Table 4.
Fe K-edge EXAFS structural fitting parameters
| Shell | Smectite A | Smectite B | Smectite C | Smectite D | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| unaltered | air-ox | re-xtll | re-ox | unaltered | air-ox | unaltered | air-ox | re-xtll | re-ox | perox | unaltered | air-ox | perox | |||
| Fe-O1a | Na | 2 | 2 | 2 | 2 | 0 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | |
| Rb | 2.016(18)f | 2.10(13) | 1.936(21) | 2.084(26) | - | 1.963(17) | 1.986(19) | 1.936(13) | 1.951(29) | 1.914(13) | 2.065(49) | 2.011(28) | 1.994(30) | 2.066(57) | ||
| σ2 c | 0.006g | 0.015 | 0.009 | 0.008 | - | 0.009 | 0.004 | 0.006 | 0.009 | 0.006 | 0.008 | 0.004 | 0.006 | 0.008 | ||
| Fe-O1b | N | 4 | 4 | 4 | 4 | 6 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | |
| Rb | 2.140(7) | 2.008(38) | 2.094(12) | 1.943(10) | 2.101(7) | 2.109(8) | 2.124(11) | 2.108(10) | 2.096(14) | 2.080(9) | 1.951(11) | 2.135(14) | 2.132(17) | 1.958(12) | ||
| σ2 | 0.006(1) | 0.0149 | 0.009(1) | 0.008(1) | 0.009(1) | 0.009(1) | 0.004(1) | 0.006(1) | 0.009(2) | 0.006(1) | 0.008(3) | 0.004(2) | 0.006(2) | 0.008(3) | ||
| Fe-Fe | N | 5.45 | 2.6(8) | 3.2(1.1) | 1.2(7) | 4.87 | 3.6(7) | 3.19 | 3.1(4) | 2.6(5) | 2.9(4) | 1.6(6) | 1.80 | 1.8(2) | 0.9(5) | |
| R | 3.177(22) | 3.149(17) | 3.218(45) | 3.018(28) | 3.153(14) | 3.139(16) | 3.115(18) | 3.133(17) | 3.136(27) | 3.112(18) | 2.955(51) | 3.095(21) | 3.105(18) | 3.099(92) | ||
| σ2 | 0.012(2) | 0.012i | 0.012 | 0.012 | 0.012(2) | 0.012 | 0.011(2) | 0.011 | 0.011 | 0.011 | 0.011 | 0.008(2) | 0.008 | 0.008 | ||
| Fe-Aloct | N | 0.55 | 0.28(9) | 0.33(10) | 0.1(7) | 0.57 | 0.42(8) | 0.38 | 0.38(5) | 0.31(6) | 0.35(5) | 0.18(7) | 0.58 | 0.6(1) | 0.11(6) | |
| R | 3.177h | 3.149 | 3.218 | 3.018 | 3.153 | 3.139 | 3.115 | 3.133 | 3.136 | 3.112 | 2.955 | 3.095 | 3.105 | 3.099 | ||
| σ2 | 0.012h | 0.012i | 0.012 | 0.012 | 0.012 | 0.012 | 0.011 | 0.011 | 0.011 | 0.011 | 0.011 | 0.008 | 0.008 | 0.008 | ||
| Fe-Mg | N | 0 | 0 | 0 | 0 | 0.56 | 0.41(8) | 2.42 | 2.4(3) | 2.0(4) | 2.2(3) | 1.2(4) | 3.63 | 3.7(4) | 2.2(1.3) | |
| R | - | - | - | - | 3.153h | 3.139 | 3.115 | 3.133 | 3.136 | 3.112 | 2.955 | 3.095 | 3.105 | 3.099 | ||
| σ2 | - | - | - | - | 0.012h | 0.012i | 0.011 | 0.011 | 0.011 | 0.011 | 0.011 | 0.008 | 0.008 | 0.008 | ||
| Fe-Si | N | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | |
| R | 3.296(30) | 3.278(64) | 3.271(35) | 3.246(54) | 3.304(22) | 3.309(29) | 3.290(25) | 3.276(27) | 3.278(21) | 3.246(18) | 3.252(18) | 3.276(27) | 3.273(27) | 3.226(25) | ||
| σ2 | 0.011(7) | 0.019(7) | 0.007 | 0.021(1) | 0.012 | 0.013(4) | 0.010(4) | .011(3) | 0.007(2) | 0.009(2) | 0.008(2) | 0.010(4) | 0.010(3) | 0.008(3) | ||
| ΔE0d | −5.0(1.0) | −3.7 (1.8) | −4.7 (1.5) | −2.9(1.6) | −4.8(0.9) | −4.3(1.7) | −6.1(1.7) | −5.7(1.3) | −3.6(1.7) | −6.1(1.3) | −5.4(1.6) | −6.2(2.3) | −4.2(2.4) | −6.3(2.3) | ||
| Fe-Oaverage (Å)e | 2.099 | 2.039 | 2.041 | 1.990 | 2.101 | 2.060 | 2.078 | 2.051 | 2.048 | 2.025 | 1.989 | 2.094 | 2.086 | 1.994 | ||
Coordination number.
Interatomic distance (in Å)
Debye-Waller factor (Å2)
Difference in edge energy between experiment and theory (eV)
Average Fe-O distance = (NFe-O1a *RFe-O1a + NFe-O1b *RFe-O1b) * ⅙
Statistical uncertainties on last digit(s) in fit parameters are reported in parentheses (1 standard error). Parameters with no listed uncertainties were not varied in the analyses.
The Debye-Waller factor for the Fe-O1a shell was set equal to that for the Fe-O1b shell.
The R and σ2 parameters for Fe-Al and Fe-Mg were set equal to those for the Fe-Fe shell.
The Debye-Waller factor for Fe-Fe, Fe-Al, and Fe-Mg in the oxidation products were set equal to those for the Fe-Fe shell in the corresponding unaltered sample.