XAFS Investigation for As(V) Co-Precipitation Mechanism with Ferrihydrite

Abstract

XRD/XAFS analysis were conducted to investigate the As(V) co-precipitation mechanism with ferrihydrite ( γ-FeOOH ). In As(V) co-precipitation with ferrihydrite, XRD results showed that As(V) complexation to the surface of ferrihydrite was dominant when the initial molar ratio of As/Fe was less than 0.25, whereas surface precipitation of amorphous ferric arsenate was formed when the initial molar ratio of As/Fe was more than 0.5.Both of XANES and EXAFS analysis on K-edge of As showed As(V) co-precipitates with ferrihydrite was the mixture of As(V) adsorbed ferrihydrite and amorphous ferric arsenate. Molar ratio of amorphous ferric arsenate in As(V) co-precipitates was estimated to be more than 0.5 when the initial molar ratio of As/Fe was more than 0.5. These results are in good agreement with the XRD results. EXAFS analysis assuming one surface complex for As-Fe bond showed the coordination number of As to Fe in As(V) co-precipitates increased with increasing the initial molar ratio of As/Fe. Moreover, EXAFS analysis assuming three kinds of surface complexes for As-Fe bond showed the coordination number for 2.85 Å of the atomic distance of As-Fe increased and it for 3.24 Å of the atomic distance of As-Fe decreased with increasing the initial As/Fe molar ratio. All experimental data obtained in this study showed As(V) co-precipitation mechanism shifted gradually from As(V) complexation to the surface of ferrihydrite toward amorphous ferric arsenate with increase in the initial molar ratio of As/Fe.

Sorption of arsenate on MgAl and MgFe layered double hydroxides derived from calcined dolomite

“…The EXAFS analytical results of the solid samples after arsenate sorption showed the 289 As coordination in the residues is similar to previously reported surface complexed AsO 4 3-on 290 ferrihydrites [39]. In the radial structure function (RSF: phase shift uncorrected) of As K-291 edge EXAFS spectra of 0.0983 mmol/L arsenate sorbed Mg 4 Fe-LDH showed three distinct 292 peaks (Figure 6).…”

“…Synthesis of LDHs using natural earth resources is 26 highly desired in environmental concern. Single phases of Mg 2.3 Al-, Mg 2.9 Al-and Mg 4 Fe- ion-exchange along with the formation of inner surface complexes, which leads disturbed 39 layer stacking.…”

Mechanism of As(V) Removal in Wastewater Treatment Using Fe(III)-Supported Exchange Resins

“…Poorly crystalline ferric arsenate was synthesized using the procedure described by Jia et al 16 , with slight modification. These materials were also used as reference in XAFS analysis in our previous studies that included the preparation procedures 14,15 . Figure 1 shows the relationship between residual Fe(III) concentration and exchange capacity obtained from the Fe(III) support experiments.…”

Forecast of AMD Quantity by a Series Tank Model in Three Stages: Case Studies in Two Closed Japanese Mines

“…The general treatment for AMD is neutralization and sedimentation by addition of a neutralizer, such as lime, calcium carbonate, and sodium hydroxide [2], and solid/liquid separation [3] of the produced sludge from the neutralized effluents. In these treatments, all toxic elements are concentrated into the sludge by precipitation [4][5][6] and adsorption [7][8][9][10][11][12], and the sludge is controlled in a tailing pond at a mine site or final disposal site. For these last several decades, AMD has been treated properly in Japan and has not caused severe pollution.…”