Structure and Stability of Cd2+ Surface Complexes on Ferric Oxides

Nanoparticulate Iron Oxide Minerals in Soils and Sediments: Unique Properties and Contaminant Scavenging Mechanisms

“…This element-specific behavior is consistent with a host of mostly macroscopic studies (Spadini et al, 1994;Ford et al, 1997Ford et al, , 1999Martinez & McBride, 1998, 2001Karthikeyan et al, 1999aKarthikeyan et al, , 1999bTrivedi et al, 2001;Ford, 2002;Waychunas et al, 2002) which indicate evidence for structural incorporation of certain metal cations (e.g., Cu(II) Mn(II), Ni(II), Zn(II)) and minimal incorporation of others (e.g., Cd(II), Pb(II)) either during initial iron oxyhydroxide formation or when exposed to iron oxyhydroxides that are allowed to undergo phase transitions from ferrihydrite (HFO) to goethite or hematite (a-Fe 2 O 3 ). Ion size, preferred coordination chemistry, and steric effects may distinguish between metals that are more likely to form (co)precipitates and those that are not.…”

“…Hence we expect that comparing sorption on ferrihydrite to sorption on hematite and goethite (with crystallites more commonly in the micron size range and larger) might demonstrate the effects of reduced scale. For example, Cd(II) substitutes in the goethite structure and also forms inner-sphere complexes sharing edges with FeO 6 polyhedra (Spadini et al, 1994;Manceau et al, 2000). However in HFO, there appears only to be edge-sharing inner-sphere complexation.…”

Determination of growth rates of (100) and (110) faces of synthetic goethite by scanning force microscopy

“…These "open octahedra" are thus sites of preferential iron adsorption and attachment. This is supported by the results of Spadini et al (1994) and , who found a stronger adsorption of Cd on the (021) face compared to (110). An unfavorable situation for Fe attachment is encountered on the (110) face (Fig.…”

Adsorption and surface oxidation of Fe(II) on metal (hydr)oxides

“…Such a value is more representative for the formation of a tridentate surface complex than for the formation of a bidentate surface complex. Tridentate surface complexes can be formed at the 0 2 1 face, as has been found for Cd(II) (Spadini et al, 1994;Manceau et al, 2000), but the total Fe(II) loading in the experiments of (Dixit and Hering, 2006) is relatively high which implies that the 1 1 0 face has to accommodate a considerable part of the ferrous ions. In principle, tridentate complexes can be formed at the 1 1 0 face at interaction with two "FeOH and one "Fe 3 O (double edge sharing), according to, (Table 6), but the formation of a tridentate complex cannot be excluded definitively.…”