Schwertmannite structure

Further candidates for the tunnel position in the schwertmannite structure is selenate. It seems that the oxyanions of hexavalent elements (S, Se, Cr) can be accomodated in the akaganeite structure whereas tliose of pentavalent ones (P, As) may only adsorb on the surface (Waychunas et al. 1995). 

Schwertmannite, Fei60is(0H)y(S04)z nHyO, has the same basic structure as akaganeite, but contains sulphate instead of chloride ions. This recently recognized mineral frequently occurs in nature as an oxidation product of pyrite and can be... 

Almost all the iron oxides, hydroxides and oxide hydroxides are crystalline. The degree of structural order and the crystal size are, however, variable and depend on the conditions under which the crystals were formed. All Fe oxides display a range of crystallinities except for ferrihydrite and schwertmannite which are poorly crystalline. 

Schwertmannite, is a common nanoparticle-product of neutralization of sulfuric acid-rich solutions (Bigham et al. 1994). The original structural analysis indicated that sulfate was contained within tunnels similar to those found in akaganeite (FeOOH). However, recent work by Waychunas et al. (2001) suggests that this is a defective, nanoporous phase and that sulfate occupies inner and outer sphere positions on the surface, and probably on the internal surfaces of defect regions within the structure. 

Randall et al. (1999) studied the structure and composition of Cd-+ complexes sorbed on several iron oxyhydroxide minerals goethite, lepidocrocite, akagenite, and schwertmannite using EXAFS. In all cases, adsorbed Cd-+ formed inner-sphere complexes over a wide range of solution pH and Cd-+ concentration. However, the bonding mechanism differed between minerals and depended on the availability of different types of adsorption sites at the mineral surface. For example, sorbed to goethite by the formation of bidentate surface com-... 

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