2009-05-19_REVISION - M1977416 - Laserfiche WebLink

Home Browse Search

metastibnite. However; antimony very rarely occurs in natural waters at high enough • concentrations to form antimony sulfides or oxides. Antimony Solid-Solution Phases The solid-solution reactions involoving antimony are not well documented. However, several investigations have been performed that suggest that Sb(+5) is incorporated into iron oxyhydroxide phases. Sb(+5) has been found to correlate with iron oxyhydroxide content within shooting range soils (Scheinost et al., 2006; Ackermann et al., 2009), in iron oxyhydroxide suspended. particles within a mine impacted river (Casiot et al., 2007), and in soils (Wilson et al., 2004; Manaka, 2006; Denys et al., 2009). Scheinost et al. (2006) performed an EXAFS spectroscopy analysis on a shooting range soil and found that the antimony was in the Sb(V) oxidation state and was linked to iron oxyhydroxides via inner-sphere complexes. A. reasonable solid solution reaction based on these data would be as follows: Fe+3 + (3-3x)Sb(OH)6- + 3xOH- -> Fe[Sb(OH)613-3x(OH)3x (1) Landrum et al. (2009) found that Sb(III) did not partition into the ferric oxides of a hot springs geyser depost, but was instead present within the silica sinter matrix. However, it was not determined if the antimony was present as a solid-solution within the silica or as a finely disminated pure phase within the sinter. Antimony Adsorption . Sb(+5) adsorbs to solid surfaces due partly to interactions between the negatively charged ions (mainly Sb(OH)6-)and a positively charged surface. Therefore, Sb(+5) adsorption tends to be favored for solid materials which are positively charged. The surface charge of the material depends on the type of solid, the pH of the water, and the concentration of other anions in solution. At low pH values, the water and mineral surfaces have higher concentrations of hydronium ion (H30+) which imparts a positive charge to the surface. As the pH increases, the hydronium ion concentration decreases relative to the hydroxide ion (OH-) concentration in both the water and the solid materials within the water. At a specific threshold pH value called the pH of the zero-point-of-charge (ZPC), the surface charge transitions from positive to neutral to negative. Once the surface charge becomes negative, adsorption of the negatively charged Sb(+5) ions become less prevalent. The pH of the ZPC is different for different materials, as shown in Table 1. Table 1 PH of the Zero-Point-of-Charae (oHzac) for Various Minerals' Material Formula Hzrc Magnetite Fe304 6.5 Goethite Fe00H 7.8 Hematite Fe203 6.7 Amorphous Ferric hydroxide Fe(OH)3 8.5 Aluminum Hydroxide y-AI OH 8.2 Aluminum Hydroxide A-AI OH 3 5.0