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Metal oxides in soils

Barium reacts with metal oxides and hydroxides in soil and is subsequently adsorbed onto soil particulates (Hem 1959 Rai et al. 1984). Adsorption onto metal oxides in soils and sediments probably acts as a control over the concentration of barium in natural waters (Bodek et al. 1988). Under typical environmental conditions, barium displaces other adsorbed alkaline earth metals from MnO2, SiO2, and TiO2 (Rai et al. 1984). However, barium is displaced from Al203 by other alkaline earth metals (Rai et al. 1984). The ionic radius of the barium ion in its typical valence state (Ba+) makes isomorphous substitution possible only with strontium and generally not with the other members of the alkaline earth elements (Kirkpatrick 1978). Among the other elements that occur with barium in nature, substitution is common only with potassium but not with the smaller ions of sodium, iron, manganese, aluminum, and silicon (Kirkpatrick 1978). [Pg.81]

Violante, A., Krishnamurti, G. S. R., and Huang, P. M. (2002). Impact of organic substances on the formation and transformation of metal oxides in soil environments. In Interactions Between Soil Particles and Microorganism Impact on the Terrestrial Ecosystem, ed. Huang, P. M., Bollag, J.-M., and Senesi, N., lUPAC Series on Analytical and Physical Chemistry of Enviromnental Systems, Vol. 8, Wiley, Chichester, West Sussex, England, 133-188. [Pg.51]

Iron oxides are the most abundant metallic oxides in soils (Schwertmann and Taylor, 1989 Cornell and Schwertmann, 1996 Bigham etal., 2002). Iron oxides usually form via solution from Fe + ions released from Fe(II)-bearing silicates and sulfide minerals on weathering (Oades, 1963 Schwertmann and Taylor, 1989 Cornell and Schwertmann, 1996). Once formed in soil and other natural environments, the mineral phase, composition, and distribution of iron oxides can be continually modified by the alteration of their environments (Schwertmann and Taylor, 1989). Therefore, the formation and transformation of pedogenic iron oxide mineral phases depend on the pedo-environmental conditions under which they have formed. [Pg.184]

In summary, the removal of organic matter and Fe oxides significantly changes the physicochemical and surface chemical properties of soils. Thus, this pretreatment affects the overall reactivity of heavy metals in soils. The removal of organic matter and Fe oxides may either increase or decrease heavy metal adsorption. The mechanisms responsible for the changes in metal adsorption in soils with the removal of organic matter and Fe oxides include increases in pH, surface area, CEC and electrostatic attraction, decreases in the ZPC, shifts of positive zeta potentials toward... [Pg.144]

Sulfate poorly prevents arsenate sorption onto metal oxides and soils (Wu et al. 2001 Inskeep et al. 2002 Violante et al. 2005b). Violante et al. (2005b) found that high concentrations of sulfate (sulfate/arsenate molar ratio (rf) 4-10) retarded but not prevented arsenate sorption onto ferrihydrite (see their Fig. 15.10) or other metal oxides. Roy et al. (1986) showed that the sorption of arsenate by two soils (an Ultisol and a Typic Apludults) was reduced in the presence of molybdate. [Pg.48]

In groundwater, hexavalent chromium tends to be mobile due to the lack of solubility constraints and the low adsorption of CH6 anion species by metal oxides in neutral to alkaline waters (Calder 1988). Above pH 8.5, no CH6 adsorption occurs in groundwater Cr adsorption increases with decreasing pH. Trivalent chromium species tend to be relatively immobile in most groundwaters because of the precipitation of low-solubility Cr 3 compounds above pH 4 and high adsorption of the Cr+3 ion by soil clay below pH 4 (Calder 1988). [Pg.81]

Iron oxides in soils and those used as pigments, are often associated with adsorbing species or with dopants such as phosphate, silicate and various metal ions their iep s/pzc s will differ from those of the pure compounds. Soils rich in Fe oxides, therefore, have pzc s of 4-7, i.e. lower than those of pure iron oxides (see Chap. 16). [Pg.239]

Among all layered silicate clays, the smectite family of 2 1 layer lattice structures are preeminent in their ability to adsorb organic molecules and to catalyze their chemical transformations. All metal oxides in the soil environment may exhibit some degree of surface reactivity. However, the adsorptivity and reactivity of typical smectites are facilitated by their relatively high internal surface areas 700 m2/g) and external surface areas (10-50 m2/g). [Pg.452]

Laboratory studies provide some insight into the possible role of DOM onstituents in metal mobilization in soils. These studies suggest that LMW organic ligands, specifically bidentate ligands, are more likely to promote min-rral dissolution than are humic substances. LMW organic acids have been identified in soil waters and in leachates of forest litter at concentrations sufficient to effect oxide dissolution. [Pg.107]

The adsorption of heavy metals onto amorphous or crystalline forms of iron oxide and clays occurs in nature and is phenomenologically related to the binding of contaminant to the superhcial ferric and/or aluminium ions. Although, this behavior explains the concentration of metal contaminants in soils, it does not constitute a viable method for trapping low concentrations of contaminants from aqueous streams because of its limited adsorption capacity. [Pg.290]

Changes in the oxidation state of trace metals can occur depending on the redox condition of the environment. Redox reactions are thus important in influencing the chemical speciation of a number of metals and metalloids, notably Hg, As, Se, Cr, Pu, Co, Pb, Ni, and Cu (Oscarson et al., 1981 Bartlett and James, 1993 Alloway, 1995 Myneni et al., 1997 Huang, 2000 James and Bartlett, 2000 Adriano, 2001 Sparks, 2003). Redox reactions also exert a great influence in the transformation and reactivity of Fe and Mn oxides in soils tliat have an enormous capacity to adsorb metals and metalloids (Huang and Germida, 2002). Furthermore, reduction of sulfate to sulfide in an anerobic environment also affects... [Pg.17]


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See also in sourсe #XX -- [ Pg.62 ]




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Oxidation soils

Oxides soils

Soil metals

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