Iron Hydr oxide Coatings

FeClj was added to a quartz dispersion, then NaOH was added. Properties Contains akageneite [1756], 

Acidified Fe(NO3)3 solution and an equivalent amount of NaOH solution were added to a dispersion of Ludox silica. The procedure was repeated several times. 

Properties Specific surface area 144 mVg (more than original Ludox) [1192]. 

The sand (Ottawa, 99.5% SiO2) was acid-washed and dried. 20 g of Fe(NO3)3-9H2O dissolved in 50 cm of water was poured over 200 g of sand and stirred. The mixture was heated at 110°C for 16 h, and then washed. 

PZC/IEP of Fe Hydroxide-Coated Ottawa Sand Electrolyte T Method Instrument pH Reference 

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In a study of the Waquoit Bay subterranean estuary, a large accumulation of iron (hydr)oxide-coated sediments within the fresh-saline interface was encountered. These iron-oxide-rich sands could act as a geochemical barrier by retaining and accumulating certain dissolved chemical species carried to the subterranean estuary by groundwater and/or coastal seawater. Significant accumulation of phosphorus in the iron oxide zones of the Waquoit cores exemplifies this process (Figure 8). 

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

Iron (oxy)(hydr)oxide-coated sand filtration Joshi and Chaudhuri (1996), Ko et al. (2007)... 

Zerovalent iron is often used in PRBs to remove arsenic from groundwater (Lien and Wilkin, 2005, 378). Other barriers for removing arsenic consist of lime, portlandite, steel industry byproducts, iron compounds, iron (oxy)(hydr)oxide-coated sands, and/or limestone (Ko et al., 2007 Blowes et al., 2000, 129-130 Ahn et al., 2003). Mixtures of lime, iron (oxy)(hydr)oxides, and limestone may remove dissolved As(III) and As(V) to less than 3pgL-1 (Blowes et al., 2000, 129-130 Table 7.1). 

Solid-Phase Preparation. To obtain surface sensitivity, both manganese- and iron-(hydr)oxide minerals were synthesized as thin coatings on an inert, high-surface area silica substrate. 

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). 

If substantial arsenic is present in a sandstone or conglomerate, it may occur in hematite or other iron (oxy)(hydr)oxide cements or coatings on mineral grains. Arsenic may also be enriched in sandstones, conglomerates, and other clastic sedimentary rocks if hydrothermal or other secondary sulfide minerals are present (e.g. St. Peter Sandstone, (Gotkowitz et al., 2001) arsenian pyrite cement in the Marshall Sandstone of the Michigan Basin, USA, (Kolker et al., 2000 Szramek, Walter and McCall, 2004)). Sections of the St. Peter Sandstone in eastern Wisconsin, USA, are enriched in sulfide minerals and contain about 500 mg kg-1 of arsenic. In contrast, unmineralized portions typically have <10 mg kg-1 (Gotkowitz et al., 2001). If present in sedimentary rocks, hydrothermal sulfide deposits often tend to concentrate in veins and faults more than the rock matrices. 

Desorption on Iron and Arsenic Reduction The effects of biological (dissimilatory) Fe(III) and As(V) reduction on As transport under dynamic flow conditions in an Fe (hydr)oxide-dominated system illustrate the complexity of reactions influencing arsenic dynamics within soils. We examined the impact of a model freshwater anaerobic bacterium, Sulfurosprillum harnesii strain SES-3, that reduces both Fe(III) and As(V) through respiratory processes (Oremland et al., 1994 Zobrist et al., 2000), on the desorption of arsenic from ferrihydrite-coated sands (Herbel and Fendorf, 2005, 2006). As noted above for As(III)-loaded... 

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