a California aquifer. Appl. Geochem., 25, 377-381. 

Hydrous Manganese oxides, widely distributed in natural systems, are stronger oxidants than iron(III)(hydr)oxide. These oxides readily oxidize many natural and xenobiotic organic compounds. Various substituted phenols, naturally present in... 

Additional information on adsorption mechanisms and models is in Stollenwerk (2003), 93-99 and Prasad (1994). Foster (2003) also discusses in considerable detail how As(III) and As(V) may adsorb and coordinate on the surfaces of various iron, aluminum, and manganese (oxy)(hydr)oxides. In adsorption studies, relevant laboratory parameters include arsenic and adsorbent concentrations, adsorbent chemistry and surface area, surface site densities, and the equilibrium constants of the relevant reactions (Stollenwerk, 2003), 95. Once laboratory data are available, MINTEQA2 (Allison, Brown and Novo-Gradac, 1991), PHREEQC (Parkhurst and Appelo, 1999), and other geochemical computer programs may be used to derive the adsorption models. 

Adsorption of arsenic Iron, aluminum, and manganese (oxy)(hydr)oxides widely occur as sorbents and coatings on other solid materials in nature. They are often important in adsorbing arsenic from water ((Stollenwerk, 2003), 73 Chapter 3). Below the ZPCs of the (oxy)(hydr)oxides, the presence of... 

Aqueous As(III) rapidly oxidizes to As(V) in the pipes and drains of some geothermal power plants. Yokoyama, Takahashi and Tarutani (1993, 109-110) speculated that rapid oxidation could be due to iron and manganese (oxy)(hydr)oxides suspended in the water or coating the walls of the pipes. Once oxidized, As(V) may sorb onto the iron (oxy)(hydr)oxides in pipe and drain scales (Webster and Nordstrom, 2003, 116). 

Reductive dissolution of iron and manganese (oxy)(hydr)oxides... 

Groundwaters in the loess aquifers of La Pampa, Argentina, may contain > 5 mgL-1 of arsenic ((Smed-ley et al., 2005 Smedley et al., 2002) Table 3.13). The aquifers are very oxidizing and As(V) is the dominant arsenic species. The alkalinity of the groundwaters (pH 7.0-8.8) and the unusual presence of vanadium probably hinders the sorption of As(V) onto iron and manganese (oxy)(hydr)oxides. The alkalinity and vanadium may also desorb arsenic from the minerals (Smedley et al., 2005). 

Like sediments, colloids are often important in sorbing and transporting arsenic in soils (Sadiq, 1997 Waychunas, Kim and Banheld, 2005). Colloids may consist of clay minerals, organic matter, calcium carbonate, and various aluminum, manganese, and iron (oxy)(hydr)oxides (Sadiq, 1997). Important iron (oxy)(hydr)oxides include goethite, akaganeite (/J-FeO(OH)), hematite, ferrihydrites, and schwertman-... 

Arsenic is most prone to form surface complexes by adsorption on metal (mostly iron and manganese) (oxy)(hydr)oxides, followed by clays and feldspars (Lin and Puls, 2003). As discussed in Chapters 3 and 7, iron (oxy)(hydr)oxides are groups of Fe(III) Fe(II) (hydrous) oxides, (hydrous) hydroxides, and (hydrous) oxyhydroxides. Individual compounds, such as ferrihydrite, often have highly variable and... 

Oxidation of arsenic-bearing pyrite with adsorption onto iron oxides and/or other metal (oxy)(hydr)oxides Nitrate reduction by pyrite oxidation (note that Appelo and Postma, 1999 referred to pure rather than arsenian pyrite) Manganese oxide reduction and release of sorbed arsenic Fe(lll) reduction on oxide surfaces changes net charge leading to arsenic desorption Iron oxide reductive dissolution and release of sorbed arsenic catalyzed by NOM degradation... 

Table 7.1 Treatment methods that have the potential to reduce inorganic arsenic concentrations in water to below 10pg L-1. For some inorganic As(lll) treatment methods, sorbents (such as, manganese (oxy)(hydr)oxides) may actually oxidize the As(lll) to inorganic As(V) before sorbing it.

Manganese (oxy)(hydr)oxide-coated sand filtration... 

Manganese (oxy)(hydr)oxide sorbents and manganese-oxidizing bacteria Permeable reactive barriers with lime, iron oxides, and limestone Siderite (coprecipitation and possibly sorption)... 

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