Table 6 EXAFS analyses

Scale factor (S₀²) = 1.5. ^aFirst-shell Cd–S coordination fixed at 4; R and σ² were varied. ^bFor the sulfide component, R and σ² were fixed on the average of values determined from fits to reference precipitates; N was varied. If N_Cd–S = 4 and N_cd–O = 6 are assumed, then the sulfide component is 47% and the oxide component is 53% of the total absorption spectrum. ^cCadmium sulfide was precipitated by adapting an FeS method.¹⁰ XAS spectra collected on wet samples immediately after precipitation. ^dCrystallographic values for greenockite from ref. 58. ^eParameter varied in least-squares fits.

Scale factor (So²) = 1.0. ^fSulfide component: Interatomic distances (R) for Zn–S and Zn–Zn fixed on Crystallographic values in sphalerite; first-shell σ² for Zn–S was fixed on an empirical value determined from fits to sulfide reference compounds. For higher Zn–Zn and Zn–S shells, N was fixed on the value calculated from the proportion of sphalerite component determined in fits to filtered first-shell spectra and σ² was varied. ^gOxide component: Values for σ² were fixed for all shells based on empirical fits to reference compounds; R and N were varied. ^hBackscatterer is Fe or similar transition metal cation; edge-sharing octahedra. ⁱBackscatterer is Mg or Al; edge-sharing octahedra. ^jBackscatterer is Fe or Si; corner-sharing octahedra or tetrahedra. ^kCrystallographic values for sphalerite from ref. 28. ^lParameter varied in least-squares fit.

Scale factor (So²) = 0.90. ^mOxide component: First-shell Cr–O coordination fixed at 6; σ² was varied. For higher shells, values for σ²were fixed based on empirical fits to reference compounds; R and N were varied. ⁿBackscatterer is Mg or Al; edge-sharing octahedra. ^oBackscatterer is Fe or similar transition metal cation; edge-sharing octahedra. ^pFit with single shell of Fe atoms; probably a disordered shell of Al, Mg, and Fe atoms. ^qCrystallographic values from ref. 59. ^rCrystallographic values from ref. 60. ^sParameter varied in least-squares fits.

Iron EXAFS analysis

^tPyrite component: Interatomic distances (R) were fixed on crystallo-graphic values from pyrite and σ² was fixed on values determined from fits to reference sulfide compounds. N for each shell was floated as a linked variable in proportions based on the known coordination in pyrite. Relative percent (Rel. %) for pyrite or oxide components is calculated from the integrated fit areas of all atomic shells comprising each component (normalized to 100%). ^uOxide component: Values for σ² were fixed for all shells based on empirical fits to reference compounds of similar composition and structure; R and N were varied, except for the Fe–Si shell, which will co-vary with Fe shells if floated independently. This shell was fixed on a typical crystallo-graphic distance for Fe–Si in phyllosilicates. ^vCrystallographic values from ref. 61. ^wParameter varied in least-squares fit.