TABLE 2.
Fe(II) inorganic and organic speciation at equilibrium
| Ligand | Fe(II) species |
% of total Fe(II) |
|||
|---|---|---|---|---|---|
| Speciesa | Charge | pH 6 | pH 7 | pH 8 | |
| Citrate | Fe2+ (aqueous) | 2 | 9.1 | 5.9 | 1.5 |
| Fe-CIT (aqueous) | −1 | 88.9 | 92.3 | 38 | |
| Fe-CIT2 (aqueous) | −4 | 0 | 1.8 | 0 | |
| Fe(II)-CO3 (solid) | Solid | 0 | 0 | 60.5 | |
| Picolinate | Fe2+ (aqueous) | 2 | 21.6 | 15.3 | 1.5 |
| Fe-PIC (aqueous) | 1 | 52.3 | 49.8 | 9.8 | |
| Fe-PIC2 (aqueous) | 0 | 26.1 | 34.9 | 14 | |
| Fe(II)-CO3 (solid) | Solid | 0 | 0 | 74.7 | |
| NTA | Fe2+ (aqueous) | 2 | 5 | 0.5 | 0 |
| Fe-NTA (aqueous) | −1 | 95 | 99.5 | 100 | |
| Fe(II)-CO3 (solid) | Solid | 0 | 0 | 0 | |
| None | Fe2+ (aqueous) | 2 | 95 | 16.6 | 2.5 |
| Fe-HCO3 (aqueous) | 1 | 5 | 1.8 | 0 | |
| Fe(II)-CO3 (solid) | Solid | 0 | 81.4 | 97.5 | |
a
CIT, citrate; PIC, picolinate.