Table 2.
Fits to Fe EXAFS data for Fe-hydroxide (FH) and HA/Fe coprecipitates containing humic acid (YHA and AHA) with initial C/(C + Fe) ratio of 0.17, 0.29, and 0.33 (YFC17/29/33 and AFC17/29/33)a.
| sample | Fe-Fe1b | Fe-Fe2b | ||
|---|---|---|---|---|
| R (Å) | CN | R (Å) | CN | |
| FH | 3.07 (0.01) | 4.3 (0.7) | 3.45 (0.01) | 3.2 (0.9) |
| YFC17 | 3.05 (0.02) | 1.5 (0.7) | 3.43 (0.03) | 1.3 (0.9) |
| YFC29 | 3.07 (0.01) | 4.5 (0.8) | 3.45 (0.01) | 3.5 (1.0) |
| YFC33 | 3.07 (0.02) | 4.7 (1.7) | 3.45 (0.02) | 3.6 (2.0) |
| AFC17 | 3.07 (0.01) | 4.2 (0.6) | 3.45 (0.01) | 3.6 (0.7) |
| AFC29 | 3.07 (0.01) | 4.5 (0.7) | 3.45 (0.01) | 3.3 (1.0) |
| AFC33 | 3.07 (0.02) | 3.9 (0.8) | 3.45 (0.02) | 2.8 (1.0) |
aFitting was done across the k range of 2.5 to 11.5 Å−1 and an R range of 1.0 to 3.5 Å. Numbers in parentheses are uncertainties calculated for the EXAFS model. Paths used in EXAFS fitting are all single-scattering paths. All samples were fit simultaneously, yielding a normalized sum of squared residuals [R-factor = Σ(data-fit)2/Σdata2) of 0.0064 (0.64%)]. S02 (fixed amplitude reduction factor based on first-shell fitting of hematite) = 0.83. ΔE (fitted energy shift parameter) = −1.49 (0.35) eV for all samples. The fitted R (interatomic distance) of Fe-O path across all samples was 1.97–1.99 Å. The CN (coordination number) for the Fe-O path was fixed at 6.0. With the exception of YFC17, the fitted σ2 (mean-square displacements of interatomic distances) of the Fe-O path for all samples was 0.013 (0.003) Å2. The fitted σ2 value of the Fe-O path in YFC17 was 0.022 (0.002) Å2.
bThe fitted σ2 values of the Fe-Fe1 and Fe-Fe2 path in YFC17 were both 0.013 (0.002) Å2, which for theFe-Fe1 and Fe-Fe2 path in other samples were 0.017 (0.002) and 0.016 (0.002) Å2, respectively.