Adsorption mechanisms of selenium oxyanions at the aluminum oxide/water interface

Adsorption and co-precipitation behavior of arsenate, chromate, selenate and boric acid with synthetic allophane-like materials

“…Evidently, Se(VI) adsorption was relatively higher, which is also consistent with well established results, that iron and aluminum oxide minerals are the most common geosorbents for selenium oxyanions [27]. However, the low uptake of boric acid and Cr(VI) by allophane suggests that ionic charge and anionic competition with silicate are the important factors that influence the extent of their retention, respectively.…”

“…In contrast, the surface charge characteristics of allophane after Cr(VI) and Se(VI) adsorption showed no significant change which indicates that the binding is largely controlled by outer-sphere complexation (Figure 7c and 7d). Using EXAFS spectroscopy, Peak [27] concluded that Se(VI) adsorption on the surface of hydrous aluminum oxide primarily forms outer-sphere complexes. On the other hand, the adsorption of oxyanions and boric acid on polymerized silica is not supported because it did not contain OH groups as revealed by zeta potential measurement.…”

Selenium adsorption to aluminum-based water treatment residuals

“…The Se-Al shell for WTR at pH 9 and the reference mineral phases further supports the formation of inner-sphere Se(IV) complexation. Peak [15] found similar Se-O and Se-Al shell values for Se(IV) adsorbed onto hydrous aluminum oxide at pH 8, and suggested innersphere complexation as the adsorption mechanism at this pH. Others have suggested Se(IV) inner-sphere complexation on goethite [12,14].…”

“…Manceau and Charlet [14] identified similar selenate binding chemistry on goethite. Peak [15] further studied selenate and selenite adsorption on to hydrous aluminum oxide, noting that selenate formed outer-sphere while selenite formed a mixture of outer-and inner-sphere complexes. Wijnja and Schulthess [16] also noted that selenate formed mainly outer-sphere associations on aluminum oxide.…”

“…The Se-O shell bond distances remained at 1.64 Å while the coordination number remained approximately 4.00 across the pH range studied, suggestive of Se(VI) outer-sphere complexation (see illustration in Table 2). Wijnja and Schulthess [16] showed that Se(VI) adsorption on to Al oxide existed mainly as an outer-sphere complex above pH 6, while Peak [15] suggested that Se(VI) adsorption on a hydrous aluminum oxide, regardless of pH, was as an outer-sphere complex. Others have shown Se(VI) adsorption as inner-sphere complexation [12][13][14], although all of these studies focused on adsorption onto iron (hydr)oxide phases.…”