Studies on Ferric Oxide Hydroxides

Sorption of Selenite (SeO32−) on Hydroxyapatite: An Exchange Process

“…According to the surface complexation theory, lowering the pH increases the positive charge of the surface, thus increasing the sorption of the two negative species SeO 2− 3 and HSeO − 3 . If such a mechanism were involved, since biselenite is the major species in solution between pH 4 and 7.5 and the neutral species H 2 SeO 3 is negligible above pH 4 (pK 1 = 2.50 and pK 2 = 8.17, measured in KNO 3 0.1 M), the adsorption of SeO 2− 3 and HSeO − 3 would normally result in a maximum of sorption down to the lowest pH values, as was observed for several oxides and clays (17)(18)(19)(20)(21)(22).…”

“…2, the time required for reaching the equilibrium increases with increases in the amount of Se in the solution. For an initial Se concentration of 1.0 × 10 −3 mol/L, the equilibrium was reached within 160 h, which is a rather long time in comparison to time spans observed for the sorption of selenite on metal oxides, e.g., 2 h for goethite (17). This suggests that metal oxides and HAP undergo different phenomena in terms of selenite sorption.…”

Removal of Fluoride from Aqueous Solution by Using Alum Sludge

“…If the surface is homogeneous, the K D values at a given pH should not change with adsorbent concentration. Note that heterogeneous surface sites are reported on homogeneous solids also (13).…”

Studies on Mg/Fe Hydrotalcite-Like-Compound (HTlc)

“…Due to the ubiquitous occurrence of Fe and Mg in soil and sediments and their strong affinity in sequestering many elements, a great deal of literature on the removal/adsorption of selenium on oxide/oxyhydroxides of Fe and oxides of Mg is nowadays available (8,(11)(12)(13)(14)(15)(16). Hydrotalcite-like compounds (HTlc) are the layered metal double hydroxides having the general formula [M…”